The structural and compositional properties of three samples such as as-deposited single-phase anatase-TiO2 polycrystalline thin films on slide glass substrates (No. 1), the sample surface-treated by N-2-H-2 mixed-gases plasma (No. 2), and the sample being additionally anneal-treated in N-2 gases (No. 3), are characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The primitive lattice cells of three thin films are verified as distorted in comparison with that of bulk from the TEM results. This distortion of primitive lattice cell causes the increase of optical band gap for the films when we compared it with that of bulk, while the decrease of optical band gap should be attributed to the substitution of N into TiO2. Higher concentration of nitrogen in sample No. 3 is confirmed by line-EDS profiles under scanning TEM (STEM) when compared with sample No. 2 and this confirms that plasma surface treatment is an effective way for N-doping in TiO2. (c) 2004 Elsevier B.V All rights reserved.