I have read a few papers where the O 1s energy loss was used determine the band gap of the material. However, will the measured band gap be electrical or optical band gap of the material?
This is a bit of a tricky question.
You see, photoemission spectroscopy leads to excitations from valence states to the continuum, so it will be the optical gap that is measured normally. Usually, measuring the band gap with XPS involves using another technique for the conduction states (e.g. IPES).
However, I know that there are tricks to measure the LUMO using purely XPS results along with some particular assumptions on the system, but I don't know much about these things sadly.
@Rémi Pasquier thank you for your reply. It was really helpful.
Generally, we get the optical band gap from photoemission spectroscopy. one can use UPS measurements to find the work function and valance band onset so that logically you can get the valance band position. so in my knowledge, it will be an optical band gap.
When you combine UPS or XPS with IPE, the result will definitely be the electronic band gap.
If you use a doping-based approximation as done here, I would say it's the electronic gap:
Article Properties of non-IPR fullerene films versus size of the bui...
while if you use the method suggested by Thorsten Schultz in his answer here:
https://www.researchgate.net/post/Is_there_any_recommended_way_to_measure_band_gap_and_fermi_level_of_wide_band_gap5eV_materials
is associated with an excitation, so I would say there it's optical, but you could ask him personally, he'll probably answer it.
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