| AVS 57th International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS2-WeM |
| Session: | Electron, Photon and Ion Beam Induced Surface Modification |
| Presenter: | M. Conrad, University of South Florida |
| Authors: | M. Conrad, University of South Florida S. Gutmann, 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 a number of metal oxide thin films was measured using low intensity x-ray and ultraviolet photoemission spectroscopy (LIXPS, UPS).
Our experiments revealed that UPS based work function measurements of a variety of metal oxide surfaces previously exposed to the ambient or in contact with water vapor caused an immediate work function reduction of the order of 0.5 eV. This artifact was demonstrated using LIXPS work function measurements, which expose the sample surface to only a small fraction of the radiation flux encountered during UPS measurements. This enabled the measurement of the work function prior to the UPS characterization, revealing the UPS-related work function reduction. LIXPS measurement performed after the UPS measurements showed that sample charging effects can be ruled out as causes of the work function reduction, and that the work function change is permanent. These results suggest that a photochemical hydroxylation of the surface through photodissociation of water molecules occurs during the UPS measurement, which results in a surface dipole reducing the work function. Additional experiments investigated the influence of standard XPS measurements as well as LIXPS measurements on the work function. These experiments demonstrated that XPS measurements also cause a work function reduction similar to UPS measurements, albeit during a longer exposure time frame. In contrast, LIXPS measurements do not result in a significant work function reduction, i.e. can be used as a reliable work function characterization tool for oxide surfaces.