Effects of mechanical roll-milling on electronic and optical properties of ZnO nanoparticles

Abstract

In this study, UV-<em>vis</em> absorption spectroscopy, electrical conductivity, band gap energy, particle size and morphology of prepared ZnO nanoparticles were examined after roll-milling process. A roll-milling process works with two rolls rotating at reverse directions and the ZnO powder goes through a narrow gap between these two cylindrical metal rolls. The roll-milling process was applied to the ZnO powder in several times by reducing the gap between the rotating cylinders. It was seen that the white color of the ZnO particles turned into yellow color. The UV-<em>vis</em> spectroscopy measurements showed that the absorption band of the ZnO particles shifted to the low energy wavelengths upon the roll-milling process. The band gap energy of the ZnO decreased from 3.10 eV to 2.68 eV. Also, it was observed that the electrical conductivity increased from 0.19 to 42.47 S/cm. Furthermore, the SEM and AFM measurements showed that the particle size of the ZnO decreased significantly and the particle morphology changed after the roll-milling process. It is concluded that the property changes in spectroscopy, electrical conductivity and band gap energy is due to the reduced particle size and the increase of the number of deformation defects in crystalline structure of ZnO particles.