X-ray photoelectron spectroscopy involves irradiating a surface with soft X-rays and energy analysing the emitted photoelectrons. Since these electrons have energies which are typically less than 1500 eV they interact strongly with material, and so can only escape from the top few atomic layers. The binding energy of the core levels from which the photoelectrons are emitted are sensitive to the number of electrons in the valence band, and so the technique enables chemical state information to be obtained from the top few atomic layers of a surface. Analyses may be obtained from both conducting and insulating material and the data is relatively easy to quantify. Modern instruments are also able to produce photoelectron images with a spatial resolution of the order of a micron.
The photograph shows the Kratos Axis Ultra located in the School of Materials at the University of Manchester.
The instrument has an aluminium/magnesium dual anode and a monochromated aluminium X-ray sources. It is capable of:
- Spectroscopy from a single point, from an area 700 microns by 300 microns, down to 15 microns diameter.
- Imaging acquired in parallel, with a selectable field of view from 800 microns to 200 microns.
- Spectroscopic Imaging, also known as spectromicroscopy, where a series of images, incremented in energy, are collected so that each pixel in the image contains a spectrum. This allows quantification of images by measuring photoelectron peak areas and separation of overlapping photoelectron peaks using peak fitting to the spectrum at every pixel in the image. Multivariate analytical techniques are required to improve the signal/noise in the data and to facilitate analysis of the large amount of data acquired.
A glove box is available for mounting samples in inert atmospheres.
This instrument is available for use by all university researchers and external organisations. Further details concerning access, sample preparation and charges are available from the facility manager, Dr Ben Spencer