Hotspots Engineered Nanostructure Arrays for Surface-Enhanced Raman Scattering by Tilted Metal Deposition

Noble metallic nanostructures with complicated morphology are usually utilized as high-performance SERS-active substrates because the hotspots are introduced at the tips or gaps. In this paper, hotspots engineered nanostructure arrays have been successfully fabricated for surface-enhanced Raman scattering based on the combination of nanosphere lithography and tilted metal deposition technique. A generally applicable equation is exploited for nanostructure morphology design. Accordingly, a series of nanostructure arrays, including circular hole, ellipse hole, tip-protruded stripe and nanowire arrays, were fabricated by modifying the metal deposition angle through the NSL process. The changing of the metal deposition angle facilitates the fabrication of nanostructures having nanotips. The hotspots are visualized by the finite-difference time-domain calculation. The surface plasmon tends to concentrate along the edges, especially at the tips of the nanostructures providing intensive hotspots. The hotspots contribution to the Raman signal enhancement is validated by the SERS measurement using the Rhodamine 6G as the probe molecule. All the fabricated nanostructures provide good signal-to-noise SERS spectra with the highest enhancement yielded by the tip-protruded array. The morphology design, electric field calculation and SERS characterization illustrate that the tilted metal deposition technique facilitates the hotspots engineering and provides a class of robust, high-yield, and cost-effective platform for SERS-based bio-sensing, and trace analyte monitoring.