Growth and characterisation of CVD diamond wires for x-ray detection

In order to gain insight into the mechanism of diamond growth on metallic wires (50-500 mu m diameter), we have investigated the deposition process in a hot filament chemical vapour deposition (HFCVD) reactor. A two-dimensional model of our HFCVD reactor was developed in order to interpret the experimental data which indicate an evident influence of the substrate wire diameter on the gas species concentration and oil the diamond growth rate. The theoretical model indicates a reduction of the growth rate as the substrate diameter increases due to the reduction of hydrogen and the active radicals concentrations at the substrate as its growth area increases. In view of a possible application of. such samples as X-ray detectors, we investigated their electrical properties by analysing the current/voltage characteristic in, a metal/diamond/metal geometry at different temperatures. The activation energy of the conductivity is found to be dependent on the applied electric field. The experimental data support a Poole-Frenkel conduction with overlapping centres. Finally the response of our diamond wires to X-ray radiation flux was investigated. A sensitivity of about 5 x 10(-6) AsGy(-1) was measured under a 100 keV Bremsstrahlung X-ray flux and the photocurrent is almost linear with respect to X-ray tube current. (C) 1997 Elsevier Science S.A.