X-ray photoelectron spectroscopy: XPS / ESCA

X-ray photoelectron spectroscopy at the Fraunhofer IST.
© Fraunhofer IST, Jan Benz
X-ray photoelectron spectroscopy at the Fraunhofer IST.

How XPS works

XPS is a chemical analysis method that is characterized by secular surface sensitivity with a signal depth of around only 5 nm. X-ray bombardment produces photoelectrons whose energy allows conclusions to be drawn concerning the material composition on the basis of element-specific energy levels (all elements except H and He). Since the chemical environment of an atom influences the energy levels of the electrons, XPS also offers the possibility of making statements regarding bonding states, oxidation states or the proportion of different bonding partners.

Areas of application

XPS analysis provides information on chemical composition and bonding states near the surface and also allows depth profiles as a result of the integrated ion gun. XPS is used, for example, in the following areas:

  • Analysis of surface impurities, e.g. in the form of slight discoloration
  • Inspection of cleaning processes
  • Chemical analysis of ultrathin layers, e.g. passivation layers
  • Analysis of surface treatments, e.g. plasma treatments

Surface segregation of a Ni-Ag layer

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 spectra of a co-deposited 50nm Ni-Ag layer. There is a strong Ag signal at the surface (black). Below the surface (red, approx. 30nm ablated), the Ni signal predominates. The Ag has accumulated on the surface during layer deposition.

Characterization of binding states

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

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

X-ray photoelectron spectroscopy in application

 

Interfacial chemistry and adaptive adhesion

Pretreatment and functionalization

 

Interfacial chemistry and adaptive adhesion

Hygiene and cleaning

 

Atmospheric pressure plasma processes

Plasma polymerization and chemical functionalization

 

Chemical vapor deposition

Atomic layer deposition

 

Chemical, mechanical and thermal surface treatment

Environmentally-friendly surface cleaning