Two-dimensional (2-D) periodic arrays of aluminum nanopillars for highly efficient bulk and localized plasmonic sensing in the UV spectral regime

In this paper, we describe plasmonic sensors based on two dimensional (2-D) periodic arrays of aluminum nanopillars having narrow gaps between the plasmonic nanostructures, such that these sensors operate in the ultra-violet (UV) spectral regime (200–400 nm). Employing finite difference time domain (FDTD) simulations, we design highly efficient plasmonic sensors exhibiting high bulk and localized sensitivities in the UV spectral regime. Aluminum has been taken as the plasmonic metal in our simulations as nanostructures of aluminum have plasmon resonance wavelength tuned in the UV spectral regime. A thin layer of aluminum oxide (Al 2 O 3 ) is generally formed on the surface of the aluminum nanopillars due to oxidation. In order to capture the oxidation on the surface of the aluminum nanostructures, we have taken a 2–3 nm layer of Al 2 O 3 on the surface of the nanostructures in all the FDTD simulations performed in this paper. In our FDTD simulations, we optimize the heights, widths, periodicities in the x - and y - directions, and the aspect ratios of the aluminum nanopillars, as well as the thickness of the oxide layer to ensure that the plasmon resonance wavelengths in the reflectance spectra for these nanostructures lie in the UV spectral regime, so that these optimized nanostructures could be employed for plasmonic sensing in the UV spectral regime. The shifts in the reflectance spectra, and in particular the plasmon resonance wavelengths, with a change in the bulk as well as localized refractive indices around the plasmonic nanostructures were calculated to determine the bulk and localized sensitivities of these sensors. Employing FDTD simulations, we demonstrate that the proposed plasmonic sensors can be employed for bulk sensing of glucose, and localized sensing of bio molecules (proteins, DNA etc) in the UV spectral regime.We observe that plasmonic sensors operating the UV spectral regime that were based on 2D periodic arrays of aluminum nanopillars had a much higher bulk and localized sensitivities than those based on 1D periodic arrays of aluminum nanowires. We also studied the effect of rounding of edges and corners of the nanopillars on the sensitivities of these sensors. We also observe that the 2D periodic arrays of aluminum nanopillars are significantly less polarization dependent as compared to 1D periodic arrays of aluminum nanowires.