Oxygen doping effect on the wettability of diamond-like carbon thin films

Diamond like carbon (DLC) thin films as a great coating to protect biomedical tools and optical devices are being developed. Modifying the surface properties, such as wettability, is necessary in some application. In this research, oxygen doping effect on the DLC films wettability was investigated. Oxygen doped diamond-like carbon (DLC) thin films were deposited by the RF-PECVD method with different oxygen concentrations in feeding gas (0.0, 1.9, 3.8, 5.6, 7.4 and 9.1 vol%). The film's structure was studied by Raman spectroscopy (RS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The chemical composition was determined by a combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). Surface roughness and morphology of the films were analyzed by an atomic force microscopy (AFM). Wettability of the films was characterized by measuring the contact angles of the films with water. The results showed that by increasing the incorporation of oxygen into the films' structure, the contact angles of water with films were reduced. The increase in the oxygen content of the films, from zero to 11 at%, caused to reduce water contact angles from 78.4° to 66.0°. By adding the oxygen into the film's structure, CO and CC bonds content increased in the films. Due to the more polarizability of CO and CC bonds in comparing with CC and CH bonds, a polar component of films' surface energy was increased by adding the oxygen to the films' structure. The surface roughness of the un-doped and doped DLC films were so low (less than 1 nm) that they had no roles in the films' surface energy. Doping the DLC films with oxygen caused to increase wettability, without no significant change in the morphology and surface roughness.