AN ELECTRON-PARAMAGNETIC-RESONANCE INVESTIGATION OF PARAMAGNETIC DEFECTS IN DIAMOND FILMS GROWN BY CHEMICAL-VAPOR-DEPOSITION

Defects in free-standing diamond films grown by microwave-plasma-assis ted chemical vapour deposition have been studied by electron paramagne tic resonance (EPR). The EPR spectra observed for the as-grown materia l each consisted of two distinguishable Lorentzian lines at g = 2.0028 (2), along with weak satellites centred on g = 2.0028 and separated fr om each other by 1.15-1.35 mT. Comparison of the local concentration ( up to 500 ppm) determined by lineshape analysis and the bulk concentra tion (0.3-8 ppm) determined from the total EPR absorption revealed tha t the defects were inhomogeneously distributed in the diamond film. Mu lti-frequency EPR measurements showed that the satellite separation de pended on the microwave frequency. It is proposed that the satellite l ines originate from a pair of coupled electron spins which form a bira dical centre. This appears to be the only model which is consistent wi th the observed microwave frequency dependence of the satellite separa tion.