NMR studies of amorphous silicon and aluminosilicate glass

Shao, William
Major Professor
Bernard C. Gerstein
Committee Member
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An aluminosilicate glass, ZERODUR, sample has been investigated by high resolution solid state [superscript]29Si and [superscript]27Al NMR. The results revealed the presence of two regions in the sample, one being highly ordered and the other relatively disordered. The [superscript]29Si NMR spectrum showed clearly peaks and shoulders representing Si (OAl)[subscript] n species in the ordered region. In the disordered region these peaks were inhomogeneously broadened, merged together and were not able to be separated. The Loewenstein rule was basically obeyed in both regions. The [superscript]27Al NMR spectrum showed that the tetrahedral center of SiO[subscript]2 and AlO[subscript]sp2- had near cubic symmetry in the ordered region, and axial symmetry in the disordered region. All Al Sites were tetrahedrally coordinated. No 5- or 6-coordinated Al sites were found in the sample;High resolution solid state [superscript]29Si NMR studies have also been performed on amorphous silicon films whose short range order has been modified. Measurements were made on low pressure rf sputtered a-Si deposited at room temperature and subsequently annealed to elevated temperatures. The NMR spectra under conditions of high resolution solid state NMR were a single broad line, whose second moment decreased upon annealing. The dominant contribution to the line width was associated with a broad distribution of isotropic chemical shifts. The variation of the NMR second moment with annealing temperature exhibited a monotonic decrease up to 610°C, where an additional sharp line associated with c-Si is observed. After annealing at 640°C, the broad line disappeared, leaving only the sharp line. The changes in second moment with annealing were compared to recent data on the distribution function of two sputtered a-Si films whose bond angle deviation was known, as well as to Raman scattering measures of structural order. The results indicated that the NMR width variations were related to changes in the electronic states about Si sites and the associated narrowing of the bond angle distribution.