Investigation of Composition in Nano-Scaled Self-Assembled SiGe Islands

A modified model is proposed to explain the influence of Si concentration on shape transition of self-assembled SiGe islands on Si substrates. The experimental results show that the critical sizes for shape transition from pyramids to domes (44, 50 and 60hm) increase with the increasing Si concentration (0.032, 0.09 and 0.17) from sample A to C. Based on the proposed model, the quantitative relation between the Si concentration and the critical size is established. Then the composition exactly in nano-scaled self-assembled SiGe islands is calculated from the measured critical size. The result shows that the Si concentration deduced from Raman spectrum is much larger than the actual values. It is demonstrated that the quantitative relation we obtained can be used to investigate the composition in nano-scaled SiGe islands.     

反常输运与非线性自持磁岛的自洽分析

从沿磁力线的等离子体电流与粒子径向输运相关的新经典ＭＨＤ型的广义欧姆定律出发，提出了分析反常输运与非线性自持磁岛的自洽理论模型，基于该模型导出了反常扩散系数及反常电子热导。结果表明，非线性磁岛链可由磁岛调制的反常输动维持，反过来又通过磁岛短路效应维持反常输运。     

原子表面扩散的对称破缺对二维岛形成的控制

文章阐述了当CO吸附改变时Pt/Pt(111)同质外延单层岛的的微观选择机制，即岛的取向由沉积原子的边－角扩散运动的不对称性惟一决定，对没有CO介入的理想真空生长情况，衬底温度不能改变三角形岛的取向。CO的吸附反转了边－角扩散牟不对称性，从而使岛的取向发生变化。     

Si组分对SiGe量子点形状演化的影响

研究了自组织生长SiGe岛（量子点）中Si组分对形状演化的影响.采用UHV/CVD方法生长了 不同Si组分的SiGe岛，用AFM对其形状和尺寸分布进行了分析，实验结果表明SiGe岛从金字 塔形向圆顶形转变的临界体积随Si组分的增大而增大.通过对量子点能量的应变能项进行修正，解释了量子点中Si组分对形状演化的影响.在特定的工艺条件下得到了单模尺寸分布的 金字塔和圆顶形量子点.结果表明，通过调节SiGe岛中的Si组分，可以实现对SiGe岛形状和 尺寸的控制. 关键词： 自组织生长SiGe岛 Si组分 临界体积     

基于Au纳米岛修饰的CdSSe纳米带光电探测器

三元合金CdS_xSe_1–x兼具CdS和CdSe的物理性质,其带隙可以通过改变元素的组分来调节.该合金具有优异的光电性能,在光电器件方面具有潜在的应用价值.本文首先通过热蒸发法制备了单晶CdS_0.42Se_0.58纳米带器件,在550 nm光照及1 V偏压下,器件的光电流与暗电流之比为1.24×10³,光响应度达60.1 A/W,外量子效率达1.36×10⁴%,探测率达2.16×10¹¹ Jones,其上升/下降时间约为41.1/41.5 ms.其次,通过Au纳米岛修饰该CdS_0.42Se_0.58纳米带后,器件的光电性能显著提升,在550 nm光照及1 V偏压下,器件的光开关比、响应度、外量子效率及探测率分别提高了5.4倍、11.8倍、11.8倍和10.6倍,并且上升/下降时间均缩短了近一半.最后基于Au纳米岛的局域表面等离子共振解释了器件光电性能增强的微观物理机制,为在不增大器件面积的前提下,...     

Si衬底上生长的铁硅化合物结构和取向分析

采用分子束外延法分别在650-920℃的Si(110)和920℃的Si(111)衬底表面生长出铁的硅化物纳米结构,并主要分析了920℃高温下纳米结构的形貌、组成相及其与Si衬底的取向关系.扫描隧道显微镜(STM)研究表明,920℃高温下,Si(110)衬底上生长的铁硅化合物完全以纳米线的形式存在,且其尺寸远大于650℃低温下外延生长的纳米线尺寸;Si(111)衬底上生长出三维岛和薄膜两种形貌的铁硅化合物,其中三维岛具有金属特性且直径约300 nm、高约155 nm,薄膜厚度约2 nm.电子背散射衍射研究表明920℃高温下Si(110)衬底上生长的纳米线仅以β-FeSi2的形式存在,且β-FeSi2相与衬底之间存在唯一的取向关系:β-FeSi2(101)//Si(11 1);β-FeSi2[010]//Si[110];Si(111)衬底上生长的三维岛由六方晶系的Fe2Si相组成,Fe2Si属于164空间群,晶胞常数为a=0.405 nm,c=0.509 nm;与衬底之间的取向关系为Fe2Si(001)∥Si(111)和Fe2Si[1 20]//Si[112].     

Numerical study of fast ion behavior in the presence of magnetic islands and toroidal field ripple in the EAST tokamak

A peculiar first orbit loss type was found apart from the normal ones when we use ORBIT code to simulate fast ion orbits in the EAST tokamak. Fast ion orbits were studied in the presence of toroidal field （TF） ripple and magnetohydro- dynamic （MHD） perturbations. We analyzed the properties of the drifted orbits in detail and compared their differences, finding that the combined effects of ripple and magnetic islands are much greater than the effects of either one of them alone. Then we investigated the orbitdeviations as a function of pitch angle in different radial positions. The modeling results demonstrate that the loss of trapped particles is mainly caused by the ripple, while MHD＇perturbation mainly plays an important role in the passing particles. Furthermore we modeled the loss rate using different equilibriums. Results prove that a higher beta can indeed improve the confinement of fast ions, while a little change in the q profile can make the topologies of magnetic islands become quite different and results in quite different total particle losses.     

磁层顶涡旋诱发撕裂模不稳定性的二维MHD数值模拟研究——饱和后长时间渐近状态

用二维磁流体力学数值模拟方法,研究了磁层顶边界区剪切流涡旋诱发撕裂模不稳定性饱和后的准定常渐近状态。该渐近态由大尺度涡旋及同心磁岛组成,磁涡旋管与涡管重合。管内流线、磁力线和等涡度线接近互相平行,等离子体密度和电流密度近似为常数。管内磁场的法向分量显示出双极特征。这一特征及管内外密度变化均与卫星对FTE的观测特征相符。磁涡旋管的直径¹R_E,也与观测一致。     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜