Insulating and Semi-Metallic Quasiperiodic and Periodic Alloys of Metals

9319084 Poon建议研究一类新的金属合金的电子性质，这种合金表现出从半金属到半导体到绝缘体的非金属行为。化学设计的二十面体和十方准晶合金以及高结构质量和热稳定性的晶态合金将被合成和测量，以评估原子势的准周期和强度对电子和光学性质的影响。将进行的实验包括磁输运、热容、热电势、光学传导性、核磁共振、X射线光谱分析和中子散射。其中几项研究将与其他小组联合进行。这项研究的其他目标将是了解这些新型金属合金中局域和巡游态的带隙和性质，以及探索这些材料中可能出现的新的电子和磁现象。要研究的电子合金是新的和不寻常的，因为它们是完全由元素金属组成的半导体和绝缘体，与传统研究的共价或离子非金属，如硅和砷化镓形成对比。这些材料中有一些具有教科书晶体学无法描述的结构；这些固体中的原子以准周期方式排列，因此被称为准晶体。由于它们的准结晶性，已经预测了一些新的物理性质，这些将在本提案中进行研究。目前准晶材料的商业应用是需要具有低粘着系数、高热稳定性和低表面附着系数的材料。*

9319084 Poon It is proposed to study the electronic properties of a new class of metallic alloys that exhibits non-metallic behavior ranging from that of a semimetal to semiconductor to insulator. Chemically designed icosahedral and decagonal quasicrystalline alloys, as well as crystalline alloys of high structural quality and thermal stability, will be synthesized and measured in order to evaluate the effects of quasiperiodicity and strength of atomic potential on the electronic and optical properties. Experiments to be performed include magneto-transport, heat capacity, thermopower, optical conductivity, NMR, x-ray spectroscopy, and neutron scattering. Several of these studies will be performed jointly with other groups. Other goals of the study will be to understand the bandgap and nature of localized and itinerant states in these novel metallic alloys, as well as to explore possible new electronic and magnetic phenomena in these materials. %%% The electronic alloys to be studied are new and unusual in the sense that they are semiconductors and insulators composed entirely of elemental metals, in contrast to the traditionally studied covalent or ionic non-metals such as silicon and gallium arsenide. Some of these materials have structures not describable by text- book crystallography; the atoms in these solids order in a "quasi- periodic fashion, hence the name quasi-crystal. Because of their quasi-crystallinity, a number of novel physical properties have been predicted and these will be investigated in this proposal. Current commercial applications of quasicrystalline materials are where materials are required which have low sticking coefficients, have a high thermal stability and have low surface sticking coefficients. ***