空间晶体生长

 无论在陆地、海洋还是天空,地球上的物体,包括我们人类,一直在一个G₀决定的重力下存在着、发展着。人们似乎习惯了这样的环境,要想摆脱重力影响倒成了不可思议的事情.然而,一些科学工作者从高处跌落的瞬间“失重”现象中受到了启迪,开始思考如何在材料制备中利用近地空间的特殊环境,探索晶体生长研究的新途径.     

GaSb单晶空间生长

空间的微重力给晶体生长提供了一个消除自然对流、由纯扩散控制的生长环境,为提高晶体质量创造了条件,引起晶体生长研究人员的关注.中国科学院物理研究所和日本东京大学电子工程系合作,1992年在中国第14颗返回式卫星上成功地生长了一根φ6 mm×30 mm外形完整的GaSb单晶.对空间生长的晶体的研究显示：晶体在空间生长部分无Ⅰ类生长条纹,表明晶体生长时既无自然对流也没有Marangoni对流.位错密度测定表明,晶体在空间生长期间熔体未与坩埚器壁接触时生长的晶体位错密度接近于零,而熔体与坩埚器壁接触后位错密度迅速增高.详细叙述了该晶体的生长和研究,分析了微重力对晶体生长的影响,并对空间晶体生长的发展提出看法.     

Mn12-Ac磁性分子团簇单晶的热重-差热分析与结构转变

通过热重-差热分析(TG-DTA)，考察了Mn12-Ac磁性分子晶体从室温到270℃的热失重过程.结合x射线粉末衍射分析，认为在第一个失重阶段，即25—110℃，Mn12-Ac失去了处于团簇分子间隙的结晶乙酸和结晶水，同时失去了团簇分子中与4个Mn3+配位的4个H2O，Mn12-Ac单晶结构被破坏，但是团簇分子的基本结构依然存在；在第二个失重阶段，即180—230℃，Mn12-Ac转变为γ-Mn2O3，其中混有少量Mn3O4. 关键词： Mn12 分子团簇 热重-差热分析 x射线衍射     

Effects of interface kinetics and anisotropyon the stability of the growing crystal faceand dissolution face during crystallization from solution under microgravity

The stability of the shapes of the growing crystal face and dissolution face in a two-dimensional mathematical model of crystal growth from solution under microgravity is studied. Effects of the interface kinetics and anisotropy of crystallization and dissolution on the stability are also studied. It is proved that the stable shapes of crystal growth face and dissolution face do exist, which are of suitably shaped curves with their upper parts inclined backward properly no matter whether the interface kinetics and the anisotropy are taken into account or not. The stable shapes of the growing crystal faces and dissolution faces are calculated for various cases. The interface kinetics will make the inclination degree of stable crystal growth face reduce and that of stable dissolution face reduce slightly. The anisotropy of crystallization and dissolution may make the inclination degree of stable-growing crystal face smaller or larger, and that of the stable dissolution face varies very slightly.     

X射线形貌法观察空间电荷缀饰的α—LiIO3单晶的缺陷

实验观察到:α-LiIO₃单晶在c向静电场作用下,与c轴平行的观察面上X射线衍射形貌图有明显的变化。去掉电场,形貌图又复原。此种变化和复原都有个弛豫过程。形貌图形的变化与外电压的极性和大小有关,而基本上与辐射波长无关。静电场下,形貌图上显现的是空间电荷缀饰的晶体的宏观缺陷。即加静电场后,空间电荷在缺陷周围富集,增大了缺陷处的晶格畸变,使原来观察不到的缺陷显示了出来。 关键词：     

单晶硅中杂质氢导致的局域模的红外吸收

本文提出在氢气氛中生长的单晶硅中,氢原子能够以四种组态存在:它们分别为一,二,三,四个氢原子取代一个硅原子,每个氢原子偏离阵点位置与最近邻的一个硅原子成键,应用准分子模型和群论分析方法对上述四种组态计算了其红外活性局域模频率,与红外吸收实验相符,确定了各红外吸收线所对应局域模的振动模式。     

GaAs单晶滑移位错X射线形貌术研究

应用X射线形貌技术研究了掺In和不掺In砷化镓单晶的滑移位错。观察到由于位错密度不同,其滑移位错的组态不同。对滑移位错和胞状网络进行了初步的理论解释。 关键词：     

INFLUENCE OF INTERFACE KINETICS ON THE RELAXATION BEHAVIOR IN SOLUTION SYSTEM FOR CRYSTAL GROWTH UNDER MICROGRAVITY

The influence of the interface kinetics at the growth face of a crystal and at the surface of material of solute source on the relaxation behavior in a solution system for crystal growth under microgravity is studied. Because the variation of the solution density caused by the solute concentration change can be omitted and only that caused by the temperature change is taken into account, the interface kinetics does not influence the relaxation behaviors of the fluid velocity and the temperature distribution index S_θ (see text). The relaxations of the concentration distribution index S_φ (see text) and dimensionless average growth rate of crystal \bar{V}_cg are calculated under the square pulsed fluctuations of the gravity level or the temperature at the growth face of crystal. Introduction of the interface kinetics makes the value of S_φ enlarged and the perturbation peak of the S_φ-τ curve caused by the gravity level or temperature fluctuation lowered. While the perturbation peak and the valley of the \bar{V}_cg-τ curve caused by the negatively and positively pulsed temperature fluctuation, respectively, is lowered and shallowed by the interface kinetics.     

硅单晶中片状沉淀物X射线形貌研究

本文利用X射线截面形貌术、限区形貌术、回摆形貌术以及扫描电子显微镜等方法研究了硅单晶中一个片状沉淀物,确定其组态及在晶体内的位置,并对其形成作了简略的分析。 关键词：     

硅单晶中硅氢键的存在及其影响

通过红外吸收光谱的测定,证实了氢气氛浮区硅单晶中存在硅氢键,三个特征吸收峰在4.51,4.68和5.13μm波长处。根据有关的理论计算报道分析,认为氢原子在硅晶格中处于几种间隙位置。研究表明这种在晶体生长中形成的硅氢键对晶体完整性隐含着影响,并发现硅单晶中氢致缺陷的形成与硅氢键在高温下的断裂有密切关系。 关键词：