Material effects on V-nanoantenna performance

There is great interest in aluminum based plasmonic devices due to the relatively high plasma frequency of this material as well as its low cost and self-passivating oxide layer. The passivation layer provides aluminum plasmonics with the long-term stability required for practical applications. While several studies have investigated the impact of this oxide layer on the plasmon resonances of aluminum nanostructures on glass substrates, little is known about the effect of high-refractive index substrates on these resonances. Here we present an investigation of aluminum V-shaped antennas resonant in the visible on a silicon substrate. Through comparison between numerical and experimental results, we show that the aluminium passivation layer has little effect on the antenna resonances by comparing numerical simulations both with and without. We show, however, that inclusion of the native oxide layer of the silicon substrate in numerical models is critical for achieving good agreement with experimental data. Furthermore, we computationally explore the influence of the 1.5 eV interband transition of aluminum on plasmon resonances, and find that its effect on the material properties of the resonant structures results in narrower resonances in the blue part of the spectrum than if it was not present.