Probing Gap Plasmons Down to Subnanometer Scales Using Collapsible Nanofingers

Abstract

Gap plasmonic nanostructures are of great interest due to their ability to concentrate light into small volumes. Theoretical studies, considering quantum mechanical effects, have predicted the optimal spatial gap between adjacent nanoparticles to be in the subnanometer regime in order to achieve the strongest possible field enhancement. Here, we present a technology to fabricate gap plasmonic structures with subnanometer resolution, high reliability, and high throughput using collapsible nanofingers. This approach enables us to systematically investigate the effects of gap size and tunneling barrier height. The experimental results are consistent with previous findings as well as with a straightforward theoretical model that is presented here.

Dual‐Electromagnetic Field Enhancements through Suspended Metal/Dielectric/Metal Nanostructures and Plastic Phthalates Detection in Child Urine

“…First, high‐density arrays of Au nanofingers with a flexible polymer support on the glass substrates are fabricated by our well‐developed NIL method . The polymer material is a UV‐curable NIL resist (I‐UVP, EZImprinting Inc.), which is different from the conventional photoresist (much more cross‐linked).…”

“…Compared to metal/air/metal nanostructures, metal/dielectric/metal nanostructures are more accessible for achieving the tunable quantum plasmon effects because no other conventional fabrication technology has enough resolution . By tuning the electron affinity (EA) of dielectric spacers, the tunneling barrier height, which is defined by the difference between the Fermi level of a metal and the EA of the dielectric layer, can be more precisely adjusted over a broad range . Through the optimization of the tunneling barrier width decided by doubling the dielectric film's thickness and tunneling barrier height, the maximum enhancement of an EM field determined by both the classical EM theory and quantum mechanics can be obtained .…”

“…By tuning the electron affinity (EA) of dielectric spacers, the tunneling barrier height, which is defined by the difference between the Fermi level of a metal and the EA of the dielectric layer, can be more precisely adjusted over a broad range . Through the optimization of the tunneling barrier width decided by doubling the dielectric film's thickness and tunneling barrier height, the maximum enhancement of an EM field determined by both the classical EM theory and quantum mechanics can be obtained . On the other hand, due to their relatively high refractive index, the supporting substrates have a significant influence on the plasmon mode, which is originally excited at the metal/air interface .…”

“…Figure a shows a schematic fabrication process of a typical suspended metal/dielectric/metal gap‐plasmon nanostructure. In brief, the flexible Au‐nanofinger matrix with a high aspect ratio is first generated by our well‐developed nanoimprint lithography (NIL) method, in which each Au‐nanofinger is composed of a polymer nanopillar capped with an Au nanodisk with the same diameter through a physical deposition process . After selective‐etching in an oxygen plasma, the diameter of the polymer nanopillar decreases, while the Au cap retains its original size.…”

Mechanical Deformation–Assisted Fabrication of Plasmonic Nanobowties with Broken Symmetry and Tunable Gaps

“…Perhaps more significantly, it is difficult to independently modulate the size of the triangles making up the nanobowtie and the gap of the nanobowtie since both are coupled to the size of the colloids making up the mask. Ideally both could be modulated independently since the field enhancement is a function of both …”