Alkali-metal adsorption and manipulation on a hydroxylated TiO2(110) surface using atomic force microscopy
We report on the adsorption and manipulation of K atoms on a hydroxylated TiO2(110)-1×1 surface using low-temperature noncontact atomic force microscopy. At low coverage, first-principles GGA + U calculations reveal favorable adsorption sites that are consistent with the experimentally observed adsorption positions on the upper-threefold hollow site, in which the K atom is bound to two bridging-oxygen (Obr) and one in-plane oxygen atoms, forming an ionic bond with three oxygen by transferring almost one of the K 4s electrons to the substrate. K atoms can be manipulated preferentially along the  direction over the Obr row by the tip through attractive force. Density functional theory calculations have provided diffusion paths for the adsorbed K atoms, which indicate a channel that provides ease of diffusion for a single K atom along the Obr rows associated with an energy barrier of 0.21 eV.