Tuning of Reciprocal Plasmonic Metasurface Resonances by Ultra-Thin Conformal Coatings

Abstract

Metamaterials, in the form of perfect absorbers, have recently received attention for sensing and light-harvesting applications. The fabrication of such metamaterials involves several process steps and can often lead to nonidealities, which limit the performance of the metamaterial. A novel reciprocal plasmonic metasurface geometry composed of two plasmonic metasurfaces separated by a dielectric spacer was developed and investigated here. This geometry avoids many common fabrication-induced nonidealities by design and is synthesized by a combination of two-photon polymerization and electron-beam-based metallization. Infrared reflection measurements revealed that the reciprocal plasmonic metasurface is very sensitive to ultra-thin, conformal dielectric coatings. This is shown here by using Al2O3 grown by atomic layer deposition. It was observed experimentally that incremental conformal coatings of amorphous Al2O3 result in a spectral red shift of the absorption band of the reciprocal plasmonic metasurface. The experimental observations were corroborated by finite element model calculations, which also demonstrated a strong sensitivity of the reciprocal plasmonic metasurface geometry to conformal dielectric coatings. These coatings therefore offer the possibility for post-fabrication tuning of the reciprocal plasmonic metasurface resonances, thus rendering this novel geometry as an ideal candidate for narrow-band absorbers, which allow for cost-effective fabrication and tuning.

Switchable reciprocal metasurfaces for infrared scene projection

“…The top metallic layer is a Au bar array suspended above the bottom Au layer of reciprocal holes by a set of dielectric fins. 6,7 A cross section of the configuration is depicted in the inset of Figure 1(a). For this study the dielectric fins have the optical properties of a twophoton polymerization compatible resin, IP-Dip (Photonic Professional GT, Nanoscribe GmbH).…”

“…Woollam Co., IR-Vase) and are used in the FEM. 7,8 The FEM of the unit cell results in a reflectance minimum located at 4.75 µm when uncoated and shifts to 4.78 µm when coated with 10 nm of Al 2 O 3 shown in Figure 1(a). The results were experimentally verified by fabricating a 50×50 µm 2 array of the metasurface using two-photon polymerization and electron beam evaporation.…”

“…We have corroborated these numerical findings experimentally where narrow spectral perfect absorption and sensitivity to changes in ambient index was found in an RPM tuned for the infrared spectral range. 7 Here, an approach is explored numerically where the RPM geometry is combined with a thin conformal coating of a phase change material. Phase change materials are well known correlated electron systems that exhibit extreme changes of their electrical and optical properties as a function of external stimuli.…”

Bi-encoded metasurfaces for the infrared spectral range

“…Two-photon polymerization has been established as a mask-less lithographic technique which allows the fabrication of metasurfaces. 6,7 This work aims to show proof of concept for the encoding of information into a plasmonic metasurface fabricated using two-photon polymerization techniques. A metasurface composed of an arrangement of rectangular dipoles on a dielectric surface was designed and fabricated using two-photon polymerization with subsequent metallization.…”