OXYGEN-INDUCED RESTRUCTURING OF THE RUTILE TIO2(110)(1X1) SURFACE

We report scanning tunneling microscopy (STM) results of bulk-reduced rutile TiO2 single crystals. TiO2(110) surfaces, prepared by sputterin g and annealing at 850 K in UHV, exhibit a (1 x 1) surface termination and flat, several-hundred-angstrom-wide terraces. After exposure to o xygen at elevated temperatures (onset similar to 470 K;), the surfaces are covered with small (typically tens of angstroms wide) terraces wi th monoatomic step height and the same (1 x 1) structure. On top and i n between these terraces appear patches of an irregular network consis ting of interconnected rosettes (width similar to 7 Angstrom) with pse udohexagonal symmetry. The positions of atoms within the network are c onsistent with an incomplete TiO2(110) layer. This is a kinetically li mited, metastable phase that easily transforms into the regular (1x1) structure upon further annealing. Oxygen-induced surface segregation o f interstitial Ti atoms from the reduced bulk is invoked for this ''re structuring'' of the initially flat TiO2(110)(1 x 1) surface. (C) 1998 Published by Elsevier Science B.V. Al rights reserved.