Synthesis and optical properties of Co and Zn-based metal oxide nanoparticle thin films

Abstract

ZnO, Co doped ZnO (ZnO:Co) and CoO thin films were deposited on glass substrates by using the spark discharge technique with Zn-Zn, Zn-Co and Co-Co metal electrodes (tips). The structural and optical properties of the films were characterized by X-ray diffraction, scanning electron microscopy measurements and UV-Vis spectrometry. Cubic phase reflection of CoO (200) was observed in the samples containing Co. The size of nanoparticles had varied between 38 nm and 200 nm in ZnO thin films. When Co electrode was used, spherical structure had deteriorated and clusters of particles, with smaller radii, were observed. In addition, when Co-Co electrode pairs were used, various cavities with different sizes were formed. Especially, it was observed that the optical transmittance had generally increased with the decreasing spark (charge) voltage, while increasing with the number of sparks. The Co-containing samples were green in color and it was observed that the loss of transmission appears in a specific region in the Co-doped ZnO thin films due to characteristic d-d transition of Co2+ ions. The thickness of the films had decreased with the increasing number of sparks. In addition, the band gap energy, Eg, evaluated by UV-Vis spectroscopy measurements has been shifted to higher wavelengths (red shift) for the ZnO:Co thin films.