Microanalysis of the SmS Films Obtained by Magnetron Sputtering of a Target

Crystallography Reports - The thin SmS films obtained by magnetron sputtering of a SmS target with the 1.3Sm:1S composition have been investigated. The microanalysis of the sputtered target has...     

Effect of gravitation vector orientation relative to the solidification front on the micro- and macrohomogeneity of semiconductor crystals grown under terrestrial and space conditions

The influence of gravitation vector orientation relative to the solidification front on the dopant distribution micro- and macrohomogeneity in vertical oriented crystallization of highly Ga-doped Ge crystals has been investigated using computer simulation. The deviation of the axis for crystal growth relative to the g ₀ vector, when a free surface of the melt is present, has been found to provide the formation of striations with a reduced dopant concentration. The influence of the solidification rate, convective and diffusion mass flows on the dopant distribution macrohomogeneity has been investigated.     

Optimization of boundary conditions for a distributed control system on the growing of crystals

Boundary conditions for a distributed system simulating the temperature distribution in a growing crystal and the heat exchange with the environment under nonlinear boundary conditions have been optimized by the example of a garnet crystal grown by the Czochralski method. Quasi-stationary conditions for the temperature distribution in a growing crystal have been used. The obtained results allow the optimization of technological parameters for the growth of crystals with a high degree of structure perfection.     

Problems, prospects, and alternatives for semiconductor single crystal growth in space

Experimental results for growing semiconductor single crystals under real microgravitation conditions aboard spacecraft have been analyzed. The causes for the formation of dopant distribution micro- and macroinhomogeneities in crystals have been studied. It has been shown that it is necessary to provide diffusion heat and mass transfer conditions in a melt to achieve a high homogeneity of properties in grown crystals. These conditions and expected optimal parameters of crystals can be obtained in the absence of thermogravitational convection, when a free surface of the melt is eliminated, and also under conditions of minimizing external quasi-static effects on the melt causing forced convective flows in them and, correspondingly, inhomogeneity of composition and properties for grown crystals due to the increasing gravitational sensibility of melts under microgravitation conditions.     

Mathematical modeling and experimental investigation of the effect of temperature gradients on crystallization processes under terrestrial and space conditions

Mathematical modeling of the processes of heat and mass transfer during directed crystallization under terrestrial and space conditions is performed on the basis of experimental data on the temperature distribution (boundary conditions). Convective processes are described by the system of Oberbeck-Boussinesq equations together with the heat-conduction equation (the Stefan problem). A dependence of the intensity of thermal gravitational convection on the radial and axial temperature gradients is established. It is shown that one of the necessary conditions for the growth of homogeneous semiconductor crystals under both terrestrial and zero-gravity (on board spacecraft) conditions is the absence of the free surface of a melt (the Marangoni convection) and optimization of the temperature gradients (first of all, the radial gradient).     

Implementation of Temperature-Controlled Method of Protein Crystallization in Microgravity

An experimental scientific equipment for implementing temperature-controlled protein crystallization in capillaries under microgravity has been developed, fabricated, and tested. This crystallization method, providing on-line separate control of crystal growth both in the stage of nucleation of crystals and during their further growth, requires small amounts of protein solution. The equipment has been tested on board of Foton-M4 spacecraft (growth of lysozyme protein crystals of high structural quality in microgravity) using a cyclogram developed in ground-based experiments. The results obtained have demonstrated efficiency and importance of the developed equipment and method for growing biomacromolecular crystals of high-structural quality.

     

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.     

Lysozyme crystallization in a precision-controlled temperature gradient

The possibility to control the crystallization process of biomaterials by the temperature was examined by the mathematical simulation of lysozyme crystallization. The precision-temperature control with creation of a local temperature gradient in solution was demonstrated to allow the growth of lysozyme crystals with high structural perfection.     

Sol-gel films with immobilized acid-base indicators

Nanoporous silica films containing a number of immobilized acid-base indicators have been obtained using the sol-gel method. The variation in their absorption spectra in the visible range depending on the hydrogen ion exponent (pH) has been characterized, and the durability of their application as pH sensors has been estimated.     

Behavior of the Melt in the Vertical Bridgman Method with a Low Axial Temperature Gradient

The thermal conditions for the growth of Ge crystals with a diameter of 50 mm by the vertical Bridgman method in the case of low thermal-gravitational convection are studied using model experiments. Distilled water being hydrodynamically similar to the Ge melt is used as the model liquid. When modelling by means of the light cut method, it is established that mixture particles move along the heat flow direction from top to bottom. It is shown that an axial temperature gradient of 2 K/cm or more increases the contribution of thermal diffusion to mass transfer at a vertical flow rate of 0.09 mm/s or more. The numerical simulation of thermal convection in the Oberbeck–Boussinesq approximation confirms the absence of convection under the given thermal conditions. However, the deviation of the container axis from the vertical by 0.5° during the process of crystal growth contributes to the increase in the flow rates in the liquid phase up to 0.55 mm/s.