FORMATION OF ZN NANOPARTICLES ON ZNO CRYSTAL SURFACE WITH ND: YAG LASER RADIATION: EXPERIMENT, MODEL AND APPLICATION
Dr.Phys. Pāvels Onufrijevs (RTU Institute of Technical Physics)
The possibility to control electrical conductivity of ZnO crystal and optical properties such as photoluminescence and optical permeability by Nd:YAG laser radiation. A five-fold increase in the conductivity of ZnO crystal was observed after irradiation by Ith1 = 3.2 MW/cm². Simultaneously, an increase in intensity of free excitons (with photon energy 3.27 eV) and a decrease in the intensity of the deep level emission band (with photon energy 2.16 eV) were observed in the photoluminescence spectra. These results indicate an improvement in the quality of the ZnO crystal. Further increasing the laser intensity only reduces the intensity of both bands in the photoluminescence spectra. This means that laser irradiation at Ith1 = 3.2MW / cm² is the first threshold at which the quality of the ZnO crystal begins to deteriorate. Increasing the intensity of laser radiation above Ith2 = 212.0 MW / cm², crack formation was observed on the irradiated surface. In addition, the conductivity of ZnO continues to increase and exceeds the baseline value 277 times. The intensity of this laser radiation is the second threshold for ZnO crystal damage. Total photoluminescence intensity decreases rapidly, especially around cracks. Further increasing the laser intensity to Ith3 = 290.0 MW / cm² leads to the formation of "black ZnO" on the irradiated crystal surface, which can be seen with unaided eye. It is caused by the formation of Zn nanoparticles with a diameter of 40 nm. The change in the optical and electrical properties of the ZnO crystal after irradiation with Nd: YAG laser radiation can be explained by generation of spatial Zn interstitial atoms and their spatial redistribution. “Black ZnO” is formed because at certain concentration of Zn intermolecular atoms their agglomeration takes place.