X-ray photoelectron analysis of surface functional groups on diamond-like carbon films by gas-phase chemical derivatization method

Oxygen-related surface functional groups on diamond-like carbon (DLC) films were derivatized with fluorine- and nitrogenrelated groups by the gas-phase chemical derivatization (GCD)method, and the groups were analyzed quantitatively by X-ray photoelectron spectroscopy (XPS). It is desirable that a derivatization reaction is unique to the target group; however, it usually causes undesirable side reactions which affect other groups. This diversity of the reactions has complicated the analysis. In this report, we have overcome the problem by applying amathematical treatment which takes the side reactions into account. This improved analysis shows that it is no longer necessary to have derivatization reactions unique to the target groups. As a result, it is demonstrated that the carbonyl (C=O) group is the dominant surface functional group on both the DLC and its wet-oxidized films, the carboxyl (COOH) group plays a minor role, and the presence of the hydroxyl (OH) group is logically denied. Considering the oxidation steps of these oxygen-related surface functional groups, it is suggested that the C=O group on the DLC films requires the cleavage of the carbon-carbon bond with a relatively high activation energy barrier to change into the COOH group.