高温高压生长宝石级金刚石单晶的表面特征研究

本文利用高温高压温度梯度法,NiMnCo合金作为触媒,分别采用籽晶{100}和{111}作为生长面,合成了Ib型宝石级金刚石单晶,对其表面特征进行了分析和讨论.结果发现,宝石级金刚石单晶的表面特征不具有唯一性,多数情况下,晶体{111}面明显较{100}面平整,而且{100}面生长台阶的棱角不清晰,经常会出现经触媒融融过的痕迹,并且这种现象的出现跟籽晶生长面不同和合成温度条件高低无关;{111}面有时也会出现明显的生长台阶,棱角清晰,并且形状较为规则.宝石级金刚石晶体表面特征的不唯一性说明晶体表面特征对生长条件稳定性有更高的要求.     

Anisotropy of the electro-optic effect in magnesium-doped LiNbO3 crystals

Specific features of constructing indicatory surfaces of the electro-optic effect (EOE) are described. The generalized case for the symmetry class 3m and all three possible indicatory surfaces under orthogonal experimental conditions, when the directions of light propagation and electric field are orthogonal, is considered. The EOE surfaces are constructed for magnesium-doped lithium niobate crystals. The specific features of anisotropy of these surfaces are discussed and their extreme values and corresponding angular coordinates are found. To construct the indicatory surfaces, all absolute coefficients of the linear electro-optic effect are determined by the interferometric method. The difference in the electro-optic coefficients of pure and magnesiumdoped crystals does not exceed 10%. An advantage of doped crystals is their high durability to high-power laser radiation.

     

Epitaxial growth of GaAs and GaN by gas source molecular beam epitaxy using organic group V compounds

GaAs and GaN epilayers were grown on GaAs substrates by gas source molecular beam epitaxy technique using triethylarsine (TEAs) and diethylarsine (DEAsH) as As sources, and dimethylhydrazine (DMHy) as an N source. It was found that GaAs grows layer by layer even when organic arsine molecular sources are used. Cubic GaN was found to grow epitaxially on sufficiently nitrided surfaces of GaAs (001) substrates, in contrast with the growth of hexagonal GaN on GaAs (111) surfaces. It was also found that nitridation of GaAs surfaces does not occur when DEAsH and DMHy beams are supplied onto the GaAs substrates, simultaneously. Thus, GaN/GaAs multilayers were obtained only by intermittent supply of a DEAsH beam.     

The aging of silicate glass surfaces in humid air

Slicate glass surfaces were observed over several weeks in normally humid laboratory air by atomic force microscopy. Auger spectroscopy and lateral force microscopy measurements were also made. Samples in the study include; vitreous quartz, bulk insulation glass, bulk and fibrous textile e-glass, and bulk container glass. Various features developed on these surfaces are consistent with patterns seen in crystal growth from supersaturated solution. Auger spectroscopy reveals the presence of chemically bound carbon and supports the hypothesis that these crystals are alkali and alkali earth carbonate species. The presence of these crystals is expected to affect the bonding of a coating to silicate surfaces.     

NbB2（0001）表面性质的第一性原理研究

应用密度泛函理论的第一性原理的方法分析了两种不同终端的NbB2(0001)表面的几何结构和电子结构。结果表明:两种不同终端的(0001)表面结构弛豫主要发生在前三层,并且硼终端的表面弛豫程度小于铌终端表面的弛豫。表面能分析结果表明,终止于硼终端的(0001)表面结构在更宽的范围内具有较低的表面能,即硼终端的(0001)表面比铌终端的表面更稳定。进一步分析NbB2(0001)两种终端表面的电子结构表明:在金属铌和硼之间发生了电子转移,加强了化学键的相互作用,导致第一间层向内弛豫。对于铌终端的表面第一层铌转移到第二层的电子数比硼终端表面第二层铌转移到第一层的电子数多,这是导致铌终端表面弛豫程度大于硼终端表面的主要原因。     

GaAs initial growth on InAs(001) vicinal surfaces observed by scanning tunneling microscopy

GaAs initial growth on InAs surfaces misoriented by 2° toward the [110] and [1 0] directions was investigated by scanning tunneling microscopy (STM). In the STM images of both InAs vicinal surfaces after GaAs deposition, white lines running in the [1 0] direction, corresponding to the grown GaAs surface, were observed. Almost all of the lines were attached only to steps running in the [110] direction (B-type steps) on both InAs surfaces; that is, the lines were seldom attached to steps running in the [1 0] direction (A-type steps). These results indicate that the B-type steps are more favorable for the sticking of deposited Ga atoms than the A-type steps during GaAs initial growth on InAs vicinal surfaces.     

Near-electrode processes in lanthanum-gallium tantalate crystals

The near-electrode processes on the surfaces of the polar cuts of lanthanum-gallium tantalate crystals grown in different atmospheres were investigated. The temperature dependences of short-circuit currents in the temperature range 20–700°C were measured and phase analysis of the sample surfaces after the temperature tests were performed. It is shown that short-circuit currents arise on the surfaces of polar cuts with identical conducting coatings without preliminary polarization. These currents are caused by the generation of intrinsic emf as a result of the electrochemical reactions on opposite polar cut surfaces coming in contact with a conducting coating. It is established that the crystal growth atmosphere and the conducting coating material significantly affect the temperature dependences of short-circuit currents.     

晶体的超精密抛光

超光滑表面在现代科学技术中具有重要意义.超精密抛光技术是实现超光滑表面的主要方法.本文对超光滑表面的概念、影响超精密抛光质量的因素、几种超精密抛光方法及其所能达到的抛光效果、抛光效果的测量与评价方法等进行了介绍.同时描述了超精密抛光的发展阶段、现状和发展趋势.     

Magnitude and polarity of strain-induced fields in pseudomorphic In0.22Ga0.8As quantum well structures on (112) GaAs substrates

When pseudomorphic (In,Ga)As/(Al,Ga)As heterostructures are grown on certain surfaces of the general crystallographic planes of GaAs denoted by (11l), the strain in the structures induces an electric field because of the piezoelectric nature of the III-V semiconductors. We report the experimental determination of the direction and magnitude of the strain-induced electric field by photoluminescence spectroscopy on one of these substrate surfaces: the one for which l = 2. We confirm that for the two surfaces of the (112) GaAs substrate, the induced field is directed out of the substrate for the A surface and toward the substrate for the B surface.     

From C60 to negatively curved graphite

With the discovery of C₆₀ or Buckminsterfullerene a new kind of materials with important applications has emerged. Orginary graphite is composed of flat hexagonal layers. If pentagons are introduced, the graphite sheets start to curve in such a way that 12 pentagons are needed to close the structure and form fullerenes. Starting from the properties of 2D manifolds or surfaces, we have found that by introducing rings with more than six carbon atoms, periodic structures with the same topology as triply periodic minimal surfaces, we have found that by introducing rings with more than six carbon atoms, periodic structures with the same topology as triply periodic minimal surfacds can be constructed. The D, G, P, H and I-WP type surfaces have been obtained from graphite-like sheets. In terms of the Gaussian curvature K, ordinary and cylindrical graphite have K=O, Fullerenes have K>O and triply periodic surfaces decorated with graphite have K60. Geometric and physical properties of hypothetical periodic graphite foams will be discussed.     

Decoration of growth and dissolution steps on the surfaces of L-arginine phosphate monohydrate crystals

Observations of decoration of growth and dissolution steps on the {100} surfaces of non-linear optical L-arginine phosphate monohydrate (LAP) crystals during their withdrawal through an n-hexane layer placed above its supersaturated and undersaturated solutions are described. This is the first report of decoration of growth or dissolution steps on the surfaces of crystals at or near room temperature in a liquid medium by the crystallizing or dissolving material.     

Adsorption of proteins on glass surfaces and pertinent parameters for the immobilization of enzymes in the pores of inorganic carriers

The forces involved in the adsorption reactions between proteins and glass surfaces are primarily ionic amine-silanol bonding and hydrogen bonding. When protein solutions are exposed to porous glass surfaces, two rates of reaction are noted. The first appears to be dependent upon the relative number of amines on the protein surface and is very rapid. The second reaction is considerably slower than the first and is dependent upon the molecular weight of the protein. This second reaction, then, is governed by the ability of the protein to diffuse into the porous structure of the glass. The surface reaction of glass has been utilized to bind enzymes (biological catalysts) and other biologically active molecules. Enzymes, a precious material, can be immobilized on inorganic oxide surfaces and effectively employed, economically, in a manner similar to that of inorganic catalysts. The pore morphology of the carrier utilized to immobilize the enzyme offers a protected environment for extending the use of this unstable molecule.     

六方Fe2Ge合金块体及其(001)表面电子结构和磁性的第一性原理

采用基于密度泛函理论第一性原理的赝势平面波方法,计算了块体Fe₂Ge及其(001)表面的电子结构和磁性。考虑了两种类型的终端(001)表面:Ge(Ⅰ)-(001)表面和Ge(Ⅱ)-(001)表面。电子结构方面,不同类型的Fe₂Ge(001)表面都表现出金属特性,这与块体的金属性保持一致。通过计算它们的自旋极化率,得出Ge(Ⅰ)-(001)表面的自旋极化程度最高。磁性方面,在块体和Ge(Ⅱ)-(001)表面的Ge原子是铁磁自旋有序的,而在Ge(Ⅰ)-(001)表面第一层的Ge原子是亚铁磁自旋有序的。此外,Ge(Ⅱ)-(001)表面Ge原子的自旋磁矩优于块体中和Ge(Ⅰ)-(001)表面Ge原子的自旋磁矩。这些结果与Fe的d态和Ge的p态电子的杂化有关,本文中通过分析它们的态密度进行了讨论。     

Second harmonic generation optimization in thermally poled borophosphate glasses and characterization by XANES and XPS

Second harmonic generation (SHG) in poled glasses opens new opportunities in material research and device development for optics. SHG results that relate to thermally poled new borophosphate glasses have been analyzed. By a cycling poling–depoling process an optimization of the SHG response can be obtained. As the signal is localized near the surfaces in contact with the electrodes during poling, XPS and X-ray absorption near-edge spectroscopy (XANES) spectroscopies have been performed to characterize cathodic and anodic surfaces of these glasses before poling, and after poling or depoling treatments. Structural differences are observed by XANES at the O K-edge after poling on both surfaces. Moreover, an accumulation of Na⁺ mobile cations is evidenced on the cathodic surface by XPS spectroscopy confirming the migration of Na⁺ mobile cations after the glass has been submitted to high dc field. Finally, the XPS and XANES investigations of poled glasses evidences some breakage of phosphate chains in the glass network which occur during the poling treatment. Conversely, bridging bonds are partly restored after thermal depoling.     

KDP(KD*P)晶体结构研究进展

本文回顾了70多年来人们对KDP(KD*P)晶体结构的研究成果,尤其对近年来在晶体表面界面结构、氢键结构等方面所取得的重大突破进行了综述,并力图强调晶体性能对结构的依赖关系.KDP晶体的表面及界面结构对于晶体的生长及缺陷的形成具有重要影响.表面X射线衍射研究结果表明:水溶液中的KDP晶体表面上有四层特殊结构的水分子层,前两层水分子象冰层一样牢固地结合在晶体表面上,后两层相对弥散.     

On the internal nucleation of melting

Crystals of quartz have been superheated by some 450°C and crystals of albite by some 185°C above their respective melting points. In all cases, melting took place by the nucleation of liquid at the external surfaces (and internal boundaries as well in the case of albite). No evidence for the internal nucleation of liquid was found at any superheat for either material.The results of quartz indicate an exceptionallu large barrier to the internal nucleation of liquid. It is suggested that this large nucleation barrier is associated with the strain energy of forming a liquid nucleus within the crystalline phase.It is also indicated that the nucleation of liquid at the external surfaces of crystals at negligible superheats suggests that the free surfaces of liquids do not per se serve as preferred nucleating sites for crystallization — and that the crystal nucleation often observed at external surfaces or internal surfaces is in fact associated with condensed second-phase impurities.     

Generation mechanism of CuAu-I type ordered structures in InGaAs crystals grown on (110) InP substrates by molecular beam epitaxy

The generation mechanism for CuAu-I type ordered structures in InGaAs grown on (110) InP substrates by molecular beam epitaxy is discussed. On the basis of previous work together with considerations of the atomic arrangement of the ordered structure and surface reconstruction on the (110) plane, we propose four possible models for the ordering. Through precise evaluation of these models, two models are selected as the most probable ones: these involve formation of the ordered structures on surfaces dominated by two monolayer steps. This model have been experimentally proven by the analyses of electron diffraction patterns from different crystals grown on different growth surfaces.     

Radial segregation due to weak convection in a floating zone

The influence of weak convection, caused by surface tension forces, on radial dopant segregation occurring in crystals grown under microgravity conditions is studied numerically. The geometry considered corresponds to a floating-zone configuration with partially coated melt surfaces consisting of small evenly distributed spots of free surfaces. In order to distinguish dopant distribution due to weak convection clearly from distribution due to diffusion the spots only cover one quarter of the periphery. Thus, surface tension-driven convection is allowed only over one quarter of the floating-zone configuration resulting in an asymmetric dopant distribution. The percentage of free surfaces present is varied in order to alter the Marangoni flow rates. The maximum dopant concentration due to radial segregation is plotted as a function of a certain convection level. The results of the present numerical study are supposed to be used to design corresponding space experiments launched at the end of the year 2000.     

In situ surface passivation of III–V semiconductors in MOVPE by amorphous As and P layers

A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.