Surface analysis | X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) is the most broadly applicable surface analysis technique today. It relies on measurements of the energy distribution of photon excited electrons from atoms in the surface region of the solid. It can detect all elements except hydrogen with a sensitivity that varies by only a factor of ~ 30 across the periodic table. The absolute sensitivity is around 0.01-0.3 at.% depending on the element. The electron binding energies are sensitive to the chemical state of the atom and this is used to determine the chemical state of the atoms. Because of this feature, the XPS technique is also known under the acronym ESCA (electron spectroscopy for chemical analysis). It is a non destructive technique (although damage by the X-ray beam can be significant in some organic materials) and in general it is less destructive than the other electron or ion impact techniques (Auger electron spectroscopy AES, and secondary ion mass spectroscopy (SIMS)). The technique is highly surface sensitive with a probing depth of ~ 1-10 nm. The surface area detected can be as large as 1 cm × 1 cm or as small as 3 µm × 3 µm and imaging XPS has become a common feature of the current generation of XPS spectrometers. In recent years, lateral resolutions in the 100 nm range have been achieved by using the new generations of synchrotron light sources with high brightness. With special design of the spectrometer, XPS may be used to analyze gaseous and liquid samples, but it is mostly used for solids.