Rutile titanium dioxide (TiO2) (100) surfaces covered by silicon oxide (SiO2) ultrathin films were examined by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and frequency modulation atomic force microscopy (FM-AFM) techniques. The SiO2 films were fabricated on TiO2 crystals by annealing in a quartz case which was used as a SiO2 source. The amount of Si increased with annealing time, and a (3 x 4) LEED pattern was observed on surfaces with the XPS peak intensity ratio of Si 2p to O 1s of TiO2 larger than 0.023. FM-AFM observation in pure water showed that the (3 x 4) surface consists of atomically flat terraces. Within the terraces, rows which extend in the [001] direction were observed. Every fourth row appeared brighter, consistent with the x4 periodicity in the [010] direction observed in LEED. Models where rutile SiO2 units are accumulated on the TiO2(100) surface via rutile Ti1-xSixO2 units are consistent with the results.
