Monolithic III-V on Metal for Thermal Metasurfaces.

It has been proposed that metal-semiconductor-metal (MSM) structures can be used to tune the absorptivity of a metasurface at infrared wavelengths. Indium arsenide (InAs) is a low-band-gap, high-electron-mobility semiconductor that may enable rapid index tuning for dynamic control over the infrared spectrum. However, direct growth of III-V thin films on top of metals has typically resulted in small-grain, polycrystalline materials that are not amenable to high-quality devices.

Blackbody-cavity ideal absorbers for solar energy harvesting.

Spectrally selective solar absorbers (SSAs), which harvest heat from sunlight, are the key to concentrated solar thermal systems. An ideal SSA must have an absorptivity of unity in the solar irradiance wavelength region (0.3-2.

Highly effective photon-to-cooling thermal device.

Photon-to-cooling phenomenon relies on the atmospheric transparency window to dissipate heat from the earth into outer space, which is an energy-saving cooling technique. This work demonstrates a highly effective aluminized Polymethylpentene (PMP) thin-film thermal structure. The emissivity of aluminized PMP thin films matches well to the atmospheric transparency window so as to minimize parasitic heat losses.

Spectral selectivity of multiple nanoparticles doped thin films.

Microscopic thin film doped with different species of nanoparticles displays a unique wavelength selectivity in the context of micro/nanoscale radiative heat transfer. We propose a methodology to shift, broaden, and suppress the thermal radiative selectivity in the desired wavelength ranges. Measured transmittance spectra of potassium bromide pellet doped with a single species of nanoparticles are compared with the theoretical prediction using refractive indices that are extracted by refitting transmittance spectra curve according to the Lorentz-Drude model.

Tunable wavelength selectivity of photonic metamaterials-based thermal devices.

Wavelength-selective thermal devices have great applications in concentrating solar power systems, high-temperature thermoelectric systems, and solar thermophotovoltaics (STPVs). Lack of high-temperature stability and spectrally selective emissivity in different wavelength regions limits their efficiency. We propose a one-dimensional HfO/AlO-W nanocomposites/W/AlO/W multilayered photonic structure as potential wavelength selective thermal devices, and theoretically investigate the emission properties of the proposed Mie-resonance metamaterials from visible (VIS) to midinfrared (MIR) region.

Performance enhancement of near-field thermoradiative devices using hyperbolic metamaterials.

We analyze a near-field thermoradiative device that consists of an indium arsenide-based photodiode under negative illumination. We analyze a possible enhancement of conversion efficiency by use of hyperbolic metamaterial (HMM) in place of bulk metallic heat sink. A stack of alternating thin-films of metal [zirconium carbide (ZrC)] and dielectric [silicon dioxide (SiO)] is chosen to be the HMM under investigation.

Near-infrared optics of nanoparticles embedded silica thin films.

This work investigates experimentally the near-infrared optical properties of SiO thin film embedded with tungsten (W) nanoparticles at varying volume fractions. The samples are prepared by using the technique of magnetron sputtering. The formation and distribution of W nanoparticles are characterized using transmission electron microscopy, and the volume fraction of W nanoparticles is validated by Auger electron spectroscopy.

Dynamic optical response of SU-8 upon UV treatment.

We report the optical properties of SU-8 in the mid-infrared (mid-IR) region before and after UV treatment. Samples consisted of SU-8 films of thickness ranging from 10 um to 157 um deposited on gold coated silicon substrates and were prepared using spin coating. Mid-IR diffuse reflectance measurements were conducted using Fourier transform infrared spectroscopy.

Strain-induced modulation of near-field radiative transfer.

In this theoretical study, we present a near-field thermal modulator that exhibits change in radiative heat transfer when subjected to mechanical stress/strain. The device has two terminals at different temperatures separated by vacuum: one fixed and one stretchable. The stretchable side contains one-dimensional grating.

A Review of Tunable Wavelength Selectivity of Metamaterials in Near-Field and Far-Field Radiative Thermal Transport.

Radiative thermal transport of metamaterials has begun to play a significant role in thermal science and has great engineering applications. When the key features of structures become comparable to the thermal wavelength at a particular temperature, a narrowband or wideband of wavelengths can be created or shifted in both the emission and reflection spectrum of nanoscale metamaterials. Due to the near-field effect, the phenomena of radiative wavelength selectivity become significant.

Near-field thermal rectification devices using phase change periodic nanostructure.

We theoretically analyze two near-field thermal rectification devices: a radiative thermal diode and a thermal transistor that utilize a phase change material to achieve dynamic control over heat flow by exploiting metal-insulator transition of VO near 341 K. The thermal analogue of electronic diode allows high heat flow in one direction while it restricts the heat flow when the polarity of temperature gradient is reversed. We show that with the introduction of 1-D rectangular grating, thermal rectification is dramatically enhanced in the near-field due to reduced tunneling of surface waves across the interfaces for negative polarity.

Optimal Design of Wavelength Selective Thermal Emitter for Thermophotovoltaic Applications.

We theoretically and numerically demonstrate optimal design of wavelength selective thermal emitter using one-dimensional (1D) and two-dimensional (2D) metal-dielectric gratings for thermophotovoltaic (TPV) applications. Proposed design consists of tungsten (W) and silicon dioxide (SiO) gratings which can withstand high temperatures. Radiative properties of 1D grating were calculated using a numerical method, while effective medium approximation was used for 2D gratings.

Mie-Metamaterials-Based Thermal Emitter for Near-Field Thermophotovoltaic Systems.

In this work, we theoretically analyze the performance characteristics of a near-field thermophotovoltaic system consisting a Mie-metamaterial emitter and GaSb-based photovoltaic cell at separations less than the thermal wavelength. The emitter consists of a tungsten nanoparticle-embedded thin film of SiO 2 deposited on bulk tungsten. Numerical results presented here are obtained using formulae derived from dyadic Green's function formalism and Maxwell-Garnett-Mie theory.

High Contrast Far-Field Radiative Thermal Diode.

We propose a theoretical concept of a far-field radiative thermal rectification device that uses a phase change material to achieve a high degree of asymmetry in radiative heat transfer. The proposed device has a multilayer structure on one side and a blackbody on other side. The multilayer structure consists of transparent thin film of KBr sandwiched between a thin film of VO and a reflecting layer of gold.

Novel and efficient Mie-metamaterial thermal emitter for thermophotovoltaic systems.

We theoretically demonstrate a novel, efficient and cost effective thermal emitter using a Mie-resonance metamaterial for thermophotovoltaic (TPV) applications. We propose for the first time the design of a thermal emitter which is based on nanoparticle-embedded thin film. The emitter consists of a thin film of SiO on the top of tungsten layer deposited on a substrate.

Role of nanoparticles in wavelength selectivity of multilayered structures in the far-field and near-field regimes.

Microscopic thin films have shown wavelength selectivity in the context of radiative heat transfer. We propose a methodology to shift the wavelength selectivity in the desired location. This work deals with the far-field and near-field radiation from thin films embedded with nanoparticles.