№ 4 (2024)

Using solid-phase and molecular-beam epitaxy methods at 350°C, polycrystalline and epitaxial films of iron monosilicide (FeSi) with a thickness of 3.2 to 20.35 nm were grown on a Si(111) substrate, which was confirmed by X-ray diffraction data. Morphological studies have shown that the films are continuous and smooth with a root-mean-square roughness of 0.4–1.1 nm when grown by solid-phase epitaxy, and in the case of molecular beam epitaxy, they have an increased roughness and consist of coalesced grains with sizes up to 1 μm and a puncture density up to 1 × 10⁷ cm^–2. In solid-phase epitaxy, an increase in thickness leads to incomplete silicide formation and the appearance of a layer of disordered iron monosilicide with a thickness of 10 to 20 nm. This is confirmed by a change in the temperature dependence of resistivity ρ from semiconductor to semi-metallic and a decrease in resistivity by one and a half to two times. The nonmonotonic nature of the temperature dependence of the resistivity ρ ultrathin FeSi film with a thickness of 3.2 nm has been established, in which a maximum at 230–240 K, a region of growth from 160 to 65 K with E_g = 14.8 meV and further growth without saturation to a temperature of 1.5 K are observed. With increasing thickness of FeSi films grown by molecular-beam epitaxy, the minimum and maximum are not observed, but the tendency of nonmonotonic growth of ρ(T) with decreasing temperature and the opening of the band gap E_g = 23 meV remains. The probable reasons for the occurrence of effects in the dependences ρ(T) are considered. In ultrathin and thin FeSi films grown by solid-phase and molecular-beam epitaxy, respectively, an anomalous Hall effect was found, which was confirmed by the weak ferromagnetic properties of the films. The results obtained proved the possibility of growing and controlling the properties of ultrathin and thin FeSi films on silicon obtained by solid-phase and molecular-beam epitaxy, which ensured the appearance of their unique transport and magnetic properties that are absent in single crystals.

The structure and chemical composition of nanocomposite films based on poly(p-xylylene) with cadmium sulphide (CdS) as a filler were studied by X-ray diffraction and IR-spectroscopy. The films were synthesized by co-deposition 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 filler content and film thickness on polymer matrix and filler structure was demonstrated. Differences in the chemical compositions of 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 structural transformations upon changes in the CdS content with the previously obtained dependences of dark conductivity and photoconductivity for films with a thickness of ~0.2 μm.

In this work, we studied the influence of the III/V flux ratio on the structural and optical properties of InGaN nanowires grown by plasma-assisted molecular beam epitaxy. It was found that the formation of InGaN nanowires with a core–shell structure occurs if the III/V flux ratio is about 0.9–1.2 taking into account the In incorporation coefficient. At the same time, an increase in the III/V flux ratio from the intermediate growth regime to metal-rich one leads to a decrease in the In content in nanowires from ~45% to ~35%. This nanowires exhibit photoluminescence at room temperature with a maximum in the range of 600–650 nm. A further increase in the III/V flux ratio to ~1.3, or its decrease to ~0.4 leads to the formation of coalesced 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 on them.

During the study of the optical properties of solid solutions of Bi₂Te₃–Sb₂Te₃ p-type conductivity in the infrared range, it was found that in a single crystal Bi_0.6Sb_1.4Te₃, deformation of the reflection coefficient spectra is observed in the frequency range of observation of the plasma resonance of free charge carriers. The deformation of the plasma edge increases with a decrease in temperature. Using the Kramers–Kronig dispersion relations from experimental reflection spectra, the spectral dependences of the real ε₁ and imaginary parts ε₂ of the permittivity function, as well as the energy loss function characterizing the rate of energy dissipation, are calculated. Splitting of the peak of the energy loss function was found, indicating the effect on the plasma resonance from another process occurring in the electronic system. It is established that such a process is the transition of electrons between nonequivalent extremes of the valence band. Convergence of collective and single-particle energies.

Molecular dynamic simulation was used to study the processes of impact of 2–14 keV C₆₀ molecular ions on the Si(100) surface at temperatures of 0–1000 K. Tersoff–ZBL and Airebo interaction potentials were used and the electronic energy loss of fast particles was taken into account. It is shown that when simulating single impact events, the target temperature does not affect the development of the displacement cascade, but affects its thermalization and the formation of the crater on the surface. As the energy increases, the carbon penetration depth, the size of the formed crater and the rim increase. The sputtering coefficient of silicon atoms in this case increases linearly with energy, and in the case of carbon atoms it reaches a steady-state value at 10 keV. Using the Tersoff potential gives a larger number of atomized carbon atoms for single impact events compared to Airebo potential. During cumulative events, the formation of an etch pit is observed at the initial stage, followed by the carbon film growth. In contrast to single events, the use of the Airebo potential in the case of cumulative ion accumulation gives a higher sputtering coefficient than the Tersoff potential. The formation of carbide bonds in the crystal and an increase in their concentration with ion fluence slightly reduces the number of sputtered particles. Therefore, for correct comparison of simulation results with experiment, it is not enough to use the results of the analysis of single impact event. It is necessary to perform the simulation of the cumulative fluence accumulation.

Layered composite materials based on niobium and cermet were produced via self-propagating high-temperature synthesis of pre-structured samples using metal foils (Ti, Nb, Ta, Ni) and reaction tapes (Ti + 1.7B) and (5Ti + 3Si). Reaction tapes for synthesis were produced by rolling process of powder mixtures. The microstructure, elemental and phase compositions of the synthesized multilayer composite materials were studied by scanning electron microscopy and X-ray phase analysis. Particular attention was paid to the formation of intermediate layers and surface modification occurring during combustion. The strength characteristics of synthesized materials were determined according to the three-point loading scheme at temperatures of 1100°C. The analysis of obtained materials showed that joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation and chemical reactions occurring in the reaction tapes and on the surface of metal foils. The formation of thin intermediate layers in the form of cermet and eutectic solutions provides the synthesized multilayer materials with good strength properties up to 87 MPa at 1100°C. These results are of interest for the development of structural materials operating under extreme conditions.

A review of the results of a series of works performed by a joint group of researchers from the INR RAS and the SSC RF–IPPE on the lead slowing-down neutron spectrometer SVZ-100 to measure the fission cross-sections of americium isotopes ²⁴¹Am, ^242mAm, ²⁴³Am by neutrons with energies below 100 keV is presented. Due to the large mass of the working substance (100 tons of high-purity lead) and the generation of neutrons by protons with an energy of 209 MeV at the INR RAS accelerator, the high aperture ratio of the SVZ-100 made it possible to study neutron-nuclear processes in microgram samples of radioactive nuclides, which is not available in experiments using time-of-flight spectrometry. Unique scientific information has been obtained, partially compensating for the missing, or supplementing the existing, but often contradictory or insufficient data of experiments performed both on time-of-flight facilities and on lead slowing-down neutron spectrometers at other research centres. The results of the work of INR RAS–SSC RF–IPPE are reflected in international nuclear databases and indicate in a number of cases the need to adjust the recommended approximating and calculated values. Information is provided on the few carried out experiments and planned studies of neutron-induced fission cross-sections of americium isotopes in other centres after the completion of the work of the INR RAS–SSC RF–IPPE.