This research project, supported in the Analytical and Surface Chemistry Program, is focussed on electrochemical and photoelectrochemical processes at semiconductors. During the tenure of this three-year continuing grant, Professor Bard and his students at the University of Texas at Austin will pursue a broad experimental program having four primary thrusts: (1) investigations od semiconductor/liquid interfaces using scanning probe microscopies; (2) studies of semiconductor nanoparticles, known as "Q-particles," and thin films of Q-particles on conducting substrates; (3) the identification and evaluation of new materials and the modification of titanium dioxide as more efficient photocatalysts; and (4) fundamental investigations of mechanisms of electrode processes at insulators modeled by conducting electrodes covered with insulating thin films. This research, which builds upon results obtained under the aegis of NSF grant CHE-9119851, seeks to provide a better understanding of the semiconductor/liquid interface and to improve the efficiency of technologically important semiconductor photoprocesses. Photoelectrochemistry at semiconductor surfaces is vital to the effective utilization of solar energy in applications such as the production of useful chemicals or the destruction of chemical wastes. This research is aimed at improving our understanding of both dark and photoprocesses at semiconductor/liquid interfaces and the utilization of that knowledge in the improved design of technoloeically important photoelectrochemical systems and devices.