Understanding atomic-resolved STM images on TiO2(110)-(1 x 1) surface by DFT calculations

We present a combination of experimental STM images and DFT calculations to understand the atomic scale contrast of features found in high-resolution STM images. Simulating different plausible structural models for the tip, we have been able to reproduce various characteristics previously reported in experimental images on TiO2(110)-(1 x 1) under controlled UHV conditions. Our results allow us to determine the influence of different chemical and morphological tip terminations on the atomic-resolution STM images of the TiO2(110)-(1 x 1) surface. The commonest images have been properly explained using standard models for a W tip, either clean or with a single O atom located at the apex. Furthermore, a double transfer of oxygen atoms can account for different types of bizarre atomic-resolution features occasionally seen, and not conclusively interpreted before. Importantly, we discuss how typical point-defects are imaged on this surface by different tips, namely bridging O vacancies and adsorbed OH groups.