Plasmonic Properties of Al2O3 Nanoshell with a Metallic Core

Background: Al is the promising candidate for deep UV and longer wavelength range plasmonic applications. But it is difficult to have the pure aluminium nanostructure as it is easily oxidized, forming a thin layer of Al2O3. In this paper, we have evaluated the field enhancement of oxide layer on metallic shell (Al-Al2O3 and Au-Al2O3) for single and dimer core-shell configuration and showed potential of the oxide layer in SERS. Methods: The Finite Difference Time Domain (FDTD) has been used to evaluate the LSPR and field enhancement of single and dimer Al-Al2O3 and Au- Al2O3 nanostructure. Results: The results exhibit the tunable plasmon resonance on varying the inner and outer radii of the Al2O3 shell. A redshift and decrease in enhancement were observed as shell thickness increases, whereas on increasing the core size, the enhancement increases in the case of Au-Al2O3 and decreases in Al- Al2O3 due to quadrupole contribution. But on comparing the Au-Al2O3 with Al-Al2O3 for the same particle size, Al-Al2O3 shows larger enhancement because Au has to compete with its interband transition. Conclusion: By optimizing the thickness of the shell and core size, it can be concluded that an ultrathin shell of Al2O3 can give higher enhancement. With Al as a core metal, the enhancement increases as compared to Au-Al2O3. Since a single Al-Al2O3 nanoshell has shown a huge enhancement we have considered the multimer configuration of two identical nanoshells. Due to coupling between two nanoshells a huge increase in enhancement factor ~1012 was observed for Al-Al2O3 dimer nanoshell in the UV region.