Plasmonic metamaterials allow confinement of light to deep subwavelength dimensions, while allowing for the tailoring of dispersion and electromagnetic mode density to enhance specific photonic properties. 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. Surface-enhanced 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 is demonstrated. It is shown that high spatial uniformity plasmonic enhancement can be used for single-molecule level SERS sensing and super-resolution Raman imaging. Complementary to Raman scattering, infrared absorption can also be enhanced by plasmonic surfaces, a method typically referred to as SEIRS. Such improvement in IR absorption based sensing can be achieved using metasurfaces with resonances in the infrared.
We demonstrate that optical and chemical properties of Aluminum can be advantageous in fabricating metasurfaces that exhibit multiple resonances spanning the visible and the infrared. Particularly, we use all-aluminum metal-insulator-metal (MIM) resonators using the native oxide of the bottom aluminum layer as the dielectric layer and demonstrate tunable structures featuring two simultaneous resonances in the infrared and one plasmonic resonance in the visible region. Hierarchical metasurfaces are also fabricated by depositing silver nanoislands on top of the aluminum layers, where a MIM structure is obtained due to the presence of the native oxide layer. Monolayer sensitivity is demonstrated using infrared plasmonic metasurfaces based on aluminum nanostructures.