Multiparameter imaging and understanding the role of the tip - Atomic resolution images of rutile TiO ₂(110)

A major challenge for scanned probe microscopy is to identify structures and chemical species on a surface, which have not already been inferred from other analytical techniques. Progress is impeded by the fact that in general the structure and composition of the tip atom is not known. To illustrate some of the issues involved, we report simultaneous scanning tunneling microscopy/atomic force microscopy (STM/AFM) of the TiO ₂ (110) surface. The use of small amplitudes enabled the simultaneous acquisition of force gradient and barrier height images during standard STM imaging. Surprisingly, we find most STM images exhibit a corrugation contrast inverse to that usually reported in the literature. However, regardless of the contrast in STM, force gradient images always showed greater attraction over O rows. Barrier height images also show this consistency, always being greater over O rows. This supports the theoretical model of the electronic structure of the surface, but shows that the tip structure and interaction cannot be ignored in modeling STM images. We conclude that there is a fine balance between topography and local density of states (LDOS) in STM imaging of this surface; which of them dominates the STM image is determined by the tip. Simultaneous multi-parameter imaging is useful in interpreting images reliably, particularly on multi-component surfaces.