Analysis of surface structures using XPS with external stimuli

Abstract

X-ray Photoelectron Spectroscopy, XPS, due to the perfect match of itsprobe length (1-10 nm) to nanoparticle size, chemical specificity, andsusceptibility to electrical charges, is ideally suited for harvestingchemical, physical and electrical information from nanosized surfacestructures. In addition, by recording XPS spectra while applyingexternal d.c. and/or pulsed voltage stimuli, it is also possible tocontrol the extent of charging and extract various analyticalinformation. In the simplest form, application of a static (d.c.)voltage stimuli enhances separation of otherwise overlapping peaks ofgold nanoparticles from that of metallic gold. When the voltage stimuliis applied in the form of rectangular pulses, dynamic information isobtained from the frequency dependence of the charging shifts. Thisenables 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, byrecording the data in different time windows, XPS spectra can berecorded ill time-resolved fashion. Time-resolved spectra can be usedto detect, locate and quantify the charges developed in various surfacestructures like gold(core)/silica(shell) nanoparticles oil a coppersubstrate.