Pulsed EPR hole-burning experiment on dangling bond centers in a-Si : H aerosol particles formed by thermal decomposition of silane

Si dangling bond centers in aerosol particles of amorphous hydrogenated sil icon formed by thermal decomposition of SiH4 in Ar were studied by pulsed e lectron paramagnetic resonance. The hole-burning and inversion-recovery exp eriments demonstrate that large-scale rapid spectral diffusion takes place in the samples with high spin concentration. Correlation times tau(c) of th e spectral diffusion and spin-lattice relaxation times T-1 were obtained in the temperature range between 77 and 290 K. Above 130 K, tau(c), and T-1 a re proportional one to the other. The unusual feature of this spectral diff usion is that the shape of the central part of the spectral hole does not c hange when the delay time increases. The other paramagnetic centers previou sly investigated showed a remarkable change of the hole shape which was ind uced by modulation of dipolar interaction due to spin flips. It is suggeste d that the observed anomaly in the Si dangling bond centers arises due to c ooperative spin flips.