Effect of Ga Implantation and Hole Geometry on Light Transmission through Nanohole Arrays in Al and Mg

The
study of plasmonic nanostructures in the ultraviolet (UV) is
a relatively uncharted field because of the challenges in both engineering
and materials science. In this work, two-dimensional periodic nanohole
arrays in aluminium (Al) and magnesium (Mg) films were fabricated
using gallium (Ga) focused ion beam. Optical transmission through
the arrays was obtained in the UV–visible range for varying
array periodicity. Transmission results show strong resonance transmission
enhancement and suppression with corresponding red shift as the period
increases and the presence of stationary waveguide modes. Comparing
Al and Mg, Al hole arrays enable greater transmission than those of
Mg. Numerical analysis was carried out through the finite-difference
time-domain method, which showed far-field transmission consistent
with experiments. The simulation model was constructed based on transmission
electron microscopy of cross-sectioned samples to take into account
tapered sidewall geometry and undercut into the substrate. Energy-dispersive
X-ray spectroscopy was used to assess elemental composition, including
oxidation and alloying. The effect of Ga implantation was qualitatively
studied, which indicates that Ga implants inside the hole, with greater
implantation concentration within Mg than within Al, and affects the
transmission through both Al and Mg arrays.