Similar to X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS) is based on the photoelectric effect, but uses much lower energy ultraviolet light (21.2eV) to eject valence electrons from the near-surface (~1nm) of materials. UPS is typically used for studying electronic structure of solids.

Figure 1

Schematic of UPS experiment.

Figure 2

Semiconductor band structure with valence electrons accessible in a UPS experiment showing VBM, WF, and IP.

Figure 3

UPS spectra showing work function (left) and valence band maximum (right) for a halide perovskite solar material.

Information Obtained

  • Valence Band Maximum (VBM) = Highest occupied energy state below the Fermi level
  • Work Function = Energy required to remove an electron from the surface
  • Ionization Potential = Energy difference between vacuum level and valence band maximum or minimum energy required to remove a valence electron from the surface

Sample Requirements

  • Generally need a conducting or semiconducting sample that is 3mm X 3mm or larger
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