Scanning Tunneling Microscopic Observations of “Nonconductive” Oxide Surfaces: SiO2 Thin Films Formed on n- and p-Si(100)

Abstract

Scanning tunneling microscopy (STM) observations for “nonconductive” silicon oxide (silica) surfaces under ambient conditions were attempted. Thin (approximately 0.6 nm thick) silica films spontaneously formed on p- and n-type Si(100) surfaces were employed as silica samples. X-ray photoelectron spectra from these native-oxide-covered Si surfaces indicate that the valence band edges of the silica thin films are located at the binding energies of 3.0-3.3 eV. In the STM bias voltage dependence of the tip-sample distance on these surfaces under constant current, features attributable to conduction band edges of the silica films are observed at 2.5-3.5 eV above the Fermi edge. From these data it is conjectured that at the bias voltages beyond the range of approximately ±3.5 V, it may be possible to obtain the surface images of these thin silica films by means of STM. Silica surface images thus obtained was presented and discussed.