Raman Enhancement on a Broadband Meta-Surface

Abstract

P lasmonic excitations of metallic nanostructures have attracted a great deal of attention in past decades, due to the rich variety of geometric configurations, the associated optical properties and phenomena, and the wide range of present and potential future applications. 1,2 Propagating and localized plasmons have been utilized in the design of photonic structures to efficiently couple free-space propagating light onto highly confined surface modes, resulting in the enhancement of electromagnetic field intensities. Nonlinear optical effects benefit from plasmonic field enhancement, 3,4 and plasmonics has the potential to be an enabling technology for quantum optics and all-optical information processing. 5,6 It has been shown that plasmonic field enhancement allows the observation of Raman scattering from single molecules with low excitation powers down to microwatts. 7,8 The lack of reliability resulting from the spatially non-uniform nature of plasmonic field enhancement can be a problem for applications requiring repeatability. In the case of surfaceenhanced Raman scattering (SERS), regions with high enhancement (so-called hot spots) are typically major contributors to the observed signal. Raman intensity enhancement is estimated through I SERS = I 0 |E(ω exc )E(ω det )/E 0 (ω exc )E 0 (ω det )| 2 , where ω exc and ω det are the excitation and detection frequencies, and E and E 0 are the electric field intensities with and without the presence of plasmonic structures. Defining an enhancement factor, EF(ω) = |E(ω)/E 0 (ω)| 2 , overall Raman enhancement factor can be written as the product of excitation and detection factors, EF SERS = EF(ω exc )EF(ω det ). Spatial nonuniformity of the electric field directly translates into a spatial non-uniformity of EF SERS and can be an important disadvantage for repeatability. Hot spots are typically formed when two metal regions come close (within a few nanometers) to each other, and even periodic structures may display a wide distribution of enhancement factors. 9 In order to achieve high and spatially uniform field enhancement, engineered surfaces that exhibit plasmon modes at both the excitation and scattering wavelengths are needed. 10À13 Previously, metal nanoparticle clusters (bottom-up approach) and sparse structures or biharmonic gratings with however, benefits of strong coupling of dimers have been overlooked. Here, we construct a plasmonic meta-surface through coupling of diatomic plasmonic molecules which contain a heavy and light meta-atom. Presence and coupling of two distinct types of localized modes in the plasmonic molecule allow formation and engineering of a rich band structure in a seemingly simple and common geometry, resulting in a broadband and quasi-omni-directional meta-surface. Surfaceenhanced Raman scattering benefits from the simultaneous presence of plasmonic resonances at the excitation and scattering frequencies, and by proper design of the band structure to satisfy this condition, highly repeatable and spatially uniform Raman enhancement ...

Plasmonically enhanced hot electron based photovoltaic device

“…In the proposed configuration, the center frequency, the strength and the width of the resonance can be controlled by the nanoparticle size, shape and distribution. The insulator thickness of the top MIM can also be tuned to control the resonance conditions [12,13]. The thickness of the bottom insulator, however, is tightly constrained by the tunneling probability considerations.…”

Sensitivity comparison of localized plasmon resonance structures and prism coupler

“…In LSPR sensing using an isolated plasmonic resonator where the mode field can be assumed to isotropically decay into the surrounding medium, the wavelength shift upon binding is given similarly by ı = S ın d (1 − exp(− 2h/1 d )), where s is the sensitivity factor (shift in resonance per RIU change in environment refractive index) and l d is electromagnetic decay length of the LSPR mode [8][9][10][11][12][13][14][15][16][17]. However, for anisotropic resonators, such as prism or disk shaped, the mode field is non-uniformly distributed on the resonator and sensitivity of binding assumes a location dependent form.…”

“…1 [19]. Previously, lumped circuit element models and transmission lines were used to calculate band structure for such coupled resonators [12]. Because of the complexity of the band structures of coupled LSPR resonators, we do not attempt to model the band structures using such models.…”

“…In order to perform plasmon resonance imaging with high spatial resolution, it is desirable to have plasmonic surfaces that are not sensitive to angle of excitation (omnidirectionality), while maintaining a high refractive index sensitivity, thereby allowing sensing of monolayer biomolecular coatings. Periodic localized plasmon structures can be designed with optical band structures which exhibit quasi-omnidirectional response [12].…”

Rounding corners of nano-square patches for multispectral plasmonic metamaterial absorbers

“…Multiplexing different resonator structures in a unit cell is a route to obtain multispectral absorption which requires precise control of dimensions of multiple nanostructures [11,[37][38][39][40][41][42][43]. Multispectral MMAs based on simultaneous excitation of electric and magnetic plasmon modes are the least exploited structures [28,44,45]. MMAs are usually fabricated by using electron beam (e-beam) or optical lithography which typically result in structures slightly different from the design.…”