AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS1+MC-ThA

Paper SS1+MC-ThA9
Work Function Changes and Surface Chemistry of Oxygen and Hydrogen on Indium Tin Oxide

Thursday, October 5, 2000, 4:40 pm, Room 208

Session: Oxidation and Molecule-Oxide Interactions
Presenter: J.A. Chaney, Naval Research Laboratory
Authors: J.A. Chaney, Naval Research Laboratory
P.E. Pehrsson, Naval Research Laboratory
Correspondent: Click to Email
Indium tin oxide (ITO) is used as a transparent, semiconducting substrate for many device applications. However, there is an inadequate understanding of ITO surface properties, its interaction with gaseous species, and the physical/electronic changes imposed by its surface chemistry. The surface physics and chemistry of oxygen plasma treated ITO were investigated under ultra high vacuum conditions. The work function (@PHI@) of ITO was determined by a vibrating Kelvin probe calibrated with a graphite standard. Sample composition, electronic structure and chemistry were examined by Auger electron spectroscopy (AES), energy loss spectroscopy (ELS), and high resolution electron energy loss spectroscopy (HREELS). Commercial ITO films were heated in-vacuo to remove physisorbed species and then exposed in-situ to oxygen or deuterium activated with a hot metal filament. Oxidation increased the work function from 5.2 to 5.6 eV, but @PHI@ then decayed to <5.2 eV, possibly due to oxygen diffusion into the bulk along defects and grain boundaries. The AES oxygen level was stable after oxidation, and the ELS spectrum consistently showed a strong feature at 0.7 eV for oxidized samples. Deuteration visibly metallized the film and sharply reduced the surface oxygen level. The ELS feature simultaneously disappeared, and the work function decreased to 4.6 eV. The HREELS of clean ITO revealed substantial C-H contamination, which persisted after heating to ~300°C. Even substantial oxygen treatment did not remove the hydrogen signal, suggesting that C-H permeates the ITO film.