This project focuses on the spectroscopy and dynamics of size-selected group IV and III-V semiconductor clusters using several experimental techniques based on negative ion photodetachment to characterize how the properties of these species vary with size and stoichiometry. The corresponding bulk compounds play a key role in the semiconductor and electronics industries so these studies are highly relevant to nano-device technologies in that they probe how the properties of the bulk materials evolve from their atomic and molecular constituents. The project will focus on binary III-V nitride compounds, silicon clusters, and indium phosphide clusters. Properties of interest include vibrational frequencies and electronic state splittings in small clusters, the evolution of valence and conduction bands as the cluster size increases, electronic relaxation dynamics in excited states of the clusters, and the fragmentation patterns resulting from photodissociation. In all the experiments, mass-selected beams of semiconductor cluster anions are generated and photodetached. The primary experimental method is fixed-frequency anion photoelectron spectroscopy, which provides a general means to determine the electronic and vibrational structure of a size-selected neutral cluster. This technique will be complemented by tunable laser photodetachment, time-resolved photoelectron spectroscopy, and fast beam photofragment translational spectroscopy experiments. %%% Understanding how physical and chemical properties of matter evolve with size is crucial to many potential applications designed to meet significant societal needs. Emphasis is placed on select elemental clusters, for which the corresponding bulk compounds play a major role in the fabrication of fast devices such as transistors and photodiodes. The proposed studies are important because they provide training for future scientists and engineers in key areas of national interests.