Improved optical and electrical stability of ZnO nanorods via electrophoretic deposition of graphene thin film

In the present study, the optical stability of ZnO nanorods (NRs) was improved at different ambient temperatures through the deposition of graphene flakes. The optical instability of ZnO nanostructures is mostly due to the elevated surface area and adsorption/desorption of oxygen molecules. These terminations are influenced by variation in ambient temperature which can alter the optical characteristics of ZnO nanostructures. To solve this problem, a thin layer of reduced graphene oxide (rGO) was deposited on the surface of ZnO NRs using an electrophoretic deposition technique. The morphological studies of the samples revealed that ZnO NRs substrate was completely covered by rGO. For investigating the influence of rGO on optical stability of ZnO NRs, the photoluminescence (PL) spectra of ZnO NRs were measured at different temperatures before and after deposition of rGO. After transferring graphene sheets, the intensity of PL peaks was reduced due to the slight absorption of emitted photons in the graphene layers. The presence of graphene on ZnO nanostructures reduced the temperature dependence of the PL spectrum at elevated temperatures. Therefore, graphene can be assumed as a transparent layer to improve the optical stability of ZnO nanostructures while preserving its structural properties. To investigate the electrical properties, metal-semiconductor-metal UV sensors were developed based on ZnO NRs before and after deposition of graphene. The optoelectrical characteristics of both devices were measured by recording the current-voltage plots under ultraviolet radiation at different temperatures. The results showed that the photocurrent of the bare ZnO NRs was diminished at elevated temperatures due to the presence of oxygen interstitials and vacancies. However, after deposition of the graphene layer, the rate of this decay was minimized at elevated temperatures, improving the optoelectrical stability of ZnO nanostructures.