Synthesis, characterization and structural control of nano crystalline molybdenum oxide MoO3 single phase by low cost technique

• Single phase α-MoO3 nano crystalline MoO3 thin films have been synthesized.
• Amorphous-to-crystalline phase transition occurs at 325 °C for MoO3 thin films.
• A clear change in the Uv–Vis absorption spectrum for the MoO3 thin films.
• The colors of films are changed from sky blue to deep blue.
• The plasmonics peak positions are depending on the substoichiometry of the MoO3.

Thermodynamically stable α- MoO3 thin film is prepared without any other phases of the molybdenum oxides. Simple and low coast spray pyrolysis technique is used. Growth conditions are optimized to produce pure α- MoO3 with controlled crystallite size and surface morphology. Small angle (GAXRD) diffractometer is used to elucidate the structure. Profile shape function (PSF) model is made for the experimental data. WinFit software is going first to fit (PSF) to use the refined profile parameters for determination of crystallite size and internal residual strain. The (GAXRD) patterns prove the existence of α- MoO3 only with layered structure, indicated by the appearance of only (0k0). The calculated crystallite sizes and the strain are found to range from 10 to 28 nm and 0.28%–0.05% respectively. Ultraviolet and Visible transmission measurements were performed over a wavelength range 190–2500 nm on the MoO3 thin films synthesized by spray pyrolysis technique at different substrate temperature. The two sub-bands corresponds to the electronic transition between the molybdenum oxidation states Mo4+, Mo5+ and Mo6+ are observed. Quantitative information on the temperature-induced blue shift of the sub-bands was obtained by fitting the spectra with Lorentz functions. The transition from Mo5+ to Mo6+ oxidation states show a blue shift up to Tc = 325 °C. Above Tc, the transition Mo5+ to Mo6+ increases more drastically, resulting in an anomaly in the temperature-induced shift at Tc. The anomaly can be attributed to the amorphous-to-crystalline phase transition at 325 °C. In addition, both refractive index and extinction coefficient are calculated as a function of substrate temperature.

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