Hydrothermally Grown Copper-Doped ZnO Nanorods on Flexible Substrate

Abstract

In this study, we observe the effect of Cu doping on the ZnO nanorod (NR) structure grown on a polyethylene terephthalate flexible substrates by hydrothermal growth of sol–gel method proceeded at 150 °C. Copper (II) nitrate trihydrate (Cu-nitrate) and copper (II) acetate monohydrate (Cu-acetate) are employed as precursors for Cu dopants in aqueous growth solution to examine the evolutionary change of the growth morphology, optical characteristics, and chemical composition of as-grown ZnO NRs. A significant influence of dopant molarity on the morphology of wurtzite ZnO nanocrystals is observed by field-emission scanning electron microscopy. X-ray diffraction analysis also reveals more enhanced crystalline quality from Cu-doped NR crystals prepared by Cu-acetates than that grown with Cu-nitrate precursor. Near band-edge emission of 2 mM Cu-acetate doped NRs is greatly enhanced by 2.5 times compared to those grown with Cu-nitrate precursors. A great reduction in visible emissions is also realized, and this phenomenon is associated with overall improvement in NR crystalline quality by suppressing the oxygenated carbon groups or hydroxyl introduced by the aqueous solution-based growth. X-ray photoelectron spectroscopy also shows that a very high O/Zn atomic ratio of 0.73 can be achieved in the case of NR crystals prepared by 2 mM Cu-acetate. Cu doped ZnO nanostructures of improved optical and structural properties achieved in this study can be utilized in the wide emerging field of flexible device applications such as laser diodes, light-emitting diodes, piezoelectric transducers and generators, gas sensors, and ultraviolet detectors.