X-ray photoelectron spectroscopy – XPS/ESCA

X-ray photoelectron spectroscopy is a chemical analysis method that features an especially high surface sensitivity with a signal depth of approximately 5 nm. X-ray exposure generates photoelectrons. Due to the element-specific energy level, their energy allows conclusions to be drawn regarding the material composition (all elements except H and He). The detection limit is around 0.1 percent and the analysis accuracy is in the percentage range. This method even makes it possible to analyse monolayers or minor surface contaminants.

The surface of materials or coatings often has a different composition than the base material because of reaction layers, adsorbates or surface tension-driven processes. In combination with ion beam induced erosion (sputtering), surface concentrations can be identified and depth profiles with a depth of 100 nm and more can be prepared for example.

XPS also allows statements to be made about bonding states, oxidation states or the proportion of various bonding partners, for example in polymers (e.g. CH2 = CH and -CH2-O) since the chemical environment of an atom influences the energy level of the electrons.

XPS characterization of thin metal films

XPS characterization of thin metal films. XPS spectrums of a 50 nm Ni-Ag film before and after abrasion (approx. 30 nm) of the surface.
© Fraunhofer IST

XPS spectrums of a 50 nm Ni-Ag film before and after abrasion (approx. 30 nm) of the surface. Ag is concentrated on the surface.

Characterization of bonding states

Characterization of bonding states. C-peak of an XPS measurement on PET film.
© Fraunhofer IST

C-peak of an XPS measurement on PET film. The different bonding partners of the carbon atoms lead to peak splitting.