Modification of Monomolecular Self-Assembled Films by Nitrogen−Oxygen Plasma

• Published in: The journal of physical chemistry. B Vol. 110; no. 25; pp. 12523 - 12529
• Main Authors: Weng, Chih-Chiang, Liao, Jiunn-Der, Wu, Yi-Te, Wang, Ming-Chen, Klauser, Ruth, Zharnikov, Michael
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 29.06.2006
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp060572r

The modification of octadecanethiolate self-assembled monolayers on Au and Ag by nitrogen−oxygen downstream microwave plasma with variable oxygen content (up to 1%) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy. The primary processes were dehydrogenation, desorption of hydrocarbon and sulfur-containing species, and the oxidation of the alkyl matrix and headgroup−substrate interface. The exact character and the rates of the plasma-induced changes were found to be dependent on the substrate and plasma composition, with the processes in the aliphatic matrix and headgroup−substrate interface being mostly decoupled. In particular, the rates of all major plasma-induced processes were found to be directly proportional to the oxygen content in the plasma, which can be, thus, considered as a measure of the plasma reactivity. Along with the character of the observed changes, exhibiting a clear dominance of the oxidative processes, this suggests that the major effect of the oxygen−nitrogen downstream microwave plasma is provided by reactive oxygen-derived species in the downstream region, viz. long-living oxygen radicals and metastable species.