Metal-dielectric-metal resonators with deep subwavelength dielectric layers increase the near-field SEIRA enhancement

Abstract

Plasmonic nanostructures presenting either structural asymmetry or metal-dielectric-metal (M-D-M) architecture are commonly used structures to increase the quality factor and the near-field confinement in plasmonic materials. This characteristic can be leveraged for example to increase the sensitivity of IR spectroscopy, via the surface enhanced IR absorption (SEIRA) effect. In this work, we combine structural asymmetry with the M-D-M architecture to realize Ag-Ag(2)O-Ag asymmetric ring resonators where two Ag layers sandwich a native silver oxide (Ag(2)O) layer. Their IR response is compared with the one of fully metallic (Ag) resonators of the same size and shape. The photothermal induced resonance technique (PTIR) is used to obtain near-field SEIRA absorption maps and spectra with nanoscale resolution. Although the native Ag(2)O layer is only 1 nm to 2 nm thick, it increases the quality factor of the resonators' dark-mode by ≈27% and the SEIRA enhancement by ≈44% with respect to entirely Ag structures.

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.…”

Polarization-Dependent Atomic Force Microscopy–Infrared Spectroscopy (AFM-IR): Infrared Nanopolarimetric Analysis of Structure and Anisotropy of Thin Films and Surfaces

“…Photothermal expansion of absorbing organic films is greatly enhanced by the confined near-field produced by plasmonic metasurfaces. 56,59,63,99,104 The anisotropic SEIRA effect in oriented ASSRs discussed in Aksyuk et al 56 is therefore also directly accessible by polarization-dependent AFM-IR, 56 as presented in Fig. 10.…”

“…Therefore, in order to increase sensitivity and to avoid the interference of plasmonic mode patterns of metasurfaces with the AFM tip in contact with the sample, bottom-up illumination setups have been widely used. 56,59,60,99,103,104 It is important to note that under specific conditions, e.g., using bare silicon tips without gold coating, a reflection setup (Fig. 2) with polarization restricted to the in-plane direction ( s -polarization) is suitable for analyzing plasmonic effects.…”

All-Semiconductor Plasmonic Resonator for Surface-Enhanced Infrared Absorption Spectroscopy

“…Infrared (IR) spectroscopy of the distinct vibrational and rotational molecular resonances provides a powerful tool for the analysis and characterization of a wide range of molecules [ 1 , 2 , 3 ]. However, the wavelength of light required to excite these resonances is often orders of magnitude larger than the absorption cross-sections of the molecules.…”