Analysis of surface structures using XPS with external stimuli

X-ray Photoelectron Spectroscopy, XPS, due to the perfect match of its probe length (1-10 nm) to nanoparticle size, chemical specificity, and susceptibility to electrical charges, is ideally suited for harvesting chemical, physical and electrical information from nanosized surface structures. In addition, by recording XPS spectra while applying external d.c. and/or pulsed voltage stimuli, it is also possible to control the extent of charging and extract various analytical information. In the simplest form, application of a static (d.c.) voltage stimuli enhances separation of otherwise overlapping peaks of gold nanoparticles from that of metallic gold. When the voltage stimuli is applied in the form of rectangular pulses, dynamic information is obtained from the frequency dependence of the charging shifts. This enables us to better probe the composition of nanoparticles produced (i.e. silicide formation, or whether or the extent of reduction, etc.) when platinum salt is deposited on silicon substrates. Finally, by recording the data in different time windows, XPS spectra can be recorded in time-resolved fashion. Time-resolved spectra can be used to detect, locate and quantify the charges developed in various surface structures like gold(core)/ silica(shell) nanoparticles on a copper substrate.