ABSTRACT
A narrowband thermal emitter exhibits higher energy efficiency and sensitivity in molecule sensing and other mid-infrared (MIR) spectral range applications compared to a blackbody emitter. Most narrowband thermal emitters involving surface plasmons have a relatively low quality factor (Q-factor) and require complex fabrication processes. Here we propose a bilayer cavity-enhanced Tamm plasmon (TP) structure with a high/low refractive index bilayer sandwiched between a metal and distributed Bragg reflector (DBR) to achieve an enhanced Q-factor and maintain higher emittance over a conventional pure DBR-metal TP structure-based emitters. The large optical thickness of the high/low index bilayer cavity aids in increasing the Q-factor (â¼172 for emission) of the cavity resonance. Furthermore, a tunable Q-factor is achieved (Q from 172 to 47 for emission) by incorporating phase-changing material Ge2Sb2Te5. This easy-to-fabricate and tunable high Q-factor emitter is competent as a narrowband MIR light source in molecule sensing, typically gas sensing applications.
ABSTRACT
Polar crystals can enable strong light-matter interaction at an infrared regime and provide many practical applications including thermal emission. However, the dynamic control of thermal emission based on polar crystals remains elusive as the lattice vibrations are solely determined by the crystal structure. Here, a nonvolatile tunable midinfrared thermal emitter enabled by a phase-changing film Ge2Sb2Te5 on silicon carbide polar crystal is demonstrated. By controlling the state of Ge2Sb2Te5 from an amorphous to a crystalline state, the emissivity of the thermal emitter is tuned from a low value to near unity with a maximum change in peak emissivity exceeding 10 dB over the Reststrahlen band of SiC (11.4 µm to 12.3 µm). This nonvolatile tunable thermal emitter, which presents a lot of advantages in terms of tunability, zero static power, angular insensitivity, and ease of fabrication, can be potentially applied for light sources, infrared camouflage, and radiative cooling devices.
ABSTRACT
The ability to continuously tune the emission wavelength of mid-infrared thermal emitters while maintaining high peak emissivity remains a challenge. By incorporating the nonvolatile phase changing material Ge2Sb2Te5 (GST), two different kinds of wavelength-tunable mid-infrared thermal emitters based on simple layered structures (GST-Al bilayer and Cr-GST-Au trilayer) are demonstrated. Aiming at high peak emissivity at a tunable wavelength, an Al film and an ultrathin (â¼5 nm) top Cr film are adopted for these two structures, respectively. The gradual phase transition of GST provides a tunable peak wavelength between 7 µm and 13 µm while high peak emissivity (>0.75 and >0.63 for the GST-Al and Cr-GST-Au emitters, respectively) is maintained. This study shows the capability of controlling the thermal emission wavelength, the application of which may be extended to gas sensors, infrared imaging, solar thermophotovoltaics, and radiative coolers.
ABSTRACT
Camouflage technology has attracted growing interest for many thermal applications. Previous experimental demonstrations of thermal camouflage technology have not adequately explored the ability to continuously camouflage objects either at varying background temperatures or for wide observation angles. In this study, a thermal camouflage device incorporating the phase-changing material Ge2Sb2Te5 (GST) is experimentally demonstrated. It has been shown that near-perfect thermal camouflage can be continuously achieved for background temperatures ranging from 30 °C to 50 °C by tuning the emissivity of the device, which is attained by controlling the GST phase change. The thermal camouflage is robust when the observation angle is changed from 0° to 60°. This demonstration paves the way toward dynamic thermal emission control both within the scientific field and for practical applications in thermal information.
ABSTRACT
Controlling the emissivity of a thermal emitter has attracted growing interest, with a view toward a new generation of thermal emission devices. To date, all demonstrations have involved using sustained external electric or thermal consumption to maintain a desired emissivity. In the present study, we demonstrated control over the emissivity of a thermal emitter consisting of a film of phase-changing material Ge2Sb2Te5 (GST) on top of a metal film. This thermal emitter achieves broad wavelength-selective spectral emissivity in the mid-infrared. The peak emissivity approaches the ideal blackbody maximum, and a maximum extinction ratio of >10 dB is attainable by switching the GST between the crystalline and amorphous phases. By controlling the intermediate phases, the emissivity can be continuously tuned. This switchable, tunable, wavelength-selective and thermally stable thermal emitter will pave the way toward the ultimate control of thermal emissivity in the field of fundamental science as well as for energy harvesting and thermal control applications, including thermophotovoltaics, light sources, infrared imaging and radiative coolers.
ABSTRACT
A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.
