title: Neutron scattering studies of hydrogenated, deuterated and fluorinated amorphous silicon.
abstract: A comprehensive neutron scattering study has been performed of hydrogenated (Si0.78H0.22), deuterated (Si0.77D0.23) and partially fluorinated deuterated (Si0.725D0.120F0.155) 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 Si0.77D0.23exhibits 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 Si0.78H0.22show that there are approximately equal numbers of [Formula: see text] and = SiH2groupings, there being no indication of excitations corresponding to -SiH3groupings. 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 H2molecules 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 H2(D2) molecules. The data for the Si0.725D0.120F0.155sample are consistent with a previously suggested model of network cages predominantly containing molecular SiF4.
authors.affiliation: J J Thomson Physical Laboratory, University of Reading, Whiteknights, Reading RG6 6AF, UK.
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Wright
authors.forename: Alex C
authors.initials: AC
authors.lastname: Hannon
authors.forename: Roger N
authors.initials: RN
authors.lastname: Sinclair
authors.forename: Thierry M
authors.initials: TM
authors.lastname: Brunier
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Guy
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Stewart
authors.forename: Matthias B
authors.initials: MB
authors.lastname: Strobel
authors.forename: Frank
authors.initials: F
authors.lastname: Jansen