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

Abstract

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.

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“…Similar reports showed the temperature-dependent field emission (FE) in LaB 6 nanowires (70–130 nm thick and 10 μm length), and the emission current of aligned LaB 6 nanowire arrays increased by ∼45 times (to 9.05 mA/cm 2 ) at 2.20 V/μm when the temperature increased from RT to 723 K. The authors of this study suggested that such good FE performance LaB 6 nanowires have the potential for thermionic emission, field-induced emission valuable for TEM, SEM, and flat panel displays, as well as direct thermal to electrical converters . Besides being a field emitter, LaB 6 is also a plasmonic material with absorption in the range of 600 to 2000 nm; Tran et al reported a photothermal absorber using LaB 6 –Al 2 O 3 –LaB 6 trilayers . The ⟨100⟩ orientation-grown LaB 6 films were developed by a lithographic process using laser direct writing and reactive ion etching.…”

“…164 Besides being a field emitter, LaB 6 is also a plasmonic material with absorption in the range of 600 to 2000 nm; Tran et al reported a photothermal absorber using LaB 6 −Al 2 O 3 −LaB 6 trilayers. 184 The ⟨100⟩ orientation-grown LaB 6 films were developed by a lithographic process using laser direct writing and reactive ion etching. The sputtered films showed low surface roughness of ∼2.5 nm, and their optical performance in the near-infrared (NIR) regions showed better performance than those of molybdenum, tungsten, and titanium nitride.…”

“…The sputtered films showed low surface roughness of ∼2.5 nm, and their optical performance in the near-infrared (NIR) regions showed better performance than those of molybdenum, tungsten, and titanium nitride. The LaB 6 films could be promising candidates for application in photothermal transducers such as IR plasmonic sensing, thermal emitters for spectroscopic heating, and thermophotovoltaics . There are few reports on using LaB 6 NCs (∼25–60 nm) dispersed in a polymeric film to test the near IR shielding properties, concluding that the LaB 6 thin films are a promising material for solar radiation shielding filters for windows with high visible light transmittance. − A recent report in 2022 by Guo et al suggested LaB 6 dispersed in pH-controlled DI water could be used for photothermal conversion.…”