Tuning the Localized Surface Plasmon Resonance of Al-Al2O3 Nanosphere Towards NIR Region by Gold Coating

Abstract

Background: A relatively narrow LSPR peak and a strong interband transition ranging around 800 nm make Al a strongly plasmonic active material. Usually, Al nanoparticles are preferred for UV-plasmonic as the SPR of small size Al nanoparticles is located in the deep UV-UV region of the optical spectrum. This paper focused on tuning the LSPR of Al nanostructure towards the infrared region by coating the Au layer. The proposed structure has Au as the outer layer, which prevents further oxidation of Al nanostructure. Methods: The Finite Difference Time Domain (FDTD) and Plasmon Hybridization Theory has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3-Au MDM nanostructure. Results: It is observed that the resonance mode shows dependence on the thickness of the Al2O3 layer and also on the composition of the nanostructure. The Au layered MDM nanostructure shows two peaks of equal intensities simultaneously in UV and visible region tuned to the NIR region. The extinction spectra and electric field distribution profiles of dimer nanoparticles are compared with the monomer to reveal the extent of coupling. The dimer configuration shows higher field enhancement ~107 at 1049 nm. By optimizing the thickness of the dielectric layer, the MDM nanostructure can be used over the UV-visible-NIR region. Conclusion: The LSPR peak shows dependence on the thickness of the dielectric layer and also on the composition of the nanostructure. It has been observed that optimization of size and thickness of the dielectric layer can provide two peaks of equal intensities in the UV and Visible region, which are advantageous for many applications. The electric field distribution profiles of dimer MDM nanostructure enhanced the field by ~107 in visible and NIR region showing its potential towards SERS substrate. The results of this study will provide valuable information for the optimization of LSPR of Al-Al2O3- Au MDM nanostructure to have high field enhancement.