A highly surface sensitive technique for the analysis of valence bands and the workfunction of materials.
Ultraviolet Photoelectron Spectroscopy (UPS) is similar to application to XPS, the difference being that the ionising radiation, typically below 50 eV, are used. Ultraviolet photons are produced using a gas discharge lamp typically filled with helium (argon and neon can also be used); the photons emitted by helium gas have energies of 21.2eV (He I) and 40.8eV (He II).
As lower energy photons are used, most core level photoemission lines are not accessible using UPS, so spectral acquisition is limited to the valence band region.
UPS is commonly used to determine material work functions - important when understanding electronic materials.
As UPS primarily probes valence electrons and bonding orbitals - it can reveal crucial details about bonding structures on the right system.
Generate energy level diagrams
In combination with other techniques such as REELS or UV-Vis spectrophotometry - UPS can aid in developing electronic structure diagrams and further understand your materials.
One of the more niche uses of UPS - identifying the orientation of self-assembled monolayers. Unlike average tilt angle techniques, UPS can identify these arrangements independently.
High resolution valence band measurements
Highly surface sensitive (very sensitive to contamination)
Work function measurements
Characterisation of adsorbed monolayers
Dopant concentration measurements
Semiconductor junction parameters (e.g. barrier heights and band edges)
Systems at Harwell and UCL are equipped with UPS capabilities.