XPS and UPS have their own specific application domains. These domains relate to physical parameters like excitation energy or linewidth. UPS sources can excite core energy level like carbon 1s level. They can be used in applications ranging from 0 tot 60 eV. XPS sources cannot be used for studying the fine structure of the valence band. The following diagram differentiates the two techniques.
Respective UPS and XPS applications domains.
These last years however, a number of breakthroughs have been done; monochromatic sources and charge neutralisation guns have revealed XPS as a valuable investigation tool for polymer studies.
The main advantage of UPS is a very thin excitation line and a photon flux intensity higher than with an X-ray monochromator.
By using an X-ray monochromator and a charge neutralisation gun it is possible to study core level, valence band and Auger transitions without changing the technique. It allows a more comfortable reading of the spectra and a better interpretation of the specimen chemical nature.
UV emission advantages.