The influence of the bulk reduction state on the surface structure and morphology of rutile TiO2(110) single crystals

We have investigated the relationship between different types and amounts o f bulk defects and the surface morphology of TiO2(110) single crystals prep ared by annealing in ultrahigh vacuum rind in oxygen. Rutile TiO2(110) spec imens were cut from the same crystal and were heated in a furnace to differ ent temperatures which resulted in different states of reduction (colors of the crystals). After characterization of the bulk defects with electron pa ramagnetic resonance (EPR), the specimens were studied with scanning tunnel ing microscopy (STM), low-energy He+ ion scattering (LETS), and work Functi on measurements. EPR reveals that darker rutile crystals exhibit higher con centrations of extended Ti3+ related bulk defects such as crystallographic shear planes (CSP), with a decrease in substitutional and interstitial defe cts as compared to lighter crystals. Surface structures with (1 x 2) featur es are preferably formed upon UHV annealing on these darker crystals. LEIS measurements show that all of the crystals' (110) surfaces are reoxidized u pon annealing in O-18(2) (573 K, 1 x 10(-6) mbar, 10 min) and that the O-18 surface content is proportional to the bulk reduction state. UV-visible ad sorption spectra and resistivity measurements also scale with the reduction states of crystals. Only the (1 x 1) structure is observed on the surface of slightly reduced crystals. Annealing in oxygen induces additional metast able structures, i.e., TiO2 clusters on blue crystals and rosette networks on dark blue crystals.