Direct and catalyst-free synthesis of ZnO nanowires on brass by thermal oxidation

Abstract

In this research work, nanowires were grown on brass (Cu - 37.2 wt% Zn) substrate by thermal oxidation. The substrate was oxidized at temperatures ranging from 350 °C to 600 °C in the presence of varying concentrations of O2 (1%–100%) in N2 flown at a rate of 200 sccm. The oxidized brass surface was characterized by field emission scanning electron microscope equipped with energy dispersive x-ray spectroscope and transmission electron microscope. Four different types of morphological variations such as thin, thick with branches, circular-flake and flat-cone shape nanostructures were observed during oxidation at different conditions. However, the prevalence of thin and thick morphology with branches was more prominent and found in all growth conditions. The length and diameter of the nanowires varied from 1 to 30 μm and 50 to 500 nm, respectively, whereas the length of the branches varied from 1 to 3 μm. The composition of the nanowires was ZnO possessing of hexagonal wurtzite structure. The selected area diffraction confirms that the nanowires grew along 〈1 1 0〉 directions. Based on the results, a stress induced mechanism is proposed for the growth of ZnO nanowires on Cu - 37.2 wt% Zn substrate.

Synthesis of ZnO and CuO Nanowires by Thermal Oxidation on Metallic Substrates

“…At oxidation temperature of 400 °C, combination of long and short nanowires is seen (Fig. 1(c)) [38]. The length of long nanowires is up to 6 µm from the root to the tip.…”

“…For the oxidation temperature of 450 °C, high coverage of long nanowires with thin and thick morphologies is seen all over the brass wire (Fig. 1(d)) [38]. The diameter of thin nanowires is 50-200 nm with length of up to 30 µm.…”

“…However, these methods often have associated problems including removal of catalyst and template, multi-steps and complex synthesis procedure, poor adhesion with underlying substrate, less scalability and expensive equipment [38]. Alternatively, thermal oxidation is a simple, single-step and inexpensive route for the formation of metal oxide nanostructures directly on metal substrates [38][39][40][41][42], which is desirable for many in-situ device fabrication processes [40]. In principle, nanowires of metal oxide based arrays synthesized by thermal oxidation can be electrically addressed by the supporting interdigitated electrodes for some applications, such as gas sensor and field emitter [40,43,44].…”

“…In principle, nanowires of metal oxide based arrays synthesized by thermal oxidation can be electrically addressed by the supporting interdigitated electrodes for some applications, such as gas sensor and field emitter [40,43,44]. The resultant nanostructures obtained by thermal oxidation are highly crystalline and pure, which do not require any further treatment [38][39][40][41][42].…”

Arrays Formation of Zinc Oxide Nano-Objects with Varying Morphology for Sensor Applications

“…When the value of the temperature increases to 500–600 °C (and briefly up to 800 °C) during oxidation, takes place the exfoliation of the oxide layer and this process becomes more intense with time. The thermal expansion coefficient of brass in this range is more than six times greater than that of ZnO [ 64 , 65 ]. During cooling process, the brass plate shrinks more than ZnO layer, due to the big difference in thermal expansion coefficient.…”