LEED and STM studies of rutile (1x1) and (1x2) TiO2(110).


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The structures and properties of rutile (1x1) and (1x2) TiO2(110) surfaces are studied using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). For (1x1) TiO2, LEED analysis shows common relaxation features reported in literatures: The bond length for bridging oxygen is contracted to 1.852 Å and 5-fold coordinated titanium is sagged downward by 0.182 Å. In addition, the sequence of alternatively contracted-elongated Ti-O bonds has been observed and discussed. The partial reduced (1x1) surface exposed under formaldehyde (CH2O) environment is also investigated using variable temperature (75-300 K) STM. At low temperature, a diolate formed via coupling between two CH2O molecules is discovered. At room temperature, such diolate is further found forming a stable coverage of adsorption. For (1x2) reconstructed TiO2(110), LEED simulation of Ti2O added row model is performed with low temperature (T = 190K) experimental spectra of fractional diffraction spots. The resultant structure yields a Rp value of 0.51 which suggests an indefinite structural correlation to the experimental data. The modeling details are discussed to explain such LEED result and suggestions are given to improve it. A novel method using a chemical probe to investigate (1x2) TiO2(110) is also utilized. TMAA as a chemical probe is dosed on the surface and imaged using room temperature STM. The adsorptions of TMAA are observed on sites of (1x2) trough and strand, and also on cross-linked sites with varying preferences. Three proposed (1x2) added row models, Ti2O, Ti2O3 and Ti3O6, are compared to the observed adsorption behaviors. Ti2O added row model is found consistent with such adsorption behaviors and models of TMAA adsorptions are proposed.



TiO2(110). 1x1 and 1x2 LEED. Formaldehyde STM.