Oxidation-induced changes of work function and interfacial electronic states on Si (001) surfaces studied by real-time ultraviolet photoelectron spectroscopy

The oxidation reaction kinetics on a Si (001) 2 × 1 surface was investigated by real-time ultraviolet photoelectron spectroscopy to measure the changes of work function and band bending with the oxygen uptake. By analyzing a spectral shape of the low-energy cutoff in secondary electron spectra, it was found that two values of work function can be obtained for the surface oxidation manner of two-dimensional oxide island growth; one corresponds to the unoxidized clean surface area and the other to the growing oxide island. At the initial stage of oxide island nucleation in this oxidation manner, it was observed that the changes of band bending and work function due to the surface dipole layer originating from a charge transfer of adsorbed oxygen were very small, although they were quit significant under the oxidation manner of Langmuir-type adsorption. Based on the observed changes of band bending and work function, the behavior of adsorbed oxygen in the two-dimensional oxide island growth is discussed in comparison with that in the Langmuir-type adsorption.