Stability of the surface termination of nanocrystalline diamond and diamond-like carbon films exposed to open air conditions

Abstract

Tailorable surface termination of nanocrystalline diamond (NCD) and diamond-like carbon (DLC) films significantly contribute to their wide potential applications in biomedicine which require defined and stable surface towards aging. Here, we present a comparative study on the surface termination stability of NCD and DLC films in terms of XPS and water contact angle (WCA) measurements. The samples were plasma-treated with hydrogen, oxygen or nitrogen containing functional groups employing low temperature radio frequency (RF) or high temperature microwave (MW) plasma. The samples were exposed to air up to 30 days, during which the termination stability was analyzed by XPS, WCA, AFM, Raman spectroscopy and SEM measurements. It was shown that NCD films were more efficiently hydrogenated in the high temperature MW plasma than in RF plasma, and also the surface stability was better. However, the MW plasma deteriorated the surface of the DLC film. In RF plasma treatment, a contrast between WCA and XPS data was observed. Surprisingly, while the XPS measurements showed relatively stable surface termination for all cases (H-, O- and NH2-terminated surfaces), the WCA values for O- and NH2-treated samples increased by ~200 ÷ 300%. Generally, the NCD film showed more stable surface termination than DLC. The possible reasons of the different behavior of WCA and XPS results, as well as complex characterization of the surface properties of H-, O- and NH2-terminated NCD and DLC film regarding to the aging and surface termination stability are discussed in the article.