Dynamic wetting of low-index diamond planes and polycrystalline diamond with H-terminated and O-terminated surfaces

Control of wettability of diamond surfaces is important for many applications, including chemical sensors, electronic devices based on surface conductivity, electrochemistry, biomolecules immobilization. The contact angle for liquid droplet is sensitive to crystallographic orientation of the facet. We report on the wetting dynamics for single crystal diamond (SCD) plates with low-index planes (111), (100), (110), and for polycrystalline diamond (PCD) film with mixed grain orientations, subjected to different surface treatments – hydrogenation, thermal oxidation and UV-ozone exposure. Also, advancing angle of (311) plane in undersaturated vapor conditions was studied. The water spreading kinetics was monitored by measuring temporal dynamics of the contact angle θ at room temperature in a saturated vapor atmosphere for prolonged time, up to 60 h. Depending on surface state it took a few minutes to several hours to approach the equilibrium contact angle. It was shown that the transition from hydrogenated surfaces to thermally oxidized and then to ozonized ones is accompanied by a significant surface hydrophilization of all the facets studied. The oxidized and ozonized surfaces reveal faster dynamics of θ equilibration in comparison with that for H-terminated diamond. The plane orientation noticeably affects the contact angle: the measured difference Δθ for the diamond planes is significant, especially for ozonized surfaces (Δθ up to 17°), as a consequence of the difference in chemical structure and composition for those facets. Finally, the wetting of polished coarse-grain PCD is discussed by taking into account a spread in the grain orientation and pinning effect for the drop spreading on nanosteps on the grain boundaries. [Display omitted]