Aluminum-based fishnets with complex aperture shapes

Plasmonic structures ensure electromagnetic field localization and concentration within subwavelength volumes, thus enabling numerous practical applications. Structuring at levels much below the operating wavelength can be used to obtain novel electromagnetic modes, an example being the designer plasmon structures where one utilizes ordered arrays of subwavelength holes to mimic the behavior of metals in different frequency ranges and obtain the designer (spoof) plasmons, surface waves with a resonant frequency tailorable by design in a wide range. In this paper we consider structures with aperturebased pattern that use aluminum for the negative permittivity part instead of the usual gold or silver. We experimentally investigate patterns with complex aperture shapes which ensure richer modal behavior of the structures, including a possibility to customize their frequency dispersion and to obtain tailorable deeply subwavelength electromagnetic field hotspots. To this purpose we utilize the proximity effects (field concentration in deep subwavelength gaps) and the edge effects (localization on sharp corners). We conclude that a new degree of design freedom is obtained when utilizing aluminum-based aperture arrays and that the proximity and edge effects at a deep subwavelength level can be used to enhance the effects of spoof plasmons. It is important at that to take into account the influence of native oxide of aluminum that appears in practical structures, as well as the increased absorption losses