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Abstract This work presents a novel approach to achieve directional and normal thermal emission from epsilon‐near–zero (ENZ) materials. ENZ materials exhibit near–zero permittivity at the ENZ point, resulting in some unique properties compared to conventional optical materials including infinite wavelength, constant phase distribution, and decoupling of spatial and temporal fields inside the ENZ material. These properties are used to engineer the far‐field thermal emission from optical antennas fabricated on ENZ film in the mid‐infrared. By coupling the antenna resonance mode with the Berreman mode of the ENZ material, highly directional and normal emission is demonstrated. This approach could have significant implications for thermal management, energy conversion, and sensing applications.
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Large Mid‐Infrared Magneto‐Optic Response from Doped Cadmium Oxide at Its Epsilon‐Near‐Zero Frequency
Abstract The epsilon‐near‐zero (ENZ) frequency regime of transparent conducting oxide materials is known to yield large enhancements in their optical nonlinearity and electro‐optic response. Here, Faraday rotation is investigated in Gd and In‐doped CdO films and it is found that the Verdet constant peaks at values >3 105 deg T−1 m−1near the ENZ frequency, which is tunable in the wavelength range 2 < λ< 10 µm by varying the doping concentration. These results are among the highest reported to date in the mid‐infrared spectral range and are in good agreement with the Drude model, which confirms that the magneto‐optic response of doped CdO derives from its free carriers. The combination of a tunable Verdet constant, low optical loss compared to other plasmonic materials, and the ability to deposit CdO on Si with no loss in performance make this material a promising platform for integrated magneto‐optic and magnetoplasmonic devices that operate across the mid‐infrared.
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- Award ID(s):
- 2011839
- PAR ID:
- 10541064
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 12
- Issue:
- 25
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Controlling both the spectral bandwidth and directionality of emitted thermal radiation is a fundamental challenge in contemporary photonics. Recent work has shown that materials with a spatial gradient in the frequency range of their epsilon‐near‐zero (ENZ) response can support broad spectrum directionality in their emissivity, enabling high total radiance to specific angles of incidence. However, this capability is limited spectrally and directionally by the availability of materials with phonon‐polariton resonances over long‐wave infrared wavelengths. Here, an approach is designed and experimentally demonstrated using doped III–V semiconductors that can simultaneously tailor spectral peak, bandwidth, and directionality of infrared emissivity. InAs‐based gradient ENZ photonic structures that exhibit broadband directional emission with varying spectral bandwidths and directional ranges as a function of their doping concentration profile and thickness are epitaxially grown and characterized. Due to its easy‐to‐fabricate geometry, it is believed that this approach provides a versatile photonic platform to dynamically control broadband spectral and directional emissivity for a range of emerging applications in heat transfer and infrared sensing.more » « less
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Abstract Due to its transparent and conductive nature, indium tin oxide (ITO) offers substantial benefits in several industries, such as thin film transistors, displays, and nanophotonics. Previous studies on ultrathin ITO have so far focused on its electrical properties but have neglected the technologically important epsilon-near-zero (ENZ) optical features due to the difficulty of extracting the refractive index and the thickness-dependent degradation of the optical properties. Here, we demonstrate a complementary metal-oxide-semiconductor (CMOS)-compatible deposition procedure for sub-percolation thickness (below 4 nm) ITO using a dry-etch assisted radiofrequency magnetron sputtering technique that yields continuous films in a precisely controlled manner. Through interface engineering and post-deposition annealing optimization, we show that these ITO films can retain high carrier mobility (43 cm2V−1s−1) while achieving a tunable near-zero-index (NZI) regime throughout the telecommunications band using a Berreman-assisted optical characterization technique. Our result opens the possibility of efficiently designing ENZ/NZI materials at the nanoscale using a robust fabrication approach for applications in nanophotonics.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adom.202400803
