Dual-band quasi-coherent radiative thermal source

Abstract

Thermal radiation from an unpatterned object is similar to that of a gray body.The thermal emission is insensitive to polarization, shows only Lambertian angular dependence, and is well modeled as the product of the blackbody distribution and a scalar emissivity over large frequency bands. Here, we design, fabricate and experimentally characterize the spectral, polarization, angular and temperature dependence of a microstructured SiC dual band thermal infrared source; achieving independent control of the frequency and polarization of thermal radiation in two spectral bands. The measured emission of the device in the Reststrahlen band (10.3-12.7 µm) selectively approaches that of a blackbody, peaking at an emissivity of 0.85 at λ x = 11.75 µm and 0.81 at λ y = 12.25 µm.This effect arises due to the thermally excited phonon polaritons in silicon carbide. The control of thermal emission properties exhibited by the design is well suited for applications requiring infrared sources, gas or temperature sensors and nanoscale heat transfer. Our work paves the way for future silicon carbide based thermal metasurfaces.

High-Temperature Polaritons in Ceramic Nanotube Antennas

“…The temperature dependence of the emissivity spectrum reveals the shift of polaritonic properties of hBN at elevated temperatures. This is consistent with previous studies of the temperature dependent emission of other polar dielectrics like SiC. , …”

“…This is consistent with previous studies of the temperature dependent emission of other polar dielectrics like SiC. 24,45 Thermal Antenna Effect in Disordered Nanotubes. In general, a disordered system of particles such as this should exhibit no angularly dependent emission behavior.…”

“…One specific design that has been experimentally demonstrated for thermophotovoltaic applications is epsilon-near-zero thermal metamaterials. ,, However, the high-loss and low melting point of metals reduces the choice of materials available for such thermal metamaterials. Polar dielectric materials supporting phonon polaritons have also been investigated with great success − but these materials are limited to low frequency mid-IR optical phonons <1200 cm –1 (>8.6 μm). Interestingly, hBN is a natural hyperbolic material that has shown thermal stability at temperatures up to 1173 K .…”

“…Thermal emission measurements are performed with a custom high-temperature vacuum chamber IR spectroscopy set up shown in Figure S1 and described in more detail in Supporting Information and ref . To isolate thermal emission from the BNNTs one must suppress background thermal radiation generated by the substrate heater.…”

“…To characterize the red shift of the absorption bands at elevated temperatures, we measure emissivity from 560 to 938 K. Figure 5 shows the emissivity spectrum over this temperature range, where we observe a frequency shift of ∼18 cm −1 for the T mode and ∼13 cm −1 for the L mode. This is the result of red shifting of optical phonon frequencies of hBN at elevated temperatures 24 likely caused by thermal expansion. We note that the shift in the RB mode appears to be less pronounced, now occurring at 803 and 814 cm −1 .…”