Aluminum plasmonics for optical applications

Overview & Synopsis

Plasmonics is based on the intense and confined electromagnetic fields appearing near metallic nanostructures illuminated at frequencies near their surface plasmon resonances. Among the different metals, aluminum sustains a broad range of plasmonic resonances from deep UV to near IR. Due to high losses in the visible, aluminum plasmonic structures require an improvement to compete with noble metals. First, we present a strategy to increase the resonance quality based on diffractive coupling in periodic arrays. This approach, studied with simulations and experimental methods, provides a change of quality factor of resonance up to 7 times in comparison with an isolated particle. Then, we couple aluminum nanostructures with a wide band gap semiconductor to enhance its emission. Periodic arrays of Al nanoparticles were fabricated onto a ZnO epitaxial layer. Results show an enhancement of emission of 1.5 times in comparison with pristine ZnO. To increase the effect and get a more efficient surface coverage, we then used a fractal geometry inspired from radiowave technology. FDTD simulations were performed to design an effective geometry and the structures were fabricated with an adapted electron beam lithography process. Finally, we propose a concept of chiral fractals. Using the complex geometry of fractals, it is possible to push optical chirality of plasmonic structures toward the UV part of the spectrum. Samples were fabricated and the existence of circular dichroism in fractal structures was proven