The abundance of accessible colloidally prepared nanoparticles forms the basis for nanoparticle-based aerogels. Synthetic methods have been developed to destabilize colloidal nanoparticle solutions in a controlled manner, resulting first in wet gels and then in aerogels. In addition to other ways to make aerogels, efforts have been made, in particular, to transfer particles of different sizes, shapes, natures, and compositions together into aerogels. All this happens in the context of the phenomenon of self-organization at the nanoscale, which is due to Brownian motion and complex potentials between particles. Some of these ways are traced, recent developments are compiled as examples and some ideas for the further development of this fruitful research field are collected.

Complex metal hydrides are promising hydrogen storage materials with their high volumetric and gravimetric capacities, but they are limited by high temperatures for hydrogen release and slow kinetics for hydrogen uptake. These limitations necessitate modifications to allow hydride materials to become more technologically viable. It has been shown that chemical additives can reduce the hydrogen desorption temperature and improve reaction rates of a hydride matrix. Currently, the most common method to integrate chemical additives is through ball milling. In contrast, this work investigates the vapor-phase delivery of chemical additives to the gamma phase of Mg(BH4)2, adapted from atomic layer deposition which uses sequential precursor exposures on a material surface to grow thin films. The modified Mg(BH4)2 materials demonstrated up to 7.6 wt % hydrogen release at temperatures as low as 100 °C. The materials in this work were characterized extensively using temperature-programmed desorption, the Sieverts method, and X-ray diffraction. Additionally, identical location scanning transmission electron microscopy was conducted to identify the chemical complexities of the modifications introduced from the vapor-phase delivery process and through the hydrogen desorption process. Findings from the microscopy study were combined with the aforementioned characterization techniques to illuminate the mechanism of decomposition and allow for a better understanding of the vapor-phase-modified materials. Overall, this work demonstrates how combining a diverse suite of characterization techniques, especially electron microscopy, enables the discovery and understanding of the sorption and chemical processes that take place in hydrogen storage materials and contribute to accelerate research in this field.

We developed a novel semimicroscopic theory for diffusion and migration-controlled oxidative and reductive charge transfer for fully and partially supported systems under single-potential-step perturbation on a planar electrode. The electric field-induced asymmetrical migration contribution of oxidized and reduced species in the electric double layer (EDL) region is accounted for using our jellium-dipole-underscreened-diffuse-layer model for the electric double layer. The essential nonlinearity that appears in the Nernst–Planck equation is circumvented through a novel approach by projecting migration contributions to modified Nernstian boundary constraint. Our formulation also accounts for the ionic strength-dependent anomalies in the interfacial electric field due to ionic underscreening, electrostatic interaction on diffusivity, the ion size effect of supporting electrolyte, and the charge of electroactive species in the migration current. The formula is derived for the current transient, and it accounts for the influence of the supporting electrolyte, electroactive species, solvent, electrode through jellium, and applied potential. The extent of migration–diffusion coupling is characterized by a dimensionless coupling number δMα (0 ≤ δMα < 1). A smaller magnitude represents a weak coupling regime with a limiting ideal Cottrell behavior, and δMα sim 0.5 represents a strong coupling regime. The theory elucidates that δMα is dependent on the potential at IHP, OHP, diffuse electric double layer, ion size-corrected screening length, interfacial diffusivity, the charge on electroactive species, and the operative resistance from bulk to interface. Finally, we validate the theory with experiments and show that migration has a significant influence on the chronoamperometric response at all time scales.

Recently, the development of efficient and non-noble photoelectrocatalysts with enhanced light absorption and high photoelectrochemical (PEC) performance has attracted increasing attention due to their potential in addressing the global fossil energy and environment crisis. In this work, we designed and prepared a topological insulator Bi2Te3 film and non-noble plasmonic Cu nanoparticles onto one-dimensional (1D) TiO2 nanorod (NR) array, forming TiO2/Bi2Te3/Cu photoanode. Benefiting from the synergistic effect of plasmonic Cu-induced hot electrons and Bi2Te3-supplied topological high-mobility electron channels, the PEC performance and charge separation of TiO2 were enhanced. Accompanied by the improved light absorption, the optical band gap was narrowed from 3.02 eV for TiO2 to 2.47 eV for TiO2/Bi2Te3/Cu. Moreover, the photocurrent density of pure TiO2 was increased by about 3.05 times, from 0.77 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) for TiO2 to 2.33 mA/cm2 for TiO2/Bi2Te3/Cu. Moreover, the recombination of photogenerated electron–hole pairs was also suppressed, and the carrier lifetime was prolonged from 24.6 ns for bare TiO2 to 33.4 ns for TiO2/Bi2Te3/Cu. As a result, the TiO2/Bi2Te3/Cu photoanode showed good long-term cycling stability, with the H2 generation rate from PEC water splitting reaching 20.3 μmol/cm2/h. Our results suggest that co-decorating topological insulators and plasmonic materials could be a promising strategy to improve the PEC performance of TiO2 and may be applied in other photoelectrocatalysts.

Two-dimensional (2D) Dion–Jacobson (DJ) perovskites have recently drawn much attention owing to their superior charge transport and high environmental stability. We fabricated centimeter-sized BDAPbI4 (BDA = NH3C4H8NH32+) 2D perovskite single crystals with an optical band gap of 2.30 eV, as well as the corresponding photodetectors. Based on the density functional theory calculations, rational design of the ion implantation scheme was carried out to improve the performance of the BDAPbI4 photodetector. The Cu ion is screened out to be the best element, which can introduce the additional sub-bands below the CBM of the pristine perovskite. The Cu 4s orbital dominates the CBM states, and the Cu 3d orbital dominates the VBM states. It exhibits high charge collection efficiency and improves light harvesting ability. The reduced band gap, enhanced density of states, and improved absorption coefficient indicate that Cu-ion implantation could significantly increase the charge carrier concentration and promote the charge dissociation and extraction across the band edge, which is beneficial to improve the performance of BDAPbI4-based photodetectors. In particular, the BDAPbI4 photodetector modified by Cu-ion implantation exhibits improved photoresponse performance with the best responsivity of 0.66 mA W–1 under a high light intensity of 10.8 mW cm–2 at 40 V bias, which is about twice as that of the pristine BDAPbI4 devices. This study provides a promising way to improve the performance of 2D perovskite single-crystal photodetectors by ion implantation.

To overcome electronic transport issues of layered titanates in sodium-ion batteries, we have designed and synthesized composites of lepidocrocite titanates with reduced graphene oxide through a solution-based self-assembly approach. The parent lepidocrocite titanate (K0.8[Ti1.73Li0.27]O4) was exfoliated by a soft-chemical approach and mechanical shaking. Exfoliated layered titania sheets (LTO) were then combined with reduced graphene oxide (rGO) layers to assemble into composites through flocculation. Countercations (i.e., Mg2+) were used for the self-assembly of negatively charged titania and rGO nanosheets via flocculation. The carbon content in the composites was tuned from 1 to 17% by changing the ratio of titania and rGO sheets in the mixed colloidal suspensions. Electrodes were processed with as-prepared LTO–rGO composites without any carbon additives and tested in sodium half-cell configurations. Mg+-coagulated LTO–rGO composite electrodes deliver higher capacities than electrodes prepared with coagulated titania sheets and 10% acetylene black in sodium half-cells and display good capacity retention after 50 cycles. Electrochemical impedance spectroscopy results indicate lower charge transfer resistance for LTO–14.5%rGO composites than that of coagulated titania sheets with 10% acetylene black. A power law analysis of cells containing the composites indicate a hybrid mechanism consisting of both surface and diffusional processes. A comparison with a similar system, that of dopamine-derived LTO-C heterostructures, reveal significant differences. While capacities showed a strong dependence on carbon content for the dopamine-derived materials, this was not true for the LTO–rGO composites. Instead, the highest capacity was obtained for the 14.5% rGO sample, with a lower value obtained for the 17% rGO sample. A greater proportion of the redox processes were surface rather than diffusional in nature for the LTO–rGO composites as well.

The development of Mg rechargeable batteries is hindered by both oxidative and reductive electrolyte decomposition on the positive electrode, which results in poor cyclability. Although improving the stability of the electrolyte is one solution, we found that the oxidative decomposition of the electrolyte can be suppressed by introducing Fe ions to spinel oxides. Furthermore, the mechanism was clarified from the viewpoint of the electronic state of the spinel oxides, with MgFe2O4 exhibiting the lowest valence band maximum in our previous study. Here, by developing an interpretation of this mechanism, we demonstrated that the type of transition metal ions in spinel oxides has an effect on the reductive decomposition of the electrolyte. Based on the above knowledge, we synthesized mixed Co–Fe spinel oxides that exhibited a suppressive effect on both oxidative and reductive electrolyte decomposition and successfully improved the cyclability. This study provides guidelines for developing positive electrode active materials for Mg rechargeable batteries.

Understanding the ion-conduction mechanism in concentrated electrolyte solutions of Li salts is helpful in designing electrolytes for advanced Li batteries. In certain highly concentrated electrolytes, the Li+ ion hopping/ligand exchange mechanism contributes to ionic conduction, and the transference number of Li+ becomes higher than 0.5, which mitigates the concentration polarization in Li batteries. However, details of the hopping mechanism remain unclear. In this study, we investigated the temperature dependence of the transport properties of Li salt/sulfolane (SL) electrolytes. Using pulsed-field gradient nuclear magnetic resonance spectroscopy, we found that Li+ ion diffuses faster than SL and anion in highly concentrated electrolytes, suggesting that Li+-ion-hopping conduction occurs. The apparent activation energy (Ea) of the diffusivity of Li+ in highly concentrated electrolytes is slightly lower than Ea of the fluidity of liquid, which indicates that Li+-ion conduction is partially decoupled from the viscosity. The ratio of the actual molar conductivity to the calculated one based on the Nernst–Einstein relationship increases with decrease in temperature, leading to a lower Ea for ionic conduction compared to that of the fluidity and the ion diffusivity.

High-performance bifunctional electrocatalysts that simultaneously and efficiently catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have become the bottleneck and main challenge for rechargeable zinc–air batteries. The components need to be comprehensively designed to enhance the formation possibility for the respective activities of ORR and OER. Nevertheless, the elements and types of chemical bonds generate an almost infinite space of potential candidates. In this work, we proposed a rational design strategy for efficient bifunctional oxygen electrocatalysts by a data-driven method. According to the inferred ΔE from E10 and E1/2 machine learning models among all the bond combinations, a bond combination of C–N, C–C, Fe–N, Ru–O, and C–P was considered with superior possibility to have bifunctional activity owing to its highest occurrence frequency. The experimental results further confirmed that this component and bonding method indeed have ORR/OER bifunctional activity, which has not been reported yet. This strategy brings novel and efficient insights for bifunctional electrocatalyst design from a huge potential exploration space.

Submonolayer coverages of V-oxide on Rh(111) condense during catalytic methanol oxidation into a pattern of macroscopic stripes or islands. Under reaction conditions, a phase separation occurs within the VOx islands that has been studied in a pressure range of 10–6–10–4 mbar with photoemission electron microscopy (PEEM), low-energy electron microscopy (LEEM), microspot-low-energy electron diffraction (μLEED), and microspot-X-ray photoelectron spectroscopy (μXPS). An oxidized outer ring with a (√7 × √7)R19.1° structure coexists with an inner (12 × 12) Moiré-type boundary layer and a reduced core exhibiting a (√3 × √3)R30° Moiré type pattern. The dependence of the substructure on the reaction conditions, on V coverage, and on island size was investigated. With μXPS, the V coverages of the different phases in the VOx islands were determined.

The N-doped carbon-based catalysts have emerged as potential alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR). Understanding the delicate interplay between dopants and graphene structures at the atomic level is crucial to rational designing high-performance carbon-based catalysts. Herein, we deeply explore the role of the edge structure of graphene, N doping configuration, position, and content in modulating the 4e– and 2e– ORR mechanisms using density functional theory calculations and comprehensively evaluate the ORR activity by combining the active site density and theoretical overpotential. We find that graphene with zigzag and armchair edges (GZ-A) has extra spin density and high ORR activity compared to graphene with only armchair edges (GA-A). The N doping position is more important than N doping content in improving ORR activity in N-doped GZ-A because only the proper N doping position, such as along the armchair edge, can increase the effective active sites by modulating the spin density. On the contrary, increasing N doping content is more efficient in boosting the ORR activity of N-doped GA-A since high N doping content contributes to the increased spin density and active site density. On the whole, N-doped GZ-A has a much higher turnover frequency (TOF) value than N-doped GA-A, and the GZ-A with pyridinic-N doping along the armchair edge exhibits the highest TOF value of 1.37 × 1012 (U = 1.23 V)/s–1.

In the present work, ferrous oxalate dihydrate (FOD) microspheres were prepared by the one-step hydrothermal method using the interaction between ferric chloride and disodium tartrate dihydrate in the presence of β-cyclodextrin (β-CD). Although reaction temperature and time have important effects on the formation of the FOD microspheres, these effects can only be achieved in the presence of β-CD. In the absence of β-CD, the hydrothermal reaction will only form ferrous tartrate (FeTA) nanorods. The role of β-CD is to dominate and promote the time-dependent structural transformation from one Fe(II) complex FeTA to another Fe(II) complex polymer FOD. This discovery is new and meaningful. It provides a new perspective on the synthesis of inorganic micro- and nanomaterials. UV–vis diffuse-reflectance spectra show that these microsphere structures such as 1 and 2 indicate excellent light absorption capacities, including high absorption intensity in a very wide wavelength range (200–1000 nm). Magnetic studies show that these FOD materials exhibit typical paramagnetic properties near room temperature. The correlation between magnetic properties and structures shows that the magnetic similarity of these FOD materials is mainly reflected by the similarity of the surface structure. On the contrary, the difference of magnetism is more reflected by the difference of the crystal structure. In addition, we also found that these FOD microspheres showed good photocatalytic activity for several different types of organic dyes, including cationic Rhodamine B, Rhodamine 6G, crystal violet, and anionic methyl orange. Based on these meaningful experimental results, we have reason to believe that this work will help stimulate the in-depth study of FOD micro- and nanomaterials in controllable synthesis, physical properties, and photocatalytic applications.

Gas–solid interactions between molecular oxygen and metallic vanadium surfaces and the systematic evolution in the electronic structure of vanadium oxide (VOx) surfaces have been explored in the present work by near-ambient pressure photoelectron spectroscopy (NAPPES). The current article studies the evolution of various oxides of vanadium as a function of partial pressure of O2 (ultrahigh vacuum to 1 mbar), temperature (298–875 K), and the exposure time to oxygen (up to 18 h). Valence-band (VB) and core-level spectral measurements recorded with UV (He–I = 21.2 eV) and Al Kα (1486.6 eV) photons, respectively, show interesting changes. (1) Oxidation is limited to the top layers of vanadium at 298 K and up to a partial pressure of 1 mbar O2. About 50% of vanadium gets oxidized, and the remaining amount exists as metal within the top 10 nm. (2) Metallic vanadium disappears above 625 K, and it is predominantly oxidized to a mixture of V4+ and V5+ oxidation states at a 0.1 mbar partial pressure of O2. Points 1 and 2 suggest the predominantly thermodynamically controlled nature of vanadium oxidation through oxygen diffusion into the subsurface and bulk layers. (3) The Fermi-level (EF) feature observed first at ≥725 K at a 0.1 mbar O2 pressure demonstrates the formation of metallic VO2; however, its metallic nature is preserved even at ambient temperature due to interweaving nanodomains of VOx with VO2. (4) Only partial conversion of surface layers to V5+ (V2O5) along with VO2 and V2O3 (within the probing depth of 8–10 nm by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS)) was observed even after prolonged heating (18 h) in 1 mbar O2 pressure. (5) The nature of the surface changes between metal and semiconducting/insulator oxides is substantiated by the observation of changes in work function (ϕ) and EF features. Typical VB features and Fermi intensity of V-metal and vanadium oxides were observed, and the results were corroborated with core-level and VB spectra. The present results extend the capabilities of NAPPES to explore the electronic structure evolution as a function of reaction conditions and underscore its relevance to areas such as heterogeneous catalysis and sensing.

The dynamic structural evolution of Rh species in mordenite (MOR) zeolite was investigated using in situ spectroscopic techniques and density functional theory (DFT) calculations. In situ X-ray absorption spectroscopy and operando infrared (IR) revealed that metallic Rh species were oxidized to afford isolated [Rh(NO)2]+ species under NO flow at 200 °C, whereas small Rh metal clusters are formed under the subsequent H2 flow. Ab initio thermodynamics analysis shows that the plausible structures under NO and H2 at 200 °C are [Rh(NO)2]+ and Rh clusters in MOR, which is consistent with the experimental observations. A comparative study of Rh-loaded Al2O3 suggests that Al sites in MOR increase the thermodynamic stability of isolated Rh+ species and thus prevent their overoxidation to Rh2O3 under NO. NO capture in the form of [Rh(NO)2]+ and its selective reduction toward NH3 under H2 flow were observed by in situ IR measurements. The RhMOR catalyst exhibited ∼60% of NOx conversion above 200 °C under periodic lean/rich conditions. Transition-state calculations showed that the activation barrier for NO reduction to NH3 on [Rh(NO)2]+ (178 kJ/mol) is higher than that for Rh13 (156 kJ/mol), suggesting that Rh metal clusters are preferable NH3 formation sites, where the Rh13-catalyzed NO reduction into N2 and N2O was less preferable than NH3 formation, which is consistent with the experimental results. Combined with operando IR experiments under lean (NO + O2) and rich (NO + H2) conditions, we show that the reversible dynamic structural evolution of Rh species ([Rh(NO)2]+ ↔ Rh metal clusters under lean and rich conditions) is a key mechanistic feature for unsteady-state de-NOx via the capture of NO, its selective reduction to NH3, and the selective reduction of NO with NH3 formed in situ.

Metal and ligand exchange in metal–organic frameworks (MOFs) opens up an avenue of functionalization of the postsynthetic-modified MOF as the single-atom catalyst for the heterogeneous catalysis. Here, the adsorption and degradation of the G-type nerve agent soman (GD) and its simulant dimethyl 4-nitrophenylphosphate by the postsynthetic-modified MFU-4l MOFs, M-MFU-4l-(OH) (M = Mn, Fe, Co, Ni, Cu, and Zn), have been investigated by molecular dynamics simulations and density functional theory calculations. Due to the structural confinement of Zn-MFU-4l-(OH), the substrate is generally adsorbed at the Zn–OH site of the large pore. The whole degradation of GD involves two key steps, the formation of a five-coordinated phosphorus intermediate with the free energy barriers of 17.0–21.4 kcal/mol and the release of the degraded product with the free energy requirement of 20.3–25.8 kcal/mol. Overall, Fe-MFU-4l-(OH) was predicted to have the best performance for the catalytic degradation of GD among these MOF materials. The related Brønsted–Evans–Polanyi relationships among the thermodynamic quantities for these two crucial steps as well as the volcano curve are established, which may be used to screen MOF-based single-atom catalysts for the detoxification of nerve agents.

Conversion of alkanes to liquid fuels and other chemicals has a great demand in many industrial applications. The key challenge in the alkane conversion is the activation of the C–H bond. Protonated zeolites are known to activate the C–H bond in alkanes. Modeling of such catalytic reactions and estimation of reaction free energies especially when entropy has a non-negligible contribution in the reactant state due to the translational motion in the pores are computationally challenging. The large size of the zeolite systems also poses difficulty in modeling such reactions. We address these problems through extensive fully relaxed hybrid quantum mechanics- and molecular mechanics-based molecular dynamics simulations and free energy calculations using the temperature-accelerated sliced sampling approach. We model a proton-exchange reaction between methane and the Brønsted acid site of zeolite at 300 K. We investigate the differential reactivity of H-ZSM-5 and H-MCM-22 zeolites toward proton exchange and probe the role of acid strength, internal structure, and entropy.

The green synthesis of oxime in a titanosilicates/H2O2 (TS/H2O2) system is based on the synergistic effect of the in situ synthesis of hydroxylamine (NH2OH) by the oxidation of NH3 and the subsequent noncatalytic oximation reaction. However, NH2OH has a highly unstable character, leading to its easy decomposition to release greenhouse gas N2O. Herein a comprehensive investigation was carried out to clarify the mechanism of NH2OH decomposition in the -TS/H2O2 system. The reaction pathway network with NH2OH oxidation decomposition was established, and effective ways to inhibit the formation of byproduct N2O were proposed. We proposed that the oxidative decomposition of NH2OH was divided into two main competitive pathways: (a) by H2O2 and the free radicals formed by the activation of H2O2 with nonframework titanium species to produce N2O and N2 and (b) by active intermediate Ti-OOH species formed by the activation of H2O2 with framework titanium species to product only inert N2. We found that promoting the formation Ti-OOH species by enhancing the Lewis acidity strength of the titanosilicates could significantly inhibit the pathway of NH2OH oxidation decomposition to N2O. Meanwhile, proper additives to stabilize Ti-OOH species through hydrogen bonding would achieve the same effect. The reaction behavior of H2O2 determines the types of products of NH2OH oxidation decomposition. By analyzing the decomposition pathways of NH2OH deeply, we could realize clearly how the products of NH2OH oxidation decomposition were generated, which can be applied to the actual industrial production of the TS/H2O2 ammoximation system to achieve a greener chemical process.

Scanning tunneling microscopy (STM) was employed to quantitively investigate in situ binding of 3-phenyl thiophene (PhTh) to Co(II)octaethyl porphyrin (CoOEP) supported on highly ordered pyrolytic graphite (HOPG) in fluid solution. To our knowledge, this is the first single-molecule level study of a complexation reaction between a metalloporphyrin and a sulfur base at the solution/solid interface and one of the few examples of thiophene coordination with a d7 transition metal. Real-time imaging experiments revealed that PhTh binds reversibly to HOPG-supported CoOEP at room temperature. The coordination process increases with increasing PhTh concentration. The nearest-neighbor analysis of STM images indicates that the complexation reaction is cooperative. Because PhTh does not bind to CoOEP in solution, the STM results strongly suggest that the presence of HOPG is crucial to observe ligand binding and cooperativity in this system. Periodic plane-wave density functional theory (DFT) computations corroborate that PhTh has low binding affinity toward CoOEP in solution but predict that the ligand can adsorb to CoOEP/HOPG through coordination with S atoms or interact through noncovalent π–π bonding with the porphyrin chromophore. Three possible structures were considered, and DFT theory was used to calculate binding energies and free energies. In solution and on the HOPG surface both a π–π configuration and a η1(S) configuration have similar computed energies. The η1(S) structure shows the largest stabilization in going from the vapor to adsorbed on HOPG. We also show that statistical analysis of nearest neighbors is more sensitive to cooperative binding than is fitting with the Temkin or Langmuir isotherm. The implication is that isotherm fitting alone is insufficient for identifying cooperative binding on surfaces.

Electro-oxidation of neutral substrates to produce cationic species, such as protons or metal cations to serve as Bronsted acids or Lewis acids, can potentially be coupled with the CO2 reduction reaction at the cathode. In particular, coupling the electrochemical CO2 reduction reaction with the anodic generation of a Lewis acid can be a new approach to synthesizing new products from CO2 while avoiding a high proton environment. In this study, we explored the coupling of the anodic Lewis acid generation by the dissolution of a titanium anode and the cathodic production of formate from CO2 in a methanol electrolyte. As a result, we observed methyl formate as a CO2 conversion product with the highest faradaic efficiency of 69% under ambient conditions. Interestingly, methyl formate was observed only when NaBF4 was used in an undivided electrochemical cell, whereas only formic acid/formate was produced when sodium salts of other anion counterparts were utilized. We have shown that the anodic generation of Ti4+ cations surrounded by less coordinating anions led to fluoride abstraction from BF4– anions. This resulted in BF3, the active Lewis acid in the esterification reaction of formate and methanol, producing methyl formate.

The chemical potential (μ) is a substantial but ignored factor in many theoretical studies of electrochemical nitric oxide reduction (NORR). Herein, by means of the grand canonical density functional theory in the JDFTx, the chemical-potential-dependent intermediate configurations and catalytic activities have been investigated on the designed nine single-cluster catalysts, which are composed of the trimeric-transition-metal cluster-embedded graphitic carbon nitride (TM3@C3N4, TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu). The Co3@C3N4, Ni3@C3N4, and Cu3@C3N4 with small or even no thermodynamic energy barriers are considered to be efficient NORR catalysts at μ= 0 eV vs SHE. By the analysis of the chemical-potential-dependent density of state (DOS), electron variation, and global softness (S), the intrinsic charge effect induced by the applied chemical potential (μ) has been revealed. We refer to the fact that chemical potential plays an important role in catalytic activity evaluation and electronic property analysis, which cannot be described in the traditional electric neutral model.

Despite years of research, detailed understanding of the coupling between metallic and upconverting nanoparticles (UCNPs) remains elusive. Although many studies reported modified upconverted luminescence (UCL) intensity and/or lifetime upon coupling, the driving force behind the change was often vague. Published reports clearly indicate that surface plasmon polaritons (SPPs) can impact each step of the photon upconversion: excitation, energy transfer, relaxation, and emission. For silver nanowires, which do not exhibit a clear, single plasmon resonance, clarification of the role played by SPPs is additionally complex. In this work, we employ studies of hyperspectral mapping and luminescence dynamics combined with finite-difference time-domain simulations to reveal how SPPs in silver nanowires impact the UCL. We present evidence that the interaction with SPPs leads to shortening of the emitting state, not the intermediate state, lifetime. The faster population decay alters the excitation pathways and results in modifications of the UCL spectra. This work shows that interactions with SPPs not only changes the UCL intensity and dynamics but can also be used to tune the spectral properties of UCNPs.

We investigate the charge carrier dynamics in HgTe quantum dots emitting in the second near-infrared window (1000–2500 nm). To provide a link between fundamental physics and practical application, we made consistent studies of the charge carrier dynamics evolution for quantum dots in different states: colloidal solutions of quantum dots capped with a long-chain ligand; thin films made from them; and finally, exchanged to short-chain ligand films suitable for field effect transistor based devices. Ultrafast transient absorption spectroscopy reveals an ultralow Auger-related nonradiative relaxation threshold at 0.1 exciton per quantum dot, both in colloidal solutions and solid films, with a rate of 30 ns–1. The exchange from long- to short-chain ligands causing closer packing of the HgTe quantum dots leads to a strong increase of the Auger recombination rate of up to 100 ns–1. The competition between the Auger process and excitonic recombination significantly affects the performance of HgTe-based thin film photodetectors operating at room temperature, resulting in a 2 orders of magnitude drop in responsivity when the excitation flux was increased from 0.01 to 5 W·cm–2.

We investigated the effects of oxygen on the optical properties of wet-chemically synthesized colloidal CdSe quantum wires using confocal spectroscopy. By comparing the photoluminescence characteristics of CdSe quantum wires in oxygen and in inert gas atmospheres, we observed both irreversible photoluminescence enhancement and quenching processes in oxygen as well as reversible changes in the emission spectra and Raman spectra when changing the gas atmosphere during continuous excitation. We attribute the irreversible photoluminescence enhancement to reduction of Auger recombination by formation of oxides on the surface, which eventually leads to photoluminescence quenching. The reversible atmosphere-dependent changes in the emission intensity and wavelengths, accompanied by changes in the Raman spectra, are attributed to electron scavenging by oxygen. This was demonstrated as the presence of excess negative charge carriers led to radiative emission of higher excited states and reduced Raman frequencies when illuminating in inert gas atmospheres. Thereby, this work provides insight into the possible photoinduced effects of oxygen on the optical properties of semiconducting nanoparticles and thus contributes to a more detailed understanding of photobrightening mechanisms.

A series of three perylenemonoimide-p-oligophenylene-dimethylaniline molecular dyads undergo photoinduced charge separation (CS) with anomalous distance dependence as a function of increasing donor–acceptor (DA) distances. A comprehensive experimental and computational investigation of the photodynamics in the donor–bridge–acceptor (DBA) chromophores reveals a clear demarcation concerning the nature of the CS accessed at shorter (bridgeless) and longer DA distances. At the shortest distance, a strong DA interaction and ground-state charge delocalization populate a hot excited state (ES) with prominent charge transfer (CT) character, via Franck–Condon vertical excitation. The presence of such a CT-polarized hot ES enables a subpicosecond CS in the bridgeless dyad. The incorporation of the p-oligophenylene bridge effectively decouples the donor and the acceptor units in the ground state and consequentially suppresses the CT polarization in the hot ES. Theoretically, this should render a slower CS at longer distances. However, the transient absorption measurement reveals a fast CS process at the longer distance, contrary to the anticipated exponential distance dependence of the CS rates. A closer look into the excited-state dynamics suggests that the hot ES undergoes ultrafast geometry relaxation (τ < 1 ps) to create a relaxed ES. As compared to a decoupled, twisted geometry in the hot ES, the geometry of the relaxed ES exhibits a more planar conformation of the p-oligophenylene bridges. Planarization of the bridge endorses an increased charge delocalization and a prominent CT character in the relaxed ES and forms the origin for the evident fast CS at the longest distance. Thus, the relaxation of the hot ES and the concomitantly enhanced charge delocalization adds a new caveat to the classic nature of distance-dependent CS in artificial DBA chromophores and recommends a cautious treatment of the attenuation factor (β) while discussing anomalous CS trends.

Strong light–matter coupling hybridizes light and matter to form states known as polaritons, which give rise to a characteristic anticrossing signature in dispersion plots. Here, we identify conditions under which an anticrossing can occur in the absence of strong coupling. We study planar silver/dielectric structures and find that, around the epsilon-near-zero point in silver, the impedance matching between the silver and dielectric layers gives rise to an anticrossing. Our work shows that care must be taken to ensure that anticrossing arising from impedance matching is not misattributed to strong coupling.

Extinction at 400 nm is a convenient, cheap, and fast method for in situ determination of Au concentration in colloids with good accuracy even in the presence of Au(+3) ions and other interference factors. However, these possibilities have been validated only with common citrate gold nanospheres and, in part, with gold nanorods. Here, we demonstrate the universality of the UV–vis extinction method with six experimental and theoretical models: (1) CTAC-stabilized gold nanospheres; (2) small and large nanosphere clusters; (3) gold nanorods with plasmon resonances (PRs) ranging from 670 to 980 nm; (4) 2D nanotriangles and (5) 2D nanoplates with PRs from 600 to 775 nm; and (6) gold nanostars with PRs from 680 to 820 nm. In total, we fabricated 34 samples with different nanoparticle sizes, shapes, morphologies, and Au concentrations. From COMSOL, T-matrix, and generalized multiparticle Mie simulations, we derived a universal relation between the extinction cross section and the particle or cluster volume V: Cext (nm2) = 0.51 × V (nm3), 102 ≤ V (nm3) ≤ 105, which gives a universal relation between the gold concentration and extinction [Au0] (mM) = 0.44 × A400. The same relation is derived from atomic absorption spectroscopy and inductively coupled plasma mass spectroscopy experimental determination of [Au0] concentration correlated with A400. While the universality of the derived equation is demonstrated by an unprecedented set of gold nanoparticle sizes, shapes, morphologies, and particle clusters, its accuracy can be limited by 20–30%. This uncertainty results from the light scattering contribution that violates the proportionality between the extinction cross section and the particle or cluster volume. However, for a particular colloidal system, the application of the derived relation can be useful in monitoring reduction or aggregation processes.

Colloidal 2D PbSe nanoplatelets (NPLs) are promising near- and short wave-infrared emitters for optoelectronic applications at telecommunication wavelengths. However, their photoluminescence quantum yield (PLQY) is limited by the ubiquitous presence of surface-related trap states. Here, we apply a treatment of colloidal PbSe NPLs with different metal halides (MX2, M = Zn, Cd, Pb; X = F, Cl, Br, I) to improve their emission brightness. A surface passivation of the NPLs by PbI2 leads to the best results with a strongly increased PLQY (27% for PbSe NPLs emitting at 0.98 eV (1265 nm) and up to 61% for PbSe NPLs emitting at 1.25 eV (989 nm)). Simultaneously, the full width at half-maximum of the NPL photoluminescence decreased by 10% after the treatment. X-ray photoelectron spectroscopy and complementary surface treatment of PbSe NPLs with organic halides reveal the combined passivating role of both X-type binding halides X– and Z-type binding metal halides MX2 in enhancing the optical properties of the PbSe NPLs. Our results emphasize the potential of 2D PbSe NPLs for efficient emission tailored for the application in fiber optics.

Doping of zinc blende ZnS semiconductor quantum dots with Mn is interesting for the developing field of quantum information. A potential way to enhance the magnetic and magneto-optical responses of such materials is to increase the dopant concentration. This strategy will only be successful if the spin coupling between the dopants is ferromagnetic since antiferromagnetic coupling would lead to lower magnetic activity. In this work, we study the spin coupling and the energetics of Mn clusters by means of density functional theory calculations. We find that the spin coupling between nearest neighbor Mn dopant spins is moderately antiferromagnetic, while it becomes negligible already when the Mn atoms are in second nearest neighbor position (5.4 Å). Furthermore, the structures where the Mn atoms are clustered are more stable over the more homogeneous distribution of Mn dopant atoms. Our findings hint at a potential shortcoming of the strategy to enhance magnetic and magneto-optical responses of Mn-doped ZnS quantum dots by increasing the dopant concentration.

The common method for producing graphene, the oxidation and reduction method, is not green due to application of corrosive oxidants and reductants, and the obtained graphene is rich in surface defects. Here, we show a novel edge-decoration strategy for the facile exfoliation of graphene layers from graphite. By grafting methyl isopropyl ketone (MIBK) onto the edges of graphite via the aldol condensation reaction, the dense graphene layers become loose, facilitating the exfoliation process and promoting largely the graphene yield from 1.6 to 10.9 wt %. The edge-decoration strategy produces graphene with 5–10 layers and few surface defects. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and activation experiments prove that the edges of graphite reacted with MIBK via C═O as the active site, causing the grafting of MIBK. We anticipate that the edge-decoration strategy will show great potential in the large-scale production of graphene due to its high efficiency and greenness.

The spectator exciton method follows stepwise changes in a nanocrystal’s absorption with the accumulated number of excitons. It involves comparison of pump–probe spectra in pristine samples with that from nanocrystals excited with a progressive number of cold excitons. Using this approach, 50% of hot electrons were shown to be blocked from cooling directly to the band edge in CdSe nanodots already excited with a single cold exciton due to electron spin orientation conflicts. Similar experiments which are reported here in quantum-confined PbS nanodots have not detected spin-related relaxation blockades. Instead, a progressive broadening of the 1Se1Sh absorption band with loading of cold excitons is manifest in the difference spectra, demonstrating the inadequacy of any single-probe wavelength to quantify band-edge state filling. Comparing data for single and double spectator states proves that the sub band gap induced absorption characteristic of hot exciton states in all quantum dots is not the low-energy half of biexciton shifting to the 1Se1Sh absorption band. Instead, it is part of a broad induced absorption characteristic of hot excitons regardless of the spectator count. Finally, the unique capability of spectator excitons (SXs) to detect contributions of stimulated emission to pump–probe signals is demonstrated in singly excited PbS nanocrystals. Contrary to recent literature reports of such contributions, none are observed. These outcomes call for revisions to the conventional interpretation of excited state spectroscopy in quantum confined nanocrystals.

Metallic nanomaterials with an amorphous structure and unique properties have received increasing attention. However, the formation of the amorphous structure is strictly limited by the preparation method, and at the same time, the control of the proportion of amorphous regions is difficult to realize. Here, for the first time, we report that PdCu nanodots with an amorphous or crystal structure can be successfully modulated with the assistance of supercritical carbon dioxide (SC CO2), including their thickness, crystallinity, and valence state. In addition, the corresponding applications of the as-prepared PdCu nanodots are also demonstrated; amorphous PdCu nanodots can realize efficient photothermal conversion, while crystal PdCu nanodots can help realize excellent electrocatalytic activity for formic acid oxidation. The mass activity is 1502.6 mA/mgPd, which is 3.7 times higher than that of the commercial Pd/C catalyst. More importantly, this study sheds light on the amorphization mechanism of a pure metal material system in SC CO2 and provides inspiration for preparing more amorphous nanomaterials with fascinating structures and properties.

Photocatalysis of bismuth vanadate (BiVO4) particles can be enhanced by selectively loading cocatalysts on different facets. Using BiVO4 loaded with CoOx on oxidation facets and Rh on the reduction facets as a model, we studied the effects of selectively loaded cocatalyst on the local charge carrier dynamics by pattern-illumination time-resolved phase microscopy. The local charge carrier dynamics were analyzed by clustering analyses of the charge carrier responses, and they were categorized in the presence and absence of the cocatalysts. From the mapping of the charge carrier types with and without scavengers, the electron and hole responses trapped to cocatalysts were assigned successfully, and they were spatially separated at the local positions of the particles and/or aggregates. It was clarified that CoOx and Rh could keep the holes and electrons on the order of several microseconds and hundreds of nanoseconds, respectively.

Recent experiments have shown that exfoliated few-layer CrI3, a prototypical van der Waals magnet, undergoes a phase transition from the high-temperature monoclinic structure to the low-temperature rhombohedral structure under pressure. To understand how the magnetism of CrI3 responds to these structural changes, we perform ab initio density functional theory simulations on bilayer CrI3. We simulate the interlayer lateral shift-dependent potential energy surface of bilayer CrI3 to examine the stability and magnetism as a function of external pressure. Using the hybrid PBE0 functional, we are able to give qualitatively correct exchange coupling energies, without using an on-site Coulomb interaction correction. Thus, we avoid using tunable parameters. The results show that under external pressure, the monoclinic crystal structure is destabilized in comparison with the rhombohedral structure, in agreement with the observed phase transition in few-layer CrI3 devices under pressure. We also look into the microscopic origins of the interlayer exchange coupling. We identify the competing orbital pathways that favor ferromagnetic and antiferromagnetic kinetic exchange, respectively, which are consistent with previous reports. This study opens a new direction of using hybrid functionals with Gaussian orbitals and a cluster-based approach for obtaining Heisenberg J values to accurately simulate the magnetic properties of 2D materials.

Advanced instrumentation and modern analysis tools such as transmission electron microscopy (TEM) have led to phenomenal progress in understanding crystallization, in particular from solution, which is a prerequisite for the design-based preparation of a target crystal. Nevertheless, little has been understood about the crystallization pathway under high-temperature annealing (HTA) conditions. Metal oxide crystals are prominent materials that are usually obtained via HTA. Despite the widespread application of hydro-/solvothermal methods on the laboratory scale, HTA is the preferred method in many industries for the mass production of metal oxide crystals. However, poor control over the morphology and grain sizes of these crystals under extreme HTA conditions limits their applications. Here, applying ex-situ TEM, the transformation of a single amorphous spherical submicrometer precursor particle of SrAl12O19 (SA6) at 1150 °C toward a nanosized thermodynamically favored hexagonal crystal is explored. It is illustrated in real space, step by step, how both kinetic and thermodynamic factors contribute to this faceting and morphology evolution. These results demonstrate a nonclassical nucleation and growth process consisting of densification, crystallite domain formation, oriented attachment, surface nucleation, 2-dimensional (2D) growth, and surface diffusion of the atoms to eventually result in the formation of a hexagonal platelet crystal. The TEM images further delineate a parent crystal driving the crystal lattice and morphological orientation of a network of interconnected platelets.

Understanding low-dimensional quantum materials is important both in fundamental research and technological applications. One goal is to understand their structural and electronic phase diagrams in a multi-parameter phase space involving variation of several control parameters. Here, we examine the response of the charge density wave (CDW) material 1T-TaS2 to molecular intercalation with triethylenediamine (TED, C6H12N2) followed by application of hydrostatic pressure. Significant modifications in the CDW structure are observed in the pressurized TaS2–TED intercalation complex. This is characterized by changes in CDW modulation wavelength and a decrease in CDW long-range order. In addition, molecular electron-energy-loss spectra (EELS) reveal changes in the TED molecular structure as a result of pressure application. EELS spectra also show that changes in the molecular structure are more likely than changes in the orientation of the molecules within the van der Waals gap. Combining pressure and intercalation shows a way to create organic–inorganic hybrid structures with properties different from the individual components.

The temperature-dependent effective potential (TDEP) method for anharmonic phonon dispersion is generalized to the full potential case by combining with path integral formalism. This extension naturally resolves the intrinsic difficulty in the original TDEP at low temperatures. The new method is applied to solid metallic hydrogen at high pressure. A colossal nuclear quantum effect (NQE) and subsequent anharmonicity are discovered, which not only leads to unexpectedly large drift of protons but also slows down the convergence rate substantially when computing the phonon dispersions. By employing direct ab initio path integral molecular dynamics simulations as the benchmark, a possible breakdown of phonon picture in metallic hydrogen due to the colossal NQE is indicated, implying novel lattice dynamical phenomena might exist. Inspired by this observation, a general theoretical formalism for quantum lattice dynamics beyond phonon is proposed, with the main features being discussed.

Owing to the polycrystalline nature of hybrid perovskite thin films, the trap states in grain boundaries (GBs) introduced by charged defects play an important role in determining the charge collection efficiency and have a significant impact on their optoelectronic properties. Herein, we show the direct imaging of the GB passivation of perovskite films through an anti-solvent treatment and the anomalous charge distribution across the films due to the passivation. The downward band bending at the GBs has been observed at nanometer scale using Kelvin probe force microscopy. This revealed that a hot chlorobenzene treatment decreases the band bending at GBs and allows more homogeneous electronic properties throughout the film after passivation. Conductive atomic force microscopy has been employed to show the charge transport mapping across the films. It was found that the passivation effect not only changes the surface potential at GBs but also enhances the overall charge collection efficiency of the film. Our work provides a solution to reduce the density of charge defects at GBs through hot anti-solvent treatment, which is demonstrated to be a promising strategy to decrease the recombination losses at GBs and, thereby, increase the electronic quality of the perovskite films as well as enhance the device performance.

On-top hydrogen on a Pd cathode (Pd–H) was observed for the first time by operando infrared (IR) spectroscopy at 2030 cm–1, being stabilized by co-adsorbed solvent (n-alkane) molecules. A proton-exchange membrane (PEM) reactor with Pt/C (anode) and Pd/C (cathode) catalysts was modified to transmit an IR beam for operando observation. Pd–H species was observed when (1) H+ was supplied to the cathodic chamber through the PEM, (2) solvent was flowed at the cathode, and (3) an appropriate bias was applied to the cathode. Because atomic H on Pd surfaces interacts with multiple Pd atoms, on-top Pd–H is proposed to be stabilized by co-adsorbed solvent molecules. Spectra of the solvent were deformed when Pd–H species were present: the peak intensity increased and nonfundamental bands at 2800–2500 cm–1 became pronounced. The intensification of these bands was caused by resonance with free-electron absorption bands in the IR region.

The absorption and emission spectra of six rhodamine dyes are examined in dilute aqueous solution and as thin films on a glass substrate. The absorption and emission spectra in water can be described using the displaced harmonic oscillator (DHO) model. The changes of the absorption maxima in aqueous solution are controlled by the substitution of alkyl groups on the xanthene nitrogen atoms, which is supported by density functional theory calculations. In addition, the nature of the alkyl substitution influences the excited state lifetimes. In contrast, the photophysical behavior of thin films of the dyes cannot be described using the DHO model. Rather, the spectral changes depend on interactions with the glass substrate for thin films and by aggregation for thicker films. The intensity of the emission spectra can be maximized by controlling the film thickness to be less than a monolayer.

Because of its metal-like conductivity, excellent catalytic activity, and acid resistance, lead dioxide (PbO2) is the most used electrocatalyst for the practical electrochemical ozone production (EOP) technique. Introducing fluorine (F) into PbO2 electrodes or electrolytes can significantly improve EOP activity. However, there is still lack of valid evidence on understanding the role of doping F in the PbO2 electrode. In this work, we report a comprehensive study on the effect of F on EOP activity on electrochemically prepared PbO2 electrodes. F doping suppresses the side reaction of dioxygen (O2) evolution by inhibiting the formation of an α phase impurity of PbO2 electrodes. The more hydrophobic surfaces by doping F promote O2 adsorption as evidenced by low-temperature O2-temperature-programmed desorption experiments and thus are more favorable for ozone (O3) generation. The in situ isotope labeling oxygen (18O2) experiment proves that at room temperature, O2 can adsorb and dissociate on the operando PbO2 electrode surface and participate in the formation of O3 molecules. This work provides a comprehensive understanding of doping F for enhanced EOP.

The experimental measurement of slow F– ions (v < 0.1 a.u.) scattered from a clean and flat LiF(001) surface at a grazing angle of incidence shows that there is a large fraction of F– projectile destruction. Here, from detailed energy defect and transition probability calculations, we find that the large F– destruction observed was due to the formation of a local pre-existing surface band-gap electronic state, Li2+(12Σu+,R = aLiF/√2) (aLiF = lattice constant of the LiF crystal), via a nearly resonant charge transfer between the F– projectile and two nearest-neighbor Li+ lattice ions along the ⟨110⟩ or ⟨1̅10⟩ channel at the LiF(001) surface. In combination with the related energy loss, the physical pictures of the producing mechanism of various products for 1 keV F+ incidence based on this state are also presented. An internuclear distance of R = 2.84 Å makes the efficient and controllable preparation of this state on a LiF surface possible, paving the way for atomic-scale microdevice fabrication.

Silver–bismuth halide double perovskites have recently emerged as one of the most promising green candidates for X-ray detection. However, their sensitivity still leaves behind the lead-based counterparts owing to the poor intrinsic optoelectronic properties and challenging crystal growth. Therefore, we conducted the space cation engineering by introducing fluorinated aromatic spacers to silver–bismuth perovskites, and the large (FPEA)4AgBiBr8 (FPEA+ is 4-fluorophenethylammonium) single-crystals were synthesized for the first time. The p−π coupling, large dielectric constant, and strong interlayer binding were revealed by ab initio calculation in this system. These effects further lead to better crystal quality and electrical properties, which was confirmed by the experimental characterizations. Consequently, X-ray detector based on (FPEA)4AgBiBr8 single-crystal exhibits low dark current as well as noise level and a good sensitivity of 27 μC Gyair–1 cm–2. This work reveals the effects of fluorinated aromatic spacer in Ag–Bi double perovskite and offers an inspiring strategy for materials design.

There is a growing interest in the development of routes to produce formic acid from CO2, such as the electrochemical reduction of CO2 to formic acid. The solubility of CO2 in the electrolyte influences the production rate of formic acid. Here, the dependence of the CO2 solubility in aqueous HCOOH solutions with electrolytes on the composition and the NaCl concentration was studied by Continuous Fractional Component Monte Carlo simulations at 298.15 K and 1 bar. The chemical potentials of CO2, H2O, and HCOOH were obtained directly from single simulations, enabling the calculation of Henry coefficients and subsequently considering salting in or salting out effects. As the force fields for HCOOH and H2O may not be compatible due to the presence of strong hydrogen bonds, the Gibbs–Duhem integration test was used to test this compatibility. The combination of the OPLS/AA force field with a new set of parameters, in combination with the SPC/E force field for water, was selected. It was found that the solubility of CO2 decreases with increasing NaCl concentration in the solution and increases with the increase of HCOOH concentration. This continues up to a certain concentration of HCOOH in the solution, after which the CO2 solubility is high and the NaCl concentration has no significant effect.

The electronic and spintronic properties of the monovacancies in freestanding and isotopically compressed graphene are investigated using hybrid exchange density functional perturbation theory. When the effects of electronic self-interaction are taken into account, an integer magnetic moment of 2 μB is identified for a Jahn–Teller reconstructed V1(5–9) monovacancy in freestanding graphene. For graphene with stable ripples induced by a compressive strain of 5%, a bond reconstruction produces a V1(55–66) structure for the monovacancy, which is localized at the saddle points of the ripple. The sizeable local distortion induced by reconstruction modifies both the geometric and electronic properties of rippled graphene and quenches the magnetic moment of the vacancy due to the sp3 hybridization of the central atom. The nonmagnetic V1(55–66) structure is found to be stable on rippled structures, with the formation energy ∼2.3 eV lower than that of the metastable distorted V1(5–9) structures localized at sites other than the saddle points. The electronic ground state of distorted V1(5–9) corresponds to a wide range of fractional magnetic moments (0.50–1.25 μB). The computed relative stabilities and the electronic and magnetic properties of the V1(5–9) structures are found to be closely related to their local distortions. This analysis of the fundamental properties of defective graphene under compression suggests a number of strategies for generating regular defect patterns with tuneable magnetic and electronic properties and may, therefore, be used as a novel technique to achieve more precise control of graphene electronic structure for various application scenarios such as transistors, strain sensors, and directed chemisorption.

Utilizing a hybrid functional method, the transparency and p-type conductivity of BeSe are investigated. Our studies confirm that N- and P-substituted Se (labeled as NSe and PSe) are promising p-type defects due to their smaller ionization energy. BeN2 and BeP2 are efficient dopant sources for their moderate formation energy. Based on the thermodynamic equilibrium fabrication method together with the rapidly quenching scheme, we find the hole density, induced by NSe (PSe) defects, can reach 4.44 × 1018 (3.83 × 1016) cm–3. A high density of holes, smaller hole effective mass (along the Γ-X and W-X directions, the hole effective masses are 0.466 and 0.759m0 (m0 is the electron’s static mass)), wide band gap, and weak plasmonic effect show that BeSe with NSe defects is an excellent transparent p-type semiconductor. These findings provide significant insight to explore a transparent p-type semiconductor.

The discovery of new and stable two-dimensional (2D) materials with exotic properties is essential for technological advancement. Inspired by the recently reported penta-PdPSe, we proposed penta-NiPS as a new member of the penta-2D materials based on first-principles calculations. The penta-NiPS monolayer is stable in two polymorphs including the α phase with an identical structure as penta-PdPSe and the newly proposed β phase with rotated sublayers. Comprehensive analyses indicated that both phases are thermodynamically, dynamically, mechanically, and thermally stable. The penta-NiPS is a soft material with 2D Young’s modulus of Ea = 208 N m–1 and Eb = 178 N m–1 for the α phase and Ea = 184 N m–1 and Eb = 140 N m–1 for the β phase. Interestingly, the α-penta-NiPS showed nearly zero Poisson’s ratios along the in-plane direction, where its dimensions would be maintained when being extended. For electronic application, we demonstrated that penta-NiPS is a wide band gap semiconductor with an indirect band gap of 2.35 eV for the α phase and 2.20 eV for the β phase.

High dielectric constant organic semiconductors, often obtained by the use of ethylene glycol (EG) side chains, have gained attention in recent years in the efforts of improving the device performance for various applications. Dielectric constant enhancements due to EGs have been demonstrated extensively, but various effects, such as the choice of the particular molecule and the frequency and temperature regime, that determine the extent of this enhancement require further understanding. In this work, we study these effects by means of polarizable molecular dynamics simulations on a carefully selected set of fullerene derivatives with EG side chains. The selection allows studying the dielectric response in terms of both the number and length of EG chains and also the choice of the group connecting the fullerene to the EG chain. The computed time- and frequency-dependent dielectric responses reveal that the experimentally observed rise of the dielectric constant within the kilo/megahertz regime for some molecules is likely due to the highly stretched dielectric response of the EGs: the initial sharp increase over the first few nanoseconds is followed by a smaller but persistent increase in the range of microseconds. Additionally, our computational protocol allows the separation of different factors that contribute to the overall dielectric constant, providing insights to make several molecular design guides for future organic materials in order to enhance their dielectric constant further.

Metal halide perovskites (MHPs) have soft lattices with strong anharmonicity and will undergo entropy-driven solid–solid phase transitions upon heating. Here, we investigate the polymorph stabilities and phase transitions in one of the lead-free MHPs, CsSnI3, by several molecular simulation techniques. Three different phase transitions (γ ↔ β, β ↔ α, and yellow → black) in CsSnI3 have been successfully reproduced by molecular dynamics (MD) simulations with a newly developed empirical force field. The heating and annealing MD simulations and free-energy calculations with the non-equilibrium thermodynamic integration (NETI) method predict the transition temperatures of 275, 385, and 280 K for the γ ↔ β, β ↔ α, and yellow → black transitions, respectively. Lattice dynamics (LD) simulations within the harmonic approximation fail to predict the correct phase stability in CsSnI3 at high temperatures. The quasiharmonic approximation (QHA) calculations that include the volume dependence of the phonon frequencies and lattice energies correctly predict all phase transitions in CsSnI3. However, the transition temperatures of the γ ↔ β and β ↔ α transitions predicted by the QHA calculations significantly deviate from those by MD simulations. By comparing the Gibbs free energies calculated by the LD simulations within the QHA and MD-based NETI method, we find the differences of 3–30 meV for different polymorphs. Although calculations based on the harmonic model can provide valuable information, the anharmonic terms need to be included for accurate predictions of transition temperatures of phase transitions in CsSnI3 and other MHPs.

Zeolites are widely used for molecular adsorption, gas separation, and catalyst support due to their high specific surface area, but few studies have focused on their electrical properties. More than 200 types of zeolites have been reported due to differences in their composition and structure, but analcime has been discarded as an industrial waste because it does not have the aforementioned functions. In this study, we not only clarified that the direction of sodium ion conduction in analcime is ⟨211⟩ and ⟨110⟩ by crystal structure analysis and the AC impedance method but also revealed that the ionic conductivity of a polycrystalline dense body of analcime is comparable to that of its single crystal (0.44 S/cm at 873 K). In addition, we found that the electromotive force of polycrystalline dense analcime on carbon dioxide is comparable to that of NASICON (225 mV at 723 K), an expensive sodium ion conductor used as a solid electrolyte for carbon dioxide detection. The results of this study indicated that analcime can be a candidate for low-cost solid electrolytes.

Methane is widespread in the Universe, and its occurrence is intimately connected with that of water, often as clathrate hydrate, likely the priority form in which methane is stored in icy moons, water-rich exoplanets but also in the depths of Earth’s oceans. Arrangement and stability range of the crystalline structures, decomposition conditions, and miscibility of the resulting dense fluid mixtures are crucial for modeling the static and dynamic properties of these complex extraterrestrial environments and for identifying possible prebiotic reactive events under transient favorable conditions of pressure, temperature, and irradiation. Here, we report a high-pressure study of methane hydrate up to 4 GPa and 550 K. Ex situ synthesis of crystalline methane hydrate allowed the analysis of homogeneous samples by state of the art Raman and FTIR spectroscopy, accessing information which considerably expands and modifies our knowledge of the crystalline structures, of the decomposition conditions, and of the molten fluid’s characteristics in a wide pressure and temperature range.

Highly rigid membrane materials with tailored structures have exhibited permeabilities and selectivities that exceed the polymer upper bound in gaseous and organic solvent separations for challenging mixtures containing species that are similar in size and shape. One potential question is whether such membrane materials can maintain meaningful guest diffusivities in situations where the microporous spaces are essentially full of guest molecules. Here, we use a simplified transition state theory approach to estimate the diffusivity of water and small organics within a microporous membrane. The transition state theory model is parameterized using experimental values from zeolites and carbon molecular sieve materials found in the literature. We demonstrate the differences in transport and Maxwell–Stefan diffusivities based on guest species loading with different isotherm behaviors. These calculations theorize a path forward for highly selective reverse osmosis membranes for aqueous phase separations.

Depletion-driven assembly has been widely studied for micrometer-sized colloids, but questions remain at the nanoscale where the governing physics are impacted by the stabilizing surface ligands or wrapping polymers, whose length scales are on the same order as those of the colloidal core and the depletant. Here, we probe how wrapping colloidal tin-doped indium oxide nanocrystals with polymers affects their depletion-induced interactions and assembly in solutions of poly(ethylene glycol). Copolymers of poly(acrylic acid) grafted with poly(ethylene oxide) provide nanocrystal wrappings with different effective polymer graft densities and molecular weights. (Ultra)small-angle X-ray scattering, coarse-grained molecular dynamics simulation, and molecular thermodynamic theory were combined to analyze how depletant size and polymer wrapping characteristics affect depletion interactions, structure, and phase behavior. The results show how depletant molecular weight, as well as surface density and molecular weight of polymer grafts, sets thresholds for assembly. These signatures are unique to depletion-driven assembly of nanoscale colloids and mirror phase behaviors of grafted nanoparticle–polymer composites. Optical and rheological responses of depletion-driven assemblies of nanocrystals with different polymer shell architectures were probed to learn how their structural differences impact properties. We discuss how these handles for depletion-driven assembly at the nanoscale may provide fresh opportunities for designing responsive depletion interactions and dynamically reconfigurable materials.

Multimodal contrast agents, which take advantage of different imaging modalities, have emerged as an interesting approach to overcome the technical limitations of individual techniques. We developed hybrid nanoparticles comprising an iron oxide core and an outer gold spiky layer, stabilized by a biocompatible polymeric shell. The combined magnetic and optical properties of the different components provide the required functionalities for magnetic resonance imaging (MRI), surface-enhanced Raman scattering (SERS), and fluorescence imaging. The fabrication of such hybrid nanoprobes comprised the adsorption of small gold nanoparticles onto premade iron oxide cores, followed by controlled growth of spiky gold shells. The gold layer thickness and branching degree (tip sharpness) can be controlled by modifying both the density of Au nanoparticle seeds on the iron oxide cores and the subsequent nanostar growth conditions. We additionally demonstrated the performance of these hybrid multifunctional nanoparticles as multimodal contrast agents for correlative imaging of in vitro cell models and ex vivo tissues.

While amorphous metal–organic frameworks form an emerging class of materials of growing interest, their structural characterization remains experimentally and computationally challenging. Out of the many molecular simulation methods that exist to model these disordered materials, one strategy consists in simulating the phase transition from a crystalline MOF to the amorphous state using molecular dynamics. ReaxFF reactive force fields have been proposed for this purpose in several studies to generate models of zeolitic imidazolate framework glasses by melt quenching. In this work, we investigate the accuracy and reliability of this approach by reproducing the published procedures and comparing the structure of the resulting glasses to other data, including ab initio modeling, in detail. We find that the in silico melt-quench procedure is extremely sensitive to the choice of methodology and parameters and suggest adaptations to improve the scheme. We also show that the glass models generated with ReaxFF are markedly different from their ab initio counterparts, as well as known experimental characteristics, and feature an unphysical description of the local coordination environment, which in turn affects the medium-range and bulk properties.

Spin coating is one of the most common techniques for the production of thin films in laboratories. In this work, we investigate spin coating of a P3HT/PC71BM blend while in situ measuring the change in transmission to gain a general understanding of the film-forming-process. We show that spin coating can be divided into three phases: first, the distribution phase; second, a film thinning phase; and finally, film crystallization. The final morphology of the crystalline film at the end of the spin coating process is almost entirely influenced by the crystallization phase, whereas the other phases do not have the same influence on the final film quality. We found that processing conditions, such as decreasing the solution temperature, decreasing the spin speed, or increasing the solution concentration, increase the crystallinity of the film. This is always related to an increase in crystallization phase duration. When using additives in the solution, such as 1,8-diiodooctane, we observe a similar behavior in the timing of the crystallization phase.

Using surface sensitive techniques (photoemission, low-energy electron diffraction, and scanning tunneling microscopy), the present work reveals the competitive formation upon oxidation of two epitaxial oxide bilayer films of self-limited thickness on the surface of the ferritic random A2 body-centered alloy Fe0.85Al0.15(110). When oxidizing the substrate at 1193 K, a film (herein labeled oxide-A) similar to that studied in depth at NiAl(110) [Kresse et al., Science 2005, 308, 1440] is found. At a slightly lower annealing temperature (1073 K), alumina patches segregated from the bulk act as seeds for the growth of a new long-range ordered alumina film (oxide-B) with two domains having a ∼(23 × 23) Å2 hexagonal rotated unit cell. While showing different anion/cation chemical environments, the two films have a Al2O2.5±0.2 stoichiometry and stand on an Al-enriched subsurface with a similar ∼3 nm deep segregation profile. Most importantly, thermal treatments show that the new structure B is more stable than A. This finding conflicts with the apparent ubiquity of oxide-A that has been observed on many substrates of various symmetries and compositions. This competitive formation of ultra-thin alumina oxides questions the origin of their structural (di)similarity and the actual role of these seeds in the transition toward thicker alumina films at higher pressure.