A self-organized network structure was discovered after annealing TiO2(001) rutile single crystals under non-equilibrium conditions. This novel structure appeared after annealing under ultrahigh vacuum conditions to above 1000C and subsequent quenching at a rate of ≈100C/s. The surface structure was investigated by scanning tunnelling microscopy and reflection high-energy electron diffraction. One-dimensional structures running along the [110] and [¯110] directions were observed, thus forming a two-dimensional network of ridges separated by 4nm. From atomically resolved scanning tunnelling microscopic images and reflection high-energy electron diffraction observations, a two-domain (7√2 x √2)R45° surface reconstruction was deduced. The network formation requires a massive rearrangement of atoms starting from the initially epi-polished surface, suggesting that kinetic processes play a crucial role in establishing the network structure. After further annealing to 1500 to 1600C the structure remained but the ridges appeared fragmented, presumably as result of stress which was induced by deformation of the crystal after high-temperature annealing. Several factors such as readily available oxygen diffusing from the bulk to the surface, titanium diffusing from the surface to the bulk and a high surface energy of the (001) surface of TiO2 seem to favour the appearance of the network structure.

Network-Like (7√2 x √2)R45° Surface Reconstruction on Rutile TiO2(001) by Non-Equilibrium Self-Organization. Nörenberg, H., Dinelli, F., Briggs, G.A.D.: Surface Science, 1999, 436[1-3], L635-40