Oxidation of silicon with a 5 eV O− beam

A silicon wafer has been oxidized at room temperature in vacuum using a pure, ground-state beam of O− ions. The beam was of sufficiently low energy that no displacement damage or implantation was energetically possible. The resulting SiO2 films were analyzed with x-ray photoelectron spectroscopy. A logarithmic dependence of oxide thickness on dose was observed, with an extrapolated oxidation efficiency of unity for the clean silicon surface. A distinct initial oxidation phase was observed, with an anomalously high level of silicon suboxides. In addition, the valence-band offset between the silicon and the oxide was unusually small, suggesting a large interfacial dipole.