Overwhelming Analogies between Plasmon Hybridization Theory and Molecular Orbital Theory Revealed: The Story of Plasmonic Heterodimers

Abstract

Plasmon hybridization theory (PHT), an analogue of molecular orbital theory (MOT) for plasmonic molecules, has enjoyed tremendous success over the last decade in discerning the optical features of hybrid nanostructures in terms of their constituent monomeric nanostructures. Dimers of metal nanoparticles served as prototypes in elucidating many of the key aspects of plasmon hybridization. Employing quantum two-state model, in conjunction with the quasi-static approximation and the finite-difference time-domain simulations, we demonstrate that the analogy between PHT and MOT can be further propelled by a theoretical estimation of the plasmon-coupling strengths and the relative contributions of the unhybridized monomeric states toward the hybrid dimeric states in plasmonic Ag–Au nanorod heterodimers. The aspect ratio of the constituent nanorods and the gap size between the monomeric nanorods can further be used as handles to tune the relative contributions of (i) the bonding and the antibonding modes to the total extinction and (ii) the monomeric states toward the dimeric states, with meaningful implications for surface-enhanced spectroscopy. The tunability in light absorption properties of heterodimers in the 400–800 nm region arising as a result of broken symmetry is also suggestive of their potential role as plasmonic rulers for measuring distances.

Porous Polydimethylsiloxane/Au Composites as Solar‐Light Absorbers for Light‐Driven Thermoelectric Applications

“…[20] In another approach, specific NP assemblies have been prepared to induce broadband NP absorption by plasmonic hybridization. [21,[24][25][26][27][28] As is well known, LSPR is the collective oscillation of free electrons in metal NPs and produces an intensive electric near-field localized at the NP surface. [24][25][26][27][28] Therefore, by assembling multiple metal NPs close to one another, the near-field of one NP can interact with that of another NP to induce plasmonic hybridization, resulting in the broadband absorption with enhanced intensity.…”

“…[21,[24][25][26][27][28] As is well known, LSPR is the collective oscillation of free electrons in metal NPs and produces an intensive electric near-field localized at the NP surface. [24][25][26][27][28] Therefore, by assembling multiple metal NPs close to one another, the near-field of one NP can interact with that of another NP to induce plasmonic hybridization, resulting in the broadband absorption with enhanced intensity. [26][27][28] Since the NP mixtures or NP assemblies exhibited an enhanced photothermal effect with broadened extinction, they have been placed onto the top of TE device to enhance the output power under artificial sunlight.…”

Plasmonic Modes in Au and AuAg Nanowires and Nanowire Dimers Studied by Electron Energy Loss Spectroscopy

“…Up to now, we have focused only on surface plasmon coupling in structures consisting of two wires with very similar dimensions. In literature, several examples of mode coupling in nanostructures of different material [74][75][76][77][78] or dimensions [35,[79][80][81][82] have been reported. Figure 14 shows clear evidence that surface plasmon coupling is also possible in heterodimers even between modes of different multipole order.…”

Insights on the Coupling of Plasmonic Nanoparticles from Near-Field Spectra Determined via Discrete Dipole Approximations

“…Assemblies of plasmonic gold nanoparticles (Au NPs) into dimers, trimers, and multimers have been under extensive studies for the last 2 decades due to their fascinating properties and diverse potential applications. − A great wealth of knowledge has been accumulated. For example, it is well-known that when the incident electric field is aligned parallel to the multimer axis, the resulting plasmonic resonance peak in the extinction spectra is red-shifted as the gap distance decreases.…”

“…For example, it is well-known that when the incident electric field is aligned parallel to the multimer axis, the resulting plasmonic resonance peak in the extinction spectra is red-shifted as the gap distance decreases. This phenomenon can be explained either by approximating the particles as point dipoles interacting with dipolar coupling or by making use of the plasmon hybridization model. , A scaling law dependence between the fractional shift of the peak position and particle gap distance has been proposed by Jain et al based on experimental results and numerical data obtained via the discrete dipole approximation (DDA). Such phenomenon has been called a “plasmonic ruler” and has been suggested that it could be used to measure distance at the nanometer scale based on the shift in the plasmonic peak .…”