Chapter 3 Magnetic Resonance Measurements in a-Si:H

Taylor, P. C.

doi:10.1016/s0080-8784(08)63067-7

Cited by 18 publications

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References 156 publications

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“…As discussed in [2], it has been suggested, as a result of nuclear magnetic resonance (NMR) [15,[39][40][41][42][43][44][45][46][47] and infra-red (IR) [48,49] measurements, that a significant fraction of the hydrogen is present in the form of H 2 molecules trapped under high pressure within the cages defined by the amorphous covalent network (figure 1(C)) and that this molecular hydrogen undergoes a very broad solid-fluid transition between ∼20 and ∼30 K, a temperature considerably higher than the melting and boiling points for normal (n-) H 2 at atmospheric pressure (13.8 and 20.3 K, respectively [50]). (Note that, at normal pressure, the H-H stretching mode for molecular H 2 is not IR active.)…”

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Neutron scattering studies of hydrogenated, deuterated and fluorinated amorphous silicon

Wright

Hannon

Sinclair

et al. 2007

J. Phys.: Condens. Matter

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A comprehensive neutron scattering study has been performed of hydrogenated (SiH), deuterated (SiD) and partially fluorinated deuterated (SiDF) amorphous silicon, prepared by the glow-discharge technique. The measurements performed include diffraction, small-angle neutron scattering (SANS) and inelastic neutron scattering, and the data obtained are discussed in terms of various structural models in the literature. The real-space correlation function for SiD exhibits sharp peaks at 1.49 and 2.36 Å, due to Si-D and Si-Si covalent bonds, respectively, while peaks centred at 3.2 and 3.8 Å are due to Si-D and Si-Si second-neighbour distances. High-energy resolution inelastic scattering measurements for SiH show that there are approximately equal numbers of [Formula: see text] and = SiH groupings, there being no indication of excitations corresponding to -SiH groupings. The presence of molecular hydrogen is demonstrated unambiguously by the observation of the ortho-to-para conversion, via molecular rotation modes at 14.5 and 29.4 meV. The shift in the Si-H stretch modes introduced by deuteration is slightly less than the value of [Formula: see text] expected for free hydrogen, indicating a small but observable influence of the amorphous silicon matrix. The size of the cages containing the H molecules has been investigated via SANS, which yields a mean Guinier radius of ∼5-6 Å. In addition, the use of the H-D SANS contrast technique indicates that each cage contains on average about 60 H (D) molecules. The data for the SiDF sample are consistent with a previously suggested model of network cages predominantly containing molecular SiF.

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