Strengthening optical enhancement with Ag_xAu_1−x alloy and Ag/Au heteromaterial sub-micro disk arrays

Material modification on plasmonic nanostructures is recognized as one of many approaches to increase optical near-field enhancement and resonance wavelength tuning. In this work, with finite-difference time-domain simulation, we showed that closed-hexagonal sub-micro disk arrays of the Ag_xAu_1−x alloy increase electric-field enhancement in the near-infrared spectra at reduced Ag fraction in the alloy, while the arrays of pure Ag does so in the visible spectra. For the enhancement factor in the near-infrared region, the Au array is dominant around the wavelength of 800 nm, whereas the Ag_0.74Au_0.24 array is slightly stronger at 820 nm. Furthermore, the local confinement in the near-infrared region (800-900 nm) is strengthened by the heteromaterial array of Ag/Au sub-micro disks with alternating rows, which can boost the electric field enhancement at 1.3 and 3.9 times better than those of the pure Au and Ag arrays, respectively. The Ag, Au and Ag/Au plasmonic hexagonal arrays yield the Purcell factors of 2.42 × 10⁵, 1.17 × 10⁴ and 2.72 × 10⁴, respectively, at wavelengths of 695 nm, 828 nm and 795 nm that would be suitable for spontaneous emission rate enhancement in quantum dots.