TiO2 thin films have been prepared at temperatures between 298 and 523 K by plasma enhanced chemical vapor deposition at working pressures of 4 X 10(-3) and 4 X 10(-4) Torr, in this latter case by using electron cyclotron resonance conditions. Ti isopropoxide has been used as the precursor and oxygen or mixtures of oxygen + argon as the plasma gas. The refraction indexes of the films (from 1.95 to 2.4) have been correlated with their microstructure and surface roughness as observed, respectively, by scanning electron microscopy and atomic force microscopy. Optical emission spectroscopy analysis of plasma indicates a higher fragmentation of the precursor in a plasma of pure O-2 than in another of Ar + O-2. Heating at T > 503 K induces the crystallization of the films into the anatase structure. The differences in the structure, microstructure, and optical properties are accounted for by assuming that the type of interactions of the plasma species with the growing film change with the deposition conditions. (c) 2007 The Electrochemical Society.