Effect of Heating in Ammonia on the Photoconductivity of a Diamond Soft X-Ray Detector

Polycrystalline diamond films are promising materials for the fabrication of X-ray detectors. This work concerns the effect of heating a polycrystalline diamond film in an ammonia atmosphere at 600 °C on the surface chemical state and photoconductivity under irradiation with bremsstrahlung from a copper anode X-ray tube. The diamond film is synthesized by chemical vapor deposition from a hydrogen-pentane mixture activated by microwave plasma discharge. Conductive electrodes having the comb-shaped meander geometry are formed on the film surface by ultraviolet laser irradiation at a wavelength of 355 nm. The chemical state of the material surface is investigated by X-ray photoelectron and Raman spectroscopic techniques. Heating in ammonia is found to alter the compositions and structures of both the initial diamond film surface and the laser–treated regions. Amino groups are attached to the diamond film surface (with a nitrogen concentration of about 1 at. %), increasing its electrical conductivity. The laser–treated regions contain approximately 7 at. % of nitrogen in graphitic and pyridinic forms as well as in amino groups. The chemical modification of the sample and the increased structural ordering of the carbon material in the conductive electrodes enhance the diamond film photoconductivity upon soft X-ray radiation absorption.