Raman Scattering and Electronic States of Nanoscale Group 4 Materials

9623315兰宁这项工作的目的是获得在超高真空中制备和研究的有序和无序半导体纳米系统的声子态的基本信息。用干涉增强拉曼散射(IERS)方法对IV族材料的声子进行基础研究，这些材料是在非常小的、1-2 nm纳米晶的超薄膜和在选定的晶体氧化物上生长的超薄膜外延层上进行的。这些结果将提供关于没有化学吸附物种的非常小的微晶和超薄晶体半导体层的声子态的新信息。对于外延层，不同的表面几何结构，如表面二聚体和悬挂键对拉曼散射的作用是有意义的。IERS将提供有关半导体/氧化物界面中界面结合的更多信息。研究了吸附原子对纳米系统声子态的影响。拉曼散射将被扩展为研究表面和近表面原子动力学和结构的工具。在Si、Ge和C纳米尺度系统中的互补镜面、偶极电子能量损失谱(EELS)研究将提供有关随着尺寸或薄膜厚度的减小而发生的带间电子跃迁、光学带隙和亚带隙状态的变化以及化学吸附物种的影响的信息。用高分辨率电子发射光谱研究了脉冲激光沉积非晶类金刚石材料中近表面原子振动态的变化。这些对类金刚石薄膜的原位测量将使超薄和薄膜的结合增加4倍。随着凝聚态系统的尺寸在一个或多个维度缩小到纳米级，表面和近表面原子在决定物理和化学性质方面发挥着越来越重要的作用。因此，当尺寸减小到1-2 nm尺度时，电子和声子态、磁性和光学性质都会受到实质性的影响。在这样的系统中，有限大小的量子效应和新的成键几何结构的存在导致了物理性质的非常实质性的变化。因此，这种小规模系统的基本科学知识和潜在的技术应用目前都引起了相当大的兴趣。我们将研究不同类别的纳米系统，以获得有关有限大小和近表面原子对振动态和电子带间跃迁的影响的信息。这些研究将涉及新的和正在开发的实验方法的使用和推广，以研究有序和无序的纳米系统。双层干涉增强拉曼散射(IERS)方法的改进将增强拉曼散射作为超薄半导体及其界面的表面科学工具的作用。此外，反射电子能量损失谱(EELS)将被用于研究纳米晶、非晶和外延超薄膜的新的带间电子态。这些有序和无序纳米半导体的研究将使用在专门的超高压系统中原位沉积和研究的超薄膜。***

9623315 Lannin The objectives of this work are to obtain basic information on the phonon states of ordered and disordered semiconducting nanoscale systems prepared and studied in ultrahigh vacuum. Basic studies of the phonons of group IV materials will be performed by interference enhanced Raman scattering (IERS) methods on ultrathin films of very small, 1-2nm, nanocrystallites and on ultrathin films epitaxial layers grown on selected crystalline oxides. The results will provide new information about the phonon states of very small crystallites, without chemisorbed species, and ultrathin crystalline semiconductor layers. For epitaxial layers the distinct surface geometry, such as the role of surface dimers and dangling bonds on Raman scattering are of interest. IERS will provide additional Information about interfacial bonding in semiconductor/oxide interfaces. The influence of adsorbate atoms on the phonon states of nanoscale systems will be studied. Raman scattering will be expanded as a tool for the study of surface and near surface atom dynamics and structure. Complementary specular, dipolar electron energy loss spectroscopy (EELS) research in Si, Ge and C nanoscale systems will provide information about interband electronic transitions with decreasing size or film thickness, about changes in the optical gap and subgap states, and the effects of chemisorbed species. Changes in the vibrational states of near surface atoms in amorphous diamond-like carbon materials prepared by pulsed laser deposition will be studied by high resolution EELS. These in situ measurements of diamond-like films will allow a means to increase 4-fold bonding in ultrathin and thin films. %%% As the size of condensed matter systems is reduced in one or more dimensions to nanoscale levels, surface and near surface atoms play an increasingly important role in determining physical and chemical properties. Thus electrons and phonon states, magnetic and optical properties are su bstantially influenced when dimensions decrease to a scale of 1-2nm. In such systems finite size quantum effects and the presence of new bonding geometries lead to very substantial changes in physical properties. Both basic scientific knowledge and potential technological applications of such small scale systems are thus of considerable current interest. Different classes of nanoscale systems will be studied to obtain information on the effects of finite size and near surface atoms on both the vibrational states and electronic interband transitions. These studies will involve the use and extension of new and developing experimental methods for studies of both ordered and disordered nanoscale systems. Improvements in bilayer interference enhanced Raman scattering (IERS) methods for ultrathin films in the form of nanocrystalline island particles and epitaxial layers will enhance Raman scattering as a surface science tool for ultrathin semiconductors and their interfaces. In addition, reflection electron energy loss spectroscopy (EELS) will be utilized for new interband electronic state studies of nanocrystalline, amorphous and epitaxial ultrathin films. These studies of ordered and disordered nanoscale semiconductors will employ ultrathin films deposited and studied in situ in a specialized uhv system. ***