Work function changes and surface chemistry of oxygen, hydrogen, and carbon on indium tin oxide

The surface chemistry of indium. tin oxide (ITO) has been investigated with Auger electron spectroscopy (AES) and high resolution electron energy loss spectroscopy (HREELS). A vibrating Kelvin probe (KP) with a graphite refer ence was used to monitor the absolute work function (fl of ITO as a functio n of chemical modification. The ITO was exposed in situ to molecular hydrog en (H-2), hot-filament-activated oxygen (O-2(*)), and hot-filament-activate d deuterium (D-2(*)). The initial Phi of ITO was determined to be 5.2 eV, a nd surface chemical changes had strong effects on this value, as seen by KR Exposure of clean ITO to O-2(*) increased Phi to similar to5.6 eV, but the increase was short-lived. The changes in Phi over time were correlated wit h the uptake of carbon impurities in ultra high vacuum (UHV), as monitored by AES. The HREELS of ITO revealed significant hydrocarbon impurities. Chemical red uction of ITO produced a metallic surface and dehydrogenated the adsorbed h ydrocarbons. Both re-oxidation of metallic ITO and oxidation of clean ITO t emporarily removed adventitious carbon from the surface, but oxidized ITO a dsorbed an even larger quantity of carbon over time. (C) 2001 Elsevier Scie nce B.V. All rights reserved.