Effects of hydrothermal synthesis temperature and annealing process on properties of MnCO3 thin films

In the first part of this thesis, which was carried out in two parts, MnCO3 thin films were grown on glass substrates by hydrothermal method at different synthesis temperatures, and the effect of synthesis temperature on the structural properties of the films was examined. XRD results showed that the films grown at 80 °C synthesis temperature had an amorphous structure, and the structure turned into polycrystalline with increasing synthesis temperature. In addition, it was determined that there was Mn3O4 as the secondary phase in the structure. From the SEM images, it was observed that the MnCO3 thin films had a cubic morphology and the number of these cubic structures increased with increasing synthesis temperature. The EDAX measurements showed that the film thickness increased when the synthesis temperature was increased and that the films produced at 110 °C exhibited the appropriate stoichiometric ratio. Considering this result and the particle size values obtained using XRD measurements and the peak intensities of the Mn3O4 secondary phase, it was seen that the most suitable synthesis temperature for MnCO3 thin films was 110 °C. In the second part, the effects of annealing on the structural and optical properties of the films were investigated by annealing the films grown on quartz substrates at 110 ºC in different atmospheres. XRD results showed that films annealed in air atmosphere at 600 ºC for 1 hour converted to Mn2O3, while films annealed in nitrogen atmosphere at the same temperature and time converted to MnO. In addition, it was determined that Mn3O4 was present as the secondary phase in the films annealed in nitrogen atmosphere. SEM images showed that annealing did not cause a significant change in the general morphology of MnCO3 thin films, only pores were formed on the surfaces of the cubic structures due to the release of carbon from the structure. Release of carbon from the films was also confirmed by EDAX measurements. From optical absorption measurements performed at room temperature, direct band gap values of MnCO3 thin films and films annealed in air and nitrogen atmospheres were calculated as 3.27 eV, 2.30 eV and 2.71 eV, respectively.