The magnetic and structure properties of room-temperature ferromagnetic semiconductor (Ga,Mn)N

Diluted magnetic semiconductor (Ga,Mn)N were prepared by the implantation of Mn ions into GaN/Al2O3 substrate. Clear X-ray diffraction peak from (Ga,Mn)N is observed. It indicates that the solid solution (Ga,Mn)N phase was formed with the same lattice structure as GaN and different lattice constant. Magnetic hysteresis-loops of the (Ga,Mn)N were obtained at room temperature (293 K) with the coercivity of about 2496.97 A m(-1). (C) 2003 Elsevier B.V. All rights reserved.

Ga1-xMnxSb grown on GaSb substrate by liquid phase epitaxy

The Gal(1-x)Mn(x)Sb epilayer was prepared on the n-type GaSb substrate by liquid phase epitaxy. The structure of the Gal(1-x)Mn(x)Sb epilayer was analyzed by double-crystal X-ray diffraction. From the difference of the lattice constant between the GaSb substrate and the Ga1-xMnxSb epilayer, the Mn content in the Ga1-xMnxSb epilayer were calculated as x = 0.016. The elemental composition of Ga1-xMnxSb epilayer was analyzed by energy dispersive spectrometer. The carrier concentration was obtained by Hall measurement. The hole concentration in the Ga1-xMnxSb epilayer is 4.06 x 10(19)cm(-3). It indicates that most of the Mn atoms in Ga1-xMnxSb take the site of Ga, and play a role of acceptors. The current-voltage curve of the Ga1-xMnxSb/GaSb heterostructure was measured, and the rectifying effect is obvious. (C) 2003 Elsevier B.V. All rights reserved.

InAs0.3Sb0.7 films grown on (100) GaSb substrates with a buffer layer by liquid-phase epitaxy

The growth of InAsxSb1-x films on (100) GaSb substrates by liquid-phase epitaxy (LPE) has been investigated and epitaxial InAs0.3Sb0.7 films with InAs0.9Sb0.09 buffer layers have been successfully obtained. The low X-ray rocking curve FHWM values of InAs0.3Sb0.7 layer shows the high quality of crystal-orientation structure. Hall measurements show that the highest electron mobility in the samples obtained is 2.9 x 10(4) cm(2) V-1 s(-1) and the carrier density is 2.78 x 10(16)cm(-3) at room temperature (RT). The In As0.3Sb0.7 films grown on (10 0) GaSb substrates exhibit excellent optical performance with a cut-off wavelength of 12 mu m. (c) 2007 Elsevier B.V. All rights reserved.

Concentration distribution in crystallization from solution under microgravity

Concentration distribution in crystallization from solution under microgravity is numerically studied. A quasi-steady state growth and dissolution in a 2D rectangular enclosure filled with sodium chlorate (NaClO3) aqueous solution, in which one wall is the growth surface of the crystal and the opposite one is the dissolution surface, is considered. The solute transport process at the growth surface is described by the diffusion-reaction theory with finite interface kinetics coefficient. The results show that the concentration at the growth surface is supersaturated and the supersaturation distribution is of non-uniformity, i.e. the supersaturation in a region facing an incoming flow is high. On the other hand, the non-uniformity of supersaturation at the growth surface is closely related to the gravity level even under microgravity, it exponentially increases as the thermal Rayleigh number on behalf of the gravity level rises.

Influence of liquid bridge volume on the onset of oscillation in floating-zone convection .1. Experiments

The onset of oscillation in the floating zone convection driven by the gradient of surface tension was experimentally studied, and discussions were concentrated on the influence of liquid bridge volume on the onset of oscillation. Distributions of critical applied temperature difference and frequency depending on the volume of the liquid bridge were obtained, and there was a gap range of liquid volume which separated the curve of marginal stability into two parts for fixed rod diameter and aspect ratio. The results imply that the volume of the liquid bridge is a sensitive critical parameter for the onset of oscillation. The implication on the instability is also discussed in the present paper.

Influence of liquid bridge volume on the onset of oscillation in floating-zone convection .2. Numerical-simulation

The onset of oscillation in the floating zone convection driven by the gradient of surface tension was studied numerically for an unsteady and two-dimensional model, and studies were concentrated on the influence of liquid bridge volume on the onset of oscillation in comparison with the experimental results in the Paper I. The numerical results agree with the experimental ones presented in the previous paper, in which the distributions of critical applied temperature difference depending on the volume of liquid bridge and a gap range of liquid volume in marginal stability curve were obtained.

Coupling of melting-solidification phase-change convection with floating-zone convection under microgravity

A finite element algorithm is used to analyze the process of floating zone crystal growth under microgravity. The effect of phase change convection coupled with surface tension convection is considered. The results show that the rate of crystal growth is very important. The single-crystal-melt interface is steeper than the feed-melt interface during the process of crystal growth. When the rate exceeds a critical value, the Marangoni vortex near the feed-melt interface will become so large that a secondary vortex will exist.

微小晶体生长过程的光学诊断实验研究

将光学干涉技术与显微技术相结合，应用计算机技术、图像处理技术发展形成一种实时细观诊断的实验方法——光学细观干涉诊断技术；实时观测了KCl晶体在容积为3mm * 3mm * 4.5mm的生长池内的结晶过程，得到了该过程的晶体的表面形貌、生长速率、以及晶体生长尺寸与时间、浓度与时间的定量的关系，观测到由重力引起的浮力对流现象，它直接影响晶体的生长。实验表明重力对晶体生长形态有很大的影响；生长速率与浓度存在很大的依赖关系。

气相扩散速率对溶菌酶晶体生长的影响

为研究气相扩散速率对溶菌酶晶体生长的影响,特设计了一种可方便调节气相扩散速率的晶体生长样品池,并用动态光散射法对不同气相扩散速率下晶体生长过程进行了研究.实验结果表明,随着气相扩散速率的增加,晶体生长过程中的成核阶段缩短.气相扩散速率通过影响溶菌酶溶液形成过饱和的速率来影响生长出的晶体的数量和大小.

Oscillatory Instability of Rayleigh-Marangoni-Benard Convection in Two-Layer System

The convective instabilities in two or more superposed layers heated from below were studied extensively by many scientists due to several interfacial phenomena in nature and crystal growth application. Most works of them were performed mainly on the instability behaviors induced only by buoyancy force, especially on the oscillatory behavior at onset of convection (see Gershuni et. Al.(1982), Renardy et. Al. (1985,2000), Rasenat et. Al. (1989), and Colinet et. Al.(1994)) . But the unstable situations of multi-layer liquid convection will become more complicated and interesting while considering at the same time the buoyancy effect combined with thermocapillary effect. This is the case in the gravity reduced field or thin liquid layer where the thermocapillary effect is as important as buoyancy effect. The objective of this study was to investigate theoretically the interaction between Rayleigh-Bénard instability and pure Marangoni instability in a two-layer system, and more attention focus on the oscillatory instability both at the onset of convection and with increasing supercriticality. Oscillatory behavious of Rayleigh-Marangoni-Bénard convective instability (R-M-B instability) and flow patterns are presented in the two-layer system of Silicon Oil (10cSt) over Fluorinert (FC70) for a larger various range of two-layer depth ratios (Hr=Hupper/Hdown) from 0.2 to 5.0. Both linear instability analysis and 2D numerical simulation (A=L/H=10) show that the instability of the system depends strongly on the depth ratio of two-layer liquids. The oscillatory instability regime at the onset of R-M-B convection are found theoretically in different regions of layer thickness ratio for different two-layer depth H=12,6,4,3mm. The neutral stability curve of the system displaces to right while we consider the Marangoni effect at the interface in comparison with the Rayleigh-Bénard instability of the system without the Marangoni effect (Ma=0). The numerical results show different regimes of the developing of convection in the two-layer system for different thickness ratios and some differences at the onset of pure Marangoni convection and the onset of Rayleigh-Bénard convections in two-layer liquids. Both traveling wave and standing wave were detected in the oscillatory instability regime due to the competition between Rayleigh-Bénard instability and Marangoni effect. The mechanism of the standing wave formation in the system is presented numerically in this paper. The oscillating standing wave results in the competition of the intermediate Marangoni cell and the Rayleigh convective rolls. In the two-layer system of 47v2 silicone oil over water, a transition form the steady instability to the oscillatory instability of the Rayleigh-Marangoni-Bénard Convection was found numerically above the onset of convection for ε=0.9 and Hr=0.5. We propose that this oscillatory mechanism is possible to explain the experimental observation of Degen et. Al.(1998). Experimental work in comparison with our theoretical findings on the two-layer Rayleigh-Marangoni-Bénard convection with thinner depth for H<6mm will be carried out in the near future, and more attention will be paid to new oscillatory instability regimes possible in the influence of thermocapillary effects on the competition of two-layer liquids

溶菌酶晶体生长过程中的扩散传质问题

采用Mach-Zehnder干涉测量系统与图象处理系统相结合实时观测溶菌酶蛋白质晶体生长过程中的流体动力学现象,对汽相扩散法溶菌酶蛋白质晶体生长过程进行了研究,观测到溶菌酶晶体生长时晶体周围存在的干涉条纹.分析了晶体生长时的重力沉降效应和溶质扩散过程.实验结果表明,该生长过程中的流体物理特征直接影响了生长晶体的晶面.根据实验结果,给出对蛋白质晶体生长过程流体物理现象的讨论。 

Direct observation of adsorption sites of protein impurities and their effects on step advancement of protein crystals

We measured noninvasively step velocities of elementary two-dimensional (2D) islands on {110} faces of tetragonal lysozyme crystals, under various supersaturations, by laser confocal microscopy combined with differential interference contrast microscopy. We studied the correlation between the effects of protein impurities on the growth of elementary steps and their adsorption sites on a crystal surface, using three kinds of proteins: fluorescent-labeled lysozyme (F-lysozyme), covalently bonded dimers of lysozyme (dimer), and a 18 kDa polypeptide (18 kDa). These three protein impurities suppressed the advancement of the steps. However, they exhibited different supersaturation dependencies of the suppression of the step velocities. To clarify the cause of this difference, we observed in situ the adsorption sites of individual molecules of F-lysozyme and fluorescent-labeled dimer (F-dimer) on the crystal surface by single-molecule visualization. We found that F-lysozyme adsorbed preferentially on steps (i.e., kinks), whereas F-dimer adsorbed randomly on terraces. Taking into account the different adsorption sites of F-lysozyme and F-dimer, we could successfully explain the different effects of the impurities on the step velocities. These observations strongly suggest that 18 kDa also adsorbs randomly on terraces. Seikagaku lysozyme exhibited a complex effect that could not alone be explained by the two major impurities (dimer and 18 kDa) present in Seikagaku lysozyme, indicating that trace amounts of other impurities significantly affect the step advancement.

硅生长过程中尖形磁场对流场及提拉速率的影响

通过使用基于非正交网格有限体积法的FLUTRAPP(fluid flow and transport phenomena pro-gram)程序模拟了工业8 in单晶硅提拉法生长过程.数值模拟结果表明,流场及提拉速率在单晶硅生长过程中具有振荡特性,提拉速率的振荡周期大约为2 min.尖形磁场的引入能够抑制坩埚中熔体流动的振荡,减小提拉速率的振幅,从而有利于提高所生长单晶的质量.

Wire array photovoltaics

Over the past five years, the cost of solar panels has dropped drastically and, in concert, the number of installed modules has risen exponentially. However, solar electricity is still more than twice as expensive as electricity from a natural gas plant. Fortunately, wire array solar cells have emerged as a promising technology for further lowering the cost of solar.

Si wire array solar cells are formed with a unique, low cost growth method and use 100 times less material than conventional Si cells. The wires can be embedded in a transparent, flexible polymer to create a free-standing array that can be rolled up for easy installation in a variety of form factors. Furthermore, by incorporating multijunctions into the wire morphology, higher efficiencies can be achieved while taking advantage of the unique defect relaxation pathways afforded by the 3D wire geometry.

The work in this thesis shepherded Si wires from undoped arrays to flexible, functional large area devices and laid the groundwork for multijunction wire array cells. Fabrication techniques were developed to turn intrinsic Si wires into full p-n junctions and the wires were passivated with a-Si:H and a-SiNx:H. Single wire devices yielded open circuit voltages of 600 mV and efficiencies of 9%. The arrays were then embedded in a polymer and contacted with a transparent, flexible, Ni nanoparticle and Ag nanowire top contact. The contact connected >99% of the wires in parallel and yielded flexible, substrate free solar cells featuring hundreds of thousands of wires.

Building on the success of the Si wire arrays, GaP was epitaxially grown on the material to create heterostructures for photoelectrochemistry. These cells were limited by low absorption in the GaP due to its indirect bandgap, and poor current collection due to a diffusion length of only 80 nm. However, GaAsP on SiGe offers a superior combination of materials, and wire architectures based on these semiconductors were investigated for multijunction arrays. These devices offer potential efficiencies of 34%, as demonstrated through an analytical model and optoelectronic simulations. SiGe and Ge wires were fabricated via chemical-vapor deposition and reactive ion etching. GaAs was then grown on these substrates at the National Renewable Energy Lab and yielded ns lifetime components, as required for achieving high efficiency devices.

用半导体激光器对 Yb3+:LYSO 晶体的高效率激光特性的研究

本文报导了采用半导体激光器泵浦的高效连续可调谐Yb:LYSO激光器的输出特性。LYSO晶体同时具有LSO晶体良好的激光性能和YSO晶体易于生长且成本低廉的优点，实验中我们采用5at%掺杂的Yb:LYSO晶体进行研究，获得了最大输出功率2.84W、输出波长1085nm、光-光转换效率54.5%的高效输出。并且得到了1030-1111nm，一共81nm的波长调谐范围，这是目前我们所知道的从Yb:LYSO激光器获得的最宽的调谐输出。