Electron Spectroscopy Methods Research Articles

Физические процессы в датчике низкого вакуума типа Пирани

Auger electron spectroscopy and thermoresistive methods are used to study the physical processes leading to gas cooling of heated molybdenum filaments in a wide temperature range of 350 - 1300 K and pressures of 760 - 10-3 Torr, corresponding to the operating range of a Pirani-type vacuum sensor. Nitrogen was used as the gas. It is shown that nitrogen atoms chemisorbed on the surface do not contribute to gas cooling, which occurs only due to physisorbed N2 molecules. In the intermediate vacuum region of 10-3 – 1 Torr, the heater is cooled due to the equilibrium between the flux of incident and thermally desorbed molecules, which is well described by the Hertz-Knudsen formula and first-order desorption with an activation energy of ~ 0.55 eV. On the contrary, at high pressures close to atmospheric, this cooling occurs due to the thermal desorption of gas molecules from an almost filled monolayer, which reduces its relative efficiency by many orders of magnitude.

Physical processes in the Pirani type low vacuum sensor

Auger electron spectroscopy and thermoresistive methods are used to study the physical processes leading to gas cooling of heated molybdenum filaments in a wide temperature range of 350-1300 K and pressures of 760-10-3 Torr, corresponding to the operating range of a Pirani-type vacuum sensor. Nitrogen was used as the gas. It is shown that nitrogen atoms chemisorbed on the surface do not contribute to gas cooling, which occurs only due to physisorbed N2 molecules. In the intermediate vacuum region of 10-3-1 Torr, the heater is cooled due to the equilibrium between the flux of incident and thermally desorbed molecules, which is well described by the Hertz--Knudsen formula and first-order desorption with an activation energy of ~0.55 eV. On the contrary, at high pressures close to atmospheric, this cooling occurs due to the thermal desorption of gas molecules from an almost filled monolayer, which reduces its relative efficiency by many orders of magnitude. Keywords: vacuum, adsorption, Pirani sensor, molybdenum, thermal desorption, nitrogen.

Changes in the electronic structure of the Si surface as a result of ion implantation

The composition, structure, and physicochemical properties of the surface and near-surface layers of silicon doped with low-energy (E0<5 keV) Ba+ and O2+ ions have been studied using a set of photoelectron and secondary electron spectroscopy methods. It has been established that in the process of ion implantation, chemical bonds are formed between the atoms of the alloying element and the matrix, the width of the energy bands and the density of electronic states in the bands change.

Hyperbranched Polyester Polyfumaratomaleate Doped with Gd(III) and Dy(III) Ions: Synthesis, Structure and Properties.

For the first time, metal-polymer complexes have been synthesized using hyperbranched polyester polyfumaratomaleate as a matrix, the structure of which has been established by 1H NMR, IR, electron spectroscopy, and elemental analysis methods. The formation of complexes with Gd(III) and Dy(III) ions involving fumarate and maleate groups of the polyester was proved by IR and electron spectroscopy methods. It was established that the structure of the coordination units has the form of a square antiprism. The compositions and conditional logarithms of the stability constants of the complexes were determined. It was established that complexation with lanthanide ions promotes emission enhancement in the ligand.

In Situ Assembly of Well-Defined MoS2 Slabs on Shape-Tailored Anatase TiO2 Nanostructures: Heterojunctions Role in Phenol Photodegradation

MoS2/TiO2-based nanostructures have attracted extensive attention due to their high performance in many fields, including photocatalysis. In this contribution, MoS2 nanostructures were prepared via an in situ bottom-up approach at the surface of shape-controlled TiO2 nanoparticles (TiO2 nanosheets and bipyramids). Furthermore, a multi-technique approach by combining electron microscopy and spectroscopic methods was employed. More in detail, the morphology/structure and vibrational/optical properties of MoS2 slabs on TiO2 anatase bipyramidal nanoparticles, mainly exposing {101} facets, and on TiO2 anatase nanosheets exposing both {001} and {101} facets, still covered by MoS2, were compared. It was shown that unlike other widely used methods, the bottom-up approach enabled the atomic-level growth of well-defined MoS2 slabs on TiO2 nanostructures, thus aiming to achieve the most effective chemical interactions. In this regard, two kinds of synergistic heterojunctions, namely, crystal face heterojunctions between anatase TiO2 coexposed {101} and {001} facets and semiconductor heterojunctions between MoS2 and anatase TiO2 nanostructures, were considered to play a role in enhancing the photocatalytic activity, together with a proper ratio of (101), (001) coexposed surfaces.

Template-Less and Surfactant-Less Synthesis of CeO2 Nanostructures for Catalytic Application in Ipso-hydroxylation of Aryl Boronic Acids and the aza-Michael Reaction.

Due to its excellent physicochemical properties, CeO2 has found great importance as an electrochemical and in electronics, photocatalysis, sensing, and heterogeneous catalysis. Herein, we report the surfactant-less and template-less synthesis of CeO2 nanostructures by the hydrothermal method. The synthesized CeO2 nanostructures have been characterized in detail by electron microscopy, spectroscopy, diffractometry, and other analytical methods. The XRD studies revealed the formation of pure crystalline CeO2, possessing a cubic fluorite structure with an average crystallite size of 15.6 to 16.4 nm. Electron microscopy studies reveal the formation of cube-shaped CeO2 nanostructures with sizes below 25 nm. The cube-shaped CeO2 nanostructures exhibited a higher BET surface area compared to their bulk counterparts. The XPS analysis has confirmed the existence of Ce in the mixed oxidation states of +3 and +4, while O is present as O2- in the sample. The as-synthesized CeO2 nanostructures exhibit excellent catalytic activity in both the ipso-hydroxylation of aryl boronic acids and the aza-Michael reaction. The analysis of the used catalyst has confirmed its stability under the reported reaction conditions. The catalysts retain their catalytic activity up to the fifth run in both types of reactions, which is economically beneficial for industrial application.

Metal-Support Interactions in Molecular Single-Site Cluster Catalysts.

This study provides atomistic insights into the interface between a single-site catalyst and a transition metal chalcogenide support and reveals that peak catalytic activity occurs when edge/support redox cooperativity is maximized. A molecular platform MCo6Se8(PEt3)4(L)2 (1-M, M = Cr, Mn, Fe, Co, Cu, and Zn) was designed in which the active site (M)/support (Co6Se8) interactions are interrogated by systematically probing the electronic and structural changes that occur as the identity of the metal varies. All 3d transition metal 1-M clusters display remarkable catalytic activity for coupling tosyl azide and tert-butyl isocyanide, with Mn and Co derivatives showing the fastest turnover in the series. Structural, electronic, and magnetic characterization of the clusters was performed using single crystal X-ray diffraction, 1H and 31P nuclear magnetic resonance spectroscopy, electronic absorption spectroscopy, cyclic voltammetry, and computational methods. Distinct metal/support redox regimes can be accessed in 1-M based on the energy of the edge metal's frontier orbitals with respect to those of the cluster support. As the degree of electronic interaction between the edge and the support increases, a cooperative regime is reached wherein the support can deliver electrons to the catalytic site, increasing the reactivity of key metal-nitrenoid intermediates.

Using Collisional Electron Spectroscopy to Detect Gas Impurities in an Open Environment: CH4-Containing Mixtures.

The collisional electron spectroscopy method for analyzing and determining gaseous impurities was further developed to realize the operation in an open environment. In addition, the method not only facilitates the registration of the impurity components, but also the reactive radicals generated from the discharge reaction. The sandwich-like discharge structure was used to generate a stable, non-local, negative glow equipotential plasma in an open environment, and the I–V characteristic curve of the plasma was collected using an additional sensor electrode. The collisional electron spectroscopy was obtained from the first derivative of the probe current I with respect to the probe potential V by adding a diffusion function to correct it. In addition, our experiment verifies the reliability of the sink theory.

Advanced zirconia ceramics stabilized with yttria and magnesia: Structure and Vickers microhardness

The samples 8YSZ containing 70, 75, 80 mol% ZrO2 and other oxides were prepared by.a high temperature solid state reaction process. Using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and spectroscopic methods were evaluated the effect of oxide addition on the properties of yttria-doped zirconia.X-ray data shows the formation of zirconia (Y-doped), YSZ and/or tetragonal zirconia crystalline phases in all samples. IR data indicate the stretching vibrations of the Si–O bonds from tetrahedral [SiO4] units and the stretching vibrations of the Fe–O bonds from [FeO6] structural units, respectively. EPR results indicate the destroying of the local ordering of the Fe+3 ion vicinities situated in the rhombic distorted octahedral geometries by the increasing of ZrO2 content in the host ceramic.The highest values of Vickers hardness were recorded for the ceramics containing 70 and 75 mol% ZrO2. This superior performance can be explained considering the presence of a smaller amount of monoclinic ZrO2 crystalline phase in the ceramic structure.The analysis of the X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) data shows the presence of Fe+2 and Fe+3 ions. In the ceramics with higher ZrO2 contents the iron atoms adopt a randomly structure due to the highly distorted [FeO6] structural units and non-equivalent Fe–O distances in the first coordination shell.

Visible light-Fenton degradation of tetracycline hydrochloride over oxygen-vacancy-rich LaFeO3/polystyrene: Mechanism and degradation pathways

In this study, the oxygen–vacancy–rich (OV) lanthanum ferrite (LaFeO3) perovskite (also called LFO) was successfully prepared by an ultrasound–assisted sol–gel method and hydrothermally loaded onto polystyrene (PS) to obtain LaFeO3/polystyrene–oxygen–vacancies (LFO/PS–OVs). The structure and properties of LFO/PS–OVs were investigated using scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X–ray photo–electron spectroscopy (XPS), photoluminescence spectra (PL) and other characterization methods. The authors also investigated the effects of hydrogen peroxide (H2O2) concentration, catalyst dosage, solution concentration, pH and inorganic anions on the tetracycline hydrochloride (TC) removal efficiency. According to the results, the ultrasonic cavitation treatment and the composite reaction significantly increased the specific surface area of LFO as well as the content of oxygen vacancies and broadened the forbidden band width of LFO. The significant improvement in catalytic activity can be attributed to solving the agglomeration problem of powdered LFO and the introduction of a large amount of OVs. The degradation mechanism was proposed according to the free radical capture experiments and the electron spin resonance (ESR) tests. Based on the DFT calculations and identification of intermediates by LC/MS, the main degradation pathways of TC were proposed. The results showed that reactive oxygen species (ROS) may preferentially attack atoms with the high f0 values of Fukui index. This study gives an insight into the promising application of oxygen–vacancy–rich perovskite/polystyrene composites in environmental remediation.

Calculation of the electron-optical scheme of a new type mirror energy analyzer of charged particles

Further studies of the electron-optical properties of electrostatic multipole-cylindrical fields, synthesized from the fields of a cylindrical mirror and circular multipoles, are continued in the work. The implementation of electron spectroscopy methods is based on the use of complex equipment, one of the main elements of which is an electron energy analyzer of low and medium energies. Application of the multipole approach to the synthesis of deflecting fields makes it possible to develop effective methods for energy analysis of charged particle beams. The electron-optical scheme of new type mirror energy analyzer of charged particle beams based on an electrostatic axially symmetric octupole-cylindrical field is proposed in the work. An axially symmetric octupole-cylindrical field is constructed as a superposition of a basic cylindrical field and a circular octupole. When the fields were added, the central circle of the octupole was combined with the zero equipotential of the logarithmic field. The motion of charged particles in the electrostatic octupole-cylindrical field. An integrodifferential equation for the motion of charged particles in an electrostatic octupolecylindrical field is derived. Calculation of trajectories in an energy analyzer with an octupole-cylindrical field was performed on the basis of the method of expansion into a fractional-power series of the particle motion equation presented in the integrodifferential form. Coefficients of the series, representing the trajectory of motion in an analytical form, accessible for further studies of the electron-optical characteristics of the octupole-cylindrical field, are obtained. Based on an octupole-cylindrical field, high luminosity energy analyzers can be built to determine the composition of charged particle beams with energies from units of eV to tens of keV in space plasma.

Шлаки из раскопок археологического памятника — городище Кобылиха (Ненецкий автономный округ)

The results of studies of slag from excavations of the archaeological monument of the settlement of Kobylikha (Nenets Autonomous District) are presented. The analytical studies were based on optical and scanning electron microscopy and spectroscopic methods.
 Our detailed mineralogical and geochemical studies resulted in determining siliceous-ferruginous composition of slags with impurities of aluminum, calcium, phosphorus, and potassium. Concentrations of Cu, Pb, Mg, Ni, Ti, Cr, V impurity elements are not large. According to the chemical composition, the viscosity and basicity of the melt were evaluated. The viscosity index indicates the fluidity of the melt. The basicity coefficient in the studied slags can be attributed to the group of acidic slags. Microprobe studies revealed the predominance of fayalite, wustite, iron-siliceous glass and reduced iron. The conducted studies allowed concluding on the use of a single ore from a single source. It is possible to assume the use of oxide easy-to-mine iron ores. Melting was carried out in a furnace at fairly high temperatures in the range of 1200—1400 oC and using fluxes. The slag cooled down rather slowly and directly in the furnace. Probably, the melting lasted for a long time. In the settlement of Kobylikha, metallurgical production had an average scale using simple technological schemes.

A Co-Doped Carbon Dot/Silver Nanoparticle Nanocomposite-Based Fluorescence Sensor for Metformin Hydrochloride Detection.

In this study, a fluorescence sensor based on nitrogen and phosphorus co-doped carbon dot/silver nanoparticle (NPCD/AgNP) nanocomposites was developed for metformin hydrochloride (MFH) detection. We first utilized the reducing nature of the NPCDs to prepare AgNPs from Ag+ and subsequently prepare NPCD/AgNP nanocomposites. The nanocomposite material was characterized by various methods, including electron microscopic methods (SEM and TEM), spectroscopic methods (UV-Vis, PL, FTIR, and XPS spectroscopy), light scattering (ELS), and XRD. Further, we utilized the enhanced fluorescence of the NPCDs as well as the overlap between the fluorescence emission spectrum of the NPCDs and the absorption spectrum of the AgNPs to use the NPCD/AgNP nanocomposites as an effective inner filter effect (IFE) pair for sensing MFH. The IFE between NPCDs and AgNPs in the nanocomposite material resulted in a significant quenching of the fluorescence intensity of the nanocomposites compared to that of the pure NPCDs. However, the fluorescence was recovered when MFH was introduced into the nanocomposite solution. The fluorescence intensity of the nanocomposites increased linearly as the MFH concentration increased from 2 to 100 µg/L. This detection method showed good sensitivity compared to other methods. It also showed high selectivity and high sensing potential for MFH in human serum and yielded acceptable results.

Полевая электронная спектроскопия оксидных катодов

The results of studying the bulk and surface electronic structure of a graphite-oxide field cathode and an oxide thermal cathode using a cylindrical electrostatic dispersive energy analyzer are presented. Oxides based on ternary carbonate of alkaline earth metals were used. The energy spectra of electrons in the auto- and thermal automodes are obtained, and the possibility of studying the energy electronic band structure of an oxide thermal cathode by the method of field electron spectroscopy is shown.

Emerging Electrochemical Techniques for Probing Site Behavior in Single-Atom Electrocatalysts.

Single-atom catalysts (SACs) have aroused tremendous interest over the past decade, particularly in the community of energy and environment-related electrocatalysis. A rapidly growing number of recent publications have recognized it as a promising candidate with maximum atomic utilization, distinct activity, and selectivity in comparison to bulk catalysts and nanocatalysts. However, the complexity of localized coordination environments and the dispersion of isolated sites lead to significant difficulties when it comes to gaining insight into the intrinsic behavior of electrocatalytic reactions. Furthermore, the low metal loadings of most SACs make conventional ensemble measurements less likely to be accurate on the subnanoscale. Thus, it remains challenging to probe the activity and properties of individual atomic sites by available commercial instruments and analytical methods. In spite of this, continuing efforts have lately focused on the development of advanced measurement methodologies, which are very useful to the fundamental understanding of SACs. There have recently been a number of in situ/operando techniques applied to SACs, such as electron microscopy, spectroscopy, and other analysis methods, which support relevant functions to identify the active sites and reaction intermediates and to investigate the dynamic behavior of localized structures of the catalytic sites.This Account aims to present recent electrochemical probing techniques which can be used to identify single-atomic catalytic sites within solid supports. First, we describe the basic principles of molecular probe methods for the study and analysis of electrocatalytic site behavior. In particular, the in situ probing technique enabled by surface interrogation scanning electrochemical microscopy (SI-SECM) can measure the active site density and kinetic rate with high resolution. An alternative electrochemical probing technique is further demonstrated on the basis of single-entity electrochemistry, which allows the unique electrochemical imaging of the size and catalytic rate of single atoms, molecules, and clusters. The merits and limitations of different electrochemical techniques are then discussed, along with perspectives for future prospects. Apart from this, we further showcase the powerful capability of emerging electrochemical probing techniques for determining significant effects and properties of SACs for various electrocatalytic reactions, including oxygen reduction and evolution, hydrogen evolution, and nitrate reduction. Overall, electrochemical techniques with atomic resolution have greatly increased opportunities for observing, measuring, and understanding the surface and interface chemistry during energy conversion. In the future, it is anticipated that the development of electrochemical probing techniques will be advanced with innovative perspectives on the behavior and features of SACs. We hope that this Account can contribute in several ways to promoting the fundamental knowledge and technical progress of emerging electrochemical measurements for studying SACs.

Mott\u2013Hubbard insulating state for the layered van der Waals hbox {FePX}_3 (X: S, Se) as revealed by NEXAFS and resonant photoelectron spectroscopy

A broad family of the nowadays studied low-dimensional systems, including 2D materials, demonstrate many fascinating properties, which however depend on the atomic composition as well as on the system dimensionality. Therefore, the studies of the electronic correlation effects in the new 2D materials is of paramount importance for the understanding of their transport, optical and catalytic properties. Here, by means of electron spectroscopy methods in combination with density functional theory calculations we investigate the electronic structure of a new layered van der Waals hbox {FePX}_3 (X: S, Se) materials. Using systematic resonant photoelectron spectroscopy studies we observed strong resonant behavior for the peaks associated with the 3d^{n-1} final state at low binding energies for these materials. Such observations clearly assign hbox {FePX}_3 to the class of Mott–Hubbard type insulators for which the top of the valence band is formed by the hybrid Fe-S/Se electronic states. These observations are important for the deep understanding of this new class of materials and draw perspectives for their further applications in different application areas, like (opto)spintronics and catalysis.

Sorption-photocatalytic performance of NbOx nanocrystals synthesized via heat-stimulated oxidation of niobium carbide

In this work, nano-sized niobium oxides with different crystal structures can be produced by thermal treatment of nonstoichiometric nanocrystalline niobium carbide (NbCy) and serve as effective sorbents and photocatalytic materials. Differential thermal analysis of initial NbCy powder was carried out, and temperatures of thermal treatment for the were chosen. The nanopowders were studied using powder X-ray diffraction, scanning electron microscopy, low-temperature N2 adsorption–desorption, X-ray photoelectron spectroscopy and diffuse reflectance electron spectroscopy methods. The specific surface area of samples annealed at 100, 200, 300, 400, 500 °C was about 224, 255, 273, 224 and 47 m2/g, respectively. The photocatalytic activity of the obtained nanopowders was analyzed during the oxidation of an aqueous solution of methyl orange on exposure to visible light. The photocatalytic activity of nanopowders grows with the annealing temperature increasing from 100 to 500 °C and reaches the maximum value for the higher niobium oxide Nb2O5. The time of complete decoloration of dye was 165 min. The tests performed to establish the sorption equilibrium between catalyst and dye in the dark revealed that the nanopowder produced during annealing at 300 °C possesses a high sorption capacity of 76.5%, which allows it to be considered as an effective sorbent.

Spectral study of the structure and properties of complexes of unsubstituted indoline spiropyran with aluminum ions

The methods of absorption electronic and NMR spectroscopy were used to study the processes of complexation during the interaction of molecules of unsubstituted indoline spiropyran with aluminum salts. The mechanism of formation and structure of complexes of two types has been established. Negative photochromism of the complex of the merocyanine form of spiropyran with aluminum ions was found. The stability of metal complexes to the action of various agents has been investigated. Keywords: photochromism, spiropyrans, metal complexes, aluminum salts, electron spectroscopy, NMR spectroscopy.

Electronic structure of variants of compositions of scandate and nickel-oxide cathodes of microwave devices

By methods of electron spectroscopy for chemical analysis and spectroscopy of characteristic losses of electron energy, the electronic structure of barium oxide crystallites doped with other chemical elements, including scandium from scandium-containing phases, was investigated. The physical and physicochemical conditions are formulated, the fulfillment of which allows to form the electronic structure of the scandate cathode with a high level of thermionic emission: the achievement of the minimum ratio of the surface volume concentration of oxygen vacancies and the maximum distance between the top of the valence band and the Fermi level. Keywords: microwave devices, cathodes, thermionic emission, output operation, electronic structure, electron spectroscopy.

Электронная структура вариантов составов скандатных и оксидно-никелевых катодов СВЧ приборов

By methods of electron spectroscopy for chemical analysis and spectroscopy of characteristic losses of electron energy, the electronic structure of barium oxide crystallites doped with other chemical elements, including scandium from scandium-containing phases, was investigated. The physical and physicochemical conditions are formulated, the fulfillment of which allows to form the electronic structure of the scandate cathode with a high level of thermionic emission: the achievement of the minimum ratio of the surface volume concentration of oxygen vacancies and the maximum distance between the top of the valence band and the Fermi level.