[14p-A32-1~16] 6.6 Probe Microscopy

[14p-A32-16] UHV-STM and XPS Analysis of TiO₂(110)-(1×1) Surfaces Exposed to Highly Humid Environments

〇Akira Sasahara^1,2, Masahiko Tomitori¹ (1.JAIST, 2.Kobe Univ.)

Keywords:titanium dioxide, water, scanning tunneling microscope

Rutile titanium dioxide (110)-(1×1) surfaces prepared in ultrahigh vacuum (UHV) were exposed to humid environments and returned to the UHV to be examined by scanning tunneling microscope (STM) and X-ray photoelectron spectroscopy (XPS) techniques. After exposure to water vapor of several 10 Pa, molecule-sized spots appeared on the surface. Most of the spots were protruding on the 5-fold coordinated Ti (Ti_5c) atom rows by 0.15 nm and were assigned to hydroxyl (OH) groups terminating the Ti_5c atoms (OH_t groups). The minor spots protruding on the Ti_5c atom rows by 0.1 nm were assigned to hydroperoxyl (OOH) groups. The density of the OH_t groups was higher than that of another type of the OH groups involving the bridging O atoms (OH_b groups) intrinsically present on the (1×1) surface. The OH_t groups were proposed to be formed by dissociation of H₂O molecules promoted by the evacuation of the water layer. The OOH groups were formed by the reaction of the OH_b groups with the O₂ molecules dissolved in the water layer. The formation of the OH_t groups and the OOH groups were also confirmed on the (1×1) surfaces exposed to laboratory air or immersed in liquid water. The densities of the OH_t groups and the OOH groups in STM images agreed with those estimated from the O 1s XPS peak intensities.