Nanostructured SERS substrates produced by nanosphere lithography and plastic deformation through direct peel-off on soft matter

Abstract

We present a novel fragmented-film surface-enhanced Raman scattering (SERS) substrate produced by nanosphere lithography and direct peel-off for SERS efficacy enhancement. The 2D hexagonally close-packed polystyrene nanospheres on the polydimethylsilozane (PDMS) substrate are covered with silver film and then directly peeled off using sticky tape. During the peel-off process, the pulling force induces the stretch and contraction of the PDMS substrate and causes fracture of the 2D triangular silver film. Under laser excitation, a stronger localized electric field is induced in the smaller cracks and enhances the SERS intensity. The origin of this SERS enhancement is confirmed by numerical simulation using the finite element method and substrate annealing to smoothen the cracks. For the case using nanospheres with a diameter of 740 nm, an enhancement factor 6.5 × 106 can be achieved. The proposed fragmented-film SERS substrate gains 1.8 and 2.6 times larger Raman intensity at the 1358 cm−1 SERS peak than those using pyramidal silver islands and silver nanoshell array. The proposed SERS substrate has the features of easy fabrication, low production cost, short fabrication time and high enhancement factor.

Review of Experimental Setups for Plasmonic Photocatalytic Reactions

“…The exchange of energy involves the gain or loss of vibrational energy by a molecule as incident photons from a visible laser shift to lower or higher energy states. Surface-enhanced Raman scattering (SERS) [111,[119][120][121][122] involves the amplification of Raman scattering signals by SPs on a metallic surface with high charge carrier density. Brooks et al conducted an in-depth review of Raman spectroscopy applications for understanding plasmon-mediated photocatalysis [20].…”

“…Energy transformation in plasmonic material sensing (i.e., chemical and biosensing [136][137][138][139][140][141] and SERS [119][120][121][122]) resembles that in plasmonic photocatalytic reactions. Therefore, methods of obtaining larger or enhanced signal readings in plasmonic sensing resemble to a higher enhanced processing efficiency in plasmonic photocatalytic reactions.…”

Fabrication and Characterization of a Metallic–Dielectric Nanorod Array by Nanosphere Lithography for Plasmonic Sensing Application

“…Plasmon resonances occur, and these resonances are dependent on the geometrical structures of the metal nanostructures, like the localized surface plasmon resonance (SPR) and gap plasmon resonance (GPR) of metallic nanorods [1][2][3][4]. Studies have reported the potential use of these resonances, e.g., plasmonic sensors [5,6], infrared band filters [7,8], surface-enhanced Raman scattering (SERS) substrates [9,10], and heat radiation/absorption manipulation [11]. The advances in nanofabrication technologies [12,13] have a significant impact in promoting the use of plasmonic nanorod arrays as SPR sensors [14][15][16][17].…”

Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

“…back in 1982 and pioneered by Van Duyne’s group2345 in the late 1990 s, has come a long way by manifesting itself as a fast, low cost and high throughput nanofabrication method to produce regular arrays of nanostructures6. NSL can be divided broadly into three steps: colloidal mask generation, diameter control and lift-off.…”

“…Lastly, the PNs are etched away in a solvent by lift-off, leaving onto the substrate, regular arrays of the material deposited. Nanoparticle arrays produced by this method are often used as surface enhanced Raman scattering substrates6 for biological and chemical sensors as well as catalysts for the growth of one-dimensional nanostructures1415161718. Industry has pushed researchers far enough to implement and make the user-friendly spin-coating process viable and able to produce films with controlled thicknesses over large areas.…”