SCANNING-TUNNELING-MICROSCOPY STUDY OF OXIDE NUCLEATION AND OXIDATION-INDUCED ROUGHENING AT ELEVATED-TEMPERATURES ON THE SI(001)-(2X1) SURFACE

Room temperature scanning tunneling microscopy images of Si(001)-(2 x 1) surfaces exposed to O2 at pressures 1 x 10(-8) < P(ox) < 4 x 10(-6) torr and temperatures 500 < T < 700-degrees-C show dramatic surface roughening via formation of long step ''fingers'' and multilevel Si islands. This is caused by nucleation of oxide clusters, which pin step edges during oxidation-induced surface etching. The nucleation rate J(ox) (estimated by counting pinning sites) was found to scale as P(ox)m, with m less-than-or-equal-to 2. This is consistent with a simple model in which two diffusing surface oxygen species are required to nucleate a stable oxide cluster.