Formic Acid Adsorption on Anatase TiO2(001)−(1 × 4) Thin Films Studied by NC-AFM and STM†

Abstract

Atomic resolution scanning tunneling microscopy (STM), noncontact atomic force microscopy (NC-AFM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and formic acid adsorption experiments were used to characterize the (001) surface of anatase TiO2. A combination of NC-AFM and STM imaging was used to distinguish features due to geometrical and electronic effects. The contrast in images of the bare (1 × 4) surface and the formate-covered surface is dominated by the surface topography in both NC-AFM and STM, although electronic effects in the troughs contribute features to the STM images that are absent from NC-AFM images. High-resolution imaging by STM and NC-AFM revealed that the highest point of the ridge of the (1 × 4) structure consists of a single row of atoms. Formate adsorbs at under-coordinated Ti sites in the added rows with a minimum separation of 2a0 and never adsorbs in the trenches even though the trenches also likely expose under-coordinated Ti atoms. The stickin...