In this work we investigated the physical and chemical nature of ultraflat titanium dioxide (TiO2) samples which we had previously used as substrates for the investigation of adsorbed protein molecules (Cacciafesta, P.; Humphris, A. D. L.; Jandt, K. D.; Miles, M. J. Langmuir 2000, 16, 8167). Titanium films were prepared by thermal evaporation on a heated mica surface and either separated from the mica to investigate the resulting surface or left in contact with the mica to analyze the titanium−mica interface. Atomic force microscopy (AFM) of the surfaces exposed after removal of the mica showed very flat surfaces [root-mean-square roughness of 0.29 nm ± 0.03 nm] and the presence of disordered as well as ordered structures. Different degrees of order were observed, such as a square lattice with spacing of a0 = 0.49 nm, a regular pattern with spacings of a0 = 0.47 nm and b0 = 0.35 nm with an angle of ∼80° between a0 and b0, or the presence of surface defects. These ordered structures were not stable upon lo...