FRG: Nanoscale Order in Amorphous Solids: Structure, Transformations, and Electronic Properties

该FRG项目是五个合作PI和其他具有非晶材料专业知识的合作者的共同努力：制备和分析（Abelson，Bishop），FEM技术（吉布森，Voyles），TEM（Zuo），分子动力学和量子力学模拟（Drabold）以及无序网络的统计力学和拓扑结构（Goldbart）。该项目的目标是定量确定IV族和硫属化物非晶材料中的纳米结构，以及这种顺序与电子性质和相变的关系。该方法是基于波动电子显微镜（FEM）-一种新的分析技术与MRO（中程秩序）目前唯一的纯结构视图。有限元法包括从纳米尺寸体积的样品散射的强度作为体积、尺寸和散射条件的函数的统计分析。该项目致力于纳米级秩序的代表性非晶和玻璃材料-非晶硅和硫属化物-这是没有长程有序。已知这些材料表现出中程有序，但对这种有序的性质知之甚少。中程有序（MRO）是一种典型的结构相关性，其长度尺度大于第三配位壳层的直径，但小于结构因子中出现布拉格峰的有序尺度。对于非晶硅（a-Si），其转化为1-4 nm的长度尺度。历史上，在无序存在的情况下，这些长度尺度的结构很难测量。由于大多数无序材料的各向同性性质，标准衍射技术在中程产生的信息很少。PI表明，应变影响a-Si中的小拓扑结晶区域，使其在衍射中无法检测到。%该项目涉及具有技术相关性的电子材料科学领域的基础研究问题。该项目的一个重要特点是高度重视教育，并将研究与教育相结合。合并后的资源，包括实验和理论方法，为从事高度跨学科前沿研究的博士后助理，研究生和本科生提供教育和培训的特殊机会。

This FRG project is a collaborative effort among five co-PIs, and additional collaborators with expertise in amorphous materials: preparation and analysis (Abelson, Bishop), FEM technique (Gibson, Voyles), TEM (Zuo), molecular dynamics and quantum mechanical simulations (Drabold), and statistical mechanics and topology of disordered networks (Goldbart). The project goals are to quantitatively determine the nanostructure in group IV and chalcogenide amorphous materials, and the relationship of this order with electronic properties and phase transformations. The approach is based on fluctuation electron microscopy (FEM)-a new analytical technique with the only purely structural view of MRO (medium range order) currently available. FEM in-volves a statistical analysis of the intensity scattered from nanometer-sized volumes of the sam-ple as a function of the volume, size, and scattering conditions. The project addresses nanoscale order in representative amorphous and glassy materials-amor-phous silicon and chalcogenides- which are without long range order. These materials are known to exhibit medium range order, but little is known about the nature of this ordering on the na-noscale. Medium-range order (MRO) is typically a structural correlation at length scales longer than the diameter of the third coordination shell but shorter than the scale at which ordering ap-pears as Bragg peaks in the structure factor. For amorphous silicon (a-Si), that translates to length scales of 1-4 nm. Structure at those length scales in the presence of disorder has historically been difficult to measure. Standard diffraction techniques yield little information at medium-range because of the isotropic nature of most disordered materials. The PIs have shown that strain affects small topologically crystalline regions in a-Si, rendering them not detectable in diffraction.%%% The project addresses fundamental research issues in areas of electronic materials science having technological relevance. An important feature of the project is the strong emphasis on education, and the integration of research and education. The combined resources, including experimental and theoretical methods, provide special opportunities for education and training of post doctoral associates, graduate and undergraduate students involved in highly interdisciplinary forefront research.***