Electron Work Function Research Articles

The critical roles of surface-bound radicals in the nickel phosphide/biochar-persulfate catalytic oxidation system for tetracycline removal: The synergistic catalysis between nickel phosphides and biochar

Exploring efficient and cost-effective heterogeneous persulfate (PS) oxidation systems is meaningful for addressing recalcitrant organic pollutants in wastewater. Herein, nickel phosphide/biochar (NixP/biochar) composite, with Ni12P5 as the predominant crystalline phase, is firstly synthesized utilizing a biomass phosphorus source, phytic acid (PA). NixP/biochar demonstrates outstanding catalytic capacity in activating PS for removing tetracycline (TC). At 1 mM PS, 0.15 g/L catalyst, and pH 7.0, 94.55 % of TC (20 mg/L) can be removed within 180 min, markedly superior to Fe-, Cu-, and Co-based phosphide/biochar composites. The NixP/biochar-PS system exhibits superior catalytic degradation efficiency (>94.00 %) against varying concentrations (1–20 mg/L) of TC and robustly resists interferences from complex water matrices, including sodium humate solution, surface water, anions (>90.00 %). The ideal catalytic efficiency is ascribed to surface-bound radicals (including SO4-• and •OH), with •O2– and 1O2 assisting in. Density functional theory (DFT) calculations indicate that due to the electron donations from Ni, P, and C, S2O82- may undergo homolysis to produce the surface-bound SO4-•, which may induce the generation of other reactive oxygen species (ROSs) through radical chain reactions. Besides, the electronic structures and work functions of NixP in NixP/biochar composites can be modulated by the biochar, enhancing the catalytic selectivity of NiP, Ni2P, and Ni12P5 with Ni as the electron-donating center, while diminishing that of P-centered Ni3P. These findings may serve as a reference for the theoretical study of Ni-based catalysts and the practical application of NixP in AOPs.

Improving the emission properties of graphene–carbon nanotube hybrid nanostructures through functionalization with BaO nanoparticles and laser treatment

This paper presents the manufacturing technology of hybrid nanostructures based on a buffer layer of reduced graphene oxide (rGO) flakes with vertical single-walled carbon nanotubes (SWCNTs) and their bundles functionalized with BaO nanoparticles. Using density functional theory (DFT) calculations, supercells of rGO/SWCNT/BaO films were constructed and the patterns of the electron work function were revealed. It has been demonstrated that the electron work function is influenced by both the mass fraction of BaO nanoparticles and the inter-tube distance. Branched carbon nanostructure was formed using a pulsed laser irradiation. Fragmentation of BaO nanoparticles on the carbon surface was achieved. It was shown that after laser treatment, Ba(NO3)2 particles up to 200 nm in size were fragmented into smaller BaO nanoparticles with sizes of a few nanometers, covering the nanotubes. The field emission current–voltage characteristics (CVCs) were measured and showed a 42-fold increase in emission current compared to the nanostructure without BaO functionalization and laser treatment. BaO-functionalized hybrid carbon nanostructures are predicted to be efficient field cathodes, with a current density of at least 2 A/cm2, for use in X-ray tubes, field emission displays, and vacuum microwave devices.

Comparative studies of different solutes effects on microstructure and comprehensive performance of coherent precipitation-strengthened Cu–Ni–Al alloys

Multi-componentization can further improve the heating resistance of Cu–Ni–Al alloys, enabling them to withstand more demanding situations. Unfortunately, the limited researches have been done on the wear and corrosion resistance of the heat-resistant Cu–Ni–Al alloys, resulting in the lack of relevant evidence in the practical application. In this work, a comparative study of differential types of trace element, Si (the stronger enthalpy interaction element), Sn (the weaker enthalpy interaction element) Cr or Zr (grain boundary strengthening element), effects on microstructure, wear and corrosion resistance will be done, Furthermore, the effect of different trace elements on the surface electron work function and electrochemical behavior of Cu–Ni–Al alloys is reflected by SPM surface potential model. The results indicate that the precipitation of dual nano-phase and accelerated precipitation of γ′ phase can be realized through the addition of Si, Sn, Cr and Zr, in which the value of δγ-γ′ increase sharply after adding Si and it is not conducive to the preservation of cuboidal γ′ phase. The addition of Si, Cr and Zr can improve electron work function distribution and mechanical property, wear, and corrosion resistance of the alloys, in which Si is more conducive to the improvement of wear resistance and mechanical properties of the alloy, while the alloy with Cr and Zr shows the excellent corrosion resistance. The addition of Sn will weaken the enthalpy interaction of the alloy system, reduce the electron work function of the alloy, and have adverse effects on the wear and corrosion resistance of the alloy.

Study on the quenching sensitivity of corrosion properties in 7199 aluminum alloy

This study used electrochemical corrosion, intergranular corrosion (IGC), and exfoliation corrosion tests, as well as microscopic observations of the microstructure and first-principles calculations, to investigate the effect of different quenching rates on the microstructure and corrosion properties of the 7199 alloy. The results show that as the quenching rate decreases, the size, Zn, and Mg content of precipitated phases at grain boundaries (GBs), as well as the width of the precipitation-free zone (PFZ), increase, resulting in a decrease in corrosion properties. During slow quenching, the η phase (MgZn2) at the GBs continuously absorbs surrounding Zn and Mg atoms, causing Zn and Mg atom depletion near the GBs. This results in the formation of a wide PFZ. Enlargement of the η phase and PFZ at the GBs leads to anodic dissolution channels, allowing for rapid corrosion expansion along the GBs. Additionally, at slow quenching rates, not only does the η phase precipitate at the subgrain boundaries (SGBs) but also the T and S phases. In corrosive environments, the η phase is more prone to corrosion than the T and S phases. Electron work function calculations show that the S phase has the highest corrosion potential, whereas the η phase has the lowest. As a result, SGBs containing T and S phases are unlikely to serve as corrosion pathways. Corrosion preferentially extends along SGBs containing η phases.

Ionization Processes of Negative Corona Discharge Part 1. Review and Experiment

The purpose of the research is an experimental study of physical processes in the near-electrode zones of negative point electrodes in an electronegative gas (air) under the condition of a high-voltage field.Methods. Video image analysis, current-voltage characteristics measurements, and spectroscopy are used. The current-voltage characteristics of the corona discharge ignition voltage in the environment are measured, the problem of experimental identification of surface charges, the mechanism of negative corona discharge ignition, and the ionic structure of streamers is studied, degradation of electrodes during negative corona discharge, spectrum of corona discharge creation and electromagnetic sound.Results. It is shown that at small radii of curvature of needle electrodes, the development of a negative corona discharge is due to the cold emission of electrons, and on flat and slightly curved negative electrodes, due to the capture of surface electrons by electron-withdrawing molecules. The mechanism of ignition of a corona discharge in an electronegative gas with a negative needle, the structure of streamers from negative needles, the emission spectrum and ethonic degradation of electrodes have been studied.Conclusions. The ignition of a negative corona discharge at small radii of the tips of the pointed needles (ro less than tens of microns) is due to the cold emission of electrons followed by impact ionization of neutral molecules. With slightly curved electrodes, the appearance of a negative corona discharge is due to the capture of surface electrons by electronegative gas molecules with subsequent plasma-chemical reactions. The formation of surface electrons depends on many factors: the presence and structure of oxide films (roughness, defects, etc.), which determine the electron work function and form local fields at the tips of microtips. The appearance of a corona discharge leads to degradation of the corona electrodes, expressed in the spraying of the tips of the points and the melting of the needles. In the dark region of the negative corona discharge (U < U*), photons in the in the ultraviolet spectrum (UV spectrum) are emitted, and when U > U*, in addition to UV photons, photons in the visible region of the spectrum are emitted. Glow fluctuations are caused by the chaotic dynamics of the formation of injection centers (melted tubercles - ectons) on the surface of the corona electrode. The ignition of a corona discharge is accompanied by sound emission with a frequency of about 300 Hz.

On the specific behavior of the work function and surface potential of an asymmetric metal-dielectric nanosandwich

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.

UV Irradiated SiO2 Nanoparticles as Insulin and Immunoglobulin Molecule Carriers

Abstract 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.

In-Depth Understanding of the Chemical Stripping Mechanism of AlSiY Coatings on Nickel Superalloys by First-Principles Calculation

In order to repair a failed AlSiY coating on aeroengine turbine components, the AlSiY coating was stripped using a nitric acid-based removal reagent. The homogeneity of chemical stripping was evaluated and the stripping mechanism was clarified using first-principles calculations. The effects of hydrofluoric acid (HF) and chromium trioxide (CrO3) on the homogeneity of chemical stripping were investigated by calculating the electronic work functions (EWFs) of the stripped surfaces. The results showed that the stripped surfaces of the AlSiY coating exhibited a serrated appearance when it was etched by a single nitric acid solution, indicating severely inhomogeneous stripping. With the addition of HF and/or CrO3, the homogeneity of chemical stripping could be greatly improved, which was attributed to the increased EWF of the (200) surface and the decreased EWF of the (110) surface, causing the corrosion cathode to transition from the (110) surface to the (200) surface. The HF+CrO3+HNO3 mixed reagent was the optimal combination for the uniform stripping of the AlSiY coating, while the inner layer was not broken. The Al atoms on the surface could be preferentially removed due to the strong bonding with acid ions. The research method proposed in the present work will provide a new means to design chemical removal reagents.

Graphdiyne (g-CnH2n-2) nanosheets encapsulated Cu-Co Prussian blue Analogues formed double S-scheme heterojunction for wide spectrum photocatalytic H2 evolution

The frontier of sustainable energy research includes the advancement and creation of stable and efficient photocatalysts for the process of photocatalytic hydrogen evolution (PHE). Graphdiyne (GDY), an innovative carbon allotrope, demonstrates a narrow band gap and exceptional photogenerated charge mobility, making it extremely promising in the field of photocatalysis. In addition, Prussian Blue Analogues (PBA) are a unique category of metal–organic frameworks (MOFs) with open framework structures and strong stability. Compounds formed by ligands and various metal ions in PBA materials exhibit excellent performance. This work primarily enhances wide spectrum PHE by in situ growing GDY nanosheets onto Cu-Co PBA to construct a double S-scheme Cu-Co PBA@GDY/CuI (CCGC) heterojunction. The amorphous GDY can provide abundant active sites for photocatalytic hydrogen evolution reaction. Furthermore, the nanosheet properties of GDY were confirmed using Atomic Force Microscopy (AFM). The highest PHE rate of Cu-Co PBA@GDY/CuI-10 (CCGC-10) reaches 12947.8 μmol h−1 g−1 with a apparent quantum efficiency (AQE) of is 4.37 % at 520 nm, and exhibits good cycling stability. Based on the bandgap matching theory, the spatial behavior of photogenerated carriers in GDY, CuI, and Cu-Co PBA was effectively controlled, resulting in a close interface with a double S-scheme heterojunction charge transfer in Cu-Co PBA@GDY/CuI. The S-scheme photogenerated charge transfer pathway in CCGC was further confirmed through in-situ XPS, electron spin resonance (ESR) and work function (Wf). This work proposes a novel approach for the synthesis of solar energy conversion composite photocatalysts based on GDY and PBA.

XPS INVESTIGATION OF THE WORK FUNCTION OF GLASS CARBON COATINGS AFTER EXTENDED STAY ON THE INTERNATIONAL SPACE STATION (ISS)

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 of successfully 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 the 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 obtained results of this original technological experiment are unique for development of sensitive elements - sensors for measuring weak electric fields in the cosmic plasma.

Facile synthesis of Ag lattice doped mesoporous In2O3 nanocubes for high performance ethanol sensing.

Ag lattice doped In2O3 with a mesoporous structure was synthesized through a combination of hydrothermal and calcination methods. The structural and morphological characteristics were assessed using XRD, SEM, TEM, TGA, BET, and XPS analyses. Gas sensing measurements revealed that the 7.0 mol% Ag-doped In2O3 sensor displayed a response of 420 towards 100 ppm ethanol at 140 °C, which was 19 times higher than that of the pure In2O3 gas sensor. Density functional theory calculations indicated that Ag-doped In2O3 exhibited enhanced adsorption performance, higher adsorption energy, and electron transfer, resulting in higher sensitivity to ethanol. These findings were also supported by the electronic band structure, work function, and DOS analyses. These results indicated that the Ag doped mesoporous In2O3 has high potential for the preparation of high-performance ethanol sensors in practical applications.

Investigation into electronic interaction and work function tuning of phthalocyanine molecules and graphene interfaces.

Understanding the interfacial electronic structures of organic semiconductor phthalocyanines (MePc) and graphene is essential for their practical application in various fields. In this study, we investigated the electronic structure and the tuning of the work function of free metal phthalocyanine (Pc4), cobalt phthalocyanine (CoPc), and copper phthalocyanine (CuPc) molecules deposited on a graphene monolayer using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We found that the functionalization of MePc molecules induces p-doping to the graphene substrate due to the charge transfer mechanism with the MePc molecule. XPS analysis shows that the electronic interaction at the interface between Pc molecules and graphene substrate mainly occurs through the pyrrole species. Comparatively, it was observed that the electronic coupling between graphene and CuPc is relatively stronger than that between CoPc and graphene. The electronic interaction of the CuPc/Gr sample principally occurs through the Cu2+ 3d states of CuPc, the molecule, and the graphene 2p π states. This electronic interaction increases the work function of the graphene substrate to 5.75 eV, 6.05 eV, and 6.12 eV after depositing the Pc4, CoPc, and CuPc molecules, respectively. These results show that the MePc/Gr samples investigated in this study can be considered promising candidates for applications requiring a high work function to increase hole injection efficiency.

High-throughput development of tough metallic glass films.

Fast development of metallic glass films with high toughness has been a long-sought goal of humankind in view of their superior properties and great potential for application in the field of soft electronics. However, until now, there has been no effective experimental strategy because of the lack of suitable and precise toughness measurement technology. In the present work, we introduced a feasible route for developing tough metallic glass films using combinatorial material library preparation and high-throughput toughness measurement via nanoindentation. Based on this route, tough metallic glass films for the quaternary Zr-Ti-Cu-Al system were successfully screened out. The corresponding electron work function map was detected to uncover the physical mechanism for the composition dependence of toughness. In addition, the preliminary assessments of the screened tough metallic glass films as strain-sensing materials were also conducted. Our current research not only provides a versatile toolbox for high-throughput development of tough metallic glass films, but also exemplifies their potential as strain-sensing materials.

Effect of temperature on the emission properties of quasi 2D glass-like carbon placed on silicon and silicon dioxide substrates

In this work, in silico methods are used to study the temperature effect of the emission properties, including the electron work function, of quasi 2D glass-like carbon (GLC) films deposited on few/multi-layer Si/SiO2 substrates of two types. The equilibrium configuration of the structures under study at different temperatures is established by molecular dynamics (MD) method using reactive force field (ReaxFF) due to the polyatomic nature of supercells. The electronic structure is determined using the self-consistent charge density-functional based tight-binding (SCC-DFTB) method. The temperature range under consideration is 50–1000 K. The effect of one substrate layer and several substrate layers on the electronic structure and emission properties of GLC is considered. In the case of one layer of Si and SiO2, in fact, the functionalization of the GLC film occurs. This leads to a decrease in the work function by ∼ 6 % and ∼ 21 %, respectively, at a temperature of 300 K. As the temperature increased to 1000 K, the work function of the GLC with one SiO2 layer further decreased by ∼ 7 %. An increase in the substrate thickness to five Si layers and two SiO2 layers leads to a decrease in the work function by 7.3 % and 20.5 %, respectively. An increase in temperature leads to a change in the work function of the GLC with five Si substrate layers and two SiO2 layers by 0.2 % and 3.8 %, respectively.

On the Description of Electrode Materials Based on the Quantification of Ionic and Electronic Work Functions

During decharging of a lithium ion battery (LIB) electrons are transferred from the cathode material to the outer circuit and lithium ions are transferred into the electrolyte. Here, the energy required to take electrons and lithium ions out of two prototypical cathode materials, LixFePO4 and LixMn2O4 is investigated as a function of the state of lithiation, x [1]. Ionic work functions are measured by thermionic emission, electronic work functions are measured either by thermionic emission or by photoelectron spectroscopy. The work functions measured vary significantly with x for LixFePO4 with moderate, low-dimensional ionic and electronic conductivities but rather little for cubic LixMn2O4 with ca. three orders of magnitude higher ionic and electronic conductivities [2]. The experimental data are supported and rationalized by static energy-landscape calculations and molecular dynamics simulations of the Lithium migration as a function of Lithium content and electric field strength [1]. This study provides new insight into the role of ionic contributions to the energy balance in LIBs. Current efforts are aimed at a complete energetic description of LIBs as previously discussed for LiCoO2 [3].[1] J. Schepp, J. Schuch, J.P. Hofmann, S. Adams, K.-M. Weitzel, to be published[2] M. Park, X. Zhang, M. Chung, G.B. Less, A.M. Sastry, A review of conduction phenomena in Li-ion batteries, Journal of Power Sources 195 (2010) 7904–7929.[3] S. Schuld, R. Hausbrand, M. Fingerle, W. Jaegermann, K.-M. Weitzel, Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2 A Thermodynamic Cycle Combining Ionic and Electronic Structure, Adv. Energy Mater. 8 (2018) 1703411.

(Keynote) Experimental and Computational Insights into Electronic Structure and Redox Properties of Bare and Doped Co3O4 Nanocrystals of Euhedral Morphology and Their Heterojunctions with Alien Oxides and Carbon Materials

One of the most attractive oxide materials with remarkable record of widespread applications are cobalt spinels and their derivatives obtained by doping with alien redox (3dn) and nonredox (Li) cations or via hybridization with other oxides (CeO2, TiO2, a-Al2O3) or carbon support. They have recently received a great deal of theoretical and practical attention because of an outstanding activity in many redox processes important for photo/electro/catalysis. Among many potential applications, their relevance as promising substitutes for platinum in oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) can be mentioned, in particular. The properties of nanostructured cobalt spinel materials depend on their size, shape, doping and interfacing features. In this context, euhedral spinel nanocrystals that expose well defined crystallographic planes, allow for sensible investigations into establishment of the surface/bulk structure-redox reactivity relationships in real conditions.In this presentation application of S/TEM and inverse Wulff hull matching techniques supported by image simulation was discussed for elucidation the mechanism of hydrothermal synthesis of euhedral cobalt spinel nanocrystals the their shape retrieving. Periodic spin unrestricted DFT-PW91+U and hybrid DFT/HSE06 calculations were applied for modeling the morphology, structure and electronic properties (DOS structure) relevant for redox behavior of bare and doped cobalt spinel nanocrystals. The results allowed for thorough characterization of the structure and reconstruction of the exposed low index (100), (110), and (111) planes, and explain the influence of dopants. The effect of the valence state of lithium (Li+ or Li0), and its locus on the valence pining of the cobalt cations was determined. DFT calculations together with the ab initio thermodynamic modeling were used to study the electronic structure of the created defects, and stability of different terminations of cobalt spinel and Li-doped Co3O4 under various redox conditions. The associated electronic and spin relaxation processes were discussed as well. For the most stable stoichiometric (100) and (111) facets, the surface redox state diagrams in a wide stoichiometry range were constructed, and analyzed in detail. Intrinsic charge transfer processes involving electron (n-conductivity) and hole (p-conductivity) transfer between the octahedral and tetrahedral cobalt cations were modeled using a small polaron approximation (Marcus-Dupuis model). Formation of n-p junctions (Co3O4|CeO2, Li-Co3O4|CeO2) and MxCo3-xO4/carbon hybrids were analyzed by S/TEM, XPS spectroscopy (band alignment), contactless electronic conductivity and work function measurements, corroborated by DFT modeling. The redox properties of the interface and spinel faceting, and the role of electric conductivity and the nature of the carbon support functional groups were discussed in the context of the ORR, OER performance, and catalytic redox reactivity (activation of O2).AcknowledgmentsS.W. thanks for the financial support of the project “High-performance electrocatalyst for oxygen reduction reaction with low platinum content” carried on within the Program “Pearls of Science” of the Ministry of Education and Science of Poland.

Graphene encapsulated MnO2 nanorods boosts interfacial polarization for microwave absorption

The lightweight and efficient electromagnetic wave (EMW) absorption materials have been a popular research topic. In this work, MnO2 @graphene (MnGr) nanofibers with core-shell structure were synthesized by a one-step hydrothermal method. This one-dimensional linear structure was further self-assembled into a three-dimensional hierarchical MnGr aerogel network structure due to the interlayer forces of graphene sheets. The addition of graphene greatly enhances the interfacial polarization. The significant differences in electronic structure and work function between the outer graphene layer and the inner MnO2 layer greatly enhance the interfacial polarization. The formation of 3D hierarchical MnGr aerogel network structure constructs more fast electron transport channels. With the addition of graphene oxide at 7.5 wt% of the theoretical yield of MnO2, MnGr-7.5 exhibits excellent wave absorption properties. The effective absorption bandwidth (EAB) can reach 6.40 GHz at 2.2 mm. And the minimum reflection loss (RLmin) is − 41.3 dB at 1.8 mm and 17.36 GHz. Finite element physical simulation is used to simulate the response of 3D conductive network to electromagnetic wave. Through calculation, it is found that the inter-lap network structure is beneficial to enhance the loss. The low-cost MnO2 compounded with a small amount of graphene has excellent wave absorption performance and a great application prospect.

The value of charge of Fe single to multiple atoms doped in Ge: Combined experimental and density functional theory study

With the aim to find out the value of an electronic charge that the Fe atoms acquire when they are doped in Ge bulk, a set of experimental and density functional theory (DFT) studies have been carried out of the model systems consisting of intermixed Fe–Ge films. Such films were prepared by electron and thermal evaporation in ultra-high vacuum (UHV) on the surface of Mo(110) substrate by initial formation of the Ge film of a mean thickness of 7.5 nm, onto which the Fe films were subsequently deposited, maintaining certain Fe to Ge concentration ratio, namely, 0.2, 0.4, 0.7 and 1.0. Annealing of such double Fe–Ge films results in notable interdiffusion of the components with quite uniform distribution of the elements throughout the intermixed layer. The details of formation of such layers were in-situ controlled by Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), low-energy electron diffraction (LEED) and work function measurements, in combination with Ar ion depth profiling. By analyzing the Fe Auger LMM-triplet, the absolute values of the charge that Fe atoms acquire when doped in Ge, were estimated for four different Fe–Ge intermixed layers with above-mentioned different Fe to Ge concentration ratio. The corresponding plot of the charge versus Fe to Ge concentration allows to estimate the charge of a single doped Fe atom, which equals to +0.34e (electron charge units) and gradually decreases to 0.07e for high Fe concentration. To verify the experimental values of the Fe charge the calculations were done by periodic DFT as implemented in full-potential FHI-aims code. Among the used algorithms of Mulliken, Hirshfeld, and Bader's atoms-in-molecules, the latter gives good correlation between charges of Fe dopant and its concentration.

Size Effect of the Electron Yield Work on Single-Crystal Silicon Samples

Changes in electron work function (EWF) @=(ft) during the separation of Si(100) single-crystal silicon wafers into smaller samples (scribing operation) have been studied by the method of kinetic curves of EWF. The observed effect can be attributed to the sorption of water vapor on the Si(100) surface. The Helmholtz formula has been applied to estimate the amount of water absorbed by the samples, causing a change in the EWF. To determine the localization of sorbed water, we have used the method of layer-by-layer etching of the surface of Si(100) samples using low-temperature SF6-plasma. It has been shown that with a decrease in the size (area) of the samples, the size effect of the EWF takes place. For a whole plate (with an area of 80 cm2) is characterized by the EWF value close to its reference value (@=5.0) eV), while for small samples (~1 cm2), this value decreases to 4.5 eV, which indicates a significant water content in the samples (~0.3 × 1015 molecules cm–2). The data on sample etching by plasma have showed that water is unevenly distributed over the thickness of the sample, and is mainly concentrated in its deeper layers, not changed by mechanical processing (grinding and polishing). The results obtained are consistent with the theory of the secondary structure of a crystal (SSC), according to which crystalline solids have regular gaps (“T-space”) with a size of “1 atomic layer,” in which impurity transfer processes occur. Apparently, chemisorption of water takes place in the micropores of the T-space, which leads to size effects on Si(100).

Hierarchically Organized MoS2 Films as Promising Electrodes for Flexible Supercapacitors

The formation of hierarchically organized MoS2 films on various substrates by a hydrothermal method was studied. The influence of synthesis conditions and the substrate (a glass or a flexible carbon paper substrate) on the crystal structure of sulfide films was determined using X-ray powder diffraction (XRD). Scanning electron microscopy (SEM) showed that the films on glass substrates comprised structurally different elements, namely a continuous dense layer of spherical nanoparticles on the surface of which hierarchically organized globular agglomerates of two types are arranged. A molybdenum disulfide shell about 1.5 μm thick, consisting of hierarchically organized nanosheets less than 10 nm thick, was formed on the surface of carbon fibers that make up the carbon paper. Elemental mapping was used to evaluate the homogeneity of the MoS2 film formed on the carbon paper. Atomic force microscopy (AFM) showed that an individual carbon fiber modified with a sulfide film had a mean square roughness of about 13 nm (over an area of about 100 μm2). According to Kelvin-probe force microscopy (KPFM) data, the electron work function of the material was 4.53 eV. The electrochemical characteristics of the manufactured flexible electrode based on a hierarchically organized molybdenum disulfide film were investigated. The specific capacitance and the stability of functional and microstructural properties of the manufactured supercapacitor electrode in 2000 charge–discharge cycles were evaluated. Thus, the proposed strategy is promising for the fabrication of efficient hierarchically organized MoS2 electrodes for flexible supercapacitors.