Anisotropy of the Work of Adhesion for a Nemiatic Crystal on a Shaped Support

Under dynamic conditions, experimental data on contact angles of wetting for p-azoxyanizole on glass have been obtained. The contact angle of wetting is found to depend on support relief and the values of the contact angle are observed to change at the temperature of the liquid crystal phase transition. The value of energy required for turning a molecule of a nematic crystal by 90° on a shaped surface has been calculated.     

Plasmonic Features in the Absorption Spectrum of a Monodisperse Ensemble of Gold Nanoislands on Sapphire

Plasmonic features in the absorption spectrum of a monodisperse ensemble of gold nanoislands on a sapphire substrate are considered. An explanation of the long-wavelength and UV bands in the absorption spectrum of the sample is proposed. The long-wavelength feature is interpreted as a consequence of surface plasmon polariton excitation under coherent scattering from a regular lattice of gold particles on sapphire, and the short-wavelength feature is considered to be a plasmon resonance, localized on individual gold nanoparticles.     

Hillock formation observed in MOMBE of InGaAs grown on a patterned GaAs substrate

We observed hillock formation during metalorganic molecular beam epitaxy (MOMBE) of InGaAs on a mesa-grooved (100) GaAs substrate. Hillocks were formed under specific growth conditions and comprised mostly InAs. The distribution of hillocks formed in InGaAs MOMBE using trimethylindium (TMIn) and metal Ga depended strongly on the widths of mesa-grooves; the density decreased with decreasing width and hillocks were hardly observed on the ridges. The hillock density also varied, depending on the off-angle of the substrate from the (100) plane. This indicates that the observed anomalous distribution of InGaAs hillocks was caused by both the formation of facets and a vicinal tilted surface near the edge of mesa-grooves, due to the growth of a GaAs buffer layer on a patterned substrate.     

Molecular beam epitaxy (MBE) growth and structural properties of GaN and AlN on 3C-SiC(0 0 1) substrates

AlN and GaN was deposited by molecular beam epitaxy (MBE) on 3C-SiC(0 0 1) substrates on low-temperature (LT) GaN and AlN buffer layers. It is shown that not only GaN but also epitaxial AlN can be stabilized in the metastable zincblende phase. The zincblende AlN is only obtained on a zincblende LT-GaN buffer layer; on the other hand, AlN crystallizes in the wurtzite phase if it is grown directly on a 3C-SiC(0 0 1) substrate or on a LT-AlN buffer layer. The structural properties of the layers and in particular the orientation relationship of the wurtzite AlN on the 3C-SiC(0 0 1) were analyzed by conventional and high-resolution transmission electron microscopy.     

Determination of lateral block size and mosaicity of crystals using X‐ray diffraction from the edge of the sample

In this paper a novel lateral block size characterization method based on X‐ray diffractometry (XRD) is presented. The developed method based on scans of plans perpendicular to the surface visible from the edge of the sample and subconsequent numerical analysis based on Scherrer equation. In presented investigations as a reference sample bulk GaN substrate fabricated by AMMONO Ltd. was used. The GaN layers deposited on sapphire substrate were investigated as a case of study. Moreover, a method of analyzing the magnitude of the tilt and twist mosaicity based on the scans of rocking curves and reciprocal lattice maps (RLM) from the edge of sample is presented. As an example for this methodology highly mosaicited SiC crystal was used. Presented approach allows to directly determine the value of the angular deviation of mosaicity in a direction perpendicular and parallel to the sample surface.     

香花石形态所反映的一种可能的孪晶结构

香花石是我国发现的第一个新矿物,它的形态非常复杂.本文基于香花石形态上出现了左形与右形相聚的现象,对香花石形态进行了重新思考,认为同一单形的左形与右形不能相聚形成单晶体,只能形成孪晶,因此,对原香花石晶体图进行了一些修正,认为原香花石晶体图可能是一个孪晶图.这对深入认识晶体形态及晶体对称理论、澄清长期以来人们并没有足够重视的一些基本概念有重要意义.     

Electrocrystallization of silver: Growth kinetics of screw-dislocation-free (100) crystal faces

At given conditions, especially at higher supersaturation, the growth rate of a close packed, perfect crystal face depends on the formation rate of two-dimensional nuclei and on the propagation rate of the monoatomic layers. This multinuclear multilayer growth as well as the advancement rate of growth steps have been studied experimentally on electrocrystallization of silver. The advancement rate of mono- and polyatomic growth steps has been measured on screw dislocation-free (100) crystal faces. For low overvoltages a linear dependence of the rate on overvoltage has been found. A strong influence of the surface condition of the crystal face — “fresh” or “aged” on the step advancement rate has been established. It was also found that on a “fresh” surface mono- and polyatomic steps advance with the same rate. The average monoatomic step spacing of the polyatomic step has been determined. The kinetic constants of the step growth rate are established and a conclusion regarding the mechanism of electrolytic deposition of silver is drawn. The initial current—time curves were recorded on applying potentiostatic pulses on a perfect crystal face. The shape of these curves coincides very well with those theoretically calculated for the cases of multinuclear growth. On the basis of the theoretical dependences, one can determine from these curves the formation rate J of two-dimensional nuclei at a given overvoltage η since the rate of step advancement is known. A linear dependence of log J on 1/η has been established. The values of the pre-exponential term in Volmer's equation and the specific edge energy of the two-dimensional nucleus have been determined. The surface condition of the crystal face influences strongly also the process of two-dimensional nucleation.     

Modelling of the isothermal melt flow due to rotating magnetic fields in crystal growth

The use of a rotating magnetic field promises the feature of a contactless flow control in crystal growth especially for configurations where an increase of the material transport in a definite way is desired. This paper gives the comparison of numerically calculated and experimentally obtained results on the flow due to a rotating magnetic field as well as numerical results on the influence of the field parameters (frequency, amplitude) on the fluid flow in the melt.     

Crystal growth and transport rates of GeSe and GeTe in micro-gravity environment

Six vapor transport experiments on the systems GeSe-GeI₄ and GeTe-GeI₄ were performed on Skylab to determine the effects of micro-gravity on crystal growth and transport rates. Based on a direct comparison of crystals and transport data obtained on earth and in space, employing X-ray diffraction, microscopic and etching techniques, the results demonstrate a considerable improvement of the space grown crystals in terms of growth morphology and bulk perfection. The observation of greater mass transport rates than expected in micro-gravity for diffusion-controlled transport could indicate the existence of other transport modes in a reactive solid-gas phase system. The combined results show that the interference of gravity-driven convection with the transport process causes negative effects on crystal growth as observed on earth for otherwise identical conditions. This points to the unique environment of weightlessness for the observation of basic transport phenomena.     

New aspect of diffraction of a highly divergent characteristic X-ray beam

A new way of implementing the diffraction of a highly divergent characteristic X-ray beam has been developed. This method is based on the formation of a diffraction image by the X rays exiting particular (active) points on the crystal surface which lie on hyperbolas. There is a correspondence between the points on the crystal surface and the points in the diffraction image. Local distortions of the crystal structure lead to local deviations of the diffraction lines from proper hyperbolas. This method makes it possible to reveal the block structure of crystals, separate blocks, and estimate the degree of misorientation.     

Influence of reaction between silica crucible and graphite susceptor on impurities of multicrystalline silicon in a unidirectional solidification furnace

The influence of silica crucible reaction with graphite susceptor on carbon and oxygen impurities in multicrystalline silicon was studied by global numerical simulations. Results showed that the crucible reaction has a marked effect on carbon and oxygen impurities in the crystal. When the activity of carbon on the surface of the graphite susceptor increases, both oxygen and carbon impurities in the melt increase rapidly. Therefore, the production of high-purity multicrystalline silicon requires setting a free space between the silica crucible and the graphite susceptor or depositing a layer of SiC film on the surface of susceptor to prevent reaction between them.     

Growth and Characterization of GaP Substrates for Liquid Phase Epitaxy

GaP light-emitting diodes were prepared by a single LPE process on LEC and SSD substrates. Red LEDs with a maximal efficiency of 5% could be grown reproducibly on SSD substrates with grains. The effciency of the best LEDs on substrates grown by the conventional LEC method is essentially lower (0.5%) but it can be improved considerably by a modification of the growth conditions. The substrates were characterized by structural, chemical, electrical and optical measurements and the observed differences in the luminescence efficiency between the LEDs grown on LEC and SSD subtrates, respectively, were discussed under consideration of these investigations.     

Technological properties of CSK-1 crystallizer for material research in space

The crystallizer CSK-1 is based on a tubular furnace with five heating elements. The crystallizer operates in an automatic mode, i.e., the setting up of the temperature fields, setting of the sample position in the tube and of the rate and direction of their movement are controlled by a microprocessor running according to a program stored on a magnetic tape. The crystallizer is placed on the Soviet Orbital Laboratory “MIR”. Basic technological properties of the crystallizer were studied by means of an standard probe connected with a computer and of the special ARP device, respectively. The topic of the study was especially the creation of various types of axial temperature fields and of various temperature gradients, the rate of heating and spontaneous cooling of the furnace, the temperature stability, and so on.     

Quasi-two-dimensional crystalline clusters on a sphere: Method of topological description

The formation of a “quasicrystal” on a closed surface has been considered for the Thomson problem on the arrangement with the lowest energy of N Coulomb charges on a sphere. The stable and metastable states of the system of charges with the charge number N = 2–100 and the symmetry groups of the corresponding configurations have been determined. The structure and possible structural transitions between the system states are described in terms of the introduced notion of a closed quasi-two-dimensional triangular lattice with topological defects. The graph of lattice defects is defined. A method for classifying the system in terms of the charge and the arrangement of topological defects in the lattice is suggested and extended to the case of an arbitrary lattice. The use of the model is considered on various physical examples, in particular, on a closed hexagonal lattice with disclinations in fullerenes.     

A combination of oscillating slit and oscillating film techniques for the investigation of lattice defects

A combination of oscillating slit and oscillating film techniques is described. This X-ray topographical method allows reflections due to the same places on the crystal surface to be recorded first in form of a topogramme registrated on the oscillating film set in the parallel position to the crystal surface. Second on the stationary film set parallel to the crystal surface in the form of an interference line Kα₁ or Kß outgoing from the investigated area and registrated on the first topogramme at the fixed angular position of the crystal and slit and next, recorded separate on the oscillating film and on the stationary film set in the distance of 50 mm from the crystal (oscillation axis). As an example a serie of photographs corresponding to four types of pattern obtained in the case of a PbSnTe crystal with small angle boundaries are presented.     

Critical layer thickness of In0.82Ga0.18As/InP quantum wells

We present results on a study of strained In_0.82Ga_0.18As/InP quantum wells (QWs) grown by gas source MBE. From transmission electron microscopy, we find that the onset of dislocation creation occurs for thickness around 60 Å. Strain release is found to induce a dramatic effect on the carrier lifetime as shown by time-resolved photoluminescence technique: lifetimes values of 2 ns are measured on QWs with thickness of 18 and 40 Å, but drop to 60 ps on a 64 Å thick QW.     

Study of the crystal device for deflecting high-energy proton beams using synchrotron radiation diffraction

Currently, bent silicon single crystals are used at large accelerators to extract and collimate proton beams. A device for multiple deflection of a proton beam based on several bent silicon strips operating in the volume reflection mode has recently been developed. In this device, the bending of silicon strips successively located on the surface of a thick plate is implemented due to the internal stress induced by grooves mechanically formed on the crystal surface (Twyman effect). Topography based on angular scanning and synchrotron radiation was applied to measure the bending of individual deflector strips and the crystal as a whole. The measurement results are compared with the data obtained with a proton beam.     

Review of carbon nanotubes production by thermal chemical vapor deposition technique

We have reviewed carbon nanotubes (CNTs) production on a silicon wafer by thermal chemical vapor deposition (TCVD) using acetylene as a carbon source, cobalt as a catalyst and ammonia as a reactive gas. The DC-sputtering system was used to prepare cobalt thin films on Si substrates. Energy Dispersive X-ray (EDX) measurements were used to investigate the elemental composition of the Co nanocatalyst deposited on Si substrates. Atomic Force Microscopy (AFM) was used to characterize the surface topography of the Co nanocatalyst deposited on Si substrates. The as-grown CNTs were characterized under Field Emission Scanning Electron Microscopy (FESEM) to study the morphological properties of CNTs.     

Inline deposited thin-film silicon solar cells on imprinted foil using linear PECVD sources

The standard way to improve the light management of thin film solar cells is to introduce a light scattering structure, either on the front window or at the back reflector. Usually, growth conditions of TCO layers are adjusted to get random surface roughness on the front window. In this paper we present an alternative method, which can be applied both on the front window and at the back reflector. It involves imprinting a UV curable coating layer allowing full control on the texture (random or periodic) to fully optimise the light trapping. Light trapping is even more important for microcrystalline Si solar cells. We have fabricated thin film nip Si solar cells with sputtered Ag/ZnO back contacts on embossed barrier layers on steel foil. We show that the UV curable coating is well-suited as imprintable barrier layer between the steel foil and the active layers. For nip a-Si cells we can obtain light trapping, as measured by the short-circuit current, that is almost as good as that of nip a-Si cells made on Asahi U-type glass, covered with a Ag/ZnO back reflector. Furthermore, we show that dynamically processed a-Si nip cells on foil realised efficiencies of over 7%, which are only slightly less than for cells made in a UHV lab-scale cluster tool in static processing. Finally, a-Si/a-Si tandems and μc-Si/a-Si tandems have been fabricated. Initial efficiencies of around 8% on textured barrier layer on steel foil have been achieved.