Neutron Scattering Studies of Hydrogenated and Deuterated Amorphous Silicon.

Abstract

A comprehensive neutron scattering study has been performed of hydrogenated and deuterated amorphous silicon, prepared by the glow discharge technique, and the measurements performed are discussed in terms of current structural models. The real space correlation function for Si_0.77D_0.23 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. Inelastic scattering measurements show that approximately equal numbers of hydrogen atoms are contained in ≡SiH and =SiH₂ groupings, there being no indication of excitations corresponding to -SiH₃ 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 meV. Use of the H-D SANS contrast technique indicates that these molecules are trapped in cages containing on average about 60 H₂ (D₂) molecules.