Maskless fabrication of slanted annular aperture arrays.

We report maskless fabrication of high-aspect-ratio slanted annular aperture arrays (SAAAs) in gold films using focused ion beam lithography. By tilting the substrate, SAAAs with the desired tilting angle can be fabricated. Our experimental results demonstrate accurate control over aperture size, obliqueness, and reproducibility. We also show that the resulted plasmonic resonances of SAAAs can be effectively tuned via obliqueness control. This versatile approach may enable fabrication of more complicated plasmonic nanostructures. The demonstrated gold SAAAs could also find many potential applications in plasmon-assisted sensing and surface enhanced spectroscopy.