Accessing Surface Plasmons with Ni Microarrays for Enhanced IR Absorption by Monolayers

Abstract

Surface plasmons have been accessed with mid-IR light on Ni microarrays of subwavelength apertures using zeroth-order FTIR transmission spectra. A number of transmission resonances are observed throughout the mid-IR region, which is particularly interesting because nickel's dielectric properties are unfavorable in the visible. On the strongest resonance, these microarrays transmit about 3 times the intensity of light that is directly incident upon the holes (i.e., they exhibit Ebbesen's extraordinary transmission effect). A study is presented of the dispersion and line shape of resonances for a mesh of well-defined geometry (6.5-μm-wide square holes, square lattice with 12.7-μm hole-to-hole spacing, and 5-μm thickness). The dispersion diagram reveals large band gaps (as a fraction of the resonance energy) that are complicated by the lifting of nominally degenerate resonances. The line shape of the most isolated resonance was fit to a damped harmonic oscillator model revealing the complex dielectric parameters including the damping constant. Lifetimes obtained from the damping constants range from 80 to 510 fs and exhibit an exponential dependence on the resonance wavelength. A great enhancement of resonant transmission relative to the fractional open area has also been observed upon stacking two or more meshes on top of each other. The metallic microarray transmission geometry converts the photon energy to surface plasmon polaritons traveling along the metal surface and therefore through coatings, membranes, or monolayers on the mesh. This dramatically changes the path length in absorption experiments from about twice the thickness of the coating (as it is in reflection absorption experiments) to the thickness of the microchannel and more, which could amount in practice to a 1000-fold enhancement in the fraction of light absorbed. These observations suggest opportunities for using these resonances in sensitive detection schemes with vibrational spectroscopies to detect molecular surface species. We show one exciting outcome that involves some unusually large absorbances by 1-dodecanethiolate monolayers on these Ni meshes.

Ultra-sensitive vibrational spectroscopy of protein monolayers with plasmonic nanoantenna arrays

“…The enhanced signal mainly comes from a small quantity of molecules at the close vicinity of the N 2 nanorod tips (n ϭ 63 is the number of rows and columns). Second, in contrast to the studies conducted with self-assembled monolayers (SAMs) (7)(8)(9)(10)(11)(12)(13), here the protein molecules are physisorbed (see SI Text), which results in the following differences. (i) Unlike the SAMs, the transition dipole moments of the physisorbed proteins have no fixed orientation with respect to the metal surface normal.…”

“…The plasmonic enhancement of optical near fields can also be extended to the infrared frequencies enabling dramatic signal enhancement in infrared (IR) spectroscopy. In analogy to SERS, this method is called surface enhanced infrared absorption (SEIRA) spectroscopy (7)(8)(9)(10)(11)(12)(13)(14). Until recently, the bulk of SEIRA studies have revolved around enhancements achieved via chemically prepared or roughened metal surfaces (7)(8)(9)(10)14).…”

Nanohole-Enhanced Raman Scattering

“…In contrast, examples of enhanced fluorescence and IR absorption from species adsorbed on this class of substrates can be found in the literature. [16][17][18] In principle, the enhanced- …”

Noncovalent Deposition of Nanoporous Ni Membranes on Spatially Organized Poly(p‐xylylene) Film Templates

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Nickel metal is widely used in catalytic, [1,2] energy storage, [3,4] and optical applications [5,6] due to its favorable physicochemical properties. Although Ni morphology, topology, and surface chemistry are critically important for these applications, their control is limited by: 1) Ni deposition conditions and treatments, [7][8][9] and 2) properties and available architectures of sacrificial metallization templates, [1,6,[10][11][12][13] (Fig.

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