Nucleation and growth of Pt nanoparticles on reduced and oxidized rutile TiO2 (110).

The nucleation and growth of Pt nanoparticles (NP's) on rutile TiO2 (110) surfaces with O on-top atoms (oxidized TiO2), surface O vacancies, and H adatoms, respectively (reduced TiO2), was studied by means of scanning tunneling microscopy (STM) experiments and density functional theory calculations. At room temperature, Pt was found to be trapped at O on-top atoms and surface O vacancies, leading to rather small Pt NP's. In contrast, on surfaces with H adatoms the mobility of Pt was much larger. As a result, large Pt NP's were found at room temperature on TiO2 (110) surfaces with H adatoms. However, at ∼150 K the diffusion of Pt was kinetically hindered on all TiO2 (110) surfaces considered. STM data acquired after vacuum-annealing at 800 K showed comparable results on all TiO2 (110) surfaces because the diffusion of Pt is not influenced by surface defects at such high temperatures.

Packing defects into ordered structures: strands on TiO2.

We have studied vicinal TiO2(110) surfaces by high-resolution scanning tunneling microscopy and density functional theory calculations. On TiO2 surfaces characterized by a high density of <111> steps, scanning tunneling microscopy reveals a high density of oxygen-deficient strandlike adstructures. With the help of density functional theory calculations we develop a complete structural model for the entire strand and demonstrate these adstructures to be more stable than an equivalent amount of bulk defects such as Ti interstitials. We argue that strands can form particularly easy on stepped surfaces because building material is available at step sites. The strands on TiO2(110) represent point defects that are densely packed into ordered adstructures.