The role of (sub)-surface oxygen on the surface electronic structure of hydrogen terminated (100) CVD diamond

In this work, scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) were applied to investigate the surface morphology and the surface electronic structure of plasma-treated (100)-oriented CVD diamond films. These films were hydrogenated using a conventional MWPE-CVD (microwave plasma enhanced chemical vapour deposition) reactor containing a H2 or a H2 / O2 mixture. A comparison is made between (100)-oriented CVD diamond films hydrogenated with and without a small addition of oxygen (1%). X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS) measurements point to the presence of O-atoms at the (sub)-surface of the diamond film. The measured conductivity is significantly different for the two processes of hydrogenation. Annealing experiments point out that the samples, which were terminated using the H2 / O2 mixture are still conductive enough after annealing at 410 °C to enable STM experiments. Here, we discuss the mechanism for STM imaging of H2 / O2 treated diamond films, associated with surface states induced by the oxygen incorporation.