Search

The S vacancy at metal/ MoS 2 interface plays a much important role than the semiconductor itself. In this work, the influence of different configurations of S vacancy concentrations on the effective work function and band structure of the Au/ MoS 2 interface has been investigated systematically using first-principles calculations. The study specifically explores the effective work function of the Au/ MoS 2 interface, the deviation of interface effects from the vacuum work function, and the dipole moment caused by interface charge transfer. The results reveal that the electronic work function of Au/ MoS 2 increases with the increase in S vacancy concentration, but the rate of increase tends to slow down with higher S concentrations. The variation in the effective work function of the Au/ MoS 2 interface may be attributed to the presence of S vacancies and the exposure of Mo atoms. S vacancies lead to a reduction in the Schottky barrier, resulting in increased leakage current. The Fermi pinning caused by S vacancy concentration and location is also observed. The results obtained in this study can serve as a theoretical foundation for applications in electronic devices that rely on metal/ MoS 2 contact. [ABSTRACT FROM AUTHOR]

The unstable plume mode of hollow cathodes should be avoided in practical applications because it severely degrades the overall cathode lifetime. In this study, we investigate the spot-plume transition and plasma stability characteristics of an unused segmented lanthanum hexaboride emitter. The expansion of the unstable plume mode region is observed during a discharge experiment. Subsequently, the segmented emitter is retrieved, the inner surface of the emitter is observed, and the work function on the surface is measured at room temperature. The emitter surface exhibits color variations with oxygen and carbon detection. The downstream edge shows the original purple color and almost no degradation in the work function. The high temperature in this region promotes the desorption of carbon and oxygen. In the spot mode, this region mainly contributes to thermionic electron emission; therefore, the discharge voltage in the spot mode does not change during the discharge experiment. Carbon or carbide is detected in the middle of the axial direction on the emitter surface, where the surface temperature is not sufficiently high to desorb carbon during discharge. Based on the surface analysis results, the dominant substance in the region where carbon is detected was lanthanum carbide. An increase in the work function is indicated in the region, which appears to increase the plasma instability. According to previous studies, an increase in the work function results in a rise in the potential in the emitter, and an increase in the electron temperature in the outside plume region induces the plasma instability. Further investigation is needed to understand the mechanism connecting the rise in the work function and the rise in the electron temperature in the plume region. [ABSTRACT FROM AUTHOR]

The dependence of electron work function, Φ , on the thickness of Ti layers was investigated by making use of the Kelvin method under ambient conditions. Layers were produced by vacuum phase deposition and were analyzed by x-ray photoelectron spectroscopy and transmission electron microscopy. A quantum size effect was revealed finding work function to increase as the layer thickness, z, decreased below 4 nm. The extent of increase, Δ Φ , was understood in terms of a simple particle-in-a-box model arriving at the function Δ Φ = ℏ 2 π 2 / 2 m e z 2 . This equation being free of any adjustable parameter, consisting only of the Planck constant and electron mass, seems to be a reasonable first approximation. [ABSTRACT FROM AUTHOR]

Graphite (Gr)‐based lithium‐ion batteries with admirable electrochemical performance below −20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+‐solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically‐stable solid electrolyte interphase (SEI) without compromising strong Li+‐solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature‐dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low‐temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e−) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4‐based, inorganics‐enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e− blocking and rapid desolvation, and as a result, much suppressed Li‐metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low‐temperature battery performances. Overall, our work originally provides visualized guides to improve low‐temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry. [ABSTRACT FROM AUTHOR]

As a class of predominantly used cathode interlayers (CILs) in organic solar cells (OSCs), perylene‐diimide (PDI)‐based polymers exhibit intriguing characteristics of excellent charge transporting capacity and suitable energy levels. Despite that, PDI‐based CILs with satisfied film‐forming ability and adequate solvent resistance are rather rare, which not only limits the further advance of OSC performances but also hinders the practical use of PDI CILs. Herein, we designed and synthesized two non‐conjugated PDI polymers for achieving high power conversion efficiency (PCE) in diverse types of OSCs. The utilization of oligo (ethylene glycol) (OEG) linkage enhanced the n‐doping effect of PDI polymers, leading to an improved ability of the CIL to reduce work function and improve electron transporting capability. Moreover, the introduction of the non‐ionic OEG chain effectively improve the wetting property and solvent resistance of PDI polymers, so the PPDINN CIL can withstand diverse processing conditions in fabricating different OSCs, including conventional, inverted and blade‐coated devices. The binary OSC with conventional structure using PPDINN CIL showed a PCE of 18.6 %, along with an improved device stability. Besides, PPDINN is compatible with the large‐area blade‐coating technique, and a PCE of 16.6 % was achieved in the 1‐cm2 OSC where a blade‐coated PPDINN was used. [ABSTRACT FROM AUTHOR]

Graphite (Gr)‐based lithium‐ion batteries with admirable electrochemical performance below −20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+‐solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically‐stable solid electrolyte interphase (SEI) without compromising strong Li+‐solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature‐dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low‐temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e−) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4‐based, inorganics‐enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e− blocking and rapid desolvation, and as a result, much suppressed Li‐metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low‐temperature battery performances. Overall, our work originally provides visualized guides to improve low‐temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry. [ABSTRACT FROM AUTHOR]

As a class of predominantly used cathode interlayers (CILs) in organic solar cells (OSCs), perylene‐diimide (PDI)‐based polymers exhibit intriguing characteristics of excellent charge transporting capacity and suitable energy levels. Despite that, PDI‐based CILs with satisfied film‐forming ability and adequate solvent resistance are rather rare, which not only limits the further advance of OSC performances but also hinders the practical use of PDI CILs. Herein, we designed and synthesized two non‐conjugated PDI polymers for achieving high power conversion efficiency (PCE) in diverse types of OSCs. The utilization of oligo (ethylene glycol) (OEG) linkage enhanced the n‐doping effect of PDI polymers, leading to an improved ability of the CIL to reduce work function and improve electron transporting capability. Moreover, the introduction of the non‐ionic OEG chain effectively improve the wetting property and solvent resistance of PDI polymers, so the PPDINN CIL can withstand diverse processing conditions in fabricating different OSCs, including conventional, inverted and blade‐coated devices. The binary OSC with conventional structure using PPDINN CIL showed a PCE of 18.6 %, along with an improved device stability. Besides, PPDINN is compatible with the large‐area blade‐coating technique, and a PCE of 16.6 % was achieved in the 1‐cm2 OSC where a blade‐coated PPDINN was used. [ABSTRACT FROM AUTHOR]

[Display omitted] The sluggish kinetics and inferior stability of oxygen electrocatalyst in rechargeable zinc air battery (ZAB) hamper its industrialization. In this work, we activate cobalt telluride (CoTe) by introduction of metallic cobalt (Co) to modulate the work function to facilitate the electron transfer from Co to CoTe during oxygen catalysis; additionally, the three-dimensional porous carbon nanosheets (3DPC) are invited to reduce the resistance towards electrolyte/oxygen diffusion. Thereby, Co-CoTe@3DPC only demands 280 mV overpotential to reach 10 mA cm−2 under alkaline oxygen evolution reaction (OER) condition, relatively lower than commercial iridium oxides (IrO 2); besides, the operando electrochemical impedance spectroscopy (EIS) indicates a better resistance towards surface reconstruction than Co@3DPC leading to a superior stability. A Pt-like oxygen reduction reaction (ORR) performance, half-wave potential associated with kinetic current density, is achieved for Co-CoTe@3DPC. A maximum power density of 203 mW cm−2 is achieved and sustains for 800 h. Furthermore, the all-solid-state ZAB offers 97 mW cm−2. Theoretical calculation suggests that the incorporation of metallic Co to CoTe maintains the superb ORR activity and promotes the OER catalysis. [ABSTRACT FROM AUTHOR]

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO2/Ga2O3 core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO2 core. At temperatures above 530 °C, the thermal reduction of SnO2 and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga2O3 shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO2 nanobelts, as both structures are likely connected through existing SnO2/SnO2 homojunctions comprising thin amorphous layers. [ABSTRACT FROM AUTHOR]

The effects of different Mn concentrations on the generalized stacking fault energies (GSFE) and elastic properties of MnxCoCrFeNi high-entropy alloys (HEAs) have been studied via first-principles, which are based on density functional theory. The relationship of different Mn concentrations with the chemical bond and surface activity of MnxCoCrFeNi HEAs are discussed from the perspectives of electronic structure and work function. The results show that the plastic deformation of MnxCoCrFeNi HEAs can be controlled via dislocation-mediated slip. But with the increase in Mn concentration, mechanical micro twinning can still be formed. The deformation resistance, shear resistance, and stiffness of MnxCoCrFeNi HEAs increase with the enhancement of Mn content. Accordingly, in the case of increased Mn concentration, the weakening of atomic bonds in MnxCoCrFeNi HEAs leads to the increase in alloy instability, which improves the possibility of dislocation. [ABSTRACT FROM AUTHOR]

Oxyhydrides have attracted attention as materials with various unique properties derived from lattice hydride ions (H−). However, their instability makes synthesis by conventional thermal synthesis methods difficult, so an appropriate synthesis strategy is required. Here, the mechanochemical synthesis of perovskite oxyhydrides BaREO2H (RE = Y, Sc) for catalyst applications is reported. The formation of BaYO2H is known to be thermodynamically unstable; however, a mechanochemical process that inevitably proceeds under non‐equilibrium conditions enables the synthesis of such a metastable oxyhydride material without any heat treatment. Furthermore, BaScO2H, which is typically obtained at very high temperatures (1000 °C) and pressure (>4 GPa), is successfully synthesized at room temperature by the mechanochemical method. The ammonia synthesis reaction over these oxyhydrides supporting Ru is significantly enhanced at low temperatures, and the ammonia synthesis rates are significantly higher than conventional oxide‐supported Ru catalysts. The mechanochemically synthesized BaREO2H has many anionic electrons with low work function at the site of H− vacancies, which enables strong electron donation to Ru and the storage of excess hydrogen adatoms from the Ru surface that results in high catalytic performance. [ABSTRACT FROM AUTHOR]

Electron transfer from a metal surface to a molecule is very important at the gas–surface interface, which can lead to electron-mediated energy transfer during molecular scattering from the surface, as evidenced by numerous state-to-state molecular beam experiments of NO and CO scattering from noble metal surfaces. However, it remains challenging to determine relevant charge-transfer states and their nonadiabatic couplings from first principles in such systems involving a continuum of metallic electronic states. In this work, we propose a pragmatic protocol for this purpose based on the constrained density functional theory (CDFT) approach. In particular, we discuss the influence of the charge partitioning algorithm used in CDFT to define the constraint property in molecule–metal systems. It is found that the widely used Bader charge analysis is adequate to define the physically sound CDFT diabatic states corresponding to a molecule with or without extra electron transferred from the metal. Numerical tests validate that the proposed CDFT scheme properly describes the electron transfer behaviors in several benchmark systems, namely, NO or CO interacting with Au(111) or Ag(111). The effects of the surface work function and the molecular electron affinity on electron transfer are discussed in detail by comparing the CDFT states of the four systems. This pragmatic CDFT protocol lays the foundation for constructing accurate global diabatic potential energy surfaces for these important systems and can be generalized to study other interfacial electron transfer related problems. [ABSTRACT FROM AUTHOR]

This article reports a study on the modification of bulk and Young's moduli of MoC carbide by partially substituting Mo with selected metallic elements, which influence the strengths and contributions of covalent, ionic, and metallic bond components to the overall atomic bonding of the carbide and thus its mechanical properties. Electron work function (EWF) analysis demonstrates that this parameter plays a promising role as an indicator similar to an encoded parameter with material "genetic" information for guiding the substitute selection. The higher the carbide's EWF, the higher are its bulk and Young's moduli. A substitute having a higher EWF generally enhances the covalent bonding at the expense of ionic bonding. The covalent bond plays a primary role in determining the carbide's strength, while the ionic bonding also contributes to the strength to some degree. A substitute having a higher EWF enhances the metallic bonding, which improves the carbide's strength as well, although such a contribution is minor. [ABSTRACT FROM AUTHOR]

Considered patterns of formation of the nanostructural state of the surface layer of machine parts during friction under conditions of complex dynamic loading. The results of the complex assessment of the state of the surface layer of samples after friction continuous indentation and scanning methods indenter, an analysis of changes in the work function of the electron from the surface of the samples. Shown that during the friction of steel surfaces, an increase in transverse slippage contributes to the formation of a more uniform surface layer. This decreases its strength, wear resistance, and a more uniform surface microgeometry. This is accompanied by a decrease in the magnitude and spread of the electron work function over the surface. The relationship between the nanostructural state of a polished surface and roughness and reflectivity is presented. [ABSTRACT FROM AUTHOR]

Inverted organic light-emitting devices (OLEDs) have been aggressively developed because of their superiorities such as their high stability, low driving voltage, and low drop of brightness in display applications. The injection of electrons is a critical issue in inverted OLEDs because the ITO cathode has an overly high work function in injecting electrons into the emission layer from the cathode. We synthesized hexagonal wurtzite ZnO nanoparticles using different oxidizing agents for an efficient injection of electrons in the inverted OLEDs. Potassium hydroxide (KOH) and tetramethylammonium hydroxide pentahydrate (TMAH) were used as oxidizing agents for synthesizing ZnO nanoparticles. The band gap, surface defects, surface morphology, surface roughness, and electrical resistivity of the nanoparticles were investigated. The inverted devices with phosphorescent molecules were prepared using the synthesized nanoparticles. The inverted devices with ZnO nanoparticles using TMAH exhibited a lower driving voltage, lower leakage current, and higher maximum external quantum efficiency. The devices with TMAH-based ZnO nanoparticles exhibited the maximum external quantum efficiency of 19.1%. [ABSTRACT FROM AUTHOR]

Insulin and immunoglobulin therapy is commonly administered through injections that are invasive and painful. They cannot be taken orally because digestive enzymes break them down. To protect against enzymes, drug molecules may be "packed", which decreases interaction of the active surface of the molecule with the environment. Silica nanoparticles (SiO2) may be used to attach proteins like insulin or immunoglobulin for use in drug delivery. They are stable and biocompatible. Exposing SiO2 nanoparticles to UV radiation may control molecule–nanoparticle attachment because of their electrostatic interactions. This study demonstrates the influence of UV radiation of SiO2 nanoparticles on insulin and immunoglobulin molecule attachment. Alteration of the surface electric potential of SiO2 nanoparticles by UV radiation was determined using electron work function measurements. Influence of radiation on formation of molecule-nanoparticle complexes was assessed by spectrophotometry of their sedimentation rate in solution. Increasing UV exposure time negatively charges the surfaces of SiO2 nanoparticles. Insulin exhibits better adsorption with SiO2 nanoparticles compared to immunoglobulin, likely due to favourable conditions promoting attractive electrostatic interactions. Longer UV exposure weakens insulin adsorption but does not significantly affect immunoglobulin adsorption. [ABSTRACT FROM AUTHOR]

We examine thin film on a dielectric substrate (vacuum/Al/SiO2) in the stabilized jellium model and the Kohn–Sham method. We investigate surface and size effects on the effective potential and the electron work function, and analyze the spatial distributions of electrons and potentials. It is found that a dielectric environment generally leads to a decrease in the work function. The effect of dielectric confinement for the electron work function of the asymmetric metal-dielectric nanosandwiches is reduced only by the surface area weighted average value of the dielectric constants. This conclusion follows from the application of the Gauss theorem for a conducting sphere with an inhomogeneous dielectric coating. The flow of electrons from the dielectric face to the vacuum one due to the contact potential difference manifests itself in the appearance of an additional dipole between the left and right face within the spatial distributions of ions. This leads to the fact that in a vacuum the electrostatic and effective potentials change sign twice, as a result of which a potential barrier appears above the vacuum level. We introduced the position of an electron conduction band in the dielectric as the input parameter in the self-consistency procedure for one of the sandwich approximations. As it turned out, the barrier height depends only on the used local or non-local approximation of the exchange-correlation energy. The nontrivial origin and behavior of the calculated effective potential on the vacuum side of the film, as well as the reasons for it, are discussed. [ABSTRACT FROM AUTHOR]

In this paper, structural, electronic properties, optical spectra, stability, as well as the quantum efficiency of bulk, monolayer and two different stacking heterostructure configurations (XY2/XY2) of dichalcogenide compounds XY2 (where X = Mo or W and Y = S or Se) were performed using density functional technique. Our findings reveal the strong chemical bonds and high interlayer banding energy for MoSe2/WSe2 heterostructure of configuration-2, which confirms its stability and its feasibility for synthesizing. Besides, the elastic stiffness coefficients demonstrate all studied heterostructures are mechanically stable at ambient pressure, this means that the studied heterostructures are harder to separate their components, making them more durable and less reactive under certain conditions, especially MoSe2/WSe2 heterostructure-configuration 2. Otherwise, the electronic band structure highlights an indirect semiconductor behavior for bulk XY2. In contrast, a strong ionic bonding between the chalcogen and metal atoms leads to the electrons confinement in the direction perpendicular to the plane revealing direct semiconductor behavior for monolayers XY2 at Γ point. Besides, after combining two monolayers with different work functions the holes and electrons are accumulated in different layers, therefore indirect excitons have been observed for XY2/XY2 heterostructures (Γ → K). Furthermore, due to the presence of the type-II band alignment, the optical absorbance spectra proves that the absorbance is enhanced along both x and z directions for all investigated heterostructures. In addition, the MoSe2/WSe2 heterostructure of configuration-2, has about 65% of photons converted into usable electrical power, while 35% of photons are lost as heat and/or reflected. Finely, its high stability, its suitable forbidden band, its high visible light absorption, as well as its high quantum efficiency make the 2D Van der Waals MoSe2/WSe2 heterostructure-configuration-2 as new potential candidate for upcoming nano-electronic, photovoltaic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

A numerical simulation of an intense thermionic emission of electrons from the cathode into the air medium in an electrode system has been performed with regard for the possible changes in the voltage across the electrodes and in the electronic work function of the cathode. Spatial distributions of the electrons, the electron energy, the ions, the electric-field strength, and the concentration of the atomic oxygen in the air medium were constructed with the use of a simplified set of kinetic reactions. A possibility of using the thermionic emission of electrons from a cathode for the cooling of the members of flying vehicles with the aim to proof them against heat loads was demonstrated. The numerical calculations have shown that the thermionic emission of electrons from the cathode in a system of electrodes with no protective resistor at a high pressure does not provide a cooling of the system. [ABSTRACT FROM AUTHOR]

In order to explore the possibility of CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayers as high‐performance gas sensors, the electronic properties and gas sensing performance of CH4 ${{{\rm C}{\rm H}}_{4}}$ , CO ${{\rm C}{\rm O}}$ , CO2 ${{{\rm C}{\rm O}}_{2}}$ , NO ${{\rm N}{\rm O}}$ , H2S ${{{\rm H}}_{2}{\rm S}}$ and Cl2 ${{{\rm C}{\rm l}}_{2}}$ gas molecules adsorbed on CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayers were investigated using a first‐principles approach. It was found that CH4 ${{{\rm C}{\rm H}}_{4}}$ , CO ${{\rm C}{\rm O}}$ and CO2 ${{{\rm C}{\rm O}}_{2}}$ had a weak chemisorption effect on the CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayer, while the physisorption of H2S ${{{\rm H}}_{2}{\rm S}}$ effectively altered the electronic properties and the work function of the CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayer. Compared with other gases, the CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayer has relatively high sensitivity to NO ${{\rm N}{\rm O}}$ , H2S ${{{\rm H}}_{2}{\rm S}}$ and Cl2 ${{{\rm C}{\rm l}}_{2}}$ , and the band gap of the system after adsorption changes significantly compared with the intrinsic CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayer, and the characteristics of the work function can effectively distinguish various gases. The results indicate that the CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayer has the ability to detect NO ${{\rm N}{\rm O}}$ , H2S ${{{\rm H}}_{2}{\rm S}}$ and Cl2 ${{{\rm C}{\rm l}}_{2}}$ gases with high sensitivity, especially for Cl2 ${{{\rm C}{\rm l}}_{2}}$ , and provide a theoretical basis for the development of CdS2 ${{{\rm C}{\rm d}{\rm S}}_{2}}$ monolayers for potential applications as gas sensors or scavengers for NO ${{\rm N}{\rm O}}$ , H2S ${{{\rm H}}_{2}{\rm S}}$ and Cl2 ${{{\rm C}{\rm l}}_{2}}$. [ABSTRACT FROM AUTHOR]

Structural optimization promotes water sterilization by low-voltage pulsed electric field. [Display omitted] • Cu 7 S 4 nanowire coated with N -doped carbon film is beneficial to the anchoring of Ag, and the loaded silver particles enhance the adsorption of O 2. • The successful coating of N -doped carbon layer and Ag particles improved the poor durability and conductivity of Cu 7 S 4. • The work function and electron difference density of different kinds of N -doped Cu 7 S 4 @NC@Ag demonstrate the direction of interface carrier transport. • The removal efficiency can still reach 99% after 8 h of continuous treatment at 6 V and 1000 mL min−1 flow rate. There are many methods of water disinfection, and how to realize low energy consumption, high efficiency and safety sterilization has always been a research hotspot. In this work, Cu 7 S 4 nanowires were grown on copper foam, and coated with N -doped carbon layer and Ag particles, which not only improved the conductivity and local field enhancement regions of the material, but also improved the durability and mechanical stability of Cu 7 S 4. DFT (Density functional theory) calculation shows that different kinds of N doping make the electron difference density and work function of the surrounding C different, which leads to high carrier transport capacity at the interface, and Ag anchored in N -doped carbon films can adsorb O 2. The band gap of the material is 2.12 eV, and the material has the potential to generate superoxide anion under energy excitation. Under the condition of 6 V voltage and 1000 mL min−1 water flow rate, the long-term water filtration sterilization of high-concentration bacteria can be realized, and the removal efficiency can still reach 99% after 8 h continuous treatment. This work has great application prospects for the purification of highly polluted water in the future. [ABSTRACT FROM AUTHOR]

Using XPS, the electron work function values on the surface of glassy carbon coatings of graphite samples, after an extended stay on a board of the ISS in open space conditions, were investigated. The results were compared with the characteristics of glassy carbon coatings of samples left on the ground for the same period. It was found that the electron work function does not change significantly, and this proves the possibilities for the successful application of these coatings, obtained by original Bulgarian technology, for space experiments on the board of satellites for measuring electric fields in the ionospheric-magnetospheric plasma. The minimal observed variations in the values of the electron work function are explained by small differences in the content of traces of different chemical elements on the surface of the coatings. It has been established that glassy carbon coatings have stable characteristics after a long stay in space, despite the small fluctuations in the values of the electron work function. The results show that glassy carbon coatings are chemically and mechanically stable. The results from this original technological experiment are unique for the development of sensitive elements, such as sensors for measuring weak electric fields in cosmic plasma. [ABSTRACT FROM AUTHOR]

The adsorption and reactions of water with surfaces is of immense importance in catalysis and corrosion. Charge transfer of ion scattering is sensitive to changes of work function and electronic structure caused by adsorption of water on a surface. In this work, as the model systems of metals and semiconductors the water adsorbed copper and silicon surfaces have been chosen and the research progress of charge transfer of the negative and positive ion scattering in our group were reviewed. [ABSTRACT FROM AUTHOR]

There is a widespread interest in time-resolved electron spectroscopies such as ultrafast electron diffraction, ultrafast electron microscopy, and ultrafast electron energy loss spectroscopy. These techniques require pulsed electron beams with both high current and brightness. LaB6 is commonly used as a thermionic emitter because of its low work function and high electron yield. However, its use as a pulsed photocathode has not been widely explored. Here, we present measurements of the electron yield from a LaB6 filament exposed to 392 nm UV ultrafast laser pulses under a wide range of filament temperatures. We find that sample heating strongly enhances photoelectron yield, an effect known as thermionically enhanced photoemission. However, it also creates potentially undesirable, continuous thermionic background. We conclude that the ideal optimal operating conditions strongly depend on the type of measurement and require defining and quantifying an appropriate figure of merit. [ABSTRACT FROM AUTHOR]

The presented work discusses an analytical setup that is capable of detecting surface alterations of aerosol nanoparticles. Utilizing the photoelectric effect, Aerosol Photoemission Spectroscopy (APES) is introduced as an online technique that determines the electron work function (eWF) of an aerosol particle material at ambient pressure. Beyond the detailed presentation of the experimental setup, the limitations and possibilities of APES are discussed with regard to metal oxide formation in technical and ultra-clean process gases. Deploying APES as an analytical tool operating at atmospheric pressure, the interaction of oxidizing and reducing gas species becomes observable for various metallic nanoparticles. As shown by APES measurements, even nitrogen with a purity of 7.0 (99.99999%) enables oxide formation when a metallic particle material is processed as an aerosol. Contrary to this, ultra-clean process gases, such as nitrogen with 10−13 ppm residual oxygen, allow the synthesis of oxide-free particles. In addition to the influence of oxygen and hydrogen on mono-metallic particles, this work includes the first results of the surface properties of so called "hetero-aggregates," nanoparticles that consist of two metals. Binary particles, such as CuNi or PtFe, exhibit varying alloying and oxidation behaviors, depending on the process gas used, which can be evaluated based on the development of the eWF during particle formation. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

In the present work, the adsorption of some simple organic sulfur gases (CS2, OCS, and CH3SH) on the g-C3N4 was studied using periodic and non-periodic density functional theory (DFT). PBE-D3/DNP and B3LYP-D3/6-31G(d) levels of theory were employed for periodic and non-periodic calculations, respectively. The calculated CS2, OCS, and CH3SH adsorption energies were obtained to be −4.35, −5.82, and −8.58 Kcal/mol. The interactions of simple organic sulfur gases with g-C3N4 were characterized by NBO second-order perturbation theory and quantum theory of atom in molecule (QTAIM). The bandgap energies and work function of g-C3N4 and its complexes with simple organic sulfur gases were extracted from their band structures. The CS2 and OCS adsorptions didn't significantly alter the bandgap and work function of g-C3N4. Therefore, g-C3N4 is not a proper sensor for detecting CS2 and OCS. The bandgap and work function of g-C3N4 were averagely changed by 18% and 2.7%, respectively, after CH3SH adsorption. Accordingly, g-C3N4 may use as a suitable sensor for detecting CH3SH based on electronic conductivity and work function. [ABSTRACT FROM AUTHOR]

An accurate atomistic treatment of aqueous solid–liquid interfaces necessitates the explicit description of interfacial water ideally via ab initio molecular dynamics simulations. Many applications, however, still rely on static interfacial water models, e.g., for the computation of (electro)chemical reaction barriers and focus on a single, prototypical structure. In this work, we systematically study the relation between density functional theory-derived static and dynamic interfacial water models with specific focus on the water–Pt(111) interface. We first introduce a general construction protocol for static 2D water layers on any substrate, which we apply to the low index surfaces of Pt. Subsequently, we compare these with structures from a broad selection of reference works based on the Smooth Overlap of Atomic Positions descriptor. The analysis reveals some structural overlap between static and dynamic water ensembles; however, static structures tend to overemphasize the in-plane hydrogen bonding network. This feature is especially pronounced for the widely used low-temperature hexagonal ice-like structure. In addition, a complex relation between structure, work function, and adsorption energy is observed, which suggests that the concentration on single, static water models might introduce systematic biases that are likely reduced by averaging over consistently created structural ensembles, as introduced here. [ABSTRACT FROM AUTHOR]

Hafnium (Hf) has been used as a cathode material for thermionic emission in high temperature environments for a long time. However, the effect of grain boundaries (GBs) on its work function has not been reported. In this work, by using first-principles calculations, we find that the introduction of GBs would reduce the work function of Hf surface as compared with that of the perfect crystal, and by increasing the distance between two grain boundaries, the work function converges gradually to the value of monocrystalline Hf. By analyzing the surface atomic structure and charge density distribution, we find that the reduced work function of GB-containing structures originates from the increase of atomic distance and the changes of atomic coordination environments at the GB region, which results in redistribution of electrons and enhances the electronic density of states at the Fermi level. [ABSTRACT FROM AUTHOR]

Doped hole (respectively electron) transport layers [HTLs (respectively ETLs)] are commonly used in evaporated organic devices to achieve high work function hole contact (respectively low work function electron contact) in organic LEDs to inject large current, in solar cells to increase the open circuit voltage, and in photodetectors to minimize the dark current. However, optimization of the HTL thickness results from a delicate trade-off. Indeed, on the one hand, to minimize the impact of HTLs on light propagation and series resistance effects, it is commonly admitted that HTLs must be kept as thin as possible. In this work, a model, validated by drift and diffusion simulations, has shown that, depending of the doping level, a minimum thickness between 10 and 20 nm was needed to prevent the transport layer work function from degradation due to field effects. Experiments have been performed on template p-only devices featuring a single HTL of various thicknesses and doping, confirming the validity of the model. Finally, simulations have been performed on a p-i-n device featuring both HTL and ETL. These results constitute precious indications for the design of efficient evaporated organic LEDs, solar cells, or photodetectors. [ABSTRACT FROM AUTHOR]

The effects of alloy surface composition and pre-adsorbed oxygen on the behaviors of H2O over Ni–Cr binary alloy surfaces were investigated by using the first-principles method. The surface energies and work functions for a series of Ni–Cr (111) alloy surfaces with different Cr concentrations were addressed to track the surface reactivities. An enhancement effect on the surface reactivity from Cr doping in the top-surface layer (TSL) of nickel substrates was identified. The locations of Cr in the TSL dramatically promoted exothermic adsorption of H2O and its decomposed products, including OH, O, and H. The calculated potential dissociation pathways further demonstrated that the successive dissociation of H2O molecules was substantially triggered in the presence of Cr doping in the TSL. By contrast, the Cr doping in the sub-surface layer hindered the dehydrogenation of H2O with a relatively higher energy barrier for OH dissociation. Moreover, with pre-adsorbed oxygen atoms closer to Cr, the first elementary step of H2O dissociation was easily fostered, whereas the OH dissociation was hindered. The Cr doping and O pre-adsorption accelerated the dissociation of H2O, which plays a critical role in the initial oxidation of nickel-based alloys in water- or oxygen-bearing environments. [ABSTRACT FROM AUTHOR]

Lanthanum hexaboride ( LaB 6) hollow cathodes have demonstrated a capability for long life operation, which is critical to many space exploration missions. Thermal characterization of LaB 6 hollow cathodes has revealed lower than expected electron emitter temperatures when the cathode reaches a steady state. This phenomenon is observed at discharge currents ranging from 5 to 35 A and xenon mass flow rates of 5–25 SCCM in cathodes with three different orifice diameters. Thus, the currently accepted value of the work function for polycrystalline LaB 6 , 2.67 eV, does not describe well the emission characteristics of LaB 6 hollow cathodes operating with internal gas discharges at a steady state. We use empirically measured temperatures combined with a model of the hollow cathode emitter and xenon discharge to estimate the value of the work function, yielding a value ranging from 2.1 to 2.44 eV. This lower work function value implies that LaB 6 hollow cathodes are expected to have even longer lifetimes than previously anticipated, further establishing them as a more suited alternative to other conventional cathode technologies for the task of long duration travel. Direct measurements of the work function as a function of depth on a hollow cathode emitter using x-ray photoelectron spectroscopy and ion beam milling indicate that the work function decreases with depth. We postulate several mechanisms that could explain the observed work function enhancement. Altogether, our results have important implications to the design, study approach, and operation of LaB 6 cathodes and potentially other cathodes with hollow configuration. Finally, our work opens the question of why the work function is reduced upon interaction with Xe plasma. [ABSTRACT FROM AUTHOR]

Self-heating thermionic hollow cathodes are essential components in modern plasma thrusters. To fully understand their operation, three interdependent physical domains must be considered: plasma discharge physics, thermal response of the cathode structure, and chemical evolution of plasma exposed surfaces. In this work, we develop the first self-consistently coupled plasma–thermal–chemical simulation platform for hollow cathode operation using lanthanum hexaboride (LaB 6) and Xe and study its performance against our experimentally determined temperature measurements. Results show that the customary assumptions of single-step resonant neutralization and full energy accommodation in ion-surface collisions fail to reproduce our empirical observations. We propose a two-step neutralization mechanism that consists of resonant neutralization to the first excited state of xenon followed by Auger de-excitation to the ground state, along with system specific accommodation factors. In this way, the agreement between the results of the simulations and experiments was achieved. These fundamental processes could govern neutralization in other cathode technologies where low work function emitters are employed and should therefore be accounted for in physical models. In addition, the new simulation platform allows us to better estimate the equilibrium work function of LaB 6 hollow cathode emitters. In the cathode studied here, we found that the effective work function is 2.25 eV, which is significantly lower than previous estimates, and leads to better than expected cathode material performance with important implications for space missions. [ABSTRACT FROM AUTHOR]

Materials descriptors with multivariate, multiphase, and multiscale of a complex system have been treated as the remarkable materials genome, addressing the composition–processing–structure–property–performance (CPSPP) relationships during the development of advanced materials. With the aid of high‐performance computations, big data, and artificial intelligence technologies, it is still a challenge to derive an explainable machine learning (ML) model to reveal the underlying CPSPP relationship, especially, under the extreme conditions. This work supports a smart strategy to derive an explainable model of composition–property–performance relationships via a hybrid data‐driven and knowledge‐enabled model, and designing superhard high‐entropy diboride ceramics (HEBs) with a cost‐effective approach. Five dominate features and optimal model were screened out from 149 features and nine algorithms by ML and validated in first‐principles calculations. From Shapley additive explanations (SHAP) and electronic bottom layer, the predicted hardness increases with the improved mean electronegativity and electron work function (EWF) and decreases with growing average d valence electrons of composition. The 14 undeveloped potential superhard HEBs candidates via ML are further validated by first‐principles calculations. Moreover, this EWF‐ML model not only has better capability to distinguish the differences of solutes in same group of periodic table but is also a more effective method for material design than that of valence electron concentration. [ABSTRACT FROM AUTHOR]

Coupled electron/ion transport is a decisive feature of Li plating/stripping, wherein the compatibility of electron/ion transport rates determines the morphology of deposited Li. Local Li+ hotspots form due to inhomogeneous interfacial charge transfer and lead to uncontrolled Li deposition, which decreases the Li utilization rate and safety of Li metal anodes. Herein, we report a method to obtain dendrite‐free Li metal anodes by driving electron pumping and accumulating and boosting Li ion diffusion by tuning the work function of a carbon host using cobalt‐containing catalysts. The results reveal that increasing the work function provides an electron deviation from C to Co, and electron‐rich Co shows favorable binding to Li+. The Co catalysts boost Li+ diffusion on the carbon fiber scaffolds without local aggregation by reducing the Li+ migration barrier. The as‐obtained dendrite‐free Li metal anode exhibits a Coulombic efficiency of 99.0 %, a cycle life of over 2000 h, a Li utilization rate of 50 %, and a capacity retention of 83.4 % after 130 cycles in pouch cells at a negative/positive capacity ratio of 2.5. These findings provide a novel strategy to stabilize Li metal by regulating the work function of materials using electrocatalysts. [ABSTRACT FROM AUTHOR]

Coupled electron/ion transport is a decisive feature of Li plating/stripping, wherein the compatibility of electron/ion transport rates determines the morphology of deposited Li. Local Li+ hotspots form due to inhomogeneous interfacial charge transfer and lead to uncontrolled Li deposition, which decreases the Li utilization rate and safety of Li metal anodes. Herein, we report a method to obtain dendrite‐free Li metal anodes by driving electron pumping and accumulating and boosting Li ion diffusion by tuning the work function of a carbon host using cobalt‐containing catalysts. The results reveal that increasing the work function provides an electron deviation from C to Co, and electron‐rich Co shows favorable binding to Li+. The Co catalysts boost Li+ diffusion on the carbon fiber scaffolds without local aggregation by reducing the Li+ migration barrier. The as‐obtained dendrite‐free Li metal anode exhibits a Coulombic efficiency of 99.0 %, a cycle life of over 2000 h, a Li utilization rate of 50 %, and a capacity retention of 83.4 % after 130 cycles in pouch cells at a negative/positive capacity ratio of 2.5. These findings provide a novel strategy to stabilize Li metal by regulating the work function of materials using electrocatalysts. [ABSTRACT FROM AUTHOR]

The localized corrosion induced by different kinds of inclusions in low‐nickel stainless steel is studied through immersion tests and first‐principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce‐O‐S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium‐containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium‐containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS > Si‐Mn(‐Al)‐O > MnS > Ce‐C‐O‐S > Ce‐Si‐Mn(‐Al)‐O > Ce‐O‐S. For cerium‐containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium‐containing inclusions is cerium oxides > cerium sulfides > cerium oxysulfide. [ABSTRACT FROM AUTHOR]

A simple expression for the Gamow factor is obtained using a second-order curvature-corrected tunneling potential. Our results show that it approximates accurately the "exact-WKB" transmission coefficient obtained by numerically integrating over the tunneling region to obtain the Gamow factor. The average difference in current density using the respective transmission coefficients is about 1.5 % , across a range of work functions ϕ ∈ [ 3 − 5.5 ] eV, Fermi energy E F ∈ [ 5 − 10 ] eV, local electric fields E l ∈ [ 3 − 9 ] V/nm, and radius of curvature R ≥ 5 nm. An easy-to-use correction factor λ P is also provided to approximately map the "exact-WKB" current density to the "exact" current density in terms of E F / ϕ. The average error on using λ P is found to be around 3.5 %. This is a vast improvement over the average error of 15 % when λ P = 1. Finally, an analytical expression for the curvature-corrected current density is obtained using the Gamow factor. It is found to compare well with the "exact-WKB" current density even at small values of local electric field and the radius of curvature. [ABSTRACT FROM AUTHOR]

The interface of Pt/TiO2 plays an essential role in device engineering and chemical reactions. Here, we report the electrostatic potential distribution of a Pt/TiO2 interface by electron holography. The decrease in the electrostatic potential exists at TiO2 in the vicinity of the interface, indicating the presence of negative charge due to electron transfer from TiO2 and Pt. The decrease in the electrostatic potential can be understood in the difference in work functions between Pt and TiO2. This study reveals the interplay between Pt and TiO2 and the usefulness of electron holography for probing the potential in nanoscale interfaces. [ABSTRACT FROM AUTHOR]

Analysis of field emission requires the inclusion of the internal potentials that shape the electronic wavefunctions and tunneling probabilities; details of the work function that are dependent on material quality and defects; and the role of the density of states (DOS) that influences the electronic supply. Here, these factors are collectively included on the basis of density functional theory to obtain predictions of field-dependent electron tunneling current densities. Results are obtained in copper for three different orientations. The DOS is predicted to be broadened by an externally applied electric field. The (100) copper is shown to yield the largest current density, and the (111) orientation is the lowest. The presence of an oxide surface monolayer is shown to increase the work function, leading to the emission of current reductions. The technique is general and can be applied to other materials (e.g., carbon fibers) that have shown promise as cathode emitters. [ABSTRACT FROM AUTHOR]

The classic sliding wear model, represented by Archard's equation, has long been used to estimate the service life of equipment and guide selection and modification of tribo-materials. However, the model was developed based on the asperity contact geometry without directly dealing with the wearing energy, rendering it unable to precisely describe wear under some conditions, e.g., it fails to predict wear of strain-hardened materials, which has never been clarified. In this study, incorporating with the plastic deformation–electron work function relationship, we reexamined and modified the classic model by taking account of the deformation energy consumption during wear. The modified model, or termed a wearing-energy model, is verified with relevant experimental observations. [ABSTRACT FROM AUTHOR]

Nb-doped ZnO (NbxZn1−xO, NZO) thin films with various Nb additions (x = 0, 0.2, 0.5, and 0.8 at. %) were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron sputtering. The Nb doping concentration was found to affect the microstructure, the number of oxygen vacancies, and work function of the Pt/NZO/Pt structures. Among the various devices, the film with 0.5 at. % Nb addition showed a better switching-voltage stability [i.e., the optimal coefficient of variation (Cv) for reset (7.02%) and set (2.73%) operations, respectively], a high endurance (∼1000 cycles), and lower reset (0.57 V) and set (1.83 V) voltages due to a larger number of oxygen vacancies and a lower work function. In general, the results show that the present NZO thin films are promising candidates for stable and low power-consumption resistive random access memory applications. [ABSTRACT FROM AUTHOR]

Using molecular beam cooled samples and quantum state-selective detection, we observe v = 0 → 1 vibrational transitions when HCl (v = 0) collides with an Ag(111) surface and derive both the incidence energy and surface temperature dependence of the transition probability. Our observations reveal that both electronically adiabatic and non-adiabatic mechanisms are at play in this inelastic process. A comparison to other systems shows similarities and trends that are consistent with an electron transfer mechanism forming a transient HCl−. For example, the electronically nonadiabatic coupling is stronger than for HCl scattering from Au, where the solid's work function is higher. HCl differs from other systems in that dissociation is possible over a low barrier. Vibrationally inelastic v = 1 → 2 transitions could not be seen when HCl (v = 1) collides with an Ag(111) surface. We suggest that scattering events, where HCl (v = 1) is subject to dynamical influences that increase its vibrational energy, lead efficiently to dissociation before the HCl (v = 2) molecule can escape the surface. This system appears to be an excellent candidate to study electronically nonadiabatic effects in dissociative adsorption. [ABSTRACT FROM AUTHOR]

The electronic work function, w(e−), and the ionic work function, w(Li+), of a lithium ultraphosphate, Li0.67PO2.8, have been measured by thermionic emission in the Richardson–Dushman regime. The values derived are w(Li+) = 1.99 ± 0.18 eV and w(e−) = 2.64 ± 0.38 eV. The measurements have been made possible by the implementation of a micro-channel plate detector, allowing the counting of single charge carrier particles, equivalent to a detection limit on the order of 1 aA. The ionic work function is demonstrated to increase with increasing lithium content in a series of lithium phosphates. [ABSTRACT FROM AUTHOR]

In field-effect transistors (FETs) with two-dimensional (2D) transition metal dichalcogenide channels, the dependence of field-effect mobility on atomic layer thickness has been studied and interpreted in terms of interface scattering and interlayer coupling resistance (Rint). However, a model for 1/f noise, such as in MoS2 and in MoSe2 FETs, for various contact metals and layer number thicknesses has not been reported. In this work, we have experimentally studied current–voltage and 1/f noise on MoS2 and MoSe2 FETs with source and drain contacts of high and low work function metals to understand both the mobility and the noise behavior. We have developed a noise model incorporating layer number dependent Hooge parameters and Rint. The noise and mobility models utilize screening lengths for charge, mobility, and Hooge parameter to describe the variation of these quantities with a layer number. Using our single model topology with appropriate fitting parameters for each material and each contact metal, the model captures the experimentally observed layer thickness dependence of the Hooge parameter. Our noise analysis is fully comprehensive and, hence, could be applied to any 2D layered systems. [ABSTRACT FROM AUTHOR]

We theoretically investigate the thermionic emission from nodal-ring semimetals. The thermionic emission is found to be anisotropic in the x - and y -directions. The anisotropic emission can be enhanced by increasing the radius of nodal-ring b. The main feature of nodal-ring semimetals not only results in anisotropic thermionic emission but also affects the value of thermionic emission current density (TECD). The TECD of the lower branch of the energy–momentum dispersion increases with b , while the TECD of the upper branch decreases with b. Unlike in conventional materials, the TECD in nodal-ring semimetals depends on Fermi energy that is similar to the situation in Dirac semimetals. The underlined reason is that Dirac semimetals and nodal-ring semimetals have a linear or a linear-like energy–momentum dispersion while conventional materials have a parabolic energy–momentum dispersion. The TECD of nodal-ring semimetals depends strongly on work function and temperature. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have great potential for future high-performance and energy-efficient transistor technology. To realize this potential, methods to dope the CNTs need to be developed to achieve low parasitic resistance of the transistor. Two key issues present themselves: (a) understanding the doping mechanism of the various methods and (b) stability of the doping method. For instance, although studies on molybdenum oxide (MoOx) demonstrate its ability to heavily dope nanomaterials, the interaction between MoOx and the CNT is unclear. Here, we observe an unstable effect of MoOx on the CNT and demonstrate dielectric passivation as a means to preserve the doping strength. The semiconducting CNTs exhibit greater than 103× reduction in resistance after stably doped with MoOx. By exploiting the instability of MoOx, we delve deeper into clarifying the doping mechanism. The relationship between the time-dependent material property of MoOx and the change in the electrical measurements of CNT devices is investigated to study the role of work function in doping the CNTs. We conclude that the doping mechanism of MoOx on the CNT is due to bandgap modulation by charge transfer, which occurs due to the difference in work function between MoOx and the CNT. [ABSTRACT FROM AUTHOR]

We present the theoretical basis for a new photoemission regime, transient work function gating (TWFG), which temporally and energetically gates photoemission and produces near-threshold photoelectrons with thermally limited emittance, percent-level quantum efficiency, and control over temporal coherence. The technique consists of actively gating the work function of a generalized photocathode using a non-ionizing long-wavelength optical field to produce an adiabatic modulation of the carrier density at their surface. We examine TWFG as a means to circumvent the long-standing trade-off between low emittance and high quantum efficiency, untethered to particle source or photocathode specifics. TWFG promises new opportunities in photoemission physics for next generation electron and accelerator-based x-ray photon sources. [ABSTRACT FROM AUTHOR]

Layer-number-dependent performance of metal–semiconductor junctions (MSJs) with multilayered two-dimensional (2D) semiconductors has attracted increasing attention for their potential in ultrathin electronics and optoelectronics. However, the mechanism of the interaction and the resulting charge transfer/redistribution at the two kinds of interfaces in MSJ with multilayered 2D semiconductors, namely, the metal–semiconductor (M–S) and the semiconductor–semiconductor (S–S) interfaces, have not been well understood until now, although that is important for the overall Schottky barrier height and the energy-band-offset between different layers of the 2D semiconductors. Here, based on state-of-the-art density functional theory calculations, the mechanisms of bonding and asymmetric electron redistribution at the M–S and S–S interfaces of metal–bilayer MoS2 junctions are revealed. Multiple mechanisms collectively contribute to the electron redistribution at the two kinds of interfaces, and the dominant mechanism depends on both the dimensionality (2D vs 3D) and the work function of metal electrodes. For the M–S interface, the pushback effect and metal-induced gap states play a dominant role for MSJs with 3D metal, while the covalent-like quasi-bonding feature appears for MSJs with medium-work-function 2D metals, and charge transfer plays a main role for MSJs with 2D metals that have very large or small work functions. For the S–S interface, it inherits the electron-redistribution behavior of the M–S interface for MSJs with 2D metal, while opposite electron-redistribution appears in MSJs with 3D metal. These mechanisms provide general insights and new concepts to better understand and use MSJs with multilayered 2D semiconductors. [ABSTRACT FROM AUTHOR]

The deposition of transition metals (TM) on barium titanate (BaTiO3, BTO) surfaces is involved in the development of several BTO-based devices, such as diodes, catalysts, and multiferroics. Here, we employ density functional theory to investigate the adsorption of 3d TM on both BaO- (type-I) and TiO2-terminated (type-II) surfaces of cubic BaTiO3(001) at low levels of surface coverage, which is important to comprehend the initial stages of the formation and growth of TM overlayers on BTO. The most stable adsorption site is identified for each adatom on both surfaces. Our discussion is based on analyses of structural distortions, Bader charge, electron density difference, magnetic moments, work function, density of states, and adsorption energies. For the type-I surface, most of the adatoms bind covalently on top of the surface oxygens, except for Sc, Ti, and V atoms, which adsorb preferentially on the bridge site, between O ions, to form two polar TM–O bonds. On the type-II surface, the TM are located at the fourfold hollow site, which allows the formation of four TM–O interactions that are predominantly ionic. Upon the adsorption, we noticed the formation of in-gap states originated mostly from the adatom. When electrons are transferred to the substrates, their conduction bands become partially occupied and metallic. We observed a decrease in the work function of the type-II surface that is fairly proportional to the charge gained, which suggests that the BTO work function can be manipulated by the controlled deposition of TM. [ABSTRACT FROM AUTHOR]

We show, using density functional theory calculations, that the charge, magnetic moment, and morphology of deposited Au nanoclusters can be tuned widely by doping the oxide support with aliovalent cations and anions. As model systems, we have considered Aun (n = 1, 2, or 20) deposited on doped MgO and MgO/Mo supports. The supports have been substitutionally doped with varying concentrations θ of F, Al, N, Na, or Li. At θ = 2.78%, by varying the dopant species, we are able to tune the charge of the Au monomer between −0.84e and +0.21e, the Au dimer between −0.87e and −0.16e, and, most interestingly, Au20 between −3.97e and +0.49e. These ranges can be further extended by varying θ. These changes in charge are correlated with changes in adsorption and/or cluster geometry and magnetic moment. We find that the work function Φ of the bare support is a good predictor and descriptor of both the geometry and charge of the deposited Au cluster; it can, therefore, be used to quickly estimate which dopant species and concentration can result in a desired cluster morphology and charge state. This is of interest as these parameters are known to significantly impact cluster reactivity, with positively or negatively charged clusters being preferred as catalysts for different chemical reactions. It is particularly noteworthy that the Na-doped and Li-doped supports succeed in making Au20 positively charged, given the high electronegativity of Au. [ABSTRACT FROM AUTHOR]