We formulate the anchoring problem for discrete-state lattice models. Anchoring is the selection of a bulk equilibrium state from a degenerate set of equivalent equilibrium states in semi-infinite samples in contact with a substrate, a phenomenon widely discussed in the context of liquid crystalline displays. As a concrete example we consider this problem for the three-state Potts model employing two different approximations, viz., a layered mean-field approximation and a Bethe lattice approach. The anchoring behaviour of the model is shown to be completely determined by the symmetry properties of the Hamiltonian. 相似文献
The connection between the way of development and appearance of mesa structures and typical hillocks developing during anisotropic etching of monocrystalline silicon in 5 M KOH saturated with isopropanol has been studied both theoretically and experimentally. A simple geometrical model of mesa formation was presented. Then, the process of hillock growth in result of mesa transformation caused by etch mask underetching was analyzed. At the second part of the paper, the model of hillocks formation was verified experimentally. For this purpose, a series of experiments with etching of mini-mesas through the masks with various patterns in the conditions favoring hillock formation was carried out. It was shown that at the final stage of the etching process the mesas transform into hillocks, bounded by the planes close to {1 1 1}. Probably at the first stage of hillocks formation, mini-mesas develop. Such stable mini-mesas, produced in the presence of random micro-masks, may transform into typical hillocks in effect of successive releasing of {1 1 1} mini-faces. It seems that the process of hillock formation is similar to mesa etching.
The shapes of hillocks produced on the substrates with different from (0 0 1) crystallographic orientations have been also analyzed. The similarities of the hillocks and intentionally prepared mesas were underlined. It was stated that the morphologies of hillocks are strictly connected with crystallographic orientation of etched substrate. Different shapes of hillocks developing on the substrates with different crystallographic orientations, reflect the arrangement and inclination of {1 1 1} planes on considered substrate. 相似文献
A method is derived for precise sample positioning with a four circle diffractometer. The sample can be oriented either with respect to a crystallographic plane or with respect to the sample surface with an accuracy of about 0.001°. The miscut angles can be easily deduced with an accuracy of a few 1/1000°. 相似文献
Silicon sheets from powder (SSP) ribbons have been prepared by modified SSP technique using electronic-grade (9N purity) silicon powder. The surface morphology, crystallographic quality, composition and electric properties of the SSP ribbons were investigated by surface profiler, X-ray diffraction (XRD), scanning electron microscopy (SEM), metallurgical microscope, Auger electron spectroscopy (AES) and four-point probe apparatus, respectively. The results show that the SSP ribbon made from electronic-grade silicon powder is a suitable candidate for the substrates of crystalline silicon thin film (CSiTF) solar cells, which could meet the primary requirements of CSiTF solar cell process on the substrates, including surface smoothness, crystallographic quality, purity and electric conductivity, etc. 相似文献
After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 1014 cm−3 have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.
Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential. 相似文献
A set of 25 low-molecular-weight substrates for protein tyrosine phosphatase PTP1 has been investigated by comparative molecular field analysis (CoMFA). The quality of the model was assessed by cross-validations, predictions for a test set of substrates, bootstrapping, randomization of biological data, grid characteristics tests, and comparison with the X-ray-determined binding site of a closely related enzyme. The CoMFA study provides new insight into the steric and electrostatic factors influencing binding around the active site in protein tyrosine phosphatase and complement existing information available from X-ray data. 相似文献
In this article, an alternative method for site-specific growth of In2O3 nanorod arrays, which relies on the vapor–liquid–solid growth mechanism, is demonstrated using Cu–Sn (5 at% Sn) alloy as substrate. By annealing Cu–Sn alloy slightly below the solidus line, grain-boundary triple junctions can be wetted preferentially. As a result, the catalyzing Cu droplets will be present at the sites of grain-boundary triple junctions, which will control the growth of In2O3 nanorods at defined locations. This growth technique provides a cost-effective and simple approach to fabricate ordered nanorod arrays with the sites controlled, which may benefit nanorod device applications. 相似文献
The growth of ZnO single crystals and crystalline films by solvothermal techniques is reviewed. Largest ZnO crystals of 3 inch in diameter are grown by a high-pressure medium-temperature hydrothermal process employing alkaline-metal mineralizer for solubility enhancement. Structural, thermal, optical and electrical properties, impurities and annealing effects as well as machining are discussed. Poly- and single-crystalline ZnO films are fabricated from aqueous and non-aqueous solutions on a variety of substrates like glass, (100) silicon, -Al2O3, Mg2AlO4, ScAlMgO4, ZnO and even some plastics at temperatures as low as 50 °C and ambient air conditions. Film thickness from a few nanometers up to some tens of micrometers is achieved. Lateral epitaxial overgrowth of thick ZnO films on Mg2AlO4 from aqueous solution at 90 °C was recently developed. The best crystallinity with a full-width half-maximum from the (0002) reflection of 26 arcsec has been obtained by liquid phase epitaxy employing alkaline-metal chlorides as solvent. Doping behavior (Cu, Ga, In, Ge) and the formation of solid solutions with MgO and CdO are reported. Photoluminescence and radioluminescence are discussed. 相似文献