The Influence of Oxygen on the Structural and Optical Properties of MoO3 Thin Films Prepared Using the Laser-Assisted Evaporation Technique

In this study, MoO3 thin films were prepared using the CO2 laser-assisted evaporation technique. The effect on the structural and optical properties of the oxygen content in the sample was evaluated. The samples were grown at a substrate temperature of 230 °C, pressure base of 5.3×10−3 Pa, and at various oxygen pressures. The material was characterized through X-ray diffraction and optical transmittance in the visible spectral range (250–900 nm). The analysis showed that both structural and optical properties are critically dependent on the oxygen content. The samples prepared without oxygen crystallized in the β-Mo8O23 phase, indicating the presence of non-stoichiometric MoO3. With increasing oxygen content during the growth of the film, it becomes stoichiometric in the alpha phase of MoO3. An energy gap of 3.7 eV was observed in samples prepared without oxygen; the value increased up to 3.98 eV for the final 7.5×10−2 Pa oxygen pressure. An absorption center appeared around 780 nm in the transmittance spectra of samples prepared in vacuum, and the intensity of this center diminished as the oxygen content increased in the chamber. This indicates that the absorption center is associated with the oxygen vacancies.