Temperature evolution of the surface region of CVD diamond: an electron spectroscopy study

An electron spectroscopic investigation (photoemission and X-ray induced Auger emission) of the near surface region of undoped CVD polycrystalline diamond is presented. The focus is on compositional and structural changes brought about by desorption processes (either photon or thermally induced) and on the associated changes in the material’s properties. Photon and low temperature induced desorption of O containing species, resulting in a clean H terminated diamond surface, is found to decrease the diamond surface conductivity (SC) and to lower the vacuum energy. Electron emission is highly favoured from such a surface, as witnessed by its negative electron affinity (NEA). H desorption at T ≈ 900 °C leads to surface reconstruction and causes both the vacuum energy to rise and the electron energy levels to bend downwards. As a result, the diamond electron affinity is driven from negative to positive. At T = 1050 °C, the first stages of a graphitization process that propagates from the surface inwards are revealed by an increasing conductivity in the film surface region, though still not by the development of graphitic features in the spectra.