It has been observed that the transmittance decreases with etching time for all samples. For Au NPs of a given size, a higher transmittance is reported at an etching time of 5 min, and the overall transmittance decreases with etching time. The higher transmittance can be attributed to the fabricated structures (elongated pits) that are located far apart after 5 min of etching (as shown in Figure (a)), and their comparatively smaller size. As time goes on, more structures are formed and covered a larger area on the substrate, leading to a decrease in transmittance and further scattering more light. For a given etching time, there does not seem a definite trend with particle size, except for 5 min. This is because the size of the initially formed elongated structures increases with the size of the Au NPs. This, in turn, causes more scattering and a decreased transmittance. With time, these elongated structures merge to form arrays and then the transmittance is more or less insensitive to the initial particle size. At 30 min, transmittance values are reported in the same range for different substrates. The morphology of the fabricated surface structures, with varying sizes of Au NPs, is similar to that reported for G 1 masked etched structures (as shown in Figure ). SEM images of selected samples (of varying Au NP sizes) are included in Figure .