A comprehensive study of oxygen induced restructuring of rutile titanium oxide(110) surfaces
Description
The rutile TiO2(110) surface is studied systematically in this dissertation. Sputtering and annealing in ultra-high-vacuum (UHV) renders flat (1 x 1) surfaces. After exposure to oxygen at elevated temperatures (onset ∼470 K), the surfaces are covered with small (1 x 1) islands and inter-connected rosette network patches. The rosette structure is a kinetically limited, metastable phase that easily transforms into the regular (1 x 1) structure upon further annealing. Oxygen-induced surface segregation of interstitial Ti atoms from the reduced bulk is invoked for this 'restructuring' of the initially flat TiO2(110)(1 x 1) surface A comprehensive investigation of preparation parameters (annealing temperature, time, oxygen gas pressure and sample history) which affects reoxidized surfaces is performed with the combination of scanning tunneling microscopy (STM), low energy ion scattering (LEIS) and static secondary ion mass spectroscopy (SSIMS). The formation of rosette networks and (1 x 1) islands induced between 470 K and 660 K. After annealing above 830 K, only regular (1 x 1) terraces and (1 x 2) strands exist. The rosette model is supported by first principles density functional calculations UHV annealing of reoxidized TiO2(110) surface smoothens the surfaces and converts the rosette networks into (1 x 2) strands and finally into the regular (1 x 1) terrace The relationship between sample reduction states and the surface morphology of TiO2(110) single crystals prepared by annealing in UHV and in oxygen is investigated with electron paramagnetic resonance (EPR), uv-visible absorption spectra, STM and LEIS. On darker crystals, the (1 x 2) structures are preferably formed upon UHV annealing. Annealing in oxygen induces additional metastable structures on such crystals. Only the (1 x 1) structure is observed on the surface of slightly reduced crystals upon either UHV or oxygen annealing Finally, the importance of this work for the surface chemistry of TiO 2(110) surfaces are discussed as well as open research directions