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 nitrogen-related 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 a mathematical 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. Copyright (C) 2010 John Wiley & Sons, Ltd.