UPS only investigates occupied states, but the bandgap is the energy difference between the lowest unoccupied and the highest occupied state so you need to determine the lowest unoccupied state from somewhere else. UPS is not enough, you can try IPE, STS or UV-Vis, but carful with the latter because the optical bandgap may be larger than the actual one.

Hello Chandra,

photoelectron spectrometry allows to measure the bandstructure E(k) for occuoied bands. That means, the Fermi energy must cut the band of conductivity. If this is the case, you can find the band gap.

With Regard

R. Mitdank

UPS provides precise information for valence band dispersion, whereas XPS helps to understand atomic occupancies, oxidation state, stoichiometry etc. Many photoelectron spectrometers have both the facilities. If so, you may acquire data for both, which will give you more detailed information regarding the band-structure. Alone UPS may or may not be helpful in determining bandhap.

Regarding the sample preparation, you may try pure bulk pellets. In case of thin films, the idea is photoelectron spectroscopy is a surface probing technique i.e., if your thin film has a micron-order thickness, you'll get right information. But, if it is of nanometer scale, then it's difficult to say. It'll depend on the penetration capability of the radiation, you are using. It depends on the source i.e., you can know about it from the instrumental specifications.