NCESS

The National Centre for Electron Spectroscopy and Surface Analysis (NCESS), brings together industry and academia to address problems in materials science, surface science
and engineering.

Collaborative programmes with industry and the academic community have been set up for targeted research areas, ranging from studies of polymers and composites through to ceramics, semiconductors, metals and novel materials. It offers repayment services to industry and has an EPSRC user programme which provides and supports access to its facilities to help academic groups with their own research.

High Resolution X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) is a powerful technique widely used for the surface analysis of materials. At low energy resolution it provides qualitative and quantitative information on the elements present. At high energy resolution it gives information on the chemical state and bonding of those elements.

Further chemical information is available from the XPS valence band. Variation of electron take-off angle or sputter depth profiling can provide information on the vertical heterogeneity of samples, and imaging/microanalysis techniques allow determination of lateral homogeneity with resolutions of <50µm. Samples can be subjected to various treatments within the spectrometer vacuum system prior to analysis, e.g. heating, cooling, scraping, cleaving, sputter cleaning etc.

XPS is commonly used for the surface analysis of polymers, coatings, catalysts, composites, fibres, ceramics, pharmaceutical/medical materials and materials of biological origin.

In the XPS technique, X-ray photons of a well defined energy (e.g. Al K (alpha) radiation at 1486.7eV) impact the sample and eject photoelectrons from the atomic core level and valence levels. The photoelectrons travel only a relatively short distance (~3nm) in solids before impacting the lattice and suffering an inelastic collision. This makes the technique inherently surface sensitive. The ejected photoelectrons are energy analysed (usually by a combination of an electrostatic lens and an electrostatic hemispherical analyser) and strike an electron detector. A computer based data system scans the electron energy and accumulates counts of the detected electrons, hence generating the photoelectron spectrum. The data system is also used for subsequent manipulation of spectra, e.g. elemental identification, quantification, curve fitting and plotting.

Click here for a case study detailing NCESS' x-ray photoelectron spectroscopy characterization of technological polymer surfaces.