Thermoelastic stress in thin large-area windows grown from melt by the Stepanov method

The mathematical model for thermoelastic stress in a thin large-area window grown from melt by the Stepanov method is considered. The distribution and magnitude of stress are analyzed depending on the height of the radiative shield and on the distance between the shield and growing window. The model includes the heat-conduction equation and the integral equations relating the thermal radiation fluxes and the temperatures of the surfaces involved in heat transfer.     

Tribological properties of aluminum oxide single crystals grown by the Stepanov method

The friction coefficient and relative wear rate of the aluminum oxide single crystals grown by Stepanov much have been determined for dry friction and water lubrication of different material combinations. A comparative evaluation of the surface fatigue strength of aluminum oxide singleand polycrystals is performed.     

Dielectric properties of ZnSe crystals grown from melt

The frequency and temperature dependences of the real and imaginary parts of the permittivity of ZnSe crystals grown from melt have been measured in the low-frequency range. It has been found that the crystal samples cut from different parts of the ingot exhibit different properties depending on their distance from the ingot origin. The difference in the properties is explained by the dominant influence exerted on the polarization by point defects, the formation of which is associated with the deviation of the composition from stoichiometry, as well as by residual impurities and stresses in the crystals.     

Defect structure in EuS single crystals grown from the melt

The defect structure in EuS single crystals grown form the melt is studied by etch pitting, scanning and high-voltage electron microscopy. Circular and square etch pits and a second phase in the shape of thin hexagonal platelets are observed by etching. Microprobe analysis indicates the platelets to consist of Eu metal. In the transmission electron microscope, smoothly curved dislocations and helical dislocations, small dislocation loops and inclusions associated with dislocations are observed. The possible origin of the detected dislocation structure is considered with reference to climb and glide processes occurring during cooling down the grown crystals. The results corroborate the glide geometry of the NaCl lattice for EuS. On leave from Institute of Physics, Academic Sinica, Peking, VR China     

Fractal structure formation in GaSe crystals grown from melt

The structure of GaSe single crystals prepared by rapid cooling of melt has been studied. These crystals are shown to contain dendrites due to the nonequilibrium conditions of single-crystal preparation. Dendrites have a fractal structure with the Hausdorff measure equal to 1.7.     

Damage studies in cubic ZnSe single crystals grown from melt

A microscopy study of the morphology of the damage produced by TEA-CO₂ laser pulses in cubic ZnSe single crystals grown from melt is presented. The observed bulk filamentary damage consists of relatively uniformly distributed elementary damaged zones, located at specific sites where absorbing inclusions could exist. Transmission electron microscopy and laser ion mass spectroscopy investigations revealed the absorbing inclusions to be thin graphite foils, originating from the crucible used for crystal growth.     

Convergent-beam electron diffraction analysis of GaSe crystals grown from the melt by different doping elements

Summary A systematic investigation of the structural modifications of GaSe crystals, grown from the melt by different doping elements, has been performed by convergent-beam electron diffraction technique, in order to analyse the dependence of the structure on the doping atoms. Iodine-doped crystals have shown the ɛ-2H hexagonal and γ-3R rhombohedral polytypes. The structure of crystals doped either by silver, or copper, or cadmium, or zinc, or arsenic has been proved a mixture of the ɛ-2H hexagonal and of γ, 9 R, 12 R, 15 R rhombohedral phases. Ingots doped either by zinc or arsenic have shown the ɛ polytype prevailing in some zones and the γ structure in the other ones. The ɛ modification is dominant in ingots doped by the remaining atoms.     

Study of the trapping states in ZnS single crystals grown from gallium melt

The trapping levels in zinc sulphide single crystals grown from gallium melt have been investigated using thermoluminescence techniques. The observed peak at 175° K consists of two overlapping components at 173 and 200° K respectively. Thermal activation energies and frequency factors were calculated for both traps. The dependence of glow curve shape on excitation conditions is caused by the retrapping by non-filled 200° K traps of electrons freed from 173° K traps in the course of the glow curve run. In addition to the results on “pure” crystals, measurements were made on samples grown with chlorine, oxygen and copper impurities, as well. Although no positive identification of the chemical nature of the 173 and 200° K trapping centers has been possible, we find that our results are not inconsistent with a previously suggested model in which the traps are identified as complex defects. Comparison is also made with trap spectra observed earlier in gallium-doped zinc sulphide samples prepared by the usual methods.     

Alkali halide crystals grown from a drop of melt and their anisotropy of surface energy

LiF, NaF and NaCl were investigated; they nearly form cubes. Their faces are not perfectly plane, they are optically smooth but slightly curved and surrounded by a stepped area. These areas touch without a gap if a small speed of solidification is applied. Thus the equilibrium crystal has sharp edges, its corners are probably rounded. The decrease of anisotropy with increasing temperature observed for alkali halides and fcc metals investigated recently, seems to be similar.     

Time-dependent model of the growth of oxide crystals from melt by the Czochralski method

A numerical time-dependent model of the growth of oxide crystals from melt by the Czochralski method with weight sensor control has been developed. The approach proposed was used in a series of calculations of bismuth germanate and gallium-gadolinium garnet crystal growth.     

The distribution of silicon in single crystals of Fe-Si alloys grown from the melt

A method of measuring the distribution of the silicon concentration in single crystals of Fe-Si alloys was elaborated on the basis of determining the relative Seebeck coefficient of these alloys with respect to the reference metal. The dependence of the relative Seebeck coefficient of Fe-Si alloys versus copper on the concentration of silicon was measured in the range of 2–12 weight % Si. The distribution of silicon in a series of single crystals of Fe-Si alloys grown from the melt was also determined.The author thanks the members of the department of the mechanical properties of solids of the Institute of Physics, Czechoslovak Academy of Sciences, and especially the head of the department, Ing. B. esták, CSc., for making it possible to prepare the single crystals and for discussion of the paper. He also thanks Dr. M. Matyá, CSc., for valuable remarks and Ing. Z. Kubita for passing on his experience in the use of the measuring method. He is indebted to members of the analytical laboratory of the State Research Institute for Materials Protection, the analytical laboratory of the Metals Research Institute and the chemical department of the. Institute of Physics, Czechoslovak Academy of Sciences, for careful analyses of the samples.     

Dislocation structure of kcl crystals grown with vibration of the melt

Summary The amplitude at all frequencies was 0.04 mm. Three crystals were grown at each frequency, with seeds of dislocation density D = 6 × 10⁴ cm^–2. Figure 1 shows the frequency dependence of the final D. Each point in Figs. 1 and 2 is the mean from 50 measurements (50 fields of view). At all frequencies except 180 Hz, D was 2–4 times less than that without vibration, while at 100 and 160 Hz it was less by nearly an order of magnitude.The effects of amplitude (0.02 to 0.2 mm) were examined at 100 Hz, the minimum D occurring at 0.1 mm (Fig. 2). At 0.04–0.08 mm, D was less by a factor 3–4 than for crystals grown without vibration, while at 0.1 mm it was less by an order of magnitude, being 2 × 10^–4 cm^–2. The size of the etch pits on crystals grown at amplitudes up to 0.1 mm did not differ from that for crystals grown at rest, but above 0.1 mm the size increased, by more than a factor 3 at 0.2 mm. Figure 3 illustrates these effects.Optimal vibration reduces D by improving the growth conditions (reduction of temperature gradients by mixing, more uniform impurity distribution).     

Physicochemical and technological peculiarities of multicomponent oxide crystal growth from melt by modified Stepanov technique

The peculiarities of the modified Stepanov technique are considered. The advantages of the method for growth of oxide crystals from melts of complex compositions are shown. Crystallization conditions are given to obtain optically homogeneous Sr _x Ba_{1 − x} Nb₂O₆, BaWO₄, SrMoO₄, LiNbO₃, and Ca₃(Nb, Ga)₂Ga₃O₁₂ single crystals using dies of capillary type.     

CVD TiC/alumina multilayer coatings grown on sapphire single crystals

Multilayers of TiC/α-Al₂O₃ consisting of three (1 μm thick) alumina layers separated by thin (∼10 nm) oxidized TiC layers have been deposited onto c-, a- and r-surfaces of single crystals of α-Al₂O₃ by chemical vapour deposition (CVD). The aim of this paper is to describe and compare the detailed microstructure of the different multilayer coatings by using transmission electron microscopy (TEM).The general microstructure of the alumina layers is very different when deposited onto different surfaces of α-Al₂O₃ single crystal substrates. On the c- and a-surfaces the alumina layers grow evenly resulting in growth of single crystal layers of TiC and alumina throughout the coating. However, when deposited on the r-surface the alumina layers generally grow unevenly. No pores are observed within the alumina layers, while a small number of pores are found at the interfaces below the TiC layers. The TiC and alumina layers grow epitaxially on the c- and a-surface substrates. On the r-surface, epitaxy is present only at some rare locations. The TiC layers were oxidized in situ for 2 min in CO₂/H₂ prior to the alumina layer deposition. For all three samples chemical analyses show that the whole TiC layer is oxidized. On the c- and a-surfaces the TiC layer was oxidized to an fcc TiCO phase. On the r-surface the oxidation stage resulted in a transformation of the initially deposited fcc TiC to a monoclinic TiCO phase, which appears to be a modified TiO structure with a high carbon content.     

Formation of F-centers in KCL crystals grown with vibration of the melt

Russian Physics Journal -     

Properties of n-type gallium arsenide doped with germanium when single crystals are grown from the melt

The temperature dependences of the density, mobility, and lifetime of electrons, and the photoconductivity and cathodoluminescence spectra of gallium arsenide with different electron densities doped with germanium when single crystals are grown by the Czochralski method are investigated. An analysis of the scattering mechanism is given, and the acceptor and donor densities are determined. The acceptor-type capture levels are found from the temperature dependence of the electron lifetime. The results of a study of the cathodoluminescence spectra indicate the presence in the specimens of complex radiational recombination centers similar to germanium-atom complexes with inherent lattice defects.     

Dislocations in GaAs single crystals grown by the Czochralski method

The influence was studied of growth conditions on the dislocation density in gallium arsenide single crystals grown by the Czochralski method from a gallium-enriched melt. Etching in a solution of 1 part cone. HNO₃ and 2 parts H₂O served to determine the dislocation density across and along a single crystal. The dislocation density along the crystal was found to depend mainly on the angle of crystal diameter increase.     

Effect of polarity on properties of CdSnP2 and CdSnAs2 crystals grown from melt

The best-developed polar faces (112) and (¯1¯1¯2) of CdSnP₂ and CdSnAs₂ crystals were identified by etch pits and by x-ray analysis. It is shown that the (112) faces are completed by group V atoms (phosphorus, arsenic), while the (¯1¯1¯2) faces are completed by cadmium and tin atoms. It is established that these faces of doped and undoped crystals differ in surface resistivity, conductivity type, and photoluminescence yield, and the material of their growth sectors has different Hall parameters.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 49–52, November, 1981.