The goal of this research is to understnd the fundamental features of ion induced surface reactions in focused ion beam microfabrication, and of the materials and surfaces that are produced by the resulting deposition or etching. This will be accomplished by bringing to bear expertise from chemical engineering, materials science, and microfabrication technology. In the case of the deposition, understanding of the basic process is expected to point to ways of eliminating unwanted carbon impurities, for example, by the addition of a second, appropriately reactive, precursor gas or an atomic beam. Eliminating or significantly reducing the impurities in the deposited material would be a major breakthrough. The reduced resistivity and increased density would immediately make focused ion beam device and circuit repair processes more effective and open the door to new applications of maskless, resistless, patterned conductor deposition by projection ion techniques and to in situ processing. %%% Ion induced deposition and ion assisted etching are new processes for material addition and removal. Since ion beams can be focused to extremely small dimensions (0.05 microns and below), this permits material manipulation with unprecedented resolution and flexibility and has spawned commercial applications in micro- repair of integrated circuits and in microsectioning for fault diagnosis. By developing a better understanding of the mechanisms of these new processes, and by extending them to new materials, the proposed research work aims to broaden the applications to the deposition of the original wiring of future ultrafast integrated circuits.