MolecularH2: Nuclear-spin-relaxation centers for protons ina-Si: H

Abstract

It is proposed that dilute ${\mathrm{H}}_2$ molecules are the source of proton spin-lattice relaxation in those $a$-Si: H samples which show a $T_1$ minimum. Two-phonon Raman processes relax the ${\mathrm{H}}_2$ molecular rotational states, modulating the intramolecular dipolar interactions and relaxing the protons of the ${\mathrm{H}}_2$. The majority of protons in the sample then relax to the ${\mathrm{H}}_2$ by spin diffusion. The model explains the reported temperature and frequency variations of $T_1$ as well as the change in $T_1$ upon dilution of H with D.