X-ray photoelectron spectroscopy
Principles
X-ray photoelectron spectroscopy (XPS - ESCA) was developed in the mid 1960s by the K. Siegbahn group (University of Uppsalla, Sweden). The first Belgian XPS system was installed in our laboratory beginning 1970s. A sample, introduced in an ultra high vacuum chamber, is bombarded with an X-ray beam. The kinetic energy (in electron volts, eV) of emitted electrons of all elements (except H and He) present at the surface (analyzed depth between 1 and 10 nm) is measured with a precision of about 0.2 eV. Shape and position of peaks depend on the chemical state of the element (the so-called " chemical shift " effect). Area of peaks used in combination with sensitivity factors allow to calculate mole fractions with a detection limit of a few tenths of percent. A detailed analysis of certain well-resolved peaks allows quantifying functionalities present at the surface. On most recent systems the minimum spatial resolution is of about 15 µm and 5 µm for XPS analysis and XPS imaging respectively. In most cases XPS can be considered as a non-destructive technique.
Applications
XPS can be used to characterize the surface of all types of materials, quite exclusively solids (powders or bulk specimen): biomaterials, catalysts, ceramics, fibers, glass, metals, minerals, polymers... The laboratories sharing the XPS facilities of the Surface Characterisation platform have an uncommon expertise in using the method.
Systems
SSX 100/206 spectrometer from Surface Science Instruments (USA): monochromatized and microfocused AlKα X-ray beam, parking chamber, automatic sample analysis.
Kratos Axis Ultra spectrometer from Kratos Analytical (UK): monochromatized AlKα X-ray beam, Al/Mg non monochromatized twin anode, XPS imaging, catalyst cell (maximum 800°C), sample cooling (~160°C) in both introduction and analysis chamber, ion gun, parking chamber, automatic sample analysis.
Access
Our XPS systems are accessible to academic and industrial research teams. For more information please contact Pierre Eloy
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Useful links
UK ESCA Users Group Surface Science Site (http://www.uksaf.org/home.html)
Surface Science Network (http://www.surfacesciencenetwork.com/forum/)
NIST Standard Reference Data Product Catalog (http://srdata.nist.gov/xps/Default.aspx)