Producing BiI/BiOI Thin Films via Chemical Bath Deposition

In this paper, we tried to describe a different method for producing BiI and BiOI thin films, which is chemical bath deposition on glass substrates. Structural and optical properties of BiI and BiOI thin films were examined using X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-VIS measurements. Film thicknesses of the films were measured by Atomic Force Microscope (AFM). Chemical analysis by EDX was performed with an EDX spectrometer attached to SEM. Various concentrations of bismuth and iodine solutions were tested to determine optimum parameters for BiI and BiOI production. Structures of the films were changed with the concentrations of the compounds in the bath. Some properties of the films, such as transmittance, reflectivity and refractive index were also changed with the change of concentrations in the chemical bath. When the concentration of the bismuth and iodine, which was added to the bath, was 10^-1 M, the dominant character observed in the structure was tetragonal BiOI, whereas when 10^-2 M bismuth and iodine were added, monoclinic BiI structure was observed with (205) and (31-1) in planes. The mixed phase of BiI and BiOI was also observed with 10^-2 M concentration. The refractive index and optical band gap (Eg) were changed with deposition concentration, which were 1.41-1.86 and 3.37-3.67 eV, respectively. The lowest film thickness was measured as 98 nm at 0.1 M concentration. The EDX results were almost equal to the stoichiometric ratio of BiI and BiOI compounds.

Keywords:
BiI/BiOI thin film; crystal growth; thin film