X-ray photoelectron spectroscopy (XPS) involves irradiating a surface with soft X-rays and analysing the kinetic energy of 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 sampling depth for XPS is usually between 3 and 10 nm). The binding energy of the atomic 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. Larger chemical shifts in binding energy are observed from more electronegative bonding environments, and so chemical species are distinguishable and quantifiable. Metallic (incl. grpahitic carbon) and oxide environments are also distinguished by notable changes in the peak shape of photoelectron peaks.
The photograph shows the Kratos Axis Ultra Hybrid located in the School of Materials at the University of Manchester (in The Mill).
The instrument is comprised of:
- Al Kα monochromated X-ray source (1486.6 eV)
- Non-monochromated dual anode Al and Mg Kα (1253.4 eV) X-ray "flood" source
- Argon ion gun for destructive depth-profiling (note that this will alter the chemical state of the sample)
- A glove box may be mounted on the load lock vacuum chamber for sample moutning under inert environments
It is capable of:
- Spectroscopy from a single point, from an area of typically 700 μm × 300 μm, down to 15 μm diameter.
- Imaging acquired in parallel, with a selectable field of view from 800 μm to 200 μm.
- 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-to-noise ratio and to facilitate analysis of the large amount of data acquired
This instrument is managed by Experimental Officer Dr Ben Spencer.
The facility is available for use by all university researchers and external organisations. Contact us for further details concerning access, sample preparation and charges.
For external/ commercial access please contact us through the Materials Testing and Analysis unit.
Data are analysed using CASAXPS
Analysis is often not straightforward, and so we run regular in-house workshops on XPS data analysis.
The faculty includes some specialised XPS techniques including near ambient pressure (NAP) XPS, based in the Photon Science Institute and the School of Chemistry. Find more details on the NAP-XPS website.