Scanning tunnelling microscopy and Auger electron spectroscopy study of Pdon TiO2(110)

The deposition of Pd at room temperature on a rutile TiO2(110) surface has been studied by scanning tunnelling microscopy (STM) and Auger electron spe ctroscopy (AES) in the coverage range from similar to 0.5 ML to similar to 5 ML. STM images of the as-deposited surface show varying structure, from t hree-dimensional islands at lower coverages to a sponge-like thin film at h igher coverages. We have studied the effect of annealing the surface formed after deposition to temperatures of 473, 773 and 973 K. For the lower cove rage (0.6 ML) well-defined islands (similar to 30 Angstrom in diameter and 5 Angstrom high) with a narrow size distribution are formed, whereas anneal ing of this overlayer to 473 and 773 K results in a slight increase in isla nd size. For the higher coverage (1.7 ML) there is particle formation (simi lar to 40 Angstrom in diameter and 7 Angstrom high) after annealing to 473 K. However, major changes in particle size/shape are observed for all cover ages after annealing to 973 K and cluster aggregation is observed. At this temperature the smaller islands have sintered to form larger particles. The AES data show a decrease in the Pd/Ti ratio with annealing, which is consi stent with the STM observations. The Ti/O ratios indicate reduction of the substrate and a (1 x 2) low-energy electron diffraction pattern is observed after annealing to 773 K. (C) 1999 Elsevier Science B.V. All rights reserv ed.