Laser interference lithography. a Optical setup used for prism holographic lithography. b Geometry of the prism used to obtain the 4-beam interference. c 3D interference patterns calculated from the 4-beam interference patterns using the FCC geometry. d Procedures used to fabricate a hexagonally ordered Au-capped silicon nanowire using prism holographic lithography. e, f Au-capped silicon nanowire structures obtained over a 3 min etching time. g, h Au-capped silicon nanowire structures obtained over 6 min (g) or 9 min (h) etching times. i Comparison of the SERS spectra obtained from Au-capped silicon nanowire arrays prepared with different etching times. j Schematic diagram of the phase shift lithography setup. k Laser interference patterns applied to the different underlying substrates. A silicon wafer has a larger refractive index than a glass wafer, resulting in a high-intensity reflected beam that creates a vertical standing wave effect. l, m Nanopillar arrays generated using a silicon substrate (l) or a glass substrate (m). n Nanopillar arrays with smooth side walls. o SERS spectra of benzenethiol obtained from three different nanopillar arrays, (i–n). p FDTD simulation of the electric field intensity distributions near the undulating nanopillar array structures (i). q SERS spectra mapping, collected in 1 µm intervals, to measure the uniformity of the SERS substrate.