[en] Thin films of WO₃, MoO₃, V₂O₅ and VO₂ have attracted enormous interest in the recent years due to their applications as optical coatings, gas sensors, electrochromic and thermochromic displays. Amorphous and crystalline coatings of these transition metal oxides can be easily prepared by thermal evaporation. WO₃ films deposited without any in situ-substrate heating are amorphous and crystallize into the monoclinic phase with heat treatment. Raman studies show that the short-range structure of amorphous, crystalline films and nanoparticles of WO₃ are similar, but the amorphous phase contains W=O terminal bonds which do not exist in bulk and nanocrystalline samples. Raman studies confirm that amorphous film contain higher concentration of hydrogen and hydroxyl ion impurities, which affect the optical bandgap. Thin films of WO₃ show a response of 3 towards 150 ppm of H₂S and 7 for 2000 ppm of C₂H₅OH. Platelet shaped nanoparticles exhibit higher response of 37 and fast response and recovery times of 1 to 2 min for 150 ppm of H₂S (author)