Scanning tunnelling microscopy and Auger electron spectroscopy study of Pd on 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 spectroscopy (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 three-dimensional islands at lower coverages to a sponge-like thin film at higher coverages. We have studied the effect of annealing the surface formed after deposition to temperatures of 473, 773 and 973 K. For the lower coverage (0.6 ML) well-defined islands (similar to 30 Angstrom in diameter and 5 Angstrom high) with a narrow size distribution are formed, whereas annealing of this overlayer to 473 and 773 K results in a slight increase in island size. For the higher coverage (1.7 ML) there is particle formation (similar 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 coverages 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 consistent 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 reserved.