This research investigates localized etching phenomena which occur in metals and nonmetals. The program explores the factors that determine where etch pits initiate and how they grow. For instance, in aluminum and some other metals etch pits can exhibit oxide passivation at their sidewalls; this leads to etching of deep micron-sized cavities with constant sidewall widths. Sites of pitting are correlated with surface composition profiles determined by scanning transmission electron microscopy. Important variables that are controlled through systematic processing include dislocation substructure, impurity segregation, and vacancy concentration. The model system selected for these studies is aluminum etched in chloride solutions. The ultimate goal is to use the information on etch pit initiation gained from this research to preprogram specific patterns of etch pitting on metal surfaces.
