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.

紫外（UV）波段等离子体纳米结构（plasmonic nanostructures）的研究仍属相对未被探索的领域，这源于工程与材料科学两方面均存在诸多挑战。本研究采用镓（Ga）聚焦离子束，在铝（Al）与镁（Mg）薄膜上制备了二维周期性纳米孔阵列。针对不同阵列周期，表征了其在紫外-可见光波段的光透射特性。透射结果表明，随着周期增大，体系出现显著的共振透射增强与抑制现象，并伴随相应的红移，同时存在稳态波导模式。对比Al与Mg纳米孔阵列，Al孔阵列的透射性能优于Mg孔阵列。本研究通过时域有限差分法（finite-difference time-domain method）开展数值分析，仿真所得远场透射结果与实验结果高度吻合。仿真模型基于截面样品的透射电子显微镜表征结果构建，以纳入锥形侧壁几何结构与衬底侧蚀凹陷的影响。采用能量色散X射线光谱（Energy-dispersive X-ray spectroscopy）对样品的元素组成进行了表征，涵盖氧化与合金化两种情况。本研究还定性分析了镓注入的影响：镓会注入至纳米孔内部，且Mg样品中的注入浓度高于Al样品，同时会对Al与Mg两种阵列的透射性能产生影响。