Scanning Tunneling Microscopy study of Oxide Nucleation and Oxidation-Induced Roughening at Elevated Temperatures on the Si(001)-(2 × 1) Surface

Room temperature scanning tunneling microscopy images of Si(001)-(2 ×{} 1) surfaces exposed to O₂ at pressures 1×10⁸<Pₒₓ<4×10^-6 torr and temperatures $500<T<700$^∘{}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 Jₒₓ (estimated by counting pinning sites) was found to scale as Pₒₓᵐ, with m≥2. This is consistent with a simple model in which two diffusing surface oxygen species are required to nucleate a stable oxide cluster.