Thermally induced formation of vacancy-islands on the atomic terraces of TiO2(1 1 0) surface covered by Pt

Thermal stability of ultrathin Pt layers deposited onto TiO2(1 1 0)-(1×n) surface was studied by scanning tunneling microscopy in the temperature range of 300–1200 K. Besides the formation of 3D particles and the gradual sintering of the initial clusters, a unique morphological feature––one monolayer (ML) deep vacancy-islands (pits)––developed as a result of annealing above 1000 K. This appeared on the atomic terraces of the substrate covered by Pt of a few percent monolayer. The edge of these pits were typically decorated by Pt nanoparticles grown during the annealing procedure, showing that the bonding between the admetal and the substrate is the strongest at these sites. The formation of the vacancy-islands can be explained by the decoration process activated by the thermal treatment above 500 K. Depending on the Pt coverage, two types of morphological states can be distinguished: (1) at very low coverages (<0.05 ML) one pit contains one Pt nanoparticle; (2) in the case of higher coverages (>0.15 ML) few Pt nanoparticles are localized in a particular vacancy-island of round shape, typically at the perimeter of the pit.