The influence of temperature, droplet size, direction and misorientation angle of vicinal GaAs(111)A substrates on the motion of Ga droplet, formed during the annealing under Langmuir evaporation conditions, is analyzed using Monte Carlo simulations. It is demonstrated that the droplet velocity increases with temperature and decreases with increasing droplet size. It is found that at the fixed droplet size the Ga droplet velocity is higher on surfaces with the misorientation in $[01 \overline{1}]$ and $[0 \overline{1} 1]$ directions than in the $[\overline{2} 11]$ direction. The step structure of the vicinal surfaces misoriented in these directions is different. This results in a different step arrangement during the annealing. Steps on the surface misoriented in the $[\overline{2} 1 1]$ direction become more winding than on the surfaces misoriented in $[01 \overline{1}]$ and $[0 \overline{1} 1]$ directions. It is shown, that during the annealing, gallium droplets form local step bunches on vicinal GaAs(111)A substrates with high misorientation angles. It is shown that the bunch height is determined by the gallium droplet size and is independent of the surface misorientation angle.

The initial stages of planar self-catalyzed GaAs nanowire growth via the vapor-liquid-solid mechanism are considered by a kinetic lattice Monte Carlo model. The shapes of the nanocrystals being formed under a catalyzed droplet are presented for three GaAs substrate orientations (111)A, (111)B, (001). The most stable planar GaAs nanowire growth was observed on GaAs(111)A substrates.

Structures with arrays of planar and tilted quasi-one-dimensional GaAs nanocrystals have been grown on GaAs(001) substrates. An epitaxial silicon layer oxidized in air was used as a passivation coating. The amount of silicon deposited varied from structure to structure and was equivalent to 1, 2, 4, and 6 atomic layers. It has been found that in the case of a passivation layer based on silicon with a thickness of 1 atomic layer, an array of planar nanocrystals is formed, and in other cases, inclined quasi-one-dimensional nanocrystals. Nanocrystals are surrounded by crystallites, the shape, size, orientation, and distribution density of which change with the amount of silicon. The lowest density of crystallites was achieved with a silicon layer 6 atomic layers thick. Keywords: molecular-beam epitaxial, GaAs, Si, quasi-one-dimensional nanocrystals, vapour-liquid-crystal.

The present paper is devoted to the Monte Carlo simulation of the motion of Au–Si melt drops over vicinal Si(111) surface during gold deposition onto a silicon substrate. The behavior of drops on the Si surfaces with orientations (100) and (111) is considered. It was found that the direction of Au–Si drops motion over vicinal Si(111) surface is governed by asymmetry in the lateral drop–substrate interface. The reason of asymmetry in the lateral interface on vicinal Si(111) surface is steps. The motion of a drop occurs due to the dissolution of a silicon substrate in striving to an equilibrium Au–Si melt concentration in the volume of a drop. The kinetics of Au–Si melt drops motion over the silicon surface is analyzed.

Structures with arrays of planar and tilted quasi-one-dimensional GaAs nanocrystals have been grown on GaAs(001) substrates. An epitaxial silicon layer oxidized in air was used as a passivation coating. The amount of silicon deposited varied from structure to structure and was equivalent to 1, 2, 4, and 6 atomic layers. It has been found that in the case of a passivation layer based on silicon with a thickness of 1 atomic layer, an array of planar nanocrystals is formed, and in other cases, inclined quasi-one-dimensional nanocrystals. Nanocrystals are surrounded by crystallites, the shape, size, orientation, and distribution density of which change with the amount of silicon. The lowest density of crystallites was achieved with a silicon layer 6 atomic layers thick.

The simulation of Au droplet formation and motion along the Si(111) surface was carried out using a kinetic lattice Monte Carlo model. It was shown that the Si substrate orientation affects the shape of the etching pits created under golden drops. The absence of droplet directed motion on singular surfaces was demonstrated. A necessary condition for the directional droplet motion is the asymmetry of lateral facets at a liquid-crystal interface. The reason for this asymmetry may be the presence of steps on the vicinal surfaces. The influence of the surface misorientation angle and the substrate annealing temperature on the surface morphology and the characteristics of gold drops movement was analyzed. It was shown that gold deposition on the vicinal silicon surface at high temperature leads to step faceting. Monte Carlo simulations confirmed that the reason for the Au droplet movement during the gold deposition is the silicon substrate dissolution in the Au-Si melt in the tendency to reach the equilibrium silicon concentration in the melt.

Subject of study. In this paper, we describe the luminescence properties of nanopowders of composition (Nd0.008Y0.992)(2)O-3, (Nd0.008Y0.992)(2)O-3 + 6 mol% ZrO2, and (Nd0.008Gd0.496Y0.496)(2)O-3 + 5 mol.% ZrO2 with various percentages of monoclinic and cubic phases. Method. Photoluminescence and pulsed cathodoluminescence spectra are recorded, followed by interpretation of the results obtained. Main results. In the process of studying the luminescence bands corresponding to the F-4(3/2 )-> I-4(9/2) and F-4(3/2) -> I-4(11)/2 energy transitions for neodymium ions in nanopowder crystalline lattices, we identify several spectroscopic and kinetic properties that can be used to identify the substances and determine the crystal phases present. We show that there is slight broadening of the spectral lines in the continuum base of the F-4(3/2) -> I-4(11/2) manifold; the intensity level below which the bands merge into a continuum increases as the amount of structural disorder caused by the zirconium- and gadolinium-ion dopants in the Y2O3 increases. Practical significance. The distinctive features of the photolumines- cence spectra and the kinetics of neodymium-ion luminescence in the F-4(3/2 )-> I-4(9/2) and F-4(3/2) -> I-4(11)/2 bands can be used for unique identification of the substances present and determination of the crystal phases thereof; this will be of practical interest in the development of high-bandwidth ceramic active elements. (C) 2022 Optica Publishing Group

Subject of study. The possibility of using the nonlinear current mode of operation of a photomultiplier tube for measurements of luminescence kinetics was investigated. Aim of study. This study aimed to validate the possibility of using the nonlinear current mode of operation of a photomultiplier tube to determine the kinetic properties of small luminescence signals of condensed media, including the signals that cannot be detected in a linear current mode. Method. The signal arriving at a high-impedance (1 MS?) input of a digital oscilloscope from a photomul-tiplier tube via a coaxial cable was measured. This signal is a convolution of a photocurrent pulse with a kinetic instrument function determined by the discharge of capacitance in the measurement circuit of the photomultiplier tube. The bandwidth of the circuit was determined by the lowest frequency of its elements instead of the character-istic time of the instrument function. The real photocurrent signal was reconstructed by the deconvolution of the digital convoluted array. The pulsed cathodoluminescence method was used to detect the kinetics. Main results. A method for measuring the kinetics of small optical signals in the current mode of operation of a photomulti-plier tube connected to a high-impedance input of a digital oscilloscope was presented. The results of using this method to measure the kinetics of pulsed cathodoluminescence of impurity and intrinsic centers in ceramic and monocrystalline samples of yttrium aluminum garnet were presented. The direct determination of characteristic decay times by approximating the convoluted curves without deconvolution was demonstrated for an exponential luminescence decay profile. Practical significance. The proposed method for the characteristic time detection of luminescence kinetics enables comprehensive analysis of luminescence that can be applied in various sectors of the national economy.(c) 2023 Optica Publishing Group

The Langmuir evaporation (LE) of GaAs vicinal surfaces with various crystallographic orientations is analyzed at the atomistic level by Monte Carlo simulation. The evolution of the surface morphology and LE characteristics (gallium and arsenic evaporation rates, congruent evaporation temperature T-c, effective activation energy of Ga desorption) are studied under the increasing annealing temperature for GaAs(1 1 1)A and GaAs(1 1 1)B singular, and vicinal surfaces with various atomic step density. At low temperatures T < T-c, the step-terraced morphology of a vicinal surface is preserved in the LE process. At high temperatures T > T-c, the characteristics and crystallographic orientation specificity of surface morphology are determined by the formation of liquid Ga droplets. It is shown by simulation that, as compared to the (1 1 1)B surface, on the (1 1 1)A surface, the congruent evaporation temperature is substantially higher and is more sensitive to the atomic step density, as well as to the concentration of intentionally introduced defects on the terraces of the initial step-terraced surface. These observations are explained by two morphological peculiarities of LE on (1 1 1)A and B surfaces: (i) on the (1 1 1)A surface, Ga droplets penetrate deep into the substrate; (ii) on the (1 1 1)B surface, vacancy islands are more readily formed on terraces.

In this work, simulation of high-temperature annealing of GaAs (111) substrates has been carried out. The dependences of the substrate morphological transformations on the temperature and the presence of surface defects are analyzed.

Abstract The Langmuir evaporation (LE) of GaAs vicinal surfaces with various crystallographic orientations is analyzed at the atomistic level by Monte Carlo simulation. The evolution of the surface morphology and LE characteristics (gallium and arsenic evaporation rates, congruent evaporation temperature Tc, effective activation energy of Ga desorption) are studied under the increasing annealing temperature for GaAs(111)A and GaAs(111)B singular, and vicinal surfaces with various atomic step density. At low temperatures T Tc, the characteristics and crystallographic orientation specificity of surface morphology are determined by the formation of liquid Ga droplets. It is shown by simulation that, as compared to the (111)B surface, on the (111)A surface, the congruent evaporation temperature is substantially higher and is more sensitive to the atomic step density, as well as to the concentration of intentionally introduced defects on the terraces of the initial step-terraced surface. These observations are explained by two morphological peculiarities of LE on (111)A and B surfaces: (i) on the (111)A surface, Ga droplets penetrate deep into the substrate; (ii) on the (111)B surface, vacancy islands are more readily formed on terraces.

In this paper, we present the findings of research on absorption spectra, reflection spectra, and luminescence spectra for a new decorative stone-rayizite, which is a mixture of antigorite, dolomite, and a small amount of talc. This stone exhibits the alexandrite effect, and the color is due to chromian antigorite. The Y and U bands in the absorption spectra and the R line at 686.6 nm in the luminescence spectra indicate that Cr3+ ions are present. The emission spectrum also includes the emission of Fe2+ ions at wavelength 615 nm. The band at 650 nm, which becomes active under the action of a pulsed electron beam and does not occur during photoexcitation, is a distinguishing feature. This band belongs to a center associated with emission fromnonbridging oxygen. In this paper, we discuss the mechanism for the formation of such luminescence centers. (C) 2021 Optica Publishing Group

The high-temperature GaAs annealing kinetics is studied by Monte Carlo simulation. The evaporation rate dependences on the annealing time are obtained for (111)A and (111)B substrate surfaces in a 800-1200 K temperature range. The surface morphology evolution and evaporation kinetics are shown to be dependent on the GaAs substrate orientation. The congruent evaporation of (111)A surface corresponds to the layer-by-layer evaporation mode, while, on the (111)B surface, multilayer vacancy islands are formed. At temperatures exceeding the congruent evaporation temperature, the initial evaporation stage before the gallium droplet formation agrees with the congruent evaporation mode. The appearance of Ga droplets on the surface, corresponding to the start of incongruent evaporation regime, results in a sharp fall of the GaAs evaporation rate. It is found that the Ga droplet on vicinal surfaces locally inverts the step movement direction.

Using Monte Carlo simulation, the self-catalyzed GaAs planar nanowire growth with a gallium droplet as a catalyst was considered. Planar nanowires were formed by molecular beam epitaxy via the vapor-liquid-solid mechanism. The vicinal GaAs(111)A substrates with a film-mask coverage were used. The planar nanowire formation kinetics was analyzed. For the planar nanowire growth, the arsenic adhesion coefficient and the gallium surface diffusion should be increased on vicinal surfaces, in comparison with singular substrates. The nanowire growth directions are determined by the GaAs crystallography and are limited by vicinal surface steps.

В работе представлены результаты Монте-Карло моделирования ленгмюровского испарения подложек арсенида галлия. Анализировалось влияние ориентации поверхности подложек на характеристики неравновесных высокотемпературных отжигов. Рассматривались сингулярные и вицинальные поверхности GaAs(111)A и GaAs(111)В с разными углами разориентации. Моделирование осуществлялось в температурном диапазоне 700 – 1000 K, включающем температуры конгруэнтного испарения Тс подложек с разным углом отклонения.

Using a kinetic lattice Monte Carlo model, the self-catalyzed growth of planar GaAs nanowires was analyzed. The nanowire growth via the vapor-liquid-crystal mechanism was considered. The effect of temperature and the catalyst droplet location on the morphology and growth direction of planar GaAs nanowires was studied. For GaAs(111)A and GaAs(111)B substrates, a temperature range corresponding to stable growth of planar GaAs nanowires was revealed. The special asymmetric arrangement of droplets allows the one-directional nanowire growth.

Clinical and immunological parallels in inflammatory periodontal diseases are considered taking into account some features of the functioning of general and local structures of the immune system in periodontitis of varying severity, chronic generalized periodontitis, aggressive periodontitis. In the analysis of immunopathogenesis of inflammatory periodontal diseases, an essential role is given to an imbalance in the immune and cytokine system.

In this paper, we analyze the effect of the GaAs substrate orientations on the evaporation kinetics under nonequilibrium annealing conditions. GaAs substrates with the (III)A and (III)B orientations were considered. The dependence of evaporation kinetics on the substrate orientation appears at high annealing temperatures, when a liquid gallium layer can be formed on the substrate. The surface roughness, the presence and merging of gallium droplets were shown to affect the evaporation kinetics.

•GaAs Langmuir evaporation is studied at the atomic level by Monte Carlo simulation.•Characteristics of Langmuir evaporation are different for GaAs(111)A and B surfaces.•Supply of Ga atoms by vacancy island reduces the congruent evaporation temperature.•Supply of Ga atoms by vacancy island facilitates the Ga droplet formation at (111)B.•Surface misorientation affects evaporation at (111)A stronger than at (111)B.