Effect of dispersion on metal-insulator-metal infrared absorption resonances

Calhoun, Seth; Lowry, Vanessa C.; Stack, Reid; Evans, R. N.; Brescia, Jonathan R.; Fredricksen, Christopher J.; Nath, Janardan; Peale, Robert E.; Smith, Evan M.; Cleary, Justin W.

doi:10.1557/mrc.2018.88

Cited by 8 publications

(6 citation statements)

References 10 publications

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“…Thus, TiO 2 would be better than SiO 2 as an index contrast material for LWIR photonic planer waveguides due to its comparatively low loss [6]. Moreover, TiO 2 lacks the derivative-like dispersion feature observed for n of SiO 2 , which allows TiO 2 -based metal-insulator-metal (MIM) absorbers to have single resonances for spectral sensing applications as opposed to the complicated spectra observed for SiO 2 -based devices [15]. The onset of extinction beyond 12 µm wavelength suggests optical phonon energies less than 0.1 eV.…”

Section: Resultsmentioning

confidence: 99%

Smooth TiO2 Thin Films Grown by Aqueous Spray Deposition for Long-Wave Infrared Applications

et al. 2018

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Self-assembled TiO2 films deposited by aqueous-spray deposition were investigated to evaluate morphology, crystalline phase, and infrared optical constants. The Anatase nano-crystalline film had ∼10 nm characteristic surface roughness sparsely punctuated by defects of not more than 200 nm amplitude. The film is highly transparent throughout the visible to wavelengths of 12 μm. The indirect band gap was determined to be 3.2 eV. Important for long-wave infrared applications is that dispersion in this region is weak compared with the more commonly used dielectric SiO2 for planar structures. An example application to a metal-insulator-metal resonant absorber is presented. The low-cost, large-area, atmospheric-pressure, chemical spray deposition method allows conformal fabrication on flexible substrates for long-wave infrared photonics.

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Section: Resultsmentioning

confidence: 99%

Smooth TiO2 Thin Films Grown by Aqueous Spray Deposition for Long-Wave Infrared Applications

et al. 2018

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“…Compatibility with common microfabrication technology makes SiO2 and Si3N4 two of the simplest choices for lossy dielectrics in the LWIR. SiO2 has a very sharp absorption peak at ~9.22 µm, resulting in highly dispersive characteristics in the LWIR [38]. Si3N4 has multiple vibrational phonon peaks in between 8 ̶ 12 µm, which correspond to a comparatively moderate dispersion and broader absorption profile in the LWIR [39].…”

Section: Metal-dielectric Subwavelength Grating Cellsmentioning

confidence: 99%

Enhanced absorption per unit mass for infrared arrays using subwavelength metal–dielectric structures

Das¹,

Talghader²

2020

J. Opt. Soc. Am. B

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The absorption-to-mass ratio of the infrared arrays is enhanced to ~1.33 ̶ 7.33 times larger than the previously reported structures by incorporating two design characteristics: first, the coupling of evanescent fields in the air gaps around pixels to create effectively larger pixel sizes, and, second, the use of guided mode resonance (GMR) within the subwavelength metaldielectric gratings. The bilayer Ti-Si3N4 gratings achieve broadband long-wave infrared (LWIR,  ~ 8 ̶ 12 m) absorption by the combined effects of free carrier absorption by the thin Ti films and vibrational phonon absorption by the thick Si3N4 films. In the presence of GMR, this broadband absorption can be enormously enhanced even with low fill factor subwavelength grating cells. Further, the spacing and design of the cells can be modified to form a pixel array structure that couples the light falling in the air gaps via evanescent field coupling. Calculations are performed using the finite difference time domain (FDTD) technique. Excellent broadband absorption is observed for the optimized arrays, yielding maximum absorption of 90% across the LWIR and an average absorption-per-unit-mass (absorption/mass) per pixel of 3.45×10 13 kg -1 .

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“…Our group proposed [8] groups the data according to square size l, and guide lines indicate the longest wavelength bands as they shift with changing t. The observed complexity of these spectra is expected due to high LWIR dispersion for SiO2. [9] There are multiple solutions for the same (b,m) = (1,0) values, and it is difficult to unambiguously identify the different bands. The red guide lines indicate the longest LWIR fundamental resonance wavelength, which will be considered in Figure 6 and For l = 4.0 and 4.5 m, the t/l ratio never reaches that value, but it is clear that the experimental values begin to approach the theoretical ones at the largest t/l.…”

Section: Standing Wave Resonancesmentioning

confidence: 99%

“…The red guide lines indicate the longest LWIR fundamental resonance wavelength, which will be considered in Figure 6 and For l = 4.0 and 4.5 m, the t/l ratio never reaches that value, but it is clear that the experimental values begin to approach the theoretical ones at the largest t/l. Previously studied devices [9] were fabricated with poor control over l values, so the results were focused on a relationship between the fundamental resonance wavelength and the geometrical factor presented in Eq. (6).…”

Section: Standing Wave Resonancesmentioning

confidence: 99%

“…The first is responsible for the resonance line observed near 10 m AlN compared to SiO2. [9] As in the case of TiO2, the l values were poorly controlled during fabrication, so that the spots probed by the IR beam may have somewhat different square sizes Figure 19 presents the available index spectrum for AlN, which does not extend into the far-IR. However, the far-IR extinction spectrum is available [12] , and that curve is plotted, in the form of a large and sharp absorption peak.…”

Section: Sio2mentioning

confidence: 99%

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Far-infrared bands in plasmonic metal-insulator-metal absorbers optimized for long-wave infrared

et al. 2019

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Metal–insulator–metal (MIM) resonant absorbers comprise a conducting ground plane, a dielectric of thickness t, and thin separated metal top-surface structures of dimension l. The fundamental resonance wavelength is predicted by an analytic standing-wave model based on t, l, and the dielectric refractive index spectrum. For the dielectrics SiO2, AlN, and TiO2, values for l of a few microns give fundamental resonances in the 8-12 μm long-wave infrared (LWIR) wavelength region. Agreement with theory is better for t/l exceeding 0.1. Harmonics at shorter wavelengths were already known, but we show that there are additional resonances in the far-infrared 20 - 50 μm wavelength range in MIM structures designed to have LWIR fundamental resonances. These new resonances are consistent with the model if far-IR dispersion features in the index spectrum are considered. LWIR fundamental absorptions are experimentally shown to be optimized for a ratio t/l of 0.1 to 0.3 for SiO2- and AlN-based MIM absorbers, respectively, with TiO2-based MIM optimized at an intermediate ratio.

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Effect of dispersion on metal-insulator-metal infrared absorption resonances

Abstract: Abstract

Cited by 8 publications

References 10 publications

Smooth TiO2 Thin Films Grown by Aqueous Spray Deposition for Long-Wave Infrared Applications

Smooth TiO2 Thin Films Grown by Aqueous Spray Deposition for Long-Wave Infrared Applications

Enhanced absorption per unit mass for infrared arrays using subwavelength metal–dielectric structures

Far-infrared bands in plasmonic metal-insulator-metal absorbers optimized for long-wave infrared

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