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 < 1 (1) over bar1 > 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.