Optical Coupling of Plasmonic and Surface Lattice Resonances in Gold Nanocube Arrays

The ability of localized surface plasmon to confine light to a sub-diffraction-limited mode volume can drive coherence effects in quantum emitter systems that lead to quantum photonic applications. Periodic arrays of plasmonic nanostructures can further sustain photonic lattice resonances (also referred to as surface lattice resonance) that can be tuned to couple with plasmonic resonance. Here, we will demonstrate the varying degrees of optical coupling that arise when periodic arrays of gold nanocubes (AuNC) are grown atop a gold mirror. This architecture allows us to independently control the two distinct optical modes, a plasmonic gap mode between the AuNC and the gold surface and a lattice resonance mode resulting from constructive interference from the scattering of the periodic array. From electromagnetic simulation and reflectance spectroscopy, we will show that these two resonance modes can be tuned and show a varying degree of coupling that is dependent on the nanostructure geometry, lattice pitch and lattice symmetry. A series of periodic arrays of 73 nm of AuNC on top of a 100 nm Au mirror with a 4.6 nm polymethyl methacrylate (PMMA) spacer and with periodicity ranging from 500 nm to 950 nm were fabricated through a Si nanofabrication services. The gaps between the AuNCs are partially filled by SiO2 spacer. Electromagnetic simulation of these structured arrays has shown that the breadth and peak of the lattice resonance mode sharpens and red-shits with increasing periodicity. In the lowest periodicity array, only plasmonic gap modes are observable. When the periodicity reaches 500 nm, two optical modes become visible with the longer wavelength reflectance peak corresponding to the plasmonic gap mode and the shorter wavelength peak associated with the lattice resonance. A visible coupling of the plasmonic gap mode to the surface lattice mode was observed in an AuNC array with 600 nm periodicity which is indicative of mode hybridization. We will also discuss the impact that particle geometry and material have in this presentation.