Abstract

We report on experiments using optical second-harmonic (SH) generation to probe the evolution of the surface structure on clean and oxidized Al surfaces with increasing temperature. An incident beam from a synchronously pumped dye laser with a wavelength of 580 nm was used to generate SH light at the specimen surface. The SH intensity was monitored as the sample temperature was ramped from room temperature to 550°C. Above 450°C, a sharp increase in the SH signal from the oxidized Al surfaces signalled the onset of a structural transformation. Complementary studies using Auger electron spectroscopy and scanning electron microscopy indicate that this transformation involves the breaking up of the oxide film into islands of 50 nm or less in size, separated by atomically clean Al. In similar experiments on atomically clean Al surfaces, the crystalline anisotropy of the SH signal decreased with increasing temperature. A possible mechanism for this effect, which involves the evolution of steps on the surface, will be discussed.

© 1990 Optical Society of America