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

The methods of light, scanning, and transmission electron microscopy are used to study the structure, phase composition, and properties of multilayer plasma surfacings made of high-speed steel R18YU in a protective-alloying nitrogen medium, followed by a fourfold high-temperature tempering and additional electron beam processing. After tempering, the deposited layer on the 30KHGSA high-speed steel R18YU has a polycrystalline structure with a cell size of 7–22.5 µm with layers of the second phase along the boundaries and at the joints of the grains. It is shown that the irradiation of surfaised layers with a pulsed electron beam (energy density 30 J/cm², pulse duration 50 µs, number of pulses 5, and pulse repetition rate 0.3 s^–1) leads to the formation of a thin (30–50 µm) surface layer with a cellular crystallization structure. The volume of grains is formed by a solid solution based on α-Fe. Nanoscale (10–45 nm) particles of iron, chromium, and tungsten carbides of complex composition, such as M₆C and M₂₃C₆, are located in the volume and along the boundaries of the crystallization cells. Fragmentation of the surface layer by a grid of microcracks is revealed, indicating relaxation of thermal stresses formed during high-speed cooling after electron beam processing. The particles have a faceted or globular shape. After irradiation with an electron beam, the wear resistance of the material increases by more than 3 times, while maintaining the microhardness of the modified layer (~5.3 GPa).

Using the methods of Auger electron spectroscopy, scanning electron microscopy, and measuring the angular dependences of the coefficient of inelastically reflected electrons, changes in the morphology, composition, and structure of CaF₂ surface layers under electron bombardment with an energy of E_e = 1–8 keV are studied. The composition of the CaF₂ surface changes noticeably at E_e = 2–3 keV and an electron dose of D ≥ 10¹⁸ cm^–2. It is found that at a dose of less than 10¹⁸ cm^–2, electrons are incident on separate sections of the CaF₂ film. As D increases, the sizes of these sections increase, and starting from D = 8 × 10¹⁸ cm^–2, the boundaries of neighboring sections overlap. The surface is completely covered with Ca atoms. After annealing at 900 K, a single-crystal Ca film is formed. At E_e = 3 keV, the thickness of the Ca film is ~25–30 Å.

Quasi-two-dimensional systems play an important role in the manufacture of various devices for the needs of nanoelectronics. Obviously, the functional efficiency of such systems depends on their structure, which can change during phase transitions under the influence of external conditions (e.g., temperature). Until now, the main attention has been focused on the search for signals of phase transitions in continuous two-dimensional systems. One of the central issues is the analysis of conditions for the nucleation of the hexatic phase in such systems, which is accompanied by the appearance of defects in the Wigner crystalline phase at a certain temperature. However, both practical and fundamental questions arise about the critical number of electrons at which the symmetry of the crystal lattice in the system under consideration will begin to break and, consequently, the nucleation of defects will start. The dependences of the orientational order parameter and the correlation function, which characterize topological phase transitions, as functions of the number of particles at zero temperature have been studied. The calculation results allow us to establish the precursors of the phase transition from the hexagonal phase to the hexatic one for N = 92, 136, and 187 considered as an example.

The features of formation of surface morphology of chlorinated polyvinyl chloride (pure and with the addition of the catalyst—ferrocene) under the influence of a high-power ion beam of nanosecond duration after the preliminary pulsed laser treatment of the polymer surface have been investigated. It was found that the morphology of the irradiated surface of chlorinated polyvinyl chloride after pulsed laser surface pretreatment differs significantly from the morphology of the irradiated surface of chlorinated polyvinyl chloride after preliminary stationary heat treatment. For pure chlorinated polyvinyl chloride, pulsed laser pretreatment with increasing power leads to an increase in the porosity of the surface layer after high-power ion beam irradiation, whereas different surface morphologies, including fibers (including polymer fibers) of different diameters, can be obtained for the pre-stationary thermal treatment of this polymer. Pre-stationary thermal pretreatment of chlorinated polyvinyl chloride with the addition of ferrocene (Fe(C₅H₅)₂) leads to a decrease in the diameter of the formed carbon nanofibers (with an increase in the treatment temperature). During the pulsed laser pretreatment, an increase in the porosity of the treated layer and a slight increase in the proportion of nanofibers of a larger diameter are observed. To explain the obtained differences for pulsed laser and stationary thermal pretreatment, the effect of polymer heating rate on the features of chlorinated polyvinyl chloride decomposition was analyzed.

The morphology, topography, and wettability with distilled water of Al–1.5 at % Fe alloy films with thicknesses of 25–90 nm are investigated. These films are formed on glass by ion-assisted deposition using a resonance ion source of vacuum arc plasma. Scanning probe microscopy reveals that the longitudinal and transverse roughness parameters, as well as dimensionless complexes, vary depending on the deposition mode and time. Measurement of these dimensionless parameters yields a quantitative description of cone formation processes in the Al–Fe/glass system. The mean roughness of the films increases in the range of 20–40 nm within the duration of deposition. Under self-irradiation conditions, the transition from island growth of the films to layered growth is observed. The effect of the substrate relief on the longitudinal step parameters of the film topography is found. Scanning electron microscopy is employed to examine the size and surface density of microdroplet-fraction particles. The size-frequency distributions of the microdroplet fraction are satisfactorily approximated by a lognormal distribution. Under self-ion irradiation conditions, 60–70% of particles comprising the microdroplet fraction are up to 0.8 µm in size. For the first time, a double Gaussian function is employed to approximate histograms of the distribution of relief features in the films, improving the accuracy in the description compared to a normal distribution law. The effectiveness of this approach in analyzing the structural formation of nanoscale films at various growth stages is demonstrated. By employing a bi-Gaussian model of the surface, the role of topographic characteristics in controlling the wetting of modified coatings is determined. The mechanism of the heterogeneous wetting of hydrophilic films in the Cassie state with contact edge angles of 50°–80° is discussed. In the potential mode, with an increase in deposition duration up to 10 h, the relief distribution of the films approximates a normal distribution, and the development of a submicrometer conical morphology on the surface leads to mixed wetting.

In this study, for the first time, the influence of the III/V flux ratio on the structural and optical characteristics of InGaN nanowires grown by plasma-assisted molecular beam epitaxy are investigated. It is found that the formation of InGaN nanowires with a core–shell structure occurs when the III/V flux ratio (taking into account the In-incorporation coefficient) is about 0.9–1.2. At the same time, an increase in the III/V flux ratio from the intermediate growth conditions to metal-rich conditions leads to a decrease in the In content in nanowires from ~45 to ~35%. Samples of this type exhibit photoluminescence at room temperature with a maximum in the range from 600 to 650 nm. A further increase in the III/V flux ratio to ~1.3 or its decrease to ~0.4 lead to the formation of merged nanocolumnar layers with a low In content. The results obtained may be of interest for studying the growth processes of InGaN nanowires and creating RGB light-emitting devices based on them.

The effect of a high-power ion beam of nanosecond duration on the phase composition and morphology of the surface of aluminum composite material SAP-2 is studied. It is found that after irradiation with a high-power ion beam under all irradiation modes used in the experiments no changes in the phase composition are observed. However, the observed shifts and broadening of the diffraction peaks from irradiated samples indicate the formation of residual stresses and transformation of the initial dislocation structure. The observed decrease in the dislocation density results in a decrease in the microhardness of SAP-2 irradiated at current densities of 50 and 100 A/cm². It is shown that the increase in the ion-current density leads to an increase in the oxygen fraction in the surface layer of SAP-2, which is apparently associated with the partial evaporation of aluminum and an increase in the concentration of inclusions of Al₂O₃, which is part of the material. A nonlinear character of the dependence of the average ratio of the oxygen content to aluminum on the ion-current density of the beam is observed, the maximum value of which is recorded upon irradiation with a beam-current density of 100 A/cm². Intense heating of the SAP-2 surface under ion-beam irradiation leads to changes in the dispersion of Al₂O₃ inclusions on the irradiated surface. The maximum coagulation of Al₂O₃ particles is found in the case of irradiation by a high-power ion beam with a current density of 100 A/cm².

The structure and chemical composition of nanocomposite films based on poly(p-xylylene) with cadmium sulfide (CdS) as a filler were studied by X-ray diffraction and infrared (IR) spectroscopy. The films were synthesized by the codeposition of p-xylylene monomer and CdS vapors on quartz and silicon substrates, had a thickness of ~0.2 and ~1.5 µm and contained 5–90 vol % of CdS. The effect of the filler content and film thickness on polymer matrix and filler structure was demonstrated. The differences in the chemical compositions of the films with thicknesses of ~0.2 and ~1.5 µm were revealed, caused by their partial oxidation upon contact with air after synthesis. The possible influence of hydroxyl groups on the formation of CdS crystalline structures in films was discussed. A correlation was established between the structural transformations upon changes in the CdS content with the previously obtained dependences of the dark conductivity and photoconductivity for films with a thickness of ~0.2 μm.

The mutual influence of the primary and secondary order parameters when high pressure torsion is applied is studied. Equilibrium and nonequilibrium cases are considered. The first is realized with a continuous increase in torque, and the second, when studying the transition from one state to another, described by a traveling wave. The consideration is carried out on the basis of Landau’s thermodynamic theory.

The preparation of Fe-based wear-resistant coating by high-speed laser cladding method can well solve the problem of poor wear resistance of aluminum alloy surface. However, due to the large expansion coefficient difference of Fe and Al, the Fe-based laser cladding layer on the Al surface often has cracks, poor molding morphology, and poor mechanical properties. In this work, La₂O₃ is added as an additive in order to improve the morphology and mechanical properties of Fe-based laser cladding layer on the surface of Al alloy. High-speed laser cladding technology was used to prepare the coating of 18Ni300 + XLa₂O₃(X = 0.5, 1, 1.5, 2 wt %) on ZL205A aluminum alloy. The morphology, microstructure, hardness, wear resistance and heat shock resistance of the cladding layer were studied. The morphology and crack characteristics of the fusion zone were observed by scanning electron microscopy. Under the present test conditions, the addition of La₂O₃ improved the forming morphology, refined the microstructure of the cladding, and significantly improved the mechanical properties of the cladding. The optimal addition of La₂O₃ with the best properties was 1.5 wt % which provided: flat cladding surface, absence of internal cracks, refined grain size, improved wear resistance and thermal shock resistance, 47% higher hardness when compared to 18Ni300.