P.J.R. Honeybone

Inelastic neutron scattering of molecular hydrogen in amorphous hydrogenated carbon

Abstract We have, by use of inelastic neutron scattering detected the presence of molecular hydrogen in amorphous hydrogenated carbon. We have found the hydrogen to be in a high-pressure, asymmetric environment formed by the compressive stresses in the a-C:H films. On comparing two samples, we have also found that the sample with higher molecular hydrogen concentration has a lower total hydrogen composition. This is caused by a higher network density, trapping the molecular hydrogen during network growth.

The structure of a C:H by neutron and X-ray scattering

Abstract Whilst the short-range order in a-C:H is of central importance in explaining its mechanical properties, it is order at intermediate distances that is likely to account more fully for the electronic and optical properties. The role of hydrogen would appear to be significant in promoting tetrahedral bonding — but no direct study of the hydrogen sites has been made. It is in this context that the preliminary results of neutron diffraction measurements, and of some novel synchrotron X-ray experiments, are presented and discussed. The X-ray diffraction studies were carried out using a technique which may prove useful for as-deposited films in which the angle of incidence is fixed at, or near, the critical angle. The results of a “reverse Monte Carlo” computer modelling study of the neutron data are presented.

The effect of hydrogen dilution on the interatomic bonding of amorphous hydrogenated silicon: carbon

Abstract The effect of hydrogen dilution of the precursor gas mixture on the local bonding environment in glow-discharge deposited a-Si:C:H has been studied by neutron diffraction and inelastic neutron scattering. The neutron diffraction results show a large increase in the silicon-carbon bonding upon hydrogen dilution, at the expense of silicon-silicon bonding. The inelastic neutron scattering provides complementary information on the hydrogen bonding environment. The hydrogen is predominantly bonded in SiH and SiH 2 groups, with a large increase in the SiH 2 group concentration occurring upon hydrogen dilution. The data presented here show that SiH 3 and CH n groups are present as a very small fraction of H bonding sites, if at all.

Inelastic neutron scattering of amorphous hydrogenated carbon

The hydrogen bonding environment of three samples of a-C:H have been extensively studied by means of inelastic neutron scattering. The observed inelastic neutron scattering spectra can be modelled by approximately equal quantities of sp3 CH and CH2 groups,i.e. approximately two-thirds of the hydrogen incorporated in a-C:H is in the form of CH2 groups.

A high-resolution neutron-diffraction study of the structure of amorphous hydrogenated carbon, a-C:H

Current structural models for amorphous hydrogenated carbon (a-C:H) are called into question on the basis of neutron-diffraction experimental work carried out at the ISIS pulsed neutron source (UK) on a-C:H. The nature of the neutron source allows the collection of data over an exceptionally wide dynamic range that ensures a real-space resolution sufficient to allow direct observation, for the first time, of contributions from the principal C-C bond types. The data also reveal details of the C-H correlations, and the presence of trapped molecular hydrogen.

The use of neutron scattering experiments for studying molecular hydrogen in amorphous hydrogenated carbon

Abstract The presence of molecular hydrogen in a-C:H has been demonstrated by a series of neutron scattering experiments. Neutron diffraction gives a peak in the pair correlation function corresponding to the H-H bond distance. Inelastic neutron scattering experiments have shown peaks consistent with the H 2 rotation and stretch, and revealed details of the hydrogen environment.

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:CH 2 ratio.

The Structure Of Amorphous Hydrogenated Silicon Carbon Alloys Using X-Ray And Neutron-Scattering And Computer-Simulation - The Effect Of Hydrogen Dilution

Neutron and X-ray diffraction techniques have been applied to the study of two samples of a-Si:C:H. Both samples were prepared using conventional glow discharge methods, but the hydrocarbon/silane precursor gas was diluted with hydrogen in one case. Analysis of the X-ray diffraction data gives a clear picture of the silicon network, since the scattering profile is dominated by the Si-Si correlations. The high real-space resolution neutron diffraction data, however allows one to comment on the effect of this dilution on the silicon-carbon bonding morphology, and in particular on the degree to which the additional hydrogen enhances hetero-coordination. In addition we present the results of a preliminary computer simulation study of the structure of a-C:H and a-Si:H using an approximate molecular dynamic density functional theory, and discuss its viability in the study of the more complex a-Si:C:H ternary alloy.