We report the formation processes of interface dangling bonds ($P_b$ centers) during initial oxidation of a clean Si(111) surface using an ultrahigh-vacuum electron-spin-resonance technique. At the oxidation of one or two Si layer(s), the $P_b$ center density reached around $2.5–3.0\times {10}^{12}{\mathrm{cm}}^{-2}$, which is the same density as in the case of thick ${\mathrm{SiO}}_2$. This result shows that the $P_b$ center density does not originate from the long-range accumulation of the structural stress between two materials, but from the chemical reactions of oxidation within a few Si atomic layers.

• Received 4 August 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.105505