One dimensional Au-ZnO hybrid nanostructures based CO2 detection: Growth mechanism and role of the seed layer on sensing performance

In the present research, hybrid Au-ZnO one-dimensional (1-D) nanostructures were grown on silicon substrates with an Al-doped ZnO (AZO) seed layer (Ultrasonic Spray Pyrolysis: USP grown) and no seed layer (NSL) using two different catalytic gold films of 2 nm and 4 nm, respectively. Consequently, such 1-D nanostructures growth was associated with the vapor-liquid-solid (VLS) and vapor-solid (VS) processes. Scanning electron microscopy (SEM) imaging analysis confirms that heat treatment triggered Au nanoparticles nucleation with varying diameters. The Au nanoparticles size and underneath seed layer texture strongly affect the morphology and aspect ratio of 1-D ZnO nanostructures. The seed layer (1-D USP) sample resulted in the growth of longer nanowires (NWs) with a high aspect ratio. The NSL sample showed the formation of nanorods (NRs) with a low aspect ratio mainly via VS growth process. X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and photoluminescence (PL) analysis also revealed the differences in the NWs and NRs properties and confirmed VLS and VS growth mechanisms. CO2 gas sensing performance at different concentrations was demonstrated, and NWs with seed layer showed a relatively higher sensing response. In contrast, NSL samples (NRs) exhibited two times faster response. A detailed gas sensing mechanism with different CO2 adsorption modes based on properties of 1-D nanostructures has been discussed. Currently, CO2 sensing and capturing are critical topics in the green transition framework. The present work would be of high significance to the scientific field of NW growth and fulfill the urgent need for CO2 gas sensing.