Abstract
We investigate the thermal radiative emission of few-layer structures deposited on a metallic substrate and its dependence on temperature with the Fluctuational Electrodynamics approach. We highlight the impact of the variations of the optical properties of metallic layers on their temperature-dependent emissivity. Fabry-Pérot spectral selection involving at most two transparent layers and one thin reflective layer leads to well-defined peaks and to the amplification of the substrate emission. For a single Fabry-Pérot layer on a reflective substrate, an optimal thickness that maximizes the emissivity of the structure can be determined at each temperature. A thin lossy layer deposited on the previous structure can enhance interference phenomena, and the analysis of the participation of each layer to the emission shows that the thin layer is the main source of emission. Eventually, we investigate a system with two Fabry-Pérot layers and a metallic thin layer, and we show that an optimal architecture can be found. The total hemispherical emissivity can be increased by one order of magnitude compared to the substrate emissivity.
Highlights
The control of radiation emitted by a body is a topic of large and growing interest, for instance for tailoring the spectral distribution of radiation emitted by thermal sources in order to improve the performances of thermophotovoltaic converters
We have highlighted the impact of the variations with temperature of the optical properties of metallic layers on the hemispherical emissivity
We have shown that when interferences occur in an emitting layer, the spectral hemispherical emissivity of the structure exhibits sharp peaks, whose frequencies depend on the size of the layer and its refractive index
Summary
The control of radiation emitted by a body is a topic of large and growing interest, for instance for tailoring the spectral distribution of radiation emitted by thermal sources in order to improve the performances of thermophotovoltaic converters. The dependence on temperature of the hemispherical emissivity of the structure should be affected by interferences To illustrate this phenomenon, the total hemispherical emissivity of a structure consisting of a Si monolayer of thickness t1, acting as a Fabry-Perot layer, and deposited on a reflective Al substrate is analyzed. (6), we can observe that when t becomes much larger than c nωmax factor that accounts for multireflections in the Fabry-Perot layer reduces to 1 meaning a lot of multireflections occur in the spectral range where the blackbody extends, leading to a constant value of the total hemispherical emissivity. Total hemispherical emissivities increase with temperature, but at different rates when considering different layer thicknesses This increase is due to two separated effects: the frequency shift of the blackbody spectrum and the variations of the optical properties of Al when temperature varies. Interferences affect the total hemispherical emissivity of the structure and its temperature dependence, and it is possible to determine the Si layer thickness that maximizes it for each temperature
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