Ultraviolet photoelectron spectroscopy: Practical aspects and best practices

Ultraviolet photoelectron spectroscopy (UPS) is an important technique for measuring the energies of the valence states of metallic, semiconducting and adsorbate-covered metal and semiconducting surfaces. Applications include catalysis, organic electronics, optoelectronic devices and photovoltaics. While it is relatively straightforward to obtain a UPS spectrum in a laboratory photoelectron spectrometer equipped with an ultraviolet discharge lamp, obtaining a meaningful spectrum is more difficult and depends on various factors, including proper sample preparation and the elimination of surface charging. The basics of the technique, along with procedures for proper measurement of valence spectra of bare and adsorbate-covered metal and semiconducting surfaces, and conjugated polymer/oligomer films, are described. Best practices for presenting UPS data and measuring work functions from UPS spectra are also discussed.