Thermally grown Si(001)/SiO2 samples were studied by x-ray reflectivit
y. Fits of model electron density profiles to the data reveal the exis
tence of an interfacial layer at the Si/SiO2 interface up to 15-Angstr
om-thick, with density higher than either the crystalline Si or the ma
in oxide layer. This density of the layer is reduced by a postoxidatio
n anneal. (C) 1997 American Institute of Physics.