Studies of Ion Channelling and Dechannelling in Diamond.

The dechannelling of protons in diamond has been investigated, in good crystals, in crystals containing high concentrations of defects, and in crystals overlaid with amorphous surface layers. The energy loss of light ions in diamond has also been investigated. Measurements have been made of the dechannelling in good diamond crystals for the three major axes <110>, <111> and <100>, at room temperature, over a range in energy of 1.0 MeV to 8.9 MeV, and at 1.0 MeV, at room temperature, at 300(DEGREES)C and at 600(DEGREES)C. Measurements are also reported for planar channelling along {110}, {111} and {100} at 1.0 MeV and room temperature. The energy dependence of the axial dechannelling is found to scale with a length z(,e) which depends on electronic scattering; it is concluded that this is the major source of dechannelling in good crystals. The temperature dependence of dechannelling is found to be rather small compared with other crystals. The experimental results are compared with calculations based on the diffusion model. The relative effect of various approximations in the diffusion model is explored. The effect of surface layers of carbon, gold and aluminium on the 1.0 MeV, <110>, yield, both at the surface and as a function of depth, has been investigated. The yield at the surface is compared with calculations based on Thomas-Fermi multiple scattering theory, with a number of approximations for the yield as a function of angle. The yield calculated with the experimental azimuthal-averaged angular yield is in good agreement with experiment. The yield as a function of depth is compared with diffusion model calculations, and good agreement is found. Approximations have been derived for the increase in yield due to thin layers, and are found to be in reasonable agreement with experiment. The application of a scaling law for different layers, based on a power-law scattering potential has been investigated and is applied to compensate the aluminium measurements for a small amount of oxygen present in the layer. Dechannelling by defects, namely platelets and nitrogen aggregates, in Type Ia diamond has been investigated and it is shown that the increase in yield in these diamonds can be explained in terms of the defects known to be present in the diamond from infra-red spectroscopy. Models are derived for the dechannelling effect of stacking faults and of dislocation loops, and are applied to the dechannelling by platelets. The relation between platelets and B-aggregates of nitrogen is considered. The energy loss, in thin diamond crystals, of 3 to 12 MeV protons, 12 to 18 MeV alpha particles and 24 MeV lithium ions has been measured, both in random and in channelled directions. Results are also reported for the random straggling of protons. For random stopping, the results are in agreement with a recent compilation of stopping data. The ratio of channelled to random stopping -power is compared with the predictions of the theories of Esbensen and Golovchenko and of Dettmann. An expression has been derived for the stopping-power of a periodic electron gas and is used to modify the theory of Dettmann. The results suggest that the channelled energy loss is determined in this case by the energy loss in the major plane passing through the axis under study.