A comprehensive study on hydrogenated diamond surfaces as obtained by using molecular hydrogen

Diamond surface hydrogenation is generally carried out with atomic hydrogen obtained by either microwave plasma or heated filaments. Both these techniques present some drawbacks, given by some instabilities and containment difficulties in the former case, and by some surface contamination by the elements of the filaments themselves, which must be very close to the substrate, in the latter. Surface hydrogenation can be easily obtained by molecular hydrogen, at substrate temperatures not much different from those used in the above methods, but only via thermal means and without the aforementioned drawbacks. In this paper we describe a systematic study carried out on hydrogenated surfaces obtained at different temperatures, from 700 to 900 °C, and on different diamond materials (natural and HPHT), by exposing different surfaces such as (100), (111) and (110) to molecular hydrogen. The results indicate that values of surface resistivity are comparable to those obtained using hot filaments, particularly at temperatures around 800 °C, and that the activation energy related to the establishment of surface conductivity is relatively low. Surface resistivity, XPS (X-ray Photoelectron Spectroscopy), AFM and µ-FTIR in reflection-transmission mode data indicate that the efficiency of surface hydrogenation with the consequent low values of surface resistivity is quite similar for the three surface orientations, but also that in the case of (100) orientation this efficiency is lower.