Monitoring the interaction of sulfur dioxide with a TiO<f>2</f>(<f>1 1 0</f>) surface at 300 K by scanning tunneling microscopy

Scanning tunneling microscopy (STM), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) were used to study the interaction of sulfur dioxide with the bulk-terminated (<f>1×1</f>) and the reconstructed (<f>1×2</f>) structure of the TiO<f>2</f>(1 1 0) surface at 300 K. During exposure new features appear first on the added rows of the reconstructed (<f>1×2</f>) surface structure. In general these new features are randomly distributed, i.e., no ordered adsorbate phase builds up. However, in some areas locally ordered linear structures can be observed along the (<f>1×2</f>) rows with a periodicity two or three times higher than the substrate. Similar to these observations, randomly distributed spots also appear on single added rows of the (<f>1×2</f>) surface structure that are located on top of the (<f>1×1</f>) structure of the TiO<f>2</f>(1 1 0) surface. In contrast, additional features on the (<f>1×1</f>) structure itself can be seen only after higher SO<f>2</f> exposure. Here, an ordered adsorbate phase with a (<f>2×1</f>) structure is formed. The new features of this (<f>2×1</f>) structure are located on top of the (<f>1×1</f>) rows along the [0 0 1] direction, which previously have been shown to represent the fivefold coordinated Ti surface cations. Subsequent AE spectra display a single peak in the sulfur region at 151.3 eV, confirming the predominant formation of Ti–S bonds during SO<f>2</f> exposures. In LEED a diffuse (<f>1×2</f>) structure with faint (<f>1×2</f>) half-order reflections can be seen, demonstrating the overall disorder on the surface. Point defects on the stoichiometric (<f>1×1</f>) surface structure as well as on the reconstructed (<f>1×2</f>) surface structure are unaffected by SO<f>2</f> exposure. [Copyright &y& Elsevier]