Selective area growth of GaAs using a Ga beam with a step-function lateral intensity profile

Selective area growth of GaAs has been carried out in order to investigate the surface diffusion of Ga atoms using molecular beam epitaxy (MBE) with the aid of a Ga beam with a lateral step-function intensity profile. This step-function profile was obtained using a closely fitted GaAs shadow mask. When the mask edge was parallel to [01 ], a (311)A facet was typically observed near the edge of the Ga beam, while in the case of the mask edge parallel to [011], a (111)B facet was formed. MBE growth simulation based on the diffusion model was carried out in order to understand the mechanism of this selective area growth. The calculated results were in good agreement with the experimental results, and the diffusion lengths of Ga atoms were determined to be 0.10 μm along [011] direction on the (100) GaAs surface, 0.37 μm along [233] direction on the (311)A GaAs surface and 0.17 μm along [21 ] direction on the (111)B GaAs surface during MBE growth. These diffusion lengths seem to be smaller than those previously observed, which is probably due to a large V/III ratio in the region of the substrate close to the mask edge.     

Crystal growth of mixed AlN–SiC bulk crystals

Bulk AlN–SiC mixed single crystals are prepared by sublimation growth employing pure AlN or mixed AlN–SiC sources and 6H-SiC seed crystals. As the growth temperature is increased from 1900 to 2050 °C, using seeds with different off-axis orientations, inclined up to 42° from the basal plane toward the (0 1 –1 0)-plane, or using different source materials, crystals with different Si/C contents are obtained. Dependent on the Si and/or C content, crystal coloration changes from yellowish to greenish to blackish. Modification in crystals’ coloration and corresponding changes in below band-gap optical absorption and cathodoluminescence spectra are discussed.     

Growth of boron nitride films on w‐AlN (0001), 4° off‐cut 4H‐SiC (0001), W (110) and Cr (110) substrates by Chemical Vapor Deposition

Boron Nitride is a promising group 13–group 15 compound material that exhibits various interesting properties like wide band gap, chemical stability, attractive mechanical properties and other. The growth behavior of this material has not been investigated in sufficient details to tailor properties of the resulting films. In this work we present the results on the growth of turbostratic boron nitride (t‐BN) thin films at a relatively high growth rate of 3 μm/h with the aim to investigate the potential use of boron trichloride in combination with ammonia as precursors for growth. Deposition experiments were conducted in a vertical cold wall high temperature chemical vapor deposition reactor in the temperature range 1000°C–1700°C depending on the substrate used. Templates of w‐AlN (0001), 4° off‐cut 4H‐SiC (0001), Cr (110) and W (110) were employed as substrates for the BN growth. As‐grown BN layers were characterized by Scanning Electron Microscopy, X‐Ray Diffraction, Electron Diffraction and Raman Spectroscopy. The results indicate that temperature and N/B ratio have a great influence on the crystallinity of the deposited films. For AlN and SiC substrates, a temperature of 1600°C and N/B ratio in range between 3 and 7.5 were identified as the best parameters for the growth of a 2 μm thick t‐BN layer with a spacing between basal planes of about 3.36 Å compare to the 3.33 Å spacing between basal planes of hexagonal or rhombohedral BN (h‐BN or r‐BN). For Cr and W substrates which have a lower mismatch with h‐BN (1 and 8.8 %), layers of t‐BN were deposited at much lower temperature (1000°C–1150°C) with a spacing between basal planes of 3.5 Å and morphology similar to that observed on SiC substrates. We obtained t‐BN layers with in plane strong disorder but out of plane orientation (c‐axis normal to the surface).     

Understanding supersaturation‐dependent crystal growth of L‐alanine in aqueous solution

The dependence of crystal growth rate of L‐alanine on solution supersaturation was investigated by combining experiments and molecular dynamics (MD) simulations. The experimental results show that lower supersaturated solution yields more elongated L‐alanine crystals along the c‐axis, i.e., the aspect ratio (c/b) of the crystal decreases with the increase of solution supersaturation, which is due to the higher supersaturation inducing a rise in the relative growth rate between the main side surface (the (120) surface) and the main end surface (the (011) surface). MD simulations on the two surfaces in contact with different supersaturated solutions revealed that the solute molecules tend to be more efficiently attached to the (011) surface than to the (120) surface at both supersaturations studied, as the interaction between the solute molecules and the L‐alanine molecules in the first layer of the (011) surface is stronger than that of the (120) surface. However, higher supersaturation leads to larger relative interaction energy between the (120) and (011) surfaces, suggesting an increase in the relative growth rate of the two surfaces (R₍₁₂₀₎/R₍₀₁₁₎) with supersaturation, which is in agreement with the experimental results.     

The morphology of succinic acid crystals: The role of solvent interaction

Succinic acid crystals grown from aqueous solutions are platy with a (100) basal plane and side faces (111) and (011), while crystals grown from iso-propanol are needle-like with (100) and (010) planes. These habits are not predicted from PBC analyses. In this study, the role of solvent interaction is related to habit controlling factors in the screw dislocation mechanism. The solvent interaction with various faces of succinic acid crystals was determined with the aid of molecular mechanics calculations. The observed habits from water and from iso-propanol could be explained satisfactorily in a semi-quantitative way.     

Oxygen and silver diffusion into float glass

In the float glass process, molten glass is floated on a molten metallic tin bath, such that tin penetrates the glass surface. Consequently, the glass has distinctly two different faces; the tin-penetrated face (bottom face) and the opposite face (top face). In this paper, the effects of tin on oxygen and silver diffusion into the top and bottom faces of a soda–lime–silica float glass are reported. It was revealed that oxygen diffusion from the atmosphere into the bottom face at temperatures above glass transition temperature was extremely suppressed near the surface region of the glass. This was not observed for the top face. This effect was ascribed to chemical reactions between the diffused oxygen and Sn²⁺ near the surface of the glass. Silver diffusion was also influenced by the tin due to chemical reactions of Ag⁺ ions with Sn²⁺, leading to the precipitation of nanometer-sized Ag crystals. As a result, the coloration due to the surface plasmon resonance of the Ag crystals was significantly different between the top and bottom faces because of differences in the nucleation and growth processes associated with the Ag crystals.     

Reciprocal crystal and P.B.C.-vector method. Crystal growth of a-sulphur

The morphological lattice of α-sulphur (F ddd) has coordinates 1/8, 1/8, 0. The reciprocal crystal is a polyhedron with 15 faces and point symmetry 112. The arrangements of the polyhedra parallel to the crystal faces confirm that (100), (101), (010), (011), (111), (113), (001) are F-faces and (110), (112) S-faces according to Hartman and Perdok. Under consideration of the extinction rules of the morphological lattice (101) and (011) have to be regarded as S-faces. The size of the polyhedra faces is proportional to the interaction energy given by Hartman. It will be shown that the face area of the net planes, divided by the number of molecules per growth layer, represent a good approximation to the attachment energy calculated according to Hartman. The average deviation for α-sulphur is 3%, for olivine and SnJ₄ 8.5% and for anthracene 10.5%. The Wulff-plots correspond fully to the experimental observations.     

The growth of gallium arsenide films from a thin solution layer between substrates

The method of GaAs film growth from a solution between two substrates was considered. The calculated thickness as a function of growth temperature and distance between substrates was in a good agreement with experimental results. The investigation of the film roughness as a function of cooling rate, distance between substrates and their orientations was fulfilled. Electrical properties of the films as a function of substrate orientations in the interval (100)–(111)–(011) were demonstrated. The possibility of application of this method for the investigation of film doping as a function of temperature and growth rate was shown.     

Effect of orientation on the microstructure of nickel‐based crystalline superalloys

The effect of crystal orientation on the microstructure of a nickel‐based crystalline superalloys during directional solidification was explored. Differently oriented crystals with [001] and [011] orientations were fabricated with seeding technique. The results showed that primary dendrite arm spacings decreased simultaneously with the increase of misroientation. The primary dendrites arrange in lines in [011] single crystal. For [001] oriented crystals, the size of γ′ phase increased with the increasing of misorientation. However, it was observed that the size of γ′ decreased with large misorientation for [011] orientated growth. Meanwhile, more γ′ in [011] crystals tended to be triangular. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rhombohedral epitaxy of cubic SiGe on trigonal c-plane sapphire

Highly [1 1 1]-oriented rhombohedral hetero-structure epitaxy of cubic SiGe semiconductor on trigonal c-plane sapphire was achieved and characterized with two new advanced X-ray diffraction methods to control the formation of primary-twin crystals. The formation of twin crystals on (1 1 1) plane was controlled with growth parameters such that the volume percentage of primary-twin crystal was reduced from 40% to 0.3% compared to the majority single crystal. The control of stacking faults can yield single-crystalline semiconductors without defects or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. In this study, about 94% of all epitaxial layers were fabricated in a single-crystalline phase. We propose the temperature-dependent alignment model of energetically favored majority single-crystalline SiGe layer on c-plane sapphire. This study shows that nearly single-crystalline cubic semiconductors can be grown in the [1 1 1] orientation on the basal (0 0 0 1) planes of selected trigonal crystal substrates.     

Zur plastischen Verformung von Antimoneinkristallen im Druckversuch bei Raumtemperatur

The plastic deformation of antimony single crystals dynamically tested in compression at room temperature has been investigated. As macroscopic deformation mechanisms twinning, dislocation slip, and kinking have been observed. The critical resolved shear stress for basal slip and twinning was measured and the orientation dependence of the deformation mode was explained. It is shown that basal slip dominates compared to rhombohedral slip.     

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH₄)₂C₂O₄ · H₂O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.     

Kinetic investigations within the transition region from polyhedral to skeletal growth mode (I). Growth kinetics of the basal face of zinc single crystals under diffusion conditions

The effect of diffusion in the vapour phase on the kinetics of growth of zinc single crystals in the presence of argon has been studied. The shift of the basal face in normal direction as a function of the time has been measured at constant temperature and supersaturation and argon pressures varying within the range 5–250 Torr as well as in vacuum 1 × 10⁻⁶ Torr. It has been established that the crystal size R changes with the time t following a linear and a parabolic law in the kinetic and the diffusion regimes, respectively. The kinetic critical size R_k for the transition from a kinetic to a diffusion regime has been experimentally obtained. A relatively good agreement is found between the experimentally established and theoretically calculated values of the critical size. The problems related to the transition of the basal faces of zinc single crystals from a kinetic to a diffusion growth mode is discussed.     

Changes of the Surface Structure of Quartz Monocrystals as a Result of the Influence of Sodium Salts at High Temperature

As a supplementary work to the previously described formation of superstructures on quartz monocrystal surfaces, which take place if the crystals interact with simple gases, this article deals with structural changes resulting from the influence of sodium salts on the rhombohedral face (1011) and the prism face (1010) of quartz. In addition to alredy known phenomena a new superstructure arises, when NaNO₃ is influencing the prism face. The investigation method is the Reflection High Energy Electron Diffraction (RHEED)     

On the morphology of cadmium sulphide epitaxial layers on germanium,observation of six-pointed star optic figures and their explanation

The morphology was investigated of the cadmium sulphide epitaxial layers, grown on germanium substrate with orientation (111), in a quasi-closed “sandwich” system in hydrogen atmosphere. Regular hexagonal compound pyramids were observed, tipped and truncated, with a plane slope abruptly changed. With the orientation of the layer (000)_CdS ∥ (111)_Ge, the orientations of the pyramid planes were determined to be of the type (011 3), (011 4) and (011 5). Regular six-pointed optic stars were observed in those pyramids. Explanation of the stars observed is presented. A method is proposed for the determination of the cadmium sulphide layer thickness, using the data from the pyramids and the optic stars. The same stars were obtained with the elaborated models as well.     

On the origin of the (1216)-orientation in epitaxial AIN layers on R-plane sapphire

Epitaxial AIN grown by MOCVD on (011 2)Al₂O₃ substrates usually is (12 10)-oriented. Here for the first time (12 16)AIN was found in MOCVD layers. This AIN orientation is known from other growth techniques, its origin is generally not understood. An explanation is given based on twinning in the early growth stages which is also applicable to the growth of (12 16)ZnO on (011 2)Al₂O₃.     

The Influence of Interstitials and Growth Conditions on the X-Ray Colorability of Synthetic Quartz Crystals

The saturation colorability of quartz crystals depends not only on the contamination of the material but also on the regarded growth sector. But even in the same sector the colorability varies locally. Investigations of crystals with induced growth striations and defined local growth rate showed that the dependence of the colorability on the growth conditions is very complex. The growth rate to colorability characteristics may have positive or negative slopes regarding e.g. —x-or z-sections. Optical investigations of —x-sections prove that under certain circumstances light and/or dark striations may occur or even uncolorable regions may be observed, althought the contamination is sure. We explain this by the interaction of the coloration centres with interstitials. That effect might be of importance for the evaluation of the impurity by means of the coloration of natural or synthetic quartz crystals.     

配合物晶体MnHg(SCN)4的晶形分析

配合物晶体MnHg(SCN)4中维系晶体结构的化学键是-Mn-NCS-配位键.从MnHg(SCN)4晶体中配位键的分布特点出发,对属于点群4的单形四方四面体、四方柱和平行双面进行分析,确定晶形中不能出现平行双面{001}、四方柱{110},可以出现的单形为四方四面体{101}和{011}及四方柱{100},而且四方四面体{101}和{011}单形最发育.由结构分析得出的晶形特点与实际晶体晶形特点相符.     

Growth kinetics of zinc(tris)thiourea sulphate (ZTS) crystals

Growth kinetics of zinc (tris) thiourea sulphate (ZTS) crystals investigated as a function of supersaturation is reported in this communication. Crystal growth rates were investigated normal to the (100), (010) and (001) faces under growth conditions employed for bulk crystal growth. The growth rates normal to (010) and (100) were found to follow the continuous growth model (R_G = Cσ) with respect to the supersaturation whereas the growth rates normal to (001) was found to satisfy birth and spread (B+S) model (R_G = Aσ^5/6 exp(‐B/σ)). The growth rates observed normal to the studied face are in agreement with the growth mechanism predicted from the estimated α (Jackson) factor. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observation of optical inhomogeneities in flux grown KTP crystals

Optical inhomogeneities in potassium titanyl phosphate crystals grown from different fluxes have been investigated. In the crystals grown from a flux which contains tungsten, striations parallel to the {011} faces were observed. The main reason for forming striations is the change in tungsten concentration with change in growth rate. In the case of a potassium phosphate flux, no striations were observed in the crystal which was grown at almost the same temperature and stirring conditions as for the tungstate flux. We can conclude that the phosphate flux is more suitable for the growth of optically good crystals for KTP as laser harmonic converters.