Nanoporous thin films were deposited onto glass substrates by painting with a solution of nanocrystlline anatase TiO_2 particles (with a size of either 6 nm or 16 nm) suspended in an organic solvent. Upon drying in air for about 1 day, the films were tempered at 450 ℃ in air for 1 h. This procedure results in stoichiometric TiO_2 films with a thickness of several μm and a milky whitish appearance. Scanning force microscopy of the surface revealed that the nanoparticles of the films gglomerated into structures with lateral dimensions of some 100 nm. Transmission electron micrsocopy was utilized to investigate the structural arrangement of the crystallites in the films. High-resolution electron diffrction and X-ray diffraction analyses demonstrated, furthermore, that the material consists exclusively of a single TiO_2 phase, namely anatase, and that the films do not exhibit any preferential texture. The elemental stoichiometry and the possible presence of impurities were monitored throughout the films by means of secondary-ion mass spectrometry depth profiling. Electrical measurements have been carried out as a function of both the sample temperature T and the ambient oxygen partial pressure p(O_2). From these data the electrical conductivity σ of the porous films was determined in dependence of those parameters.
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