Effects of higher-Jstates on nuclear-spin relaxation times forH2andD2in amorphous silicon

Fedders’ calculations of the effects of molecular J>1 states on the nuclear-spin-lattice relaxation of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ are applied to the interpretation of proton and deuteron relaxation in amorphous silicon. The temperature dependence of proton relaxation in three plasma-deposited a-Si:H samples indicates that the effectively dilute o-${\mathrm{H}}_2$ molecules controlling the relaxation occupy at least two different kinds of sites. Depending on sample preparation conditions, there are predominant o-${\mathrm{H}}_2$ sites with large static electric field gradients of different symmetries. Deuteron relaxation times in the a-Si:D,H sample cannot be fitted by the calculated temperature dependence of ${\mathrm{D}}_2$-related relaxation. It is probable that motional narrowing reduces the effectiveness of the spin-diffusion contact between deuterons and ${\mathrm{D}}_2$ relaxation centers above 40 K.