| AVS 56th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS1-TuM |
| Session: | Oxide Surfaces: Reactions and Structure |
| Presenter: | S. Gutmann, University of South Florida |
| Authors: | S. Gutmann, University of South Florida M. Wolak, University of South Florida M. Conrad, University of South Florida M.M. Beerbom, University of South Florida R. Schlaf, University of South Florida |
| Correspondent: | Click to Email |
The work function of conductive oxide thin films is an important parameter determining the band line-up at interfaces to active electronic materials in optoelectronic devices. The presented experiments aimed at the measurement of the work function of indium tin oxide (ITO), and nanocrystalline TiO2 and ZnO thin films using photoemission spectroscopy. Traditionally, ultraviolet photoemission (UPS) is used to measure the work function of solid surfaces by means of the photoelectric effect. Such measurements are able to yield absolute work function values.
Our experiments showed that UPS measurements reduce the work function of oxide surfaces by up to 0.5 eV. This effect occurs within seconds, effectively preventing measurements of the ‘true’ work function of surfaces prior to UV exposure. A similar effect is observed when exposing oxide surfaces to x-ray doses typical for x-ray photoemission spectroscopy measurements. It was possible to quantify these effects through the use of low intensity XPS (LIXPS) based work function measurements, which allow a time-window sufficiently long for work function measurements without significantly influencing the work function. The experiments suggest that the work function reduction occurs through the hydroxylation of oxygen vacancies in the oxide surfaces by means of photochemical dissociation of adsorbed water molecules.