Visualization of precipitation induced crystallographic shear planes as one-dimensional structures on surfaces: an STM and RHEED study on TiO 2(110)

Abstract

Surface sensitive techniques [scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED), and Auger electron spectroscopy (AES) have been used to study the effects of changes in the bulk on the surface structure in TiO 2. Annealing of TiO 2(110) at elevated temperatures leads to straight steps on the surface with lengths in excess of 500 Å. The structure of these steps has been investigated in detail by voltage dependent STM and electron diffraction. The steps are caused by crystallographic shear (CS) during annealing creating areas of different crystallographic structure. STM and RHEED studies showed that the dominant directions of the steps are along [1̄10], [1̄11̄] and [1̄11]. From these experimental finding and the tetragonal symmetry of rutile it was concluded that the CS planes belong to the close packed family {112} of planes. CS is correlated to Ca precipitation. CaO diffusion to the surface may be an important process in the creation of oxygen vacancies. The calcium precipitates induce a (1 × 3) surface reconstruction which is visible both in STM images and electron diffraction patterns.