Free-standing films were grown by means of microwave plasma-assisted chemical vapor deposition, and were studied by using electron paramagnetic resonance techniques. The electron paramagnetic resonance spectra for as-grown material each consisted of 2 distinguishable Lorentzian lines at g = 2.0028, together with weak satellites that were centered on g = 2.0028 and were separated from each other by 1.15 to 1.35mT. A comparison of the local concentrations (up to 500ppm) that were determined by line-shape analysis, and the bulk concentrations (0.3 to 8ppm) that were deduced from the total electron paramagnetic resonance absorption, revealed that the defects were inhomogeneously distributed in the films. Multi-frequency electron paramagnetic resonance data showed that the satellite separation depended upon the microwave frequency. It was proposed that the satellite lines originated from a pair of coupled electron spins which formed a bi-radical center. This appeared to be the only model which was consistent with the observed microwave frequency dependence of the satellite separation.

D.F.Talbot-Ponsonby, M.E.Newton, J.M.Baker, G.A.Scarsbrook, R.S.Sussmann, C.J.H.Wort: Journal of Physics - Condensed Matter, 1996, 8[7], 837-49