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

The relevance of laser modification of the surface of metal parts is shown; experimental data are presented on the effect of surface treatment of tool steel 3Kh2V8F with a pulsed ytterbium fiber laser with the addition of a paste of B₄C and B₄C–Al powders. It is shown that a functional layer 30–40 μm thick with a microhardness of 1200–1400 HV and a surface roughness of the second class was obtained when processing the surface of the steel sample, on which a layer of paste 1–2 mm thick from F220 (B₄C) powder was previously applied using glue, for 15 min with a laser at optimal operating mode settings. With a similar treatment, but with the addition of PA-4 (Al) powder to the powder F220 (B₄C) in a ratio of 7 : 3, a functional layer 40–60 μm thick with a microhardness of 1100–1300 HV and a surface roughness of the seventh class was obtained. In the diffraction patterns of the modified surfaces of the samples, a more preferable Fe₂B phase was detected; the FeB phase, which leads to a sharp embrittlement of the functional layer, was not identified.

Using an original magnetocapacitance method, based on the simultaneous measurement of capacitances between a quasi-two-dimensional electron system in a single quantum well of GaAs and two gates located on opposite sides of it, we investigate the magnetic field-induced quantum phase transitions between the double-layer and single-layer-like states of the system. The measurements are performed for samples with quantum-well widths of 50 and 60 nm. The double-layer state is formed by layers of two-dimensional electrons located near opposite walls of the quantum well. It is characterized by quantum magnetic oscillations of the compressibility of each layer, with the oscillation frequency determined by the electron density in the corresponding layer. In the single-layer-like state, compressibility minima are observed only when all electrons fill one or two spin sublevels of the lowest Landau level (i.e., when the total filling factor ν_tot = 1 or 2). In this state, a relationship between the measured capacitances is observed, which is characteristic of the presence of only a single electron layer between the gates. One transition from the double-layer- to the single-layer-like state occurs upon reaching the quantum limit, i.e., when ν_tot ≈ 2, regardless of the electron density in the system and the quantum-well width. In the range of 1 < ν_tot < 2, different behaviors of the electron systems in wells of different widths are observed. In the 50-nm-wide well, the single-layer-like state exists for all investigated values of the filling factor ν_tot ≤ 2. In the 60-nm-wide well, for 1 < ν_tot < 2, a double-layer state is observed with an incompressible state of electrons in the layer with higher density at a filling factor of one in that layer. As a result, three magnetic-field-induced quantum phase transitions are observed for samples with a quantum-well width of 60 nm, while for the sample with a 50-nm-wide quantum well, only one transition is observed. This dependence of the patterns of quantum phase transition on the quantum-well width is presumably due to the different tunnel coupling between the layers. For the first time, the existence of a magnetic-field-induced compressible single-layer-like state in a nominally double-layer electron system is established.

Using electron beam evaporation, thin films of various compositions (Al, Co, Ge, SiO₂) were obtained on inclined Si(001) substrates. It was found that at angles of incidence of the evaporated material on the substrate of more than 70° (sliding deposition), arrays of free-standing inclined nanocolumns with lateral dimensions from 10 to 100 nm and an aspect ratio (length/transverse dimension) of at least 10 were formed on the substrate. When substrate rotation was switched on during film growth, an array of nanospirals twisted in one direction was formed. Such films are chiral metamaterials and show pronounced optical activity. Simulation of film growth processes under oblique angle deposition conditions using the Monte Carlo method showed good qualitative agreement with the experimental data. It was found that the observed processes of nanostructuring during oblique angle deposition are based on universal mechanisms of competition between growing crystalline grains under conditions of neighbor shading. This makes it possible to obtain nanostructured films of various materials with the required functional characteristics under such conditions.

The results of comparative atomistic simulation are presented for segregation and thermally induced structural transformations (melting/crystallization) in binary Pt–Pd nanoalloys and ternary Pt–Pd–Ni nanoparticles, where Ni (20 at %) acted as a doping component. Atomistic simulation was carried out using an integrated approach combining molecular dynamics and Monte Carlo methods. In addition, two independently developed computer programs, LAMMPS and Metropolis, two different parameterizations of potentials corresponding to the embedded atom method, as well as an alternative force field, the tight-binding potential, were used for the simulation. Surface segregation of Pd was observed in both binary and ternary nanoparticles consisting of 2500 and 5000 atoms. Most noticeably, doping affected structural segregation, inducing a transition from a nanocrystal consisting of several fcc grains to a nanocluster with approximately pentagonal symmetry. It has been established that the size effect is more noticeable for parameters of the melting–crystallization hysteresis than for the structural segregation patterns, that is, the division of a nanoparticle into areas corresponding to different crystal structures and the segregation of components.

The metal–insulator–metal sandwich structures with the end surface of the insulator film (insulating slit) open to the gas environment were manufactured using thin-film technology. Electroforming, which consists of applying voltage according to a specific algorithm, causes the formation of conductive phase particles due to the destruction of organic molecules adsorbed on the open surface of the insulator by electron impact during the electric current flow. The accumulation of particles leads to the growth of a linked conductive cluster (a conductive carbon medium) and the formation of a conductive nanostructure with the memristor properties in the insulating slit. The practical use of such structures is limited by the low efficiency of electroforming: relatively long process times (on the order of several seconds) and an increased probability of electrical breakdown of the structure. Several ways to improve the efficiency of the electroforming process are presented. Firstly, the use of the correct voltage polarity for the open TiN–SiO₂–W sandwich structure, where W should be the anode, which sharply reduces the probability of breakdown. Secondly, the use of two-stage electroforming: first, the formation of conductive channels in an “oil-free” vacuum after annealing in it, when the voltage can be applied in parallel to a large number of structures, and then in an “oil” vacuum containing organic molecules at significantly lower voltages and exposures. Thirdly, replacing the tungsten anode with a molybdenum one, which, while maintaining the advantages of tungsten, leads to an increase in the initial conductivity of the open sandwich structure (TiN–SiO₂–Mo) by several orders of magnitude, and, therefore, to an acceleration of the electroforming process and a decrease in the applied voltages.

A large number of oxide particles in dispersion-strengthened alloys and steels provides a significant increase in heat resistance to these materials. For detailed characterization of these nanostructed materials, multiple techniques are used such as transmission electron microscopy (TEM), atom probe tomography (APT), as well as small-angle X-ray and neutron scattering. Small-angle X-ray (SAXS) scattering is useful for analyzing comparatively large volumes of materials combined with an ability to detect phases from few to tens of nanometers in a single measurement. Thermal aging experiments can be used to determine the stability of oxides in dispersion-strengthened alloys and determine their usability in high heat applications. In this work, a stability of three different oxide dispersion-strengthened steels: Eurofer ODS, 10Cr ODS and KP-3 ODS (with different alloying systems) was studied using SAXS in the initial state and after thermal aging at 650°C up to 1000 h. To achieve most accurate results from SAXS analysis, a combination of TEM and APT was used to get proper parameters for correct data processing. The results of SAXS and TEM showed a good correlation in the oxides in the initial state of the steels. However, no cluster data was acquired from SAXS due to their relatively small contrast. According to SAXS results, there is no oxide dissolution present under thermal aging at 650°C up to 1000 h; meanwhile there is evidence of increase of number of oxides in KP-3 ODS due to the interaction between oxide and cluster subsystems.

A study was carried out on sputtering yields for PbX (X = S, Se, Te) single crystals with (100) orientation and PbTe and PbSe single-crystal films with (111) orientation under ion-plasma bombardment with argon ions. The PbX single crystals were grown by the vertical zone melting method and oriented along the [100] growth axis. Single-crystal films of lead chalcogenides 2–4 μm thick with an orientation (111) relative to the normal to the substrate were formed by molecular beam epitaxy on silicon substrates. The surface treatment was carried out in a high-density argon plasma reactor of a high-frequency inductive discharge (13.56 MHz) of low pressure at an average ion energy of 50, 100, 150, and 200 eV. Based on the comparative analysis of sputtering rates, it was shown that for the (100) orientation, the sputtering yields for lead telluride were lower compared to lead sulfide and lead selenide. The sputtering yields for PbTe and PbSe for the (111) crystallographic orientation was found to be higher compared to (100) orientation.

The work presents the results of physical, mechanical, and tribological studies of five types of nitride-containing coatings of various architectural structures formed by simultaneous and sequential vacuum-arc evaporation of cathodes made of zirconium alloy E110 and/or cathodes TiBSiNi obtained by self-propagating high-temperature synthesis (SHS). The synthesis of coatings was carried out with the assisting influence of gas-discharge plasma from an autonomous plasma source with a heated cathode. All coatings were deposited on a substrate made of VK8 hard alloy (WC + 8% Co). Using calotesting, it was determined that the thickness of the coatings under study was 3–4 μm. Compared to the ZrN mononitride coating, whose microhardness was 31 GPa, the hardness of other variants of multicomponent and/or multilayer coatings was in the range of 40–42 GPa. X-ray phase analysis, in the case of using TiBSiNi SHS cathodes for evaporation, revealed the presence of high-hard titanium borides in the coating composition, which obviously affected the hardness of the coatings in general. Tribotechnical tests performed according to the pin-on-disk scheme have shown that for multicomponent and multilayer coatings with a composition-gradient binder sublayer and an upper thin, running-in layer, friction coefficients paired with a counterbody (indenter) made of hardened steel 100Cr6 are reduced compared to other types of coatings. In terms of wear resistance, a particularly pronounced advantage was found on the Zr + Zr_xN_y + (Zr + TiBSiNi)N + (TiBSiNi)N coating, in combination with both the counterbody made of 100Cr6 steel and high-hard silicon carbide SiC. In most cases, this is expressed as a multiple reduction in wear parameters compared to other types of coatings. This effect is probably due to the properties of the top layer that provides favorable running-in conditions with a low coefficient of friction and an increase in the adhesion strength of the coating to the substrate, as is confirmed by the results of scratch testing. Taking into account the formed gradient in composition and hardness on such coatings, as well as the layered architecture, the authors believe that they can be characterized as “gradient-layered coatings.”

The prospects for using high-resolution X-ray microlenses for coherent visualization tasks are discussed. Modern technologies and methods of microprocessing for the manufacture of 2D microlenses are considered using laser systems, ion-beam lithography, and additive technologies as an example. The efficiency of various materials for X-ray micro-optics applications is evaluated, and the time spent on manufacturing 100 nm resolution micro objectives using ion-beam lithography systems is optimized.

A composite based on magnesium hydride and nanosized aluminum powder obtained by electric explosion of wires was synthesized. Mechanical synthesis was carried out in a planetary ball mill. The time and frequency of synthesis, the mass ratio of balls and composite, and the percentage of aluminum were constant, while the diameter of grinding balls was varied: 3, 6, and 10 mm. Scanning electron microscopy was used to determine the average particle size of the composite depending on the diameter of the grinding balls. It was found that with a decrease in diameter from 10 to 3 mm the average particle size decreased from 2.7 to 2.2 μm. Energy dispersion analysis showed that nanosized aluminum particles were distributed evenly over the surface of magnesium hydride. A “core–shell” structure was formed. X-ray phase analysis revealed β-magnesium hydride, magnesium, magnesium oxide, and aluminum in the composite. X-ray diffraction patterns of the samples made it possible to calculate the structural parameters of the obtained composites, including microstresses. The average microstress value varied in the range of 0.004–0.006. A hypothesis has been put forward about an inversely proportional relationship between microstress and desorption temperature.