Metal-insulator-metal strip spectroscopic infrared photothermal absorber based on uniaxially oriented plasmonic lanthanum hexaboride films.

We report the fabrication of a mid-infrared device using LaB6 - Al2O3 - LaB6 trilayers, with an array of LaB6 strips as the top layer. Uniaxially oriented lanthanum hexaboride (LaB6) films self-organized in a (100) orientation were adopted together with a lithographic process using laser direct writing followed by reactive ion etching. The fabricated infrared absorbers based on our electromagnetic design exhibited excellent resonant absorption and flexible tunability by changing the periodicity and width of the top LaB6 strips. We examined the performance of epitaxial and sputtered LaB6 films by fabricating two different types of absorbers using sputtered LaB6(100) and epitaxial LaB6(100) films for the bottom mirror layers. Owing to a difference in crystallinity, the latter exhibited a lower background in the absorption spectra as well as in the thermal emission spectra, indicating its good spectral selectivity.

Nanoantenna Structure with Mid-Infrared Plasmonic Niobium-Doped Titanium Oxide.

Among conductive oxide materials, niobium doped titanium dioxide has recently emerged as a stimulating and promising contestant for numerous applications. With carrier concentration tunability, high thermal stability, mechanical and environmental robustness, this is a material-of-choice for infrared plasmonics, which can substitute indium tin oxide (ITO). In this report, to illustrate great advantages of this material, we describe successful fabrication and characterization of niobium doped titanium oxide nanoantenna arrays aiming at surface-enhanced infrared absorption spectroscopy. The niobium doped titanium oxide film was deposited with co-sputtering method. Then the nanopatterned arrays were prepared by electron beam lithography combined with plasma etching and oxygen plasma ashing processes. The relative transmittance of the nanostrip and nanodisk antenna arrays was evaluated with Fourier transform infrared spectroscopy. Polarization dependence of surface plasmon resonances on incident light was examined confirming good agreements with calculations. Simulated spectra also present red-shift as length, width or diameter of the nanostructures increase, as predicted by classical antenna theory.