Photodetachment Spectroscopy of Semiconductor Clusters and Nanocrystals

半导体团簇在两个非常不同的尺寸范围接近物质的分子和材料极限将使用负离子光剥离技术的组合进行研究。一组实验是针对3-20个原子大小范围内的小簇的振动和电子能谱；具体系统包括硅和锗的元素团簇以及混合III-V GaAs， InP和InSb团簇。将他们的实验结果与其他人的从头计算结果进行比较，将提供有关这些簇的结构和化学键如何随其大小而变化的详细探索。第二组实验集中在相当大的半导体“纳米晶体”的CdS和CdSe在1000原子大小范围内。他们计划对尺寸选择的纳米晶体阴离子进行光电子能谱分析，以确定中性纳米晶体的电子亲和力和电子态能。这些实验将为量子限制对这些物质的电子结构的影响提供详细的探讨。此外，光电子谱中振动激发的程度将揭示纳米晶体阴离子中额外电子的存在所引起的晶格畸变的程度。这项资助由材料研究部和化学部共同支持。

Semiconductor clusters in two very different size ranges approaching the molecular and materials limits of matter will be studied using a combination of negative ion photodetachment techniques. One set of experiments is aimed at the vibrational and electronic spectroscopy of small clusters in the 3-20 atom size range; specific systems of interest included elemental clusters of silicon and germanium as well as mixed III-V GaAs, InP, and InSb clusters. A comparison of their experimental results with the ab initio calculations of others will provide a detailed probe of how the structure and chemical bonding of these clusters varies with their size. The second set of experiments focusses on considerably larger semiconductor 'nanocrystals' of CdS and CdSe in the 1000 atom size range. They plan to perform photoelectron spectroscopy on size-selected nanocrystal anions in order to determine the electron affinities and electronic state energies of the neutral nanocrystals. These experiments will provide a detailed probe of the effect of quantum confinement on the electronic structure of these species. In addition, the extent of vibrational excitation in the photoelectron spectrum will reveal the extent of lattice distortion caused by the presence of the additional electron in the nanocrystal anion. This grant is supported jointly by the Division of Materials Research, and the Chemistry Division.