Photoreactions on a Single Isolated TiO2 Nanocrystal on Au(111): Photodecomposition of TMAA

An atomically resolved study of an adsorbate photoreaction on the surface of an isolated TiO2 nanocrystal is reported. The crystal is grown in situ on Au(111) in an ultrahighvacuum chamber. The experiments use scanning tunneling microscopy (STM) backed by temperature-programmed desorption (TPD) to determine the surface coverage of trimethylacetic acid (TMAA) on the nano crystal surfaces before and after irradiation with monochromated 305 nm UV light. A detailed determination of the surface structure of the 1-3 nm thick and 10-30 nm wide nanocrystals is presented and the importance of moire effects in controlling the reaction sites shown. The normalized TMAA photodesorption quantum efficiency from Au-supported TiO2 nanocrystals was found to be 4 times lower compared to the same reaction on rutile TiO2(110) surface, a result consistent with the lower fraction of light adsorbed in the nanocrystals.