Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques
ISSN (print): 1027-4510, ISSN (online): 1819-7094 Editor-in-Chief: Alexander A. Levchenko Publisher: Pleiades Publishing Indexed in: RUS White List (level 4), Scopus, Web of Science (ESCI)
Comprehensive Investigation of Some Ordinary Chondrites Based on X-Ray Methods and Mössbauer Spectroscopy
Comprehensive investigation into ordinary chondrites presented by the species of Markovka (H4 petrological type), Polujamki (H4 type) and Jiddat Al Harasis 055 (L4-5 type) is performed. The element and phase compositions, as well as the oxidation states of iron and nickel in the chondrites, are examined via micro X-ray fluorescence (micro-XRF), Mössbauer spectroscopy and synchrotron-based X-ray absorption spectroscopy. Elemental composition analysis is performed using micro-XRF, allowing one to obtain element distribution maps for the meteorite samples. According to Mössbauer spectroscopy data gathered on iron-containing phases, the chondrites consist mainly of olivine and goethite with a small amount of pyroxene and hematite. A low amount of troilite and kamacite is also observed in the Markovka and Polujamki specimens. The oxidation states of 3d metals in the chondrites are estimated from Fe and Ni K-edge X-ray absorption near-edge structure (XANES) spectra. Most nickel atoms in the meteorites are found to be in the Ni2+ state, while iron has an average oxidation state of +2.4 which is commensurate with the Mössbauer spectroscopy data. Infrared spectroscopy analysis of the chondrites is implemented as well. The results are important from the viewpoint of statistics acquisition on ordinary chondrites, as well as for further understanding of their formation.
Copyright (c) 2019 Pleiades Publishing, Ltd.
Focusing Properties of Bent Micro-Channel Plates in the X-Ray Range
Compact and flexible Micro-Channel Plate (MCP) devices are versatile optical systems suitable to condense and shape intense X-ray beams. Studies on propagation of both soft and hard X-ray radiations through these devices are of continuous interests because of increasing demand of synchrotron radiation X‑ray sources, in particular, to enhance the spot stability and to optimize the beam for specific experiments. In this work synchrotron radiation sources as well as a conventional X-ray tube coupled to polycapillary lenses have been used to characterize the transmission and the angular distribution of thin flat or spherically bent MCPs with different curvature radii. It is shown that the radiation beam from both synchrotron radiation and conventional X-ray sources can be efficiently condensed by thin spherically bent MCPs.
Electroluminescent Chamber for Studying the Subbarrier Fission of Transuranium Elements
An electroluminescent fission chamber is described, the operation principle of which is based on the optical detection of fission pulses. The use of an optical guide can significantly reduce statistical-measurement errors, lower the gamma-ray background, and increase the resistance to electrical and mechanical interference. Electroluminescence in strong electric fields with a large 103–104-fold increase in the light intensity allows one to detect individual fission events in the mode of counting. These advantages make it possible to measure the energy dependence of the cross section of the subbarrier fission of transuranium elements with a high resolution in lead in slowing-down spectrometers.
Color Cathodoluminescence of SrAl2O4:Eu, Dy-Based Phosphors
Single phase SrAl2O4:Eu2+ and multiphase {SrAl2O4 + Sr4Al14O25}:Eu2+ phosphors were prepared by solid state reaction and combustion synthesis. It is shown that the emission band of the phosphors can be shifted from green to blue-green spectral range by changing the synthesis method. Composite color cathodoluminescence and photoluminescent analysis were applied to control the synthesis process. The presence of different emission centers and their distribution in studied phosphors was demonstrated.
Local Atomic and Electronic Structures of β-Сoooh Nanosheets for the Hydrogen-Release Reaction
The geometric and band structures of cobalt-metahydroxide nanosheets, which are related to a new class of two-dimensional nanocatalysts for the hydrogen-release reaction, are calculated. As a result of improving the procedure, the optimal exchange-correlation functionals, basis sets, and dimensions of the “frozen” core are chosen to calculate the atomic and electronic structures, the density of states, and the width of the forbidden band. The calculated results show a decrease in the forbidden band of the cobalt-metahydroxide nanosheets compared with the crystal phase. The X-ray absorption spectra show a high sensitivity of the method to changes in the local atomic environment, especially in the first coordination sphere of cobalt atoms. The calculated model structure makes it possible to determine the features of the local atomic and electronic structures on a cobalt-metahydrixide nanosheet surface during the hydrogen-release reaction.
Transformation of the Electronic Characteristics of Ytterbium Nanofilms, Induced by Carbon-Monoxide Molecules Adsorbed on Their Surface
The adsorption of carbon monoxide (CO) molecules on ytterbium nanofilms composed of 16–200 single layers (6.1–76 nm-thick) is studied. The films are grown on grain-oriented tungsten ribbons with the preferential surface orientation (100). It is shown that, prior to the adsorption of CO molecules, ytterbium is divalent, possessing the [Xe]4f146s2 electron configuration. The adsorption of gas molecules in the surface region of the film led to the formation of a layer with trivalent ytterbium (with the [Xe]4f135d16s2 electron configuration). The minimum thickness of the ytterbium layer modified by adsorbed CO molecules is found to be composed of 16 single layers, corresponding to a thickness of 6.1 nm, which is anomalously higher than the values reported in publications.
Formation of Structure and Properties of Silumin on Electron-Beam Processing
The analysis of the gradient structure-phase states and nanohardness of hypoeutectoid silumin at 120 μm depth after the processing by high intensive electron beams in the regime of top layer melting has been carried out. It has been shown that depending on the depth to the surface of irradiation the electron beam processing leads to the dissolution of the primary inclusions of silicon and intermetallides and the formation of structure of high-speed cellular crystallization of aluminium and the grains of plastic eutectic. A 1.5‒2 fold decrease in the concentration of the alloying elements has been detected. The hardness of irradiated silumin changes in a nonmonotonous way and reaches the maximum values exceeding the hardness of the initial state by 3.8‒4.2 times in the layer located at 30–50 μm depth. The interpretation of the observed changes in structure and hardness on irradiation has been given.
On the Change in the Reflectance of Мо(111) Mirrors after Exposure to D2–N2 Plasma
The effect of D2–N2 glow discharge plasma on the reflectivity of single-crystal Mo(111) mirrors is studied. The surface of each mirror is processed by mechanical polishing with diamond pastes to a roughness of hq = 5 nm. During polishing, abrasive particles are embedded in the surface layer of the mirror. Exposure to an ion fluence of 1.4 × 1024 m–2 leads to an increase in hq = 7 nm. After irradiation and the removal of a 30 nm-thick Mo layer the total reflection coefficient Rt in a 400–1000 nm region increases by 5–10% to a steady-state value (56–58)%. The increase in Rt may be caused by the preferential removal of carbon during the ion-sputtering process.
On the Passage of Radiant Fluxes out of Discharge Plasma in Ion Sources through Openings in Ion-Extraction Systems
In ion sources, up to a third of the power released in a plasma discharge is carried away from the plasma in the form of ultraviolet radiation. Two main mechanisms for the formation of radiation are considered: radiation from excited atoms of the propellant and from ion-electron recombination coming out of plasma onto the surface bordering the discharge. The radiation-absorption coefficients of perforated electrodes of ion-extraction systems are determined.
Two-Electrode Ion-Extraction System of a Radio-Frequency Ion Source: Numerical and Experimental Studies of Erosion of the Accelerating Electrode
The results of numerical and experimental studies of the erosion rate of the accelerating electrode of an ion thruster are presented. When the ion beam propagates beyond the edge of the thruster, the process of resonant charge-exchange leads to the formation of slow ions in the engine volume. Under the action of negative electric potential of the accelerating electrode, ions bombard the electrode surface which faces the outgoing beam. Erosion due to the bombardment of the accelerating electrode by charge-exchange ions is the main factor limiting the ion-thruster lifetime. A 25-layer coating of optically contrasting copper and chromium layers, which is applied to the outer electrode surface, is used to diagnose the sputtering rate. The total time of exposure is 14 h. The time dependence of the growing cavity depth is obtained by recording the cavity profile every 3–5 hours. The results obtained in the experiment are used as the initial data for the numerical 3D modeling of multilayer-coating erosion under conditions corresponding to the experiment. Based on the results, the lifetime of the test thruster is estimated at 13 800 hours in respect to the wear of the titanium electrode at its potential of –500 V.
On the Fabrication of a High-Quality Optical Surface of an Amorphous Nickel Coating on a Beryllium Substrate
The physical and mechanical properties of modern materials used for manufacturing optical-electronic space-based devices ensuring a high mirror roughness at a level of Ra = 1 nm are analyzed. The deposition of nickel obtained as a result of nickel reduction from aqueous solutions by the chemical method on a beryllium substrate to obtain an amorphous structure is studied. The coating is analyzed by X-ray methods. The phase and chemical composition of the coating is determined and its thickness is measured. The amorphous structure of the coating is confirmed. The coating has a high chemical resistance and hardness and provides conditions for effective optical polishing. Regulation of the chemical composition during the deposition process allows thermal matching of the coating with the substrate to be achieved.
Influence of Focused Pulsed Laser Radiation on the Properties of Amorphous FeSi6B16 Metal Alloy
The effect of focused pulsed laser radiation (number of pulses and power density) on an amorphous FeSi6B16 metal film is studied. The states of the alloy before and after laser irradiation are analyzed using methods of atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and microhardness measurements. Focused laser radiation in any exposure mode is established to cause high-temperature heating of the surface of an amorphous alloy in the irradiation zone. The result of such heating is melting of the material surface and propagation of the heat wave front from the strongly heated surface to its inner layers, which induces the redistribution of elements in the Fe–Si–B system, a change in the structure, and an increase in the microhardness.
On the Structural Instability of a Nematic in an Alternating Electric Field and Its Connection with Convection and the Flexoelectric Effect
The threshold structural instability arising in the thin layer of a nematic liquid crystal (nematic) along the surface of an electrode during the flow of a weak direct injection current is described. Local, limited in length Lу, nuclei (precursors) of electrohydrodynamic and flexoelectric instabilities are assumed to be in this thin layer. In the case of electrohydrodynamic instability, such precursors have been called “bullets” (solitons) because of their specific appearance, and their length Lу is a measure of local perturbation of the orientational structure of a nematic. In the case of flexoelectric instability, pieces Lу are formed by an irregular system of short polarized flexoelectric domains. Such an instability corresponds to a system consisting of groups of stripes, which are characterized by the opposite motion of “bullets” along these stripes and the average velocity of this movement.
Structure and Surface Morphology of Cd1 −x(Mn, Fe)xSe Epitaxial Films
The optimal conditions (υк = 8−9 Å/s; Тп = 673 K) to obtain structurally perfect (W1/2 = 100″−140″) Cd1 − x(Mn, Fe)xSe epitaxial films in the (111) plane are determined. The structure and surface morphology of the epitaxial films are studied. It is established that in Cd1 − x(Mn, Fe)xSe thin films, unlike bulk samples, the sphalerite structure with the lattice parameter a = 6.05 Å is formed. Using an additional source of Se vapor during growth, Cd1 − x(Mn, Fe)xSe epitaxial films with a clean, smooth surface are obtained.
Dependence of the Degree of Reinforcement of Polymer/2D-Nanofiller Nanocomposites on the Nanofiller Surface Structure
A procedure for calculating the fractal dimension of tactoid structures of a 2D-nanofiller (graphene oxide) in the polymer matrix of a nanocomposite is proposed. The fractal nature of tactoids leads to the fact that only a part of their surface (the unscreened surface) is available for the formation of interphase polymer-matrix—2D-nanofiller contacts. An increase in the unscreened surface dimensions determines the enhancement of a relative fraction of the interphase regions and, as consequence, improvement in the mechanical properties of the nanocomposites. It is suggested that the interaction of graphene-oxide tactoids has a certain influence on the indicated properties.
Surface Segregation of the Composition in Gallium-Nitride Films
The micro- and nanomorphology and local composition of gallium-nitride GaN films synthesized according to the metalorganic chemical-vapor deposition (MOCVD) technology are studied with the aim of detecting segregation phenomena. As a result, a complex picture of autosegregation is shown and discussed. In the main thick (~15 µm) gallium-nitride film, surface nonstoichiometry of the chemical composition (gallium deficiency) is revealed. The degree of nonstoichiometry (deviation of the relation at % Ga/at %N from unity) is ~0.20, whereas in the depth the deviation is less: from 0.02 to 0.10. At the same time in the thin (~1 µm) film, there is a significant excess of gallium up to individual nanocrystallites of metallic gallium. The mechanism of segregation which is presumably associated with the selective diffusion of nitrogen atoms or of gallium atoms to the surface and with the tendency of liquid gallium nanodroplets to coagulation is discussed.
Structural Surface Features of Tellurium-Doped Bismuth Films
The effect of the degree of tellurium doping on the structural characteristics (average sizes of grains and growth figures) of bismuth films in the concentration range 0.005−0.15 at % Te and the thickness range 0.3−0.7 μm is studied. The thicknesses of the investigated films are measured by multi-beam optical interferometry. The amount of tellurium in the film is considered to be equal to that in the initial bismuth single crystal with a previously known tellurium concentration. Additional control of the tellurium content in the initial crystal is performed using a time-of-flight LYUMAS-30 mass spectrometer. To determine the average sizes of grains and growth figures, I use the technique developed by E.V. Demidov. The studies conducted reveal that an increase in the degree of tellurium doping in bismuth films leads to a significant decrease in the growth figures. The weak effect of annealing on the crystallite size in tellurium-doped bismuth films indicates the high temporal stability of their structures.
Formation of Oxide Layers on the Surface of Copper and its Alloys Modified by a High-Power Ion Beam
The change in the phase and elemental composition of the surface layers of copper and its alloys, brasses LS59-1, L63, and bronze BrAZh9-4, preliminarily irradiated with a high-power ion beam, after oxidation in air at 400°C is studied. It is shown that depletion of the brass surface by zinc under irradiation with a high-power ion beam does not lead to a noticeable increase in the oxidation of brass during thermal annealing in air due to the diffusion of Zn from the volume to the surface. The annealing of high-power ion-beam-irradiated copper under similar conditions does not change the composition of oxidation products, and the phase ratio is determined by the duration of annealing. For BrAZh9-4 bronze irradiated by a high-power ion beam, enrichment of the surface with copper leads to the intensification of oxidative processes. Possible mechanisms for the observed changes in copper and its alloys are considered.
Application of Ion-Beam Treatment in the Process of the Magnetron Deposition of Thin SnO2 Films
The effect of accompanying ion-beam treatment on the structure and properties of SnO2 films synthesized by the method of high-frequency magnetron sputtering at room temperature and at 200°C is investigated. It is established that ion-beam processing does not affect the transparency and the band gap of the obtained tin-oxide films. The refractive index and resistivity change. At room temperature, the films are X‑ray amorphous, and at 200°C they are polycrystalline. X-ray diffraction and electron diffraction studies show the presence of a single phase of SnO2. Ion-beam treatment leads to a change in the preferred orientation of the crystallites. With increasing current of ion-beam processing, the grain sizes decrease.
Composition of Catalytic Layers Formed by the Ion-Beam-Assisted Deposition of Platinum and Gadolinium on Carbon Carriers
Catalytic layers on the surface of Toray Carbon Fiber Paper TGP-H-060 T and AVCarb® Carbon Fiber Paper P50 carbon carriers are formed by the ion-beam-assisted deposition of platinum and rare-earth-metal gadolinium (as an activating additive) in order to obtain electrocatalysts for the direct oxidation of ethanol and methanol for fuel cells with a polymer membrane electrolyte. The formation of the layers is carried out in the ion-beam-assisted deposition mode, in which metal deposition and mixing of the deposited layer with the substrate surface with accelerated (U = 5 kV) ions of the same metal are carried out, respectively, from the neutral fraction of the vapor and plasma of a vacuum pulsed arc discharge. The microstructure and composition of the obtained surface layers are studied using scanning electron microscopy, electron probe X‑ray spectral microanalysis, X-ray fluorescence analysis, and Rutherford backscattering spectrometry. As a result of the ionic mixing of all components, multicomponent layers containing atoms of precipitated metals and substrate elements, as well as oxygen impurities, are obtained.
Features of the Propagation, Evolution, and Remote Collapse of a Correlated Wave Packet
The features of the spatial propagation and the evolution of a free correlated wave packet describing the process of particle motion are considered. It is shown that, unlike an “ordinary” noncorrelated packet, for which the process of spatial “spreading” and defocusing begins with the instant of its creation, in the case of a moving correlated packet, in the initial state, a self-simulated self-compression process occurs to the collapse state at a given distance; then the accelerated “spreading” mode is implemented. Some methods for forming such a packet and the possibility of using it in applied problems for particle and energy transport and for the aims of medical hyperthermia are considered.
Features of Colloidal Aggregation in Tetraethoxysilane-Water-Ethanol Ternary Mixtures by Small-Angle Neutron Scattering
The influence of the concentration of components in a tetraethyl orthosilicate (TEOS)–water–ethanol mixture on the growth of silicate aggregates in a basic environment is studied with small-angle neutron scattering. There is a general increase in the size of aggregates with an increase in the amount of both water and TEOS. At the same time, when the H2O : TEOS molar ratio is 2 : 1, the structure of the aggregates repeats, regardless of the TEOS concentration in the system. The scattering length density of the aggregates is found via hydrogen/deuterium isotopic substitution and contrast variation to analyze the possible inclusion of residual ethyl and hydroxyl groups into their structure.
The Proton Linac for Compact Neutron Source Daria
We develop a concept of the CW proton linac with the parameters of 13 MeV 162.5 MHz 5 mA. This linac designed for compact neutron source DARIA is based on the linac designed for the project BELA. The different linac layouts were considered. The most perspective linac layout includes Radio Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) sections with 6D beam matching between them. The drift tube linac section has a modular structure and consists of the separated individually phased IH-cavities with beam focusing by quadrupole magnets between the cavities. This DTL structure provides linac compactness, tuning and commissioning “cavity by cavity”. Results of the beam dynamic simulation and radio frequency parameters of the linac cavities are presented.
Spin-echo Small Angle Neutron Scattering for a Compact Neutron Source Daria
Spin-echo small-angle neutron scattering (SESANS) technique is a method to measure the correlation function of the structural organization of materials from nano- to micrometer length scales. As this method does not require neither highly collimated beams nor high incident intensity it can be easily and effectively used at the low flux sources, such as compact accelerator-driven neutron sources. Here we describe an important science case for SESANS setup designed at the compact neutron source DARIA. It was shown that SESANS method is a sensitive tool to study the packaging of DNA in the nuclei of biological cells. The sensitivity of the SESANS signal crucially depends on the neutron wavelength. The pulse character of the compact neutron source suits ideally to these investigations as it implies changeable neutron wavelength in the range from 0.2 to 1.0 nm. Such option allows one to study in great detail the internal structure of the biological cell in the length scale from 10 nm to 100 μm.
Non-Dipole Features of the Photon Emission Spectrum of a Fast Oriented Lepton in a Crystal
The probability of the non-dipole emission of photons by channeled particle is calculated. The emission of hard photons with an energy comparable with that of the incident channeled particle is studied. The quasi-Bloch energy spectrum of an oriented fast charged particle entering a crystal at an angle smaller and greater than the Lindhard angle is calculated. The initial and final spectra of the channeled particle are described by different sets of band wave functions corresponding to different energies. The processes of photon generation by a quantum particle entering into the crystal at an angle larger and smaller than the Lindhard angle are considered on an equal basis. The spectrum of hard-photon emission is shown to consist of a set of well-observed emission lines.
On Precessing Spin Neutron Reflectometry
The spin operator at a point, σ(r) ≡ σδ(r' – r), is defined for analysis of behavior of the neutron polarization vector. Polarization of neutrons in a two-level state that traverse regions with magnetic field without being scattered is described in terms of pilot velocity, precession front, nutation and dynamic axes. A scheme of reflectometry of neutrons in two-level states (precessing spin neutron reflectometry) is suggested for a more detailed study of magnetic layered structures.
Dependence of the Kinetics of Radiation-Induced Defect Formation on the Energy Absorbed by Si and SiC when Exposed to Fast Charged Particles
The kinetics of the formation of radiation-induced defects in silicon and silicon carbide as a function of the absorbed energy is analyzed. The dependence of the concentration of conduction electrons n-Si and n-SiC on the irradiation dose is studied experimentally under conditions of irradiation with electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. The advantages and disadvantages of using the integral flux (fluence) and absorbed energy as kinetic parameters are discussed. It is established in the performed studies that the visual representation of the kinetics of radiation-induced defect formation as a function of the fluence of irradiating particles is clearer for tabulating the requirements imposed to equipment stability under suitable conditions. To study the physical processes underlying the formation of radiation-induced defects in semiconductors, it is more convenient to use the dependences of the effects observed under radiation exposure as functions of the absorbed energy.
Electronic and Software Support of a Test Time-of-Flight Meter for Neutron Spectra
A description of the operation and functional units of a test time-of-flight meter for neutron spectra for a polarized neutron reflectometer that will be installed after the neutron cold source of the IR-8 reactor neutron guide is presented. The developed electronic and software support allows measurement of the neutron transit time and, accordingly, the determination of the spectral characteristics of a neutron beam, as well as controlling the exact spatial positions of a chopper disk, diaphragm, and 3He-detector using stepper motors and controllers.
Molecular Dynamics of DNA Damage and Conformational Behavior on a Zirconium-Dioxide Surface
This work is aimed at a comprehensive study of the processes of immobilization and conformational behavior of DNA on a zirconium-dioxide (ZrO2) surface. The computer-aided molecular dynamics (MD) method is used to study model systems of nanoparticles and nanoscale DNA + ZrO2 films, as well as elucidate the experimental spectral and integrated measurements, including the neutron-nuclear physical aspects of the study. Using hybrid MD potentials of classical mechanics and quantum chemistry for DNA solvated in an aquatic environment, the DNA/ZrO2 surface interactions are studied, and different DNA damage scenarios with various charge modifications are simulated. The charge modifications are introduced into the central part of the DNA molecule by means of two phosphorus atoms, Pa and Pb, for which a number of MD models of DNA + surface are constructed, thereby estimating the dynamic changes of the distance D[DNA(Pa, Pb)-ZrO2(O)] between the phosphorus atoms (Pa, Pb) and a selected oxygen atom on the surface of the ZrO2 film. In conclusion, this work is aimed at the development of the functional heterojunctions, such as biological molecules with wide-gap dielectrics. These heterojunctions are intended for use in the field of molecular electronics, in particular, to create biochips and memory arrays in computer architectures of the future.
Complex Approach to Atomistic Simulation of the Size Dependences of the Temperature and the Heat of Melting of Co Nanoparticles: Molecular Dynamics and Monte Carlo Method
The size dependences of the temperatures of melting \({{T}_{{\text{m}}}}\) and crystallization \({{T}_{{\text{c}}}}\) of Co nanoparticles and also those of the heat (enthalpy) of melting \(\Delta {{H}_{{\text{m}}}}\) and crystallization \(\Delta {{H}_{{\text{c}}}}\) are studied using a complex approach to atomistic simulation combining the use of the molecular dynamic and Monte Carlo methods. It is established that \({{T}_{{\text{m}}}}\) and \({{T}_{{\text{c}}}}\) decrease linearly with increasing inverse particle radius. The phase transition heats \(\Delta {{H}_{{\text{m}}}}\) and \(\Delta {{H}_{{\text{c}}}}\) also decrease during the transition from the bulk phase to nanoparticles, but it seems this effect is non-scalable.
Formation of a Nanoscale Graphite Hydrosol under the Influence of Terahertz Laser Radiation
The present report describes a new phenomenon, namely the formation of a nanoscale hydrosol during short-term exposure of the surface of water by focused terahertz radiation of the Novosibirsk free-electron laser. The composition of the particles is completely determined by the material of the container used. Hydrosols are technologically convenient forms for scientific and industrial applications, which are characterized by uniform deposition and high catalytic activity used in medicine, optics, and as a suspension for sample preparation for chemical and elemental analysis. This article presents the results of our study of graphite particles formed in water, a suspension, which is in demand for industrial purposes. Commercially available high purity graphite (99.5%) of GE grade is used. The initial material and the resulting particles are studied using an atomic force and electron microscope with an elemental analyzer.
Features of Degradation of the Optical Properties of Hollow Particles TiO2, ZnO, and SiO2 under the Influence of Ionizing Radiations
The reflectance spectra of ZnO, TiO2, and SiO2 micro-, nano-, and hollow powders after their exposure to 100-keV protons are analyzed at wavelengths between 250 to 2500 nm. The hollow particles are up to 5 μm in size with a specific surface area of 32 to 57 m2/g. It is established that hollow particles have a greater radiation stability to proton exposure than microcrystal particles. The effect is due to the absence of radiation-induced defects in the volume of the spherical particles, low ionization losses, and a high ability to relax radiation-induced defects in the thin layer of the sphere.
Morphological and Optical Properties of Cu1 –xZnxO Nanoparticles
This paper reports on morphological and optical properties of Cu1 – xZnxO nanoparticles (x = 1 and 3 at %) synthesized by the microwave method. Undoped and Zn doped CuO nanoparticles are characterized by SEM, EDAX, UV–vis FTIR and XRD analysis. Capsule shape and Circle shape nanoparticles are observed in SEM analysis. The at % of Cu, Zn and O in nanoparticles is estimated by EDAX analysis. The presences of various chemical functional groups are confirmed by FTIR analysis. The peaks present in the range 410–430 cm–1 are assigned to the Cu–O. The bandgap value is calculated as 3.94, 3.84 and 3.82 eV for undoped and Zn doped (1 and 3 at %) CuO nanoparticles. The average crystallite size of undoped CuO nanoparticles is calculated as 17.14 nm using the Scherrer formula by XRD analysis.
Binary and Pseudobinary Invar Materials based on Intermediate Valence Compounds
A new type of binary and pseudobinary invar materials based on intermediate valence samarium compounds Sm0.8B6, Sm1 – xLaxB6 (x = 0, 0.1, 0.22, and 0.5), Sm0.67Y0.33S, Sm0.55Y0.45S, and Sm2.75C60 are developed. The Weiss two-level invar model is used to describe the anomalous contribution to the coefficient of thermal expansion (CTE) for Sm0.8B6 and Sm1 – xLaxB6 (x = 0, 0.1, 0.22, and 0.5). The minimum position of the CTE of samarium hexaboride as a function of the degree of lanthanum doping is determined. The obtained dependence allows one to predict the CTE minimum position for Sm1 – xLaxB6 compounds in the temperature range from 40 to 180 K and to optimize the developed composite invar materials, where the positive CTE of the functional material is compensated by the negative CTE of the valence-unstable system.
Development of a Broadband Double Monochromator based on Multilayer Supermirrors for Hard X-Ray Spectroscopy on High-Intensity Beams
This work focuses on multilayer monochromatization systems (MMS) designed for X-ray spectroscopy stations of synchrotron radiation (SR) user-oriented centers for operation in a wide range of energy resolutions and at a high temporal resolution of the synchrotron experiment. The problem of providing a high SR flux density after the monochromator at required the monochromatization-system bandwidth is solved. A factor crucial for the quantitative analysis of the functional properties of the MMS is revealed and the optimum number of periods is determined. Analysis of the atomic and solid-state properties of elements and materials and detailed numerical simulation of the MMS allowed us to select several optimum pairs of materials for the synthesis of multilayer structures, in particular, Pt/Si and Au/Si. It is shown that reflectivities of more than 80% at a bandwidth of 4.4% can be achieved, which is very important for further practical development and the design of promising monochromators. The performed work concerns monochromatization systems for the SR energy range from 5 to 12 keV, which is the most sought after in X-ray spectroscopy.
Procedure of Predicting the Lifetime of the Accelerating Electrode of an Ion-Extraction System of a Gas-Discharge Ion Source
The state of studies on determination of the lifetime of ion thrusters (IT), including their methodology, is analyzed. The erosion of the accelerating electrode (AE) of an ion-extraction system caused by charge-exchange ions is a critical process responsible for the IT lifetime. It is shown that the quickest and most accurate information on the nature of AE erosion and rate at the initial test stage can be obtained by a method based on the use of multilayer coatings, consisting of several pairs of optical contrast materials, preliminarily applied to the AE surface. The method allows the use of simple photographic devices for recording the erosion pattern and is especially efficient in the case of a highly nonuniform nature of erosion. The calculation procedure is presented for the parameters of diagnostic multilayer coatings, including the optimal layer thickness and total coating thickness, which allow data to be obtained on the surface erosion profile and rate, and on the charge-exchange ion current density distribution with the highest resolution during the given test time.
Formation of a Nickel–Aluminum Intermetallic during Ion-Beam Mixing
The results of studying the X-ray photoelectron spectroscopy of the chemical composition of nickel surface layers with a deposited aluminum film, depending on the dose of irradiation with argon ions, are presented. Analysis of the spectra shows the formation of Ni3Al aluminide during ion-beam mixing. The highest content (~20%) of this compound in the modified layer is observed at an implantation dose of 5 × 1016 cm–2.
Structural Features of Pseudomorphic Spinel-Structure Films on R-Sapphire Substrates
А suspension of submicron ZnO crystallites in acetone is applied to epi-ready R(10\(\bar {1}\)2) sapphire plates with dimensions of ~10 × 10 × 0.5 mm. The composite is dried and annealed in air in a tube furnace at 1200°C for 60 min. According to the data of electron and scanning probe microscopy, X-ray and electron diffraction, thin oriented ZnAl2O4 zinc spinel films are formed on the sapphire substrate with the mutual orientation of lattices following the epitaxial relationships: (311)ZnAl2O4||(10\(\bar {1}\)2)Al2O3; 〈332〉ZnAl2O4||〈11\(\bar {2}\)0〉 Al2O3; 〈110〉ZnAl2O4||〈1\(\bar {1}\)01〉Al2O3. Due to the relatively high synthesis temperature of the films (1200°C) and the most intense cathodoluminescence of the film in the near-infrared (IR) spectrum, the formation of normal zinc spinel can be assumed. The obtained ZnAl2O4 films with the (311)-plane orientation parallel to the R plane of the sapphire substrate are supposed to be used to grow magnetic NiFe2O4 and CoFe2O4 films having the (311) plane with an easy-axis magnetization anisotropy oriented along the 〈311〉 direction.
Features of the Initial Growth Stages of ZnO Films on the Rhombohedral Plane of Sapphire
The initial growth stages of (11\(\bar {2}\)0) ZnO films on the rhombohedral plane of sapphire are studied. Grains of parasitic orientations are found to form at early growth stages. The pre-growth annealing of sapphire substrates at temperatures above 1000°C results in suppression of the growth of these grains. The presence of round and polygonal grains in (11\(\bar {2}\)0) ZnO films is explained from the standpoint of the cluster-growth mechanism.
Microstructured Substrates for Counting Bacteria Formed by Ion Implantation Through a Mask
In the present work, a novel technological approach based on ion implantation for obtaining microstructured substrates for the statistical analysis and visual characterization of ultra-small biological objects and microorganisms is developed. By means of the argon-ion implantation of silicate glasses through surface masks made of wire mesh, periodic surface nanostructures in the form of gratings with mesh sizes of 500 × 500 nm are formed. The obtained novel substrates are tested using atomic force microscopy and scanning electron microscopy with energy dispersive analysis using bacteria of the genus Bacillus deposited onto their surface.
Carbon Nanotubes Obtained from Natural Gas by CVD
Carbon nanotubes are obtained using chemical vapor deposition (CVD) equipment via the pyrolysis of natural gas in the presence of nanoscale iron. The influence of various parameters on the yield of nanomaterials synthesized is studied, and we find that the yield of nanocarbon increases with an increase in the pyrolysis temperature from 650 to 850°C. At the same time, the introduction of argon, which acts as a buffer gas, into the reactor significantly increases the yield of carbon nanotubes. The samples synthesized are studied by physical methods.
Effect of Ion Bombardment on the Density of States of Valence Electrons in CdS Films
Cd nanofilms with a thickness of 10–12 Å are obtained by bombarding a CdS surface with Ar+ ions. The obtained Cd–CdS nanofilm systems are shown to be promising for creating metal–insulator–semiconductor and semiconductor–insulator–semiconductor heterostructures and forming nanoscale barrier layers and hyperfine ohmic contacts on the semiconductor surface.
Fracture of the Surface Layers of Alumina Ceramics under the Action of a High-Power Ion Beam of Nanosecond Duration
The fracture of surface layers of alumina ceramic (polycor) under the action of a high-power ion beam of nanosecond duration is investigated. The characteristic features of such fracture are determined. An estimation of the thickness of breakaway fragments of the surface layer of the ceramics gives values in the range from 4 to 12 μm at single high-power ion beam irradiation with a current density of 150 A/cm2. Oxygen depletion in the surface layer of the ceramics is established. The effect of irradiation on the structural-phase state of the ceramics is considered. The possible mechanisms of the observed fracture are discussed.
Electron-Microscopy Studies of Microstructural Features of the Pore Space in Polymictic Sandstones
The results of studying the structural features of the pore space in lower Cretaceous polymictic sandstones from prospective sediments on the territory of the Republic of Kalmykia (East Biryuzak area) by the method of scanning electron microscopy are presented. Microstructural parameters are obtained for modeling filtration processes, “digital core model” or “digital core.”
Features of Field Electron Emission when Changing the Positional Order in Colloidal Solutions and Cetyltrimethylammonium Bromide
The features of the field electron emission through a drop of a colloidal solution of a surfactant (structured colloidal solution of cetyltrimethylammonium bromide) are studied. The results indicate the possibility of using data on the angular distribution of the electron emission intensity stimulated by a pulsed electric field from structured liquid media to study the positional order and geometry of molecular associates in solutions.
Atomic Structure Probing of Thin Metal Films via Vacuum Holographic Microscopy
A vacuum holographic microscope is designed to probe the atomic structure of thin metal films. The experimental setup is based on the use of a source of a monochromatic low-energy electron beam induced by a tip cathode spaced from the sample at a distance of several tens of nanometers. The visual resolution of atoms of the object requires a microscope magnification of at least 105, which necessitates high-accuracy movement of the electron source. The parameters of principal nodes of the microscope, which are responsible for the generation and recording of useful signals, are studied and optimized, as well.
Analysis of the Results of Silicon Sputtering Simulation as Functions of Different Ar–Si Potentials
The influence of the form of the Ar–Si interatomic potential on the results of simulating the physical sputtering of amorphous Si by low-energy Ar ions is analyzed. The yields of Si sputtering by Ar ions with an energy of 50–300 eV at normal incidence are calculated using the molecular dynamics (LAMMPS software) and the Monte Carlo methods by means of the MOTREV program developed at the Skobeltsyn Institute of Nuclear Physics, the Moscow State University, and used quantum-mechanical elastic-scattering cross sections. The semiempirical Molière and ZBL pair potentials and a potential developed on the basis of density functional theory calculations are applied to describe Ar–Si interaction. The energy dependences of the sputtering yields obtained using different potentials are analyzed in this paper. Conclusions concerning the applicability of the considered Ar—Si interaction potentials to simulation of the physical sputtering of amorphous Si in the indicated range of projectile energies are drawn.
Study of Resonance Phenomena During Thin-Film Perforation upon the Passage of Multicharged Ions
The process of the perforation of a nanometer-thick film during passage of the wave packet of a multicharged ion is studied. It is shown that the resonant behavior of vibrations of the disk released from the film has a significant effect on the perforation process. The resonance mechanism is based on the “push-pull” process. A model of the strength of the polarization interaction between the film and the wave packet of the particle is proposed. The model makes it possible to estimate the threshold value of the force required to form a pore during the passage of a multicharged ion through the film.
Test Objects with a Rectangular Profile for SEM: 1. Fabrication Technology
The design and fabrication technology of test objects in the form of slit-like grooves with a rectangular profile and certified widths in the range of 50–500 nm in silicon are described. Experimental results that substantiate sections of the technology of groove fabrication and confirm the basic properties of the produced structures are given. The test objects are intended for calibrating scanning electron microscopes (SEMs) and studying the mechanisms of SEM-image formation.
Electron Radiation during Planar Channeling in Crystals with the CsCl Structure
The interaction potentials between electrons and the principal charged (111) and (100) planes in CsCl-type crystals are calculated using the Molière, Firsov, Barrett, and Doyle—Turner approximations for single-particle ion potentials. The features of the structures of these interaction potentials are studied without considering the influence of the temperature factor and with its inclusion. For relativistic electrons with Lorentz factors of γ = 25, 50, 75 channeled in these planes, the transverse energy levels and the wave functions corresponding to them are numerically found for all crystals with CsCl-type structures. Based on these data, the spectra of channeling radiation are calculated under the condition that electron beams (with an angular dispersion θ0 equal to zero and to ≈0.3 mrad) are incident at zero angles with respect to the crystallographic (111) and (100) planes. It is shown that the generated radiation is most intense in the (100) planes of the CsCl-type crystals.
Broadband Silicon Absorber of Terahertz Radiation
A three-layer structure is fabricated on a low-resistance silicon substrate using plasma chemical etching. We study it experimentally and show that a substrate with such a structure can be used as an absorber of terahertz (THz) radiation in the frequency range of 0.5−2.0 THz. For this structure, absorbance in the indicated frequency range is measured to be more than 95%.
Electrical Conductivity of Films with Negative Dielectric Permittivity
The electrical conductivity of films from spherical nanoparticles of metal oxides Al2O3 and NiO, whose surface is saturated with hydrogen atoms, is studied. It is found that under the action of an electric field the films pass into a stable state of polarization. In this unchanged state at a current J ≥ 0, the differential electrical resistance of the films is zero. It is established that the static dielectric constant \(\varepsilon (0,\bar {k})\) of finely dispersed dielectrics Al2O3, NiO, and KMnO4 saturated with hydrogen has a negative value. At the same time, regardless of temperature (T = 295–500 K), in the case of a constant or sinusoidal current, the ohmic resistance of a powder is zero if it simultaneously satisfies the condition ε(0, \(\bar {k}\)) < 0. This effect is a consequence of the negative value of the free energy of a polarized powder.
On the Formation of Electrocatalysts for Methanol and Ethanol Oxidation by the Ion Beam-Assisted Deposition of Rare-Earth Metals and Platinum on Carbon Carriers
Active layers on the surface of AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T carbon carriers are formed by the ion-beam-assisted deposition of platinum and one of the rare-earth metals (Ce, Gd, Dy, Yb, and Ho) as an activating additive in order to obtain electrocatalysts for the direct oxidation of ethanol and methanol for fuel cells with a polymer membrane electrolyte. The deposition of metal atoms and mixing of the deposited layer with the surface of the substrate with accelerated ions of the same metal are performed from the neutral vapor fraction and the vacuum arc discharge plasma of a pulsed electric arc ion source, respectively. A distinctive feature of the obtained electrocatalysts is their higher activity in the oxidation process of more complex ethanol molecules as compared with methanol.
On the Application of the Langevin and Gorter—Casimir Two-Component Theory to Superconductor Surface Currents
Within the framework of classical electrodynamics, the model problem of current distribution on the surface of a superconducting sphere and of magnetic induction are analyzed in the presence of an external current flowing onto a given superconducting sphere. The possibility of using the Langevin and Gorter—Kasimir two-component theory to surface currents produced in superconducting structures is considered. Within the framework of the formulated problem, the current distributions are calculated in detail in the case where electrons flow onto a superconducting sphere. Theoretical analysis of the main electrodynamic and London equations shows that a constant current component, which is related to the external flowing current, appears. The boundary conditions are analyzed in detail. Using them, we conclude that there is no tangential component near the sphere surface. A part of the boundary conditions is written in terms of the surface current density, which is also fundamentally new in the theoretical presentation of this physical problem.
On Estimating the Heating of the Surface of a Homogeneous Metal Target with a Low-Energy Electron Probe
Abstract—The problem of heat distribution in metal materials irradiated by finely focused low-energy electron beams in the absence of heat exchange between the target and the surrounding environment is studied using mathematical modeling methods. The model is based on solving a multidimensional stationary heat equation using Green’s function. The source function is a model applicable to a wide class of solids and primary-electron energy ranges, based on separation description of the absorbed and backscattered electron contributions to the energy dissipated in the target. The features of this approach explain the nonmonotonic dependence of the maximum heating temperature of the target on the primary-electron energy.
Structural Transformation of the Surface of a High-Strength Steel after Hydroabrasive Action
High-strength steel subjected to hydroabrasive action is studied. Contamination of the cut surface with fragments of abrasive particles is revealed. The cut-surface relief is described. The microhardness of the cut surface and the depth of the cold-hardened layer are determined. Structural transformation near the surface is studied using X-ray diffraction analysis and transmission electron microscopy. It is found that plastic deformation of the surface layer occurs by both slipping and twinning, which is due to the high rate of deformation occurring under conditions of compressive stresses.
Structural Phase State of Surface Alloyed Y2O3 Silumin After Electron beam Processing
The structure, phase composition and tribological properties of surface layers of hypoeutectic silumin after the complex processing including the electroexplosion alloying with the yttrium oxide powder in different regimes and the subsequent electron beam processing have been analyzed by the methods of modern physical material science. With respect to the initial silumin the ≈20-fold increase in the wear resistance and ≈1.5-fold decrease in the friction coefficient have been detected. The complex processing is accompanied by the formation of the multiphase submicro—nanocrystalline layer up to 80 μm in thickness enriched by yttrium and oxygen atoms responsible for the multiple increase in the wear resistance. At the complex processing according to the first regime of electroexplosion alloying (EEA) (Y2O3 powder mass—0.0589 g, discharge voltage—2.8 kV) with the subsequent electron beam irradiation, the major phase of the modified layer is the solid solution based on Al (≈71.2 mass %), the remaining phases are SiO2, YAlO3, YSi2. The 1.5-fold increase in the mass of Y2O3 powder at EEA and 1.1-fold decrease in the discharge voltage is accompanied by the increase in the quantity of phases, the significant (more than 2.5-fold) decrease in the content of the solid solution based on Al, the ≈2.2-fold increase in the content of silicon oxide, the presence of yttrium oxide and metallic yttrium.