Structures of sulfur on TiO2(110) determined by scanning tunneling microscopy, X-ray photoelectron spectroscopy and low-energy electron diffraction

E. L. D. Hebenstreit, W. Hebenstreit, U. Diebold

Department of Physics, Tulane University, New Orleans, LA 70118, U.S.A.

Surf. Sci. 470 (2001) 347-360

The temperature dependent adsorption of sulfur on TiO2(110) has been studied with X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). Sulfur adsorbs dissociatively at room temperature and binds to fivefold coordinated Ti atoms. Upon heating to ~120 °C, 80% of the sulfur desorbs and the S 2p peak position changes from 164.3±0.1 to 162.5±0.1 eV. This peak shift corresponds to a change of the adsorption site to the position of the bridging oxygen atoms of TiO2(110). Further heating causes little change in S coverage and XPS binding energies, up to a temperature of ~430 °C where most of the S desorbs and the S 2p peak shifts back to higher binding energy. Sulfur adsorption at 150 °C, 200 °C, and 300 °C leads to a rich variety of structures and adsorption sites as observed with LEED and STM. At low coverages, sulfur occupies the position of the bridging oxygen atoms. At 200 °C these S atoms arrange in a (3×1) superstructure. For adsorption between 300 °C and 400 °C a (3×3) and (4×1) LEED pattern is observed for intermediate and saturation coverage, respectively. Adsorption at elevated temperature reduces the substrate as indicated by a strong Ti3+ shoulder in the XPS Ti 2p3/2 peak, with up to 15.6% of the total peak area for the (4×1) structure. STM of different coverages adsorbed at 400 °C indicates structural features consisting of two single S atoms placed next to each other along the [001] direction at the position of the in-plane oxygen atoms. The (3×3) and the (4×1) structure are formed by different arrangements of these S pairs.

Corresponding author: Ulrike Diebold (diebold at iap_tuwien_ac_at).

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