An electron spin resonance study was made of Pb centres (interfacial •Si=Si3) in Si(111)/SiO2 interfaces. An inherent density of 4.9 x 1012/cm2 was present in the as-grown state. The Pb density was significantly enhanced by post-oxidation annealing in an H2 ambient at high temperatures. This resulted in the observation of a distinct Pb density-dependent magnetic field angle anisotropy of the electron spin resonance spectra. This definitely established the importance of magnetic dipolar interactions to the 2-dimensional Pb defect system. A field angle dependence of dipolar origin was observed in the linewidth, line-shape and resonance position. The data were interpreted within the framework of a model which was based upon a magnetostatic approximation to the local magnetic field and resulted in a detailed analysis of the line-broadening mechanism. This successful simulation furnished evidence for Pb density-dependent variations in the strain-broadening contribution; thus indicating a growing relaxation of the interfacial strain with increasing Pb density. In addition, the spatial Pb defect distribution was found to exhibit a self-avoiding behavior, with apparently no Pb pairs occurring within third-nearest neighbour separation. The results were explained in terms of a model which linked defect generation to the relaxation of interfacial strain. Magnetic susceptibility measurements revealed an almost purely Curie-like behavior of the Pb system; with a Curie temperature of 1.3K.

Dipolar Interactions between Unpaired Si Bonds at the (111)Si/SiO2 Interface. A.Stesmans, B.Nouwen: Physical Review B, 2000, 61[23], 16068-76