Nanoscale Imaging of Plasmonic Hot Spots and Dark Modes with the Photothermal-Induced Resonance Technique

Abstract

The collective oscillation of conduction electrons, responsible for the localized surface plasmon resonances, enables engineering nanomaterials by tuning their optical response from the visible to terahertz as a function of nanostructure size, shape, and environment. While theoretical calculations helped tremendously in understanding plasmonic nanomaterials and optimizing their light matter interaction, only a few experimental techniques are available to study these materials with high spatial resolution. In this work, the photothermal-induced resonance (PTIR) technique is applied for the first time to image the dark plasmonic resonance of gold asymmetric split ring resonators (A-SRRs) in the mid-infrared (IR) spectral region with nanoscale resolution. Additionally, the chemically specific PTIR signal is used to map the local absorption enhancement of poly(methyl methacrylate) coated on A-SRRs, revealing hot spots with local enhancement factors up to ≈30 at 100 nm lateral resolution. We argue that PTIR nanoscale characterization will facilitate the engineering and application of plasmonic nanomaterials for mid-IR applications.

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

“…3(d) provides a map of the nanoantenna hotspots where absorption in the PMMA is enhanced if compared to the far-field absorption that would be measured in the absence of the antenna. 28,36 The PES map at k vib ¼ 5.8 lm in Fig. 3(d) provides a clear demonstration of enhanced energy absorption by molecules in the antenna gap.…”

“…Bowtie antennas were designed, fabricated, and embedded in a polymer matrix with e d % 2 featuring a vibrational absorption line at k vib ¼ 5.8 lm (1724 cm À1 , Polymethylmethacrylate (PMMA) carboxylic stretching). The existence of hotspots with dimensions of the order of %100 nm is verified with a near-field mid-IR nanoimaging technique, [24][25][26] recently employed for mapping the field pattern of mid-IR nanoresonators, [25][26][27][28][29] in which the electromagnetic energy absorbed by the polymer molecules and/or by the nanoresonator itself is measured locally with a scanning probe tip.…”

Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

“…Similar to the case of SPPs, there exists a momentum mismatch between the incident photons and the SPhP modes (illustrated for the 4H-SiC/ air interface in Figure 2B along with the well-known bulk phonon polariton branches). This mismatch can be overcome using the coupling of the incident field to surface modes through a diffraction grating [92], high index prism [58,93,94], scattering from a nearby sub-wavelength particle such as an SNOM tip [20,36,38,64] or via nanostructuring of the SPhP material into sub-wavelength particles [23,53,91]. By doing so, an overlap between the light line, k = ω/c and the SPhP dispersion curve, can be realized.…”

Polarization effect in tip-enhanced infrared nanospectroscopy studies of the selective Y5 receptor antagonist Lu AA33810

“…Previous research has demonstrated the application of metal plasmonic resonators to achieve local absorption enhancement in the mid-IR spectral region with nanoscale resolution [47,48]. Nevertheless, in this study, we used metal nanoparticles to obtain the local field enhancement and describe the behavior of the Lu AA33810 monolayer after conjugation with the substrate.…”