硅表面上的纳米量子点的自组织生长

纳米半导体量子点以其所具有的新颖光电性质与输运特性正在受到人们普遍重视。作为制备高质量纳米量子点的工艺技术 ,自组织生长方法倍受材料物理学家的青睐。而如何制备尺寸大小与密度分布可控的纳米量子点更为人们所注目。因为这是关系到纳米量子点最终能否器件实用化的关键。文中以此为主线 ,着重介绍了各种 Si表面 ,如常规表面、氧化表面、台阶表面以及吸附表面上 ,不同纳米量子点的自组织生长及其形成机理 ,并展望了其未来发展前景     

对ADSL接入方式铜缆可用线对率的分析

指出了为发展ADSL而提高市话音频铜线电缆的传输质量和维护水平的必要性,分析了铜线电缆线对有关指标参数低劣的原因和对传输ADSL的影响,并提出了一些改进的意见。     

固定式宽带无线接入技术--LMDS

本地多点分配业务(LMDS)是近年来在国际上兴起的固定式宽带无线接入技术,具有传输容量大、起始费用低的优点,受到了国内外电信业务经营者的普遍关注.文章介绍了LMDS提供的业务类型、工作频率、系统结构和标准化情况,并将LMDS与有线电视网络、ADSL、MMDS等现有的接入技术进行了比较.文章认为LMDS的商业推广尚需解决信号质量、服务区尺寸、费用等制约因素.     

Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications

The slow (subcritical) crack growth (SCG) resistance of Si₃N₄ and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si₃N₄ sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si₃N₄ without additives.     

化学束外延

本文介绍了化学束外延(CBE)的发明和发展,论述了CBE的原理和设备。文中还介绍了最近提出的一种生长机理。     

过共晶Al－Si合金共生区激光表面处理

用２ｋＷ连续ＣＯ２激光对过共晶Ａｌ－１８Ｓｉ合金以不同能量密度和扫描速度进行快速熔凝处理。用扫描电镜、电子微区分析仪分析了微观结构。从计算机对Ａｌ－Ｓｉ合金ｆ－ｎｆ系统的非平衡理论计算所得的共生区及实验结果的分析可见，当能量密度和扫描速度决定的凝固条件处于共生区中部时，过共晶Ａｌ－Ｓｉ合金激光表面处理可以得到共晶间距低于２００ｎｍ的完全共晶结构。     

In－BiCaVIG的晶体生长与性能

本文报导了用助熔剂法成功地生长大尺寸掺铟ＢｉＣａＶＩＧ晶体的方法以及实验结果，介绍了该单晶在近红外区的磁光器件中的重要应用。     

纤维共晶生长界面前沿三维扩散场解析

修正Ｊａｃｋｓｏｎ和Ｈｕｎｔ关于在垂直生长方向截面上溶质扩散各向同性假设，求解三维Ｌａｐｏｌａｃｅ方程，获得纤维共晶生长界面前沿三维稳态扩散场，并证明Ｊａｃｋｓｏｎ和Ｈｕｎｔ的二维模型是实际生长的二维简化和一阶近似，并用丁二腈（ＳＣＮ）一梓脑（ＣＡＭ）纤维共晶系统计算生长界面前沿溶质分布。     

大尺寸氟化铅晶体的生长

描述了不用高真空条件，在通常的Ｂｒｉｄｇｍａｎ－Ｓｔｏｃｋｂａｒｇｅｒ炉中，用高温下的反应方法，消除了原料及生长炉内残存的Ｏ＾２－及ＯＨ＾－，生长出优质，大尺寸的β－ＰｂＦ２晶体。在晶体生长时，出现的主要问题是在晶体中的针状结构及开裂，但可通过控制条件来解决。     

Studies of photoconductivity in β-Apo-8′ carotenal

The photoconductive properties of a carotenoid polyene,β-Apo-8′ carotenal in polycrystalline form has been studied. The growth of the photocurrent shows an overshoot in the growth-time curve before steady state value is attained. This behaviour of photocurrent is proposed to be due to higher value of recombination coefficient than trapping coefficient. From the temperature dependence study it is observed that the steady state photocurrent, at first increases with increase of temperature, attains a maximum at a particular temperatureT _max and then decreases with temperature. TheT _max value agrees with the temperature above and below which steady state photocurrent is attained differently. Monomolecular and bimolecular recombination processes at two temperature regimes are proposed to account for the observed behaviour. The dependence of photocurrent with excitation light intensity and wavelength study provide information on the carrier generation processes. The fast decay of photocurrent have been observed at different temperatures and from this study the decay constant is calculated and it is found to be temperature independent.