Getting more from XPS imaging: multivariate analysis for spectromicroscopy

The spherical mirror analyser (SMA) is used to acquire fast XPS images from specimen surfaces with high lateral and energy resolution. Here we review the properties of the SMA including spatial and energy resolution and provide examples of the capabilities of such an imaging analyser. In the last few years the combination of the SMA with a two-dimensional, pulse counting electron detector has again increased the level of information available for surface characterisation. The delay-line detector (DLD) represents the next generation of photoelectron detection for XPS imaging and has allowed the realisation of quantitative surface chemical state microscopy by X-ray photoelectron spectroscopy. To generate such information requires the acquisition of multi-spectral datasets comprising a series of images incremented in energy so that each pixel contains photoelectron intensity as a function of energy. The datasets generated by this method contain >65,500 spectra and are therefore ideally suited to multivariate analysis to analyse the information content of the dataset and as a tool for noise reduction in individual images or spectra. The spherical mirror analyser