Plasmonic and SERS performances of compound nanohole arrays fabricated by shadow sphere lithography.

Several plasmonic compound nanohole arrays (CNAs), such as triangular nanoholes and fan-like nanoholes with multiple nanotips and nanogaps, are designed by a simple and efficient shadow sphere lithography technique by tuning the sphere mask size, the deposition and azimuthal angles, substrate temperature T S , and the number of deposition steps N. Compared with conventional circular nanohole arrays, the CNAs show more hot spots and exhibit new transmission speaks. Systematic finite-difference time-domain calculations indicate that different resonance modes excited by the various shaped and sized nanoholes are responsible for the enhanced plasmonic performances of CNAs. Compared to the CNA samples with only one circular hole in the unit cell, the Raman scattering intensity of the CNA with multiple triangular nanoholes, nanogaps, and nanotips can be enhanced up to 5-fold. These CNAs, due to the strong resonance due to the multiple structural features, are promising applications as optical filters, plasmonic sensors, and surface-enhanced spectroscopies.