Rapidly fabricating large-scale plasmonic silver nanosphere arrays with sub-20 nm gap on Si-pyramids by inverted annealing for highly sensitive SERS detection

Abstract

A simple physical method was developed to reproducibly fabricate large-scale noble metal nanosphere arrays with controllable distribution. Different from the traditional upwards annealing process, an inverted annealing method (annealing upside down samples) is introduced to treat Ag film deposited on micro-sized Si pyramid arrays. Strikingly, high density Ag nanosphere arrays can be obtained, with the gap between the nanospheres less than 20 nm under optimized conditions, which is far superior to those made by upwards annealing. The as-formed Ag-nanospheres/Si-pyramid hybrid structure exhibited a significant high enhancement factor and highly sensitive surface enhanced Raman scattering (SERS) for Rhodamine 6G molecules. Raman mapping image of this plasmonic hybrid verified a very prominent “hot spots” effect that exists around the pyramid, which contributed mainly to an enhanced SERS signal. Our work demonstrated a feasible way to prepare high-efficiency dense plasmonic nanospheres with highly localized surface plasmon resonance response, which could be feasibly applied for other bio-sensors, and also open a potential route to fabricate a metal-coated probe for tip-enhanced Raman Spectroscopy.