Comparison of ensemble-averaged SERS enhancement factors (G) of (Λ = 200 nm, D = 200 nm) NCAs, non-patterned gold nanoparticle films, and periodic nanodisc arrays (edge-to-edge distance = 200 nm, disc diameter = 200 nm, disc height = 40 nm). The error bars indicate the standard deviation from 12 independent measurements on four substrates. The standard deviation as percentage of the mean and SEM images of all three substrates are included. Scale bars in all SEM images denote 200 nm. Adapted with permission from ref71. Copyright 2009 American Chemical Society.