Study of Au coated ZnO nanoarrays for surface enhanced Raman scattering chemical sensing

Eight 1 cm² samples of self-organising zinc oxide (ZnO) nanopillar arrays with preferential vertical orientation were grown by pulsed laser deposition and then coated with 30 nm of Au using either thermal or electron-beam evaporation. Each sample had a different set of ZnO and Au growth conditions. The Au/ZnO nanoarrays were then tested for use in surface enhanced Raman scattering (SERS) detection of thiophenol molecules. The ratio of I_SERS/I_Raman was adopted as a measure of the SERS sensitivity and was found to vary from 1.7 to 23.7 within the 8 samples. The impact of the density, width, filling factor, orientation, homogeneity and shape of the nanostructures on the average SERS intensity and the within-wafer reproducibility of the SERS response were considered for 9 paired comparisons based on fixing all but one of the growth parameters for each pairing. Overall, smaller nanopillar width was found to correlate with stronger average SERS signal while more vertically aligned arrays with higher filling factors showed better within-wafer reproducibility.