Inherently Reproducible Fabrication of Plasmonic Nanoparticle Arrays for SERS by Combining Nanoimprint and Copolymer Lithography

We present an inherently reproducible route to realizing high-performance SERS substrates by exploiting a high-throughput top-down/bottom-up fabrication scheme. The fabrication route employs self-assembly of amphiphilic copolymers to create high-resolution molds for nanoimprint lithography (NIL) spanning entire 100 mm Si wafers. The nanoporous polymer templates obtained upon NIL are subjected to galvanic displacement reactions to create gold nanorod arrays. Nanorods are subsequently converted to nanodiscs by thermal annealing. The nanodiscs were found to perform as robust SERS substrates as compared with the nanorods. The SERS performance of these substrates and its generality for catering to diverse molecules is demonstrated through the excellent Raman peak resolution and intensity for three different molecules, exhibiting different interaction modes on surface. Numerical simulations using FDTD shows plasmonic coupling between the particles and also brings out the influence due to size distribution. The approach combines distinct advantages of high-precision and repeatability offered by NIL with low-cost fabrication of high-resolution NIL molds by copolymer self-assembly.