Fig. 2

TO-inspired SERS design and fabrication. a Schematic illustration of SERS substrate configuration for nanoparticles on warped substrate (NP-on-WS) hierarchical nanostructure, with nanoparticle acting as nanolens to focus the light to its vicinity and NBs providing additional light confinement induced by the curvature. b The fabrication process of hierarchical NP-on-WS nanostructures. A silica film is deposited on Au NB fabricate from silica template. Then a monolayer of nanoparticles is uniformly deposited inside NB by gas-phase deposition. c Low-magnified SEM images of the hexagonal close-packed Au NB array. The scale bar represents 15 µm. The inset shows a horizontal view of Au NBs with scale bar representing 1 µm. d Tilted-view SEM images of the hexagonal close-packed Au NB array. The scale bar represents 1 µm. e Low magnification of experimental realisation of NP-on-WS nanostructure in a. The scale bar represents 1 µm. f High magnification of experimental realisation of NP-on-WS nanostructure in a. The scale bar represents 200 nm