Effect of electrical field on growth of gallium arsenide layers from vapour phase

The effect of electrical fields on the growth rate and morphology of gallium arsenide layers in the GaAs AsCl₃ H₂ system is investigated. The fields both parallel and perpendicular to the substrate surface are used. It is found that application of the parallel field results n increase of growth rate of (111)A face but does not change that of 2° (001). The morphology of layers grown in such a field is better than that grown without any. The application of perpendicular field results in decrease of growth rate for both crystallographic orientations, the layer morphology worthening. In both cases the effect is greater when the substrate has a negative potential. Possible mechanisms of the field influence on the growth rates of gallium arsenide layers are discussed such as: supersaturation decrease because of nucleation in vapour phase and the change in the rates of surface processes.     

Ein eindimensionales Modell zur Beschreibung von Transporteigenschaften in offenen Systemen

A simple one-dimensional model is dealt with describing the material transport by means of linear gas flow and diffusion. In the GaAs AsCl₃ H₂ system the dependence of the partial pressure on the x-coordinate is calculated, and the role of the temperature gradient near the growing interface is discussed in view of the constitutional supercooling of the gas phase.     

The significance of X-ray investigations for the classification of multicomponent systems with mixed crystals in a solid phase

The X-ray investigations of solid phases in the multicomponent systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O were conducted and the crystal lattice parameters of mixed crystals forming in these systems were determined. It was confirmed that in the KCl KBr H₂O system the continuous solid solutions were formed and in the K₂SO₄ (NH₄)₂SO₄ H₂O system the solid solutions with a miscibility gap were formed. In the KNO₃ NH₄NO₃ H₂O system the presence of two series of mixed crystals, namely the mixed crystals between ammonium nitrate and the double salt KNO₃ · 2 NH₄NO₃ and between potassium nitrate and the same double salt was confirmed. In this system a wide region of discontinuity (for x_NH4NO₃ = 0.083 – 0.67) also occurred. According to Roozeboom's classification, the KCl KBr H₂O system belongs to the 3^rd type, the K₂SO₄ (NH₄)₂SO₄ H₂O to the 5^th type (the discontinuous mixed crystals, the systems of peritonic type) and the KNO₃ NH₄NO₃ H₂O system is not comprised in this classification.     

Studies of Growth Mechanism and Sulfur Incorporation in VPE of GaAs under Nearly Equilibrium Conditions

Detailed investigations of growth rate of GaAs VPE-layers and sulfur incorporation during crystal growth have been carried out under nearly equilibrium conditions at low temperatures (680 °C). The present investigation examines the dependence of growth rate and sulfur incorporation on the initial partial pressures (p°) of GaCl and HCl in the deposition zone. The observed deviation from the 1:1 proportion between GaCl before and HCl after the growth reaction will be discussed in a model of chlorine desorption by GaCl₃. The sulfur concentration dependence in the grown layer indicates an identic growth mechanism and supports the idea of sulfur incorporation through an activated complex on the GaAs surface.     

Phase relations and crystal growth of YBa2Cu3O7−δ in the system YO1.5?BaO?CuO

The liquidus face of the system YBa₂Cu₃O_7−δ BaCuO₂ CuO was investigated by DTA. We found liquidus temperatures below 1000 °C only in a narrow region with small yttrium oxide content near the eutectic of the system BaCuO₂ CuO. The crystallization path of crystal growth experiments is discussed and the principle structure of the phase diagram is derived. Single crystals are grown being superconductive after thermal treatment in oxygen atmosphere.     

Some Physicochemical Parameters of Saturated Ternary Solutions of Systems with Mixed Crystals in their Solid Phase

The measurements of density (ϱ), viscosity (η) and hydration number (n_h) of saturated solutions of ternary systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O with mixed crystals in the solid phase have been conducted. It has been confirmed, that the occurence of the extremes on the curves of dependence of the properties (ϱ, η, n_h) on the composition of saturated solution may be the base for the supposition that beside mixed crystals the double salts have also been formed in the solid phase of a given system.     

The Distribution Coefficient of Isomorphous Admixtures for KCI?KBr?H2O,K2SO4?(NH4)2SO4?H2O and KNO3?NH4 NO3?H2O Systems at 298 K

For the systems KCI KBr H₂O, K₂SO₄4-(NH₄)₂H₂O and KNO₃ NH₄NO₃ H₂ O equilibrium investigations have been performed and the distribution coefficients of isomorphous admixtures have been determined. For each solid solution the changes of the distribution coefficient D, the dependencies between the values of the real and ideal distribution coefficients and the directions of energetic changes in these systems during the co-crystallization of isomorphous and isodimorphous admixtures have been discussed.     

On the crystal structure type of 2 CsCl · CoCl2 · 2 H2O

The following three-component systems have been studied: CsCl MnCl₂ H₂O at 25 °C; 2 CsCl · CuCl₂ · 2 H₂O—2 CsCl · CoCl₂ H₂O at 10 °C and 2 CsCl · MnCl₂ · 2 H₂O—2 CsCl · CoCl₂ H₂O at 25 °C and 10 °C. It was established that Co²⁺-ions do not substitute isodimorphously the Cu²⁺-ions in the tetragonal salt 2 CsCl · CuCl₂ · 2 H₂O, whereas in the case of the triclinic salt 2 CsCl · MnCl₂ · 2 H₂O they can substitute isodimorphously the Mn²⁺-ions. The theoretical considerations supported by the results obtained allow to predict the existence of the double salt 2 CsCl · CoCl₂ · 2 H₂O as well as the type of its crystal structure — triclinic, space group P1 .     

Hydrothermal Synthesis of Zeolite Crystals Using Natural Scolecite

Natural scolecite is converted into analcime type zeolite by hydrothemal method at 180 °C at autogeneous pressure for 24 to 160 hours growth runs. Mordenite is detected in the final product. Cube and spheroid crystals of the products are illustrated and described. Crystals synthesized are characterized by X-ray diffraction, infrared spectroscopy EDAX and scanning electron microscopy. Particle size is estimated as 20–60 microns, induction period for nucleation as 12 hrs, and lattice parameter of cube crystals as 13.70 Å. Mechanism of growth, influence of anions and duration of growth etc. are discussed. It is established that the crystals grow in the system Na₂O Al₂O₃ SiO₂ H₂O.     

Microstructure and spacings of directionally solidified metal-semiconductor eutectic alloys

Directionally solidified metal-semiconductor eutectic alloys, representing nonfacetted facetted eutectics, show a variety of microstructures caused by the great differences in semiconductor volume fraction (Zn Ge 7,8 %; Ge ZrGe₂ 98.6 %), the influence of growth rate and temperature gradient at the solid-liquid interface. The Al Si, Ag Si, Ag Ge, Zn Ge, Cu₃Si Si, NiGe Ge, CoGe₂ Ge, Mn₃Ge₂ Ge, FeGe₂ Ge, Mn₁₁Si₁₉ Si, Cu₃Ge Ge, Ge TiGe₂ and Ge ZrGe₂ eutectics habe been investigated. The following three models are applicable for the calculation of the spacings as a function of growth rate and temperature gradient at the solid-liquid interface to certain microstructures: diffusion-determined growth, branchinglimited growth and phase-lead-determined growth.     

Phillipsite-type synthetic zeolite with high silica contents and accompanying phases

A zeolite of P type with a molar ratio SiO₂ : Al₂O₃ of about 6 was obtained on laboratory and on enlarged scale, by synthesis carried out at 100°C in Na₂O K₂O SiO₂ Al₂O₃ H₂O system, without complexing agents. It was found that the products depend not only on the chemical composition of hydrogel but also on the kinetic factors such as: the material of the reactor wall, the amount of substrates taken for crystallization and stiring. It was found that the stability of zeolites increases in the order: L < T < Ch < P. The factors accelerating crystallization led to the more stable zeolites as products. The paper shows difficulties in implementing the laboratory results into an industrial production.     

The Phase Relations in the Quasi-Binary System LiBaF3?AlF3. A Search for New Fluoride Laser Hosts

In a search for new fluoride laser host materials (esp. with an Al site for Cr³⁺ doping) the phase relations in the join LiBaF₃ AlF₃ of the ternary concentration diagram LiF BaF₂ AlF₃ were investigated by difference thermal analysis method from 15 samples with different compositions. A new congruently melting compound LiBaAlF₆ (T_m = 785 °C) was found. The α-β-phase transformation at 671 °C prevents the growth of β-LiBaAlF₆ single crystals from the own melt and the application to laser technology.     

The crystal and molecular structure of three homologue 1,4-dialkanoyloxy-biphenyls (SYM-n)

The three homologue compounds with the general formula C_nH_2n+1 COO C₆H₄ C₆H₄ OOC C_nH_2n+1 (SYM-n) crystallize in the following space groups: SYM-1: triclinic, P1 , a = 7.400(6), b = 9.227(3), c = 10.579(3) Å, α = 85.97(3), β = 89.09(3), γ = 71.47(3)°; SYM-2; monoclinic, P2₁/c, a = 11.712(7), b = 5.648(1), c = 12.408(6), Å, β = 103.84(3)°; SYM-5: triclinic, P1, a = 5.505(4), b = 8.342(8), c = 24.79(2) Å, α = 86.67(3), β = 85.45(6), γ = 71.74(7)°. The structures have been solved by direct methods and refined to R = 0.075, 0.061 and 0.053, respectively. The packing arrangements show a layer-like structure. The layers are almost separated for SYM-1 as well as for SYM-2 and interdigitated for the structure of SYM-5.     

The crystal structure of nematogenic 2-bromo-1,4-phenylenediyl bis(trans-4-n-propylcyclohexanoate) — a special kind of disorder

The title compound with the formula C₃H₇–C₆H₁₀–COO–C₆H₃Br OOC C₆H₁₀ C₃H₇ (BPBPC) crystallizes in a triclinic unit cell with dimensions a = 5.822(2), b = 8.732(3), c = 13.016(5) Å, α = 94.42(3)°, β = 93.47(3)°, γ = 104.85(2)° containing one molecule. The structure has been solved by heavy atom method and refined to R = 0.083. The BPBPC molecules adopt an optimum stretched form and exhibit pseudo-centrosymmetry in consequence of a special kind of disorder within the crystal lattice.     

Growth of lanthanum heptamolybdate crystals by gel technique

The growth of single crystals of lanthanum heptamolybdate is achieved by allowing controlled diffusion of La ions through silica gel using the system La(NO₃)₃ MoO₃ NH₄OH HNO₃–Na₂SiO₃. The reaction mechanism leading to the growth is reported. Mechanism of crystallization of La heptamolybdate is discussed. Formation of Liesegang rings consisting of La heptamolybdate crystals in the system is reported. It is observed that concentration programming and seeded growth enhances the size of crystals. The crystals grown in the system are single crystal platelets exhibiting squarish or octagonal facets. Some crystals exhibit a spherulitic morphology.     

Untersuchungen an Systemen aus Salzen und gemischten Lösungsmitteln (XXIII). Physikalisch-chemische Charakterisierung der im System MgCl2?CH3OH?H2O auftretenden festen Phasen MgCl2 · 6CH3OH und MgCl2 · 4H2O · 2CH3OH

In the MgCl₂ CH₃OH H₂O system there exist in the temperature region from 10 to 55°C besides the known compounds two easily decomposing ones, MgCl₂ · 6 CH₃OH and MgCl₂ · 4 H₂O · 2 CH₃OH. Until now only the first one could be partly characterized. By polarization microscopical, X-ray, IR-spectroscopical and thermal investigations the determination of the respective substantial data was successful. Some details on the structure and on the process of thermal decomposition of the two compounds are given.     

The crystal and molecular structure of 2,5-dibromo-1,4-phenylenediyl bis(trans-4-ethylcyclohexanoate)

The title compound with the formula C₂H₅ C₆H₁₀ COO-C₆H₂Br₂ OOC C₆H₁₀ C₂H₅ (DPBEC) crystallizes in the monoclinic space group P2₁/c with a = 15.37(2), b = 5.27(1), c = 15.13(2) Å, β = 92.7(1)° and two molecules per unit cell. The structure was solved using film intensity data by heavy atom method and refined to R = 0.078. The fully stretched DPBEC molecules exhibit exact C_i symmetry. Their packing in the crystal is characterized by a non-parallel (cross) arrangement of the molecular long axes.     

Epitaxial Deposition of GaAs in the Ga(CH3)3?AsH3?H2 system (II). Investigations on the Hetero-Epitaxy of GaAs on Ge

Epitaxial GaAs layers have been deposited on (111), (110) and (100) faces of Ge by pyrolysis of Ga(CH₃)₃ AsH₃ H₂. In this paper the influence of growth conditions and the lattice difference of GaAs and Ge on the quality of epitaxial GaAs layers is described and discussed. The epitaxial layers are characterized by chemical etching, X-ray investigations, and by the observation of the surface morphology.     

Crystal Structure and Thermal Phase Behaviour of 2,3-Dicyano-4-n-hexyloxyphenyl-trans-4-n-heptyleyelohexanoate

The title compound with the formula C₇H₁₅ C₆H₁₀ COO C₆H₂(CN)₂ OC₆H₁₃ (DHPHC) crystallizes in the monoclinic space group P 21/n with a = 5.633(1), b = 14.254(1), c = 33.435(7) Å, β = 91.56(2)°, and four molecules per unit cell. The structure has been solved by direct methods and refined to R = 0.082. The DHPHC molecules adopt a banana-shaped but considerably stretched form and show a parallel arrangement of their long axes in the crystal lattice. The phase transitions of DHPHC have been investigated by DSC and thermal microscopy. The compound shows a rather complicated melting behaviour and forms two solid phases and a monotropic smectic A phase.     

Kristallstrukturänderungen des Magnesiumnitrats-Hexahydrats,die infolge isodimorpher Substitution durch Co(II)- und Ni(II)-Ionen entstehen

The physico-chemical analysis data on the systems Mg(NO₃)₂ Co(NO₃)₂ H₂O and Mg(NO₃)₂ Ni(NO₃)₂ H₂O at 25.0°C have shown that due to isodimorphous substitution of Mg²⁺ in the crystals of Mg(NO₃)₂ · 6 H₂O for Co²⁺ or Ni²⁺, above a specific degree of ionic substitution, changes in the crystal structure of Mg(NO₃)₂ · 6 H₂O appear.