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Gap Opening in Double-Sided Highly Hydrogenated Free-Standing Graphene
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  • Maria Grazia Betti*
    Maria Grazia Betti
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
    *Email: [email protected]. Phone: +39 06 49914389.
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    Orcidhttps://orcid.org/0000-0002-6244-0306
  • Ernesto Placidi
    Ernesto Placidi
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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  • Chiara Izzo
    Chiara Izzo
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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  • Elena Blundo
    Elena Blundo
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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    Orcidhttps://orcid.org/0000-0003-0423-4798
  • Antonio Polimeni
    Antonio Polimeni
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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    Orcidhttps://orcid.org/0000-0002-2017-4265
  • Marco Sbroscia
    Marco Sbroscia
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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  • José Avila
    José Avila
    Synchrotron SOLEIL, Université Paris-Saclay, Saint Aubin, BP 48, 91192 Gif sur Yvette, France
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  • Pavel Dudin
    Pavel Dudin
    Synchrotron SOLEIL, Université Paris-Saclay, Saint Aubin, BP 48, 91192 Gif sur Yvette, France
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  • Kailong Hu
    Kailong Hu
    School of Materials Science and Engineering and Institute of Materials Genome & Big Data, Harbin Institute of Technology, Shenzhen 518055, P.R. China
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    Orcidhttps://orcid.org/0000-0003-0489-5836
  • Yoshikazu Ito
    Yoshikazu Ito
    Institute of Applied Physics, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan
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    Orcidhttps://orcid.org/0000-0001-8059-8396
  • Deborah Prezzi*
    Deborah Prezzi
    S3, Istituto Nanoscienze-CNR, Via Campi 213/A, 41125 Modena, Italy
    *Email: [email protected]. Phone: +39 059 2055314.
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    Orcidhttps://orcid.org/0000-0002-7294-7450
  • Miki Bonacci
    Miki Bonacci
    Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università degli Studi di Modena e Reggio Emilia, 41125 Modena, Italy
    S3, Istituto Nanoscienze-CNR, Via Campi 213/A, 41125 Modena, Italy
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  • Elisa Molinari
    Elisa Molinari
    Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università degli Studi di Modena e Reggio Emilia, 41125 Modena, Italy
    S3, Istituto Nanoscienze-CNR, Via Campi 213/A, 41125 Modena, Italy
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  • Carlo Mariani
    Carlo Mariani
    Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
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    Orcidhttps://orcid.org/0000-0002-7979-1700
Open PDFSupporting Information (1)

Nano Letters

Cite this: Nano Lett. 2022, 22, 7, 2971–2977
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https://doi.org/10.1021/acs.nanolett.2c00162
Published March 16, 2022

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Conversion of free-standing graphene into pure graphane─where each C atom is sp3 bound to a hydrogen atom─has not been achieved so far, in spite of numerous experimental attempts. Here, we obtain an unprecedented level of hydrogenation (≈90% of sp3 bonds) by exposing fully free-standing nanoporous samples─constituted by a single to a few veils of smoothly rippled graphene─to atomic hydrogen in ultrahigh vacuum. Such a controlled hydrogenation of high-quality and high-specific-area samples converts the original conductive graphene into a wide gap semiconductor, with the valence band maximum (VBM) ∼ 3.5 eV below the Fermi level, as monitored by photoemission spectromicroscopy and confirmed by theoretical predictions. In fact, the calculated band structure unequivocally identifies the achievement of a stable, double-sided fully hydrogenated configuration, with gap opening and no trace of π states, in excellent agreement with the experimental results.

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Introduction

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Maximum storage of hydrogen in carbon-based materials is ideally achieved in graphene by forming the so-called graphane, where each carbon atom in the honeycomb lattice is bound to hydrogen with alternately up and down sp3 distorted bonds. In graphane, the conjugation of graphene π electrons is thus disrupted, leading to an insulating behavior with band gap predicted to depend on the H chemisorption configuration. (1,2)
Experimentally, however, only a low H storage capacity has been reached so far (∼36 at. %) on single-layer graphene (3−14) with non-negligible contamination and defects. The maximum H uptake depends on both the morphology of graphene specimens (substrate-supported, transferred flakes, etc.) and the hydrogenation methods. Several attempts to incorporate a high percentage of hydrogen have been carried out in the last decades, exploiting a variety of strategies on different samples. Hot (6,7,10) and cold (4,14) plasma deposition and molecular H2 high-temperature cracking (5,9) were applied to exfoliated graphene layers, (3,10) to chemical-vapor-deposition (CVD) grown flakes, (6,15,16) or even to metal–supported samples, (5,8,9,11,17) reaching at most a partial hydrogenation of monolayer graphene, with an upper limit of H uptake Θ ∼ 36 at. %, (14) while an almost stoichiometric bulk graphane has been obtained from halogenated reduced wrinkled and layered graphenes. (18) The limit of hydrogenation in single-layer graphene can be due to several concurrent drawbacks, such as oxygen contamination, the influence of the substrate, and the presence of defects/edges in graphene flakes (either pre-existing or induced by the hydrogenation itself).
A crucial challenge to fully exploit graphene for hydrogen storage is to employ defect-free graphene specimens with very high specific surface area, where hydrogen can adsorb strongly enough on the surface as to form a thermodynamically stable arrangement, achieving an ideal graphane pattern. Nanoporous graphene (NPG)─constituted by a compact, bicontinuous interconnected 3D arrangement of high-quality graphene veils, composed of one to a few weakly interacting layers (19,20)─can present great advantages to achieve a high uptake of hydrogen in graphene. The free-standing, curved structure at the submicrometer scale, with intrinsically smooth rippling, can foster hydrogen chemisorption, favored by the increased electron affinity of hydrogen and the energy barrier decrease in the convex regions (21) induced by the pull out of the C atom toward the H proton. (22,23)
We here exploit high-quality NPG samples, with high specific area (1000 m2/g) (24−26) and very low density of defects, together with in situ, highly controlled hydrogenation by H2 cracking in the ultrahigh vacuum (UHV) condition. In this way, we can control the absence of contamination of the sample during the H exposure and realize a thermodynamically stable prototype of semiconducting graphane. A spectromicroscopy photoemission study, combined with state-of-the-art theoretical predictions, demonstrates an unprecedentedly high H uptake in NPG, accompanied by a spectral electronic density of states as predicted for ideal graphane, achieving for the first time an almost complete saturation in fully free-standing graphene of the available C sites with hydrogen.

Results and Discussion

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Figure 1a displays an optical picture of a free-standing NPG sample (∼0.5 cm in diameter) with large surface area density (1000 m2/g) (24−26) arranged in a compact 3D structure; see Experimental and Computational Methods for details on the sample preparation. Scanning electron microscopy (SEM) imaging (Figure 1b) zoomed at a mesoscopic level (10 × 10 μm2) unveils the porous structure (pore size in the submicrometer to few micrometer range) constituted by a folded tubular graphene sheet with continuous almost flat areas and interconnected channels, with some wrinkles and without frayed edges. (24−26) A detailed analysis of the NPG microscopic structure at the atomic scale, reported elsewhere, (19) revealed moiré superstructures due to suspended graphene layers with misoriented (turbostratic) stacking in some regions. Within this macroscopic 3D graphene architecture, the microscopic structure preserves all the 2D graphene hallmarks. (19)

Figure 1

Figure 1. (a) Optical picture of an NPG sample. (b) SEM image of NPG (10 × 10 μm2). (c) Micro-Raman spectrum taken with a 100× objective (Gaussian laser spot size with σ = 280 nm). (d) Spatially resolved micro-Raman map of the 2D/G band intensity ratio, 4 × 4 μm2 image formed by 167 × 167 nm2 pixels. (e) Spatially integrated C 1s XPS spectrum, taken with 350 eV photon energy. (f) Spatially resolved micro-X-ray photoelectron spectroscopy (micro-XPS) map of the C 1s core level intensity (282–288 eV energy range), 20 × 20 μm2 image formed by 500 × 500 nm2 pixels.

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A representative micro-Raman spectrum (see Experimental and Computational Methods) of the NPG sample is shown in Figure 1c. The measurements were performed with moderate power densities (∼20 kW/cm2), analogous to those employed for other suspended 2D systems such as hexagonal boron nitride bubbles, (27) and after verifying that no detrimental effects were induced by the laser beam on the NPG sample. The Raman spectrum presents a low intensity of the defect-activated “D” Raman peak if compared to the “G” peak, associated with the doubly degenerate (iTO and LO) phonon modes at the Brillouin zone center. More importantly, the Raman spectrum shows a high intensity of the “2D” peak, a double-resonant second order mode activated by in plane breathing of the hexagonal rings. (28) The 2D/G Raman band intensity ratio was mapped over a mesoscopic area (Figure 1d) and takes values typically larger than one. The observed pattern reflects the variety of morphological configurations in the NPG sample, as discussed in ref (19). Both the low ID/IG value and the fact that I2D/IG > 1 are fingerprints of high quality graphene specimens. A typical C 1s spectrum (see Experimental and Computational Methods) acquired on the sample is shown in Figure 1e, showing the expected narrow peak at 284.3 eV binding energy (BE) with skewed line shape associated with the semimetallic graphene signal with a planar sp2 hybridization, without any defect-derived or contaminant-associated component. (19,20) The micro-XPS mapping of the whole C 1s signal at the mesoscopic scale (Figure 1f) reveals the same tubular and continuous morphology observed in the SEM image (Figure 1b). This suspended 3D graphene continuous architecture can thus provide a novel route to obtain a 3D “graphane” structure, preventing interface/edge effects or defect induced adsorption.
Hydrogen uptake can be identified by the distortion of the pristine C–C sp2 bonds with formation of direct C–H sp3 bonds, as can be deduced by the line shape evolution of the C 1s core levels. Figure 2 displays the C 1s XPS core level spectra recorded for increasing hydrogen exposure up to saturation, along with the results of a fitting analysis carried out by using Voigt line shape curves (i.e., convolutions of a Lorentzian and a Gaussian distribution). The Lorentzian and Gaussian components are associated with the intrinsic core–hole lifetime and overall experimental resolution, respectively. After the first hydrogen exposure (30 min), a broad component at about 0.6 eV higher BE appears and increases in intensity as a function of the H dose. This component is related to the distortion of the sp2 bonding toward a sp3 hybridization of the C atoms. It is worth noting the absence of C 1s components due to unsaturated C bonds at lower binding energy, (8,29−33) ensuring that a nondestructive and nondamaging hydrogenation process took place. Similarly, no oxidation component was found at higher BE, (34−36) indicating that the high quality assessed for the clean NPG specimen was preserved. Longer H exposures until 300 min make the sp3 component dominant up to a saturated configuration, and beyond that exposure the line shape does not change. Our estimate for the sp3 bond distortion in the saturated configuration is Θ ∼ 90%, where Θ = I(sp3)/[I(sp2) + I(sp3)].

Figure 2

Figure 2. C 1s core level XPS spectra of UHV-clean NPG (top), and after atomic H exposure as a function of the exposure time, up to H saturation (300 min); experimental data (solid lines), sp2 (pinkish peaks) and sp3 (bluish peaks) fitting components.

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This extraordinary and unprecedented hydrogen uptake, which is in line with a chemisorption model for graphane with almost each C sp3 being bound, has never been achieved experimentally before in fully free-standing low-defect graphene. In fact, only partially hydrogenated graphene was observed until now─either on transferred monolayer flakes (16,37) or on substrate-supported graphene (5,8)─with maximum uptake Θ ∼ 36% (14) and with a high level of contamination and defects. The present successful procedure can be ascribed both to the morphology of the self-suspended, free-standing and bicontinuous NPG host and to the ultraclean and highly controlled, fully-UHV hydrogenation procedure.
A crucial point is to correlate the appearance of the distorted sp3 hybridization, due to the C–H bonding, to the opening of a semiconducting gap in graphane. Photoemission spectromicroscopy of both core levels and the valence band can combine local information on the hybridization state (core levels), with the evolution of the spectral density close to the Fermi level (valence band) at the same spatial scale. We measured a spatially resolved photoemission mapping of a partially hydrogenated NPG sample (Θ ≈ 50%), as to be able to identify regions with different degrees of hydrogenation, correlating valence band with core level spectral shapes. Figure 3a displays the spatially resolved intensity of the sp2 core-level component normalized to the whole sp2 + sp3 signal, as deduced by the fitting analysis (see Supporting Information) over the whole hydrogenated NPG specimen. This intensity varies in the map depending on the local hydrogenation state, as shown in the exemplifying spectra of Figure 3b,c. Areas where the sp2 hybridization is still dominant [cross in panel (a)] correspond to the C 1s spectrum displayed in panel (b), while zones with higher values of sp3 component [star in panel (a)] correspond to the C 1s spectrum in panel (c). The 10 × 10 μm2 blow up in Figure 3a shows that the normalized intensity ranges locally between 40 and 60%, thus suggesting a homogeneous hydrogenation at the local micrometer scale. A clear correlation with the core level spatial distribution can be observed by picking up the corresponding pixels in the valence band mapping, shown in Figure 3d: in the regions where the sp2 bond dominates, the spectral density of states presents a definite 2p-π peak at a binding energy of about 3 eV [see shaded area in panel (e)], which is the signature of the graphene band structure, while in the regions where the sp3 component emerges, the spectral density drastically changes and the 2p-π peak is almost quenched. It is worth noting that the density of states close to the Fermi level EF is strongly reduced for all the pixels where the sp3 component dominates.

Figure 3

Figure 3. (a) C 1s intensity map, quantified as the ratio Isp2/(Isp2 + Isp3), after background subtraction; the blow-up represents the same ratio in a 10 × 10 μm2 area; the spectra taken in the sp2-rich and in sp3-rich regions (labeled by a cross and a star, respectively) are shown in panels (b) and (c), respectively. (d) Valence band (VB) intensity map corresponding to the 2p-π intensity. The ratio was calculated as in panel (a); the intensity was found by integrating in the energy range indicated by the shadowed vertical ribbon in panel (e), which displays the VB spectrum for sp2-rich (cross) and sp3-rich (star) regions.

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At H saturation coverage (Θ ∼ 90%) the quenching of the density of states below EF suggests a definite transition to a semiconducting state, as clearly observed in Figure 4a. In this novel configuration of the graphane band structure, the valence band maximum (VBM) can be extrapolated to be located at about 3.50 ± 0.25 eV below EF. The ascertainment of a definite correlation between the emergence of C–H sp3 bonding and the position of the VBM unambiguously ascribes the gap opening to the distortion of the bond to sp3, although the assignment of the hydrogen adsorption sites cannot be unambiguously identified from the photoemission experiment.

Figure 4

Figure 4. (a) Experimental VB spectra for clean (dashed) and totally hydrogenated NPG (solid line), taken with HeIα (21.218 eV) photon energy. (b) Three model structures of 1-side and 2-side hydrogenated single- and bilayer graphene (top and side views). The colored circles in the top view highlight the H sites in the hexagon. (c) Simulated quasi-particle density of states (DoS) in the GW approximation for the models in (b); zero energy set at midgap; a homogeneous broadening of 140 meV is applied. (d) Simulated DFT (solid gray lines) and GW (open circles) band structures for the corresponding models in (b); zero energy set at the VBM.

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To corroborate and better understand the correlation between degree of H chemisorption and emergence of a wide-gap semiconducting phase, we simulated by means of density functional theory (DFT) calculations the spectral density for different hydrogenated graphene phases, including single-sided and double-sided hydrogenated single- and bilayer graphene, with different registry and hydrogenation configurations (details and configurations are reported in the Supporting Information). We hereafter report the results for three representative (the most stable ones) structures, that is (Figure 4b), single-sided hydrogenated graphene (1-side H-Gr or graphone (38)); 2-side H-Gr, i.e., graphane; (1,2) and 2-side hydrogenated bilayer graphene (H-bGr). Quasi-particle corrections within the G0W0 approximation (39) are included to overcome the DFT limitation in the description of the electronic properties and ease the comparison with experiments (see Experimental and Computational Methods). Figure 4 shows the quasi-particle density of states (DoS) (c) and band structures (d), after DFT geometric optimization. We find in all cases that the computed quasi-particle band gap for the free-standing hydrogenated sheets exceeds 3 eV (see Table S1 in Supporting Information). The single-sided hydrogenation leads to the appearance of an indirect gap of 5.6 eV. For the double-sided hydrogenation, we predict a direct gap of 4.7 eV for the H-bGr and 6.1 eV for H-Gr, the largest of the series, in line with previous calculations. (2) For a more direct comparison with experiments, in Figure 4c we plot the DoS of the three systems, with the Fermi level set to midgap, a reasonable assumption given the high experimental quality (negligible contaminations/defects) of this hydrogenated sample. (40) Irrespective of the exact position of the VBM onset, the single-sided H-Gr system noticeably presents a structured DoS at the VBM, originating from the 2p-π orbitals of the unsaturated side, that is totally absent in the experimentally achieved saturated phase of Figure 4a (solid thick line). On the contrary, the double-sided single- and bilayer hydrogenated graphene is characterized by a step-like DoS at the VBM, typical of 2D semiconductors, (41) without any 2p-π contribution, in excellent agreement with the experimental data. Most of the spectral weight is indeed arising from the sp3 hybrid orbitals, lying in the energy region below −6 eV. This compares well in terms of energies and overall shape with the experimental spectrum (Figure 4a, solid thick line), taking into account the coexistence of single-layer and bilayer graphene (19,20) in our NPG samples (see also Figure S1b). The experimental curve is, however, mostly featureless, probably due to the specific spectral amplitudes in this energy range, (42) not accounted for in our calculations. Overall, we can conclude that the calculated band structure and quasi-particle DoS unequivocally allow us to establish the achievement of double-sided hydrogenated single- and bilayer graphene configurations.

Conclusions

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The smoothly rippled surface of nanoporous graphene, with very low density of defects, can foster a complete conversion in graphane, with almost all saturated C–H bonds, thanks to a carefully monitored in situ hydrogenation in ultrahigh vacuum conditions. Low-damage hydrogen deposition for long time exposures ensures an unprecedented atomic H uptake, with almost all available C sites saturated with H, as detected by the sp3 component in the C 1s core level, and a negligible presence of unsaturated bonds or defects.
Photoemission spectromicroscopy unveils a semiconducting band gap opening─correlated to the sp3 distorted C bonds─that the predicted spectral electronic density of states associates with the realization of double-sided, fully hydrogenated single- and bilayer structures, thus confirming this as a successful strategy to realize a thermodynamically stable prototype of graphane. Most interestingly, both single-layer and bilayer doubled-sided hydrogenated graphene unveil a direct band gap opening, which makes this prototype of semiconducting graphane a promising platform for optoelectronics applications.

Experimental and Computational Methods

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Sample Preparation

Nanoporous graphene was synthesized by using a nanoporous Ni template via chemical vapor deposition (CVD). Ni30Mn70 ingots have been prepared by melting both pure metals in an Ar-protected arc melting furnace, then annealing at 900 °C to allow them to become microstructured and composition homogeneous, and rolling into thin films. The nanoporous Ni template was obtained from the ingot sheet by using chemical dealloying, before CVD grew graphene by using benzene as the carbon source. The as-grown NPG acquires the three-dimensional morphology of the substrate and is subsequently exfoliated by chemical dissolution of the Ni template. A detailed description of the process is described elsewhere. (24,43−46) Hydrogenation has been done in situ in UHV by exposing NPG to atomic H produced by H2 cracking into a capillary source locally heated at 2100 °C.

Photoemission Spectromicroscopy

The spectromicroscopy photoemission experiments were performed at the ANTARES beamline of the SOLEIL synchrotron radiation facility. The nano-X-ray photoelectron spectroscopy (XPS) microscope is equipped with two Fresnel zone plates for beam focusing, whereas higher diffraction orders were eliminated, thanks to an order selection aperture. The sample was placed on a precision positioning stage located at the common focus point of the hemispherical analyzer and the Fresnel zone plates. This setup was used for the collection of both point-mode spectra and imaging-mode spectra. In the imaging mode, the photoemitted electron intensity from the desired energy range is collected over the sample to form a 2D image resolved at the submicrometer range. Core-level and valence band spectra were taken with 350 and 100 eV photon energy, respectively. The spatial resolution was in the submicrometer range (near 600–700 nm). The analyzer pass energy was set to 100 eV (200 eV) for the spatially unresolved (resolved) mode. All measurements were made under ultrahigh vacuum (10–10 mbar), and prior to the acquisition the NPG samples were degassed at 600°C for several hours to remove contaminants from air exposure. The sample was kept cooled at the liquid nitrogen temperature to avoid radiation damage. (19) Valence band data with 21.22 eV photon energy on the saturated H-NPG sample was taken at the Lotus laboratory, Rome, by using an analogous UHV setup.

Raman Measurements

For Raman measurements, the excitation laser was provided by single frequency Nd:YVO4 lasers (DPSS series by Lasos) emitting at 532 nm. The Raman signal was spectrally dispersed by a 750 mm focal length ACTON SP750 monochromator equipped with a 300 groove/mm grating and detected by a back-illuminated N2-cooled Si CCD camera (model 100BRX by Princeton Instruments). The laser light was filtered out by a very sharp long-pass Razor edge filter (Semrock). The micro-Raman (μ-Raman) spectral resolution was 2.4 cm–1. A long working distance 100× objective with NA = 0.75 was employed to excite and collect the light, in a backscattering configuration. The laser spot size determined experimentally is characterized by a Gaussian shape with σ = 0.28 μm. Moderate laser powers (∼200 μW, corresponding to power densities ∼20 kW/cm2) were employed, after checking that the spectrum was analogous to that acquired with much lower power (a factor of ∼70).

Theoretical Modeling

The ground-state properties of H-passivate graphene were investigated from first-principles by using a plane-wave pseudopotential implementation of the density functional theory (DFT), as available in the Quantum ESPRESSO package. (47,48) The Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation for the exchange-correlation functional was used, (49) together with Optimized Norm-Conserving Vanderbilt (ONCV) pseudopotentials. (50) The quasiparticle band structure for the DFT optimized geometries was computed within the GW approximation to the electron self-energy (G0W0 scheme; (39) plasmon-pole model; (51) slab truncation scheme for the Coulomb potential, (52) random integration method for the screening potential), as implemented in the yambo code. (53,54) Calculations were performed by employing an automated yambo-AiiDA based workflow. (55−57)

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.2c00162.

  • Details on the image analysis methods of the spectromicroscopy maps and details on the first-principles simulations (PDF)

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Author Information

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  • Corresponding Authors
  • Authors
    • Ernesto Placidi - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
    • Chiara Izzo - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
    • Elena Blundo - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy;  Orcidhttps://orcid.org/0000-0003-0423-4798
    • Antonio Polimeni - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy;  Orcidhttps://orcid.org/0000-0002-2017-4265
    • Marco Sbroscia - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
    • José Avila - Synchrotron SOLEIL, Université Paris-Saclay, Saint Aubin, BP 48, 91192 Gif sur Yvette, France
    • Pavel Dudin - Synchrotron SOLEIL, Université Paris-Saclay, Saint Aubin, BP 48, 91192 Gif sur Yvette, France
    • Kailong Hu - School of Materials Science and Engineering and Institute of Materials Genome & Big Data, Harbin Institute of Technology, Shenzhen 518055, P.R. China;  Orcidhttps://orcid.org/0000-0003-0489-5836
    • Yoshikazu Ito - Institute of Applied Physics, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan;  Orcidhttps://orcid.org/0000-0001-8059-8396
    • Miki Bonacci - Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università degli Studi di Modena e Reggio Emilia, 41125 Modena, Italy;  S3, Istituto Nanoscienze-CNR, Via Campi 213/A, 41125 Modena, Italy
    • Elisa Molinari - Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università degli Studi di Modena e Reggio Emilia, 41125 Modena, Italy;  S3, Istituto Nanoscienze-CNR, Via Campi 213/A, 41125 Modena, Italy
    • Carlo Mariani - Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy;  Orcidhttps://orcid.org/0000-0002-7979-1700
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was partially supported by the MaX – MAterials design at the eXascale – Centre of Excellence, funded by the European Union’s programme H2020-INFRAEDI-2018-1 (Grant No. 824143), by JSPS Grant-in-Aid for Scientific Research on Innovative Areas “Discrete Geometric Analysis for Materials Design” (Grant Number, JP20H04628) and JSPS KAKENHI (Grant Number JP21H02037), by PRIN FERMAT (2017KFY7XF) from Italian Ministry MIUR and by Sapienza Ateneo funds, by SUPER (Supercomputing Unified Platform─Emilia-Romagna) regional project. Computational time on the Marconi100 machine at CINECA was provided by the Italian ISCRA program.

References

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    Using first principles many-body theory methods (GW + Bethe-Salpeter equation) we demonstrate that the optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielec. medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially sepd. electron and hole, which are localized out of plane and in plane, resp. The presence of such bound excitons opens the path towards an excitonic Bose-Einstein condensate in graphane that can be obsd. exptl.
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  3. 3
    Ryu, S.; Han, M. Y.; Maultzsch, J.; Heinz, T. F.; Kim, P.; Steigerwald, M. L.; Brus, L. E. Reversible Basal Plane Hydrogenation of Graphene. Nano Lett. 2008, 8, 4597– 4602,  DOI: 10.1021/nl802940s
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    Reversible Basal Plane Hydrogenation of Graphene
    Ryu, Sunmin; Han, Melinda Y.; Maultzsch, Janina; Heinz, Tony F.; Kim, Philip; Steigerwald, Michael L.; Brus, Louis E.
    Nano Letters (2008), 8 (12), 4597-4602CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The authors report the chem. reaction of single-layer graphene with hydrogen atoms, generated in situ by electron-induced dissocn. of hydrogen silsesquioxane (HSQ). Hydrogenation, forming sp3 C-H functionality on the basal plane of graphene, proceeds at a higher rate for single than for double layers, demonstrating the enhanced chem. reactivity of single sheet graphene. The net H atom sticking probability on single layers at 300 K is at least 0.03, which exceeds that of double layers by at least a factor of 15. Chemisorbed hydrogen atoms, which give rise to a prominent Raman D band, can be detached by thermal annealing at 100-200°. The resulting dehydrogenated graphene is activated when photothermally heated it reversibly binds ambient oxygen, leading to hole doping of the graphene. This functionalization of graphene can be exploited to manipulate electronic and charge transport properties of graphene devices.
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  4. 4
    Elias, D. C.; Nair, R. R.; Mohiuddin, T. M. G.; Morozov, S. V.; Blake, P.; Halsall, M. P.; Ferrari, A. C.; Boukhvalov, D. W.; Katsnelson, M. I.; Geim, A. K.; Novoselov, K. S. Control of Graphene’s Properties by Reversible Hydrogenation: Evidence for Graphane. Science 2009, 323, 610– 613,  DOI: 10.1126/science.1167130
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    Control of Graphene's Properties by Reversible Hydrogenation: Evidence for Graphane
    Elias, D. C.; Nair, R. R.; Mohiuddin, T. M. G.; Morozov, S. V.; Blake, P.; Halsall, M. P.; Ferrari, A. C.; Boukhvalov, D. W.; Katsnelson, M. I.; Geim, A. K.; Novoselov, K. S.
    Science (Washington, DC, United States) (2009), 323 (5914), 610-613CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
    Although graphite is known as one of the most chem. inert materials, we have found that graphene, a single at. plane of graphite, can react with at. hydrogen, which transforms this highly conductive zero-overlap semimetal into an insulator. Transmission electron microscopy reveals that the obtained graphene deriv. (graphane) is cryst. and retains the hexagonal lattice, but its period becomes markedly shorter than that of graphene. The reaction with hydrogen is reversible, so that the original metallic state, the lattice spacing, and even the quantum Hall effect can be restored by annealing. Our work illustrates the concept of graphene as a robust at.-scale scaffold on the basis of which new two-dimensional crystals with designed electronic and other properties can be created by attaching other atoms and mols.
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  5. 5
    Haberer, D.; Vyalikh, D. V.; Taioli, S.; Dora, B.; Farjam, M.; Fink, J.; Marchenko, D.; Pichler, T.; Ziegler, K.; Simonucci, S.; Dresselhaus, M. S.; Knupfer, M.; Büchner, B.; Gruneis, A. Tunable Band Gap in Hydrogenated Quasi-Free-Standing Graphene. Nano Lett. 2010, 10, 3360– 3366,  DOI: 10.1021/nl101066m
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    5
    Tunable Band Gap in Hydrogenated Quasi-Free-Standing Graphene
    Haberer, D.; Vyalikh, D. V.; Taioli, S.; Dora, B.; Farjam, M.; Fink, J.; Marchenko, D.; Pichler, T.; Ziegler, K.; Simonucci, S.; Dresselhaus, M. S.; Knupfer, M.; Buechner, B.; Grueneis, A.
    Nano Letters (2010), 10 (9), 3360-3366CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    From angle-resolved photoemission spectroscopy, a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via H loading and reaches ∼1.0 eV for a H coverage of 8%. The local rehybridization from sp2 to sp3 in the chem. bonding is obsd. by XPS and x-ray absorption and allows for a detn. of the amt. of chemisorbed H. The H induced gap formation is completely reversible by annealing without damaging the graphene. Calcns. of the H loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission expts. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study H storage in C materials.
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  6. 6
    Luo, Z.; Shang, J.; Lim, S.; Li, D.; Xiong, Q.; Shen, Z. Modulating the electronic structures of graphene by controllable hydrogenation. Appl. Phys. Lett. 2010, 97, 233111,  DOI: 10.1063/1.3524217
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    Modulating the electronic structures of graphene by controllable hydrogenation
    Luo, Zhiqiang; Shang, Jingzhi; Lim, Sanhua; Li, Dehui; Xiong, Qihua; Shen, Zexiang; Lin, Jianyi; Yu, Ting
    Applied Physics Letters (2010), 97 (23), 233111/1-233111/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The evolution of electronic structures of hydrogenated graphene with different amt. of H coverage was studied by UV photoemission spectroscopy and optical absorption spectroscopy. Raman spectroscopy and XPS were used to monitor and evaluate the H coverage. At low H coverage, the sp3C-H bonds embedded within a sp2 C matrix behave as defects in graphene and depress the delocalized π electron system. At high H coverage, 2 localized π electron states originating from the sp2 C clusters encircled by the sp3 C-H matrix appear in the electronic band structures, and an opening of a band gap was obsd. (c) 2010 American Institute of Physics.
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  7. 7
    Burgess, J. S.; Matis, B. R.; Robinson, J. T.; Bulat, F. A.; Perkins, F. K.; Houston, B. H.; Baldwin, J. W. Tuning the electronic properties of graphene by hydrogenation in a plasma enhanced chemical vapor deposition reactor. Carbon 2011, 49, 4420– 4426,  DOI: 10.1016/j.carbon.2011.06.034
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    Tuning the electronic properties of graphene by hydrogenation in a plasma enhanced chemical vapor deposition reactor
    Burgess, James S.; Matis, Bernard R.; Robinson, Jeremy T.; Bulat, Felipe A.; Keith Perkins, F.; Houston, Brian H.; Baldwin, Jeffrey W.
    Carbon (2011), 49 (13), 4420-4426CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Graphene films grown by CVD on Cu foils were hydrogenated using com. viable methods. Parameters such as plasma power, plasma frequency, and sample temp. were varied to det. the max. possible hydrogenation without etching the film. The kinetic energy of the ions inside the plasma is crit., in that higher kinetic energy ions tend to etch the film while lower kinetic energy ions participate in the hydrogenation process. The film sheet resistance was shown to increase, while the hole mobility was shown to decrease with increasing hydrogenation. Variable temp. measurements demonstrate a transition from semi-metallic behavior for graphene to semiconducting behavior for hydrogenated graphene. Sheet resistance measurements as a function of temp. also suggest the emergence of a bandgap in the hydrogenated graphene films.
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  8. 8
    Balog, R.; Andersen, M.; Jørgensen, B.; Sljivancanin, Z.; Hammer, B.; Baraldi, A.; Larciprete, R.; Hofmann, P.; Hornekær, L.; Lizzit, S. Controlling Hydrogenation of Graphene on Ir(111). ACS Nano 2013, 7, 3823– 3832,  DOI: 10.1021/nn400780x
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    Controlling Hydrogenation of Graphene on Ir(111)
    Balog, Richard; Andersen, Mie; Joergensen, Bjarke; Sljivancanin, Zeljko; Hammer, Bjoerk; Baraldi, Alessandro; Larciprete, Rosanna; Hofmann, Philip; Hornekaer, Liv; Lizzit, Silvano
    ACS Nano (2013), 7 (5), 3823-3832CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Combined fast XPS and d. functional theory calcns. reveal the presence of two types of hydrogen adsorbate structures at the graphene/Ir(111) interface, namely, graphane-like islands and hydrogen dimer structures. While the former give rise to a periodic pattern, dimers tend to destroy the periodicity. Distinctive growth rates and stability of both types of structures were obsd. allowing one to obtain well-defined patterns of hydrogen clusters. The ability to control and manipulate the formation and size of hydrogen structures on graphene facilitates tailoring of its properties for a wide range of applications by means of covalent functionalization.
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  9. 9
    Paris, A. Kinetic Isotope Effect in the Hydrogenation and Deuteration of Graphene. Adv. Funct. Mater. 2013, 23, 1628– 1635,  DOI: 10.1002/adfm.201202355
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    9
    Kinetic Isotope Effect in the Hydrogenation and Deuteration of Graphene
    Paris, A.; Verbitskiy, N. I.; Nefedov, A.; Wang, Y.; Fedorov, A. V.; Haberer, D.; Oehzelt, M.; Petaccia, L.; Usachov, D.; Vyalikh, D. V.; Sachdev, H.; Woell, C.; Knupfer, M.; Buechner, B.; Calliari, L.; Yashina, L. V.; Irle, S.; Grueneis, A.
    Advanced Functional Materials (2013), 23 (13), 1628-1635CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Time-dependent photoemission spectroscopy is employed to study the kinetics of the hydro-genation/deuteration reaction of graphene. Resulting in an unusual kinetic isotope effect, the graphene deuteration reaction proceeds faster than hydrogenation and leads to substantially higher max. coverages of deuterium (D/C≈35% vs H/C≈25%). These results can be explained by the fact that in the at. state H and D have a lower energy barrier to overcome in order to react with graphene, while in the mol. form the bond between two atoms must be broken before the capture on the graphene layer. More importantly, D has a higher desorption barrier than H due to quantum mech. zero-point energy effects related to the C-D or C-H stretch vibration. Mol. dynamics simulations based on a quantum mech. electronic potential can reproduce the exptl. trends and reveal the contribution of the constituent chemisorption, reflection, and associative desorption processes of H or D atoms onto graphene. Regarding the electronic structure changes, a tunable electron energy gap can be induced by both deuteration and hydrogenation.
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  10. 10
    Felten, A.; McManus, D.; Rice, C.; Nittler, L.; Pireaux, J.-J.; Casiraghi, C. Insight into hydrogenation of graphene: Effect of hydrogen plasma chemistry. Appl. Phys. Lett. 2014, 105, 183104,  DOI: 10.1063/1.4901226
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    10
    Insight into hydrogenation of graphene. Effect of hydrogen plasma chemistry
    Felten, A.; McManus, D.; Rice, C.; Nittler, L.; Pireaux, J.-J.; Casiraghi, C.
    Applied Physics Letters (2014), 105 (18), 183104/1-183104/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Plasma hydrogenation of graphene was proposed as a tool to modify the properties of graphene. However, H plasma is a complex system and controlled hydrogenation of graphene suffers from a lack of understanding of the plasma chem. Here, we correlate the modifications induced on monolayer graphene studied by Raman spectroscopy with the hydrogen ions energy distributions obtained by mass spectrometry. We measure the energy distribution of H+, H2+, and H3+ ions for different plasma conditions showing that their energy strongly depends on the sample position, pressure, and plasma power and can reach values as high as 45 eV. Based on these measurements, we speculate that under specific plasma parameters, protons should possess enough energy to penetrate the graphene sheet. Therefore, a graphene membrane could become, under certain conditions, transparent to both protons and electrons. (c) 2014 American Institute of Physics.
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  11. 11
    Panahi, M.; Solati, N.; Kaya, S. Modifying hydrogen binding strength of graphene. Surf. Sci. 2019, 679, 24– 30,  DOI: 10.1016/j.susc.2018.08.009
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    11
    Modifying hydrogen binding strength of graphene
    Panahi, Mohammad; Solati, Navid; Kaya, Sarp
    Surface Science (2019), 679 (), 24-30CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
    The effect of the substrate on the binding strength of hydrogen on single layer graphene grown on Pt(111) surfaces has been investigated via detg. its desorption activation energy. We showed that subsurface alloys on Pt(111) can dramatical modify the C-H bond strength in hydrogenated graphene. Various 3d metals, vanadium, iron, cobalt, and nickel were deposited in the subsurface layer to modify the chem. and electronic properties of the substrate. Anal. of the temp. programmed desorption data shows that subsurface alloys reduce the hydrogen desorption activation energy by weakening C-H bond energy in graphene, down to ∼57 kJ/mol in the case of Pt/Co/Pt(111) as compared to ∼111 kJ/mol obtained from hydrogenated graphene grown on a bare Pt(111).
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  12. 12
    Abdelnabi, M. M. S.; Blundo, E.; Betti, M. G.; Cavoto, G.; Placidi, E.; Polimeni, A.; Ruocco, A.; Hu, K.; Ito, Y.; Mariani, C. Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene. Nanotechnology 2021, 32, 035707,  DOI: 10.1088/1361-6528/abbe56
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    12
    Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene
    Abdelnabi, Mahmoud Mohamed Saad; Blundo, Elena; Betti, Maria Grazia; Cavoto, Gianluca; Placidi, Ernesto; Polimeni, Antonio; Ruocco, Alessandro; Hu, Kailong; Ito, Yoshikazu; Mariani, Carlo
    Nanotechnology (2021), 32 (3), 035707CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
    Graphane is formed by bonding hydrogen (and deuterium) atoms to carbon atoms in the graphene mesh, with modification from the pure planar sp2 bonding towards an sp3 configuration. Atomic hydrogen (H) and deuterium (D) bonding with C atoms in fully free-standing nano porous graphene (NPG) is achieved, by exploiting low-energy proton (or deuteron) non-destructive irradn., with unprecedented minimal introduction of defects, as detd. by Raman spectroscopy and by the C 1s core level lineshape anal. Evidence of the H- (or D-) NPG bond formation is obtained by bringing to light the emergence of a H- (or D-) related sp3-distorted component in the C 1s core level, clear fingerprint of H-C (or D-C) covalent bonding. The H (or D) bonding with the C atoms of free-standing graphene reaches more than 1/4 (or 1/3) at% coverage. This non-destructive H-NPG (or D-NPG) chemisorption is very stable at high temps. up to about 800 K, as monitored by Raman and XPS, with complete healing and restoring of clean graphene above 920 K. The excellent chem. and temp. stability of H- (and D-) NPG opens the way not only towards the formation of semiconducting graphane on large-scale samples, but also to stable graphene functionalisation enabling futuristic applications in advanced detectors for the β-spectrum anal.
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  13. 13
    Abdelnabi, M. M. S.; Izzo, C.; Blundo, E.; Betti, M. G.; Sbroscia, M.; Di Bella, G.; Cavoto, G.; Polimeni, A.; García-Cortés, I.; Rucandio, I.; Moroño, A.; Hu, K.; Ito, Y.; Mariani, C. Deuterium Adsorption on Free-Standing Graphene. Nanomaterials 2021, 11, 130,  DOI: 10.3390/nano11010130
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    13
    Deuterium adsorption on free-standing graphene
    Abdelnabi, Mahmoud Mohamed Saad; Izzo, Chiara; Blundo, Elena; Betti, Maria Grazia; Sbroscia, Marco; Di Bella, Giulia; Cavoto, Gianluca; Polimeni, Antonio; Garcia-Cortes, Isabel; Rucandio, Isabel; Morono, Alejandro; Hu, Kailong; Ito, Yoshikazu; Mariani, Carlo
    Nanomaterials (2021), 11 (1), 130CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
    A suitable way to modify the electronic properties of graphene-while maintaining the exceptional properties assocd. with its two-dimensional (2D) nature-is its functionalisation. In particular, the incorporation of hydrogen isotopes in graphene is expected to modify its electronic properties leading to an energy gap opening, thereby rendering graphene promising for a widespread of applications. Hence, deuterium (D) adsorption on free-standing graphene was obtained by highenergy electron ionisation of D2 and ion irradn. of a nanoporous graphene (NPG) sample. This method allows one to reach nearly 50 at.% D upload in graphene, higher than that obtained by other deposition methods so far, towards low-defect and free-standing D-graphane. That evidence was deduced by XPS of the C 1s core level, showing clear evidence of the D-C sp3 bond, and Raman spectroscopy, pointing to remarkably clean and low-defect prodn. of graphane. Moreover, UPS showed the opening of an energy gap in the valence band. Therefore, high-energy electron ionisation and ion irradn. is an outstanding method for obtaining low defect D-NPG with a high D upload, which is very promising for the fabrication of semiconducting graphane on large scale.
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  14. 14
    Zhao, F.; Raitses, Y.; Yang, X.; Tan, A.; Tully, C. G. High hydrogen coverage on graphene via low temperature plasma with applied magnetic field. Carbon 2021, 177, 244– 251,  DOI: 10.1016/j.carbon.2021.02.084
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    14
    High hydrogen coverage on graphene via low temperature plasma with applied magnetic field
    Zhao, Fang; Raitses, Yevgeny; Yang, Xiaofang; Tan, Andi; Tully, Christopher G.
    Carbon (2021), 177 (), 244-251CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    The chem. functionalization of two-dimensional materials is an effective method for tailoring their chem. and electronic properties with encouraging applications in energy, catalysis, and electronics. One exemplary 2D material with remarkable properties, graphene, can be exploited for hydrogen storage and large on/off ratio devices by hydrogen termination. In this work, we describe a promising plasma-based method to provide high hydrogen coverage on graphene. A low pressure (∼10 mtorr) discharge generates a fine-tunable low-temp. hydrogen-rich plasma in the applied radial elec. and axial magnetic fields. Post-run characterization of these samples using Raman spectroscopy and XPS demonstrates a higher hydrogen coverage, 35.8%, than the previously reported results using plasmas. Plasma measurements indicate that with the applied magnetic field, the d. of hydrogen atoms can be more than 10 times larger than the d. without the magnetic field. With the applied elec. field directed away from the graphene substrate, the flux of plasma ions towards this substrate and the ion energy are insufficient to cause measurable damage to the treated 2D material. The low damage allows a relatively long treatment time of the graphene samples that contributes to the high coverage obtained in these expts.
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  15. 15
    Whitener, K. E.; Lee, W. K.; Campbell, P. M.; Robinson, J. T.; Sheehan, P. E. Chemical hydrogenation of single-layer graphene enables completely reversible removal of electrical conductivity. Carbon 2014, 72, 348– 353,  DOI: 10.1016/j.carbon.2014.02.022
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    15
    Chemical hydrogenation of single-layer graphene enables completely reversible removal of electrical conductivity
    Whitener, Keith E.; Lee, Woo K.; Campbell, Paul M.; Robinson, Jeremy T.; Sheehan, Paul E.
    Carbon (2014), 72 (), 348-353CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    The chem. modification of graphene greatly expands its potential applications in electronics, chem., and biol. Here, we report the rapid and extensive hydrogenation of single layer CVD graphene using the Birch redn. method. This method hydrogenates much more extensively than cold plasmas and electrochem. methods. Moreover, use of single layer graphene enables greater control of electronic cond. than previously achieved with the Birch method using multilayer graphene or graphene oxide. Indeed, this method enables both the elimination of electronic cond. through hydrogenation and the subsequent recovery of essentially pristine graphene with thermal annealing-a reversible >107 fold change in resistance. Raman and photoelectron spectroscopies show that the reaction is complete within 90 s of immersion. Finally, we show that we can use the Birch redn. to functionalize graphene with tributyltin moieties.
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    Son, J.; Lee, S.; Kim, S. J.; Park, B. C.; Lee, H.-K.; Kim, S.; Kim, J. H.; Hong, B. H.; Hong, J. Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor. Nat. Commun. 2016, 7, 13261,  DOI: 10.1038/ncomms13261
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    16
    Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor
    Son, Jangyup; Lee, Soogil; Kim, Sang Jin; Park, Byung Cheol; Lee, Han-Koo; Kim, Sanghoon; Kim, Jae Hoon; Hong, Byung Hee; Hong, Jongill
    Nature Communications (2016), 7 (), 13261CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Graphene is currently at the forefront of cutting-edge science and technol. due to exceptional electronic, optical, mech., and thermal properties. However, the absence of a sizeable band gap in graphene has been a major obstacle for application. To open and control a band gap in functionalized graphene, several gapping strategies have been developed. In particular, hydrogen plasma treatment has triggered a great scientific interest, because it has been known to be an efficient way to modify the surface of single-layered graphene and to apply for std. wafer-scale fabrication. Here we show a monolayer chem.-vapor-deposited graphene hydrogenated by indirect hydrogen plasma without structural defect and we demonstrate that a band gap can be tuned as wide as 3.9 eV by varying hydrogen coverage. We also show a hydrogenated graphene field-effect transistor, showing that on/off ratio changes over three orders of magnitude at room temp.
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    Haberer, D. Electronic properties of hydrogenated quasi-free-standing graphene. physica status solidi (b) 2011, 248, 2639– 2643,  DOI: 10.1002/pssb.201100521
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    17
    Electronic properties of hydrogenated quasi-free-standing graphene
    Haberer, D.; Petaccia, L.; Wang, Y.; Quian, H.; Farjam, M.; Jafari, S. A.; Sachdev, H.; Federov, A. V.; Usachov, D.; Vyalikh, D. V.; Liu, X.; Vilkov, O.; Adamchuk, V. K.; Irle, S.; Knupfer, M.; Buechner, B.; Grueneis, A.
    Physica Status Solidi B: Basic Solid State Physics (2011), 248 (11), 2639-2643CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Tailoring the electronic properties of graphene is of fundamental interest regarding its application in electronic devices. One of the key strategies is chem. functionalization which modifies the π-electron system and thus can induce band gaps. However, in order to control the degree of functionalization it is crucial to know the exact amt. of the chemisorbed species. We show with angle-resolved photoemission spectroscopy (ARPES) the formation of a band gap in graphene and est. the hydrogen coverage from the scattering rate. Using X-ray photoemission spectroscopy (XPS) we identify the chem. environments in hydrogenated graphene and det. the total hydrogen to carbon (H/C)-ratio directly from the spectra. We then compare ARPES and XPS as tools for detg. the H/C-ratio and discuss the results from mol. dynamics (MD) simulations. Angle-resolved photoemission spectra of (left panel) pristine graphene intercalated with Au and (right panel) hydrogenated graphene on Au with an estd. H-coverage of 5.8%. Besides the formation of a band gap, a broadening is observable which can be used to det. the H amt. Both spectra show the π-band at the K-point.
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  18. 18
    Eng, A. Y. S.; Sofer, Z.; Bouša, D.; Sedmidubský, D.; Huber, t.; Pumera, M. Near-Stoichiometric Bulk Graphane from Halogenated Graphenes (X = Cl/Br/I) by the Birch Reduction for High Density Energy Storage. Adv. Funct. Mater. 2017, 27, 1605797,  DOI: 10.1002/adfm.201605797
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    There is no corresponding record for this reference.
  19. 19
    Di Bernardo, I.; Avvisati, G.; Mariani, C.; Motta, N.; Chen, C.; Avila, J.; Asensio, M. C.; Lupi, S.; Ito, Y.; Chen, M.; Fujita, T.; Betti, M. G. Two-Dimensional Hallmark of Highly Interconnected Three-Dimensional Nanoporous Graphene. ACS Omega 2017, 2, 3691– 3697,  DOI: 10.1021/acsomega.7b00706
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    19
    Two-Dimensional Hallmark of Highly Interconnected Three-Dimensional Nanoporous Graphene
    Di Bernardo, Iolanda; Avvisati, Giulia; Mariani, Carlo; Motta, Nunzio; Chen, Chaoyu; Avila, Jose; Asensio, Maria Carmen; Lupi, Stefano; Ito, Yoshikazu; Chen, Mingwei; Fujita, Takeshi; Betti, Maria Grazia
    ACS Omega (2017), 2 (7), 3691-3697CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) mm-size architecture without compromising its remarkable elec., optical and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining state-of-the-art spectro-microscopy and imaging techniques. The connected and bi-continuous topol., without frayed borders and edges, and with low d. of cryst. defects, has been unveiled via helium ion microscopy, Raman and transmission electron microscopy down to the at. scale. Most importantly, nano-scanning photoemission unravels a 3D NPG structure with preserved 2D electronic d. of states (Dirac conelike) throughout the porous sample. Furthermore, the high spatial resoln. brings to light the interrelationship between the topol. and the morphol. in the wrinkled and highly bent regions, where distorted sp2 C bonds, assocd. to sp3 -like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small size individual graphene sheets, and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.
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  20. 20
    Di Bernardo, I.; Avvisati, G.; Chen, C.; Avila, J.; Asensio, M. C.; Hu, K.; Ito, Y.; Hines, P.; Lipton-Duffin, J.; Rintoul, L.; Motta, N.; Mariani, C.; Betti, M. G. Topology and doping effects in three-dimensional nanoporous graphene. Carbon 2018, 131, 258– 265,  DOI: 10.1016/j.carbon.2018.01.076
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    20
    Topology and doping effects in three-dimensional nanoporous graphene
    Di Bernardo, Iolanda; Avvisati, Giulia; Chen, Chaoyu; Avila, Jose; Asensio, Maria Carmen; Hu, Kailong; Ito, Yoshikazu; Hines, Peter; Lipton-Duffin, Josh; Rintoul, Llew; Motta, Nunzio; Mariani, Carlo; Betti, Maria Grazia
    Carbon (2018), 131 (), 258-265CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    We report on a spatial mapping of the electronic and vibrational structure of three-dimensional (3D) nanoporous graphene architectures, which have a hierarchical pore structure. We demonstrate that the topol., curvature, and pores lead to local changes in the electronic and vibrational structure and in the hybridization states of the carbon atoms (sp2 vs. sp3-like). Nitrogen substitutions in pyrrolic bonding configurations also contribute to local distortions of the planar geometry of graphene. The distortions influence the electronic d. of states at the Fermi level by shifting the Dirac cone apex, opening potential avenues for applications of two-dimensional graphene in 3D devices.
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  21. 21
    Sha, X.; Jackson, B. First-principles study of the structural and energetic properties of H atoms on a graphite (0001) surface. Surf. Sci. 2002, 496, 318– 330,  DOI: 10.1016/S0039-6028(01)01602-8
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    21
    First-principles study of the structural and energetic properties of H atoms on a graphite (0 0 0 1) surface
    Sha, Xianwei; Jackson, Bret
    Surface Science (2002), 496 (3), 318-330CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
    Electronic structure calcns. based on spin-polarized d. functional theory with the generalized gradient approxn. and ultrasoft pseudopotentials are used to investigate the interaction between H atoms and a graphite (0 0 0 1) surface. An asym. slab supercell approach is employed to model the graphite surface. The calcd. equil. properties of bulk graphite, the H mol. and the graphite (0 0 0 1) surface are all in good agreement with exptl. data. The interaction of H with 3 high-symmetry sites on a graphite surface is considered. A broad and site-independent H physisorption region centered at around 4 Å above the surface has a small binding energy of 8 meV. A localized stable chem. adsorption site can be found only when H is placed on the top site, with the help of substantial surface reconstruction. The reaction of a gas-phase H atom with an H adsorbed in the chemisorption site is then considered. Numerous total energy points are computed in the region of configuration space believed to be important for this Eley-Rideal reaction. Our results are in good agreement with the studies of Sidis and co-workers [Chem. Phys. Lett. 300 (1991) 157, Proc. Conf. H2 in space]. Preliminary results from a quantum scattering calcn. using a model potential energy surface fit to these points are presented. The trapping and recombination of H atoms on graphite surfaces is discussed, taking surface reconstructions into consideration.
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  22. 22
    Ruffieux, P.; Gröning, O.; Bielmann, M.; Mauron, P.; Schlapbach, L.; Gröning, P. Hydrogen adsorption on sp2-bonded carbon: Influence of the local curvature. Phys. Rev. B 2002, 66, 245416,  DOI: 10.1103/PhysRevB.66.245416
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    22
    Hydrogen adsorption on sp2-bonded carbon. Influence of the local curvature
    Ruffieux, P.; Groning, O.; Bielmann, M.; Mauron, P.; Schlapbach, L.; Groning, P.
    Physical Review B: Condensed Matter and Materials Physics (2002), 66 (24), 245416/1-245416/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    The interaction of at. hydrogen and low-energy hydrogen ions with sp2-bonded carbon is investigated on the surfaces of C60 multilayer films, single-walled C nanotubes, and graphite (0001). These 3 materials were chosen to represent sp2-bonded carbon networks with different local curvatures and closed surfaces (i.e. no dangling bonds). Chemisorption of H on these surfaces reduces emission from photoemission features assocd. with the π electrons and leads to a lowering of the work function up to 1.3 eV. The energy barrier for H adsorption decreases with increasing local curvature of the carbon surface. Whereas in the case of C60 and single-walled C nanotubes, H adsorption can be achieved by exposure to at. H, the H adsorption on graphite (0001) requires H+ ions of low kinetic energy (∼1 eV). On all 3 materials, the adsorption energy barrier is found to increase with coverage. Accordingly, H chemisorption sats. at coverages that depend on the local curvature of the sample and the form of H (i.e., at. or ionic) used for the treatment.
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  23. 23
    Tozzini, V.; Pellegrini, V. Prospects for hydrogen storage in graphene. Phys. Chem. Chem. Phys. 2013, 15, 80– 89,  DOI: 10.1039/C2CP42538F
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    Prospects for hydrogen storage in graphene
    Tozzini, Valentina; Pellegrini, Vittorio
    Physical Chemistry Chemical Physics (2013), 15 (1), 80-89CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    A review. Hydrogen-based fuel cells are promising solns. for the efficient and clean delivery of electricity. Since hydrogen is an energy carrier, a key step for the development of a reliable hydrogen-based technol. requires solving the issue of storage and transport of hydrogen. Several proposals based on the design of advanced materials such as metal hydrides and carbon structures have been made to overcome the limitations of the conventional soln. of compressing or liquefying hydrogen in tanks. Nevertheless none of these systems are currently offering the required performances in terms of hydrogen storage capacity and control of adsorption/desorption processes. Therefore the problem of hydrogen storage remains so far unsolved and it continues to represent a significant bottleneck to the advancement and proliferation of fuel cell and hydrogen technologies. Recently, however, several studies on graphene, the one-atom-thick membrane of carbon atoms packed in a honeycomb lattice, have highlighted the potentialities of this material for hydrogen storage and raise new hopes for the development of an efficient solid-state hydrogen storage device. Here we review on-going efforts and studies on functionalized and nanostructured graphene for hydrogen storage and suggest possible developments for efficient storage/release of hydrogen under ambient conditions.
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    Ito, Y.; Tanabe, Y.; Qiu, H.-J.; Sugawara, K.; Heguri, S.; Tu, N. H. High-Quality Three-Dimensional Nanoporous Graphene. Angew. Chem., Int. Ed. 2014, 53, 4822– 4826,  DOI: 10.1002/anie.201402662
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    High-Quality Three-Dimensional Nanoporous Graphene
    Ito, Yoshikazu; Tanabe, Yoichi; Qiu, H.-J.; Sugawara, Katsuaki; Heguri, Satoshi; Tu, Ngoc Han; Huynh, Khuong Kim; Fujita, Takeshi; Takahashi, Takashi; Tanigaki, Katsumi; Chen, Mingwei
    Angewandte Chemie, International Edition (2014), 53 (19), 4822-4826CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    We report three-dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore-size dependence, together with unique angular independence. The free-standing, large-scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices.
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  25. 25
    Tanabe, Y.; Ito, Y.; Sugawara, K.; Hojo, D.; Koshino, M.; Fujita, T. Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks. Adv. Mater. 2016, 28, 10304– 10310,  DOI: 10.1002/adma.201601067
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    Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks
    Tanabe, Yoichi; Ito, Yoshikazu; Sugawara, Katsuaki; Hojo, Daisuke; Koshino, Mikito; Fujita, Takeshi; Aida, Tsutomu; Xu, Xiandong; Huynh, Khuong Kim; Shimotani, Hidekazu; Adschiri, Tadafumi; Takahashi, Takashi; Tanigaki, Katsumi; Aoki, Hideo; Chen, Mingwei
    Advanced Materials (Weinheim, Germany) (2016), 28 (46), 10304-10310CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    This paper exptl. realized a nanoporous graphene elec. double layer transistor. And demonstrated for the first time that the 3D nanoporous graphene networks possess an ambipolor electronic nature of Dirac cones with an ultrahigh carrier mobility of 5000-7500 cm2 V-1 s-1. The three dimensional graphene networks with Dirac fermions exhibit a unique nonlinear Hall resistance in a wide range of the gate voltages.
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  26. 26
    Tanabe, Y.; Ito, Y.; Sugawara, K.; Koshino, M.; Kimura, S.; Naito, T.; Johnson, I.; Takahashi, T.; Chen, M. Dirac Fermion Kinetics in 3D Curved Graphene. Adv. Mater. 2020, 32, 2005838,  DOI: 10.1002/adma.202005838
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    26
    Dirac fermion kinetics in 3D curved graphene
    Tanabe, Yoichi; Ito, Yoshikazu; Sugawara, Katsuaki; Koshino, Mikito; Kimura, Shojiro; Naito, Tomoya; Johnson, Isaac; Takahashi, Takashi; Chen, Mingwei
    Advanced Materials (Weinheim, Germany) (2020), 32 (48), 2005838CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    3D integration of graphene has attracted attention for realizing carbon-based electronic devices. While the 3D integration can amplify various excellent properties of graphene, the influence of 3D curved surfaces on the fundamental phys. properties of graphene has not been clarified. The electronic properties of 3D nanoporous graphene with a curvature radius down to 25-50 nm are systematically investigated and the ambipolar electronic states of Dirac fermions are essentially preserved in the 3D graphene nanoarchitectures, while the 3D curvature can effectively suppress the slope of the linear d. of states of Dirac fermion near the Fermi level are demonstrated. Importantly, the 3D curvature can be utilized to tune the back-scattering-suppressed elec. transport of Dirac fermions and enhance both electron localization and electron-electron interaction. As a result, nanoscale curvature provides a new degree of freedom to manipulate 3D graphene elec. properties, which may pave a new way to design new 3D graphene devices with preserved 2D electronic properties and novel functionalities.
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  27. 27
    Blundo, E.; Surrente, A.; Spirito, D.; Pettinari, G.; Yildirim, T.; Chavarin, C. A.; Baldassarre, L.; Felici, M.; Polimeni, A. Vibrational properties in highly strained hexagonal boron nitride bubbles. Nano Lett. 2022, 22, 1525,  DOI: 10.1021/acs.nanolett.1c04197
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    Vibrational Properties in Highly Strained Hexagonal Boron Nitride Bubbles
    Blundo, Elena; Surrente, Alessandro; Spirito, Davide; Pettinari, Giorgio; Yildirim, Tanju; Chavarin, Carlos Alvarado; Baldassarre, Leonetta; Felici, Marco; Polimeni, Antonio
    Nano Letters (2022), 22 (4), 1525-1533CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Hexagonal boron nitride (hBN) is widely used as a protective layer for few-atom-thick crystals and heterostructures (HSs), and it hosts quantum emitters working up to room temp. In both instances, strain is expected to play an important role, either as an unavoidable presence in the HS fabrication or as a tool to tune the quantum emitter electronic properties. Addressing the role of strain and exploiting its tuning potentiality require the development of efficient methods to control it and of reliable tools to quantify it. Here we present a technique based on hydrogen irradn. to induce the formation of wrinkles and bubbles in hBN, resulting in remarkably high strains of ~ 2%. By combining IR (IR) near-field scanning optical microscopy and micro-Raman measurements with numerical calcns., we characterize the response to strain for both IR-active and Raman-active modes, revealing the potential of the vibrational properties of hBN as highly sensitive strain probes.
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  28. 28
    Malard, L.; Pimenta, M.; Dresselhaus, G.; Dresselhaus, M. Raman spectroscopy in graphene. Phys. Rep. 2009, 473, 51– 87,  DOI: 10.1016/j.physrep.2009.02.003
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    Raman spectroscopy in graphene
    Malard, L. M.; Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.
    Physics Reports (2009), 473 (5-6), 51-87CODEN: PRPLCM; ISSN:0370-1573. (Elsevier B.V.)
    A review. Recent Raman scattering studies in different types of graphene samples are reviewed here. We first discuss the first-order and the double resonance Raman scattering mechanisms in graphene, which give rise to the most prominent Raman features. The detn. of the no. of layers in few-layer graphene is discussed, giving special emphasis to the possibility of using Raman spectroscopy to distinguish a monolayer from few-layer graphene stacked in the Bernal (AB) configuration. Different types of graphene samples produced both by exfoliation and using epitaxial methods are described and their Raman spectra are compared with those of 3D cryst. graphite and turbostratic graphite, in which the layers are stacked with rotational disorder. We show that Resonance Raman studies, where the energy of the excitation laser line can be tuned continuously, can be used to probe electrons and phonons near the Dirac point of graphene and, in particular allowing a detn. to be made of the tight-binding parameters for bilayer graphene. The special process of electron-phonon interaction that renormalizes the phonon energy giving rise to the Kohn anomaly is discussed, and is illustrated by gated expts. where the position of the Fermi level can be changed exptl. Finally, we discuss the ability of distinguishing armchair and zig-zag edges by Raman spectroscopy and studies in graphene nanoribbons in which the Raman signal is enhanced due to resonance with singularities in the d. of electronic states.
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  29. 29
    Barinov, A.; Gregoratti, L.; Dudin, P.; La Rosa, S.; Kiskinova, M. Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding. Adv. Mater. 2009, 21, 1916– 1920,  DOI: 10.1002/adma.200803003
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    Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding
    Barinov, Alexei; Gregoratti, Luca; Dudin, Pavel; La Rosa, Salvatore; Kiskinova, Maya
    Advanced Materials (Weinheim, Germany) (2009), 21 (19), 1916-1920CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Interaction with at. oxygen converts the initially metallic carbon nanotubes (CNTs) into semiconducting and, depending on the oxygen dose and reaction temp., the type and abundance of oxygenated functional groups formed changes significantly, including gasification and consumption of the CNTs at elevated temps. The most important finding is that the type and abundance of the groups formed and the gasification rate are strongly influenced by the d. and size of vacancy defects in the graphene layers of the carbon nanotube. On one hand, this introduces uncertainties when analogous procedures are employed for functionalization of CNTs with undefined d. and types of defects, but on the other hand it prompts an approach for tailoring CNTs via controlled introduction of defects, which can favor the formation of a preferred functional group.
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  30. 30
    Scardamaglia, M.; Amati, M.; Llorente, B.; Mudimela, P.; Colomer, J.-F.; Ghijsen, J.; Ewels, C.; Snyders, R.; Gregoratti, L.; Bittencourt, C. Nitrogen ion casting on vertically aligned carbon nanotubes: Tip and sidewall chemical modification. Carbon 2014, 77, 319– 328,  DOI: 10.1016/j.carbon.2014.05.035
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    Nitrogen ion casting on vertically aligned carbon nanotubes: Tip and sidewall chemical modification
    Scardamaglia, M.; Amati, M.; Llorente, B.; Mudimela, P.; Colomer, J.-F.; Ghijsen, J.; Ewels, C.; Snyders, R.; Gregoratti, L.; Bittencourt, C.
    Carbon (2014), 77 (), 319-328CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Nitrogen inclusion in vertically aligned carbon nanotubes (v-CNTs) was performed in situ and in ultra-high vacuum by nitrogen ion implantation and evaluated by X-ray photoelectron spectromicroscopy. The creation of defects induced by the ions drives the formation of different nitrogen species (pyridinic, pyrrolic, and graphitic) at the CNT surface. While nitrogen implantation in CNT sidewalls has results similar to implantation in graphene, where mainly nitrogen sp2 bonding configuration occurs, we obsd. a different behavior at the CNT tips, where nitrogen incorporation is also more efficient. A large amt. of pyrrolic nitrogen is obsd. at the CNT tips compared to the amt. at the CNT sidewalls for the same ion implantation parameters. This indicates a different reactivity of the CNT tips where the presence of natural defects may be involved in different nitrogen bonding formations between carbon and nitrogen with respect to the CNT sidewalls.
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    Susi, T.; Kaukonen, M.; Havu, P.; Ljungberg, M. P.; Ayala, P.; Kauppinen, E. I. Core level binding energies of functionalized and defective graphene. Beilstein Journal of Nanotechnology 2014, 5, 121– 132,  DOI: 10.3762/bjnano.5.12
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    Core level binding energies of functionalized and defective graphene
    Susi Toma; Kaukonen Markus; Havu Paula; Ljungberg Mathias P; Ayala Paola; Kauppinen Esko I
    Beilstein journal of nanotechnology (2014), 5 (), 121-32 ISSN:2190-4286.
    X-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn-Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone-Thrower-Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.
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  32. 32
    Massimi, L.; Ourdjini, O.; Lafferentz, L.; Koch, M.; Grill, L.; Cavaliere, E.; Gavioli, L.; Cardoso, C.; Prezzi, D.; Molinari, E.; Ferretti, A.; Mariani, C.; Betti, M. G. Surface-Assisted Reactions toward Formation of Graphene Nanoribbons on Au(110) Surface. J. Phys. Chem. C 2015, 119, 2427– 2437,  DOI: 10.1021/jp509415r
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    Surface-Assisted Reactions toward Formation of Graphene Nanoribbons on Au(110) Surface
    Massimi, Lorenzo; Ourdjini, Oualid; Lafferentz, Leif; Koch, Matthias; Grill, Leonhard; Cavaliere, Emanuele; Gavioli, Luca; Cardoso, Claudia; Prezzi, Deborah; Molinari, Elisa; Ferretti, Andrea; Mariani, Carlo; Betti, Maria Grazia
    Journal of Physical Chemistry C (2015), 119 (5), 2427-2437CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Scanning tunneling microscopy and X-ray spectroscopy measurements were combined with first-principles simulations to investigate the formation of graphene nanoribbons (GNRs) on Au(110), as based on the surface-mediated reaction of 10,10'-dibromo-9,9'-bianthracene (DBBA) mols. At variance with Au(111), two different pathways are identified for the GNR self-assembly on Au(110), as controlled by both the adsorption temp. and the surface coverage of the DBBA mol. precursors. Room-temp. DBBA deposition on Au(110) leads to the same reaction steps obtained on Au(111), even though with lower activation temps. For DBBA deposition at 470 K, the cyclodehydrogenation of the precursors precedes their polymn., and the GNR formation is fostered by increasing the surface coverage. While the initial stages of the reaction are found to crucially det. the final configuration and orientation of the GNRs, the mol. diffusion is found to limit in both cases the formation of high-d. long-range ordered GNRs. Overall, the direct comparison between the Au(110) and Au(111) surfaces unveils the delicate interplay among the different factors driving the growth of GNRs.
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    D’Acunto, G.; Ripanti, F.; Postorino, P.; Betti, M. G.; Scardamaglia, M.; Bittencourt, C.; Mariani, C. Channelling and induced defects at ion-bombarded aligned multiwall carbon nanotubes. Carbon 2018, 139, 768– 775,  DOI: 10.1016/j.carbon.2018.07.032
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    Channelling and induced defects at ion-bombarded aligned multiwall carbon nanotubes
    D'Acunto, Giulio; Ripanti, Francesca; Postorino, Paolo; Betti, Maria Grazia; Scardamaglia, Mattia; Bittencourt, Carla; Mariani, Carlo
    Carbon (2018), 139 (), 768-775CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    A detailed investigation of ion channelling and defect prodn. for a highly-ordered array of multi-wall carbon nanotubes is presented. The effects of argon ion bombardment (0.25-5 keV) carried out either parallel (top) or perpendicular (side) to their axis, have been studied by Raman, XPS and SEM. Raman spectra provided evidence of channelling of the Ar+ ions obsd. for top bombardment along the whole 180 μm carbon nanotube length, while the penetration length is limited to the first 10 μm when the ions impinge from the side. The nature of defects, detd. through the spectral fingerprints of the C 1s core level as a function of energy and flux, unveils a distorted sp3-like bonding increase and the π-excitation decrease till quenching. Dangling bond states due to displaced carbon atoms become significant only at beam energies higher than 0.25 keV and high flux. These results on anisotropic channelling and selective defects creation open new perspectives in the application of highly-ordered arrays of multi-wall carbon nanotubes as anisotropic detectors.
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    Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558– 1565,  DOI: 10.1016/j.carbon.2007.02.034
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    Carbon (2007), 45 (7), 1558-1565CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Redn. of a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high-surface-area carbon material which consists of thin graphene-based sheets. The reduced material was characterized by elemental anal., thermogravimetric anal., SEM, XPS, NMR spectroscopy, Raman spectroscopy, and elec. cond. measurements.
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    Shin, Y.-E.; Sa, Y. J.; Park, S.; Lee, J.; Shin, K.-H.; Joo, S. H.; Ko, H. An ice-templated, pH-tunable self-assembly route to hierarchically porous graphene nanoscroll networks. Nanoscale 2014, 6, 9734– 9741,  DOI: 10.1039/C4NR01988A
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    An ice-templated, pH-tunable self-assembly route to hierarchically porous graphene nanoscroll networks
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    Nanoscale (2014), 6 (16), 9734-9741CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Porous graphene nanostructures are of great interest for applications in catalysis and energy storage. However, the fabrication of 3D macroporous graphene nanostructures with controlled morphol., porosity, and surface area still presents significant challenges. Introduced is an ice-templated self-assembly approach for the integration of 2D graphene nanosheets into hierarchically porous graphene nanoscroll networks, where the morphol. of porous structures can be easily controlled by varying the pH conditions during the ice-templated self-assembly process. Freeze-casting of reduced graphene oxide (rGO) soln. results in the formation of 3D porous graphene microfoam below pH 8 and hierarchically porous graphene nanoscroll networks at pH 10. Graphene nanoscroll networks show promising electrocatalytic activity for the oxygen redn. reaction (ORR).
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    Jiménez-Arévalo, N.; Leardini, F.; Ferrer, I. J.; Ares, J. R.; Sánchez, C.; Saad Abdelnabi, M. M.; Betti, M. G.; Mariani, C. Ultrathin Transparent B–C–N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction. ACS Applied Energy Materials 2020, 3, 1922– 1932,  DOI: 10.1021/acsaem.9b02339
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    Ultrathin Transparent B-C-N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction
    Jimenez-Arevalo, Nuria; Leardini, Fabrice; Ferrer, Isabel J.; Ares, Jose Ramon; Sanchez, Carlos; Saad Abdelnabi, Mahmoud M.; Betti, Maria Grazia; Mariani, Carlo
    ACS Applied Energy Materials (2020), 3 (2), 1922-1932CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)
    Ultrathin B-C-N layers grown on Ti substrates are investigated as efficient anodes for electrochem. water splitting. A fast and direct synthetic route has been used based on plasma-enhanced chem. vapor deposition with methylamine borane as a single-source mol. precursor. The effect of growth time on the morphol. and structural properties and on the chem. compn. of the layers has been investigated by SEM, Raman spectroscopy, XPS, and transmission electron microscopy coupled with electron energy loss spectroscopy. Flat B-C-N layers on top of an amorphous titanium oxide layer present at the Ti surface have been obtained by using short growth times, while longer growth times give rise to core/shell structures formed by vertical wall B-C-N layers and titanium carbonitride phases. The obtained layers present enhanced electrocatalytic activity for the oxygen evolution reaction in alk. aq. solns. Moreover, because of their ultrathin nature, the B-C-N layers preserve the photocurrents of the underlying titanium oxide layer, acting as transparent electrodes with high cond. for the photogenerated charge carriers and improved electrocatalytic activity for the oxidn. of water to oxygen gas.
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    Luo, Z.; Yu, T.; Kim, K.-j.; Ni, Z.; You, Y.; Lim, S.; Shen, Z.; Wang, S.; Lin, J. Thickness-Dependent Reversible Hydrogenation of Graphene Layers. ACS Nano 2009, 3, 1781– 1788,  DOI: 10.1021/nn900371t
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    Thickness-dependent reversible hydrogenation of graphene layers
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    ACS Nano (2009), 3 (7), 1781-1788CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Graphene layers on SiO2/Si substrate were chem. decorated by r.f. H plasma. H coverage investigation by Raman spectroscopy and micro-XPS characterization demonstrates that the hydrogenation of single layer graphene on SiO2/Si substrate is much less feasible than that of bilayer and multilayer graphene. Both the hydrogenation and dehydrogenation process of the graphene layers are controlled by the corresponding energy barriers, which show significant dependence on the no. of layers. The extent of decorated C atoms in graphene layers can be manipulated reversibly up to the satn. coverage, which facilitates engineering of chem. decorated graphene with various functional groups via plasma techniques.
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    Zhou, J.; Wang, Q.; Sun, Q.; Chen, X. S.; Kawazoe, Y.; Jena, P. Ferromagnetism in Semihydrogenated Graphene Sheet. Nano Lett. 2009, 9, 3867– 3870,  DOI: 10.1021/nl9020733
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    Ferromagnetism in Semihydrogenated Graphene Sheet
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    Nano Letters (2009), 9 (11), 3867-3870CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Single layer of graphite (graphene) was predicted and later exptl. confirmed to undergo metal-semiconductor transition when fully hydrogenated (graphane). Using d. functional theory when half of the hydrogen in this graphane sheet is removed, the resulting semihydrogenated graphene (which the authors refer to as graphone) becomes a ferromagnetic semiconductor with a small indirect gap. Half-hydrogenation breaks the delocalized π bonding network of graphene, leaving the electrons in the unhydrogenated carbon atoms localized and unpaired. The magnetic moments at these sites couple ferromagnetically with an estd. Curie temp. between 278 and 417 K, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. This is very different from the widely studied finite graphene nanostrucures such as 1-dimensional nanoribbons and two-dimensional nanoholes, where zigzag edges are necessary for magnetism. From graphene to graphane and to graphone, the system evolves from metallic to semiconducting and from nonmagnetic to magnetic. Hydrogenation provides a novel way to tune the properties with unprecedented potentials for applications.
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    Onida, G.; Reining, L.; Rubio, A. Electronic excitations: density-functional versus many-body Green’s-function approaches. Rev. Mod. Phys. 2002, 74, 601– 659,  DOI: 10.1103/RevModPhys.74.601
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    Electronic excitations: density-functional versus many-body Green's-function approaches
    Onida, Giovanni; Reining, Lucia; Rubio, Angel
    Reviews of Modern Physics (2002), 74 (2), 601-659CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)
    A review. Electronic excitations lie at the origin of most of the commonly measured spectra. However, the 1st-principles computation of excited states requires a larger effort than ground-state calcns., which can be very efficiently carried out within d.-functional theory. However, two theor. and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a 1-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy Σ and the electron-hole interaction. A good approxn. for Σ was obtained with Hedin's GW approach, using d.-functional theory as a zero-order soln. First-principles GW calcns. for real systems were successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional deriv. of Σ. An alternative approach to calcg. electronic excitations is the time-dependent d.-functional theory (TDDFT), which offers the important practical advantage of a dependence on d. rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-d. approxn. gave promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theor. and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress.
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    While not having information on the position of the conduction band bottom from experiments, we though observe that the pristine NPG is undoped, with the Dirac point at the Fermi level. We can thus expect a similar behavior for the H-NPG sample, which supports the assumption of the Fermi level lying approximately at midgap.

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    A review. The accuracy and efficiency of electronic-structure methods to understand, predict and design the properties of materials has driven a new paradigm in research. Simulations can greatly accelerate the identification, characterization and optimization of materials, with this acceleration driven by continuous progress in theory, algorithms and hardware, and by adaptation of concepts and tools from computer science. Nevertheless, the capability to identify and characterize materials relies on the predictive accuracy of the underlying phys. descriptions, and on the ability to capture the complexity of realistic systems. We provide here an overview of electronic-structure methods, of their application to the prediction of materials properties, and of the different strategies employed towards the broader goals of materials design and discovery.
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    Ito, Y.; Qiu, H.-J.; Fujita, T.; Tanabe, Y.; Tanigaki, K.; Chen, M. Bicontinuous Nanoporous N-doped Graphene for the Oxygen Reduction Reaction. Adv. Mater. 2014, 26, 4145– 4150,  DOI: 10.1002/adma.201400570
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    Bicontinuous Nanoporous N-doped Graphene for the Oxygen Reduction Reaction
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    Advanced Materials (Weinheim, Germany) (2014), 26 (24), 4145-4150CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A bicontinuous nanoporous, N-doped graphene layer was used to fabricate nickel-based fuel cell cathodes by chem. vapor deposition. Nanoporous nickel substrates were prepd. by leaching (i.e., chem. dealloying in 1.0 M (NH4)2SO4) of annealed Ni30Mn70 cold-rolled sheets. N-doped graphene sheets were fabricated by graphene growth from added pyridine, in which a 2D-graphene structure as a 3D graphene material. The 3D graphene material is characterized by a large surface area, a high elec. cond., high electrochem. stability, and high catalytic activity.
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    Ito, Y.; Cong, W.; Fujita, T.; Tang, Z.; Chen, M. High Catalytic Activity of Nitrogen and Sulfur Co-Doped Nanoporous Graphene in the Hydrogen Evolution Reaction. Angew. Chem., Int. Ed. 2015, 54, 2131– 2136,  DOI: 10.1002/anie.201410050
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    High Catalytic Activity of Nitrogen and Sulfur Co-Doped Nanoporous Graphene in the Hydrogen Evolution Reaction
    Ito, Yoshikazu; Cong, Weitao; Fujita, Takeshi; Tang, Zheng; Chen, Mingwei
    Angewandte Chemie, International Edition (2015), 54 (7), 2131-2136CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Chem. doping has been demonstrated to be an effective way to realize new functions of graphene as metal-free catalyst in energy-related electrochem. reactions. Although efficient catalysis for the oxygen redn. reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co-doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt-free HER catalyst, 2D MoS2. The interplay between the chem. dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis.
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    Ito, Y.; Tanabe, Y.; Han, J.; Fujita, T.; Tanigaki, K.; Chen, M. Multifunctional Porous Graphene for High-Efficiency Steam Generation by Heat Localization. Adv. Mater. 2015, 27, 4302– 4307,  DOI: 10.1002/adma.201501832
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    Multifunctional Porous Graphene for High-Efficiency Steam Generation by Heat Localization
    Ito, Yoshikazu; Tanabe, Yoichi; Han, Jiuhui; Fujita, Takeshi; Tanigaki, Katsumi; Chen, Mingwei
    Advanced Materials (Weinheim, Germany) (2015), 27 (29), 4302-4307CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A solar heating unit to directly heat water droplets to steam for high-efficiency steam generation by heat localization is based on a multifunctional three-dimensional porous graphene doped with graphitic, pyridinic, and N-oxide-type nitrogen atoms. Recent d. functional theory calcns. indicate that doped nitrogen atoms in graphene lattices change the Gibbs free energy of H* absorption from pos. of pure graphene to neg., which could be the underlying mechanism that gives rise to the enhanced wettability of graphene for fast water delivery. The porous graphene materials, particularly with nitrogen doping, have a low sp. heat, effective light absorption, low thermal cond., and mesoscopic porosity, which meet all the requirements for effective steam generation by heat localization. A single piece of porous graphene can realize the energy conversion from sunlight to high-energy steam at high energy efficiency of 80%.
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    Hu, K.; Qin, L.; Zhang, S.; Zheng, J.; Sun, J.; Ito, Y.; Wu, Y. Building a Reactive Armor Using S-Doped Graphene for Protecting Potassium Metal Anodes from Oxygen Crossover in K–O2 Batteries. ACS Energy Letters 2020, 5, 1788– 1793,  DOI: 10.1021/acsenergylett.0c00715
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    Building a Reactive Armor Using S-Doped Graphene for Protecting Potassium Metal Anodes from Oxygen Crossover in K-O2 Batteries
    Hu, Kailong; Qin, Lei; Zhang, Songwei; Zheng, Jingfeng; Sun, Jiaonan; Ito, Yoshikazu; Wu, Yiying
    ACS Energy Letters (2020), 5 (6), 1788-1793CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
    Protecting alkali metals from oxygen crossover is a key unsolved challenge in metal-oxygen batteries. Herein, a new "reactive-armor strategy" is reported by using freestanding three-dimensional sulfur (S)-doped graphene with bicontinuous pore channels for protecting potassium (K) anodes from the undesired oxygen crossover. XPS and Fourier-transform IR results show that the S-dopants react with oxygen/superoxide species to form anionic sulfonate/sulfate that locally promotes the nucleation and growth of KO2. The resultant KO2 layer anchored on the graphene outer surface acts as a barrier layer that prevents oxygen from reaching the K metal surface. After 140 cycles (> 550 h), the protected K metal anodes still maintain metallic luster with little accumulation of byproducts. The use of organosulfur to build a reactive armor is applicable to other metal-oxygen batteries in suppressing the parasitic damage from oxygen crossover.
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    QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
    Giannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata M
    Journal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.
    QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
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    Advanced capabilities for materials modelling with QUANTUM ESPRESSO
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    Journal of Physics: Condensed Matter (2017), 29 (46), 465901/1-465901/30CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
    QUANTUM ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on d.-functional theory, d.-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. QUANTUM ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.
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    Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
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    Fully nonlocal two-projector norm-conserving pseudopotentials are shown to be compatible with a systematic approach to the optimization of convergence with the size of the plane-wave basis. A reformulation of the optimization is developed, including the ability to apply it to pos.-energy at. scattering states and to enforce greater continuity in the pseudopotential. The generalization of norm conservation to multiple projectors is reviewed and recast for the present purposes. Comparisons among the results of all-electron and one- and two-projector norm-conserving pseudopotential calcns. of lattice consts. and bulk moduli are made for a group of solids chosen to represent a variety of types of bonding and a sampling of the periodic table.
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  1. Dario Marchiani, Riccardo Frisenda, Carlo Mariani, José Avila, Pavel Dudin, Hayato Sueyoshi, Samuel Jeong, Yoshikazu Ito, Oreste De Luca, Sara Macchi, Marco Papagno, Raffaele G. Agostino, Daniela Pacilé, Maria Grazia Betti. Alkali Metals Adsorbed on Nanoporous Graphene: Charge Transfer and Metallic Phase. The Journal of Physical Chemistry C 2024, 128 (27) , 11255-11262. https://doi.org/10.1021/acs.jpcc.4c02915
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  • Abstract

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    Figure 1

    Figure 1. (a) Optical picture of an NPG sample. (b) SEM image of NPG (10 × 10 μm2). (c) Micro-Raman spectrum taken with a 100× objective (Gaussian laser spot size with σ = 280 nm). (d) Spatially resolved micro-Raman map of the 2D/G band intensity ratio, 4 × 4 μm2 image formed by 167 × 167 nm2 pixels. (e) Spatially integrated C 1s XPS spectrum, taken with 350 eV photon energy. (f) Spatially resolved micro-X-ray photoelectron spectroscopy (micro-XPS) map of the C 1s core level intensity (282–288 eV energy range), 20 × 20 μm2 image formed by 500 × 500 nm2 pixels.

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    Figure 2

    Figure 2. C 1s core level XPS spectra of UHV-clean NPG (top), and after atomic H exposure as a function of the exposure time, up to H saturation (300 min); experimental data (solid lines), sp2 (pinkish peaks) and sp3 (bluish peaks) fitting components.

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    Figure 3

    Figure 3. (a) C 1s intensity map, quantified as the ratio Isp2/(Isp2 + Isp3), after background subtraction; the blow-up represents the same ratio in a 10 × 10 μm2 area; the spectra taken in the sp2-rich and in sp3-rich regions (labeled by a cross and a star, respectively) are shown in panels (b) and (c), respectively. (d) Valence band (VB) intensity map corresponding to the 2p-π intensity. The ratio was calculated as in panel (a); the intensity was found by integrating in the energy range indicated by the shadowed vertical ribbon in panel (e), which displays the VB spectrum for sp2-rich (cross) and sp3-rich (star) regions.

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    Figure 4

    Figure 4. (a) Experimental VB spectra for clean (dashed) and totally hydrogenated NPG (solid line), taken with HeIα (21.218 eV) photon energy. (b) Three model structures of 1-side and 2-side hydrogenated single- and bilayer graphene (top and side views). The colored circles in the top view highlight the H sites in the hexagon. (c) Simulated quasi-particle density of states (DoS) in the GW approximation for the models in (b); zero energy set at midgap; a homogeneous broadening of 140 meV is applied. (d) Simulated DFT (solid gray lines) and GW (open circles) band structures for the corresponding models in (b); zero energy set at the VBM.

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      Felten, A.; McManus, D.; Rice, C.; Nittler, L.; Pireaux, J.-J.; Casiraghi, C.
      Applied Physics Letters (2014), 105 (18), 183104/1-183104/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Plasma hydrogenation of graphene was proposed as a tool to modify the properties of graphene. However, H plasma is a complex system and controlled hydrogenation of graphene suffers from a lack of understanding of the plasma chem. Here, we correlate the modifications induced on monolayer graphene studied by Raman spectroscopy with the hydrogen ions energy distributions obtained by mass spectrometry. We measure the energy distribution of H+, H2+, and H3+ ions for different plasma conditions showing that their energy strongly depends on the sample position, pressure, and plasma power and can reach values as high as 45 eV. Based on these measurements, we speculate that under specific plasma parameters, protons should possess enough energy to penetrate the graphene sheet. Therefore, a graphene membrane could become, under certain conditions, transparent to both protons and electrons. (c) 2014 American Institute of Physics.
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    11. 11
      Panahi, M.; Solati, N.; Kaya, S. Modifying hydrogen binding strength of graphene. Surf. Sci. 2019, 679, 24– 30,  DOI: 10.1016/j.susc.2018.08.009
      11
      Modifying hydrogen binding strength of graphene
      Panahi, Mohammad; Solati, Navid; Kaya, Sarp
      Surface Science (2019), 679 (), 24-30CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
      The effect of the substrate on the binding strength of hydrogen on single layer graphene grown on Pt(111) surfaces has been investigated via detg. its desorption activation energy. We showed that subsurface alloys on Pt(111) can dramatical modify the C-H bond strength in hydrogenated graphene. Various 3d metals, vanadium, iron, cobalt, and nickel were deposited in the subsurface layer to modify the chem. and electronic properties of the substrate. Anal. of the temp. programmed desorption data shows that subsurface alloys reduce the hydrogen desorption activation energy by weakening C-H bond energy in graphene, down to ∼57 kJ/mol in the case of Pt/Co/Pt(111) as compared to ∼111 kJ/mol obtained from hydrogenated graphene grown on a bare Pt(111).
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    12. 12
      Abdelnabi, M. M. S.; Blundo, E.; Betti, M. G.; Cavoto, G.; Placidi, E.; Polimeni, A.; Ruocco, A.; Hu, K.; Ito, Y.; Mariani, C. Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene. Nanotechnology 2021, 32, 035707,  DOI: 10.1088/1361-6528/abbe56
      12
      Towards free-standing graphane: atomic hydrogen and deuterium bonding to nano-porous graphene
      Abdelnabi, Mahmoud Mohamed Saad; Blundo, Elena; Betti, Maria Grazia; Cavoto, Gianluca; Placidi, Ernesto; Polimeni, Antonio; Ruocco, Alessandro; Hu, Kailong; Ito, Yoshikazu; Mariani, Carlo
      Nanotechnology (2021), 32 (3), 035707CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
      Graphane is formed by bonding hydrogen (and deuterium) atoms to carbon atoms in the graphene mesh, with modification from the pure planar sp2 bonding towards an sp3 configuration. Atomic hydrogen (H) and deuterium (D) bonding with C atoms in fully free-standing nano porous graphene (NPG) is achieved, by exploiting low-energy proton (or deuteron) non-destructive irradn., with unprecedented minimal introduction of defects, as detd. by Raman spectroscopy and by the C 1s core level lineshape anal. Evidence of the H- (or D-) NPG bond formation is obtained by bringing to light the emergence of a H- (or D-) related sp3-distorted component in the C 1s core level, clear fingerprint of H-C (or D-C) covalent bonding. The H (or D) bonding with the C atoms of free-standing graphene reaches more than 1/4 (or 1/3) at% coverage. This non-destructive H-NPG (or D-NPG) chemisorption is very stable at high temps. up to about 800 K, as monitored by Raman and XPS, with complete healing and restoring of clean graphene above 920 K. The excellent chem. and temp. stability of H- (and D-) NPG opens the way not only towards the formation of semiconducting graphane on large-scale samples, but also to stable graphene functionalisation enabling futuristic applications in advanced detectors for the β-spectrum anal.
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    13. 13
      Abdelnabi, M. M. S.; Izzo, C.; Blundo, E.; Betti, M. G.; Sbroscia, M.; Di Bella, G.; Cavoto, G.; Polimeni, A.; García-Cortés, I.; Rucandio, I.; Moroño, A.; Hu, K.; Ito, Y.; Mariani, C. Deuterium Adsorption on Free-Standing Graphene. Nanomaterials 2021, 11, 130,  DOI: 10.3390/nano11010130
      13
      Deuterium adsorption on free-standing graphene
      Abdelnabi, Mahmoud Mohamed Saad; Izzo, Chiara; Blundo, Elena; Betti, Maria Grazia; Sbroscia, Marco; Di Bella, Giulia; Cavoto, Gianluca; Polimeni, Antonio; Garcia-Cortes, Isabel; Rucandio, Isabel; Morono, Alejandro; Hu, Kailong; Ito, Yoshikazu; Mariani, Carlo
      Nanomaterials (2021), 11 (1), 130CODEN: NANOKO; ISSN:2079-4991. (MDPI AG)
      A suitable way to modify the electronic properties of graphene-while maintaining the exceptional properties assocd. with its two-dimensional (2D) nature-is its functionalisation. In particular, the incorporation of hydrogen isotopes in graphene is expected to modify its electronic properties leading to an energy gap opening, thereby rendering graphene promising for a widespread of applications. Hence, deuterium (D) adsorption on free-standing graphene was obtained by highenergy electron ionisation of D2 and ion irradn. of a nanoporous graphene (NPG) sample. This method allows one to reach nearly 50 at.% D upload in graphene, higher than that obtained by other deposition methods so far, towards low-defect and free-standing D-graphane. That evidence was deduced by XPS of the C 1s core level, showing clear evidence of the D-C sp3 bond, and Raman spectroscopy, pointing to remarkably clean and low-defect prodn. of graphane. Moreover, UPS showed the opening of an energy gap in the valence band. Therefore, high-energy electron ionisation and ion irradn. is an outstanding method for obtaining low defect D-NPG with a high D upload, which is very promising for the fabrication of semiconducting graphane on large scale.
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    14. 14
      Zhao, F.; Raitses, Y.; Yang, X.; Tan, A.; Tully, C. G. High hydrogen coverage on graphene via low temperature plasma with applied magnetic field. Carbon 2021, 177, 244– 251,  DOI: 10.1016/j.carbon.2021.02.084
      14
      High hydrogen coverage on graphene via low temperature plasma with applied magnetic field
      Zhao, Fang; Raitses, Yevgeny; Yang, Xiaofang; Tan, Andi; Tully, Christopher G.
      Carbon (2021), 177 (), 244-251CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      The chem. functionalization of two-dimensional materials is an effective method for tailoring their chem. and electronic properties with encouraging applications in energy, catalysis, and electronics. One exemplary 2D material with remarkable properties, graphene, can be exploited for hydrogen storage and large on/off ratio devices by hydrogen termination. In this work, we describe a promising plasma-based method to provide high hydrogen coverage on graphene. A low pressure (∼10 mtorr) discharge generates a fine-tunable low-temp. hydrogen-rich plasma in the applied radial elec. and axial magnetic fields. Post-run characterization of these samples using Raman spectroscopy and XPS demonstrates a higher hydrogen coverage, 35.8%, than the previously reported results using plasmas. Plasma measurements indicate that with the applied magnetic field, the d. of hydrogen atoms can be more than 10 times larger than the d. without the magnetic field. With the applied elec. field directed away from the graphene substrate, the flux of plasma ions towards this substrate and the ion energy are insufficient to cause measurable damage to the treated 2D material. The low damage allows a relatively long treatment time of the graphene samples that contributes to the high coverage obtained in these expts.
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    15. 15
      Whitener, K. E.; Lee, W. K.; Campbell, P. M.; Robinson, J. T.; Sheehan, P. E. Chemical hydrogenation of single-layer graphene enables completely reversible removal of electrical conductivity. Carbon 2014, 72, 348– 353,  DOI: 10.1016/j.carbon.2014.02.022
      15
      Chemical hydrogenation of single-layer graphene enables completely reversible removal of electrical conductivity
      Whitener, Keith E.; Lee, Woo K.; Campbell, Paul M.; Robinson, Jeremy T.; Sheehan, Paul E.
      Carbon (2014), 72 (), 348-353CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      The chem. modification of graphene greatly expands its potential applications in electronics, chem., and biol. Here, we report the rapid and extensive hydrogenation of single layer CVD graphene using the Birch redn. method. This method hydrogenates much more extensively than cold plasmas and electrochem. methods. Moreover, use of single layer graphene enables greater control of electronic cond. than previously achieved with the Birch method using multilayer graphene or graphene oxide. Indeed, this method enables both the elimination of electronic cond. through hydrogenation and the subsequent recovery of essentially pristine graphene with thermal annealing-a reversible >107 fold change in resistance. Raman and photoelectron spectroscopies show that the reaction is complete within 90 s of immersion. Finally, we show that we can use the Birch redn. to functionalize graphene with tributyltin moieties.
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    16. 16
      Son, J.; Lee, S.; Kim, S. J.; Park, B. C.; Lee, H.-K.; Kim, S.; Kim, J. H.; Hong, B. H.; Hong, J. Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor. Nat. Commun. 2016, 7, 13261,  DOI: 10.1038/ncomms13261
      16
      Hydrogenated monolayer graphene with reversible and tunable wide band gap and its field-effect transistor
      Son, Jangyup; Lee, Soogil; Kim, Sang Jin; Park, Byung Cheol; Lee, Han-Koo; Kim, Sanghoon; Kim, Jae Hoon; Hong, Byung Hee; Hong, Jongill
      Nature Communications (2016), 7 (), 13261CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Graphene is currently at the forefront of cutting-edge science and technol. due to exceptional electronic, optical, mech., and thermal properties. However, the absence of a sizeable band gap in graphene has been a major obstacle for application. To open and control a band gap in functionalized graphene, several gapping strategies have been developed. In particular, hydrogen plasma treatment has triggered a great scientific interest, because it has been known to be an efficient way to modify the surface of single-layered graphene and to apply for std. wafer-scale fabrication. Here we show a monolayer chem.-vapor-deposited graphene hydrogenated by indirect hydrogen plasma without structural defect and we demonstrate that a band gap can be tuned as wide as 3.9 eV by varying hydrogen coverage. We also show a hydrogenated graphene field-effect transistor, showing that on/off ratio changes over three orders of magnitude at room temp.
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    17. 17
      Haberer, D. Electronic properties of hydrogenated quasi-free-standing graphene. physica status solidi (b) 2011, 248, 2639– 2643,  DOI: 10.1002/pssb.201100521
      17
      Electronic properties of hydrogenated quasi-free-standing graphene
      Haberer, D.; Petaccia, L.; Wang, Y.; Quian, H.; Farjam, M.; Jafari, S. A.; Sachdev, H.; Federov, A. V.; Usachov, D.; Vyalikh, D. V.; Liu, X.; Vilkov, O.; Adamchuk, V. K.; Irle, S.; Knupfer, M.; Buechner, B.; Grueneis, A.
      Physica Status Solidi B: Basic Solid State Physics (2011), 248 (11), 2639-2643CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Tailoring the electronic properties of graphene is of fundamental interest regarding its application in electronic devices. One of the key strategies is chem. functionalization which modifies the π-electron system and thus can induce band gaps. However, in order to control the degree of functionalization it is crucial to know the exact amt. of the chemisorbed species. We show with angle-resolved photoemission spectroscopy (ARPES) the formation of a band gap in graphene and est. the hydrogen coverage from the scattering rate. Using X-ray photoemission spectroscopy (XPS) we identify the chem. environments in hydrogenated graphene and det. the total hydrogen to carbon (H/C)-ratio directly from the spectra. We then compare ARPES and XPS as tools for detg. the H/C-ratio and discuss the results from mol. dynamics (MD) simulations. Angle-resolved photoemission spectra of (left panel) pristine graphene intercalated with Au and (right panel) hydrogenated graphene on Au with an estd. H-coverage of 5.8%. Besides the formation of a band gap, a broadening is observable which can be used to det. the H amt. Both spectra show the π-band at the K-point.
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    18. 18
      Eng, A. Y. S.; Sofer, Z.; Bouša, D.; Sedmidubský, D.; Huber, t.; Pumera, M. Near-Stoichiometric Bulk Graphane from Halogenated Graphenes (X = Cl/Br/I) by the Birch Reduction for High Density Energy Storage. Adv. Funct. Mater. 2017, 27, 1605797,  DOI: 10.1002/adfm.201605797
      There is no corresponding record for this reference.
    19. 19
      Di Bernardo, I.; Avvisati, G.; Mariani, C.; Motta, N.; Chen, C.; Avila, J.; Asensio, M. C.; Lupi, S.; Ito, Y.; Chen, M.; Fujita, T.; Betti, M. G. Two-Dimensional Hallmark of Highly Interconnected Three-Dimensional Nanoporous Graphene. ACS Omega 2017, 2, 3691– 3697,  DOI: 10.1021/acsomega.7b00706
      19
      Two-Dimensional Hallmark of Highly Interconnected Three-Dimensional Nanoporous Graphene
      Di Bernardo, Iolanda; Avvisati, Giulia; Mariani, Carlo; Motta, Nunzio; Chen, Chaoyu; Avila, Jose; Asensio, Maria Carmen; Lupi, Stefano; Ito, Yoshikazu; Chen, Mingwei; Fujita, Takeshi; Betti, Maria Grazia
      ACS Omega (2017), 2 (7), 3691-3697CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) mm-size architecture without compromising its remarkable elec., optical and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining state-of-the-art spectro-microscopy and imaging techniques. The connected and bi-continuous topol., without frayed borders and edges, and with low d. of cryst. defects, has been unveiled via helium ion microscopy, Raman and transmission electron microscopy down to the at. scale. Most importantly, nano-scanning photoemission unravels a 3D NPG structure with preserved 2D electronic d. of states (Dirac conelike) throughout the porous sample. Furthermore, the high spatial resoln. brings to light the interrelationship between the topol. and the morphol. in the wrinkled and highly bent regions, where distorted sp2 C bonds, assocd. to sp3 -like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small size individual graphene sheets, and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.
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    20. 20
      Di Bernardo, I.; Avvisati, G.; Chen, C.; Avila, J.; Asensio, M. C.; Hu, K.; Ito, Y.; Hines, P.; Lipton-Duffin, J.; Rintoul, L.; Motta, N.; Mariani, C.; Betti, M. G. Topology and doping effects in three-dimensional nanoporous graphene. Carbon 2018, 131, 258– 265,  DOI: 10.1016/j.carbon.2018.01.076
      20
      Topology and doping effects in three-dimensional nanoporous graphene
      Di Bernardo, Iolanda; Avvisati, Giulia; Chen, Chaoyu; Avila, Jose; Asensio, Maria Carmen; Hu, Kailong; Ito, Yoshikazu; Hines, Peter; Lipton-Duffin, Josh; Rintoul, Llew; Motta, Nunzio; Mariani, Carlo; Betti, Maria Grazia
      Carbon (2018), 131 (), 258-265CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      We report on a spatial mapping of the electronic and vibrational structure of three-dimensional (3D) nanoporous graphene architectures, which have a hierarchical pore structure. We demonstrate that the topol., curvature, and pores lead to local changes in the electronic and vibrational structure and in the hybridization states of the carbon atoms (sp2 vs. sp3-like). Nitrogen substitutions in pyrrolic bonding configurations also contribute to local distortions of the planar geometry of graphene. The distortions influence the electronic d. of states at the Fermi level by shifting the Dirac cone apex, opening potential avenues for applications of two-dimensional graphene in 3D devices.
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    21. 21
      Sha, X.; Jackson, B. First-principles study of the structural and energetic properties of H atoms on a graphite (0001) surface. Surf. Sci. 2002, 496, 318– 330,  DOI: 10.1016/S0039-6028(01)01602-8
      21
      First-principles study of the structural and energetic properties of H atoms on a graphite (0 0 0 1) surface
      Sha, Xianwei; Jackson, Bret
      Surface Science (2002), 496 (3), 318-330CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)
      Electronic structure calcns. based on spin-polarized d. functional theory with the generalized gradient approxn. and ultrasoft pseudopotentials are used to investigate the interaction between H atoms and a graphite (0 0 0 1) surface. An asym. slab supercell approach is employed to model the graphite surface. The calcd. equil. properties of bulk graphite, the H mol. and the graphite (0 0 0 1) surface are all in good agreement with exptl. data. The interaction of H with 3 high-symmetry sites on a graphite surface is considered. A broad and site-independent H physisorption region centered at around 4 Å above the surface has a small binding energy of 8 meV. A localized stable chem. adsorption site can be found only when H is placed on the top site, with the help of substantial surface reconstruction. The reaction of a gas-phase H atom with an H adsorbed in the chemisorption site is then considered. Numerous total energy points are computed in the region of configuration space believed to be important for this Eley-Rideal reaction. Our results are in good agreement with the studies of Sidis and co-workers [Chem. Phys. Lett. 300 (1991) 157, Proc. Conf. H2 in space]. Preliminary results from a quantum scattering calcn. using a model potential energy surface fit to these points are presented. The trapping and recombination of H atoms on graphite surfaces is discussed, taking surface reconstructions into consideration.
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    22. 22
      Ruffieux, P.; Gröning, O.; Bielmann, M.; Mauron, P.; Schlapbach, L.; Gröning, P. Hydrogen adsorption on sp2-bonded carbon: Influence of the local curvature. Phys. Rev. B 2002, 66, 245416,  DOI: 10.1103/PhysRevB.66.245416
      22
      Hydrogen adsorption on sp2-bonded carbon. Influence of the local curvature
      Ruffieux, P.; Groning, O.; Bielmann, M.; Mauron, P.; Schlapbach, L.; Groning, P.
      Physical Review B: Condensed Matter and Materials Physics (2002), 66 (24), 245416/1-245416/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The interaction of at. hydrogen and low-energy hydrogen ions with sp2-bonded carbon is investigated on the surfaces of C60 multilayer films, single-walled C nanotubes, and graphite (0001). These 3 materials were chosen to represent sp2-bonded carbon networks with different local curvatures and closed surfaces (i.e. no dangling bonds). Chemisorption of H on these surfaces reduces emission from photoemission features assocd. with the π electrons and leads to a lowering of the work function up to 1.3 eV. The energy barrier for H adsorption decreases with increasing local curvature of the carbon surface. Whereas in the case of C60 and single-walled C nanotubes, H adsorption can be achieved by exposure to at. H, the H adsorption on graphite (0001) requires H+ ions of low kinetic energy (∼1 eV). On all 3 materials, the adsorption energy barrier is found to increase with coverage. Accordingly, H chemisorption sats. at coverages that depend on the local curvature of the sample and the form of H (i.e., at. or ionic) used for the treatment.
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    23. 23
      Tozzini, V.; Pellegrini, V. Prospects for hydrogen storage in graphene. Phys. Chem. Chem. Phys. 2013, 15, 80– 89,  DOI: 10.1039/C2CP42538F
      23
      Prospects for hydrogen storage in graphene
      Tozzini, Valentina; Pellegrini, Vittorio
      Physical Chemistry Chemical Physics (2013), 15 (1), 80-89CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      A review. Hydrogen-based fuel cells are promising solns. for the efficient and clean delivery of electricity. Since hydrogen is an energy carrier, a key step for the development of a reliable hydrogen-based technol. requires solving the issue of storage and transport of hydrogen. Several proposals based on the design of advanced materials such as metal hydrides and carbon structures have been made to overcome the limitations of the conventional soln. of compressing or liquefying hydrogen in tanks. Nevertheless none of these systems are currently offering the required performances in terms of hydrogen storage capacity and control of adsorption/desorption processes. Therefore the problem of hydrogen storage remains so far unsolved and it continues to represent a significant bottleneck to the advancement and proliferation of fuel cell and hydrogen technologies. Recently, however, several studies on graphene, the one-atom-thick membrane of carbon atoms packed in a honeycomb lattice, have highlighted the potentialities of this material for hydrogen storage and raise new hopes for the development of an efficient solid-state hydrogen storage device. Here we review on-going efforts and studies on functionalized and nanostructured graphene for hydrogen storage and suggest possible developments for efficient storage/release of hydrogen under ambient conditions.
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    24. 24
      Ito, Y.; Tanabe, Y.; Qiu, H.-J.; Sugawara, K.; Heguri, S.; Tu, N. H. High-Quality Three-Dimensional Nanoporous Graphene. Angew. Chem., Int. Ed. 2014, 53, 4822– 4826,  DOI: 10.1002/anie.201402662
      24
      High-Quality Three-Dimensional Nanoporous Graphene
      Ito, Yoshikazu; Tanabe, Yoichi; Qiu, H.-J.; Sugawara, Katsuaki; Heguri, Satoshi; Tu, Ngoc Han; Huynh, Khuong Kim; Fujita, Takeshi; Takahashi, Takashi; Tanigaki, Katsumi; Chen, Mingwei
      Angewandte Chemie, International Edition (2014), 53 (19), 4822-4826CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      We report three-dimensional (3D) nanoporous graphene with preserved 2D electronic properties, tunable pore sizes, and high electron mobility for electronic applications. The complex 3D network comprised of interconnected graphene retains a 2D coherent electron system of massless Dirac fermions. The transport properties of the nanoporous graphene show a semiconducting behavior and strong pore-size dependence, together with unique angular independence. The free-standing, large-scale nanoporous graphene with 2D electronic properties and high electron mobility holds great promise for practical applications in 3D electronic devices.
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    25. 25
      Tanabe, Y.; Ito, Y.; Sugawara, K.; Hojo, D.; Koshino, M.; Fujita, T. Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks. Adv. Mater. 2016, 28, 10304– 10310,  DOI: 10.1002/adma.201601067
      25
      Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks
      Tanabe, Yoichi; Ito, Yoshikazu; Sugawara, Katsuaki; Hojo, Daisuke; Koshino, Mikito; Fujita, Takeshi; Aida, Tsutomu; Xu, Xiandong; Huynh, Khuong Kim; Shimotani, Hidekazu; Adschiri, Tadafumi; Takahashi, Takashi; Tanigaki, Katsumi; Aoki, Hideo; Chen, Mingwei
      Advanced Materials (Weinheim, Germany) (2016), 28 (46), 10304-10310CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      This paper exptl. realized a nanoporous graphene elec. double layer transistor. And demonstrated for the first time that the 3D nanoporous graphene networks possess an ambipolor electronic nature of Dirac cones with an ultrahigh carrier mobility of 5000-7500 cm2 V-1 s-1. The three dimensional graphene networks with Dirac fermions exhibit a unique nonlinear Hall resistance in a wide range of the gate voltages.
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    26. 26
      Tanabe, Y.; Ito, Y.; Sugawara, K.; Koshino, M.; Kimura, S.; Naito, T.; Johnson, I.; Takahashi, T.; Chen, M. Dirac Fermion Kinetics in 3D Curved Graphene. Adv. Mater. 2020, 32, 2005838,  DOI: 10.1002/adma.202005838
      26
      Dirac fermion kinetics in 3D curved graphene
      Tanabe, Yoichi; Ito, Yoshikazu; Sugawara, Katsuaki; Koshino, Mikito; Kimura, Shojiro; Naito, Tomoya; Johnson, Isaac; Takahashi, Takashi; Chen, Mingwei
      Advanced Materials (Weinheim, Germany) (2020), 32 (48), 2005838CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      3D integration of graphene has attracted attention for realizing carbon-based electronic devices. While the 3D integration can amplify various excellent properties of graphene, the influence of 3D curved surfaces on the fundamental phys. properties of graphene has not been clarified. The electronic properties of 3D nanoporous graphene with a curvature radius down to 25-50 nm are systematically investigated and the ambipolar electronic states of Dirac fermions are essentially preserved in the 3D graphene nanoarchitectures, while the 3D curvature can effectively suppress the slope of the linear d. of states of Dirac fermion near the Fermi level are demonstrated. Importantly, the 3D curvature can be utilized to tune the back-scattering-suppressed elec. transport of Dirac fermions and enhance both electron localization and electron-electron interaction. As a result, nanoscale curvature provides a new degree of freedom to manipulate 3D graphene elec. properties, which may pave a new way to design new 3D graphene devices with preserved 2D electronic properties and novel functionalities.
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    27. 27
      Blundo, E.; Surrente, A.; Spirito, D.; Pettinari, G.; Yildirim, T.; Chavarin, C. A.; Baldassarre, L.; Felici, M.; Polimeni, A. Vibrational properties in highly strained hexagonal boron nitride bubbles. Nano Lett. 2022, 22, 1525,  DOI: 10.1021/acs.nanolett.1c04197
      27
      Vibrational Properties in Highly Strained Hexagonal Boron Nitride Bubbles
      Blundo, Elena; Surrente, Alessandro; Spirito, Davide; Pettinari, Giorgio; Yildirim, Tanju; Chavarin, Carlos Alvarado; Baldassarre, Leonetta; Felici, Marco; Polimeni, Antonio
      Nano Letters (2022), 22 (4), 1525-1533CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Hexagonal boron nitride (hBN) is widely used as a protective layer for few-atom-thick crystals and heterostructures (HSs), and it hosts quantum emitters working up to room temp. In both instances, strain is expected to play an important role, either as an unavoidable presence in the HS fabrication or as a tool to tune the quantum emitter electronic properties. Addressing the role of strain and exploiting its tuning potentiality require the development of efficient methods to control it and of reliable tools to quantify it. Here we present a technique based on hydrogen irradn. to induce the formation of wrinkles and bubbles in hBN, resulting in remarkably high strains of ~ 2%. By combining IR (IR) near-field scanning optical microscopy and micro-Raman measurements with numerical calcns., we characterize the response to strain for both IR-active and Raman-active modes, revealing the potential of the vibrational properties of hBN as highly sensitive strain probes.
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    28. 28
      Malard, L.; Pimenta, M.; Dresselhaus, G.; Dresselhaus, M. Raman spectroscopy in graphene. Phys. Rep. 2009, 473, 51– 87,  DOI: 10.1016/j.physrep.2009.02.003
      28
      Raman spectroscopy in graphene
      Malard, L. M.; Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.
      Physics Reports (2009), 473 (5-6), 51-87CODEN: PRPLCM; ISSN:0370-1573. (Elsevier B.V.)
      A review. Recent Raman scattering studies in different types of graphene samples are reviewed here. We first discuss the first-order and the double resonance Raman scattering mechanisms in graphene, which give rise to the most prominent Raman features. The detn. of the no. of layers in few-layer graphene is discussed, giving special emphasis to the possibility of using Raman spectroscopy to distinguish a monolayer from few-layer graphene stacked in the Bernal (AB) configuration. Different types of graphene samples produced both by exfoliation and using epitaxial methods are described and their Raman spectra are compared with those of 3D cryst. graphite and turbostratic graphite, in which the layers are stacked with rotational disorder. We show that Resonance Raman studies, where the energy of the excitation laser line can be tuned continuously, can be used to probe electrons and phonons near the Dirac point of graphene and, in particular allowing a detn. to be made of the tight-binding parameters for bilayer graphene. The special process of electron-phonon interaction that renormalizes the phonon energy giving rise to the Kohn anomaly is discussed, and is illustrated by gated expts. where the position of the Fermi level can be changed exptl. Finally, we discuss the ability of distinguishing armchair and zig-zag edges by Raman spectroscopy and studies in graphene nanoribbons in which the Raman signal is enhanced due to resonance with singularities in the d. of electronic states.
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    29. 29
      Barinov, A.; Gregoratti, L.; Dudin, P.; La Rosa, S.; Kiskinova, M. Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding. Adv. Mater. 2009, 21, 1916– 1920,  DOI: 10.1002/adma.200803003
      29
      Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding
      Barinov, Alexei; Gregoratti, Luca; Dudin, Pavel; La Rosa, Salvatore; Kiskinova, Maya
      Advanced Materials (Weinheim, Germany) (2009), 21 (19), 1916-1920CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Interaction with at. oxygen converts the initially metallic carbon nanotubes (CNTs) into semiconducting and, depending on the oxygen dose and reaction temp., the type and abundance of oxygenated functional groups formed changes significantly, including gasification and consumption of the CNTs at elevated temps. The most important finding is that the type and abundance of the groups formed and the gasification rate are strongly influenced by the d. and size of vacancy defects in the graphene layers of the carbon nanotube. On one hand, this introduces uncertainties when analogous procedures are employed for functionalization of CNTs with undefined d. and types of defects, but on the other hand it prompts an approach for tailoring CNTs via controlled introduction of defects, which can favor the formation of a preferred functional group.
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    30. 30
      Scardamaglia, M.; Amati, M.; Llorente, B.; Mudimela, P.; Colomer, J.-F.; Ghijsen, J.; Ewels, C.; Snyders, R.; Gregoratti, L.; Bittencourt, C. Nitrogen ion casting on vertically aligned carbon nanotubes: Tip and sidewall chemical modification. Carbon 2014, 77, 319– 328,  DOI: 10.1016/j.carbon.2014.05.035
      30
      Nitrogen ion casting on vertically aligned carbon nanotubes: Tip and sidewall chemical modification
      Scardamaglia, M.; Amati, M.; Llorente, B.; Mudimela, P.; Colomer, J.-F.; Ghijsen, J.; Ewels, C.; Snyders, R.; Gregoratti, L.; Bittencourt, C.
      Carbon (2014), 77 (), 319-328CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Nitrogen inclusion in vertically aligned carbon nanotubes (v-CNTs) was performed in situ and in ultra-high vacuum by nitrogen ion implantation and evaluated by X-ray photoelectron spectromicroscopy. The creation of defects induced by the ions drives the formation of different nitrogen species (pyridinic, pyrrolic, and graphitic) at the CNT surface. While nitrogen implantation in CNT sidewalls has results similar to implantation in graphene, where mainly nitrogen sp2 bonding configuration occurs, we obsd. a different behavior at the CNT tips, where nitrogen incorporation is also more efficient. A large amt. of pyrrolic nitrogen is obsd. at the CNT tips compared to the amt. at the CNT sidewalls for the same ion implantation parameters. This indicates a different reactivity of the CNT tips where the presence of natural defects may be involved in different nitrogen bonding formations between carbon and nitrogen with respect to the CNT sidewalls.
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    31. 31
      Susi, T.; Kaukonen, M.; Havu, P.; Ljungberg, M. P.; Ayala, P.; Kauppinen, E. I. Core level binding energies of functionalized and defective graphene. Beilstein Journal of Nanotechnology 2014, 5, 121– 132,  DOI: 10.3762/bjnano.5.12
      31
      Core level binding energies of functionalized and defective graphene
      Susi Toma; Kaukonen Markus; Havu Paula; Ljungberg Mathias P; Ayala Paola; Kauppinen Esko I
      Beilstein journal of nanotechnology (2014), 5 (), 121-32 ISSN:2190-4286.
      X-ray photoelectron spectroscopy (XPS) is a widely used tool for studying the chemical composition of materials and it is a standard technique in surface science and technology. XPS is particularly useful for characterizing nanostructures such as carbon nanomaterials due to their reduced dimensionality. In order to assign the measured binding energies to specific bonding environments, reference energy values need to be known. Experimental measurements of the core level signals of the elements present in novel materials such as graphene have often been compared to values measured for molecules, or calculated for finite clusters. Here we have calculated core level binding energies for variously functionalized or defected graphene by delta Kohn-Sham total energy differences in the real-space grid-based projector-augmented wave density functional theory code (GPAW). To accurately model extended systems, we applied periodic boundary conditions in large unit cells to avoid computational artifacts. In select cases, we compared the results to all-electron calculations using an ab initio molecular simulations (FHI-aims) code. We calculated the carbon and oxygen 1s core level binding energies for oxygen and hydrogen functionalities such as graphane-like hydrogenation, and epoxide, hydroxide and carboxylic functional groups. In all cases, we considered binding energy contributions arising from carbon atoms up to the third nearest neighbor from the functional group, and plotted C 1s line shapes by using experimentally realistic broadenings. Furthermore, we simulated the simplest atomic defects, namely single and double vacancies and the Stone-Thrower-Wales defect. Finally, we studied modifications of a reactive single vacancy with O and H functionalities, and compared the calculated values to data found in the literature.
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    32. 32
      Massimi, L.; Ourdjini, O.; Lafferentz, L.; Koch, M.; Grill, L.; Cavaliere, E.; Gavioli, L.; Cardoso, C.; Prezzi, D.; Molinari, E.; Ferretti, A.; Mariani, C.; Betti, M. G. Surface-Assisted Reactions toward Formation of Graphene Nanoribbons on Au(110) Surface. J. Phys. Chem. C 2015, 119, 2427– 2437,  DOI: 10.1021/jp509415r
      32
      Surface-Assisted Reactions toward Formation of Graphene Nanoribbons on Au(110) Surface
      Massimi, Lorenzo; Ourdjini, Oualid; Lafferentz, Leif; Koch, Matthias; Grill, Leonhard; Cavaliere, Emanuele; Gavioli, Luca; Cardoso, Claudia; Prezzi, Deborah; Molinari, Elisa; Ferretti, Andrea; Mariani, Carlo; Betti, Maria Grazia
      Journal of Physical Chemistry C (2015), 119 (5), 2427-2437CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Scanning tunneling microscopy and X-ray spectroscopy measurements were combined with first-principles simulations to investigate the formation of graphene nanoribbons (GNRs) on Au(110), as based on the surface-mediated reaction of 10,10'-dibromo-9,9'-bianthracene (DBBA) mols. At variance with Au(111), two different pathways are identified for the GNR self-assembly on Au(110), as controlled by both the adsorption temp. and the surface coverage of the DBBA mol. precursors. Room-temp. DBBA deposition on Au(110) leads to the same reaction steps obtained on Au(111), even though with lower activation temps. For DBBA deposition at 470 K, the cyclodehydrogenation of the precursors precedes their polymn., and the GNR formation is fostered by increasing the surface coverage. While the initial stages of the reaction are found to crucially det. the final configuration and orientation of the GNRs, the mol. diffusion is found to limit in both cases the formation of high-d. long-range ordered GNRs. Overall, the direct comparison between the Au(110) and Au(111) surfaces unveils the delicate interplay among the different factors driving the growth of GNRs.
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    33. 33
      D’Acunto, G.; Ripanti, F.; Postorino, P.; Betti, M. G.; Scardamaglia, M.; Bittencourt, C.; Mariani, C. Channelling and induced defects at ion-bombarded aligned multiwall carbon nanotubes. Carbon 2018, 139, 768– 775,  DOI: 10.1016/j.carbon.2018.07.032
      33
      Channelling and induced defects at ion-bombarded aligned multiwall carbon nanotubes
      D'Acunto, Giulio; Ripanti, Francesca; Postorino, Paolo; Betti, Maria Grazia; Scardamaglia, Mattia; Bittencourt, Carla; Mariani, Carlo
      Carbon (2018), 139 (), 768-775CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      A detailed investigation of ion channelling and defect prodn. for a highly-ordered array of multi-wall carbon nanotubes is presented. The effects of argon ion bombardment (0.25-5 keV) carried out either parallel (top) or perpendicular (side) to their axis, have been studied by Raman, XPS and SEM. Raman spectra provided evidence of channelling of the Ar+ ions obsd. for top bombardment along the whole 180 μm carbon nanotube length, while the penetration length is limited to the first 10 μm when the ions impinge from the side. The nature of defects, detd. through the spectral fingerprints of the C 1s core level as a function of energy and flux, unveils a distorted sp3-like bonding increase and the π-excitation decrease till quenching. Dangling bond states due to displaced carbon atoms become significant only at beam energies higher than 0.25 keV and high flux. These results on anisotropic channelling and selective defects creation open new perspectives in the application of highly-ordered arrays of multi-wall carbon nanotubes as anisotropic detectors.
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    34. 34
      Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide. Carbon 2007, 45, 1558– 1565,  DOI: 10.1016/j.carbon.2007.02.034
      34
      Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide
      Stankovich, Sasha; Dikin, Dmitriy A.; Piner, Richard D.; Kohlhaas, Kevin A.; Kleinhammes, Alfred; Jia, Yuanyuan; Wu, Yue; Nguyen, SonBinh T.; Ruoff, Rodney S.
      Carbon (2007), 45 (7), 1558-1565CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Redn. of a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high-surface-area carbon material which consists of thin graphene-based sheets. The reduced material was characterized by elemental anal., thermogravimetric anal., SEM, XPS, NMR spectroscopy, Raman spectroscopy, and elec. cond. measurements.
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    35. 35
      Shin, Y.-E.; Sa, Y. J.; Park, S.; Lee, J.; Shin, K.-H.; Joo, S. H.; Ko, H. An ice-templated, pH-tunable self-assembly route to hierarchically porous graphene nanoscroll networks. Nanoscale 2014, 6, 9734– 9741,  DOI: 10.1039/C4NR01988A
      35
      An ice-templated, pH-tunable self-assembly route to hierarchically porous graphene nanoscroll networks
      Shin, Young-Eun; Sa, Young Jin; Park, Seungyoung; Lee, Jiwon; Shin, Kyung-Hee; Joo, Sang Hoon; Ko, Hyunhyub
      Nanoscale (2014), 6 (16), 9734-9741CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Porous graphene nanostructures are of great interest for applications in catalysis and energy storage. However, the fabrication of 3D macroporous graphene nanostructures with controlled morphol., porosity, and surface area still presents significant challenges. Introduced is an ice-templated self-assembly approach for the integration of 2D graphene nanosheets into hierarchically porous graphene nanoscroll networks, where the morphol. of porous structures can be easily controlled by varying the pH conditions during the ice-templated self-assembly process. Freeze-casting of reduced graphene oxide (rGO) soln. results in the formation of 3D porous graphene microfoam below pH 8 and hierarchically porous graphene nanoscroll networks at pH 10. Graphene nanoscroll networks show promising electrocatalytic activity for the oxygen redn. reaction (ORR).
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    36. 36
      Jiménez-Arévalo, N.; Leardini, F.; Ferrer, I. J.; Ares, J. R.; Sánchez, C.; Saad Abdelnabi, M. M.; Betti, M. G.; Mariani, C. Ultrathin Transparent B–C–N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction. ACS Applied Energy Materials 2020, 3, 1922– 1932,  DOI: 10.1021/acsaem.9b02339
      36
      Ultrathin Transparent B-C-N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction
      Jimenez-Arevalo, Nuria; Leardini, Fabrice; Ferrer, Isabel J.; Ares, Jose Ramon; Sanchez, Carlos; Saad Abdelnabi, Mahmoud M.; Betti, Maria Grazia; Mariani, Carlo
      ACS Applied Energy Materials (2020), 3 (2), 1922-1932CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)
      Ultrathin B-C-N layers grown on Ti substrates are investigated as efficient anodes for electrochem. water splitting. A fast and direct synthetic route has been used based on plasma-enhanced chem. vapor deposition with methylamine borane as a single-source mol. precursor. The effect of growth time on the morphol. and structural properties and on the chem. compn. of the layers has been investigated by SEM, Raman spectroscopy, XPS, and transmission electron microscopy coupled with electron energy loss spectroscopy. Flat B-C-N layers on top of an amorphous titanium oxide layer present at the Ti surface have been obtained by using short growth times, while longer growth times give rise to core/shell structures formed by vertical wall B-C-N layers and titanium carbonitride phases. The obtained layers present enhanced electrocatalytic activity for the oxygen evolution reaction in alk. aq. solns. Moreover, because of their ultrathin nature, the B-C-N layers preserve the photocurrents of the underlying titanium oxide layer, acting as transparent electrodes with high cond. for the photogenerated charge carriers and improved electrocatalytic activity for the oxidn. of water to oxygen gas.
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    37. 37
      Luo, Z.; Yu, T.; Kim, K.-j.; Ni, Z.; You, Y.; Lim, S.; Shen, Z.; Wang, S.; Lin, J. Thickness-Dependent Reversible Hydrogenation of Graphene Layers. ACS Nano 2009, 3, 1781– 1788,  DOI: 10.1021/nn900371t
      37
      Thickness-dependent reversible hydrogenation of graphene layers
      Luo, Zhiqiang; Yu, Ting; Kim, Ki-jeong; Ni, Zhenhua; You, Yumeng; Lim, Sanhua; Shen, Zexiang; Wang, Shanzhong; Lin, Jianyi
      ACS Nano (2009), 3 (7), 1781-1788CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Graphene layers on SiO2/Si substrate were chem. decorated by r.f. H plasma. H coverage investigation by Raman spectroscopy and micro-XPS characterization demonstrates that the hydrogenation of single layer graphene on SiO2/Si substrate is much less feasible than that of bilayer and multilayer graphene. Both the hydrogenation and dehydrogenation process of the graphene layers are controlled by the corresponding energy barriers, which show significant dependence on the no. of layers. The extent of decorated C atoms in graphene layers can be manipulated reversibly up to the satn. coverage, which facilitates engineering of chem. decorated graphene with various functional groups via plasma techniques.
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    38. 38
      Zhou, J.; Wang, Q.; Sun, Q.; Chen, X. S.; Kawazoe, Y.; Jena, P. Ferromagnetism in Semihydrogenated Graphene Sheet. Nano Lett. 2009, 9, 3867– 3870,  DOI: 10.1021/nl9020733
      38
      Ferromagnetism in Semihydrogenated Graphene Sheet
      Zhou, J.; Wang, Q.; Sun, Q.; Chen, X. S.; Kawazoe, Y.; Jena, P.
      Nano Letters (2009), 9 (11), 3867-3870CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Single layer of graphite (graphene) was predicted and later exptl. confirmed to undergo metal-semiconductor transition when fully hydrogenated (graphane). Using d. functional theory when half of the hydrogen in this graphane sheet is removed, the resulting semihydrogenated graphene (which the authors refer to as graphone) becomes a ferromagnetic semiconductor with a small indirect gap. Half-hydrogenation breaks the delocalized π bonding network of graphene, leaving the electrons in the unhydrogenated carbon atoms localized and unpaired. The magnetic moments at these sites couple ferromagnetically with an estd. Curie temp. between 278 and 417 K, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. This is very different from the widely studied finite graphene nanostrucures such as 1-dimensional nanoribbons and two-dimensional nanoholes, where zigzag edges are necessary for magnetism. From graphene to graphane and to graphone, the system evolves from metallic to semiconducting and from nonmagnetic to magnetic. Hydrogenation provides a novel way to tune the properties with unprecedented potentials for applications.
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    39. 39
      Onida, G.; Reining, L.; Rubio, A. Electronic excitations: density-functional versus many-body Green’s-function approaches. Rev. Mod. Phys. 2002, 74, 601– 659,  DOI: 10.1103/RevModPhys.74.601
      39
      Electronic excitations: density-functional versus many-body Green's-function approaches
      Onida, Giovanni; Reining, Lucia; Rubio, Angel
      Reviews of Modern Physics (2002), 74 (2), 601-659CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)
      A review. Electronic excitations lie at the origin of most of the commonly measured spectra. However, the 1st-principles computation of excited states requires a larger effort than ground-state calcns., which can be very efficiently carried out within d.-functional theory. However, two theor. and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a 1-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy Σ and the electron-hole interaction. A good approxn. for Σ was obtained with Hedin's GW approach, using d.-functional theory as a zero-order soln. First-principles GW calcns. for real systems were successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional deriv. of Σ. An alternative approach to calcg. electronic excitations is the time-dependent d.-functional theory (TDDFT), which offers the important practical advantage of a dependence on d. rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-d. approxn. gave promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theor. and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress.
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    40. 40

      While not having information on the position of the conduction band bottom from experiments, we though observe that the pristine NPG is undoped, with the Dirac point at the Fermi level. We can thus expect a similar behavior for the H-NPG sample, which supports the assumption of the Fermi level lying approximately at midgap.

      There is no corresponding record for this reference.
    41. 41
      Singh, J. Physics of Semiconductors and Their Heterostructures; McGraw-Hill: New York, 1992.
      There is no corresponding record for this reference.
    42. 42
      Marzari, N.; Ferretti, A.; Wolverton, C. Electronic-structure methods for materials design. Nat. Mater. 2021, 20, 736– 749,  DOI: 10.1038/s41563-021-01013-3
      42
      Electronic-structure methods for materials design
      Marzari, Nicola; Ferretti, Andrea; Wolverton, Chris
      Nature Materials (2021), 20 (6), 736-749CODEN: NMAACR; ISSN:1476-1122. (Nature Portfolio)
      A review. The accuracy and efficiency of electronic-structure methods to understand, predict and design the properties of materials has driven a new paradigm in research. Simulations can greatly accelerate the identification, characterization and optimization of materials, with this acceleration driven by continuous progress in theory, algorithms and hardware, and by adaptation of concepts and tools from computer science. Nevertheless, the capability to identify and characterize materials relies on the predictive accuracy of the underlying phys. descriptions, and on the ability to capture the complexity of realistic systems. We provide here an overview of electronic-structure methods, of their application to the prediction of materials properties, and of the different strategies employed towards the broader goals of materials design and discovery.
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    43. 43
      Ito, Y.; Qiu, H.-J.; Fujita, T.; Tanabe, Y.; Tanigaki, K.; Chen, M. Bicontinuous Nanoporous N-doped Graphene for the Oxygen Reduction Reaction. Adv. Mater. 2014, 26, 4145– 4150,  DOI: 10.1002/adma.201400570
      43
      Bicontinuous Nanoporous N-doped Graphene for the Oxygen Reduction Reaction
      Ito, Yoshikazu; Qiu, H.-J.; Fujita, Takeshi; Tanabe, Yoichi; Tanigaki, Katsumi; Chen, Mingwei
      Advanced Materials (Weinheim, Germany) (2014), 26 (24), 4145-4150CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A bicontinuous nanoporous, N-doped graphene layer was used to fabricate nickel-based fuel cell cathodes by chem. vapor deposition. Nanoporous nickel substrates were prepd. by leaching (i.e., chem. dealloying in 1.0 M (NH4)2SO4) of annealed Ni30Mn70 cold-rolled sheets. N-doped graphene sheets were fabricated by graphene growth from added pyridine, in which a 2D-graphene structure as a 3D graphene material. The 3D graphene material is characterized by a large surface area, a high elec. cond., high electrochem. stability, and high catalytic activity.
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    44. 44
      Ito, Y.; Cong, W.; Fujita, T.; Tang, Z.; Chen, M. High Catalytic Activity of Nitrogen and Sulfur Co-Doped Nanoporous Graphene in the Hydrogen Evolution Reaction. Angew. Chem., Int. Ed. 2015, 54, 2131– 2136,  DOI: 10.1002/anie.201410050
      44
      High Catalytic Activity of Nitrogen and Sulfur Co-Doped Nanoporous Graphene in the Hydrogen Evolution Reaction
      Ito, Yoshikazu; Cong, Weitao; Fujita, Takeshi; Tang, Zheng; Chen, Mingwei
      Angewandte Chemie, International Edition (2015), 54 (7), 2131-2136CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Chem. doping has been demonstrated to be an effective way to realize new functions of graphene as metal-free catalyst in energy-related electrochem. reactions. Although efficient catalysis for the oxygen redn. reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co-doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt-free HER catalyst, 2D MoS2. The interplay between the chem. dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXitVWhu7fM&md5=16e3ede814a96f2926353b619d3a8b90
    45. 45
      Ito, Y.; Tanabe, Y.; Han, J.; Fujita, T.; Tanigaki, K.; Chen, M. Multifunctional Porous Graphene for High-Efficiency Steam Generation by Heat Localization. Adv. Mater. 2015, 27, 4302– 4307,  DOI: 10.1002/adma.201501832
      45
      Multifunctional Porous Graphene for High-Efficiency Steam Generation by Heat Localization
      Ito, Yoshikazu; Tanabe, Yoichi; Han, Jiuhui; Fujita, Takeshi; Tanigaki, Katsumi; Chen, Mingwei
      Advanced Materials (Weinheim, Germany) (2015), 27 (29), 4302-4307CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A solar heating unit to directly heat water droplets to steam for high-efficiency steam generation by heat localization is based on a multifunctional three-dimensional porous graphene doped with graphitic, pyridinic, and N-oxide-type nitrogen atoms. Recent d. functional theory calcns. indicate that doped nitrogen atoms in graphene lattices change the Gibbs free energy of H* absorption from pos. of pure graphene to neg., which could be the underlying mechanism that gives rise to the enhanced wettability of graphene for fast water delivery. The porous graphene materials, particularly with nitrogen doping, have a low sp. heat, effective light absorption, low thermal cond., and mesoscopic porosity, which meet all the requirements for effective steam generation by heat localization. A single piece of porous graphene can realize the energy conversion from sunlight to high-energy steam at high energy efficiency of 80%.
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    46. 46
      Hu, K.; Qin, L.; Zhang, S.; Zheng, J.; Sun, J.; Ito, Y.; Wu, Y. Building a Reactive Armor Using S-Doped Graphene for Protecting Potassium Metal Anodes from Oxygen Crossover in K–O2 Batteries. ACS Energy Letters 2020, 5, 1788– 1793,  DOI: 10.1021/acsenergylett.0c00715
      46
      Building a Reactive Armor Using S-Doped Graphene for Protecting Potassium Metal Anodes from Oxygen Crossover in K-O2 Batteries
      Hu, Kailong; Qin, Lei; Zhang, Songwei; Zheng, Jingfeng; Sun, Jiaonan; Ito, Yoshikazu; Wu, Yiying
      ACS Energy Letters (2020), 5 (6), 1788-1793CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
      Protecting alkali metals from oxygen crossover is a key unsolved challenge in metal-oxygen batteries. Herein, a new "reactive-armor strategy" is reported by using freestanding three-dimensional sulfur (S)-doped graphene with bicontinuous pore channels for protecting potassium (K) anodes from the undesired oxygen crossover. XPS and Fourier-transform IR results show that the S-dopants react with oxygen/superoxide species to form anionic sulfonate/sulfate that locally promotes the nucleation and growth of KO2. The resultant KO2 layer anchored on the graphene outer surface acts as a barrier layer that prevents oxygen from reaching the K metal surface. After 140 cycles (> 550 h), the protected K metal anodes still maintain metallic luster with little accumulation of byproducts. The use of organosulfur to build a reactive armor is applicable to other metal-oxygen batteries in suppressing the parasitic damage from oxygen crossover.
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    47. 47
      Giannozzi, P. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys.-Condens. Mater. 2009, 21, 395502,  DOI: 10.1088/0953-8984/21/39/395502
      47
      QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
      Giannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata M
      Journal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.
      QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
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    48. 48
      Giannozzi, P. Advanced capabilities for materials modelling with Quantum ESPRESSO. J. Phys.-Condens. Mater. 2017, 29, 465901,  DOI: 10.1088/1361-648X/aa8f79
      48
      Advanced capabilities for materials modelling with QUANTUM ESPRESSO
      Giannozzi, P.; Andreussi, O.; Brumme, T.; Bunau, O.; Buongiorno Nardelli, M.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Cococcioni, M.; Colonna, N.; Carnimeo, I.; Dal Corso, A.; de Gironcoli, S.; Delugas, P.; Di Stasio, R. A., Jr.; Ferretti, A.; Floris, A.; Fratesi, G.; Fugallo, G.; Gebauer, R.; Gerstmann, U.; Giustino, F.; Gorni, T.; Jia, J.; Kawamura, M.; Ko, H.-Y.; Kokalj, A.; Kucukbenli, E.; Lazzeri, M.; Marsili, M.; Marzari, N.; Mauri, F.; Nguyen, N. L.; Nguyen, H.-V.; Otero-de-la-Roza, A.; Paulatto, L.; Ponce, S.; Rocca, D.; Sabatini, R.; Santra, B.; Schlipf, M.; Seitsonen, A. P.; Smogunov, A.; Timrov, I.; Thonhauser, T.; Umari, P.; Vast, N.; Wu, X.; Baroni, S.
      Journal of Physics: Condensed Matter (2017), 29 (46), 465901/1-465901/30CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
      QUANTUM ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on d.-functional theory, d.-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. QUANTUM ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXntF2hsr0%253D&md5=17e46e5ac155b511f12deaeff078cc6d
    49. 49
      Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865,  DOI: 10.1103/PhysRevLett.77.3865
      49
      Generalized gradient approximation made simple
      Perdew, John P.; Burke, Kieron; Ernzerhof, Matthias
      Physical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XmsVCgsbs%253D&md5=55943538406ee74f93aabdf882cd4630
    50. 50
      Hamann, D. R. Optimized norm-conserving Vanderbilt pseudopotentials. Phys. Rev. B 2013, 88, 085117,  DOI: 10.1103/PhysRevB.88.085117
      50
      Optimized norm-conserving Vanderbilt pseudopotentials
      Hamann, D. R.
      Physical Review B: Condensed Matter and Materials Physics (2013), 88 (8), 085117/1-085117/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Fully nonlocal two-projector norm-conserving pseudopotentials are shown to be compatible with a systematic approach to the optimization of convergence with the size of the plane-wave basis. A reformulation of the optimization is developed, including the ability to apply it to pos.-energy at. scattering states and to enforce greater continuity in the pseudopotential. The generalization of norm conservation to multiple projectors is reviewed and recast for the present purposes. Comparisons among the results of all-electron and one- and two-projector norm-conserving pseudopotential calcns. of lattice consts. and bulk moduli are made for a group of solids chosen to represent a variety of types of bonding and a sampling of the periodic table.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsF2kt77J&md5=c1a65d8ae5ea249632f801f620a2f6af
    51. 51
      Godby, R. W.; Needs, R. J. METAL-INSULATOR-TRANSITION IN KOHN-SHAM THEORY AND QUASIPARTICLE THEORY. Phys. Rev. Lett. 1989, 62, 1169– 1172,  DOI: 10.1103/PhysRevLett.62.1169
      51
      Metal-insulator transition in Kohn-Sham theory and quasiparticle theory
      Godby; Needs
      Physical review letters (1989), 62 (10), 1169-1172 ISSN:.
      There is no expanded citation for this reference.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfosFSntQ%253D%253D&md5=69121fd8fd0b637164dd42481d194086
    52. 52
      Rozzi, C. A.; Varsano, D.; Marini, A.; Gross, E. K. U.; Rubio, A. Exact Coulomb cutoff technique for supercell calculations. Phys. Rev. B 2006, 73, 205119,  DOI: 10.1103/PhysRevB.73.205119
      52
      Exact Coulomb cutoff technique for supercell calculations
      Rozzi, Carlo A.; Varsano, Daniele; Marini, Andrea; Gross, Eberhard K. U.; Rubio, Angel
      Physical Review B: Condensed Matter and Materials Physics (2006), 73 (20), 205119/1-205119/13CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      We present a reciprocal space anal. method to cut off the long range interactions in supercell calcns. for systems that are infinite and periodic in one or two dimensions, generalizing previous work to treat finite systems. The proposed cutoffs are functions in Fourier space, that are used as a multiplicative factor to screen the bare Coulomb interaction. The functions are analytic everywhere except in a subdomain of the Fourier space that depends on the periodic dimensionality. We show that the divergences that lead to the nonanal. behavior can be exactly canceled when both the ionic and the Hartree potential are properly screened. This technique is exact, fast, and very easy to implement in already existing supercell codes. To illustrate the performance of the scheme, we apply it to the case of the Coulomb interaction in systems with reduced periodicity (as one-dimensional chains and layers). For these test cases, we address the impact of the cutoff on different relevant quantities for ground and excited state properties, namely: the convergence of the ground state properties, the static polarizability of the system, the quasiparticle corrections in the GW scheme, and the binding energy of the excitonic states in the Bethe-Salpeter equation. The results are very promising and easy to implement in all available first-principles codes.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XlvVejsbs%253D&md5=c28eea01cc1adaced6cab88941a1b617
    53. 53
      Marini, A.; Hogan, C.; Grüning, M.; Varsano, D. yambo: An ab initio tool for excited state calculations. Comput. Phys. Commun. 2009, 180, 1392– 1403,  DOI: 10.1016/j.cpc.2009.02.003
      53
      Yambo: An ab initio tool for excited state calculations
      Marini, Andrea; Hogan, Conor; Gruening, Myrta; Varsano, Daniele
      Computer Physics Communications (2009), 180 (8), 1392-1403CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
      Yambo is an ab initio code for calcg. quasiparticle energies and optical properties of electronic systems within the framework of many-body perturbation theory and time-dependent d. functional theory. Quasiparticle energies are calcd. within the GW approxn. for the self-energy. Optical properties are evaluated either by solving the Bethe-Salpeter equation or by using the adiabatic local d. approxn. is a plane-wave code that, although particularly suited for calcns. of periodic bulk systems, has been applied to a large variety of phys. systems. relies on efficient numerical techniques devised to treat systems with reduced dimensionality, or with a large no. of degrees of freedom. The code has a user-friendly command-line based interface, flexible I/O procedures and is interfaced to several publicly available d. functional ground-state codes.
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    54. 54
      Sangalli, D. Many-body perturbation theory calculations using the yambo code. J. Phys.: Condens. Matter 2019, 31, 325902,  DOI: 10.1088/1361-648X/ab15d0
      54
      Many-body perturbation theory calculations using the yambo code
      Sangalli, D.; Ferretti, A.; Miranda, H.; Attaccalite, C.; Marri, I.; Cannuccia, E.; Melo, P.; Marsili, M.; Paleari, F.; Marrazzo, A.; Prandini, G.; Bonfa, P.; Atambo, M. O.; Affinito, F.; Palummo, M.; Molina-Sanchez, A.; Hogan, C.; Gruning, M.; Varsano, D.; Marini, A.
      Journal of Physics: Condensed Matter (2019), 31 (32), 325902CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
      Yambo is an open source project aimed at studying excited state properties of condensed matter systems from first principles using many-body methods. As input, yambo requires ground state electronic structure data as computed by d. functional theory codes such as Quantum ESPRESSO and Abinit. yambo's capabilities include the calcn. of linear response quantities (both independent-particle and including electron-hole interactions), quasi-particle corrections based on the GW formalism, optical absorption, and other spectroscopic quantities. Here we describe recent developments ranging from the inclusion of important but oft-neglected phys. effects such as electron-phonon interactions to the implementation of a real-time propagation scheme for simulating linear and non-linear optical properties. Improvements to numerical algorithms and the user interface are outlined. Particular emphasis is given to the new and efficient parallel structure that makes it possible to exploit modern high performance computing architectures. Finally, we demonstrate the possibility to automate workflows by interfacing with the yambopy and AiiDA software tools.
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    55. 55
      Huber, S. P. AiiDA 1.0, a scalable computational infrastructure for automated reproducible workflows and data provenance. Sci. Data 2020, 7, 300,  DOI: 10.1038/s41597-020-00638-4
      55
      AiiDA 1.0, a scalable computational infrastructure for automated reproducible workflows and data provenance
      Huber Sebastiaan P; Zoupanos Spyros; Uhrin Martin; Talirz Leopold; Kahle Leonid; Hauselmann Rico; Yakutovich Aliaksandr V; Andersen Casper W; Ramirez Francisco F; Adorf Carl S; Gargiulo Fernando; Kumbhar Snehal; Passaro Elsa; Johnston Conrad; Cepellotti Andrea; Mounet Nicolas; Marzari Nicola; Pizzi Giovanni; Huber Sebastiaan P; Zoupanos Spyros; Uhrin Martin; Talirz Leopold; Kahle Leonid; Hauselmann Rico; Yakutovich Aliaksandr V; Andersen Casper W; Ramirez Francisco F; Adorf Carl S; Gargiulo Fernando; Kumbhar Snehal; Passaro Elsa; Johnston Conrad; Cepellotti Andrea; Mounet Nicolas; Marzari Nicola; Pizzi Giovanni; Talirz Leopold; Yakutovich Aliaksandr V; Gresch Dominik; Muller Tiziano; Merkys Andrius; Kozinsky Boris; Kozinsky Boris
      Scientific data (2020), 7 (1), 300 ISSN:.
      The ever-growing availability of computing power and the sustained development of advanced computational methods have contributed much to recent scientific progress. These developments present new challenges driven by the sheer amount of calculations and data to manage. Next-generation exascale supercomputers will harden these challenges, such that automated and scalable solutions become crucial. In recent years, we have been developing AiiDA (aiida.net), a robust open-source high-throughput infrastructure addressing the challenges arising from the needs of automated workflow management and data provenance recording. Here, we introduce developments and capabilities required to reach sustained performance, with AiiDA supporting throughputs of tens of thousands processes/hour, while automatically preserving and storing the full data provenance in a relational database making it queryable and traversable, thus enabling high-performance data analytics. AiiDA's workflow language provides advanced automation, error handling features and a flexible plugin model to allow interfacing with external simulation software. The associated plugin registry enables seamless sharing of extensions, empowering a vibrant user community dedicated to making simulations more robust, user-friendly and reproducible.
      >> More from SciFinder ®
      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB38blvFyksw%253D%253D&md5=89f4a5f6d6a831f029c8cc9f2b2b3246
    56. 56
      Uhrin, M.; Huber, S. P.; Yu, J.; Marzari, N.; Pizzi, G. Workflows in AiiDA: Engineering a high-throughput, event-based engine for robust and modular computational workflows. Comput. Mater. Sci. 2021, 187, 110086,  DOI: 10.1016/j.commatsci.2020.110086
      There is no corresponding record for this reference.
    57. 57
      The yambo-AiiDA code is available at https://github.com/yambo-code/yambo-aiida.
      There is no corresponding record for this reference.

  • Supporting Information

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