Nanoscale characterisation of TiO2(110) annealed in air

Abstract

Abstract Rutile titanium dioxide (TiO2) (110) surfaces annealed in air were examined by frequency modulation atomic force microscopy (FM-AFM), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) techniques. The terraces separated by monatomic steps showed an atomically irregular appearance in the obtained FM-AFM images, while the surface produced a (1 × 1) LEED pattern that indicated atomic ordering of the top few surface layers. Subsequent annealing in atmospheric-pressure O2 produced several ten-nanometre-sized pits with irregular shapes on the terraces. Molecule-sized spots were recognised on the subsequently O2-annealed surface. Half-order spots along the 〈001〉 directions emerged in the LEED pattern. We propose the rutile substrate covered with hydroxylated amorphous TiO2 of monatomic thickness as the structure of the air-annealed surface. The amorphous TiO2 was dehydroxylated by subsequent O2 annealing and was transformed into the thermodynamically stable rutile structure. The molecule-sized spots were attributed to hydroxyl (OH) and hydroperoxyl (OOH) groups that were produced on the area with the (1 × 1) structure. A part of the OH and OOH groups were arranged in a (2 × 1) structure and produced the half-order spots in the LEED pattern.