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.
