AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM7
STM Study of Defect Production on the TiO@sub 2@(110)-(1x1) and TiO@sub 2@(110)-(1x2) Surfaces Induced by UV-light

Thursday, November 6, 2003, 10:20 am, Room 328

Session: Oxide Structure, Growth, and Defects
Presenter: P. Maksymovych, University of Pittsburgh
Authors: P. Maksymovych, University of Pittsburgh
S. Mezhenny, University of Pittsburgh
D.C. Sorescu, University of Pittsburgh
J.T. Yates, Jr., University of Pittsburgh
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The photoinduced hydrophilicity of the TiO@sub 2@ surface has been the subject of extensive research due to its technological importance in the development of antifogging and self-cleaning coatings. The phenomenon has been postulated to be due to structural changes of TiO@sub 2@; however, the exact mechanism of the process is unknown. The effect of broadband UV radiation on the stochiometric TiO@sub 2@(110)-(1x1) and the reduced TiO@sub 2@(110)-(1x2) surfaces was observed using the scanning tunneling microscope (STM) in ultra-high vacuum. It was found that the TiO@sub 2@(110)-(1x1) surface is not affected by UV radiation within the statistical error of the experiment. The majority of defect sites on the surface are the bridging oxygen vacancies, and their surface density remains unchanged after UV irradiation. In contrast, production of line defects in the <001> direction was observed on the TiO@sub 2@(110)-(1x2) surface. The overall defective area of the surface was found to increase linearly with UV-exposure, the estimated cross section of the defect formation being 10^-23.5±0.2 cm@super 2@/photon (hv @>=@ 3.0 eV).The origin of the defects is attributed to collective removal of oxygen from the surface. In order to determine whether the UV-induced defects can cause hydrophilicity of TiO@sub 2@, adsorption of H@sub 2@O on the TiO@sub 2@(110)-(1x2) surface was studied by STM. At 300K adsorption of H@sub 2@O occurred preferrentially on the crosslinks of the TiO@sub 2@(110)-(1x2) surface. However, cooling the surface to 110K during H@sub 2@O exposure led to more efficient adsorption, which took place on the added rows of the TiO@sub 2@(110)-(1x2) surface in addition to the crosslinking sites. No changes in the topology of the UV-induced defects were observed after H@sub 2@O exposures.