The local barrier height (LBH) was measured on TiO2(1 1 0) single crystal surfaces with and without Au deposition using scanning tunneling microscopy (STM). On the clean TiO2(1 1 0) surface, the LBH values measured at (1 x 1) and (1 x 2) rows were almost the same, while the value at defect sites was much smaller. This indicates that the LBH of TiO2d surfaces is dependent on the presence of topmost oxygen atoms. On the An deposited surfaces, the LBH was dependent on the height of An particles: the LBH of large particles (>0.4 nm in height) was about 0.3 eV larger than that of the substrate, whereas the LBH of small particles (<0.4 nm in height) was comparable to that of the substrate. The critical height of 0.4 nm for the LBH could be correlated with the metal-nonmetal transition of An particles. (C) 2003 Elsevier B.V. All rights reserved.