The observed electron spin resonance hyperfine spectra which were associated with the unpaired electron of the Pb1 interface defect in thermal SiO2/(100)Si showed that the predominant interaction arose from a single 29Si isotope. The hyperfine tensor exhibited a weakly monoclinic (nearly axial) symmetry, with the principal axes of the g and hyperfine tensors coinciding. A molecular orbital analysis indicated that the unpaired electron resided, to the extent of some 58%, in a single unpaired Si hybrid orbital. This was found to be 14% s-like and 86% p-like, with the p-orbital closely aligned with a <211> direction; at 35.26º to the [100] interface normal. It was noted that O did not constitute an immediate part of the defect, and the results firmly established that a key part of the Pb1 defect was a tilted (about 20° about <011>) Si3=Si• unit.

A.Stesmans, B.Nouwen, V.V.Afanasev: Journal of Physics - Condensed Matter, 1998, 10[27], L465-72