Far-field coupling in arrays of gold and gold::vanadium dioxide nanodimers

Abstract

Previous observations on arrays of single nanoparticles (NPs) have shown that particle separation and grating constant determine the peak extinction wavelength of the local surface plasmon resonance (LSPR). Recently, it has been predicted that the LSPR peak extinction wavelength in arrays of nanodimers (NDs) exhibit enhanced sensitivity to changes in the local dielectric function compared to single NPs. In order to test this prediction, arrays of NPs, NDs and heterodimers comprising three different NP sizes were fabricated by electron-beam lithography with various grating constants, particle diameters, and interparticle separations. Another set of arrays were also fabricated and coated with approximately 60-nm of vanadium dioxide, which undergoes an insulator to metal phase transition at a critical temperature near 68.C. By tuning the temperature of the samples through the strong-correlation region around the critical temperature, we varied the effective dielectric constant surrounding the NP arrays over a significant range. Linear extinction measurements on the arrays were made at temperatures above and below the critical temperature, with linear polarizers placed in the incident beam in order to distinguish between LSPR modes. Measurements show a clear dependence of LSPR sensitivity to interparticle separation as well as the dielectric function of the surrounding medium. Finally, finite-difference time-domain (FDTD) simulations were carried out for comparison with the experimental results.