Plasmonic Enhancement of Infrared Vibrational Signals: Nanoslits versus Nanorods

Abstract

We report on systematic investigations of plasmonically active nanoslits as a beneficial substrate for surface-enhanced infrared absorption (SEIRA). Arranged in arrays, nanoslits with the proper geometry feature strong nanorod-like resonances in the infrared spectral range, as predicted by Babinet’s principle for the same geometrical dimensions. SEIRA enhancement as studied with a thin self-assembled molecular layer of octadecanethiol reaches the values obtained with nanorods if the slit geometry is optimized. We show by systematically examining the important parameters that the slit width has an especially strong influence on the near-field intensity and therefore on the SEIRA signal. Furthermore, the transversal and longitudinal couplings of nanoslits are studied. Compared to nanorod arrays, a stronger influence of the array periodicities on the plasmonic excitations is observed, which indicates coupling via surface plasmon polaritons. So the array periodicity could be further optimized toward higher SEIRA signals. Our results give access to general design rules for sensing applications based on the use of inverse nanostructures.

Heavily Doped Semiconductor Metamaterials for Mid‐Infrared Multispectral Perfect Absorption and Thermal Emission

“…The system forms a quarter wavelength cavity, allowing the appearance of the reflectance minimum. M2 resembles a typical antenna mode, similar to what is observed for typical plasmonic nanorod antenna on a substrate . For spacer thicknesses close to the crossing of the individual solutions ν L ( h s ) and ν T , the electric field associated to mode M1 evidences also the field enhancement near the grating's corners like the plasmonic antenna mode, giving further evidence that the modes hybridize.…”

In‐Situ Infrared Spectroscopy Applied to the Study of the Electrocatalytic Reduction of CO2: Theory, Practice and Challenges

“…Since metal nanoantennas are isolated nanostructures, electrochemical applications are challenged by the discontinuity and conductivity of the metal layer. A way to overcome this would be by creating nanogaps or slits rather than nanostructures . In this way, a continuous film with periodically placed slits could be used as the active enhancement material in electrochemical applications.…”

Mapping the electromagnetic field confinement in the gap of germanium nanoantennas with plasma wavelength of 4.5 micrometers

“…This reduced SPP propagation wavelength, for example, is at the basis of important predicted features, such as adiabatic compression in three-dimensions, 9,10 which is relevant for future single-molecule spectroscopy approaches in the mid-IR, 11 and it cannot be obtained in the limit e ! 0.…”