STM and LEED observations of the surface structure ofTiO2(110)following crystallographic shear plane formation

Abstract

Extended vacuum annealing of rutile ${\mathrm{TiO}}_{2}(110)$ produces macroscopic and nanoscopic changes in the surface morphology. These result from the ordering of oxygen ${\mathrm{v}\mathrm{a}\mathrm{c}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}/\mathrm{T}\mathrm{i}}^{n+}$ interstitials in bulk ${\mathrm{TiO}}_{2}$ into crystallographic shear (CS) planes. We have employed low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) to identify the surface termination of CS planes produced in the bulk. The directions of the planar defects along the surface indicate the {132} series of shear planes dominate the STM images, which is also supported by the LEED results. The spacing between planes gradually varies across the surface suggesting that a series of Magn\'eli phases are formed. LEED patterns confirm the coexistence of both relatively large areas of a single phase and a continuum of separations between planes. Formation of CS planes also leads to extensive facetting of the crystal, which is visible to the naked eye as a rippled surface finish. Some Ca segregation is observed during CS plane formation; however, when removed the CS planes remain, indicating they are not significantly stabilized by the Ca.