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Quantum Diamonds at the Beach: Chemical Insights into Silica Growth on Nanoscale Diamond using Multimodal Characterization and Simulation

  • Perla J. Sandoval
    Perla J. Sandoval
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Karen Lopez
    Karen Lopez
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Andres Arreola
    Andres Arreola
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Anida Len
    Anida Len
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Nedah Basravi
    Nedah Basravi
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Pomaikaimaikalani Yamaguchi
    Pomaikaimaikalani Yamaguchi
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Rina Kawamura
    Rina Kawamura
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Camron X. Stokes
    Camron X. Stokes
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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    Cynthia Melendrez
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Davida Simpson
    Davida Simpson
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
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  • Sang-Jun Lee
    Sang-Jun Lee
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States
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    Orcidhttps://orcid.org/0000-0002-8199-3993
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  • Charles James Titus
    Charles James Titus
    Department of Physics, Stanford University, 382 Via Pueblo Mall, Palo Alto, California 94025, United States
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    Orcidhttps://orcid.org/0000-0001-6312-8552
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  • Virginia Altoe
    Virginia Altoe
    The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
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  • Sami Sainio
    Sami Sainio
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States
    Microelectronics Research Unit, University of Oulu, Pentti Kaiteran katu 1, Linnanmaa, P.O. Box 4500, Oulu 90014, Finland
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  • Dennis Nordlund
    Dennis Nordlund
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States
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  • Kent Irwin
    Kent Irwin
    Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States
    Department of Physics, Stanford University, 382 Via Pueblo Mall, Palo Alto, California 94025, United States
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  • Abraham Wolcott*
    Abraham Wolcott
    Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-4025-3040
Cite this: ACS Nanosci. Au 2023, XXXX, XXX, XXX-XXX
Publication Date (Web):September 15, 2023
https://doi.org/10.1021/acsnanoscienceau.3c00033

© 2023 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Surface chemistry of materials that host quantum bits such as diamond is an important avenue of exploration as quantum computation and quantum sensing platforms mature. Interfacing diamond in general and nanoscale diamond (ND) in particular with silica is a potential route to integrate room temperature quantum bits into photonic devices, fiber optics, cells, or tissues with flexible functionalization chemistry. While silica growth on ND cores has been used successfully for quantum sensing and biolabeling, the surface mechanism to initiate growth was unknown. This report describes the surface chemistry responsible for silica bond formation on diamond and uses X-ray absorption spectroscopy (XAS) to probe the diamond surface chemistry and its electronic structure with increasing silica thickness. A modified Stöber (Cigler) method was used to synthesize 2–35 nm thick shells of SiO2 onto carboxylic acid-rich ND cores. The diamond morphology, surface, and electronic structure were characterized by overlapping techniques including electron microscopy. Importantly, we discovered that SiO2 growth on carboxylated NDs eliminates the presence of carboxylic acids and that basic ethanolic solutions convert the ND surface to an alcohol-rich surface prior to silica growth. The data supports a mechanism that alcohols on the ND surface generate silyl–ether (ND–O–Si–(OH)3) bonds due to rehydroxylation by ammonium hydroxide in ethanol. The suppression of the diamond electronic structure as a function of SiO2 thickness was observed for the first time, and a maximum probing depth of ∼14 nm was calculated. XAS spectra based on the Auger electron escape depth was modeled using the NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to support our experimental results. Additionally, resonant inelastic X-ray scattering (RIXS) maps produced by the transition edge sensor reinforces the chemical analysis provided by XAS. Researchers using diamond or high-pressure high temperature (HPHT) NDs and other exotic materials (e.g., silicon carbide or cubic-boron nitride) for quantum sensing applications may exploit these results to design new layered or core–shell quantum sensors by forming covalent bonds via surface alcohol groups.

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Introduction

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Diamond has excellent physical and photophysical properties that are well suited for emergent applications in photonics, (1) quantum communication, (2−5) quantum metrology, (5−7) and biosensing. (8−10) A unique combination of chemical inertness, a large optical band gap (5.5 eV), high thermal conductivity (25 W/cm•K), extreme hardness (10 on Mohs scale), and being the host of a library of color centers including the nitrogen-vacancy (NV) center makes diamond versatile in materials science. However, its all-carbon sp3 structure presents challenges in synthesizing uniform, covalently bound inorganic layers on diamond because of the high surface density of atoms (22 atoms/nm2 on (110) and 18 atoms/nm2 on (111)) and lattice mismatch. Epitaxial growth on diamond is notoriously difficult, and only SiC (11) and AlGaN/GaN (12) layers have been successfully grown. Recently, Maurer and de Leon used nonepitaxial adhesion layers of Al2O3 on 100-terminated NVC diamond for quantum sensing of biological analytes, yet it was reported that the Al2O3 layer dissolved in buffer saline solutions at a rate of ∼1 nm/day at 37 °C, reducing bound fluorescent dye counts by 50% over 1 week. (13) To date, advancements in interfacing high-pressure, high-temperature (HPHT) nanoscale diamond (ND) with inorganic materials have been limited to amorphous SiO2 or silica. Cigler and Wrachtrup used NV center ND with SiO2 shells to decorate the diamond surface and engineer pH-selective chemistry for Gd sensing. (14) Growth of SiO2 shells on HPHT NDs is typically performed on “carboxylate-rich” NDs after an acid–base-acid treatment and has been shown to yield uniform layering across the ND surface. (15−17) The uniform SiO2 shell growth is a surprising result due to the limited number of carboxylates (∼7% coverage) on the HPHT ND surface. (18) One would expect SiO2 islands if carboxylates were the functional group responsible for the nucleation and growth of SiO2. The evidence presented here explains the mechanism, whereby silica chemistry is initiated by alcohols (silyl-ether bond formation) and highlights the use of synchrotron-based X-ray absorption spectroscopy (XAS) as an impactful tool in probing the core–shell nanostructure and surface termination. Support of our findings includes core-level X-ray detection using the transition edge sensor (TES) to generate a full electronic map of occupied and unoccupied electronic states.
Synchrotron-based XAS has been versatile in investigating the electronic structure, coordination state, and bond distance of mixed material systems. In combination with electron microscopy and elemental analysis, XAS provides fundamental information about complex systems used in biolabeling, energy, and catalysis applications. Core–shell nanostructures are ubiquitous in the fields of materials chemistry, physics, and engineering, with CdSe/ZnS quantum dots (QDs) being the most investigated along with a catalogue of other core–shell structures. (19−21) XAS studies with CdSe/ZnS QDs have included ligand exchange chemistry, (22) exciton binding energy measurements, (23) and CdSe/ZnS electronic structure studies with elucidation of the ZnS shell oxidation states. (24) Magnetic Fe/Fe2O3 nanoparticles (NPs) examined with XAS revealed the iron and iron oxide bonding environment while also detecting trace boron and nickel used during the synthetic protocol. (25) An XAS investigation of Fe/Ag and Ag/Fe core–shell NPs produced by a sodium borohydride reduction of Ag and Fe salts was able to discern subtle FeB and Fe2B surface bonding environments. (26) Other materials studies of Ni/Au, (27) Fe/FexOy, (28) Pt–Ru, (29) Co–Pt, (30) Co–Au, (31) and Cu–Ru (32) all provided deeper insights into the chemical bonding with near-edge and extended X-ray spectroscopies. In contrast, this study is the first XAS examination of HPHT NDs with silica shells (ND–SiO2). Silica chemistry on HPHT NDs has been the sole shell material demonstrated to date that bonds directly to the diamond core. (14,16,33,34) The ND–SiO2 system is unique because of the known difficulties in epitaxial growth on diamond, the fingerprint electronic structure of diamond, and this study confirms that XAS characterization of diamond core–shell nanostructures is possible.
C 1s XAS is widely used to probe graphene and other allotropes of carbon including diamond and diamond-like materials and can detect trace dopants in those materials. (35−37) Diamond has a distinct electronic structure, and the first observation of the diamond core-hole exciton led to the determination of its binding energy (BE) of 0.19 eV, in good agreement with the calculated BE using the effective-mass approximation. (38) The diamond electronic structure can be tracked using the distinct core-hole exciton features at 289.0 eV and the second absolute band gap at ∼302 eV present in HPHT NDs. (39) While many layered materials and core–shell nanomaterials exist and are essential for energy, medicine, and defense, this study establishes a baseline for examining diamond-metal oxide nanostructures with XAS.
The mechanisms for detection of the diamond electronic structure in this study are based on the total electron yield (TEY) photocurrent and the effective escape depth L. Core level C 1s transitions will occur when a soft X-ray is absorbed, causing the electron to transition to an unoccupied electronic state that contains contributions from p-orbitals and is electric-dipole-allowed (L = ±1). The X-ray absorption event creates a core-hole in the material, and several well-understood mechanisms generate the TEY photocurrent. The contributions to the TEY photocurrent include low-energy electrons that have escaped the sample surface through three mechanisms: escape of primary photoelectrons, Auger electrons, and secondary inelastic Auger electrons, each with their own distinct kinetic energies, probe depths, and surface sensitivities. The main source of TEY photocurrent is due to inelastic electron–electron scattering of the Auger electrons and are of low energy (Ke < 250 eV). (40−42) The effective escape depth, L, is similar to the electron mean free path of electrons and is a function of material type and the electron’s kinetic energy. In metals and semiconductors, L is typically less than 5 nm, and insulators tend to have a larger L; Al2O3 has L as large as 13 nm. (43) Diamond being an insulator with a 5.5 eV band gap should have L within the range of other insulators such as Al2O3. The escape depth L is provided within the description of the TEY photocurrent as described by Stöhr as
I(z)=Ω4πNee−z/LhνM
(1)
where Ω is the collection angle, Ne is the number of emitted electrons, z is the depth from the substrate surface, L is the effective electron escape depth for the material, and hvM is the gain function for the transport and escape of electrons into vacuum. (44)
The exponential decay of the photocurrent, e−z/L, has a similar exponential decaying profile of direct photoemission techniques such as X-ray photoelectron spectroscopy or XPS, with L being substituted for the inelastic mean free path λ. In contrast, L represents longer length scales than λ because the initial primary Auger electrons generate a cascade of much lower energy secondary electrons (<50 eV) with mean free paths longer than 10 nm. For example, TEY measurements of silicon with silicon oxide overlayers demonstrated sampling depths of ∼5 and ∼70 nm for the Si K-edge with 100 and 1840 eV electrons, respectively. (45) An in-depth simulation study of secondary inelastic Auger electrons by Ziaja and co-workers found 20–40 secondary Auger electrons were generated per primary Auger electron in the first 100 fs when using the Ashley and Tanuma-Powell-Penn model (TPP-2). (46) The cascade of secondary Auger electrons is the main source of electronic structure information in our XAS study, and the unique diamond signatures provide a fingerprint spectrum that cannot be confused with other types of carbon, such as adventitious carbon, graphite, and amorphous carbon.
Here, we demonstrate that the model system of HPHT NDs with the wet chemical growth of silica provides ample chemical control to extract fundamental aspects of the diamond TEY signal, the growth mechanism of the silica itself, and chemical analysis. Carboxylate-rich HPHT NDs, produced by an acid–base–acid (ABA) treatment of alcohol-rich NDs, were reacted with silica precursors in solution using a modified Stöber method as described by Cigler and colleagues. (47) This study reveals that ethanol with ammonium hydroxide solutions used for silica growth adds alcohols to the ND surface (rehydroxlation) prior to silica growth and these alcohols are responsible for the silica growth via silyl-ether bond formation (C–O–Si). Conformation of the covalent attachment of the silica to the diamond surface was tested with thermogravimetric analysis-mass spectroscopy (TGA-MS) and showed no desorption of silanes or silicon-based precursors (see S2) Silane-based functionalization of the ND–SiO2 samples with polyethylene glycol, amines, azides, carboxylic acids, glycidyls, and fluorines was probed via XAS to demonstrate the chemical versatility of the silica surface. The correlation between high-resolution transmission electron microscopy (HRTEM) imaging and C 1s XAS data shows that all diamond features are fully suppressed within an ∼20 nm thick SiO2 shell on the ND core. The effective electron escape depth (L) was calculated to be ∼14 nm based on our analysis of the C 1s signal coming exclusively from the diamond core–hole exciton. These results are consistent with the TEY signal originating from inelastically scattered secondary Auger electrons (electron cascade). Modeling of the CKL1L1 (246.8 eV), CKL1L23 (257.4 eV), and CKL23L23 (268.0 eV) Auger electrons and the number of secondary collisions using the NIST SESSA program reinforces our results (see S1). Our findings elucidate the mechanism of covalent diamond-silica growth and should inspire new core–shell architectures to be explored for quantum sensing and biolabeling with quantum bits such as the nitrogen vacancy center in diamond and other alcohol-terminated exotic materials.

Results and Discussion

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Surface Rehydroxylation and Silyl Ether Bond Formation on Diamond

The growth of amorphous silica on carboxylate-rich HPHT NDs (ND–COOH) was found to proceed with alcohols on the diamond surface and led to decarboxylation. Silica growth is performed with ethanol, ammonium hydroxide, water, tetraethyl orthosilicate (TEOS), and ND–COOH in a similar fashion to SiO2 nanoparticle synthesis. Hydroxylation was confirmed in a simple control experiment without TEOS in basic ethanol and showed a definitive increase in (C–O)ν at 1100 cm–1 representative of an alcohol-rich diamond. The proposed mechanism for covalent bond formation on the oxidized surface of HPHT NDs is detailed in Figure 1 and shows the conversion from carboxylates to alcohols and subsequent silica chemistry. We found that rehydroxylation did not cause the loss of carboxylates but instead occurred after silica bond formation. TEOS is the sole silicon precursor for the formation of SiO2, and its hydrolysis is known to be base-catalyzed via nucleophilic attack of the Si atom. (48) We use mildly basic conditions (pH ∼ 11) with NH4OH to control the kinetic rate of TEOS hydrolysis and silica growth on the ND surface. Previously discussed mechanisms for hydrolysis and polymerization include both penta- and hexacoordinate intermediates, leading to the formation of silicates and SiO2 particles. (49−51) With HPHT NDs, the nucleophilic attack by alcohols (C–O–H) or alkoxide groups (C–O–) on the ND surface occurs to form the ND–Si(OH)4 intermediate and the elimination of H2O. In a classic Stöber method, the condensation reaction would form SiO2 clusters that nucleate and form submicron particles. (52) In this route we call the Cigler method, bond formation on the ND surface undergoes further −O–Si–O– polymerization reactions to produce a SiO2 shell of the desired thickness.

Figure 1

Figure 1. (A) Chemical scheme shows the growth of silica using tetraethyl orthosilicate in a base-catalyzed reaction similar to the Stöber method. The ND surface is depicted with 1 carboxylic acid and a sp2-like Pandey reconstruction. In the schematic, the alcohol groups after rehydroxylation are performing a nucleophilic attack to generate a silyl–ether bond on the diamond surface, and a subsequent removal of the acid occurs. (B) DRIFTS spectra of the ND constructs before and after silica shell growth show the reduction in the (C═O)ν at 1785 cm–1 and the increase in (Si–O–Si)ν at 1100 cm–1. DRIFTS of the rehydroxylaion control experiment is depicted and shows the increase of an alcohol peak at 1100 cm–1. (C) A cluster of diamond nanoparticles encapsulated in silica is seen by electron microscopy. High-angle annular dark field (HAADF) microscopy is used to image the embedded diamond in silica, while elemental mapping of C Kα and Si Kα EDS is used to spatially resolve the core–shell structure.

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Silica shell growth was tracked with diffuse reflectance infrared Fourier transmission spectroscopy (DRIFTS), which was confirmed with transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). DRIFTS data in Figure 1B show surface chemistry of the ND–COOH before and after silica chemistry, and distinct vibrational features can be observed. The carboxylated ND sample (ND–COOH) produced from the ABA protocol shows a distinct (C═O)ν peak at 1780 cm–1 and no peak at 1100 cm–1. Synthesis of the SiO2 shells eliminates the (C═O)ν feature and the vibrational feature is no longer observed at 1780 cm–1. A control experiment was designed whereby ND–COOH, ammonium hydroxide, water, and ethanol without the silica precursor were prepared and reacted in the same conditions as a standard synthesis (see SI methods). The resulting DRIFTS spectrum clearly shows the increase in (C–O)ν peak at 1100 cm–1 representative of alcohols. The increase in alcohols is thought to occur through the addition of hydroxides (OH−) across the Pandey chain reconstructed sp2-like ND surface and is illustrated by dashed lines in the proposed mechanism. (53) After SiO2 growth on the ND cores, the peak at 1780 cm–1 is no longer present due to the desorption of a silicate complex from the surface. After SiO2 growth, a prominent (O–Si–O)ν peak arises at 1100 cm–1 with a distinct line shape in comparison with the original alcohol termination. EDS mapping of C Kα, O Kα (not shown), and Si Kα signals was performed across an ND cluster with a 20+ nm silica shell, and a correlation of increased C Kα intensity from the ND core can be observed in Figure 1C. Si Kα signals are observed throughout the sample and consistent with the nanoparticle morphology imaged with high-angle annular dark field microscopy. The imaged ND–SiO2 cluster represents a nonuniform coating of the SiO2, which can occur when the growth conditions are nonoptimal. In a demonstration of SiO2 surface chemistry, mercaptopropyl trimethoxysilane is used to generate outward-facing sulfyl-hydryl groups (−SH) and (C–H)ν features arising from the propyl chain at 2800–2900 cm–1 can be clearly observed. Amines and poly(ethylene glycol) chains can also be grafted to the ND–SiO2 constructs and were used to stain neuronal cells in an NV center fluorescence demonstration (see S2).

Time-Dependent Silica Growth on HPHT ND Cores and Suppression of the Diamond Electronic Structure

High-resolution transmission electron and scanning electron microscopy confirmed the thickness and distribution of the SiO2 across the NDs and were used quantitatively to understand the suppression of the diamond electronic structure observed in XAS. The shell thickness was controlled by the length of the reaction as detailed in the Methods section. Representative images with scale bars are shown in Figure 2 and clearly illustrate the transition from the ND core and the amorphous SiO2 shell. The irregularly shaped ND crystallites generated through a ball milling process have edges and facets that are followed closely by the 6–10 nm SiO2 shell on the tip of an ND, as shown in Figure 2A. A collection of NDs of various sizes and shapes is also shown in Figure 2B and allows a clear contrast between the diamond core and the nanometer-thick SiO2 shells. As the SiO2 shell increases in thickness, the ND morphology transitions from irregular to spherical as previously discussed by Chu (17) and can be observed with a 20+ nm shell in panel 2C. The ND is outlined in white to clearly depict the ND–SiO2 transition and to quantify the shell thickness. Dynamic light scattering was also used to confirm the purification steps, solubility, and aggregation state (data not shown). Additional TEM images show the morphology and range of shell thicknesses on the HPHT ND cores (S4 and S5) and XPS analysis of 5 nm shells reveals the 4× reduction in the C 1s signal and the stoichiometry of the SiO2 overlayer (S6).

Figure 2

Figure 2. Thickness of silica on the HPHT ND cores is controlled by the length of the reaction time and increased growth forms nearly spherical ND–SiO2 at approximately 20 nm thickness. High-resolution TEM imaging shows ultrathin SiO2 growth surrounding an irregular nanodiamond core with measurements of 6–10 nm around the ND edge and basal plane (A). Ten nanometer SiO2 growth is depicted on an aggregate of nanodiamonds of varying diameters and morphologies (B). With increasing reaction time of 20 min, 20–25 nm shells can be synthesized and the ND–SiO2 is generally spherical. (C) High-resolution SEM image shows multiple particles in a cluster and the size distribution is demonstrated with a 85 and 142 nm being highlighted (D).

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Suppression of the diamond electronic structure was unambiguously observed as a function of SiO2 shell thickness, and the diamond TEY yield signal is dominated by inelastic Auger electrons that travel from the diamond through the amorphous silica shell. The HPHT ND electronic structure is the same as single crystal bulk diamond and includes the diamond core-hole exciton and second absolute band gap at 289.0 and 302 eV, respectively. (38) The C 1s XAS data is collected at beamlines 8–2 and 10–1 at the Stanford Synchrotron Radiation Lightsource (SSRL), and the experimental setup is detailed in the SI methods section. Raw XAS data are interpolated, and linear background subtraction is performed in the pre-edge region from 270 to 280 eV. The TEY signal is normalized to the beam current I0 and is energy calibrated to the diamond core–hole exciton at 289.0 eV (Figure 3A). The position of the core–hole exciton and second absolute band gap does not change with overlayer thickness and can be observed clearly with 0–15 nm silica shells (traces A through D). Trace E in Figure 3B with a 20 ± 5 nm shell no longer has an observable core-hole exciton peak, and a minor dip for the second absolute band gap is observed and represents a diminished diamond signal. The presence of a second absolute band gap feature, yet lacking the core-hole exciton is commonly observed with C 1s XAS of detonation NDs and indicative of the diamond electronic structure. (54) Trace F has no observable diamond features, and the C 1s signal originated from adventitious carbon on the ND–SiO2 surface. The core-hole exciton signal divided by the pre-edge background (TEY/BKGD) is plotted in Figure 3C and the natural log of TEY/BKGD was fit with a linear least-squares regression (Figure 3C inset), and the slope value was then used to produce the exponential decay fit in Figure 3C. The TEY/BKGD signal follows an exponentially decaying profile as described in eq 1 and based on the exponential fit shows a 95% decrease in TEY/BKGD signal at ∼14 nm of SiO2 thickness and a 99.9% decrease with ∼35 nm SiO2 shell thickness. Frazer et al. evaluated a 0.1% TEY/BKGD signal as the maximum probing depth (MPT) with metal films. (55) The maximum probing depth or MPD based on a 0.1% TEY/BKGD in this study shows no signatures of the diamond core-hole exciton, and therefore, an MPD of 35 nm is not justified in this study. Therefore, we conclude that diamond electronic signatures can be discerned up to ∼15 nm of SiO2 thickness.

Figure 3

Figure 3. XAS spectra was found to effectively track the growth of silica via the decrease in diamond electronic structure and decreased exponentially due to inelastic Auger electrons generating the sample current. The distinct diamond structure decreases in signal intensity with increasing silica shell as the core-hole exciton and 2nd absolute band gap decrease (A). Plots D, E, and F are C 1s XAS of ND–SiO2 samples with 13 ± 5, 20 ± 5, and 35 ± 5 nm silica shells, respectively, where the diamond core-hole features are diminished or eliminated (B). The diamond core-hole intensity (TEY/BKGD) versus SiO2 thickness shows an exponential decrease, while the inset shows the natural logarithm of the TEY/BKGD signal with a linear least-squares regression and the resultant rate was used to generate the exponential fit of the raw TEY/BKGD data (C).

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Modeling of the C 1s Auger electrons and their intensity as a function of SiO2 overlayer thickness qualitatively agree with our observations. The NIST SESSA program was used to simulate the behavior of primary Auger electrons and inelastic secondary electrons. (56) The simulation focused on the diamond core-hole exciton, which we used for our analysis, the photon energy of 289.0 eV used for excitation, and the three CKL Auger electrons that are generated (see the SI for SESSA details). Forty inelastic collisions are modeled, similar to the 20–40 inelastic collisions in the first 100 fs of Ziaja et al. (46) Figure 4 summarizes the electron spectra of a 30 nm diamond core–shell nanoparticle with varying SiO2 shell thickness from 0.1 to 20 nm on a gold substrate. Simulated electron spectra of a 5 nm SiO2 shell at varying detector angles are presented in Figure 4A, and the inset shows the Auger electrons for C KL1L1, C KL1L23, and C KL23L23 at 246.8, 257.4, and 268.0 eV, respectively. A 55° detector angle was used to simulate Auger electron spectra in the kinetic energy range 220–290 eV (see inset of Figure 4B). The C KL23L23 Auger intensity showed an exponential decay with respect to SiO2 shell thickness, in agreement with the experimental C 1s XAS signal in TEY mode. The C KL23L23 feature was completely suppressed with a 20 nm shell. TEM images of NDs with silica shells of 20–30 nm and <5 nm are shown to illustrate the actual distribution of ND core sizes and silica shell thicknesses in this study in Figure 4C. Overall, the simulations with SESSA are in good agreement with the C 1s XAS spectra, the supporting TEM images, and show that primary Auger electrons produced from 289.0 eV photons at the diamond core-hole exciton yield an inelastic electron cascade that probes ∼15 nm into the core–shell nanoarchitecture.

Figure 4

Figure 4. SESSA simulations qualitatively supported the experimental TEY data of ND–SiO2 samples with increasing shell thickness (A) SESSA-based electron spectra for 30 nm diamond with 0.1–20 nm thick SiO2 shell. The top spectrum is representative of a 30 nm diamond with a 5 nm thick shell and reveals the signals from the gold substrate, SiO2 shells, and diamond core with detector angles from 0 to 75° in 15° increments. The inset shows the 3 Auger CKL features from 245 to 268 eV for a 5 nm thick SiO2 shell. A plot of the C KL23L23 intensity versus shell thickness shows an exponential decay consistent with our C 1s XAS data. The inset of the middle panel are simulations with a detector angle of 55°, an energy range of 220–290 eV and increasing SiO2 shell thickness from 0.1 to 20 nm. (B) TEM images of thick (20–30 nm) and thin (<5 nm) silica shells on HPHT ND cores are for reference to the Auger simulations generated by SESSA (C–F).

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XAS Conformation of Decarboxylation during SiO2 Growth, Different Carboxylate-Diamond versus Molecular Carboxylate XAS Signatures, and Silane-Mediated Molecular Decoration

Amorphous silica is a wide band gap insulator (∼9 eV) and causes the removal of acids on the HPHT ND surface while providing a flexible platform for chemical functionalization with amines, amides, azides, carboxylates, and fluorines. O 1s XAS data from the 1s XAS reveal distinct features supporting the conclusion that carboxylates are removed during silica growth and that diamond surface carboxylates are distinct from molecular carboxylates from silane-based chemistry. O 1s spectra in panel A show no π*(C═O) transition and a strong σ*(C–O) for ND–OH as expected for alcohol-rich diamond, and a π*(C═O) peak does emerge for ND-COOH at 530.2 eV after ABA chemistry is used (see the SI for methods). (39,57) After silica shell growth, the ND–SiO2 constructs show no π*(C═O) transitions at 530.2 eV reinforcing that silica growth causes decarboxylation. The mechanism for the loss of carboxylates with Si(OH)4 under basic ethanolic conditions is beyond the scope of this work, yet the bonding of SiO2 and CO2 under high-pressure and high-temperature conditions has been reported. (58) Santoro et al. described uni-, bidentate-, and bridged bonding of silicon carbonates and can provide a chemical framework for our observed decarboxylation when ND−COOH → ND–SiO2. After molecular decoration of ND–SiO2 with carboxyethylsilanetriol sodium salt, a new π*(C═O) peak is observed at 532.2 eV representing a molecular carboxylate, a +2 eV shift from carboxylates bound to the diamond surface. Previous O 1s XAS studies by Outka and Stöhr of formic and propanoic acid bound to Si (111) surfaces show similar π*(C═O) peak positions at 532.8 eV. (57) In comparison, glycidyl molecular decoration (ND–SiO2 + Gly), with a strained epoxy ring, contained a σ*(C–O) and σ*(Si–O) shape resonance ranging from 535 to 540 eV, and the XAS of the O 1s largely mimics the ND–SiO2 spectrum. ND–SiO2 + Gly also contains two small peaks at 529.0 and 531.5 eV caused by X-ray beam damage (59) that formed π*(C═O) electronic states through a loss of protons, as the starting glycidyl contains only single C–O bonds.
Molecular functionalization with polyethylene glycol (PEG), amines, and azides is used for biolabeling protocols and click chemistry and was confirmed with N 1s XAS. PEG and amines are important stabilizing and linking groups for biolabeling and biosensing with NV centers. (14) Neuronal biolabeling with ND–SiO2 + PEG + NH3 containing NV centers is shown in Figure S3 and clearly demonstrates the ability to use NV center fluorescence to distinguish the axon, axon hillock, and dendrites in neurons. Linking chemistry with amines is common with sulfo-NHS/EDC coupling, and azides are widely used in click chemistry. First, we modify the amine content and examine the use of N 1s XAS for ND–SiO2 + PEG + NH3 with PEG–amine ratios of 10:1 and 4:1, showing an increased N 1s signal with the 4:1 ratio sample. Peaks at 400.9 and 405.1 eV are assigned to σ*(N–H) and σ*(N–C) transitions, respectively (Figure 5B). X-ray damage of the aminated ND sample causes a weak π*(C═N) transition to arise at 398.3 eV and has been reported previously by Leinweber et al. (59) Aminated ND–SiO2 was then conjugated to folic acid using sulfo-NHS/EDC and resulted in a strong π*(C═N) peak arising at 398.0 eV due to amides present in the folate molecules and the new amide bonds that were formed on the ND–SiO2 + PEG + NH3 surface. From our N 1s XAS study, the chemically versatile amine group can be followed from its initial state, X-ray damage side products, and bioconjugated final state after using sulfo-NHS/EDC coupling reactions. Aminated ND–SiO2 samples were also probed with the transition edge sensor at beamline 10–1, and C 1s, N 1s, and O 1s occupied and unoccupied states were extracted from resonant inelastic X-ray scattering (RIXS) maps as previously described with direct diamond–amine bond formation (see the SI). (60) The RIXS data and extracted partial fluorescence yield-XAS and X-ray emission spectroscopy (XES) data reinforce the chemical bonding assignments described here (see S7, S8, and S9 for C 1s, N 1s, and O 1s RIXS maps and spectra, respectively).

Figure 5

Figure 5. XAS spectra of ND–SiO2 samples confirms the successful decoration of various molecules, the removal of carboxylate features after silica growth and differentiates between diamond bound versus molecular carboxylates. O 1s spectra of ND–OH, ND–COOH, ND–SiO2, ND–SiO2 + COOH, and ND–SiO2 + glycidoxy (epoxide ring) are shown in the ascending order (A). Alcohol-rich ND–OH has only a σ*(C–O) shape resonance at 536.4 eV, while ND–COOH (acid–base–acid treatment) has a π*(C═O) transition at 530.2 eV that is assigned to carboxylates. ND–SiO2 shows little π*(C═O) signatures, while ND–SiO2+COOH with folic acid functionalization chemistry has a distinct feature at 532.2 eV. ND–SiO2–glycidoxy shows little π*(C═O) and a shifted σ*(C–O) transition at 537.3 eV for epoxides. N 1s XAS spectra of ND–SiO2 + PEG + NH2 (10:1 ratio), ND–SiO2 + PEG + NH2 (4:1 ratio), X-ray induced beam damage of the ND–SiO2 + PEG + NH2 with 4:1 ratio, and ND–SiO2 + PEG + NH2 + Folate provides conformation of amine functionalization and conjugation chemistry (B). N 1s XAS spectrum of ND–SiO2 + azides is complex and shows resonance peaks for N1, N2, and N3 of the linear azide electronic structure. Peaks at 398.5, 399.5, 400.7, and 402.6 eV are assigned to π*(N1≡N), π*(N1/3═N), and two π*(N2═N+) transitions, respectively. Shape resonances at 404.1 and 405.8 eV were assigned to σ*(N3–C) and σ*(N═N), respectively. In contrast, the inset shows the simple F 1s transition for σ*(C–F) at 692.0 eV of a fluorinated ND–SiO2 sample (C).

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Azides produce a complex electronic spectrum of the linear N═N⊕═N⊖ ↔ N⊖–N⊕≡N structure with six assigned peaks and shape resonances that are commonly exploited in click chemistry and is contrasted with a fluorine-decorated surface (Figure 5C). For clarity, the nitrogen atoms are denoted by N1, N2, and N3, where N1 is the terminal nitrogen of the azido moiety. N 1s peaks were observed at 398.5, 399.5, and 400.7 eV and were assigned to the triple and double bond resonance states of π*(N1≡N⊕), π*(N1/3═N⊕), and π*(N2═N⊕), respectively. Shoulders and shape resonances at 403.1 404.6, and 406.3 eV are assigned to the π*(N2═N⊕), σ*(N3–C), and σ*(N═N) electronic states, respectively. The complexity of the azide structure has been clarified by density functional theory (DFT) calculations of the N 1s XAS spectrum. (61,62) In two manuscripts, Darlatt reports two photon energies for the π*(N1≡N⊕) transition at 398.6 and 399.6 eV. Our reported value of 398.5 eV is in agreement with their first report for a “pristine azide surface adsorbed monolayer”. In contrast, Darlatt’s second report did not agree with the first and reported the triple bond π*(N1≡N⊕) and π*(N1/3═N⊕) transitions were due to the 1s → 2p resonance of the terminal N1 atom using DFT and cited values of 399.6 and 400.9 eV, respectively. (62) The triple bond notation is used here to denote the contribution from sp hybridized orbitals in the N⊖–N⊕≡N resonance structure originally described by Pauling for methyl azide. (63) In contrast, a fluorinated ND–SiO2–F sample was also produced using 3,3,3-trifluoropropyl-trimethyoxysilane and a strong F 1s TEY signal at 692.0 eV was assigned to the σ*(C–F) resonance. The F 1s spectrum was similar to disordered PTFE films produced by a plasma deposition technique that generated primarily CF3 functional groups. (64) Fluorinated HPHT NDs may be used for the preparation of hydrophobic NDs and 19F magnetic resonance imaging applications. (65,66)
In conclusion, we have found that the growth of 2–35 nm SiO2 shells on highly purified HPHT NDs can suppress the underlying electronic structure of the diamond core with a probing depth of ∼15 nm. The silica growth mechanism was discovered to be driven by alcohols on the diamond surface, where hydroxylation occurs in basic ethanolic solutions and decarboxylation is prevalent during the silica growth reaction. HRTEM and EDS were used to confirm the average SiO2 shell thickness, and C 1s XAS data taken in TEY mode allowed the submerged diamond to be detected due to the inelastic secondary electron cascade produced by Auger electrons of 245–270 eV. XAS spectra of surface-functionalized ND–SiO2 samples were collected for azide, amine, fluorine, and other surface moieties to demonstrate the chemical flexibility of the silica surface for biolabeling and biosensing applications using NV center NDs. Because the silica growth is uniform across the diamond surface due to abundant alcohol groups, this work should inspire new diamond–metal oxide core–shell nanostructures to be explored for quantum sensing and biolabeling applications.

Experimental Methods and Procedures

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Materials

HPHT ND powders were purchased from Microdiamant AG (monocrystalline diamond powder MSY 0–0.05 μm). Fluorescent HPHT NDs (5–30 nm) were provided by Bikanta, Inc. (Berkeley, CA), Adamas Nanotechnologies (Raleigh, NC), and Diamond Nanotechnologies (Boston, MA). Tetraethyl orthosilicate (TEOS #333859, 99+%), (3-mercaptopropyl) trimethyoxysilane (MPS #175617, 95%), and (3-aminopropyl)trimethoxysilane (APS #281778, 98%) were purchased from Sigma-Aldrich (St. Louis, MO). 2-[Methoxy(polyethyleneoxy)6–9propyl]trimethoxysilane (PEG–PS (n = 6–9), #SIM6492.7) and 2-[methoxy(polyethyleneoxy)9–12propyl]trimethoxysilane (PEG–PS (n = 9–12), #SIM6492.7), 3,3,3-trifluoropropyl-trimethyoxysilane (FMS) (SIT8372.0), carboxyethylsilanetriol sodium salt in water (CES) (SIC2263.0), (3-glycidyl)trimethoxysilane (SIG5840.0), and 11-azidoundecyltrimethoxysilane (11-AMS) (SIA0795.0) were purchased from Gelest, Inc. (Morrisville, PA).

Aerobic Oxidation and Acid–Base–Acid Treatment of Diamond Nanocrystals

Nanodiamond powders were placed in a ceramic boat, loaded into a tube furnace, left open to the air, and heated to a temperature of 525 °C for 5 h. After cooling to room temperature, oxidized HPHT NDs had a light yellowish tone after the oxidation of dark amorphous carbon. HPHT ND powders were then further oxidized in sequential steps. Oxidized NDs (300 mg) were placed into a 9:1:1 (H2SO4:HNO3:H2O/(54:6:6 mL)) acid mixture, stirred at 500 rpm, and heated to 80 °C for 24 h with a refluxing column. After 24 h of refluxing, an additional 500 mL of Milli-Q (18.2 MΩ·cm–1) H2O was then added to the mixture while stirring and cooled by an ice bath. The acid-ND mixture was then transferred to 50 mL conical centrifuge tubes and centrifuged at 5000 relative centrifugal force (RCF) for 30 min. The acidic supernatant was discarded and the rinsing completed three more times. The removal of all acidic ions was confirmed via pH, and purification cycles were stopped when a pH of 7.5–8.0 was reached. The ND solution (300 mg in 5 mL of Milli-Q water) was then placed into 0.1 M NaOH solution (100 mL) at 80 °C and stirred at 500 rpm with a refluxing column for 24 h. The same centrifugation, decantation, and solubilization cycles with Milli-Q H2O were repeated 3 times, and 500 μL of 1 M KCl (0.2 μm filtered) was added to induce precipitation per 50 mL of solution. The ND powders were placed in a final acid treatment in 1 M HCl at 80 °C (100 mL) with stirring for 24 h with a refluxing column. The purification steps were again repeated with the addition of 1 M NaCl to induce precipitation. The carboxylated HPHT NDs (ND–COOH) were then solubilized in 18.2 MΩ·cm–1 H2O at a concentration of 1.0 mg/mL and horn sonicated for 10 min at 70% power with 5:2 s on/off cycles. The final ND–COOH is expected to have approximately 7% carboxyls on the surface as described previously. (18)

Ultrathin SiO2 Growth Procedure of ND–COOH

Ten mL of 1.0 mg/mL ND–COOH was concentrated into a pellet via centrifugation at 21,000 RCF for 30 min in 2 mL centrifuge tubes. The purified ND–COOH pellets were concentrated into 1 mL of 18 MW water by consolidating the ND–COOH pellets to a 10 mg/mL solution. The ND pellet (10 mg) was then dispersed into 9.5 mL of 18 MW water and cup-horn-sonicated for 5 min. The ND–COOH sample in 10.5 mL of water, 37.5 mL of ethanol (99.99%), and 300 μL of neat TEOS was added to a 100 mL single neck round-bottom and was cup-horn-sonicated for 2 min at 70% power. The mixture was set stirring at 500 rpm, and 900 μL of 25% NH4OH was added to initiate the reaction and capped with a septum at 25 °C. The final concentration of TEOS is 27.3 mM for this protocol. The reaction was allowed to proceed for 5–25 min under stirring and then purified via centrifugation. Large SiO2 aggregates and microparticles were removed via centrifugation of the solution in 50 mL conical tubes for 30 min at 4000 rpm (2,500 RCF). The ND–SiO2 supernatant was collected and further purified at 21,000 RCF for 20 min, and the pellets were redispersed in ethanol. The ND–SiO2 pellets were washed in ethanol three times, methanol three times, and 18.2 MΩ water once by centrifugation at 21,000 RCF for 20 min. The ND–SiO2 samples were dispersed by bath sonication and vortexing between centrifugation and decantation cycles. The final purified product was dispersed in water at 1 mg/mL, freeze-dried with liquid nitrogen, and cryogenically desiccated in a Labconco lyophilizer. The ND–SiO2 powders were then stored at 5 °C until they were ready for chemical functionalization. Final powder weights ranged from 15 to 30 mg after silica shell growth.

Functionalization of ND–SiO2 with PEG, Amines, Fluorine, Carboxylic acids, and Azides

1 mg/mL ND–SiO2 solutions in ethanol were used for surface functionalization protocols. In a typical 9:1 (PEG:Amines) functionalization protocol, 10 mL of 1 mg/mL ND–SiO2 particles in ethanol, 20 mL of ethanol (200 proof), 1 mL of NH4OH (25%), 1.44 mL of PEG–PS (9–12 repeating units), 46 μL of APS, and 750 uL of milli-Q water were added to a 100 mL round-bottom flask with a stir bar. The solution was stirred overnight at 700 rpm for 24 h at 25°. ND–SiO2 + PEG + NH2 particles were washed in ethanol three times by centrifugation at 21,000 RCF for 15 min, sonicated, and vortexed between purification cycles. Functionalization with only amines, fluorines, carboxylates, and azides included addition of 460 μL of APS, 505 μL of FMS, 442 μL of CES, and 860 μL of 11-AMS under the above conditions.
As a demonstration of a biological staining protocol, ND–SiO2 + PEG + NH2 with nitrogen vacancy centers was used to stain hippocampal cells and imaged with a scanning confocal microscope. Neuron staining images were reproduced with consent of Profs. Dirk Englund and Edward Boyden (Massachusetts Institute of Technology, Cambridge, MA). Hippocampal cell preparation and staining are similar to work by Chang and Boyden in the literature. (67)

TEM and EDS Measurements

High-resolution transmission electron microscopy was carried out at the Molecular Foundry at Lawrence Berkeley National Laboratory on a JEOL 2100-F instrument at an accelerating voltage of 80–200 keV with an Oxford high solid-angle Silicon Drift Detector (SDD) X-ray Energy Dispersive Spectrometer (EDS) system for chemical elemental analysis and a High-Angle Annular Dark Field (HAADF) detector. Samples were deposited from solution onto ultrathin holey carbon TEM grids from Ted Pella (#01824). To render the TEM grids hydrophilic, they were plasma ecthed in a Hummer 6.2 for 3 min. A single drop from a pasteur pipet was deposited while holding the TEM grids in self-closing tweezers, and the droplet was reduced in volume with a pie-shaped piece of filter paper and allowed to air-dry. Analysis of silica shell thicknesses was performed by using Image-J software.

DRIFTS Parameters and Analysis

Diffuse reflectance infrared Fourier transmission spectroscopy (DRIFTS) was collected on a Thermo-Nicolet 6700 instrument with a Praying Mantis DRIFTS attachment and the high-temperature reaction chamber. All spectra were collected on a LN2-cooled MCT detector with 2 cm–1 resolution and 128 scans. All ND samples were mixed with spectroscopic grade KBr for data collection. Samples of 2–3 mg were typically used for DRIFTS collection. Kubelka–Munk transformations were performed individually with linear background corrections using Igor Pro software. Linear backgrounds were generated based on the averaged values of percent reflectance (raw data) in the DRIFTS regions of 2000–2200 and 3800–4000 cm–1. This slope value was then applied to a y-intercept function (y = mx + b) and applied to spectra for normalized reflectance units (R) and then transformed using the Kubleka–Munk equation to make the data proportional to concentration:
KMUnits=(1−R2)2R
(2)
Infrared values were cross-referenced to Infrared and Raman characteristic group frequencies: tables and charts by Socrates and HPHT ND studies. (54,68−71)

ND–OH, ND–COOH, and ND–SiO2 Deposition on Gold-Coated Silicon Wafers for XAS, XPS, and XES Experimentation

Gold-coated silicon wafers from LGA thin films (Santa Clara, CA) were cut into 1 cm × 1 cm squares, bath-sonicated in acetone, 2-propanol, and 18 MΩ water three times, and dried with a N2 gun. The wafers were then etched for a minimum of 10 min with a piranha solution (90 mL concentrated sulfuric acid and 10 mL hydrogen peroxide), with the gold layer facing upward in a crystallizing dish. After drying the etched Au wafer with a N2 gun, 300 μL of 1 mg/mL ND solution was deposited, dried onto the substrate, and covered with a crystallizing dish. Oxidized and silica-coated nanodiamond samples were prepared using 18 MΩ water as a solvent under open-air conditions at 1 mg/mL concentrations. Note: a 10 nm Ti or Cr adhesion layer is used prior to 100 nm gold deposition on Si substrates. Piranha etching did cause pinhole etching of the gold and adhesion layers.

Synchrotron XAS Data Collection, PFY-XAS/XES Analysis, and RIXS Measurements

X-ray absorption spectroscopy (XAS) and resonant ineleastic X-ray scattering (RIXS) measurements were performed at beamline 8–2 and 10–1 at the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory using a spot size of <1 mm2. Samples were handled in open-air conditions and mounted to an Al sample bar with conductive carbon tape (#16073-4 Ted Pella, Inc. Redding, CA). The samples were transported to the beamline in a sealed polypropylene jar, and a magnetic mounting piece was attached to the sample bar. Samples were introduced into the analysis chamber after the transfer chamber reached 1 × 10–7 Torr. The analysis chamber pressure was typically 5 × 10–9 Torr.
At 8–2 and 10–1, carbon, nitrogen, oxygen, and fluorine K-edge XAS was measured in total electron yield (TEY) mode using 42 × 42, 40 × 40, 30 × 30, and 30 × 30 μm slits, respectively. TEY mode probes approximately 5–15 nm of the sample depth in normal conditions, and all experiments were conducted under ultrahigh vacuum conditions (∼5 × 10–9 Torr). After the optics were focused, the reference absorption intensity of the incoming X-ray beam was measured using a sample of gold-coated mesh and used to correct for beam instability. XAS data were collected at an incident electric field vector of 54.7°. For the spectral analysis, the linear pre-edge background was subtracted from the raw XAS spektra. The region used to estimate the background before the absorption edge of carbon, nitrogen, oxygen, and fluorine was 260–280, 370–380, 510–530, and 670–680 eV, respectively. A postedge normalization was also performed in the continuum region at 380 eV for carbon, 420 eV for nitrogen, 580 eV for oxygen, and 730 eV for fluorine using a batch processing macro in Igor Pro. Energy calibration was performed using the signal from the diamond core-hole exciton which is determined to be 289.0 eV as described elsewhere. (38) X-ray energy calibration of the synchrotron light source was performed during grating changes with a Ni slab (Ni L3 absorption) and a 1-point fitting procedure.
Resonant inelastic X-ray scattering (RIXS) measurements were performed using the superconducting transition edge sensor (TES) X-ray detector as described elsewhere by Lee and Titus. (72,73) The TES allows for background-free X-ray detection with good energy resolution (∼1.5 eV) without diffraction grating. An RIXS measurement is performed by sweeping monochromator photon energies across the absorption edge and collecting a time-tagged X-ray pattern across the TES detector. The TES allows for all photons to be simultaneously collected across all detector elements in the array. The RIXS data were integrated to produce partial fluorescence yield (PFY)-XAS and X-ray emission spectroscopy (XES) spectra.

Laboratory XPS Measurements and Analysis

A Thermo Scientific K-Alpha Surface Analysis XPS instrument at the Molecular Foundry was utilized to probe carbon, nitrogen, and bromine signals on the surface of the ND–OH and ND–SiO2 samples. The K-Alpha XPS has a combined low energy electron and ion flood source and is utilized to suppress charging during all data collection. The XPS X-ray source is an Al Kα microfocused monochromator and is equipped with a 180° double hemispherical analyzer with a 128-channel detector. The low-resolution and high-resolution pass energies are 200.0 and 50.0 eV, respectfully. The low-resolution and high-resolution energy step sizes are 1.0 and 0.1 eV, respectively. For high-resolution scans, 50 scans were taken for nitrogen and 10 scans for oxygen, silicon, and carbon with a dwell time of 50 ms to ensure a good signal-to-noise. The electron acceptance angle was 55°, and survey scans were performed over a binding energy range of 0–1350 eV with a pass energy of 200 eV. Three scans were summed, and a dwell time of 10 ms was used.
XPS analysis was performed using Igor Pro software and the CASA-XPS software package, and standard background subtraction and fitting protocols were followed for survey and high-resolution scans. Quantitative analysis of survey scans to determine the atomic % concentrations of individual elements was performed using CASA-XPS software, and Tougaard backgrounds were applied with relative sensitive factor (RSF) values being applied for each element. RSF values for C, O, and Si were 1.0, 2.93, and 0.817, respectively. Atomic % concentrations are calculated using equation:
XA=(IAEα)/(RAT(E))∑(IiEα)/(RiT(E))
(3)
where X is the atomic percentage of element A, Ri is the RSF for the relative intensity Ii, and T(E) is the transmission function of the instrument for intensity Ii at kinetic energy E. (74) The α term in the exponent of kinetic energy E is used to adjust the analyzer specifications. The VAMAS (Versailles Project on Advanced Materials and Standards) file collected by the K-Alpha instrument allowed for all needed transmission function information to be applied for quantification purposes. The VAMAS file type is ISO 14976 compliant. XPS features from the thin film substrate include Au 4f, Si 2p, and Ti 3s found at 85, 99, and 59 eV, respectively.

SESSA Simulations

The software package Simulation of Electron Spectra for Surface Analysis (SESSA) version 2.2.0, produced by Werner, Smekal, and Powell, was used to simulate the emission of Auger electrons from diamond- and silica-coated diamond samples. The user interface is intuitive and includes the generation of the sample, peak selection, parameter selection, and experimental configuration. The sample generation was done with the layered sphere preset and included a 30 nm diamond core, 0–40 nm of silica, and a Au substrate as the underlayer. The experimental configuration was matched to the photon energy of beamlines 8–2 and 10–1 at SSRL at 289.0 eV that generates the diamond core-hole exciton. (38,39) Data collection geometry for orientation of the theta values for sample surface normal, orientation of the analyzer axis, orientation of the source axis, and orientation of polarization vector was set to 0° and ranged from 0° to 90° in increments of 15°, 54°, and 0°, respectively. All phi values were set to 0° in the geometry setting. Peaks of interest included the Auger peaks of C KL1L1 at 246.8 eV, C KL1L23 at 257.4 eV, and C KL23L23 at 268.0 eV and complementary Au 4f, Au 5s, Si 2p, and O 2s photoemission peaks. The carbon diamond core and amorphous SiO2 shells were assigned a standard band gap and atomic density of 5.5 eV (75) and 1.17 × 1023 atoms/cm3 and 9.1 eV (76) and 6.58 × 1022 atoms/cm3, respectively. The thickness of SiO2 shells was varied from 0.1 to 30 nm in the SESSA software, and the intensity of the C Auger features was tracked. Screenshots of the SESSA user interface are shown in Figure S1.

Thermogravimetric Analysis–Mass Spectroscopy (TGA–MS) of ND–SiO2

As prepared ND–SiO2 samples in ethanol or water were dried on a Si wafer and collected as a powder for TGA-MS characterization. The TGA-MS was carried out on a PerkinElmer TGA-GC-MS system with a TGA 8000, Clarus 680 gas chromatograph, Clarus SQ 8T mass spectrometer, and Transfer Line (TL) 8500 TG-GCMS interface system. The carrier gas was high-purity helium (99.9999% purity). The TGA 8000 experimental conditions included a temperature ramp from 30 to 700 °C at 10 °C/min, a sample purge of 60 mL/min, balance purge of 40 mL/min, and the use of 5 mg of ND–SiO2 into a tared ceramic sampling pan (Fisher Sci #N5320102). The evolved gas was transferred by the TL 8500 at 270 °C with a flow rate of 70 mL/min into the TG-GCMS. The gas chromatograph (GC) line was bypassed, and the evolved gas was sent into the mass spectrometer (MS). MS data collection included standard conditions of −70 V electron energy, a source temperature of 100 °C, and trap emission of 100 V.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnanoscienceau.3c00033.

  • Thermogravimetric analysis-mass spectroscopy (TGA-MS) confirming the silica-ND bonding environment, fluorescent scanning confocal images of NV center stained neurons, TEM of silica-coated NDs, X-ray photoelectron spectroscopy data, and resonant inelastic X-ray spectroscopy for C 1s, N 1s, and O 1s edges (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Perla J. Sandoval - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Karen Lopez - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Andres Arreola - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Anida Len - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Nedah Basravi - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Pomaikaimaikalani Yamaguchi - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Rina Kawamura - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Camron X. Stokes - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Cynthia Melendrez - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Davida Simpson - Department of Chemistry, San José State University, 1 Washington Square, San José, California 95192, United States
    • Sang-Jun Lee - Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States;  Orcidhttps://orcid.org/0000-0002-8199-3993
    • Charles James Titus - Department of Physics, Stanford University, 382 Via Pueblo Mall, Palo Alto, California 94025, United States;  Orcidhttps://orcid.org/0000-0001-6312-8552
    • Virginia Altoe - The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
    • Sami Sainio - Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States;  Microelectronics Research Unit, University of Oulu, Pentti Kaiteran katu 1, Linnanmaa, P.O. Box 4500, Oulu 90014, Finland
    • Dennis Nordlund - Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States
    • Kent Irwin - Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sandhill Road, Menlo Park, California 94025, United States;  Department of Physics, Stanford University, 382 Via Pueblo Mall, Palo Alto, California 94025, United States
  • Author Contributions

    P.J.S., K.L., and A.A. contributed equally. CRediT: Perla J. Sandoval data curation, investigation; Karen Leonor Lopez data curation, formal analysis, investigation; Andres Arreola data curation, investigation; Anida Len data curation; Nedah Basravi investigation, resources, software, supervision, writing-review & editing; Pomaikaimaikalani Yamaguchi data curation, formal analysis; Rina Kawamura formal analysis, investigation; Camron X. Stokes investigation; Cynthia Melendrez formal analysis, investigation; Davida Simpson investigation; Sang-Jun Lee data curation, formal analysis, investigation, methodology, writing-review & editing; Charles James Titus data curation, formal analysis, investigation; Virginia Altoe investigation, resources; Sami Sainio investigation; Dennis Nordlund formal analysis, resources, software, supervision, writing-review & editing; Kent Irwin resources, software, supervision; Abraham Wolcott data curation, funding acquisition, methodology, resources, writing-original draft.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Abraham Wolcott would like to acknowledge financial support through the National Institutes of Health NIGMS office (1SC3GM125574-01), Army Research Office (W911NF1810453 and W911NF17S000205) through the Department of Defense and the National Science Foundation #2213520. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The TES spectrometer was developed with funding from the Department of Energy, Laboratory Directed Research and Development program under Contract No. DE-AC02-76SF00515. This work was supported by the U.S. Department of Energy Office of Basic Energy Sciences Proposal No. 100487. The use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Perla Jasmine Sandoval would like to acknowledge support through the MARC and RISE program at SJSU (5T34GM008253-33 and 5R25GM071381-13). Karen Lopez would like to acknowledge support through the RISE program at SJSU (5R25GM071381-13). We would also like to acknowledge William B. Doriese, Galen C. O’Neil, Daniel S. Swetz and Joel N. Ullom, of the Quantum Electromagnetics Division at the National Institutes of Standards and Technology in Boulder, CO. for the engineering, design, manufacturing, and installation of the transition edge sensor at beamline 10-1 at SSRL.

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    http://www.nature.com/srep/2014/140328/srep04495/abs/srep04495.html#supplementary-information

  18. 18
    Nguyen, T. T.-B.; Chang, H.-C.; Wu, V. W.-K. Adsorption and hydrolytic activity of lysozyme on diamond nanocrystallites. Diamond Relat. Mater. 2007, 16 (4), 872– 876,  DOI: 10.1016/j.diamond.2007.01.030
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    Adsorption and hydrolytic activity of lysozyme on diamond nanocrystallites
    Nguyen, T.-Thanh-Bao; Chang, Huan-Cheng; Wu, Victor Wei-Keh
    Diamond and Related Materials (2007), 16 (4-7), 872-876CODEN: DRMTE3; ISSN:0925-9635. (Elsevier B.V.)
    Oxidative-acid-treated nanodiamonds exhibit high affinity for proteins, a property well suited for immobilization of enzymes for biotechnol. application. Using lysozyme as an example, this work demonstrates that the enzyme can retain much of its activity after phys. adsorption to the surfaces of 100-nm diamond crystallites. The activity relative to that of free lysozyme in soln. is ∼ 60% at the max. surface coverage of 50% and pH 5. While the enzymic activity decreases as the surface coverage is lowered, it can be recovered by blocking the empty sites on the surface with supplementary proteins such as cytochrome c to create a more "crowded" environment. A relative activity up to 70% can be attained at a partial coverage of 20%.
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    Gerion, D.; Pinaud, F.; Williams, S. C.; Parak, W. J.; Zanchet, D.; Weiss, S.; Alivisatos, A. P. Synthesis and properties of biocompatible water-soluble silica-coated CdSe/ZnS semiconductor quantum dots. J. Phys. Chem. B 2001, 105 (37), 8861– 8871,  DOI: 10.1021/jp0105488
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    Synthesis and Properties of Biocompatible Water-Soluble Silica-Coated CdSe/ZnS Semiconductor Quantum Dots
    Gerion, Daniele; Pinaud, Fabien; Williams, Shara C.; Parak, Wolfgang J.; Zanchet, Daniela; Weiss, Shimon; Alivisatos, A. Paul
    Journal of Physical Chemistry B (2001), 105 (37), 8861-8871CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
    The authors describe the synthesis of H2O-sol. semiconductor nanoparticles and discuss and characterize their properties. Hydrophobic CdSe/ZnS core/shell nanocrystals with a core size between 2 and 5 nm are embedded in a siloxane shell and functionalized with thiol and/or amine groups. Structural characterization by AFM indicates that the siloxane shell is 1-5 nm thick, yielding final particle sizes of 6-17 nm, depending on the initial CdSe core size. The SiO2 coating does not significantly modify the optical properties of the nanocrystals. Their fluorescence emission is ∼32-35 nm fwhm and can be tuned from blue to red with quantum yields up to 18%, mainly detd. by the quantum yield of the underlying CdSe/ZnS nanocrystals. Silanized nanocrystals exhibit enhanced photochem. stability over org. fluorophores. They also display high stability in buffers at physiol. conditions (>150 mM NaCl). The introduction of functionalized groups onto the siloxane surface would permit the conjugation of the nanocrystals to biol. entities.
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    Alivisatos, P. The use of nanocrystals in biological detection. Nat. Biotechnol. 2004, 22 (1), 47– 52,  DOI: 10.1038/nbt927
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    The use of nanocrystals in biological detection
    Alivisatos, Paul
    Nature Biotechnology (2004), 22 (1), 47-52CODEN: NABIF9; ISSN:1087-0156. (Nature Publishing Group)
    A review. In the coming decade, the ability to sense and detect the state of biol. systems and living organisms optically, elec. and magnetically will be radically transformed by developments in materials physics and chem. The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biol. sensors. These new systems will be capable of sensing at the single-mol. level in living cells, and capable of parallel integration for detection of multiple signals, enabling a diversity of simultaneous expts., as well as better crosschecks and controls.
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    Ghosh Chaudhuri, R.; Paria, S. Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications. Chem. Rev. 2012, 112 (4), 2373– 2433,  DOI: 10.1021/cr100449n
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    Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications
    Ghosh Chaudhuri, Rajib; Paria, Santanu
    Chemical Reviews (Washington, DC, United States) (2012), 112 (4), 2373-2433CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. The synthesis and properties of inorg./inorg., inorg./org., org./inorg., and org./org. core/shell nanoparticles are extensively reviewed. Their applications in biomedicine, catalysis, and electronic devices are discussed.
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  22. 22
    Lee, J. R. I.; Whitley, H. D.; Meulenberg, R. W.; Wolcott, A.; Zhang, J. Z.; Prendergast, D.; Lovingood, D. D.; Strouse, G. F.; Ogitsu, T.; Schwegler, E. Ligand-Mediated Modification of the Electronic Structure of CdSe Quantum Dots. Nano Lett. 2012, 12 (6), 2763– 2767,  DOI: 10.1021/nl300886h
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    Ligand-Mediated Modification of the Electronic Structure of CdSe Quantum Dots
    Lee, Jonathan R. I.; Whitley, Heather D.; Meulenberg, Robert W.; Wolcott, Abraham; Zhang, Jin Z.; Prendergast, David; Lovingood, Derek D.; Strouse, Geoffrey F.; Ogitsu, Tadashi; Schwegler, Eric; Terminello, Louis J.; van Buuren, Tony
    Nano Letters (2012), 12 (6), 2763-2767CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    X-ray absorption spectroscopy and ab initio modeling of the exptl. spectra have been used to investigate the effects of surface passivation on the unoccupied electronic states of CdSe quantum dots (QDs). Significant differences are obsd. in the unoccupied electronic structure of the CdSe QDs, which are shown to arise from variations in specific ligand-surface bonding interactions.
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    Meulenberg, R. W.; Lee, J. R. I.; Wolcott, A.; Zhang, J. Z.; Terminello, L. J.; van Buuren, T. Determination of the Excition Binding Energy in CdSe Quantum Dots. ACS Nano 2009, 3 (2), 325– 330,  DOI: 10.1021/nn8006916
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    Determination of the Exciton Binding Energy in CdSe Quantum Dots
    Meulenberg, Robert W.; Lee, Jonathan R. I.; Wolcott, Abraham; Zhang, Jin Z.; Terminello, Louis J.; van Buuren, Tony
    ACS Nano (2009), 3 (2), 325-330CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been detd. using X-ray spectroscopy. Using X-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been detd. and combined to obtain the true band gap of the QDs (i.e., without an exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to det. the EBE. The exptl. EBE results are compared with theor. calcns. on the EBE and show excellent agreement.
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    Wei, H.; Zhou, J.; Zhang, L.; Wang, F.; Wang, J.; Jin, C. The Core/Shell Structure of CdSe/ZnS Quantum Dots Characterized by X-Ray Absorption Fine Spectroscopy. J. Nanomater. 2015, 2015, 764712  DOI: 10.1155/2015/764712
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    Carpenter, E. E.; Calvin, S.; Stroud, R. M.; Harris, V. G. Passivated Iron as Core–Shell Nanoparticles. Chem. Mater. 2003, 15 (17), 3245– 3246,  DOI: 10.1021/cm034131l
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    Passivated Iron as Core-Shell Nanoparticles
    Carpenter, E. E.; Calvin, S.; Stroud, R. M.; Harris, V. G.
    Chemistry of Materials (2003), 15 (17), 3245-3246CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Core-shell passivated Fe magnetic nanoparticles were prepd. using reverse micelles of Igepal CO-430 and Igepal CO-610 (nonylphenol polyethoxylate ethers) to reduce FeCl2 with NaBH4 to form the Fe nanoparticles and reducing NiCl2 to form the passivation coating of oxide. The particles are amorphous iron with amorphous oxide coating. At 10 and 300 K the magnetization is 85.4 and 74.4 emu/g with a coercivity of 200 and <100 Oe and remanence of 14.9 and 5.6 emu/g, resp.
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    Carroll, K. J.; Hudgins, D. M.; Spurgeon, S.; Kemner, K. M.; Mishra, B.; Boyanov, M. I.; Brown, L. W.; Taheri, M. L.; Carpenter, E. E. One-Pot Aqueous Synthesis of Fe and Ag Core/Shell Nanoparticles. Chem. Mater. 2010, 22 (23), 6291– 6296,  DOI: 10.1021/cm101996u
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    One-Pot Aqueous Synthesis of Fe and Ag Core/Shell Nanoparticles
    Carroll, Kyler J.; Hudgins, Daniel M.; Spurgeon, Steven; Kemner, Kennneth M.; Mishra, Bhoopesh; Boyanov, Maxim I.; Brown, Lester W., III; Taheri, Mitra L.; Carpenter, Everett E.
    Chemistry of Materials (2010), 22 (23), 6291-6296CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    This article studies a facile one-pot method for the synthesis of Fe and Ag core/shell nanoparticles by aq. redn. under ambient conditions. The injection time of silver nitrate into a reaction vessel contg. aq. ferrous salt, sodium borohydride, and sodium citrate is a vital parameter for the precise control of a desired core/shell structure. For example, if silver nitrate is injected one minute after sodium borohydride was added to the reaction vessel, Ag will nucleate first followed by Fe, creating monodisperse Ag/Fe core/shell nanoparticles. In contrast, if the introduction time is prolonged to 5 min, Fe nanoparticles will nucleate followed by Ag producing Fe/Ag nanoparticles. The compn., morphol., and magnetic behavior were studied by x-ray absorption spectroscopy (XAS), XPS, XRD, TEM, and room-temp. vibrating sample magnetometry (VSM). Fe/Ag core/shell nanoparticles with optical and magnetic functionality offer broad opportunities in medicine, catalysis, and chem. detection.
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    Zhang, X.; Han, S.; Zhu, B.; Zhang, G.; Li, X.; Gao, Y.; Wu, Z.; Yang, B.; Liu, Y.; Baaziz, W. Reversible loss of core–shell structure for Ni–Au bimetallic nanoparticles during CO2 hydrogenation. Nat. Catal. 2020, 3 (4), 411– 417,  DOI: 10.1038/s41929-020-0440-2
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    Reversible loss of core-shell structure for Ni-Au bimetallic nanoparticles during CO2 hydrogenation
    Zhang, Xiaoben; Han, Shaobo; Zhu, Beien; Zhang, Guanghui; Li, Xiaoyan; Gao, Yi; Wu, Zhaoxuan; Yang, Bing; Liu, Yuefeng; Baaziz, Walid; Ersen, Ovidiu; Gu, Meng; Miller, Jeffrey T.; Liu, Wei
    Nature Catalysis (2020), 3 (4), 411-417CODEN: NCAACP; ISSN:2520-1158. (Nature Research)
    The high catalytic performance of core-shell nanoparticles is usually attributed to their distinct geometric and electronic structures. Here we reveal a dynamic mechanism that overturns this conventional understanding by a direct environmental transmission electron microscopy visualization coupled with multiple state-of-the-art in situ techniques, which include synchrotron X-ray absorption spectroscopy, IR spectroscopy and theor. simulations. A Ni-Au catalytic system, which exhibits a highly selective CO prodn. in CO2 hydrogenation, features an intact ultrathin Au shell over the Ni core before and after the reaction. However, the catalytic performance could not be attributed to the Au shell surface, but rather to the formation of a transient reconstructed alloy surface, promoted by CO adsorption during the reaction. The discovery of such a reversible transformation urges us to reconsider the reaction mechanism beyond the stationary model, and may have important implications not only for core-shell nanoparticles, but also for other well-defined nanocatalysts.
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    Signorini, L.; Pasquini, L.; Savini, L.; Carboni, R.; Boscherini, F.; Bonetti, E.; Giglia, A.; Pedio, M.; Mahne, N.; Nannarone, S. Size-dependent oxidation in iron/iron oxide core-shell nanoparticles. Phys. Rev. B 2003, 68 (19), 195423  DOI: 10.1103/PhysRevB.68.195423
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    Size-dependent oxidation in iron/iron oxide core-shell nanoparticles
    Signorini, Luca; Pasquini, Luca; Savini, Lorenzo; Carboni, Roberta; Boscherini, Federico; Bonetti, Ennio; Giglia, Angelo; Pedio, Maddalena; Mahne, Nicola; Nannarone, Stefano
    Physical Review B: Condensed Matter and Materials Physics (2003), 68 (19), 195423/1-195423/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    A detailed morphol. and structural characterization of iron/iron oxide core-shell nanoparticles with x-ray diffraction and x-ray absorption spectroscopy performed at both the Fe and O K edges is reported. Core-shell nanoparticles with core size ranging from 7 to 21 nm were synthesized using the inert gas condensation technique followed by 12 h of controlled surface oxidn. Rietveld anal. of diffraction patterns shows the presence of α-Fe nanoparticles surrounded by a 2-3 nm-thick oxide layer with a disordered cubic spinel structure. Magnetite (Fe3O4) and maghemite (γ-Fe2O3), two different iron oxides, share this lattice structure, but x-ray diffraction was not able to distinguish between the two. An anal. of the Fe and O x-ray absorption spectra in both the near-edge and the extended energy regions is described. The anal. of the extended spectra was performed using the ab initio calcn. of all significant contributions to the absorption cross section. There are size-dependent changes in the local structure and oxidn. state of the oxide shell, the relative fraction of maghemite increasing at the expense of magnetite as the core dimensions decrease. This size/structure correlation was explained in terms of morphol. and structural disorder.
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    Alayoglu, S.; Zavalij, P.; Eichhorn, B.; Wang, Q.; Frenkel, A. I.; Chupas, P. Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt–Ru Core–Shell and Alloy Nanoparticles. ACS Nano 2009, 3 (10), 3127– 3137,  DOI: 10.1021/nn900242v
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    Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt-Ru Core-Shell and Alloy Nanoparticles
    Alayoglu, Selim; Zavalij, Peter; Eichhorn, Bryan; Wang, Qi; Frenkel, Anatoly I.; Chupas, Peter
    ACS Nano (2009), 3 (10), 3127-3137CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are cryst. homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 Å. In contrast, the 1-2 monolayer thick Pt shells are relatively cryst. but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination nos. and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-sepd. in the core and shell components and that the interface between the core and shell is quite normal.
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    Park, J.-I.; Kim, M. G.; Jun, Y.-W.; Lee, J. S.; Lee, W.-R.; Cheon, J. Characterization of Superparamagnetic “Core–Shell” Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic “Solid Solution” Nanoalloys. J. Am. Chem. Soc. 2004, 126 (29), 9072– 9078,  DOI: 10.1021/ja049649k
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    Characterization of Superparamagnetic "Core-Shell" Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic "Solid Solution" Nanoalloys
    Park, Jong-Il; Kim, Min Gyu; Jun, Young-Wook; Lee, Jae Sung; Lee, Woo-Ram; Cheon, Jinwoo
    Journal of the American Chemical Society (2004), 126 (29), 9072-9078CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The structure, magnetism, and phase transition of core-shell type CoPt nanoparticles en route to solid soln. alloy nanostructures are systematically studied. The characterization of CocorePtshell nanoparticles obtained by a redox transmetalation process by TEM and, in particular, x-ray absorption spectroscopy (XAS) provides clear evidence for the existence of a core-shell type bimetallic interfacial structure. Nanoscale phase transitions of the CocorePtshell structures toward c-axis compressed face-centered tetragonal (fct) solid soln. alloy CoPt nanoparticles were monitored at various stages of a thermally induced annealing process and the obtained fct nanoalloys show a large enhancement of their magnetic properties with ferromagnetism. The relation between the nanostructures and their magnetic properties is in part elucidated through the use of XAS as a crit. anal. tool.
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    Lee, W.-R.; Kim, M. G.; Choi, J.-R.; Park, J.-I.; Ko, S. J.; Oh, S. J.; Cheon, J. Redox–Transmetalation Process as a Generalized Synthetic Strategy for Core–Shell Magnetic Nanoparticles. J. Am. Chem. Soc. 2005, 127 (46), 16090– 16097,  DOI: 10.1021/ja053659j
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    Redox-Transmetalation Process as a Generalized Synthetic Strategy for Core-Shell Magnetic Nanoparticles
    Lee, Woo-Ram; Kim, Min Gyu; Choi, Joon-Rak; Park, Jong-Il; Ko, Seung Jin; Oh, Sang Jun; Cheon, Jinwoo
    Journal of the American Chemical Society (2005), 127 (46), 16090-16097CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential redn. strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no addnl. reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an org. phase to an aq. phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chem. process that promotes the core-shell structure formation.
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    Foucher, A. C.; Yang, S.; Rosen, D. J.; Lee, J. D.; Huang, R.; Jiang, Z.; Barrera, F. G.; Chen, K.; Hollyer, G. G.; Friend, C. M. Synthesis and Characterization of Core-Shell Cu-Ru, Cu-Rh, and Cu-Ir Nanoparticles. J. Am. Chem. Soc. 2022, 144 (17), 7919– 7928,  DOI: 10.1021/jacs.2c02538
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    Synthesis and Characterization of Core-Shell Cu-Ru, Cu-Rh, and Cu-Ir Nanoparticles
    Foucher, Alexandre C.; Yang, Shengsong; Rosen, Daniel J.; Lee, Jennifer D.; Huang, Renjing; Jiang, Zhiqiao; Barrera, Francisco G.; Chen, Kelly; Hollyer, George G.; Friend, Cynthia M.; Gorte, Raymond J.; Murray, Christopher B.; Stach, Eric A.
    Journal of the American Chemical Society (2022), 144 (17), 7919-7928CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Optimizing the use of expensive precious metals is crit. to developing sustainable and low-cost processes for heterogeneous catalysis or electrochem. Here, we report a synthesis method that yields core-shell Cu-Ru, Cu-Rh, and Cu-Ir nanoparticles with the platinum-group metals segregated on the surface. The synthesis of Cu-Ru, Cu-Rh, and Cu-Ir particles allows maximization of the surface area of these metals and improves catalytic performance. Furthermore, the Cu core can be selectively etched to obtain nanoshells of the platinum-group metal components, leading to a further increase in the active surface area. Characterization of the samples was performed with X-ray absorption spectroscopy, X-ray powder diffraction, and ex situ and in situ transmission electron microscopy. CO oxidn. was used as a ref. reaction: the three core-shell particles and derivs. exhibited promising catalyst performance and stability after redox cycling. These results suggest that this synthesis approach may optimize the use of platinum-group metals in catalytic applications.
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    Rehor, I.; Slegerova, J.; Kucka, J.; Proks, V.; Petrakova, V.; Adam, M. P.; Treussart, F.; Turner, S.; Bals, S.; Sacha, P. Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells. Small 2014, 10 (6), 1106– 1115,  DOI: 10.1002/smll.201302336
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    Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells
    Rehor, Ivan; Slegerova, Jitka; Kucka, Jan; Proks, Vladimir; Petrakova, Vladimira; Adam, Marie-Pierre; Treussart, Francois; Turner, Stuart; Bals, Sara; Sacha, Pavel; Ledvina, Miroslav; Wen, Amy M.; Steinmetz, Nicole F.; Cigler, Petr
    Small (2014), 10 (6), 1106-1115CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    High pressure high temp. (HPHT) nanodiamonds (NDs) represent extremely promising materials for construction of fluorescent nanoprobes and nanosensors. However, some properties of bare NDs limit their direct use in these applications: they ppt. in biol. solns., only a limited set of bio-orthogonal conjugation techniques is available and the accessible material is greatly polydisperse in shape. In this work, we encapsulate bright 30-nm fluorescent nanodiamonds (FNDs) in 10-20-nm thick translucent (i.e., not altering FND fluorescence) silica shells, yielding monodisperse near-spherical particles of mean diam. 66 nm. High yield modification of the shells with PEG chains stabilizes the particles in ionic solns., making them applicable in biol. environments. We further modify the opposite ends of PEG chains with fluorescent dyes or vectoring peptide using click chem. High conversion of this bio-orthogonal coupling yielded circa 2000 dye or peptide mols. on a single FND. We demonstrate the superior properties of these particles by in vitro interaction with human prostate cancer cells: while bare nanodiamonds strongly aggregate in the buffer and adsorb onto the cell membrane, the shell encapsulated NDs do not adsorb nonspecifically and they penetrate inside the cells.
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    Rehor, I.; Mackova, H.; Filippov, S. K.; Kucka, J.; Proks, V.; Slegerova, J.; Turner, S.; Van Tendeloo, G.; Ledvina, M.; Hruby, M. Fluorescent Nanodiamonds with Bioorthogonally Reactive Protein-Resistant Polymeric Coatings. ChemPlusChem 2014, 79 (1), 21– 24,  DOI: 10.1002/cplu.201300339
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    Fluorescent Nanodiamonds with Bioorthogonally Reactive Protein-Resistant Polymeric Coatings
    Rehor, Ivan; Mackova, Hana; Filippov, Sergey K.; Kucka, Jan; Proks, Vladimir; Slegerova, Jitka; Turner, Stuart; Van Tendeloo, Gustaaf; Ledvina, Miroslav; Hruby, Martin; Cigler, Petr
    ChemPlusChem (2014), 79 (1), 21-24CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The novel synthesis of a polymeric interface grown from the surface of bright fluorescent nanodiamonds is reported. The polymer enables bioorthogonal attachment of various mols. by click chem.; the particles are resistant to nonspecific protein adsorption and show outstanding colloidal stability in buffers and biol. media. The coating fully preserves the unique optical properties of the nitrogen-vacancy centers that are crucial for bioimaging and sensoric applications.
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    Schiros, T.; Nordlund, D.; Palova, L.; Prezzi, D.; Zhao, L. Y.; Kim, K. S.; Wurstbauer, U.; Gutierrez, C.; Delongchamp, D.; Jaye, C. Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene. Nano Lett. 2012, 12 (8), 4025– 4031,  DOI: 10.1021/nl301409h
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    Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene
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    Nano Letters (2012), 12 (8), 4025-4031CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Robust methods to tune the unique electronic properties of graphene by chem. modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. C and N core-level resonant x-ray spectroscopy is a sensitive probe of chem. bonding and electronic structure of chem. dopants introduced in single-sheet graphene films. In conjunction with d. functional theory based calcns., the authors are able to obtain a detailed picture of bond types and electronic structure in graphene doped with N at the sub-percent level. Different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. These various bond types have profoundly different effects on the carrier concn., indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics.
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    Raty, J. Y.; Galli, G.; Bostedt, C.; van Buuren, T. W.; Terminello, L. J. Quantum confinement and fullerenelike surface reconstructions in nanodiamonds. Phys. Rev. Lett. 2003, 90 (3), 037401  DOI: 10.1103/PhysRevLett.90.037401
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    Quantum Confinement and Fullerenelike Surface Reconstructions in Nanodiamonds
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    Physical Review Letters (2003), 90 (3), 037401/1-037401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    We present x-ray absorption and emission expts. and ab initio calcns. showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addn., our calcns. show that the surface of nanodiamond particles larger than ≃1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features obsd. in measured absorption spectra.
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    Chang, Y. K.; Hsieh, H. H.; Pong, W. F.; Tsai, M. H.; Chien, F. Z.; Tseng, P. K.; Chen, L. C.; Wang, T. Y.; Chen, K. H.; Bhusari, D. M. Quantum Confinement Effect in Diamond Nanocrystals Studied by X-Ray-Absorption Spectroscopy. Phys. Rev. Lett. 1999, 82 (26), 5377– 5380,  DOI: 10.1103/PhysRevLett.82.5377
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    Quantum Confinement Effect in Diamond Nanocrystals Studied by X-Ray-Absorption Spectroscopy
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    This study measures the x-ray-absorption spectra of nanodiamond thin films with grain diams. ranging from 3.5 nm to 5 μm at the C K-edge using the sample drain current mode at room temp. Resonance peaks resembling the C 1s core exciton are obsd. The exciton state and conduction band edge shift to higher energies with the decrease of the grain size indicative of the presence of the quantum confinement effect.
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    Morar, J. F.; Himpsel, F. J.; Hollinger, G.; Hughes, G.; Jordan, J. L. OBSERVATION OF A C-1S CORE EXCITON IN DIAMOND. Phys. Rev. Lett. 1985, 54 (17), 1960– 1963,  DOI: 10.1103/PhysRevLett.54.1960
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    Observation of a carbon-1s core exciton in diamond
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    Physical Review Letters (1985), 54 (17), 1960-3CODEN: PRLTAO; ISSN:0031-9007.
    A well-resolved core exciton at the bulk diamond C-1s absorption edge was obsd. by using high-resoln. partial-yield spectroscopy with synchrotron radiation. The obtained excitonic binding energy, 0.19 ± 0.015 eV, agrees well with a 1st-principles effective-mass approxn. (EMA). This is in sharp contrast to other semiconductors (Si, Ge, and GaAs) where reported excitonic shifts far exceed EMA ests. In light of these results, one must question whether previous measurements overestimate the core-hole interaction or if they indicate a breakdown of the EMA for core excitons.
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    Wolcott, A.; Schiros, T.; Trusheim, M. E.; Chen, E. H.; Nordlund, D.; Diaz, R. E.; Gaathon, O.; Englund, D.; Owen, J. S. Surface structure of aerobically oxidized diamond nanocrystals. J. Phys. Chem. C 2014, 118 (46), 26695– 26702,  DOI: 10.1021/jp506992c
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    Surface Structure of Aerobically Oxidized Diamond Nanocrystals
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    Journal of Physical Chemistry C (2014), 118 (46), 26695-26702CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    We investigate the aerobic oxidn. of high-pressure, high-temp. nanodiamonds (5-50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidn. at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core-hole exciton is obsd. Both spectroscopic features are similar to those of chem. vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. The importance of these findings to the functionalization of nanodiamond surfaces for biol. labeling applications is discussed.
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    Henke, B. L.; Liesegang, J.; Smith, S. D. SOFT-X-RAY-INDUCED SECONDARY-ELECTRON EMISSION FROM SEMICONDUCTORS AND INSULATORS - MODELS AND MEASUREMENTS. Phys. Rev. B 1979, 19 (6), 3004– 3021,  DOI: 10.1103/PhysRevB.19.3004
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    Soft-x-ray-induced secondary electron emission from semiconductors and insulators: models and measurements
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    Secondary-electron energy distribution curves (EDC's) and the total secondary-electron yields relative to such for Au were measured for seven semiconductors for which electron-electron scattering losses within the emitter were considered dominant and for nine insulators (alkali halides) for which electron-phonon scattering losses were expected to be dominant in the transport process. The secondary-electron spectra were excited by Al-Kα (1487 eV) photons and were measured from evapd. dielec. films (of about 0.3 μ thickness) on conducting substrates with an electrostatic hemispherical analyzer of about 0.03-eV resoln. Some of the dielec. photoemitters have appreciably narrower energy distribution and higher yields than has Au; CuI and CsI have EDC widths at half-max. of about one-third of that for Au, and yield values of 11 and 30 times greater. The FWHM and secondary-electron yield for gold are ∼ 4eV and 0.50 electrons per normally incident photon, resp. The shapes of the EDC's are essentially unchanged for photon excitation in the 0.1-10-keV region. Strong structural features appear only in the alkali halide EDS's, and it proposed that these are mainly the result of single-electron promotion of secondaries from the valence band by plasmon deexcitation. A relatively simple model for x-ray photoemission is developed which assumes the direct excitation of secondaries by photoelectron and Auger-electron ''primaries'' is the dominant excitation mechanism, and accounts for both electron-electron and electron-photo scattering in the transport process. Free-electron conduction-band descriptions are assumed. The theor. and exptl. curves are in satisfactory agreement.
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    Henke, B. L.; Smith, J. A.; Attwood, D. T. 0.1–10-KEV X-RAY-INDUCED ELECTRON EMISSIONS FROM SOLIDS - MODELS AND SECONDARY-ELECTRON MEASUREMENTS. J. Appl. Phys. 1977, 48 (5), 1852– 1866,  DOI: 10.1063/1.323938
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    0.1-10-keV x-ray-induced electron emissions from solids - Models and secondary electron measurements
    Henke, Burton L.; Smith, Jerel A.; Attwood, David T.
    Journal of Applied Physics (1977), 48 (5), 1852-65CODEN: JAPIAU; ISSN:0021-8979.
    Anal. models are presented describing the x-ray-excited emission of "no-loss" photoelectrons and Auger electrons and the energy distribution of emitted secondary electrons. The secondary electron energy distribution is given in terms of the electron kinetic energy EK, work function W, photon energy E0, and mass photoionization coeff. μ(E0), as proportional to E0m(E0)EK(EK + W)-4. Techniques of electron spectral measurements utilizing uniform field pre-acceleration and limited acceptance angle spectrometers are discussed. Secondary electron energy distributions are measured at ∼10-8 torr from thick evaporated films of Au and Al at photon energies 277, 1487, and 8050 eV. The shapes of these distributions do not depend significantly upon photon energy. The full width at half-max. (FWHM) of these distributions are 3.9, 6.7, and 4.4 eV for Au and ion-cleaned Au and Al photocathodes, resp. The data agree well with the model predictions.
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    Maurer, P. C.; Kucsko, G.; Latta, C.; Jiang, L.; Yao, N. Y.; Bennett, S. D.; Pastawski, F.; Hunger, D.; Chisholm, N.; Markham, M. Room-Temperature Quantum Bit Memory Exceeding One Second. Science 2012, 336 (6086), 1283– 1286,  DOI: 10.1126/science.1220513
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    Room-Temperature Quantum Bit Memory Exceeding One Second
    Maurer, P. C.; Kucsko, G.; Latta, C.; Jiang, L.; Yao, N. Y.; Bennett, S. D.; Pastawski, F.; Hunger, D.; Chisholm, N.; Markham, M.; Twitchen, D. J.; Cirac, J. I.; Lukin, M. D.
    Science (Washington, DC, United States) (2012), 336 (6086), 1283-1286CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. We demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 s at room temp. The qubit consists of a single 13C nuclear spin in the vicinity of a nitrogen-vacancy color center within an isotopically purified diamond crystal. The long qubit memory time was achieved via a technique involving dissipative decoupling of the single nuclear spin from its local environment. The versatility, robustness, and potential scalability of this system may allow for new applications in quantum information science.
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    Jones, R. G.; Woodruff, D. P. Sampling depths in total yield and reflectivity SEXAFS studies in the soft X-ray region. Surf. Sci. 1982, 114 (1), 38– 46,  DOI: 10.1016/0039-6028(82)90454-X
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    Sampling depths in total yield and reflectivity SEXAFS studies in the soft x-ray region
    Jones, R. G.; Woodruff, D. P.
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    Both total photoelectron yield and reflectivity measurements display EXAFS and possess some surface sensitivity. By using Al foils with natural oxide films and anodically prepd. films of different thicknesses, the viability and surface specificity of these methods in the vicinity of the Al K-edge (1560 eV) were examd. The oxide films of only ∼130 Å thickness lead to EXAFS dominated by the oxide structure in the total yield model. A simple model is developed to account for the depth dependence of sampling in this mode which provides a reasonable match of the exptl. data.
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    Kasrai, M.; Lennard, W. N.; Brunner, R. W.; Bancroft, G. M.; Bardwell, J. A.; Tan, K. H. Sampling depth of total electron and fluorescence measurements in Si L- and K-edge absorption spectroscopy. Appl. Surf. Sci. 1996, 99 (4), 303– 312,  DOI: 10.1016/0169-4332(96)00454-0
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    Kasrai, M.; Lennard, W. N.; Brunner, R. W.; Bancroft, G. M.; Bardwell, J. A.; Tan, K. H.
    Applied Surface Science (1996), 99 (4), 303-312CODEN: ASUSEE; ISSN:0169-4332. (Elsevier)
    High resoln. Si L-edge and K-edge x-ray absorption near edge structure (XANES) spectra for SiO2 on Si substrates were recorded using total electron yield (TEY) and fluorescence yield (FY) techniques. The sampling depths of TEY and FY for Si L-edge and Si K-edge, resp., were studied in the energy range 95-120 eV and 1830-1900 eV. The max. sampling depth for TEY is ∼5 nm for the Si L-edge and ∼70 nm for the K-edge regions. The FY sampling depth at the L-edge is ∼70 nm whereas for the K-edge, the sampling depth is several hundred nm. Based on these data, and using a theor. model, electron escape depths for the TEY measurements in both energy ranges were deduced.
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    Ziaja, B.; van der Spoel, D.; Szöke, A.; Hajdu, J. Auger-electron cascades in diamond and amorphous carbon. Phys. Rev. B 2001, 64 (21), 214104  DOI: 10.1103/PhysRevB.64.214104
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    Auger-electron cascades in diamond and amorphous carbon
    Ziaja, Beata; van der Spoel, David; Szoke, Abraham; Hajdu, Janos
    Physical Review B: Condensed Matter and Materials Physics (2001), 64 (21), 214104/1-214104/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    We have analyzed cascades of secondary electrons in diamond and amorphous carbon generated by the thermalization of a single Auger electron. The elastic electron mean free path was calcd. as a function of impact energy in the muffin-tin potential approxn. The inelastic scattering cross section and the energy loss of electrons (expressed in terms of the differential inverse mean free path) were estd. from two "optical" models that utilize the measured dielec. consts. of the materials. Using these data, a Monte Carlo model describing the time evolution of the cascade was constructed. The results show that at most around 20-40 secondary cascade electrons are released by a single Auger electron in a macroscopic sample of diamond or amorphous carbon. Consideration of the real band structure of diamond reduces this no. further. The release of the cascade electrons happens within the first 100 fs after the emission of the primary Auger electron. The results have implications to planned expts. with femtosecond x-ray sources.
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    Neburkova, J.; Vavra, J.; Cigler, P. Coating nanodiamonds with biocompatible shells for applications in biology and medicine. Curr. Opin. Solid State Mater. Sci. 2017, 21 (1), 43– 53,  DOI: 10.1016/j.cossms.2016.05.008
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    Coating nanodiamonds with biocompatible shells for applications in biology and medicine
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    Current Opinion in Solid State & Materials Science (2017), 21 (1), 43-53CODEN: COSSFX; ISSN:1359-0286. (Elsevier Ltd.)
    Use of nanodiamonds (NDs) as nontoxic nanoparticles for biol. imaging, sensing, and drug delivery is expanding rapidly. The interest in NDs is triggered by their unique combination of optical properties. ND can accommodate nitrogen-vacancy color centers which provide stable fluorescence without photobleaching or photoblinking and their electronic structure is very sensitive to magnetic and elec. fields. The limited options to control ND properties during synthesis or by direct surface functionalization leave room to be improved upon by employing surface coatings engineered precisely for a particular application. The major disadvantages of unmodified NDs are their limited colloidal stability and tendency to non-specifically adsorb biomols. This review aims to summarize recent advances in coating NDs (namely with silica and polymer shells), which addresses these disadvantages and enables the use of NDs in biol. applications such as targeting of specific cells, drug delivery, and biol. imaging.
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    Harris, M. T.; Brunson, R. R.; Byers, C. H. THE BASE-CATALYZED-HYDROLYSIS AND CONDENSATION-REACTIONS OF DILUTE AND CONCENTRATED TEOS SOLUTIONS. J. Non-Cryst. Solids 1990, 121 (1–3), 397– 403,  DOI: 10.1016/0022-3093(90)90165-I
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    The base-catalyzed hydrolysis and condensation reactions of dilute and concentrated TEOS solutions
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    The synthesis of submicron SiO2 particles by the hydrolysis and condensation of dil. and concd. solns. of Si(OEt(4 (TEOS) was studied in low-mol.-wt. alcs. (C1-C4). A base (NH3) was used to catalyze the reaction. Raman spectroscopy, gas chromatog., and the molybdate method were used to establish the hydrolysis and condensation kinetics. Dynamic and classical light-scattering methods were used to monitor particle growth, particle no. concn. kinetics, and particle size distribution. The effects of solvent and TEOS concn. on the degree of monodispersity of the particles are discussed. The chem. and particle growth data were used to test theories of homogeneous nucleation and aggregative growth, proposed as mechanisms that govern the growth of submicron monodisperse SiO2 particles by TEOS hydrolysis.
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    Reactivity of penta- and hexacoordinate silicon compounds and their role as reaction intermediates
    Chuit, Claude; Corriu, Robert J. P.; Reye, Catherine; Young, J. Colin
    Chemical Reviews (Washington, DC, United States) (1993), 93 (4), 1371-448CODEN: CHREAY; ISSN:0009-2665.
    A review of the chem. reactivity of penta- and hexacoordinate silicon compds. with respect to their applications in org. synthesis and as reagents for the prepn. of organosilicon compds., with 411 refs.
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    Delak, K. M.; Sahai, N. Amine-Catalyzed Biomimetic Hydrolysis and Condensation of Organosilicate. Chem. Mater. 2005, 17 (12), 3221– 3227,  DOI: 10.1021/cm048355v
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    Amine-catalyzed biomimetic hydrolysis and condensation of organosilicate
    Delak, Katya M.; Sahai, Nita
    Chemistry of Materials (2005), 17 (12), 3221-3227CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Biogenic silica prodn. occurs at mild conditions with greater control of pore size, shape, and micropatterning than is possible with typical industrial sol-gel methods, providing inspiration for potential alternative routes to silica synthesis. Researchers have implicated the amine moieties, histidine and polylysine, on proteins isolated from sponges and diatoms as catalysts for biogenic silica pptn. Different mechanistic roles have been ascribed to the amines, but few systematic, quant. studies isolating one effect from another have been conducted. In the present study, we use 29Si NMR spectroscopy to systematically examine the different possible mechanistic roles of mono- and polyamines in catalyzing silica synthesis at mildly acidic pH (∼5) from an organosilicate starting compd., trimethylethoxysilane (TMES). TMES has a single organosilicate bond, so there are no competing reactions and the reaction progress can be followed with little ambiguity. Hydrolysis and condensation (dimerization) of TMES lead to the products trimethylsilanol (TMSiOH) and hexamethyldisiloxane (HMD). The Refocused Insensitive Nuclei Enhanced by Polarization Transfer pulse sequence (RINEPT+) provides unambiguous, quant. 29Si NMR spectra from which the hydrolysis and condensation rates in the presence of each amine can be obtained. For both mono- and polyamines, the catalytic efficiency scales with the concn. of conjugate base form and inversely with pKa. Thus, catalysis is most efficient with more acidic monoamines, such as pyridine and imidazole, as well as for the longer polyamines, where the most acidic protonation const. is lower than the exptl. pH (∼5). We postulate a nucleophile-catalyzed hydrolysis mechanism where the conjugate base of the amine attacks Si to form a pentacoordinate intermediate with TMES. Condensation is interpreted as an acid-catalyzed SN2 mechanism. Our findings potentially explain the evolutionary selection of histidine-contg. proteins for biogenic silica synthesis by sponges and address the chem. mechanisms at work for the pptn. of silica by polylysine-contg. proteins in diatoms. Along with the phys. mechanisms suggested by other research groups, the systematic results from the present study indicate that amines may be employed in more than one type of mechanistic strategy for catalyzing biogenic and biomimetic silica polymn.
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    Delak, K. M.; Sahai, N. Mechanisms of Amine-Catalyzed Organosilicate Hydrolysis at Circum-Neutral pH. J. Phys. Chem. B 2006, 110 (36), 17819– 17829,  DOI: 10.1021/jp062054m
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    Mechanisms of amine-catalyzed organosilicate hydrolysis at circum-neutral pH
    Delak, Katya M.; Sahai, Nita
    Journal of Physical Chemistry B (2006), 110 (36), 17819-17829CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Mono- and polyamines catalyze hydrolysis and condensation of alkoxyorganosilanes at neural pH values and room temp. mimeting silica synthetic pathways in biol. systems. The study is focused on understanding the mechanistic role of amines in catalyzing the hydrolysis process that precedes condensation. Variable-temp. 29Si NMR spectra in a range of pH values were used to evaluate the hydrolysis rates of trimethylethoxysilane (TMES), which, in combination with hybrid d. functional theory calcns. of putative intermediates and transition-states for TMES and tetra-Me orthosilicate (TMOS) allowed to suggest the mechanism of the hydrolysis. Comparison of calcd. energies with exptl. detd. activation energies indicates that amine catalysis of TMES is primarily a consequence of the amine acidity at neutral pH. The proton released by the amine is transferred to the organosilicate, producing a protonated ethoxy leaving group that can be displaced by water in an SN2 reaction. For TMOS, the activation energy of proton-transfer coupled with SN2 substitution is comparable to that for Corriu nucleophile-activated nucleophilic displacement, such that the mechanism of amine-catalyzed hydrolysis is dependent mostly on the ambient pH conditions as well as the type of amine. The relevance of the obtained results to biol. silica formation is discussed.
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    Stöber, W.; Fink, A.; Bohn, E. Controlled growth of monodisperse silica spheres in the micron size range. J. Colloid Interface Sci. 1968, 26 (1), 62,  DOI: 10.1016/0021-9797(68)90272-5
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    Pandey, K. C. NEW DIMERIZED-CHAIN MODEL FOR THE RECONSTRUCTION OF THE DIAMOND (111)-(2 × 1) SURFACE. Phys. Rev. B 1982, 25 (6), 4338– 4341,  DOI: 10.1103/PhysRevB.25.4338
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    New dimerized-chain model for the reconstruction of the diamond (111)-(2 × 1) surface
    Pandey, K. C.
    Physical Review B: Condensed Matter and Materials Physics (1982), 25 (6), 4338-41CODEN: PRBMDO; ISSN:0163-1829.
    Of the relaxed, graphitic, buckled, and π-bonded-chain-type models for the diamond (111)-(2 × 1) surface, only the chain model appears to account for the measured surface-band dispersion. The interaction of dangling orbitals which dets. the dispersion is large in the chain model because only in this model are the dangling bonds located on nearest-neighbor atoms. The data also suggest a dimerization of the chains.
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    Osswald, S.; Yushin, G.; Mochalin, V.; Kucheyev, S. O.; Gogotsi, Y. Control of sp(2)/sp(3) carbon ratio and surface chemistry of nanodiamond powders by selective oxidation in air. J. Am. Chem. Soc. 2006, 128 (35), 11635– 11642,  DOI: 10.1021/ja063303n
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    Control of sp2/sp3 Carbon Ratio and Surface Chemistry of Nanodiamond Powders by Selective Oxidation in Air
    Osswald, Sebastian; Yushin, Gleb; Mochalin, Vadym; Kucheyev, Sergei O.; Gogotsi, Yury
    Journal of the American Chemical Society (2006), 128 (35), 11635-11642CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The presence of large amts. of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidn. in air to selectively remove sp2-bonded carbon from ND. Thermogravimetric anal. and in situ Raman spectroscopy shows that sp2 and sp3 carbon species oxidize with different rates at 375-450 °C and reveals a narrow temp. range of 400-430 °C in which the oxidn. of sp2-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp3/sp2 ratio after oxidn. The content of up to 96% of sp3-bonded carbon in the oxidized samples is comparable to that found in microcryst. diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform IR spectroscopy studies show high purity 5-nm ND particles covered by oxygen-contg. surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purifn. techniques, the air oxidn. process does not require the use of toxic or aggressive chems., catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.
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    Frazer, B. H.; Gilbert, B.; Sonderegger, B. R.; De Stasio, G. The probing depth of total electron yield in the sub-keV range: TEY-XAS and X-PEEM. Surf. Sci. 2003, 537 (1–3), 161– 167,  DOI: 10.1016/S0039-6028(03)00613-7
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    The probing depth of total electron yield in the sub-keV range: TEY-XAS and X-PEEM
    Frazer, Bradley H.; Gilbert, Benjamin; Sonderegger, Brandon R.; De Stasio, Gelsomina
    Surface Science (2003), 537 (1-3), 161-167CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
    X-ray absorption spectra can be collected in multiple ways, each exhibiting a different probing depth. The total electron yield signal contains contributions from primary, Auger and secondary electrons. Data are presented on the total electron yield probing depth at core level energies ranging from 77 to 929 eV. By coating materials with Cr overlayers, the max. probing depth increases with core level energy from 15 to 141 A. The Auger electron contribution to total electron yield intensity is negligible, therefore x-ray absorption spectra acquired in x-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) are equiv. to spectra acquired by total electron yield. The signal intensity decreases exponentially with coating thickness, and total electron yield probing depth and Auger electron range (calcd. in the continuously slowing down approxn.) are similar at low energies, but diverge for kinetic energies >400 eV.
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    Smekal, W.; Werner, W. S. M.; Powell, C. J. Simulation of electron spectra for surface analysis (SESSA): a novel software tool for quantitative Auger-electron spectroscopy and X-ray photoelectron spectroscopy. Surf. Interface Anal. 2005, 37 (11), 1059– 1067,  DOI: 10.1002/sia.2097
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    Simulation of electron spectra for surface analysis (SESSA): A novel software tool for quantitative Auger-electron spectroscopy and X-ray photoelectron spectroscopy
    Smekal, Werner; Werner, Wolfgang S. M.; Powell, Cedric J.
    Surface and Interface Analysis (2005), 37 (11), 1059-1067, 2 platesCODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)
    A description of a new NIST database for quant. Auger-electron and XPS (AES/XPS) is given: Simulation of Electron Spectra for Surface Anal. (SESSA). This database contains extensive sets of data for the phys. quantities relevant to AES and XPS. The internal databases are linked to a user interface via a small expert system that allows a user to automatically retrieve data needed for a specific practical application. SESSA can simulate AES and XPS spectra for a multilayered thin-film sample for measurement conditions specified by the user. Exptl. information needed by SESSA is entered via an interface that matches the settings of AES/XPS instrumentation. The structure of SESSA is described together with information on special features, unique capabilities, and sources of the phys. data. Examples of practical applications of SESSA for angle-resolved XPS on Al and Si samples, detn. of the depth distribution function in XPS, and the use of empirical peak shapes for spectrum simulation are given. These and other applications are contained in SESSA as tutorial files with command-language statements that can be loaded into SESSA and modified as necessary for similar simulations.
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    Outka, D. A.; Stohr, J.; Madix, R. J.; Rotermund, H. H.; Hermsmeier, B.; Solomon, J. NEXAFS STUDIES OF COMPLEX ALCOHOLS AND CARBOXYLIC-ACIDS ON THE SI(111)(7 × 7) SURFACE. Surf. Sci. 1987, 185 (1–2), 53– 74,  DOI: 10.1016/S0039-6028(87)80613-1
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    NEXAFS studies of complex alcohols and carboxylic acids on the silicon(111)(7 × 7) surface
    Outka, D. A.; Stohr, J.; Madix, R. J.; Rotermund, H. H.; Hermsmeier, B.; Solomon, J.
    Surface Science (1987), 185 (1-2), 53-74CODEN: SUSCAS; ISSN:0039-6028.
    The adsorption of HCO2H, CH3CH2CO2H, CH2:CHCO2H, HC≡CCO2H, and the corresponding alcs. on the Si(111)(7 × 7) surface was investigated by NEXAFS. The NEXAFS spectrum of a polyfunctional mol. is simply the superposition of NEXAFS features expected of the individual functional groups in the mol. An exception to this rule was obsd. for those mols. with conjugated π orbitals. Monolayer coverages of these mols. on Si, bond strongly to the Si surface via the carboxylic acid or alc. group. In contrast, the C-C double and triple bonds do not react initially with the Si surface. Upon heating, however, the C-C double and triple bonds attached to the surface by the O functional groups become reactive on Si.
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    Santoro, M.; Gorelli, F.; Haines, J.; Cambon, O.; Levelut, C.; Garbarino, G. Silicon carbonate phase formed from carbon dioxide and silica under pressure. Proc. Natl. Acad. Sci. U. S. A. 2011, 108 (19), 7689– 7692,  DOI: 10.1073/pnas.1019691108
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    Silicon carbonate phase formed from carbon dioxide and silica under pressure
    Santoro, Mario; Gorelli, Federico; Haines, Julien; Cambon, Olivier; Levelut, Claire; Garbarino, Gaston
    Proceedings of the National Academy of Sciences of the United States of America (2011), 108 (19), 7689-7692CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    The discovery of nonmol. carbon dioxide under high-pressure conditions shows that there are remarkable analogies between this important substance and other group IV oxides. A natural and long-standing question is whether compds. between CO2 and SiO2 are possible. Under ambient conditions, CO2 and SiO2 are thermodynamically stable and do not react with each other. We show that reactions occur at high pressures indicating that silica can behave in a manner similar to ionic metal oxides that form carbonates at room pressure. A silicon carbonate phase was synthesized by reacting silicalite, a microporous SiO2 zeolite, and mol. CO2 that fills the pores, in diamond anvil cells at 18-26 GPa and 600-980 K; the compd. was then temp. quenched. The material was characterized by Raman and IR spectroscopy, and synchrotron x-ray diffraction. The expts. reveal unique oxide chem. at high pressures and the potential for synthesis of a class of previously uncharacterized materials. There are also potential implications for CO2 segregation in planetary interiors and for CO2 storage.
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    From NLM

  59. 59
    Leinweber, P.; Kruse, J.; Walley, F. L.; Gillespie, A.; Eckhardt, K.-U.; Blyth, R. I. R.; Regier, T. Nitrogen K-edge XANES - an overview of reference compounds used to identify ̀unknown’ organic nitrogen in environmental samples. J. Synchrotron Radiat. 2007, 14 (6), 500– 511,  DOI: 10.1107/S0909049507042513
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    Nitrogen K-edge XANES - an overview of reference compounds used to identify 'unknown' organic nitrogen in environmental samples
    Leinweber, Peter; Kruse, Jens; Walley, Fran L.; Gillespie, Adam; Eckhardt, Kai Uwe; Blyth, Robert I. R.; Regier, Tom
    Journal of Synchrotron Radiation (2007), 14 (6), 500-511CODEN: JSYRES; ISSN:0909-0495. (International Union of Crystallography)
    A review. The chem. nature of soil org. nitrogen (N) is still poorly understood and one-third to one-half of it is typically classified as 'unknown N'. Nitrogen K-edge XANES spectroscopy has been used to develop a systematic overview on spectral features of all major N functions in soil and environmental samples. The abs. calibration of the photon energy was completed using the 1s → π* transitions of pure gas-phase N2. On this basis a library of spectral features is provided for mineral N, nitro N, amino acids, peptides, and substituted pyrroles, pyridines, imidazoles, pyrazoles, pyrazines, pyrimidines and purine bases. Although N XANES was previously considered 'non-destructive', effects of radiation damage were shown for two compd. classes and an approach was proposed to minimize it. This new evidence is integrated into a proposal for the evaluation spectra from environmental samples with unknown compn. Thus a basis is laid to develop N K-edge XANES as a complementary std. research method to study the mol. compn. and ecol. functions of 'unknown N' in soil and the environment.
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  60. 60
    Melendrez, C.; Lopez-Rosas, J. A.; Stokes, C. X.; Cheung, T. C.; Lee, S.-J.; Titus, C. J.; Valenzuela, J.; Jeanpierre, G.; Muhammad, H.; Tran, P. Metastable Brominated Nanodiamond Surface Enables Room Temperature and Catalysis-Free Amine Chemistry. J. Phys. Chem. Lett. 2022, 13, 1147– 1158,  DOI: 10.1021/acs.jpclett.1c04090
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    Metastable brominated nanodiamond surface enables room temperature and catalysis-free amine chemistry
    Melendrez, Cynthia; Lopez-Rosas, Jorge A.; Stokes, Camron X.; Cheung, Tsz Ching; Lee, Sang-Jun; Titus, Charles James; Valenzuela, Jocelyn; Jeanpierre, Grace; Muhammad, Halim; Tran, Polo; Sandoval, Perla Jasmine; Supreme, Tyanna; Altoe, Virginia; Vavra, Jan; Raabova, Helena; Vanek, Vaclav; Sainio, Sami; Doriese, William B.; O'Neil, Galen C.; Swetz, Daniel S.; Ullom, Joel N.; Irwin, Kent; Nordlund, Dennis; Cigler, Petr; Wolcott, Abraham
    Journal of Physical Chemistry Letters (2022), 13 (4), 1147-1158CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Bromination of high-pressure, high-temp. (HPHT) nanodiamond (ND) surfaces has not been explored and can open new avenues for increased chem. reactivity and diamond lattice covalent bond formation. The large bond dissocn. energy of the diamond lattice-oxygen bond is a challenge that prevents new bonds from forming, and most researchers simply use oxygen-terminated NDs (alcs. and acids) as reactive species. In this work, we transformed a tertiary-alc.-rich ND surface to an amine surface with ~ 50% surface coverage and was limited by the initial rate of bromination. We obsd. that alkyl bromide moieties are highly labile on HPHT NDs and are metastable as previously found using d. functional theory. The strong leaving group properties of the alkyl bromide intermediate were found to form diamond-nitrogen bonds at room temp. and without catalysts. This robust pathway to activate a chem. inert ND surface broadens the modalities for surface termination, and the unique surface properties of brominated and aminated NDs are impactful to researchers for chem. tuning diamond for quantum sensing or biolabeling applications.
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    Darlatt, E.; Traulsen, C. H. H.; Poppenberg, J.; Richter, S.; Kuhn, J.; Schalley, C. A.; Unger, W. E. S. Evidence of click and coordination reactions on a self-assembled monolayer by synchrotron radiation based XPS and NEXAFS. J. Electron Spectrosc. Relat. Phenom. 2012, 185 (3–4), 85– 89,  DOI: 10.1016/j.elspec.2012.02.004
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    Evidence of click and coordination reactions on a self-assembled monolayer by synchrotron radiation based XPS and NEXAFS
    Darlatt, Erik; Traulsen, Christoph H.-H.; Poppenberg, Johannes; Richter, Sebastian; Kuehn, Julius; Schalley, Christoph A.; Unger, Wolfgang E. S.
    Journal of Electron Spectroscopy and Related Phenomena (2012), 185 (3-4), 85-89CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)
    An ethynylterpyridine was "clicked" to an azide-terminated self-assembled monolayer on gold and characterized by synchrotron radiation based surface anal. as NEXAFS and XPS. The detection of azide and terpyridine signatures confirmed a partial click reaction at room temp. The absence of the azides after reaction at 50 °C indicates an almost complete conversion. For the latter case successful Pd(II) coordination has been proven. The Au-S interface of the SAMs has been characterized by S 1s and S 2p XPS.
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    Darlatt, E.; Nefedov, A.; Traulsen, C. H. H.; Poppenberg, J.; Richter, S.; Dietrich, P. M.; Lippitz, A.; Illgen, R.; Kuhn, J.; Schalley, C. A. Interpretation of experimental N K NEXAFS of azide, 1,2,3-triazole and terpyridyl groups by DFT spectrum simulations. J. Electron Spectrosc. Relat. Phenom. 2012, 185 (12), 621– 624,  DOI: 10.1016/j.elspec.2012.09.008
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    Interpretation of experimental N K NEXAFS of azide, 1,2,3-triazole and terpyridyl groups by DFT spectrum simulations
    Darlatt, Erik; Nefedov, Alexei; Traulsen, Christoph H.-H.; Poppenberg, Johannes; Richter, Sebastian; Dietrich, Paul M.; Lippitz, Andreas; Illgen, Rene; Kuehn, Julius; Schalley, Christoph A.; Woell, Christof; Unger, Wolfgang E. S.
    Journal of Electron Spectroscopy and Related Phenomena (2012), 185 (12), 621-624CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)
    Exptl. N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in exptl. N K-edge NEXAFS spectra to nitrogen atoms within these functional groups were made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated mols., DFT spectrum simulations are useful to find measurement conditions delivering exptl. N K-edge NEXAFS data with negligible x-ray damage. The 1,2,3-triazole group is rather stable under x-ray irradn.
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    Pauling, L.; Brockway, L. O. The Adjacent Charge Rule and the Structure of Methyl Azide, Methyl Nitrate, and Fluorine Nitrate. J. Am. Chem. Soc. 1937, 59 (1), 13– 20,  DOI: 10.1021/ja01280a005
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    Adjacent-charge rule and the structure of methyl azide, methyl nitrate and fluorine nitrate
    Pauling, Linus; Brockway, L. O.
    Journal of the American Chemical Society (1937), 59 (), 13-20CODEN: JACSAT; ISSN:0002-7863.
    Application of the adjacent-charge rule (mol. structures in which adjacent atoms have elec. charges of the same sign are much less important than other structures) leads to a prediction of instability for one of the 3 reasonable configurations of each of the mols., Me azide, Me nitrate and F nitrate. Electron-diffraction data for these mols., in support of the rule, indicate reasonance between the 2 other configurations. The application of the rule to the structures of N2O5, N2O4, Cl2O6 and O acids of Si, P, S and Cl is discussed.
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    Castner, D. G.; Lewis, K. B.; Fischer, D. A.; Ratner, B. D.; Gland, J. L. DETERMINATION OF SURFACE-STRUCTURE AND ORIENTATION OF POLYMERIZED TETRAFLUOROETHYLENE FILMS BY NEAR-EDGE X-RAY ABSORPTION FINE-STRUCTURE, X-RAY PHOTOELECTRON-SPECTROSCOPY, AND STATIC SECONDARY ION MASS-SPECTROMETRY. Langmuir 1993, 9 (2), 537– 542,  DOI: 10.1021/la00026a029
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    Determination of surface structure and orientation of polymerized tetrafluoroethylene films by near-edge x-ray absorption fine structure, x-ray photoelectron spectroscopy, and static secondary ion mass spectrometry
    Castner, David G.; Lewis, Kenneth B., Jr.; Fischer, Daniel A.; Ratner, Buddy D.; Gland, John L.
    Langmuir (1993), 9 (2), 537-42CODEN: LANGD5; ISSN:0743-7463.
    Films of conventional and radio-frequency glow-discharge (RFGD) polymd. tetrafluoroethylene (I) were examd. by ultrasoft x-ray absorption spectroscopy (XAS), XPS, and SIMS. The polarization-dependent intensity changes of transitions to C-C and C-F σ* orbitals in the carbon and fluorine near-edge x-ray absorption fine structure (NEXAFS) spectra revealed different CF2-chain orientations. The surface region of skived poly-I was composed to CF2 chains oriented parallel to the surface stations present in the poly-I. XPS confirmed only CF2 groups were present in the poly-I surface region. Fluorocarbon (FC) films prepd. by RFGD deposition of I onto substrates placed indirectly in the visible glow (I-indirect) were randomly oriented. XPS showed the I-indirect films had CD, CF2, and CF3 groups in the surface region. Static SIMS indicated that the I-indirect film surface contained CF3 and C2F5 groups. XPS showed the FC films prepd. by RFGD deposition of I onto substrates placed downstream from the visible glow contained ∼90% CF2 groups. The strong polarization dependence of the C and F NEXAFS spectra of these films indicated the CF2 groups were aligned in vertical chains on the substrate. Static SIMS and XPS results suggested the outermost surface of the CF2 chains were terminated with CF3 groups. For thin (50-500 Å) FC RFGD films deposted onto polymeric substrates such as PMMA or PET, fluorescence yield detection XAS could be used to examine the substrate, while XPS, static SIMS, and electron yield detection XAS could be used to examine the FC overlayer. These results demonstrated the complementary nature of ultrasoft XAS, XPS, and static SIMS for detailed surface structural characterization of polymers.
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    Brassard, J.-D.; Sarkar, D. K.; Perron, J. Synthesis of Monodisperse Fluorinated Silica Nanoparticles and Their Superhydrophobic Thin Films. ACS Appl. Mater. Interfaces 2011, 3 (9), 3583– 3588,  DOI: 10.1021/am2007917
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    Synthesis of Monodisperse Fluorinated Silica Nanoparticles and Their Superhydrophobic Thin Films
    Brassard, Jean-Denis; Sarkar, D. K.; Perron, Jean
    ACS Applied Materials & Interfaces (2011), 3 (9), 3583-3588CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Monodispersive SiO2 nanoparticles were synthesized via the Stober process and further functionalized by adding fluorinated groups using fluoroalkylsilane in an ethanolic soln. In this process, 6 different sizes of fluorinated SiO2 nanoparticles of varying diam. from 40 to 300 nm are prepd. and used to deposit thin films on Al alloy surfaces using spin coating processes. The functionalization of SiO2 nanoparticles by fluorinated group was confirmed by the presence C-F bonds along with Si-O-Si bonds in the thin films as analyzed by FTIR spectroscopy. The surface roughness as well as the H2O contact angles of the fluorinated SiO2 nanoparticle contg. thin films are increased with the increase of the diam. of the synthesized fluorinated SiO2 nanoparticles. The thin films prepd. using the fluorinated SiO2 nanoparticles having a crit. size of 119 ± 12 nm provide a surface roughness of ∼0.697 μm rendering the surfaces superhydrophobic with a H2O contact angle of 151 ± 4°. The roughness as well as the H2O contact angle increases on the superhydrophobic thin films with further increase in the size of the fluorinated SiO2 nanoparticles in the films.
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    Kobayashi, K.; Wei, J.; Iida, R.; Ijiro, K.; Niikura, K. Surface engineering of nanoparticles for therapeutic applications. Polym. J. 2014, 46 (8), 460– 468,  DOI: 10.1038/pj.2014.40
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    Surface engineering of nanoparticles for therapeutic applications
    Kobayashi, Kenya; Wei, Jinjian; Iida, Ryo; Ijiro, Kuniharu; Niikura, Kenichi
    Polymer Journal (Tokyo, Japan) (2014), 46 (8), 460-468CODEN: POLJB8; ISSN:0032-3896. (NPG Nature Asia-Pacific)
    A review. Nanoparticles with a diam. of <100 nm are regarded as potential medical materials, as this size allows nanoparticles to circulate in vivo and possibly reach targeted tumors. Inorg. nanoparticles in particular are able to interact with light and/or magnetic fields, thus extending their potential applications to such fields as fluorescence labeling, magnetic resonance imaging and stimulus-responsive drug delivery that are essential to the diagnosis and treatment of disease. To facilitate their use in such applications, the appropriate design of surface ligands on these nanoparticles is necessary. The surface ligands det. the physicochem. properties of the surface, such as hydrophilicity/hydrophobicity and zeta potential as well as dispersibility in soln. These properties have an esp. important role in detg. nanoparticle-cell assocns., such as cellular membrane permeability, immune responses and localization in vivo. This review focuses on recent advances in the surface engineering of nanoparticles for therapeutic applications.
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    Chang, J.-B.; Chen, F.; Yoon, Y.-G.; Jung, E. E.; Babcock, H.; Kang, J. S.; Asano, S.; Suk, H.-J.; Pak, N.; Tillberg, P. W. Iterative expansion microscopy. Nat. Methods 2017, 14 (6), 593– 599,  DOI: 10.1038/nmeth.4261
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    We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resoln., high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a max. detection solid angle of 2 × 10-3 sr. The energy resoln. of all pixels combined is 1.5 eV full width at half max. at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resoln. and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering expts. obtained with the spectrometer are presented. (c) 2019 American Institute of Physics.
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  • Abstract

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    Figure 1

    Figure 1. (A) Chemical scheme shows the growth of silica using tetraethyl orthosilicate in a base-catalyzed reaction similar to the Stöber method. The ND surface is depicted with 1 carboxylic acid and a sp2-like Pandey reconstruction. In the schematic, the alcohol groups after rehydroxylation are performing a nucleophilic attack to generate a silyl–ether bond on the diamond surface, and a subsequent removal of the acid occurs. (B) DRIFTS spectra of the ND constructs before and after silica shell growth show the reduction in the (C═O)ν at 1785 cm–1 and the increase in (Si–O–Si)ν at 1100 cm–1. DRIFTS of the rehydroxylaion control experiment is depicted and shows the increase of an alcohol peak at 1100 cm–1. (C) A cluster of diamond nanoparticles encapsulated in silica is seen by electron microscopy. High-angle annular dark field (HAADF) microscopy is used to image the embedded diamond in silica, while elemental mapping of C Kα and Si Kα EDS is used to spatially resolve the core–shell structure.

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    Figure 2

    Figure 2. Thickness of silica on the HPHT ND cores is controlled by the length of the reaction time and increased growth forms nearly spherical ND–SiO2 at approximately 20 nm thickness. High-resolution TEM imaging shows ultrathin SiO2 growth surrounding an irregular nanodiamond core with measurements of 6–10 nm around the ND edge and basal plane (A). Ten nanometer SiO2 growth is depicted on an aggregate of nanodiamonds of varying diameters and morphologies (B). With increasing reaction time of 20 min, 20–25 nm shells can be synthesized and the ND–SiO2 is generally spherical. (C) High-resolution SEM image shows multiple particles in a cluster and the size distribution is demonstrated with a 85 and 142 nm being highlighted (D).

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    Figure 3

    Figure 3. XAS spectra was found to effectively track the growth of silica via the decrease in diamond electronic structure and decreased exponentially due to inelastic Auger electrons generating the sample current. The distinct diamond structure decreases in signal intensity with increasing silica shell as the core-hole exciton and 2nd absolute band gap decrease (A). Plots D, E, and F are C 1s XAS of ND–SiO2 samples with 13 ± 5, 20 ± 5, and 35 ± 5 nm silica shells, respectively, where the diamond core-hole features are diminished or eliminated (B). The diamond core-hole intensity (TEY/BKGD) versus SiO2 thickness shows an exponential decrease, while the inset shows the natural logarithm of the TEY/BKGD signal with a linear least-squares regression and the resultant rate was used to generate the exponential fit of the raw TEY/BKGD data (C).

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    Figure 4

    Figure 4. SESSA simulations qualitatively supported the experimental TEY data of ND–SiO2 samples with increasing shell thickness (A) SESSA-based electron spectra for 30 nm diamond with 0.1–20 nm thick SiO2 shell. The top spectrum is representative of a 30 nm diamond with a 5 nm thick shell and reveals the signals from the gold substrate, SiO2 shells, and diamond core with detector angles from 0 to 75° in 15° increments. The inset shows the 3 Auger CKL features from 245 to 268 eV for a 5 nm thick SiO2 shell. A plot of the C KL23L23 intensity versus shell thickness shows an exponential decay consistent with our C 1s XAS data. The inset of the middle panel are simulations with a detector angle of 55°, an energy range of 220–290 eV and increasing SiO2 shell thickness from 0.1 to 20 nm. (B) TEM images of thick (20–30 nm) and thin (<5 nm) silica shells on HPHT ND cores are for reference to the Auger simulations generated by SESSA (C–F).

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    Figure 5

    Figure 5. XAS spectra of ND–SiO2 samples confirms the successful decoration of various molecules, the removal of carboxylate features after silica growth and differentiates between diamond bound versus molecular carboxylates. O 1s spectra of ND–OH, ND–COOH, ND–SiO2, ND–SiO2 + COOH, and ND–SiO2 + glycidoxy (epoxide ring) are shown in the ascending order (A). Alcohol-rich ND–OH has only a σ*(C–O) shape resonance at 536.4 eV, while ND–COOH (acid–base–acid treatment) has a π*(C═O) transition at 530.2 eV that is assigned to carboxylates. ND–SiO2 shows little π*(C═O) signatures, while ND–SiO2+COOH with folic acid functionalization chemistry has a distinct feature at 532.2 eV. ND–SiO2–glycidoxy shows little π*(C═O) and a shifted σ*(C–O) transition at 537.3 eV for epoxides. N 1s XAS spectra of ND–SiO2 + PEG + NH2 (10:1 ratio), ND–SiO2 + PEG + NH2 (4:1 ratio), X-ray induced beam damage of the ND–SiO2 + PEG + NH2 with 4:1 ratio, and ND–SiO2 + PEG + NH2 + Folate provides conformation of amine functionalization and conjugation chemistry (B). N 1s XAS spectrum of ND–SiO2 + azides is complex and shows resonance peaks for N1, N2, and N3 of the linear azide electronic structure. Peaks at 398.5, 399.5, 400.7, and 402.6 eV are assigned to π*(N1≡N), π*(N1/3═N), and two π*(N2═N+) transitions, respectively. Shape resonances at 404.1 and 405.8 eV were assigned to σ*(N3–C) and σ*(N═N), respectively. In contrast, the inset shows the simple F 1s transition for σ*(C–F) at 692.0 eV of a fluorinated ND–SiO2 sample (C).

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      The detection of weak magnetic fields with high spatial resoln. is an important problem in diverse areas ranging from fundamental physics and material science to data storage and biomedical science. Here, we explore a novel approach to the detection of weak magnetic fields that takes advantage of recently developed techniques for the coherent control of solid-state electron spin quantum bits. Specifically, we investigate a magnetic sensor based on nitrogen-vacancy centers in room-temp. diamond. We discuss two important applications of this technique: a nanoscale magnetometer that could potentially detect precession of single nuclear spins and an optical magnetic-field imager combining spatial resoln. ranging from micrometres to millimetres with a sensitivity approaching a few fT Hz-1/2.
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    8. 8
      McGuinness, L. P.; Yan, Y.; Stacey, A.; Simpson, D. A.; Hall, L. T.; Maclaurin, D.; Prawer, S.; Mulvaney, P.; Wrachtrup, J.; Caruso, F. Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells. Nat. Nanotechnol. 2011, 6 (6), 358– 363,  DOI: 10.1038/nnano.2011.64
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      Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells
      McGuinness, L. P.; Yan, Y.; Stacey, A.; Simpson, D. A.; Hall, L. T.; MacLaurin, D.; Prawer, S.; Mulvaney, P.; Wrachtrup, J.; Caruso, F.; Scholten, R. E.; Hollenberg, L. C. L.
      Nature Nanotechnology (2011), 6 (6), 358-363CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      Fluorescent particles are routinely used to probe biol. processes. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry, but not yet in biol. environments. Here, the authors demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centers inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 1° angular precision over acquisition times of 89 ms. The quantum spin levels served as fingerprints, allowing individual centers with identical fluorescence to be identified and tracked simultaneously. Furthermore, monitoring decoherence rates in response to changes in the local environment may provide new information about intracellular processes. The expts. reported here demonstrate the viability of controlled single spin probes for nanomagnetometry in biol. systems, opening up a host of new possibilities for quantum-based imaging in the life sciences.
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    9. 9
      Atature, M.; Englund, D.; Vamivakas, N.; Lee, S. Y.; Wrachtrup, J. Material platforms for spin-based photonic quantum technologies. Nat. Rev. Mater. 2018, 3 (5), 38– 51,  DOI: 10.1038/s41578-018-0008-9
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      Material platforms for spin-based photonic quantum technologies
      Atature, Mete; Englund, Dirk; Vamivakas, Nick; Lee, Sang-Yun; Wrachtrup, Joerg
      Nature Reviews Materials (2018), 3 (5), 38-51CODEN: NRMADL; ISSN:2058-8437. (Nature Research)
      A central goal in quantum optics and quantum information science is the development of quantum networks to generate entanglement between distributed quantum memories. Exptl. progress relies on the quality and efficiency of the light-matter quantum interface connecting the quantum states of photons to internal states of quantum emitters. Quantum emitters in solids, which have properties resembling those of atoms and ions, offer an opportunity for realizing light-matter quantum interfaces in scalable and compact hardware. These quantum emitters require a material platform that enables stable spin and optical properties, as well as a robust manufg. of quantum photonic circuits. Because no emitter system is yet perfect and different applications may require different properties, several light-matter quantum interfaces are being developed in various platforms. This Review highlights the progress in three leading material platforms: diamond, silicon carbide and atomically thin semiconductors.
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    10. 10
      Kucsko, G.; Maurer, P. C.; Yao, N. Y.; Kubo, M.; Noh, H. J.; Lo, P. K.; Park, H.; Lukin, M. D. Nanometre-scale thermometry in a living cell. Nature 2013, 500 (7460), 54– 58,  DOI: 10.1038/nature12373
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      10
      Nanometre-scale thermometry in a living cell
      Kucsko, G.; Maurer, P. C.; Yao, N. Y.; Kubo, M.; Noh, H. J.; Lo, P. K.; Park, H.; Lukin, M. D.
      Nature (London, United Kingdom) (2013), 500 (7460), 54-58CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Sensitive probing of temp. variations on nanometer scales is an outstanding challenge in many areas of modern science and technol. In particular, a thermometer capable of subdegree temp. resoln. over a large range of temps. as well as integration within a living system could provide a powerful new tool in many areas of biol., phys. and chem. research. Possibilities range from the temp.-induced control of gene expression and tumor metab. to the cell-selective treatment of disease and the study of heat dissipation in integrated circuits. By combining local light-induced heat sources with sensitive nanoscale thermometry, it may also be possible to engineer biol. processes at the subcellular level. Here the authors demonstrate a new approach to nanoscale thermometry that uses coherent manipulation of the electronic spin assocd. with nitrogen-vacancy color centers in diamond. The authors' technique makes it possible to detect temp. variations as small as 1.8 mK (a sensitivity of 9 mK Hz-1/2) in an ultrapure bulk diamond sample. Using nitrogen-vacancy centers in diamond nanocrystals (nanodiamonds), the authors directly measure the local thermal environment on length scales as short as 200 nm. Finally, by introducing both nanodiamonds and gold nanoparticles into a single human embryonic fibroblast, the authors demonstrate temp.-gradient control and mapping at the subcellular level, enabling unique potential applications in life sciences.
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    11. 11
      Tsai, A.; Aghajamali, A.; Dontschuk, N.; Johnson, B. C.; Usman, M.; Schenk, A. K.; Sear, M.; Pakes, C. I.; Hollenberg, L. C. L.; McCallum, J. C. Epitaxial Formation of SiC on (100) Diamond. ACS Appl. Electron. Mater. 2020, 2 (7), 2003– 2009,  DOI: 10.1021/acsaelm.0c00289
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      11
      Epitaxial Formation of SiC on (100) Diamond
      Tsai, Alexander; Aghajamali, Alireza; Dontschuk, Nikolai; Johnson, Brett C.; Usman, Muhammad; Schenk, Alex K.; Sear, Michael; Pakes, Christopher I.; Hollenberg, Lloyd C. L.; McCallum, Jeffrey C.; Rubanov, Sergey; Tadich, Anton; Marks, Nigel A.; Stacey, Alastair
      ACS Applied Electronic Materials (2020), 2 (7), 2003-2009CODEN: AAEMBP; ISSN:2637-6113. (American Chemical Society)
      The coherent formation is demonstrated locally of SiC on diamond, a rare example of heteroepitaxy with a lattice mismatch >20%. High-resoln. TEM confirms the quality and at. structure near the interface. Guided by mol. dynamics simulations, a theor. model is proposed for the interface wherein the large lattice strain is alleviated via point dislocations in a 2-dimensional plane without forming extended defects in 3 dimensions. The possibility of realizing heterojunctions of technol. important materials such as SiC with diamond offers promising pathways for thermal management of high-power electronics. At a fundamental level, the study redefines the understanding of SiC and diamond heteroepitaxy and furthers the understanding of large lattice mismatched interfaces.
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    12. 12
      Hirama, K.; Taniyasu, Y.; Kasu, M. AlGaN/GaN high-electron mobility transistors with low thermal resistance grown on single-crystal diamond (111) substrates by metalorganic vapor-phase epitaxy. Appl. Phys. Lett. 2011, 98 (16), 3574531  DOI: 10.1063/1.3574531
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      There is no corresponding record for this reference.
    13. 13
      Xie, M. Z.; Yu, X. F.; Rodgers, L. V. H.; Xu, D. H.; Chi-Duran, I.; Toros, A.; Quack, N.; de Leon, N. P.; Maurer, P. C. Biocompatible surface functionalization architecture for a diamond quantum sensor. Proc. Natl. Acad. Sci. U. S. A. 2022, 119 (8), e2114186119  DOI: 10.1073/pnas.2114186119
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      13
      Biocompatible surface functionalization architecture for a diamond quantum sensor
      Xie, Mouzhe; Yu, Xiaofei; Rodgers, Lila V. H.; Xu, Daohong; Chi-Duran, Ignacio; Toros, Adrien; Quack, Niels; de Leon, Nathalie P.; Maurer, Peter C.
      Proceedings of the National Academy of Sciences of the United States of America (2022), 119 (8), e2114186119CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Quantum metrol. enables some of the most precise measurements. In the life sciences, diamond-based quantum sensing has led to a new class of biophys. sensors and diagnostic devices that are being investigated as a platform for cancer screening and ultrasensitive immunoassays. However, a broader application in the life sciences based on nanoscale NMR spectroscopy has been hampered by the need to interface highly sensitive quantum bit (qubit) sensors with their biol. targets. Here, we demonstrate an approach that combines quantum engineering with single-mol. biophysics to immobilize individual proteins and DNA mols. on the surface of a bulk diamond crystal that hosts coherent nitrogen vacancy qubit sensors. Our thin (sub-5 nm) functionalization architecture provides precise control over the biomol. adsorption d. and results in near-surface qubit coherence approaching 100 μs. The developed architecture remains chem. stable under physiol. conditions for over 5 d, making our technique compatible with most biophys. and biomedical applications.
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    14. 14
      Rendler, T.; Neburkova, J.; Zemek, O.; Kotek, J.; Zappe, A.; Chu, Z. Q.; Cigler, P.; Wrachtrup, J. Optical imaging of localized chemical events using programmable diamond quantum nanosensors. Nat. Commun. 2017, 8, 14701,  DOI: 10.1038/ncomms14701
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      Optical imaging of localized chemical events using programmable diamond quantum nanosensors
      Rendler, Torsten; Neburkova, Jitka; Zemek, Ondrej; Kotek, Jan; Zappe, Andrea; Chu, Zhiqin; Cigler, Petr; Wrachtrup, Joerg
      Nature Communications (2017), 8 (), 14701CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Development of multifunctional nanoscale sensors working under physiol. conditions enables monitoring of intracellular processes that are important for various biol. and medical applications. By attaching paramagnetic gadolinium complexes to nanodiamonds (NDs) with nitrogen-vacancy (NV) centers through surface engineering, we developed a hybrid nanoscale sensor that can be adjusted to directly monitor physiol. species through a proposed sensing scheme based on NV spin relaxometry. We adopt a single-step method to measure spin relaxation rates enabling time-dependent measurements on changes in pH or redox potential at a submicrometer-length scale in a microfluidic channel that mimics cellular environments. Our exptl. data are reproduced by numerical simulations of the NV spin interaction with gadolinium complexes covering the NDs. Considering the versatile engineering options provided by polymer chem., the underlying mechanism can be expanded to detect a variety of physiol. relevant species and variables.
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    15. 15
      Slegerova, J.; Hajek, M.; Rehor, I.; Sedlak, F.; Stursa, J.; Hruby, M.; Cigler, P. Designing the nanobiointerface of fluorescent nanodiamonds: highly selective targeting of glioma cancer cells. Nanoscale 2015, 7 (2), 415– 420,  DOI: 10.1039/C4NR02776K
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      Designing the nanobiointerface of fluorescent nanodiamonds: highly selective targeting of glioma cancer cells
      Slegerova, Jitka; Hajek, Miroslav; Rehor, Ivan; Sedlak, Frantisek; Stursa, Jan; Hruby, Martin; Cigler, Petr
      Nanoscale (2015), 7 (2), 415-420CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Core-shell nanoparticles based on fluorescent nanodiamonds coated with a biocompatible N-(2-hydroxypropyl)methacrylamide copolymer shell were developed for background-free near-IR imaging of cancer cells. The particles showed excellent colloidal stability in buffers and culture media. After conjugation with a cyclic RGD peptide they selectively targeted integrin αvβ3 receptors on glioblastoma cells with high internalization efficacy.
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    16. 16
      Rehor, I.; Lee, K. L.; Chen, K.; Hajek, M.; Havlik, J.; Lokajova, J.; Masat, M.; Slegerova, J.; Shukla, S.; Heidari, H. Plasmonic Nanodiamonds: Targeted Core-Shell Type Nanoparticles for Cancer Cell Thermoablation. Adv. Healthcare Mater. 2015, 4 (3), 460– 468,  DOI: 10.1002/adhm.201400421
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      Plasmonic Nanodiamonds: Targeted Core-Shell Type Nanoparticles for Cancer Cell Thermoablation
      Rehor, Ivan; Lee, Karin L.; Chen, Kevin; Hajek, Miroslav; Havlik, Jan; Lokajova, Jana; Masat, Milan; Slegerova, Jitka; Shukla, Sourabh; Heidari, Hamed; Bals, Sara; Steinmetz, Nicole F.; Cigler, Petr
      Advanced Healthcare Materials (2015), 4 (3), 460-468CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Targeted biocompatible nanostructures with controlled plasmonic and morphol. parameters are promising materials for cancer treatment based on selective thermal ablation of cells. Here, core-shell plasmonic nanodiamonds consisting of a silica-encapsulated diamond nanocrystal coated in a gold shell are designed and synthesized. The architecture of particles is analyzed and confirmed in detail using electron tomog. The particles are biocompatibilized using a PEG polymer terminated with bioorthogonally reactive alkyne groups. Azide-modified transferrin is attached to these particles, and their high colloidal stability and successful targeting to cancer cells overexpressing the transferrin receptor are demonstrated. The particles are nontoxic to the cells and they are readily internalized upon binding to the transferrin receptor. The high plasmonic cross section of the particles in the near-IR region is utilized to quant. ablate the cancer cells with a short, one-minute irradn. by a pulse 750-nm laser.
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    17. 17
      Chu, Z.; Zhang, S.; Zhang, B.; Zhang, C.; Fang, C.-Y.; Rehor, I.; Cigler, P.; Chang, H.-C.; Lin, G.; Liu, R. Unambiguous observation of shape effects on cellular fate of nanoparticles. Sci. Rep. 2014, 4, 4495,  DOI: 10.1038/srep04495
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      Unambiguous observation of shape effects on cellular fate of nanoparticles
      Chu, Zhiqin; Zhang, Silu; Zhang, Bokai; Zhang, Chunyuan; Fang, Chia-Yi; Rehor, Ivan; Cigler, Petr; Chang, Huan-Cheng; Lin, Ge; Liu, Renbao; Li, Quan
      Scientific Reports (2014), 4 (), 4495/1-4495/9CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Cellular fate of nanoparticles is vital to application of nanoparticles to cell imaging, bio-sensing, drug delivery, suppression of drug resistance, gene delivery, and cytotoxicity anal. However, the current studies on cellular fate of nanoparticles have been controversial due to complications of interplay between many possible factors. By well-controlled expts., we demonstrated unambiguously that the morphol. of nanoparticles independently detd. their cellular fate. We found that nanoparticles with sharp shapes, regardless of their surface chem., size, or compn., could pierce the membranes of endosomes that carried them into the cells and escape to the cytoplasm, which in turn significantly reduced the cellular excretion rate of the nanoparticles. Such features of sharp-shaped nanoparticles are essential for drug delivery, gene delivery, subcellular targeting, and long-term tracking. This work opens up a controllable, purely geometrical and hence safe, degree of freedom for manipulating nanoparticle-cell interaction, with numerous applications in medicine, bio-imaging, and bio-sensing.
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      http://www.nature.com/srep/2014/140328/srep04495/abs/srep04495.html#supplementary-information

    18. 18
      Nguyen, T. T.-B.; Chang, H.-C.; Wu, V. W.-K. Adsorption and hydrolytic activity of lysozyme on diamond nanocrystallites. Diamond Relat. Mater. 2007, 16 (4), 872– 876,  DOI: 10.1016/j.diamond.2007.01.030
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      Adsorption and hydrolytic activity of lysozyme on diamond nanocrystallites
      Nguyen, T.-Thanh-Bao; Chang, Huan-Cheng; Wu, Victor Wei-Keh
      Diamond and Related Materials (2007), 16 (4-7), 872-876CODEN: DRMTE3; ISSN:0925-9635. (Elsevier B.V.)
      Oxidative-acid-treated nanodiamonds exhibit high affinity for proteins, a property well suited for immobilization of enzymes for biotechnol. application. Using lysozyme as an example, this work demonstrates that the enzyme can retain much of its activity after phys. adsorption to the surfaces of 100-nm diamond crystallites. The activity relative to that of free lysozyme in soln. is ∼ 60% at the max. surface coverage of 50% and pH 5. While the enzymic activity decreases as the surface coverage is lowered, it can be recovered by blocking the empty sites on the surface with supplementary proteins such as cytochrome c to create a more "crowded" environment. A relative activity up to 70% can be attained at a partial coverage of 20%.
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    19. 19
      Gerion, D.; Pinaud, F.; Williams, S. C.; Parak, W. J.; Zanchet, D.; Weiss, S.; Alivisatos, A. P. Synthesis and properties of biocompatible water-soluble silica-coated CdSe/ZnS semiconductor quantum dots. J. Phys. Chem. B 2001, 105 (37), 8861– 8871,  DOI: 10.1021/jp0105488
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      Synthesis and Properties of Biocompatible Water-Soluble Silica-Coated CdSe/ZnS Semiconductor Quantum Dots
      Gerion, Daniele; Pinaud, Fabien; Williams, Shara C.; Parak, Wolfgang J.; Zanchet, Daniela; Weiss, Shimon; Alivisatos, A. Paul
      Journal of Physical Chemistry B (2001), 105 (37), 8861-8871CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)
      The authors describe the synthesis of H2O-sol. semiconductor nanoparticles and discuss and characterize their properties. Hydrophobic CdSe/ZnS core/shell nanocrystals with a core size between 2 and 5 nm are embedded in a siloxane shell and functionalized with thiol and/or amine groups. Structural characterization by AFM indicates that the siloxane shell is 1-5 nm thick, yielding final particle sizes of 6-17 nm, depending on the initial CdSe core size. The SiO2 coating does not significantly modify the optical properties of the nanocrystals. Their fluorescence emission is ∼32-35 nm fwhm and can be tuned from blue to red with quantum yields up to 18%, mainly detd. by the quantum yield of the underlying CdSe/ZnS nanocrystals. Silanized nanocrystals exhibit enhanced photochem. stability over org. fluorophores. They also display high stability in buffers at physiol. conditions (>150 mM NaCl). The introduction of functionalized groups onto the siloxane surface would permit the conjugation of the nanocrystals to biol. entities.
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      Alivisatos, P. The use of nanocrystals in biological detection. Nat. Biotechnol. 2004, 22 (1), 47– 52,  DOI: 10.1038/nbt927
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      The use of nanocrystals in biological detection
      Alivisatos, Paul
      Nature Biotechnology (2004), 22 (1), 47-52CODEN: NABIF9; ISSN:1087-0156. (Nature Publishing Group)
      A review. In the coming decade, the ability to sense and detect the state of biol. systems and living organisms optically, elec. and magnetically will be radically transformed by developments in materials physics and chem. The emerging ability to control the patterns of matter on the nanometer length scale can be expected to lead to entirely new types of biol. sensors. These new systems will be capable of sensing at the single-mol. level in living cells, and capable of parallel integration for detection of multiple signals, enabling a diversity of simultaneous expts., as well as better crosschecks and controls.
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      Ghosh Chaudhuri, R.; Paria, S. Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications. Chem. Rev. 2012, 112 (4), 2373– 2433,  DOI: 10.1021/cr100449n
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      Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications
      Ghosh Chaudhuri, Rajib; Paria, Santanu
      Chemical Reviews (Washington, DC, United States) (2012), 112 (4), 2373-2433CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. The synthesis and properties of inorg./inorg., inorg./org., org./inorg., and org./org. core/shell nanoparticles are extensively reviewed. Their applications in biomedicine, catalysis, and electronic devices are discussed.
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    22. 22
      Lee, J. R. I.; Whitley, H. D.; Meulenberg, R. W.; Wolcott, A.; Zhang, J. Z.; Prendergast, D.; Lovingood, D. D.; Strouse, G. F.; Ogitsu, T.; Schwegler, E. Ligand-Mediated Modification of the Electronic Structure of CdSe Quantum Dots. Nano Lett. 2012, 12 (6), 2763– 2767,  DOI: 10.1021/nl300886h
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      Ligand-Mediated Modification of the Electronic Structure of CdSe Quantum Dots
      Lee, Jonathan R. I.; Whitley, Heather D.; Meulenberg, Robert W.; Wolcott, Abraham; Zhang, Jin Z.; Prendergast, David; Lovingood, Derek D.; Strouse, Geoffrey F.; Ogitsu, Tadashi; Schwegler, Eric; Terminello, Louis J.; van Buuren, Tony
      Nano Letters (2012), 12 (6), 2763-2767CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      X-ray absorption spectroscopy and ab initio modeling of the exptl. spectra have been used to investigate the effects of surface passivation on the unoccupied electronic states of CdSe quantum dots (QDs). Significant differences are obsd. in the unoccupied electronic structure of the CdSe QDs, which are shown to arise from variations in specific ligand-surface bonding interactions.
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      Meulenberg, R. W.; Lee, J. R. I.; Wolcott, A.; Zhang, J. Z.; Terminello, L. J.; van Buuren, T. Determination of the Excition Binding Energy in CdSe Quantum Dots. ACS Nano 2009, 3 (2), 325– 330,  DOI: 10.1021/nn8006916
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      Determination of the Exciton Binding Energy in CdSe Quantum Dots
      Meulenberg, Robert W.; Lee, Jonathan R. I.; Wolcott, Abraham; Zhang, Jin Z.; Terminello, Louis J.; van Buuren, Tony
      ACS Nano (2009), 3 (2), 325-330CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been detd. using X-ray spectroscopy. Using X-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been detd. and combined to obtain the true band gap of the QDs (i.e., without an exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to det. the EBE. The exptl. EBE results are compared with theor. calcns. on the EBE and show excellent agreement.
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      Wei, H.; Zhou, J.; Zhang, L.; Wang, F.; Wang, J.; Jin, C. The Core/Shell Structure of CdSe/ZnS Quantum Dots Characterized by X-Ray Absorption Fine Spectroscopy. J. Nanomater. 2015, 2015, 764712  DOI: 10.1155/2015/764712
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      Carpenter, E. E.; Calvin, S.; Stroud, R. M.; Harris, V. G. Passivated Iron as Core–Shell Nanoparticles. Chem. Mater. 2003, 15 (17), 3245– 3246,  DOI: 10.1021/cm034131l
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      Passivated Iron as Core-Shell Nanoparticles
      Carpenter, E. E.; Calvin, S.; Stroud, R. M.; Harris, V. G.
      Chemistry of Materials (2003), 15 (17), 3245-3246CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Core-shell passivated Fe magnetic nanoparticles were prepd. using reverse micelles of Igepal CO-430 and Igepal CO-610 (nonylphenol polyethoxylate ethers) to reduce FeCl2 with NaBH4 to form the Fe nanoparticles and reducing NiCl2 to form the passivation coating of oxide. The particles are amorphous iron with amorphous oxide coating. At 10 and 300 K the magnetization is 85.4 and 74.4 emu/g with a coercivity of 200 and <100 Oe and remanence of 14.9 and 5.6 emu/g, resp.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXlvVShu7Y%253D&md5=00736fbf1d9eed133474e2db4a933274
    26. 26
      Carroll, K. J.; Hudgins, D. M.; Spurgeon, S.; Kemner, K. M.; Mishra, B.; Boyanov, M. I.; Brown, L. W.; Taheri, M. L.; Carpenter, E. E. One-Pot Aqueous Synthesis of Fe and Ag Core/Shell Nanoparticles. Chem. Mater. 2010, 22 (23), 6291– 6296,  DOI: 10.1021/cm101996u
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      One-Pot Aqueous Synthesis of Fe and Ag Core/Shell Nanoparticles
      Carroll, Kyler J.; Hudgins, Daniel M.; Spurgeon, Steven; Kemner, Kennneth M.; Mishra, Bhoopesh; Boyanov, Maxim I.; Brown, Lester W., III; Taheri, Mitra L.; Carpenter, Everett E.
      Chemistry of Materials (2010), 22 (23), 6291-6296CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      This article studies a facile one-pot method for the synthesis of Fe and Ag core/shell nanoparticles by aq. redn. under ambient conditions. The injection time of silver nitrate into a reaction vessel contg. aq. ferrous salt, sodium borohydride, and sodium citrate is a vital parameter for the precise control of a desired core/shell structure. For example, if silver nitrate is injected one minute after sodium borohydride was added to the reaction vessel, Ag will nucleate first followed by Fe, creating monodisperse Ag/Fe core/shell nanoparticles. In contrast, if the introduction time is prolonged to 5 min, Fe nanoparticles will nucleate followed by Ag producing Fe/Ag nanoparticles. The compn., morphol., and magnetic behavior were studied by x-ray absorption spectroscopy (XAS), XPS, XRD, TEM, and room-temp. vibrating sample magnetometry (VSM). Fe/Ag core/shell nanoparticles with optical and magnetic functionality offer broad opportunities in medicine, catalysis, and chem. detection.
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    27. 27
      Zhang, X.; Han, S.; Zhu, B.; Zhang, G.; Li, X.; Gao, Y.; Wu, Z.; Yang, B.; Liu, Y.; Baaziz, W. Reversible loss of core–shell structure for Ni–Au bimetallic nanoparticles during CO2 hydrogenation. Nat. Catal. 2020, 3 (4), 411– 417,  DOI: 10.1038/s41929-020-0440-2
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      27
      Reversible loss of core-shell structure for Ni-Au bimetallic nanoparticles during CO2 hydrogenation
      Zhang, Xiaoben; Han, Shaobo; Zhu, Beien; Zhang, Guanghui; Li, Xiaoyan; Gao, Yi; Wu, Zhaoxuan; Yang, Bing; Liu, Yuefeng; Baaziz, Walid; Ersen, Ovidiu; Gu, Meng; Miller, Jeffrey T.; Liu, Wei
      Nature Catalysis (2020), 3 (4), 411-417CODEN: NCAACP; ISSN:2520-1158. (Nature Research)
      The high catalytic performance of core-shell nanoparticles is usually attributed to their distinct geometric and electronic structures. Here we reveal a dynamic mechanism that overturns this conventional understanding by a direct environmental transmission electron microscopy visualization coupled with multiple state-of-the-art in situ techniques, which include synchrotron X-ray absorption spectroscopy, IR spectroscopy and theor. simulations. A Ni-Au catalytic system, which exhibits a highly selective CO prodn. in CO2 hydrogenation, features an intact ultrathin Au shell over the Ni core before and after the reaction. However, the catalytic performance could not be attributed to the Au shell surface, but rather to the formation of a transient reconstructed alloy surface, promoted by CO adsorption during the reaction. The discovery of such a reversible transformation urges us to reconsider the reaction mechanism beyond the stationary model, and may have important implications not only for core-shell nanoparticles, but also for other well-defined nanocatalysts.
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    28. 28
      Signorini, L.; Pasquini, L.; Savini, L.; Carboni, R.; Boscherini, F.; Bonetti, E.; Giglia, A.; Pedio, M.; Mahne, N.; Nannarone, S. Size-dependent oxidation in iron/iron oxide core-shell nanoparticles. Phys. Rev. B 2003, 68 (19), 195423  DOI: 10.1103/PhysRevB.68.195423
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      28
      Size-dependent oxidation in iron/iron oxide core-shell nanoparticles
      Signorini, Luca; Pasquini, Luca; Savini, Lorenzo; Carboni, Roberta; Boscherini, Federico; Bonetti, Ennio; Giglia, Angelo; Pedio, Maddalena; Mahne, Nicola; Nannarone, Stefano
      Physical Review B: Condensed Matter and Materials Physics (2003), 68 (19), 195423/1-195423/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      A detailed morphol. and structural characterization of iron/iron oxide core-shell nanoparticles with x-ray diffraction and x-ray absorption spectroscopy performed at both the Fe and O K edges is reported. Core-shell nanoparticles with core size ranging from 7 to 21 nm were synthesized using the inert gas condensation technique followed by 12 h of controlled surface oxidn. Rietveld anal. of diffraction patterns shows the presence of α-Fe nanoparticles surrounded by a 2-3 nm-thick oxide layer with a disordered cubic spinel structure. Magnetite (Fe3O4) and maghemite (γ-Fe2O3), two different iron oxides, share this lattice structure, but x-ray diffraction was not able to distinguish between the two. An anal. of the Fe and O x-ray absorption spectra in both the near-edge and the extended energy regions is described. The anal. of the extended spectra was performed using the ab initio calcn. of all significant contributions to the absorption cross section. There are size-dependent changes in the local structure and oxidn. state of the oxide shell, the relative fraction of maghemite increasing at the expense of magnetite as the core dimensions decrease. This size/structure correlation was explained in terms of morphol. and structural disorder.
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    29. 29
      Alayoglu, S.; Zavalij, P.; Eichhorn, B.; Wang, Q.; Frenkel, A. I.; Chupas, P. Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt–Ru Core–Shell and Alloy Nanoparticles. ACS Nano 2009, 3 (10), 3127– 3137,  DOI: 10.1021/nn900242v
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      Structural and Architectural Evaluation of Bimetallic Nanoparticles: A Case Study of Pt-Ru Core-Shell and Alloy Nanoparticles
      Alayoglu, Selim; Zavalij, Peter; Eichhorn, Bryan; Wang, Qi; Frenkel, Anatoly I.; Chupas, Peter
      ACS Nano (2009), 3 (10), 3127-3137CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are cryst. homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 Å. In contrast, the 1-2 monolayer thick Pt shells are relatively cryst. but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination nos. and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-sepd. in the core and shell components and that the interface between the core and shell is quite normal.
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    30. 30
      Park, J.-I.; Kim, M. G.; Jun, Y.-W.; Lee, J. S.; Lee, W.-R.; Cheon, J. Characterization of Superparamagnetic “Core–Shell” Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic “Solid Solution” Nanoalloys. J. Am. Chem. Soc. 2004, 126 (29), 9072– 9078,  DOI: 10.1021/ja049649k
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      Characterization of Superparamagnetic "Core-Shell" Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic "Solid Solution" Nanoalloys
      Park, Jong-Il; Kim, Min Gyu; Jun, Young-Wook; Lee, Jae Sung; Lee, Woo-Ram; Cheon, Jinwoo
      Journal of the American Chemical Society (2004), 126 (29), 9072-9078CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The structure, magnetism, and phase transition of core-shell type CoPt nanoparticles en route to solid soln. alloy nanostructures are systematically studied. The characterization of CocorePtshell nanoparticles obtained by a redox transmetalation process by TEM and, in particular, x-ray absorption spectroscopy (XAS) provides clear evidence for the existence of a core-shell type bimetallic interfacial structure. Nanoscale phase transitions of the CocorePtshell structures toward c-axis compressed face-centered tetragonal (fct) solid soln. alloy CoPt nanoparticles were monitored at various stages of a thermally induced annealing process and the obtained fct nanoalloys show a large enhancement of their magnetic properties with ferromagnetism. The relation between the nanostructures and their magnetic properties is in part elucidated through the use of XAS as a crit. anal. tool.
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    31. 31
      Lee, W.-R.; Kim, M. G.; Choi, J.-R.; Park, J.-I.; Ko, S. J.; Oh, S. J.; Cheon, J. Redox–Transmetalation Process as a Generalized Synthetic Strategy for Core–Shell Magnetic Nanoparticles. J. Am. Chem. Soc. 2005, 127 (46), 16090– 16097,  DOI: 10.1021/ja053659j
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      Redox-Transmetalation Process as a Generalized Synthetic Strategy for Core-Shell Magnetic Nanoparticles
      Lee, Woo-Ram; Kim, Min Gyu; Choi, Joon-Rak; Park, Jong-Il; Ko, Seung Jin; Oh, Sang Jun; Cheon, Jinwoo
      Journal of the American Chemical Society (2005), 127 (46), 16090-16097CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Although multicomponent core-shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox-transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core-shell type bimetallic nanoparticles on the sub-10 nm scale. Various core-shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential redn. strategies, this transmetalation process has several advantages for the fabrication of core-shell type nanoparticles: (i) no addnl. reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core-shell structures by transferring Co@Au nanoparticles from an org. phase to an aq. phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core-shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chem. process that promotes the core-shell structure formation.
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      Foucher, A. C.; Yang, S.; Rosen, D. J.; Lee, J. D.; Huang, R.; Jiang, Z.; Barrera, F. G.; Chen, K.; Hollyer, G. G.; Friend, C. M. Synthesis and Characterization of Core-Shell Cu-Ru, Cu-Rh, and Cu-Ir Nanoparticles. J. Am. Chem. Soc. 2022, 144 (17), 7919– 7928,  DOI: 10.1021/jacs.2c02538
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      Synthesis and Characterization of Core-Shell Cu-Ru, Cu-Rh, and Cu-Ir Nanoparticles
      Foucher, Alexandre C.; Yang, Shengsong; Rosen, Daniel J.; Lee, Jennifer D.; Huang, Renjing; Jiang, Zhiqiao; Barrera, Francisco G.; Chen, Kelly; Hollyer, George G.; Friend, Cynthia M.; Gorte, Raymond J.; Murray, Christopher B.; Stach, Eric A.
      Journal of the American Chemical Society (2022), 144 (17), 7919-7928CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Optimizing the use of expensive precious metals is crit. to developing sustainable and low-cost processes for heterogeneous catalysis or electrochem. Here, we report a synthesis method that yields core-shell Cu-Ru, Cu-Rh, and Cu-Ir nanoparticles with the platinum-group metals segregated on the surface. The synthesis of Cu-Ru, Cu-Rh, and Cu-Ir particles allows maximization of the surface area of these metals and improves catalytic performance. Furthermore, the Cu core can be selectively etched to obtain nanoshells of the platinum-group metal components, leading to a further increase in the active surface area. Characterization of the samples was performed with X-ray absorption spectroscopy, X-ray powder diffraction, and ex situ and in situ transmission electron microscopy. CO oxidn. was used as a ref. reaction: the three core-shell particles and derivs. exhibited promising catalyst performance and stability after redox cycling. These results suggest that this synthesis approach may optimize the use of platinum-group metals in catalytic applications.
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      Rehor, I.; Slegerova, J.; Kucka, J.; Proks, V.; Petrakova, V.; Adam, M. P.; Treussart, F.; Turner, S.; Bals, S.; Sacha, P. Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells. Small 2014, 10 (6), 1106– 1115,  DOI: 10.1002/smll.201302336
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      Fluorescent Nanodiamonds Embedded in Biocompatible Translucent Shells
      Rehor, Ivan; Slegerova, Jitka; Kucka, Jan; Proks, Vladimir; Petrakova, Vladimira; Adam, Marie-Pierre; Treussart, Francois; Turner, Stuart; Bals, Sara; Sacha, Pavel; Ledvina, Miroslav; Wen, Amy M.; Steinmetz, Nicole F.; Cigler, Petr
      Small (2014), 10 (6), 1106-1115CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      High pressure high temp. (HPHT) nanodiamonds (NDs) represent extremely promising materials for construction of fluorescent nanoprobes and nanosensors. However, some properties of bare NDs limit their direct use in these applications: they ppt. in biol. solns., only a limited set of bio-orthogonal conjugation techniques is available and the accessible material is greatly polydisperse in shape. In this work, we encapsulate bright 30-nm fluorescent nanodiamonds (FNDs) in 10-20-nm thick translucent (i.e., not altering FND fluorescence) silica shells, yielding monodisperse near-spherical particles of mean diam. 66 nm. High yield modification of the shells with PEG chains stabilizes the particles in ionic solns., making them applicable in biol. environments. We further modify the opposite ends of PEG chains with fluorescent dyes or vectoring peptide using click chem. High conversion of this bio-orthogonal coupling yielded circa 2000 dye or peptide mols. on a single FND. We demonstrate the superior properties of these particles by in vitro interaction with human prostate cancer cells: while bare nanodiamonds strongly aggregate in the buffer and adsorb onto the cell membrane, the shell encapsulated NDs do not adsorb nonspecifically and they penetrate inside the cells.
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      Rehor, I.; Mackova, H.; Filippov, S. K.; Kucka, J.; Proks, V.; Slegerova, J.; Turner, S.; Van Tendeloo, G.; Ledvina, M.; Hruby, M. Fluorescent Nanodiamonds with Bioorthogonally Reactive Protein-Resistant Polymeric Coatings. ChemPlusChem 2014, 79 (1), 21– 24,  DOI: 10.1002/cplu.201300339
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      Fluorescent Nanodiamonds with Bioorthogonally Reactive Protein-Resistant Polymeric Coatings
      Rehor, Ivan; Mackova, Hana; Filippov, Sergey K.; Kucka, Jan; Proks, Vladimir; Slegerova, Jitka; Turner, Stuart; Van Tendeloo, Gustaaf; Ledvina, Miroslav; Hruby, Martin; Cigler, Petr
      ChemPlusChem (2014), 79 (1), 21-24CODEN: CHEMM5; ISSN:2192-6506. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The novel synthesis of a polymeric interface grown from the surface of bright fluorescent nanodiamonds is reported. The polymer enables bioorthogonal attachment of various mols. by click chem.; the particles are resistant to nonspecific protein adsorption and show outstanding colloidal stability in buffers and biol. media. The coating fully preserves the unique optical properties of the nitrogen-vacancy centers that are crucial for bioimaging and sensoric applications.
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      Schiros, T.; Nordlund, D.; Palova, L.; Prezzi, D.; Zhao, L. Y.; Kim, K. S.; Wurstbauer, U.; Gutierrez, C.; Delongchamp, D.; Jaye, C. Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene. Nano Lett. 2012, 12 (8), 4025– 4031,  DOI: 10.1021/nl301409h
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      Connecting Dopant Bond Type with Electronic Structure in N-Doped Graphene
      Schiros, Theanne; Nordlund, Dennis; Palova, Lucia; Prezzi, Deborah; Zhao, Liuyan; Kim, Keun Soo; Wurstbauer, Ulrich; Gutierrez, Christopher; Delongchamp, Dean; Jaye, Cherno; Fischer, Daniel; Ogasawara, Hirohito; Pettersson, Lars G. M.; Reichman, David R.; Kim, Philip; Hybertsen, Mark S.; Pasupathy, Abhay N.
      Nano Letters (2012), 12 (8), 4025-4031CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Robust methods to tune the unique electronic properties of graphene by chem. modification are in great demand due to the potential of the two dimensional material to impact a range of device applications. C and N core-level resonant x-ray spectroscopy is a sensitive probe of chem. bonding and electronic structure of chem. dopants introduced in single-sheet graphene films. In conjunction with d. functional theory based calcns., the authors are able to obtain a detailed picture of bond types and electronic structure in graphene doped with N at the sub-percent level. Different N-bond types, including graphitic, pyridinic, and nitrilic, can exist in a single, dilutely N-doped graphene sheet. These various bond types have profoundly different effects on the carrier concn., indicating that control over the dopant bond type is a crucial requirement in advancing graphene electronics.
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      Raty, J. Y.; Galli, G.; Bostedt, C.; van Buuren, T. W.; Terminello, L. J. Quantum confinement and fullerenelike surface reconstructions in nanodiamonds. Phys. Rev. Lett. 2003, 90 (3), 037401  DOI: 10.1103/PhysRevLett.90.037401
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      Quantum Confinement and Fullerenelike Surface Reconstructions in Nanodiamonds
      Raty, Jean-Yves; Galli, Giulia; Bostedt, C.; van Buuren, Tony W.; Terminello, Louis J.
      Physical Review Letters (2003), 90 (3), 037401/1-037401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      We present x-ray absorption and emission expts. and ab initio calcns. showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addn., our calcns. show that the surface of nanodiamond particles larger than ≃1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features obsd. in measured absorption spectra.
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      Chang, Y. K.; Hsieh, H. H.; Pong, W. F.; Tsai, M. H.; Chien, F. Z.; Tseng, P. K.; Chen, L. C.; Wang, T. Y.; Chen, K. H.; Bhusari, D. M. Quantum Confinement Effect in Diamond Nanocrystals Studied by X-Ray-Absorption Spectroscopy. Phys. Rev. Lett. 1999, 82 (26), 5377– 5380,  DOI: 10.1103/PhysRevLett.82.5377
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      Quantum Confinement Effect in Diamond Nanocrystals Studied by X-Ray-Absorption Spectroscopy
      Chang, Y. K.; Hsieh, H. H.; Pong, W. F.; Tsai, M.-H.; Chien, F. Z.; Tseng, P. K.; Chen, L. C.; Wang, T. Y.; Chen, K. H.; Bhusari, D. M.; Yang, J. R.; Lin, S. T.
      Physical Review Letters (1999), 82 (26, Pt. 1), 5377-5380CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      This study measures the x-ray-absorption spectra of nanodiamond thin films with grain diams. ranging from 3.5 nm to 5 μm at the C K-edge using the sample drain current mode at room temp. Resonance peaks resembling the C 1s core exciton are obsd. The exciton state and conduction band edge shift to higher energies with the decrease of the grain size indicative of the presence of the quantum confinement effect.
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      Morar, J. F.; Himpsel, F. J.; Hollinger, G.; Hughes, G.; Jordan, J. L. OBSERVATION OF A C-1S CORE EXCITON IN DIAMOND. Phys. Rev. Lett. 1985, 54 (17), 1960– 1963,  DOI: 10.1103/PhysRevLett.54.1960
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      Observation of a carbon-1s core exciton in diamond
      Morar, J. F.; Himpsel, F. J.; Hollinger, G.; Hughes, G.; Jordan, J. L.
      Physical Review Letters (1985), 54 (17), 1960-3CODEN: PRLTAO; ISSN:0031-9007.
      A well-resolved core exciton at the bulk diamond C-1s absorption edge was obsd. by using high-resoln. partial-yield spectroscopy with synchrotron radiation. The obtained excitonic binding energy, 0.19 ± 0.015 eV, agrees well with a 1st-principles effective-mass approxn. (EMA). This is in sharp contrast to other semiconductors (Si, Ge, and GaAs) where reported excitonic shifts far exceed EMA ests. In light of these results, one must question whether previous measurements overestimate the core-hole interaction or if they indicate a breakdown of the EMA for core excitons.
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      Wolcott, A.; Schiros, T.; Trusheim, M. E.; Chen, E. H.; Nordlund, D.; Diaz, R. E.; Gaathon, O.; Englund, D.; Owen, J. S. Surface structure of aerobically oxidized diamond nanocrystals. J. Phys. Chem. C 2014, 118 (46), 26695– 26702,  DOI: 10.1021/jp506992c
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      Surface Structure of Aerobically Oxidized Diamond Nanocrystals
      Wolcott, Abraham; Schiros, Theanne; Trusheim, Matthew E.; Chen, Edward H.; Nordlund, Dennis; Diaz, Rosa E.; Gaathon, Ophir; Englund, Dirk; Owen, Jonathan S.
      Journal of Physical Chemistry C (2014), 118 (46), 26695-26702CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      We investigate the aerobic oxidn. of high-pressure, high-temp. nanodiamonds (5-50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidn. at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core-hole exciton is obsd. Both spectroscopic features are similar to those of chem. vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. The importance of these findings to the functionalization of nanodiamond surfaces for biol. labeling applications is discussed.
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      Henke, B. L.; Liesegang, J.; Smith, S. D. SOFT-X-RAY-INDUCED SECONDARY-ELECTRON EMISSION FROM SEMICONDUCTORS AND INSULATORS - MODELS AND MEASUREMENTS. Phys. Rev. B 1979, 19 (6), 3004– 3021,  DOI: 10.1103/PhysRevB.19.3004
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      Soft-x-ray-induced secondary electron emission from semiconductors and insulators: models and measurements
      Henke, Burton L.; Liesegang, John; Smith, Steven D.
      Physical Review B: Condensed Matter and Materials Physics (1979), 19 (6), 3004-21CODEN: PRBMDO; ISSN:0163-1829.
      Secondary-electron energy distribution curves (EDC's) and the total secondary-electron yields relative to such for Au were measured for seven semiconductors for which electron-electron scattering losses within the emitter were considered dominant and for nine insulators (alkali halides) for which electron-phonon scattering losses were expected to be dominant in the transport process. The secondary-electron spectra were excited by Al-Kα (1487 eV) photons and were measured from evapd. dielec. films (of about 0.3 μ thickness) on conducting substrates with an electrostatic hemispherical analyzer of about 0.03-eV resoln. Some of the dielec. photoemitters have appreciably narrower energy distribution and higher yields than has Au; CuI and CsI have EDC widths at half-max. of about one-third of that for Au, and yield values of 11 and 30 times greater. The FWHM and secondary-electron yield for gold are ∼ 4eV and 0.50 electrons per normally incident photon, resp. The shapes of the EDC's are essentially unchanged for photon excitation in the 0.1-10-keV region. Strong structural features appear only in the alkali halide EDS's, and it proposed that these are mainly the result of single-electron promotion of secondaries from the valence band by plasmon deexcitation. A relatively simple model for x-ray photoemission is developed which assumes the direct excitation of secondaries by photoelectron and Auger-electron ''primaries'' is the dominant excitation mechanism, and accounts for both electron-electron and electron-photo scattering in the transport process. Free-electron conduction-band descriptions are assumed. The theor. and exptl. curves are in satisfactory agreement.
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      Henke, B. L.; Smith, J. A.; Attwood, D. T. 0.1–10-KEV X-RAY-INDUCED ELECTRON EMISSIONS FROM SOLIDS - MODELS AND SECONDARY-ELECTRON MEASUREMENTS. J. Appl. Phys. 1977, 48 (5), 1852– 1866,  DOI: 10.1063/1.323938
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      0.1-10-keV x-ray-induced electron emissions from solids - Models and secondary electron measurements
      Henke, Burton L.; Smith, Jerel A.; Attwood, David T.
      Journal of Applied Physics (1977), 48 (5), 1852-65CODEN: JAPIAU; ISSN:0021-8979.
      Anal. models are presented describing the x-ray-excited emission of "no-loss" photoelectrons and Auger electrons and the energy distribution of emitted secondary electrons. The secondary electron energy distribution is given in terms of the electron kinetic energy EK, work function W, photon energy E0, and mass photoionization coeff. μ(E0), as proportional to E0m(E0)EK(EK + W)-4. Techniques of electron spectral measurements utilizing uniform field pre-acceleration and limited acceptance angle spectrometers are discussed. Secondary electron energy distributions are measured at ∼10-8 torr from thick evaporated films of Au and Al at photon energies 277, 1487, and 8050 eV. The shapes of these distributions do not depend significantly upon photon energy. The full width at half-max. (FWHM) of these distributions are 3.9, 6.7, and 4.4 eV for Au and ion-cleaned Au and Al photocathodes, resp. The data agree well with the model predictions.
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      Maurer, P. C.; Kucsko, G.; Latta, C.; Jiang, L.; Yao, N. Y.; Bennett, S. D.; Pastawski, F.; Hunger, D.; Chisholm, N.; Markham, M. Room-Temperature Quantum Bit Memory Exceeding One Second. Science 2012, 336 (6086), 1283– 1286,  DOI: 10.1126/science.1220513
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      Room-Temperature Quantum Bit Memory Exceeding One Second
      Maurer, P. C.; Kucsko, G.; Latta, C.; Jiang, L.; Yao, N. Y.; Bennett, S. D.; Pastawski, F.; Hunger, D.; Chisholm, N.; Markham, M.; Twitchen, D. J.; Cirac, J. I.; Lukin, M. D.
      Science (Washington, DC, United States) (2012), 336 (6086), 1283-1286CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. We demonstrate high-fidelity control of a solid-state qubit, which preserves its polarization for several minutes and features coherence lifetimes exceeding 1 s at room temp. The qubit consists of a single 13C nuclear spin in the vicinity of a nitrogen-vacancy color center within an isotopically purified diamond crystal. The long qubit memory time was achieved via a technique involving dissipative decoupling of the single nuclear spin from its local environment. The versatility, robustness, and potential scalability of this system may allow for new applications in quantum information science.
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      Jones, R. G.; Woodruff, D. P. Sampling depths in total yield and reflectivity SEXAFS studies in the soft X-ray region. Surf. Sci. 1982, 114 (1), 38– 46,  DOI: 10.1016/0039-6028(82)90454-X
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      Sampling depths in total yield and reflectivity SEXAFS studies in the soft x-ray region
      Jones, R. G.; Woodruff, D. P.
      Surface Science (1982), 114 (1), 38-46CODEN: SUSCAS; ISSN:0039-6028.
      Both total photoelectron yield and reflectivity measurements display EXAFS and possess some surface sensitivity. By using Al foils with natural oxide films and anodically prepd. films of different thicknesses, the viability and surface specificity of these methods in the vicinity of the Al K-edge (1560 eV) were examd. The oxide films of only ∼130 Å thickness lead to EXAFS dominated by the oxide structure in the total yield model. A simple model is developed to account for the depth dependence of sampling in this mode which provides a reasonable match of the exptl. data.
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      Kasrai, M.; Lennard, W. N.; Brunner, R. W.; Bancroft, G. M.; Bardwell, J. A.; Tan, K. H. Sampling depth of total electron and fluorescence measurements in Si L- and K-edge absorption spectroscopy. Appl. Surf. Sci. 1996, 99 (4), 303– 312,  DOI: 10.1016/0169-4332(96)00454-0
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      Sampling depth of total electron and fluorescence measurements in Si L- and K-edge absorption spectroscopy
      Kasrai, M.; Lennard, W. N.; Brunner, R. W.; Bancroft, G. M.; Bardwell, J. A.; Tan, K. H.
      Applied Surface Science (1996), 99 (4), 303-312CODEN: ASUSEE; ISSN:0169-4332. (Elsevier)
      High resoln. Si L-edge and K-edge x-ray absorption near edge structure (XANES) spectra for SiO2 on Si substrates were recorded using total electron yield (TEY) and fluorescence yield (FY) techniques. The sampling depths of TEY and FY for Si L-edge and Si K-edge, resp., were studied in the energy range 95-120 eV and 1830-1900 eV. The max. sampling depth for TEY is ∼5 nm for the Si L-edge and ∼70 nm for the K-edge regions. The FY sampling depth at the L-edge is ∼70 nm whereas for the K-edge, the sampling depth is several hundred nm. Based on these data, and using a theor. model, electron escape depths for the TEY measurements in both energy ranges were deduced.
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      Ziaja, B.; van der Spoel, D.; Szöke, A.; Hajdu, J. Auger-electron cascades in diamond and amorphous carbon. Phys. Rev. B 2001, 64 (21), 214104  DOI: 10.1103/PhysRevB.64.214104
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      Auger-electron cascades in diamond and amorphous carbon
      Ziaja, Beata; van der Spoel, David; Szoke, Abraham; Hajdu, Janos
      Physical Review B: Condensed Matter and Materials Physics (2001), 64 (21), 214104/1-214104/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      We have analyzed cascades of secondary electrons in diamond and amorphous carbon generated by the thermalization of a single Auger electron. The elastic electron mean free path was calcd. as a function of impact energy in the muffin-tin potential approxn. The inelastic scattering cross section and the energy loss of electrons (expressed in terms of the differential inverse mean free path) were estd. from two "optical" models that utilize the measured dielec. consts. of the materials. Using these data, a Monte Carlo model describing the time evolution of the cascade was constructed. The results show that at most around 20-40 secondary cascade electrons are released by a single Auger electron in a macroscopic sample of diamond or amorphous carbon. Consideration of the real band structure of diamond reduces this no. further. The release of the cascade electrons happens within the first 100 fs after the emission of the primary Auger electron. The results have implications to planned expts. with femtosecond x-ray sources.
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      Neburkova, J.; Vavra, J.; Cigler, P. Coating nanodiamonds with biocompatible shells for applications in biology and medicine. Curr. Opin. Solid State Mater. Sci. 2017, 21 (1), 43– 53,  DOI: 10.1016/j.cossms.2016.05.008
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      Coating nanodiamonds with biocompatible shells for applications in biology and medicine
      Neburkova, Jitka; Vavra, Jan; Cigler, Petr
      Current Opinion in Solid State & Materials Science (2017), 21 (1), 43-53CODEN: COSSFX; ISSN:1359-0286. (Elsevier Ltd.)
      Use of nanodiamonds (NDs) as nontoxic nanoparticles for biol. imaging, sensing, and drug delivery is expanding rapidly. The interest in NDs is triggered by their unique combination of optical properties. ND can accommodate nitrogen-vacancy color centers which provide stable fluorescence without photobleaching or photoblinking and their electronic structure is very sensitive to magnetic and elec. fields. The limited options to control ND properties during synthesis or by direct surface functionalization leave room to be improved upon by employing surface coatings engineered precisely for a particular application. The major disadvantages of unmodified NDs are their limited colloidal stability and tendency to non-specifically adsorb biomols. This review aims to summarize recent advances in coating NDs (namely with silica and polymer shells), which addresses these disadvantages and enables the use of NDs in biol. applications such as targeting of specific cells, drug delivery, and biol. imaging.
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      Harris, M. T.; Brunson, R. R.; Byers, C. H. THE BASE-CATALYZED-HYDROLYSIS AND CONDENSATION-REACTIONS OF DILUTE AND CONCENTRATED TEOS SOLUTIONS. J. Non-Cryst. Solids 1990, 121 (1–3), 397– 403,  DOI: 10.1016/0022-3093(90)90165-I
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      The base-catalyzed hydrolysis and condensation reactions of dilute and concentrated TEOS solutions
      Harris, Michael T.; Brunson, Ronald R.; Byers, Charles H.
      Journal of Non-Crystalline Solids (1990), 121 (1-3), 397-403CODEN: JNCSBJ; ISSN:0022-3093.
      The synthesis of submicron SiO2 particles by the hydrolysis and condensation of dil. and concd. solns. of Si(OEt(4 (TEOS) was studied in low-mol.-wt. alcs. (C1-C4). A base (NH3) was used to catalyze the reaction. Raman spectroscopy, gas chromatog., and the molybdate method were used to establish the hydrolysis and condensation kinetics. Dynamic and classical light-scattering methods were used to monitor particle growth, particle no. concn. kinetics, and particle size distribution. The effects of solvent and TEOS concn. on the degree of monodispersity of the particles are discussed. The chem. and particle growth data were used to test theories of homogeneous nucleation and aggregative growth, proposed as mechanisms that govern the growth of submicron monodisperse SiO2 particles by TEOS hydrolysis.
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      Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Reactivity of penta- and hexacoordinate silicon compounds and their role as reaction intermediates. Chem. Rev. 1993, 93 (4), 1371– 1448,  DOI: 10.1021/cr00020a003
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      Reactivity of penta- and hexacoordinate silicon compounds and their role as reaction intermediates
      Chuit, Claude; Corriu, Robert J. P.; Reye, Catherine; Young, J. Colin
      Chemical Reviews (Washington, DC, United States) (1993), 93 (4), 1371-448CODEN: CHREAY; ISSN:0009-2665.
      A review of the chem. reactivity of penta- and hexacoordinate silicon compds. with respect to their applications in org. synthesis and as reagents for the prepn. of organosilicon compds., with 411 refs.
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      Delak, K. M.; Sahai, N. Amine-Catalyzed Biomimetic Hydrolysis and Condensation of Organosilicate. Chem. Mater. 2005, 17 (12), 3221– 3227,  DOI: 10.1021/cm048355v
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      Amine-catalyzed biomimetic hydrolysis and condensation of organosilicate
      Delak, Katya M.; Sahai, Nita
      Chemistry of Materials (2005), 17 (12), 3221-3227CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Biogenic silica prodn. occurs at mild conditions with greater control of pore size, shape, and micropatterning than is possible with typical industrial sol-gel methods, providing inspiration for potential alternative routes to silica synthesis. Researchers have implicated the amine moieties, histidine and polylysine, on proteins isolated from sponges and diatoms as catalysts for biogenic silica pptn. Different mechanistic roles have been ascribed to the amines, but few systematic, quant. studies isolating one effect from another have been conducted. In the present study, we use 29Si NMR spectroscopy to systematically examine the different possible mechanistic roles of mono- and polyamines in catalyzing silica synthesis at mildly acidic pH (∼5) from an organosilicate starting compd., trimethylethoxysilane (TMES). TMES has a single organosilicate bond, so there are no competing reactions and the reaction progress can be followed with little ambiguity. Hydrolysis and condensation (dimerization) of TMES lead to the products trimethylsilanol (TMSiOH) and hexamethyldisiloxane (HMD). The Refocused Insensitive Nuclei Enhanced by Polarization Transfer pulse sequence (RINEPT+) provides unambiguous, quant. 29Si NMR spectra from which the hydrolysis and condensation rates in the presence of each amine can be obtained. For both mono- and polyamines, the catalytic efficiency scales with the concn. of conjugate base form and inversely with pKa. Thus, catalysis is most efficient with more acidic monoamines, such as pyridine and imidazole, as well as for the longer polyamines, where the most acidic protonation const. is lower than the exptl. pH (∼5). We postulate a nucleophile-catalyzed hydrolysis mechanism where the conjugate base of the amine attacks Si to form a pentacoordinate intermediate with TMES. Condensation is interpreted as an acid-catalyzed SN2 mechanism. Our findings potentially explain the evolutionary selection of histidine-contg. proteins for biogenic silica synthesis by sponges and address the chem. mechanisms at work for the pptn. of silica by polylysine-contg. proteins in diatoms. Along with the phys. mechanisms suggested by other research groups, the systematic results from the present study indicate that amines may be employed in more than one type of mechanistic strategy for catalyzing biogenic and biomimetic silica polymn.
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      Delak, K. M.; Sahai, N. Mechanisms of Amine-Catalyzed Organosilicate Hydrolysis at Circum-Neutral pH. J. Phys. Chem. B 2006, 110 (36), 17819– 17829,  DOI: 10.1021/jp062054m
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      Mechanisms of amine-catalyzed organosilicate hydrolysis at circum-neutral pH
      Delak, Katya M.; Sahai, Nita
      Journal of Physical Chemistry B (2006), 110 (36), 17819-17829CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Mono- and polyamines catalyze hydrolysis and condensation of alkoxyorganosilanes at neural pH values and room temp. mimeting silica synthetic pathways in biol. systems. The study is focused on understanding the mechanistic role of amines in catalyzing the hydrolysis process that precedes condensation. Variable-temp. 29Si NMR spectra in a range of pH values were used to evaluate the hydrolysis rates of trimethylethoxysilane (TMES), which, in combination with hybrid d. functional theory calcns. of putative intermediates and transition-states for TMES and tetra-Me orthosilicate (TMOS) allowed to suggest the mechanism of the hydrolysis. Comparison of calcd. energies with exptl. detd. activation energies indicates that amine catalysis of TMES is primarily a consequence of the amine acidity at neutral pH. The proton released by the amine is transferred to the organosilicate, producing a protonated ethoxy leaving group that can be displaced by water in an SN2 reaction. For TMOS, the activation energy of proton-transfer coupled with SN2 substitution is comparable to that for Corriu nucleophile-activated nucleophilic displacement, such that the mechanism of amine-catalyzed hydrolysis is dependent mostly on the ambient pH conditions as well as the type of amine. The relevance of the obtained results to biol. silica formation is discussed.
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      Stöber, W.; Fink, A.; Bohn, E. Controlled growth of monodisperse silica spheres in the micron size range. J. Colloid Interface Sci. 1968, 26 (1), 62,  DOI: 10.1016/0021-9797(68)90272-5
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      Pandey, K. C. NEW DIMERIZED-CHAIN MODEL FOR THE RECONSTRUCTION OF THE DIAMOND (111)-(2 × 1) SURFACE. Phys. Rev. B 1982, 25 (6), 4338– 4341,  DOI: 10.1103/PhysRevB.25.4338
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      New dimerized-chain model for the reconstruction of the diamond (111)-(2 × 1) surface
      Pandey, K. C.
      Physical Review B: Condensed Matter and Materials Physics (1982), 25 (6), 4338-41CODEN: PRBMDO; ISSN:0163-1829.
      Of the relaxed, graphitic, buckled, and π-bonded-chain-type models for the diamond (111)-(2 × 1) surface, only the chain model appears to account for the measured surface-band dispersion. The interaction of dangling orbitals which dets. the dispersion is large in the chain model because only in this model are the dangling bonds located on nearest-neighbor atoms. The data also suggest a dimerization of the chains.
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      Osswald, S.; Yushin, G.; Mochalin, V.; Kucheyev, S. O.; Gogotsi, Y. Control of sp(2)/sp(3) carbon ratio and surface chemistry of nanodiamond powders by selective oxidation in air. J. Am. Chem. Soc. 2006, 128 (35), 11635– 11642,  DOI: 10.1021/ja063303n
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      Control of sp2/sp3 Carbon Ratio and Surface Chemistry of Nanodiamond Powders by Selective Oxidation in Air
      Osswald, Sebastian; Yushin, Gleb; Mochalin, Vadym; Kucheyev, Sergei O.; Gogotsi, Yury
      Journal of the American Chemical Society (2006), 128 (35), 11635-11642CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The presence of large amts. of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidn. in air to selectively remove sp2-bonded carbon from ND. Thermogravimetric anal. and in situ Raman spectroscopy shows that sp2 and sp3 carbon species oxidize with different rates at 375-450 °C and reveals a narrow temp. range of 400-430 °C in which the oxidn. of sp2-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp3/sp2 ratio after oxidn. The content of up to 96% of sp3-bonded carbon in the oxidized samples is comparable to that found in microcryst. diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform IR spectroscopy studies show high purity 5-nm ND particles covered by oxygen-contg. surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purifn. techniques, the air oxidn. process does not require the use of toxic or aggressive chems., catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.
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      Frazer, B. H.; Gilbert, B.; Sonderegger, B. R.; De Stasio, G. The probing depth of total electron yield in the sub-keV range: TEY-XAS and X-PEEM. Surf. Sci. 2003, 537 (1–3), 161– 167,  DOI: 10.1016/S0039-6028(03)00613-7
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      The probing depth of total electron yield in the sub-keV range: TEY-XAS and X-PEEM
      Frazer, Bradley H.; Gilbert, Benjamin; Sonderegger, Brandon R.; De Stasio, Gelsomina
      Surface Science (2003), 537 (1-3), 161-167CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
      X-ray absorption spectra can be collected in multiple ways, each exhibiting a different probing depth. The total electron yield signal contains contributions from primary, Auger and secondary electrons. Data are presented on the total electron yield probing depth at core level energies ranging from 77 to 929 eV. By coating materials with Cr overlayers, the max. probing depth increases with core level energy from 15 to 141 A. The Auger electron contribution to total electron yield intensity is negligible, therefore x-ray absorption spectra acquired in x-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) are equiv. to spectra acquired by total electron yield. The signal intensity decreases exponentially with coating thickness, and total electron yield probing depth and Auger electron range (calcd. in the continuously slowing down approxn.) are similar at low energies, but diverge for kinetic energies >400 eV.
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      Smekal, W.; Werner, W. S. M.; Powell, C. J. Simulation of electron spectra for surface analysis (SESSA): a novel software tool for quantitative Auger-electron spectroscopy and X-ray photoelectron spectroscopy. Surf. Interface Anal. 2005, 37 (11), 1059– 1067,  DOI: 10.1002/sia.2097
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      Simulation of electron spectra for surface analysis (SESSA): A novel software tool for quantitative Auger-electron spectroscopy and X-ray photoelectron spectroscopy
      Smekal, Werner; Werner, Wolfgang S. M.; Powell, Cedric J.
      Surface and Interface Analysis (2005), 37 (11), 1059-1067, 2 platesCODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)
      A description of a new NIST database for quant. Auger-electron and XPS (AES/XPS) is given: Simulation of Electron Spectra for Surface Anal. (SESSA). This database contains extensive sets of data for the phys. quantities relevant to AES and XPS. The internal databases are linked to a user interface via a small expert system that allows a user to automatically retrieve data needed for a specific practical application. SESSA can simulate AES and XPS spectra for a multilayered thin-film sample for measurement conditions specified by the user. Exptl. information needed by SESSA is entered via an interface that matches the settings of AES/XPS instrumentation. The structure of SESSA is described together with information on special features, unique capabilities, and sources of the phys. data. Examples of practical applications of SESSA for angle-resolved XPS on Al and Si samples, detn. of the depth distribution function in XPS, and the use of empirical peak shapes for spectrum simulation are given. These and other applications are contained in SESSA as tutorial files with command-language statements that can be loaded into SESSA and modified as necessary for similar simulations.
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      Outka, D. A.; Stohr, J.; Madix, R. J.; Rotermund, H. H.; Hermsmeier, B.; Solomon, J. NEXAFS STUDIES OF COMPLEX ALCOHOLS AND CARBOXYLIC-ACIDS ON THE SI(111)(7 × 7) SURFACE. Surf. Sci. 1987, 185 (1–2), 53– 74,  DOI: 10.1016/S0039-6028(87)80613-1
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      NEXAFS studies of complex alcohols and carboxylic acids on the silicon(111)(7 × 7) surface
      Outka, D. A.; Stohr, J.; Madix, R. J.; Rotermund, H. H.; Hermsmeier, B.; Solomon, J.
      Surface Science (1987), 185 (1-2), 53-74CODEN: SUSCAS; ISSN:0039-6028.
      The adsorption of HCO2H, CH3CH2CO2H, CH2:CHCO2H, HC≡CCO2H, and the corresponding alcs. on the Si(111)(7 × 7) surface was investigated by NEXAFS. The NEXAFS spectrum of a polyfunctional mol. is simply the superposition of NEXAFS features expected of the individual functional groups in the mol. An exception to this rule was obsd. for those mols. with conjugated π orbitals. Monolayer coverages of these mols. on Si, bond strongly to the Si surface via the carboxylic acid or alc. group. In contrast, the C-C double and triple bonds do not react initially with the Si surface. Upon heating, however, the C-C double and triple bonds attached to the surface by the O functional groups become reactive on Si.
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      Santoro, M.; Gorelli, F.; Haines, J.; Cambon, O.; Levelut, C.; Garbarino, G. Silicon carbonate phase formed from carbon dioxide and silica under pressure. Proc. Natl. Acad. Sci. U. S. A. 2011, 108 (19), 7689– 7692,  DOI: 10.1073/pnas.1019691108
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      Silicon carbonate phase formed from carbon dioxide and silica under pressure
      Santoro, Mario; Gorelli, Federico; Haines, Julien; Cambon, Olivier; Levelut, Claire; Garbarino, Gaston
      Proceedings of the National Academy of Sciences of the United States of America (2011), 108 (19), 7689-7692CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      The discovery of nonmol. carbon dioxide under high-pressure conditions shows that there are remarkable analogies between this important substance and other group IV oxides. A natural and long-standing question is whether compds. between CO2 and SiO2 are possible. Under ambient conditions, CO2 and SiO2 are thermodynamically stable and do not react with each other. We show that reactions occur at high pressures indicating that silica can behave in a manner similar to ionic metal oxides that form carbonates at room pressure. A silicon carbonate phase was synthesized by reacting silicalite, a microporous SiO2 zeolite, and mol. CO2 that fills the pores, in diamond anvil cells at 18-26 GPa and 600-980 K; the compd. was then temp. quenched. The material was characterized by Raman and IR spectroscopy, and synchrotron x-ray diffraction. The expts. reveal unique oxide chem. at high pressures and the potential for synthesis of a class of previously uncharacterized materials. There are also potential implications for CO2 segregation in planetary interiors and for CO2 storage.
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      From NLM

    59. 59
      Leinweber, P.; Kruse, J.; Walley, F. L.; Gillespie, A.; Eckhardt, K.-U.; Blyth, R. I. R.; Regier, T. Nitrogen K-edge XANES - an overview of reference compounds used to identify ̀unknown’ organic nitrogen in environmental samples. J. Synchrotron Radiat. 2007, 14 (6), 500– 511,  DOI: 10.1107/S0909049507042513
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      Nitrogen K-edge XANES - an overview of reference compounds used to identify 'unknown' organic nitrogen in environmental samples
      Leinweber, Peter; Kruse, Jens; Walley, Fran L.; Gillespie, Adam; Eckhardt, Kai Uwe; Blyth, Robert I. R.; Regier, Tom
      Journal of Synchrotron Radiation (2007), 14 (6), 500-511CODEN: JSYRES; ISSN:0909-0495. (International Union of Crystallography)
      A review. The chem. nature of soil org. nitrogen (N) is still poorly understood and one-third to one-half of it is typically classified as 'unknown N'. Nitrogen K-edge XANES spectroscopy has been used to develop a systematic overview on spectral features of all major N functions in soil and environmental samples. The abs. calibration of the photon energy was completed using the 1s → π* transitions of pure gas-phase N2. On this basis a library of spectral features is provided for mineral N, nitro N, amino acids, peptides, and substituted pyrroles, pyridines, imidazoles, pyrazoles, pyrazines, pyrimidines and purine bases. Although N XANES was previously considered 'non-destructive', effects of radiation damage were shown for two compd. classes and an approach was proposed to minimize it. This new evidence is integrated into a proposal for the evaluation spectra from environmental samples with unknown compn. Thus a basis is laid to develop N K-edge XANES as a complementary std. research method to study the mol. compn. and ecol. functions of 'unknown N' in soil and the environment.
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    60. 60
      Melendrez, C.; Lopez-Rosas, J. A.; Stokes, C. X.; Cheung, T. C.; Lee, S.-J.; Titus, C. J.; Valenzuela, J.; Jeanpierre, G.; Muhammad, H.; Tran, P. Metastable Brominated Nanodiamond Surface Enables Room Temperature and Catalysis-Free Amine Chemistry. J. Phys. Chem. Lett. 2022, 13, 1147– 1158,  DOI: 10.1021/acs.jpclett.1c04090
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      Metastable brominated nanodiamond surface enables room temperature and catalysis-free amine chemistry
      Melendrez, Cynthia; Lopez-Rosas, Jorge A.; Stokes, Camron X.; Cheung, Tsz Ching; Lee, Sang-Jun; Titus, Charles James; Valenzuela, Jocelyn; Jeanpierre, Grace; Muhammad, Halim; Tran, Polo; Sandoval, Perla Jasmine; Supreme, Tyanna; Altoe, Virginia; Vavra, Jan; Raabova, Helena; Vanek, Vaclav; Sainio, Sami; Doriese, William B.; O'Neil, Galen C.; Swetz, Daniel S.; Ullom, Joel N.; Irwin, Kent; Nordlund, Dennis; Cigler, Petr; Wolcott, Abraham
      Journal of Physical Chemistry Letters (2022), 13 (4), 1147-1158CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Bromination of high-pressure, high-temp. (HPHT) nanodiamond (ND) surfaces has not been explored and can open new avenues for increased chem. reactivity and diamond lattice covalent bond formation. The large bond dissocn. energy of the diamond lattice-oxygen bond is a challenge that prevents new bonds from forming, and most researchers simply use oxygen-terminated NDs (alcs. and acids) as reactive species. In this work, we transformed a tertiary-alc.-rich ND surface to an amine surface with ~ 50% surface coverage and was limited by the initial rate of bromination. We obsd. that alkyl bromide moieties are highly labile on HPHT NDs and are metastable as previously found using d. functional theory. The strong leaving group properties of the alkyl bromide intermediate were found to form diamond-nitrogen bonds at room temp. and without catalysts. This robust pathway to activate a chem. inert ND surface broadens the modalities for surface termination, and the unique surface properties of brominated and aminated NDs are impactful to researchers for chem. tuning diamond for quantum sensing or biolabeling applications.
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    61. 61
      Darlatt, E.; Traulsen, C. H. H.; Poppenberg, J.; Richter, S.; Kuhn, J.; Schalley, C. A.; Unger, W. E. S. Evidence of click and coordination reactions on a self-assembled monolayer by synchrotron radiation based XPS and NEXAFS. J. Electron Spectrosc. Relat. Phenom. 2012, 185 (3–4), 85– 89,  DOI: 10.1016/j.elspec.2012.02.004
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      Evidence of click and coordination reactions on a self-assembled monolayer by synchrotron radiation based XPS and NEXAFS
      Darlatt, Erik; Traulsen, Christoph H.-H.; Poppenberg, Johannes; Richter, Sebastian; Kuehn, Julius; Schalley, Christoph A.; Unger, Wolfgang E. S.
      Journal of Electron Spectroscopy and Related Phenomena (2012), 185 (3-4), 85-89CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)
      An ethynylterpyridine was "clicked" to an azide-terminated self-assembled monolayer on gold and characterized by synchrotron radiation based surface anal. as NEXAFS and XPS. The detection of azide and terpyridine signatures confirmed a partial click reaction at room temp. The absence of the azides after reaction at 50 °C indicates an almost complete conversion. For the latter case successful Pd(II) coordination has been proven. The Au-S interface of the SAMs has been characterized by S 1s and S 2p XPS.
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    62. 62
      Darlatt, E.; Nefedov, A.; Traulsen, C. H. H.; Poppenberg, J.; Richter, S.; Dietrich, P. M.; Lippitz, A.; Illgen, R.; Kuhn, J.; Schalley, C. A. Interpretation of experimental N K NEXAFS of azide, 1,2,3-triazole and terpyridyl groups by DFT spectrum simulations. J. Electron Spectrosc. Relat. Phenom. 2012, 185 (12), 621– 624,  DOI: 10.1016/j.elspec.2012.09.008
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      Interpretation of experimental N K NEXAFS of azide, 1,2,3-triazole and terpyridyl groups by DFT spectrum simulations
      Darlatt, Erik; Nefedov, Alexei; Traulsen, Christoph H.-H.; Poppenberg, Johannes; Richter, Sebastian; Dietrich, Paul M.; Lippitz, Andreas; Illgen, Rene; Kuehn, Julius; Schalley, Christoph A.; Woell, Christof; Unger, Wolfgang E. S.
      Journal of Electron Spectroscopy and Related Phenomena (2012), 185 (12), 621-624CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)
      Exptl. N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in exptl. N K-edge NEXAFS spectra to nitrogen atoms within these functional groups were made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated mols., DFT spectrum simulations are useful to find measurement conditions delivering exptl. N K-edge NEXAFS data with negligible x-ray damage. The 1,2,3-triazole group is rather stable under x-ray irradn.
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    63. 63
      Pauling, L.; Brockway, L. O. The Adjacent Charge Rule and the Structure of Methyl Azide, Methyl Nitrate, and Fluorine Nitrate. J. Am. Chem. Soc. 1937, 59 (1), 13– 20,  DOI: 10.1021/ja01280a005
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      Adjacent-charge rule and the structure of methyl azide, methyl nitrate and fluorine nitrate
      Pauling, Linus; Brockway, L. O.
      Journal of the American Chemical Society (1937), 59 (), 13-20CODEN: JACSAT; ISSN:0002-7863.
      Application of the adjacent-charge rule (mol. structures in which adjacent atoms have elec. charges of the same sign are much less important than other structures) leads to a prediction of instability for one of the 3 reasonable configurations of each of the mols., Me azide, Me nitrate and F nitrate. Electron-diffraction data for these mols., in support of the rule, indicate reasonance between the 2 other configurations. The application of the rule to the structures of N2O5, N2O4, Cl2O6 and O acids of Si, P, S and Cl is discussed.
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    64. 64
      Castner, D. G.; Lewis, K. B.; Fischer, D. A.; Ratner, B. D.; Gland, J. L. DETERMINATION OF SURFACE-STRUCTURE AND ORIENTATION OF POLYMERIZED TETRAFLUOROETHYLENE FILMS BY NEAR-EDGE X-RAY ABSORPTION FINE-STRUCTURE, X-RAY PHOTOELECTRON-SPECTROSCOPY, AND STATIC SECONDARY ION MASS-SPECTROMETRY. Langmuir 1993, 9 (2), 537– 542,  DOI: 10.1021/la00026a029
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      64
      Determination of surface structure and orientation of polymerized tetrafluoroethylene films by near-edge x-ray absorption fine structure, x-ray photoelectron spectroscopy, and static secondary ion mass spectrometry
      Castner, David G.; Lewis, Kenneth B., Jr.; Fischer, Daniel A.; Ratner, Buddy D.; Gland, John L.
      Langmuir (1993), 9 (2), 537-42CODEN: LANGD5; ISSN:0743-7463.
      Films of conventional and radio-frequency glow-discharge (RFGD) polymd. tetrafluoroethylene (I) were examd. by ultrasoft x-ray absorption spectroscopy (XAS), XPS, and SIMS. The polarization-dependent intensity changes of transitions to C-C and C-F σ* orbitals in the carbon and fluorine near-edge x-ray absorption fine structure (NEXAFS) spectra revealed different CF2-chain orientations. The surface region of skived poly-I was composed to CF2 chains oriented parallel to the surface stations present in the poly-I. XPS confirmed only CF2 groups were present in the poly-I surface region. Fluorocarbon (FC) films prepd. by RFGD deposition of I onto substrates placed indirectly in the visible glow (I-indirect) were randomly oriented. XPS showed the I-indirect films had CD, CF2, and CF3 groups in the surface region. Static SIMS indicated that the I-indirect film surface contained CF3 and C2F5 groups. XPS showed the FC films prepd. by RFGD deposition of I onto substrates placed downstream from the visible glow contained ∼90% CF2 groups. The strong polarization dependence of the C and F NEXAFS spectra of these films indicated the CF2 groups were aligned in vertical chains on the substrate. Static SIMS and XPS results suggested the outermost surface of the CF2 chains were terminated with CF3 groups. For thin (50-500 Å) FC RFGD films deposted onto polymeric substrates such as PMMA or PET, fluorescence yield detection XAS could be used to examine the substrate, while XPS, static SIMS, and electron yield detection XAS could be used to examine the FC overlayer. These results demonstrated the complementary nature of ultrasoft XAS, XPS, and static SIMS for detailed surface structural characterization of polymers.
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      Brassard, J.-D.; Sarkar, D. K.; Perron, J. Synthesis of Monodisperse Fluorinated Silica Nanoparticles and Their Superhydrophobic Thin Films. ACS Appl. Mater. Interfaces 2011, 3 (9), 3583– 3588,  DOI: 10.1021/am2007917
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      Synthesis of Monodisperse Fluorinated Silica Nanoparticles and Their Superhydrophobic Thin Films
      Brassard, Jean-Denis; Sarkar, D. K.; Perron, Jean
      ACS Applied Materials & Interfaces (2011), 3 (9), 3583-3588CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Monodispersive SiO2 nanoparticles were synthesized via the Stober process and further functionalized by adding fluorinated groups using fluoroalkylsilane in an ethanolic soln. In this process, 6 different sizes of fluorinated SiO2 nanoparticles of varying diam. from 40 to 300 nm are prepd. and used to deposit thin films on Al alloy surfaces using spin coating processes. The functionalization of SiO2 nanoparticles by fluorinated group was confirmed by the presence C-F bonds along with Si-O-Si bonds in the thin films as analyzed by FTIR spectroscopy. The surface roughness as well as the H2O contact angles of the fluorinated SiO2 nanoparticle contg. thin films are increased with the increase of the diam. of the synthesized fluorinated SiO2 nanoparticles. The thin films prepd. using the fluorinated SiO2 nanoparticles having a crit. size of 119 ± 12 nm provide a surface roughness of ∼0.697 μm rendering the surfaces superhydrophobic with a H2O contact angle of 151 ± 4°. The roughness as well as the H2O contact angle increases on the superhydrophobic thin films with further increase in the size of the fluorinated SiO2 nanoparticles in the films.
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    66. 66
      Kobayashi, K.; Wei, J.; Iida, R.; Ijiro, K.; Niikura, K. Surface engineering of nanoparticles for therapeutic applications. Polym. J. 2014, 46 (8), 460– 468,  DOI: 10.1038/pj.2014.40
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      Surface engineering of nanoparticles for therapeutic applications
      Kobayashi, Kenya; Wei, Jinjian; Iida, Ryo; Ijiro, Kuniharu; Niikura, Kenichi
      Polymer Journal (Tokyo, Japan) (2014), 46 (8), 460-468CODEN: POLJB8; ISSN:0032-3896. (NPG Nature Asia-Pacific)
      A review. Nanoparticles with a diam. of <100 nm are regarded as potential medical materials, as this size allows nanoparticles to circulate in vivo and possibly reach targeted tumors. Inorg. nanoparticles in particular are able to interact with light and/or magnetic fields, thus extending their potential applications to such fields as fluorescence labeling, magnetic resonance imaging and stimulus-responsive drug delivery that are essential to the diagnosis and treatment of disease. To facilitate their use in such applications, the appropriate design of surface ligands on these nanoparticles is necessary. The surface ligands det. the physicochem. properties of the surface, such as hydrophilicity/hydrophobicity and zeta potential as well as dispersibility in soln. These properties have an esp. important role in detg. nanoparticle-cell assocns., such as cellular membrane permeability, immune responses and localization in vivo. This review focuses on recent advances in the surface engineering of nanoparticles for therapeutic applications.
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      Chang, J.-B.; Chen, F.; Yoon, Y.-G.; Jung, E. E.; Babcock, H.; Kang, J. S.; Asano, S.; Suk, H.-J.; Pak, N.; Tillberg, P. W. Iterative expansion microscopy. Nat. Methods 2017, 14 (6), 593– 599,  DOI: 10.1038/nmeth.4261
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      Iterative expansion microscopy
      Chang, Jae-Byum; Chen, Fei; Yoon, Young-Gyu; Jung, Erica E.; Babcock, Hazen; Kang, Jeong Seuk; Asano, Shoh; Suk, Ho-Jun; Pak, Nikita; Tillberg, Paul W.; Wassie, Asmamaw T.; Cai, Dawen; Boyden, Edward S.
      Nature Methods (2017), 14 (6), 593-599CODEN: NMAEA3; ISSN:1548-7091. (Nature Publishing Group)
      We recently developed a method called expansion microscopy, in which preserved biol. specimens are phys. magnified by embedding them in a densely crosslinked polyelectrolyte gel, anchoring key labels or biomols. to the gel, mech. homogenizing the specimen, and then swelling the gel-specimen composite by ∼ 4.5×× Iterative expansion microscopyJae-Byum Chang1,2, Fei Chen3, Young-Gyu Yoon1,4, Erica E Jung1, Hazen Babcock5, Jeong Seuk Kang6, Shoh Asano1, Ho-Jun Suk7, Nikita Pak8, Paul W Tillberg4, Asmamaw T Wassie3, Dawen Cai9 & Edward S Boyden1,3,10,11We recently developed a method called expansion microscopy, in which preserved biol. specimens are phys. magnified by embedding them in a densely crosslinked polyelectrolyte gel, anchoring key labels or biomols. to the gel, mech. homogenizing the specimen, and then swelling the gel-specimen composite by ∼4.5× in linear dimension. Here we describe iterative expansion microscopy (iExM), in which a sample is expanded ∼20×. After preliminary expansion a second swellable polymer mesh is formed in the space newly opened up by the first expansion, and the sample is expanded again. iExM expands biol. specimens∼ 4.5 × 4.5, or ∼ 20×, and enables ∼ 25-nm-resoln. imaging of cells and tissues on conventional microscopes. We used iExM to visualize synaptic proteins, as well as the detailed architecture of dendritic spines, in mouse brain circuitry.
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      Socrates, G. Infrared and Raman characteristic group frequencies:tables and charts; John Wiley and Sons, 2001.
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      Krueger, A.; Lang, D. Functionality is Key: Recent Progress in the Surface Modification of Nanodiamond. Adv. Funct. Mater. 2012, 22 (5), 890– 906,  DOI: 10.1002/adfm.201102670
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      Functionality is Key: Recent Progress in the Surface Modification of Nanodiamond
      Krueger, Anke; Lang, Daniel
      Advanced Functional Materials (2012), 22 (5), 890-906CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Nanoscale diamond has recently received considerable attention due to the various possible applications such as luminescence imaging, drug delivery, quantum engineering, surface coatings, seeding etc. For most of these fields a suitable surface termination and functionalization of the diamond materials are required. In this feature article we discuss recent achievements in the field of surface modification of nanoscale diamond including the establishment of a homogeneous initial surface termination, the covalent and noncovalent immobilization of different functional moieties as well as the subsequent grafting of larger (bio)mols. onto previously functionalized nanodiamond.
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      Krueger, A.; Stegk, J.; Liang, Y.; Lu, L.; Jarre, G. Biotinylated nanodiamond: Simple and efficient functionalization of detonation diamond. Langmuir 2008, 24 (8), 4200– 4204,  DOI: 10.1021/la703482v
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      Biotinylated Nanodiamond: Simple and Efficient Functionalization of Detonation Diamond
      Krueger, Anke; Stegk, Jochen; Liang, Yuejiang; Lu, Li; Jarre, Gerald
      Langmuir (2008), 24 (8), 4200-4204CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      We have developed a simple and efficient method for the covalent functionalization of detonation nanodiamond. After homogenization of the surface by borane redn., the surface was modified with (3-aminopropyl)trimethoxysilane. Subsequent grafting of biotin yielded covalently biotinylated nanodiamond, which was characterized by FTIR spectroscopy, x-ray powder diffractometry, thermogravimetry, and elemental anal. The activity was tested with horseradish peroxidase-labeled streptavidin. The surface loading of biotin was found to be 1.45 mmol g-1. The new material opens the way to covalently bonded diamond bioconjugates for labeling, drug delivery, and other applications.
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      Girard, H. A.; Petit, T.; Perruchas, S.; Gacoin, T.; Gesset, C.; Arnault, J. C.; Bergonzo, P. Surface properties of hydrogenated nanodiamonds: a chemical investigation. Phys. Chem. Chem. Phys. 2011, 13 (24), 11517– 11523,  DOI: 10.1039/c1cp20424f
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      Surface properties of hydrogenated nanodiamonds: a chemical investigation
      Girard, H. A.; Petit, T.; Perruchas, S.; Gacoin, T.; Gesset, C.; Arnault, J. C.; Bergonzo, P.
      Physical Chemistry Chemical Physics (2011), 13 (24), 11517-11523CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Hydrogen terminations (C-H) confer to diamond layers sp. surface properties such as a neg. electron affinity and a superficial conductive layer, opening the way to specific functionalization routes. For example, efficient covalent bonding of diazonium salts or of alkene moieties can be performed on hydrogenated diamond thin films, owing to electronic exchanges at the interface. Here, we report on the chem. reactivity of fully hydrogenated High Pressure High Temp. (HPHT) nanodiamonds (H-NDs) towards such grafting, with respect to the reactivity of as-received NDs. Chem. characterizations such as FTIR, XPS anal. and Zeta potential measurements reveal a clear selectivity of such couplings on H-NDs, suggesting that C-H related surface properties remain dominant even on particles at the nanoscale. These results on hydrogenated NDs open up the route to a broad range of new functionalizations for innovative NDs applications development.
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      Lee, S. J.; Titus, C. J.; Mori, R. A.; Baker, M. L.; Bennett, D. A.; Cho, H. M.; Doriese, W. B.; Fowler, J. W.; Gaffney, K. J.; Gallo, A. Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10–1. Rev. Sci. Instrum. 2019, 90 (11), 113101,  DOI: 10.1063/1.5119155
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      Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1
      Lee, Sang-Jun; Titus, Charles J.; Alonso Mori, Roberto; Baker, Michael L.; Bennett, Douglas A.; Cho, Hsiao-Mei; Doriese, William B.; Fowler, Joseph W.; Gaffney, Kelly J.; Gallo, Alessandro; Gard, Johnathon D.; Hilton, Gene C.; Jang, Hoyoung; Joe, Young Il; Kenney, Christopher J.; Knight, Jason; Kroll, Thomas; Lee, Jun-Sik; Li, Dale; Lu, Donghui; Marks, Ronald; Minitti, Michael P.; Morgan, Kelsey M.; Ogasawara, Hirohito; O'Neil, Galen C.; Reintsema, Carl D.; Schmidt, Daniel R.; Sokaras, Dimosthenis; Ullom, Joel N.; Weng, Tsu-Chien; Williams, Christopher; Young, Betty A.; Swetz, Daniel S.; Irwin, Kent D.; Nordlund, Dennis
      Review of Scientific Instruments (2019), 90 (11), 113101/1-113101/11CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)
      We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resoln., high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a max. detection solid angle of 2 × 10-3 sr. The energy resoln. of all pixels combined is 1.5 eV full width at half max. at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resoln. and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering expts. obtained with the spectrometer are presented. (c) 2019 American Institute of Physics.
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      Lee, S. J.; Mori, R.; Alpert, B.; Baker, M.; Berry, J.; Cho, H.-M.; Denison, E.; Doriese, W.; Fowler, J.; Gaffney, K. Ultrasensitive probing of the local electronic structure of nitrogen doped carbon and its applications to 2D electronics, catalysis and bio-physics. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY; AMER CHEMICAL SOC: 1155 16TH ST, NW, WASHINGTON, DC 20036 USA; Vol. 253, 2017.
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      CasaXPS. CasaXPS User’s Manual , 2001.
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      Saslow, W.; Bergstresser, T. K.; Cohen, M. L. Band Structure and Optical Properties of Diamond. Phys. Rev. Lett. 1966, 16 (9), 354– 356,  DOI: 10.1103/PhysRevLett.16.354
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      Band structure and optical properties of diamond
      Saslow, W.; Bergstresser, T. K.; Cohen, Marvin L.
      Physical Review Letters (1966), 16 (9), 354-6CODEN: PRLTAO; ISSN:0031-9007.
      The electronic band structure of diamond was calcd. by means of the empirical pseudopotential method. The analysis of the resulting band structure yields a new interpretation of the structure in the optical reflectivity. Within the scope of this interpretation, the calcd. band gaps agree with expt. to within ∼0.01 rydberg (Ry.) near the fundamental band gap and to within ∼0.05 Ry. over a range of 1.0 Ry.
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      Astašauskas, V.; Bellissimo, A.; Kuksa, P.; Tomastik, C.; Kalbe, H.; Werner, W. S. M. Optical and electronic properties of amorphous silicon dioxide by single and double electron spectroscopy. J. Electron Spectrosc. Relat. Phenom. 2020, 241, 146829,  DOI: 10.1016/j.elspec.2019.02.008
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      Optical and electronic properties of amorphous silicon dioxide by single and double electron spectroscopy
      Astasauskas, Vytautas; Bellissimo, Alessandra; Kuksa, Pavel; Tomastik, Christian; Kalbe, Henryk; Werner, Wolfgang S. M.
      Journal of Electron Spectroscopy and Related Phenomena (2020), 241 (), 146829CODEN: JESRAW; ISSN:0368-2048. (Elsevier B.V.)
      An investigation of the optical and electronic properties of amorphous silicon dioxide by means of a combination of reflection electron energy loss spectroscopy (REELS) and secondary electron-electron energy loss coincidence spectroscopy (SE2ELCS) is presented. Optical consts. for a-SiO2 were extd. from the REELS measurements and a band gap of 9.1 eV was detd. by deconvolution of multiple scattering and fitting the differential inverse inelastic mean free path with a model energy loss function (ELF). The coincidence measurements allow to det. the surface barrier height and the electron affinity was detd. to be 0.8 eV. Furthermore, the coincidence measurements show that even in the case of an insulator, plasmon decay is the main mechanism for generation of secondary electrons.
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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnanoscienceau.3c00033.

    • Thermogravimetric analysis-mass spectroscopy (TGA-MS) confirming the silica-ND bonding environment, fluorescent scanning confocal images of NV center stained neurons, TEM of silica-coated NDs, X-ray photoelectron spectroscopy data, and resonant inelastic X-ray spectroscopy for C 1s, N 1s, and O 1s edges (PDF)


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