The Structure Of Amorphous Hydrogenated Carbon By Neutron-Diffraction

Neutron diffraction data from a large, off-substrate sample of amorphous hydrogenated carbon (a-C:H) is presented and discussed. The material is prepared using a fast-atom deposition system using acetylene as the precursor gas. The experiments were performed on the ISIS pulsed neutron source (Rutherford Appleton Laboratory, UK) which is capable of yielding data over an exceptionally wide dynamic range; this ensures a real-space resolution sufficient to resolve directly, for the first time, contributions from the principle C-C bond types. Precise details on the C-H correlations are also revealed by the data, including the presence of molecular hydrogen trapped within distorted spheroidal cages. Quantitative complementary data on the vibrational states of the bonded hydrogen, derived from inelastic neutron scattering (INS) using a simple force-field model, is also presented. In particular, the INS data is used to provide a reliable estimate of the CH:CH2 ratio.