Electronic surface barrier properties of fluorine-terminated boron-doped diamond in electrolytes

The surface bond structure and electronic surface barrier in electrolytes were analysed for fluorinated boron-doped single crystal diamond. The diamond surface was exposed to a CF4 RF-plasma combined with in-situ pre-heating in ultra-high vacuum to remove adsorbates. This treatment resulted in full surface coverage by mixed carbon–fluorine functionalities of 2 nm in thicknesses and possibly with cross-linked or branched structures, leaving no traces of carbon-oxygen groups and non-diamond carbon phase, as determined by high-resolution X-ray photoemission spectroscopy. The capacitance-voltage, impedance spectroscopy and redox characteristics of the fluorinated diamond were investigated in various electrolytes. The analysis of data showed that electronic barrier at the fluorinated surface was close to zero at equilibrium, meaning no surface depletion of the boron-doped diamond. In comparison, the surface barrier of identical oxygen-terminated diamond was approx. 1.6 eV using the same evaluation methods. The low surface barrier of the fluorinated surface remained stable after anodic polarisation and did not depend on pH or ion species.