Nº 7 (2024)

The temperature dependences of the structural parameters of thin films of polystyrene–fullerene C₆₀/C₇₀ nanocomposites with a low content of nanoparticles in the vicinity of the glass transition temperature of the polymer matrix were studied by specular neutron reflectometry in the range 15–150°C. The obtained temperature dependences of film thickness were used to estimate the glass transition temperature of film composites. In the case of films with C₆₀ fullerene, the dependence had a standard form. The glass transition temperature of the composite film was found to decrease compared to the known value for the pure bulk polymer. In the case of films with C₇₀ fullerene, upon transition to high temperatures, a non-monotonic dependence of the film thickness was observed, which hindered the application of the general approach.

High-voltage gradual p⁰–i–n⁰ junctions of Al_xGa_1–xAs_1–ySb_y with y up to 15%, capable of absorbing radiation with a wavelength of 1064 nm, grown on GaAs substrates by liquid-phase epitaxy due to autodoping with background impurities, have been studied. The composition of the liquid phase and the growth temperature interval were chosen such that the content of aluminum compounds x along the thickness of the epitaxial layer monotonically decreased from the set values of about 34% to units of percent at the surface of the layer, and the content of antimony compounds y increased, while the width of the band gap gradually decreased from the substrate to the surface of the lightly doped layer and reached the desired values ~1.16 eV. Using the methods of capacitance-voltage characteristics and deep level transient spectroscopy, the configuration-bistable DX centers of Si and Se/Te donor impurities were identified in them. The absence of deep levels associated with dislocations was found in the studied heterostructures. The effective lifetime of minority carriers in the base layers of the Al_xGa_1–xAs_1–ySb_y/GaAs diode was determined using the method of reverse recovery of diodes. Assuming that the lifetime of minority carriers is determined mainly by the capture of holes at the acceptor–like deep DX-level of Si, the value of the capture cross section of holes at the DX-level was estimated. The capture cross section turned out to be equal to 6 × 10^–15 cm^–2.

This paper presents the experimental results on research of growth processes of GaAs layers on silicon substrates by molecular beam epitaxy. The formation of buffer Si layer in a single growth process has been found to significantly improve the crystalline quality of the GaAs layers formed on its surface, as well as to prevent the formation of anti-phase domains both on of fcutted towards the [110] direction and on singular Si(100) substrates. It has been demonstrated that the use of cyclic thermal annealing at temperatures 350–660°C in the flow of arsenic atoms makes it possible to reduce the number of threading dislocations and increase the smoothness of the GaAs layers surface. At the same time, the article considers possible mechanisms that lead to an improvement in the quality of the surface layers of GaAs. It is shown that the thus obtained GaAs layers of submicron thickness on the singular Si(100) substrates have a mean square value of surface roughness 1.9 nm. The principal possibility of using thin GaAs layers on silicon as templates for forming on them light-emitting semiconductor heterostructures with active area based on self-organizing InAs quantum dots and InGaAs quantum well is presented. They are shown to exhibit photoluminescence at 1.2 µm at room temperature.

The paper presents the results of a theoretical study of the electronic structure and electrical conductivity with chirality indices (4, 0), (5, 0), (6, 0), (7, 0), (4, 4), and (5, 5). The simulations were performed using the density functional theory and the method of nonequilibrium Green’s functions. The exchange-correlation functional Perdue-Burke-Ernzerhof and two-exponential basis set were used. We demonstrated the importance of polarized basis sets for the study of electrical properties. Analysis of the results showed that the transmission functions of the studied nanotubes depends on the structure of the SWGNTs in a complex way, but, in general, it increase with increasing diameter. The dependence of the transmission function on the electron energy does not allow us to speak a priori about the linearity of the current–voltage characteristic of gold nanotubes within a certain finite voltage range. In addition to defect-free single-walled gold nanotubes, gold nanotubes of different diameters with a vacancy were also studied. This allowed us to evaluate the effect of such a defect on the atomic structure and electrical conductivity of the single-walled gold nanotubes. It was demonstrated that the conductivity drop can vary within a wide range, correlating with changes in the atomic structure.

Diffraction radiation is widely used for non-destructive diagnostics of charged particle beams. In the series of the previous works, a method was developed for describing the diffraction radiation of a non-relativistic particle on a perfectly conducting sphere, based on the method of images well-known from electrostatics. This method allows one to derive the analytic formulae for two main radiation characteristics, i.e. spectral angular density and polarization. The characteristic features of these values allow the possibility of developing, on their basis, new methods for monitoring the parameters of the trajectory of a moving particle in relation to the sphere center. In this work, formulae are obtained that describe the polarization of the coherent diffraction radiation on a metal sphere from a pancake-bunch of charged particles. It is shown that the polarization of the radiation in this case makes it possible to estimate the positions of the bunch edges relative to the center of the sphere. This can be used for the non-destructive measurement of the characteristic bunch dimensions.

The formation of thin surface amorphous layers of nanoporous Ge with various morphology during low-energy high-dose implantation by metal ions of different masses ⁶³Cu⁺, ¹⁰⁸Ag⁺ and ²⁰⁹Bi⁺ of monocrystalline c-Ge substrates were experimentally demonstrated by high-resolution scanning electron microscopy. Analysis of the crystallographic structure of all nanoporous germanium layers obtained was carried out by reflected backscattering electron diffraction. It was shown that at low irradiation energies, in the case of ⁶³Cu⁺ and ¹⁰⁸Ag⁺, needle-shaped nanoformations were created on the c-Ge surface, constituting a nanoporous Ge layer, while when using ²⁰⁹Bi⁺, the implanted layer consists of densely packed nanowires. At high energies, the morphology of thin surface layers of nanoporous germanium changes with an increase in the mass of the implanted ions from three-dimensional network to spongy with separate discharged interlacing nanowires. General possible mechanisms of pore formation in Ge during low-energy high-dose ion implantation, such as cluster-vacancy, local thermal microexplosion, and point heating accompanied by melting, are discussed.

An analytical theory of the reflection of light ions from solids is presented. The theory is based on the method of solving the elastic scattering problem (the Oswald–Kasper–Gauckler method), successfully tested in the theory of electron scattering. The solution of a boundary value problem for light ion reflection from solids based on the invariant imbedding method is constructed. Particle interaction with amorphous and polycrystalline samples is considered. Analytical formulas for calculating the integral reflection coefficients of particles and energy are obtained. It is shown that an analytical solution can be obtained only within the framework of a small-angle approximation. Obtained analytical solutions are based on the path length distribution function taking into account the maximum residual range. It was shown that within the framework of an analytical theory the reflection coefficients are determined by two dimensionless parameters — the ratio of the residual range to the transport path length and the screening parameter. The results of theoretical consideration are compared with the data of computer simulation. Numerical calculations are performed for the case of reflection of protons with initial energy E₀ = 1–10 keV from Be, C, Cu and W targets for different scattering geometries. The results of the calculated integral reflection coefficients of particles and energy show the satisfactory agreement between analytics and computer simulation.

The densities of electronic states in quasi-two-dimensional vanadium nitrides have been studied using density functional theory and the method of the crystal orbital Hamilton population. The contribution of various orbital pairs and their influence on the stability of the magnetic subsystem of these compounds has been analyzed using the crystal orbital Hamilton population (COHP) algorithm. The calculation results and their analysis suggest that the formation of long-range magnetic order plays a role in the structural stabilization of magnetic quasi-two-dimensional transition metal nitrides. Comparing –COHP curves for different vanadium nitrides shows that the nitrogen stoichiometry in V_xN_y compounds affects the electronic properties and the nature of the chemical bond during the transition to the ferromagnetic state. Calculation data and total energies prove the structure-stabilizing effect of long-range magnetic ordering in quasi-two-dimensional vanadium-nitrogen compounds.