SYNTHESIS AND CHARACTERIZATION OF ZINC OXIDE/REDUCED GRAPHENE OXIDE (ZnO/RGO) NANOMATERIAL FOR BIOSENSOR APPLICATIONS

Abstract

Advances towards the nano and femto scale have been the core for improving the operation efficiencies for biosensors. However, there still exists a mismatch in understanding the correlation between these advances and the optical, structural and electrical properties of the biodetector materials used. The opto-electronic properties and the end performance of the biosensor are majorly dependent on the nanomaterial architecture and composition. Zinc Oxide, a perfect substitute for Indium Tin Oxide (ITO), is a dominating transparent conducting oxide (TCO) in optoelectronics and biosensors in particular. Zinc Oxide is less expensive compared to ITO, less toxic, and of propitious electrical and optical properties. Despite this promising nature of ZnO, it mainly suffers from high carrier recombination rates and low conductivity due to low carrier concentration. Combining ZnO with RGO is expected to improve carrier concentration, provide alternative carrier pathway and reduce charge recombination. This work sought to synthesis and characterize ZnO-rGO nanomaterial for application in biosensors. Zinc Oxide (ZnO) doped with reduced graphene Oxide (rGO) thin films were deposited by spin coating technique using a vacuum-free, compact Ossilla Spin coater. The absorbance patterns were studied using UV-VIS spectrometer. Sheet resistance was obtained using Four-point probe and light microscopy used to study the morphology of the thin films. There was a notable systematic morphological transition of the structures from spherullites at low temperatures to dendritic structures at relatively higher temperatures. This change was attributed to a favored parabolic growth at elevated temperatures. Absorption peaks were reported at 315 nm and 371 nm which were attributed to the n−π∗ transitions in C=O bonds and the transition from zinc interstitials (Zni) to the conduction band respectively. A narrowed band gap of 2.67 eV for ZnO-rGO thin films was reported as compared that of ZnO thin films which was 3.21 eV. The narrowing of the band gap was attributed to the formation of localized states near the conduction band in ZnO. The minimum value of sheet resistance, Rh of the ZnO thin films was 13.958 kΩ and 13.28 kΩ at a speed of 4500 rpm and temperature of 5000C respectively while the minimum sheet resistance for ZnO-rGO was 6.32 kΩ at 4500 rpm and 6000C. The optimum spin speed was at 4500 rpm while the optimum annealing temperature for undoped ZnO was 4500C. Doping ZnO with rGO however improved the electrical properties with minimum value of sheet resistance being 6.32 kΩ at 6000C.