The sample is illuminated with X-ray radiation of sufficient energy to create core level ionizations of the atoms. The photon energy is transferred to the electron, with some leaving the sample as photoelectrons. The kinetic energy of the emitted photoelectron is given by the difference between photon energy and binding energy of the electron in the sample. Unlike for X-ray or Auger emission, the energy of the photoelectron depends on the X-ray energy used. As X-ray radiation is almost monochromatic, the energy of the measured line can be simply converted into binding energies.
An X-ray source producing quasi-monochromatic radiation (using Al or Mg anodes) is used to generate photoelectrons of different energies. The energy of the emitted electrons is analyzed by a highly sensitive, high energy resolution energy analyzer. The filter energy is scanned over the photoelectron lines and the signal is detected using an electron multiplier. The measured energy distribution is digitalized and displayed by a computer program. Data are saved in various formats for processing and quantification.
The minimum configuration requires an X-ray source and a high resolution energy analyzer suitable for XPS. The X-ray source is equipped with two anodes, Al and Mg, delivering different photon energies so that the photoelectron lines can be differentiated from the Auger lines (at fixed kinetic energy). Modern analyzers have selectable energy resolution and large working distance (good sample clearance). Having the electron source built into the analyzer provides ease of use and alignment, with full AES capability on a single flange. The STAIB DESA- family is optimized for XPS and AES.
- It is important to analyze clean, contamination free samples. The most practical and universal cleaning method is the use of an ion beam (of Argon or other heavy gases) to sputter away the surface layers (which are mostly contamination). The same ion source can be used for Ion back-Scattering Spectroscopy (ISS).
- Computer control of the analyzer system allows users to pre-set series of measurements (i.e. for over night).
- When combined with a micro-focus source, full Auger capabilities become available, including AES, SEM and SAM.
- A special low energy electron source can be used for charge compensation on isolating samples.