A methodology for curve-fitting of the XPS Si 2p core level from thin siloxane coatings

Plasma-enhanced coating processes are recognised as a route to well-adhered, conformal coatings, and are often used as a means of modifying the surface properties of materials, while having a minimal effect on the bulk characteristics of the substrate. Here, a method for providing an understanding of the chemistry of siloxane coatings prepared by plasma liquid deposition in atmospheric pressure (AP) is described. An iterative Si 2p-C 1s method for curve-fitting the C 1s and Si 2p core levels of siloxane coatings thinner than the depth of analysis of XPS has been developed when the substrate is poly(ethylene terephthalate) (PET) film. In addition to the determination of unambiguous binding energy positions for four siloxy environments, this has allowed the elemental composition of the coating to be determined in isolation of the substrate. Application of the binding energies to the Si 2p core levels of industrially relevant materials where the composition is not known by any other means can now be carried out. This can be used to provide understanding of the relationship between coating chemistry and plasma parameters, which is essential in the development of novel processes such as AP plasma liquid deposition, and will result in the deposition of coatings with controlled properties. Copyright (c) 2007 John Wiley & Sons, Ltd.