Chemical oxidation of hydrogen passivated Si(111) surfaces in H2O2

The initial stages of oxide formation on atomically flat, monohydride terminated Si(111) surfaces by oxidation in 30% hydrogen peroxide solution (H2O2) were investigated by scanning tunneling microscopy and x-ray photoelectron spectroscopy. The reaction proceeds via homogeneous nucleation of small oxide clusters on the surface and subsequent lateral growth of these clusters within the surface bilayer. The oxidation of the topmost Si(111) bilayer in H2O2 solution is completed after 30 min, leading to a SiO1.2 average layer composition. For the next bilayer the oxidation rate decreases drastically—after 2 months only 60% of the second bilayer are oxidized. An inverse logarithmic rate of the second bilayer oxidation is consistent with a field assisted growth mechanism. The significant differences in the oxidation rates between the first and the second bilayer allow to produce well defined oxide layers of about 5 Å thickness.