Titanium dioxide surfaces and interfaces studied using ESDIAD, LEED and STM

TiO2 surfaces have been studied by electron stimulated desorption ion angular distribution (ESDIAD), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). The TiO2(100) surface was studied in its (1x1) form and in its (1x3) reconstruction. Angular distributions of O+ ions from the (1x3) reconstruction are consistent with the proposed microfacet model. The (1x3) reconstructed surface can be transferred back to (1x1) after annealing at 950 K in oxygen, through a stage of co-existing (1x1) and (1x3) domains smaller than the coherent width of the LEED electron beam. Evidence for surface reconstruction on the (1x1) surface is also found. The TiO2(110) surface was studied in its (1x1) form and in its (1x2) reconstruction. The pattern of normal O+ ion emission from a (1x1) surface changes to two off-normal lobes upon transformation to (1x2), reflecting a distinct change in oxygen anion bonding configuration at the surface and providing strong evidence in favour of an interface with added Ti2O3 rows. STM studies of the stoichiometric and electron irradiated surfaces reinforce the association of the O+ ESD contribution with majority surface sites. O+ ion emission from annealed (1x1) surfaces indicates a large degree of terracing. Adsorption of acetic acid at the TiO2(110)-(1x1) surface is dissociative, forming an ordered (2x1) overlayer at saturation coverage. H+ ESDIAD contributions can be resolved into two contributions: H atoms bonded at the oxide substrate, and the rupture of the C-H bonds of the acetate. It is proposed that acetates are bridge bonded with five-fold coordinated Ti4+ ions, with their molecular plane perpendicular to the surface. Decomposition of acetate at room temperature occurs under electron beam radiation, desorbing CH2CO and CH3/CH4. Adsorption of benzoic acid at the TiO2(110) surface is dissociative, forming benzoate and surface hydroxyls. Adsorbed benzoate is bonded with the five-fold coordinated Ti4+ cations, forming a pseudo (2x1) overlayer at a saturation coverage of 0.5 ML. Attractive interactions between benzoate aromatic rings leads to the formation of dimerised benzoate rows along the [001] direction. (author)