Nuclear magnetic resonance studies of amorphous silicon hydrides: proton spin dynamics

Fry, Charles
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The island size in amorphous silicon hydride has been estimated to be (TURN)75 (+OR-) 30(ANGSTROM) for an assumed three-dimensional domain, or 40 (+OR-) 20(ANGSTROM) for a two-dimensional domain. These results were obtained using spin-diffusion via the Goldman-Shen experiment;Arguments have been given to suggest that the interpretation of the Lorentzian line shape should be reexamined. Several reasons, and some calculations provide motive for interpreting the Lorentzian line shape as due to monohydrides bonded to the interstitial surfaces parallel to the growth direction, where the surface has reconstructed to give the larger than expected internuclear separations leading to the narrow Lorentzian line shape;A combination of spin-lattice relaxation measurements and the Carr-Purcell-Meiboom-Gill (CPMG) experiment led to the identifica- tion of two hydrogen environments in addition to the monohydride Lorentzian line shape and the clustered Gaussian line shape. The fact that the Lorentzian line shape is due to a random distribution gives part of the distribution of monohydrides having nearest-neighbor separations so large that these monohydrides echo during a Hahn echo sequence. The information obtained from these experiments led to the conclusion that poor films have a small deviation in internuclear spacings, whereas good films have a much larger deviation in internuclear spacings. This result should be a good measure of the growth conditions during deposition;Molecular hydrogen is identified and quantified using the CPMG experiment. The decay rate of the m-H(,2) during the CPMG experiment gives a direct measure of the strongest residual proton-proton dipolar;interaction, which then gives a lower limit of 10(ANGSTROM) for void dimensions. This result is a clear measure of the void size; ('1)DOE Report IS-T-1116. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

Chemistry, Physical chemistry