Difficulties in determining valence for Ag0 nanoparticles using XPS - characterization of nanoparticles inside poly (3-sulphopropyl methacrylate) brushes

The formation of silver nanoparticles (10-20 nm) inside poly (3-sulfopropyl methacrylate) brushes was studied by using transmission electron microscopy, UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). Initially, the silver forms Ag-4(2+) clusters that are stabilised by the anionic side groups of the brush. In the presence of a reducing agent, these clusters aggregate into nanoparticles or films. The apparent oxidation state for silver in the different forms was examined using XPS and a chemical state plot. It was seen that the nanoparticles do not display the same chemical shift as the silver film does. The reason for this observation is suggested to be the final and initial state effects. The latter is related to the relatively high amount of under coordinated or charged surface atoms on these particles. Copyright (C) 2010 John Wiley & Sons, Ltd.