Bonding and Antibonding Modes in Metal–Dielectric–Metal Plasmonic Antennas for Dual‐Band Applications

Abstract

Resonant optical antennas supporting plasmon polaritons (SPPs)—collective excitations of electrons coupled to electromagnetic fields in a medium—are relevant to sensing, photovoltaics, and light‐emitting devices, among others. Due to the SPP dispersion, a conventional antenna of fixed geometry, exhibiting a narrow SPP resonance, cannot simultaneously operate in two different spectral bands. In contrast, here it is demonstrated that in metallic disks, separated by a nanometric spacer, the hybridized antibonding SPP mode stays in the visible range, while the bonding one can be pushed down to the mid‐infrared range. Such an SPP dimer can sense two materials of nanoscale volumes, whose fingerprint central frequencies differ by a factor of 5. Additionally, the mid‐infrared SPP resonance can be tuned by employing a phase‐change material (VO2) as a spacer. The dielectric constant of the phase‐change material is controlled by heating the material at the frequency of the antibonding optical mode. These findings open the door to a new class of optoelectronic devices able to operate in significantly different frequency ranges in the linear regime, and with the same polarization of the illuminating wave.

Nanofocusing of acoustic graphene plasmon polaritons for enhancing mid-infrared molecular fingerprints

“…For instance, by exciting localized SPPs in mid-IR optical antennas covered by a layer of molecules, it is possible to significantly increase the infrared response of the molecular layer, which is the basis for the well-established surface-enhanced infrared spectroscopy (SEIRA) [3][4][5]. Nevertheless, at mid-IR frequencies, the confinement of SPPs on metal surfaces and simple dipole antennas is not as strong as in the visible range, such that sensing of nanometric volumes of molecules is challenging, unless one uses narrow-gap antennas [6,7] or SPP dimers [8][9][10]. The optical response of these metallic structures is, however, difficult to control in an active manner (e.g., by applying a voltage) and thus cannot be efficiently tuned through a broad spectral interval.…”

Numerical Investigation of Multifunctional Plasmonic Micro-Fiber Based on Fano Resonances and LSPR Excited via Cylindrical Vector Beam

“…Plasmonic Fano resonances and localized surface plasmon resonance (LSPR) are attractive phenomena brought by SPPs. Plasmonic Fano resonances are generated when metallic nanostructures are located at the vicinity of each other with small distance because hybridized bonding and antibonding plasmon modes arise [6][7][8], forming "bright" and "dark" modes [9][10][11], which coherently couple and interfere with each other and result in plasmonic Fano resonances [12][13][14][15][16]. LSPR [17] can be generated when metallic nanostructures have a size of sub-wavelength in three dimensions where SPPs are confined to three-dimensional bounded region.…”

Dual-Band Coupling of Phonon and Surface Plasmon Polaritons with Vibrational and Electronic Excitations in Molecules

“…However, excitonic and vibrational resonances emerge at significantly different energy domains separated by an order of magnitude, thus challenging the creation of strongly confined electromagnetic fields (hot spots) at visible and infrared frequenciesan essential ingredient for achieving SC at the nanoscaleat the same spatial position and with a similar size. Metallic antennas have already been used to enhance the light–matter interaction in both visible and mid-IR frequency bands, in particular, to combine surface-enhanced Raman and infrared spectroscopy. , However, although metallic antennas work relatively well in the visible range, it is desirable to find alternatives for achieving SC in the mid-IR frequency range due to their low quality factor at these frequencies.…”