Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

Using the electrospinning method nanofibers consisting of vanadium oxide phase mixture were obtained. Their phase and quantitative compositions were determined by X-ray phase and full-profile analysis methods. It has been shown that the calculation of relative concentrations during the analysis of the phase composition using the Qualitative Analysis program gives results with a high error. For the accurate determination of the phase concentration of vanadium oxide multiphase samples, it is necessary to use a full-profile analysis or a quantitative analysis method (if possible).

The possibility of combining plasma-electrolytic carburizing, polishing, and microarc oxidation of commercially pure titanium to increase microhardness, wear resistance, and quality of the modified surface has been demonstrated. Using X-ray structural analysis methods, structural and phase changes on the surface and in surface layers after processing were studied, solid titanium carbides TiC and Ti₈C₅ were detected in the modified layer, and the diffusion depth of carbon and oxygen was determined. The influence of each of the plasma-electrolytic treatment methods on the tribological behavior in a friction pair with structural bearing steel was studied. The lowest surface friction coefficient was observed after carburizing at 900°C, polishing at 250 V, and microarc oxidation at a current density of 12 A/dm². It was shown that an increase in the loss of mass during friction and the volume of removed material after combined treatment is associated with an increase in the contact area in the tribocoupling, which is confirmed by an increase in the wear of the counterbody. The quality of the modified surface was assessed based on the geometry data on the surface of wear marks, the complex Kragelsky–Kombalov criterion was calculated, and the type of wear was determined. The Kragelsky–Kombalov criterion after plasma-electrolytic treatment decreases by 1.2–1.4 times, which indicates an increase in the bearing capacity of the rough profile of modified samples. The wear mechanism is fatigue wear during plastic deformation of the tribological conjugation.

An analytical and numerical study of multiple small-angle neutron scattering on volume fractals is carried out. The dependence of the intensity of multiple small-angle scattering on the scattering vector is determined for different Hausdorff dimensions and scattering multiplicities. It is shown that the graph of this dependence in double-logarithmic coordinates has a linear section at a small scattering multiplicity, and when the fractal dimension changes, the slope and length of this section change. Calculations have shown that with an increase in the scattering multiplicity, the slope of the linear section first decreases, and then the linear section practically disappears.

The paper shows that the structural and phase composition of copper-carbon coatings can be controlled not only by the annealing temperature, but also by the conditions of heat treatment: the presence of a chemically active atmosphere, its pressure and composition. Heat treatment at reduced pressure or in vacuum is promising, which allows eliminating the influence of thermal destruction processes, as well as establishing the mechanisms of the effect of temperature on the activation of phase transformations. In the work, heat treatment of the deposited carbon and copper coatings was carried out at various temperatures both in vacuum (8 Pa) and in air. The choice of the annealing temperature was determined by the thermal stability of the carbon component of the coating (up to 350°C). Composite coatings were deposited using various vacuum methods characterized by the energy of carbon ions, as well as the ion current density. Using Raman spectroscopy, the size of C clusters and the ratio of sp³-hybridized bonds in the carbon matrix were analyzed. It is shown that the minimum sizes of clusters, the fusion of which forms carbon particles, are characteristic of coatings applied by the pulse evaporation method of a composite copper-carbon cathode, with the cluster size being 2.5 nm. The maximum sizes of carbon clusters for the high-pulse magnetron sputtering method at a frequency of 5 kHz are found to be 7.8 nm. It is established that the physical and mechanical properties of the coatings depend on the modes and conditions of heat treatment.

The specificity of the local atomic surrounding, the physicochemical state, and the electronic structure of five tin monolayers on a thin buffer layer of silicon formed epitaxially and their transformation as a result of thermal annealing are studied in situ in the present work. Using radiation from three synchrotron sources high-resolution surface-sensitive experimental methods, X-ray absorption near edge structure spectroscopy and X-ray photoelectron spectroscopy, were used as well as computer modeling. The possibility of oxygen atoms diffusion from tin to a buffer layer of silicon during storage of structures in laboratory conditions is shown. It is shown that during the formation of Sn/Si epitaxial nanolayers, there are no interatomic interactions at the heterogeneous boundaries of the structure, up to the possible formation of a tin-silicon solid solution, and, as a consequence, noticeable distortions of the electronic spectrum. However, high-temperature ultrahigh-vacuum annealing causes a phase rearrangement of the surface layers of such a structure accompanied by the redistribution of oxygen atoms from tin atoms to silicon of the epitaxial buffer with the formation of a thin layer of SiO₂. Within the thin tin-silicon transition layer of the studied structures and along its boundaries complex bonds can be formed between tin, oxygen, and carbon atoms.

This study addresses one major uncertainty concerning referencing the XPS binding energies (BEs) on oxidized surfaces of silicon carbide (SiC). Based on the extensive catalogue of SiC powder spectra, two spectral features are compared as potential BE references, namely, the C1s photopeak from adventitious carbon and the O1s photopeak from the native oxidized overlayer. Referencing to adventitious carbon produces a systematic shift in the BEs of all species depending upon the degree of surface oxidation. In contrast, referencing to O1s yields SiC BEs that are reproducible to ±0.2 eV across a wide range of SiO₂ surface concentrations. Stability in referencing to O1s is attributed to the prominent Si‒O‒Si coordination of oxygen over a wide range of SiC_xO_y surface compositions. When referenced to O1s, the BE values reported for different types of oxidized SiC substrates (crystal faces, films) compare favorably with those of the powders. Using the O1s reference and a few constraints to stabilize the curve fitting of the Si2p and C1s spectral envelopes, a broad range of SiC powder surface chemistries can be described in a consistent manner and in line with knowledge on other types of SiC substrates.

Electrical discharge machining of molybdenum surfaces used to increase hardness, heat resistance, and corrosion resistance of machine parts, units, and assemblies has been studied. It has been found that electrical discharge machining of molybdenum surfaces allows obtaining durable functional coatings of parts by using a high-voltage electric arc in a hydrogen atmosphere at a pressure of 0.1 MPa and a fixed gap between anode made of graphite and the processed surface of the part, cathode, at a rigid current–voltage characteristic of a pulsed current source with a voltage of 2000 V. The pulse duty cycle has been varied depending on required roughness of the molybdenum carbide Mo₂C coating. Depending on the supplied power two carbide phases in different percentage ratio α-Mo₂C : β-Mo₂C were formed on the surface.

When irradiating n-GaN obtained by the method of metal organic vapor phase epitaxy (MOVPE) with electrons with an energy of 0.9 MeV, the values of the carrier removal rate η_e for room temperature were established for the first time within the framework of the Van der Pauw method. At an initial (before irradiation) electron concentration of 1.87 × 10¹⁷ cm^–3, the values of η_e were 0.023 and 0.054 cm^–1 at room temperature (293 K) for doses Φ_n = 1.7 × 10¹⁷ and 3.7 × 10¹⁷ cm^–2, respectively. With temperature decrease, the η_e value increases: at T = –55°C, the η_e values are 0.064 and 0.086 cm^–1 for doses of 1.7 × 10¹⁷ and 3.7 × 10¹⁷ cm^–2, respectively. The maximum mobility value in nonirradiated samples is 650 cm²/Vs. After irradiation with a dose of Φ_n = 3.7 × 10¹⁷ cm^–2, the maximum mobility value decreases to 530 cm²/Vs. The change in mobility under the influence of irradiation is reliably traced at temperatures of T ≤ 260 K (1000/T ≈ 3.85).

Currently, industrialized countries are paying more and more attention to ion plasma technologies. That is because local doping of a certain zone or the entire surface instead of changing the properties of the sample’s entire volume is possible with the help of beam ion-plasma technologies. Ion bombardment changes almost all properties of the solid surface and the surface layer. The physical and mechanical properties of surface and near-surface layers of materials are the most important factors determining the durability and reliability of processed products. The article has considered the features of thermal processes and the effect of pulsed heating of near-surface silicon layers on diffusion transfer under conditions of synergy of high-intensity titanium ion implantation and the energy impact of a repetitively-pulsed beam of high power density on the surface in order to increase the ion alloying depth due to radiation-stimulated diffusion when heating of the entire sample is limited. The article presents the results of calculating the space-time distribution of temperature fields in silicon and the diffusion transfer of the implanted dopant under the action of submillisecond titanium ion beams.

A developed technology for chemical-mechanical polishing of large-sized single-crystal silicon substrates for X-ray optical applications is reported. Compared to the standard technology of chemical-mechanical polishing of silicon wafers for microelectronics, which emphasizes the atomic smoothness of substrates and a small damaged layer, high accuracy of the surface shape is demanded, which can be either flat or curved. Materials for polishing pads and suspensions for mechanical lapping and chemical-mechanical polishing, as well as the main parameters of the processing, were found that ensured an effective surface roughness of 0.17 nm in the spatial frequency range 0.025–65 μm^–1 and a root-mean-square error of 8.86 nm of the surface shape deviating from the plane. The surface obtained using the developed technology is not inferior in roughness to the results of the world leading manufacturers of silicon wafers for microelectronics and significantly surpasses it in shape accuracy.