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

Comparative studies of new double and triple selenium-containing nanosystems based on a Photoditazine photosensitizer and amphiphilic molecular brushes (graft copolymers) with a polyimide or cellulose backbone and polymethacrylic acid side chains have been performed by atomic force microscopy and UV–visible spectroscopy. The influence of the structure and topology of the graft copolymers on the morphological and spectral characteristics of amphiphilic molecular brushes loaded with selenium nanoparticles and Photoditazine has been established. It is found that amphiphilic molecular brushes prevent the association of the selenium nanoparticles in solution, forming predominantly discrete spherical nanostructures. It is shown that for a double selenium-containing nanodispersion obtained on the brush with a polyimide main chain with a polymerization degree of the side chains of polymethacrylic acid m = 180, in addition to spherical discrete nanostructures, “capsules” of 200–400 nm in size are also observed. It is suggested that formation of the hybrid multicomponent selenium-containing nanostructures occurs mainly due to the steric stabilization of selenium nanoparticles by brush macromolecules and their incorporation according to the type of metal-porphyrin complexes. Based on UV–visible spectroscopy data, the band gap energy and the diameter of the selenium nanoparticles for hybrid multicomponent selenium-containing nanostructures have been calculated.

Rigorous calculations of the absolute diffraction efficiency η performed earlier using two commercial computer solvers based on electromagnetic methods have shown that the maximum η of neutron gratings with sinusoidal and lamellar groove profiles can exceed known analytical limits. Thus, for a sinusoidal grating with a period of d = 50 μm and a groove depth of h = 53.4 nm at an incidence angle of θ = 89.72° (θ_c = 89.53°), η(–1) = 46.8% was obtained at a wavelength of λ = 1 nm, which is 38.5% higher than the maximum scalar efficiency. For a similar lamellar grating, η(–1) = 46.05% was determined, which is 13.7% higher than the scalar one. In this work, gratings with sinusoidal and lamellar groove profiles were investigated for copper, one of the most promising materials for cold neutron optics. The most efficient gratings with a triangular profile (“with a blaze”) were also considered. For a grating with d = 50 µm and h = 41.1 nm, η(–1) = 79.2% was achieved for θ = 89.37° and λ = 1 nm. The data calculated using both software with an accuracy of ~0.1% for the main diffraction orders of gratings of all groove profiles converge well and correspond to the estimates obtained using the phenomenological approach.

The structural parameters and reflective properties of multilayer X-ray mirrors based on a chromium–vanadium material pair were studied. These mirrors are optimized for operation in the spectral range of 2.42–2.73 nm. One of the key practical applications of such mirrors is X-ray microscopy, which enables real-time studies of biological samples. Achieving the highest possible reflectivity of X-ray mirrors is essential for maximizing the temporal resolution of such experiments. It was shown that Cr/V mirrors exhibit large interfacial transition zones (arising at layer boundaries due to intermixing and chemical interactions between materials), which reduce the reflectivity of the mirror. It was also found that the transition zones between different materials are uniform both within a single bilayer and across multiple periods of the mirror structure. To reduce the thickness of these transition zones, carbon barrier layers were introduced into the mirror structure. This approach significantly decreased the interfacial zone thickness, which in turn led to an increase in mirror reflectivity.

The paper presents the theoretical modeling results of the reflectivity of multilayer mirrors based on rubidium and its compounds, designed to operate in the radiation wavelength range of 11.4–17 nm and of interest to modern lithography and X-ray astronomy. Using a genetic algorithm, the problem of optimizing the multilayer design of such mirrors to achieve maximum reflection is solved, and a comparison of the theoretical reflection coefficients obtained in this work with modern developments of multilayer X-ray mirrors in the characteristic radiation regions of 11.4, 13.5, and 17 nm is presented. Due to the high chemical activity of pure rubidium, it is proposed to use a more stable compound for the potential practical implementation of rubidium-containing mirrors. It is shown that the use of boron carbide between the main layers of the mirrors leads to a significant increase in their final reflection coefficient and can be considered a barrier method to prevent interdiffusion between materials; however, experimental verification of this hypothesis is required. The integral reflection of an optical system containing a few multilayer mirrors significantly depends on increasing the reflectivity of a single mirror, thus justifying the prospects of using the proposed mirrors in the optical system of a modern lithograph.

The EK-181 and Eurofer steel samples were saturated in gaseous deuterium at 200°C and a pressure of 5 atm for 25 h. The effect of sample storage conditions (in vacuum or in air) on the deuterium release from EK-181 and Eurofer steels was studied. The deuterium retention was examined by thermal desorption spectroscopy after storage from several days to one and a half years after the samples were saturated with deuterium. The EK-181 steel samples contained 3.5–6 times more deuterium than the Eurofer steel samples. After one and a half years of storage, the deuterium retention decreased by 1.5–3 times in EK-181 steel and by 3–4 times in Eurofer steel. For the EK-181 steel samples, no unambiguous conclusion can be made about the effect of storage conditions on the deuterium release from the material. Deuterium releases more slowly from the Eurofer steel samples if they were stored in a vacuum. Time dependences of the deuterium retention under different storage conditions were obtained.

This article describes the development and adjustment of two designs of ion sources generating plasma at a frequency of 2.45 GHz. These ion sources operate in the modes with ECR discharge and RF-discharge. The working gas of the sources is helium or hydrogen. The extraction and beam formation system currently represents two-electrode optics. The diameter of the emission hole is 4 mm. At an accelerating voltage of 25 kV in the pulsed mode. The ion beam current was 7 mA (He⁺) with a helium ion fraction of up to 70% and 14 mA (H⁺) with a proton ion fraction of up to 90%.

The article simulates graphene moiré patterns on the Ir(111) substrate. The difference in substrate and graphene periods leads to the formation of a moiré superstructure, which is periodic vertical deformations with hexagonal symmetry. The interaction between carbon atoms in graphene is significantly stronger than that with substrate atoms. Therefore, graphene is considered not stretchable. Van der Waals forces determine the interaction between carbon atoms and substrate atoms. The Lennard-Jones potential models these forces. The surface potential replaces substrate exposure to carbon atoms. Our model calculates the surface potential in one unit cell and translates it using parallel transfer. The surface potential is the sum of the two-particle potentials for the atomic interaction. Comparison with experimental data and unification rules set Lennard-Jones potential parameters. The minimum energy determines the position of the graphene atoms. The simulation describes different orientations of the graphene crystal lattice relative to the substrate lattice. If the principal directions of the two lattices coincide, then the period of the moiré pattern has a maximum value of 2.54 ± 0.02 nm. This value is in good agreement with the experimental period 2.52 nm. The height of the graphene film above the substrate surface is calculated to be 0.330 ± 0.001 nm. Experimental measurements and ab inito calculations give a value of 0.330 ± 0.005 nm. Rotation of the graphene relative to the principal directions of the substrate lattice results in a shorter moiré period. A study of the dependence of the moiré pattern period on the angle of rotation of the graphene crystal lattice relative to the substrate shows a nonlinear decreasing law.

Structural transformations in Ni–Ag bimetallic nanoparticles sized 5 nm were investigated after a cycle of sequential phase transitions corresponding to melting and crystallization. The initial configuration of the Ni–Ag bimetallic nanoparticles corresponded to a Janus structure. Two alternative methods, molecular dynamics and Monte Carlo methods, were used to simulate the thermally induced effects. The tight binding potential was used as the intermolecular interaction potential. It was shown that the Ni–Ag bimetallic nanoparticles are characterized by the surface segregation of Ag atoms, and specific features of the segregation behavior of Ag atoms at different concentrations were identified. The obtained regularities are compared with the experimental results for Ni–9 wt % Ag nanoparticles synthesized by the method of electric explosion of wires, which is characterized by the formation of particles with a “core–shell” structure. Based on the analysis of calorimetric curves of the potential part of the specific internal energy, hysteresis of the melting and crystallization temperatures was revealed, allowing for the estimation of the starting and finishing temperatures of the corresponding phase transition, as well as the determination of thermal stability intervals. In addition, it was found that with an increase in the number of nickel atoms in the composition of the particles the width of the hysteresis of the melting and crystallization temperatures increases.

The article presents the results of modeling the three-dimensional distribution and accumulation of deformation defects in the volume of a single-crystal intermetallic compound with the L1₂ superstructure during deformation by uniaxial compression. The calculations are performed in a multilevel model of synthesis of dislocation kinetics and mechanics of a deformable solid for cases of deformation with and without taking into account the forces of end friction. The patterns of distribution of the intensity of plastic strain and the density of dislocations in the plane of the central longitudinal section of a deformed rectangular sample are presented. In a numerical experiment, brittle fracture of a deformed sample is obtained at a degree of strain close to the value of full-scale experiment. The influence of the end friction forces on the features of shape change and fracture of a single-crystal sample is analyzed. It is shown that due to the influence of end friction forces, a noticeable decrease in the degree of brittle fracture strain occurs. A statistical assessment of the degree of homogeneity of the distribution of deformation defects in the deformed volume is carried out. A comparison of the results of the numerical experiment obtained in the work with the results of mechanical tests and studies of the deformation relief of Ni₃Ge single-crystal intermetallic compound with the L1₂ superstructure shows good agreement.

Using the method of dynamic diffractometry with the use of synchrotron radiation beams, experimental studies of phase formation processes occurring during the high-temperature synthesis of mechanically activated powder mixture Ti + Al + C were conducted. High-temperature synthesis has been carried out in situ in thermal explosion mode using a microwave induction heater on an experimental complex adapted to the method of dynamic diffractometry. The experiments were conducted at the “Diffraction Cinema” station of VEPP-3, channel 5B, at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. It has been experimentally shown that the synthesis of a composite material occurs in multiple stages. The onset of phase changes begins at a temperature of approximately 870°C. Initially, the formation of intermetallic compound TiAl₃ is observed. Then a Ti–Al melt is formed with the release of TiC grains, which provides the main heat release and initiates a thermal explosion reaction. Further, the Ti–Al melt due to the dissolution of TiC grains in it is saturated with carbon, and when the temperature reaches 1800°C, MAX phase Ti₂AlC crystallizes from it. The maximum amount of this phase is fixed at the exposure stage. With a decrease in temperature, along with Ti₂AlC, MAX phase Ti₃AlC₂ is formed. At this stage, by controlling the temperature, it is possible to control the content of MAX phases in the reaction product. The composition of the final product includes Ti₃AlC₂, Ti₂AlC, and TiC.