Disordered and Densely Packed ITO Nanorods as an Excellent Lithography-Free Optical Solar Reflector Metasurface

Abstract

Precise control and stabilization of the operating temperature environment of spacecraft and satellites during their life cycle is of paramount importance to increase device reliabilities and reduce the thermomechanical constraints. Optical solar reflectors are the physical interface between the spacecraft and space, and they are broadband mirrors for the solar spectrum, while having strong thermal emission in the mid-infrared part of the electromagnetic spectrum. Strong light−matter interactions in metamaterials and metasurfaces offer significant advantages compared to the conventional methods in performance, weight, launch, and assembly costs. However, the fabrication complexity of these metastructures due to necessitating lithography hinders their upscaling, reproducibility, large-area compatibility, and mass production. In this regard, we propose a facile, lithography-free fabrication route, exploiting oblique deposition to design a metasurface based on disordered and densely packed Indium Tin Oxide (ITO) nanorod forests. The excellent light trapping capability of the nanorod forests, randomness in the geometrical dimensions of these nanorods, combined with the lossy plasmonic nature of ITO in the thermal-infrared range led to strong coupling of thermal radiation to broad plasmonic resonances and, consequently, an experimental emissivity of 0.968, in a very wide range from 2.5 to 25 μm. In the solar spectrum, the low-loss dielectric characteristic of ITO resulted in an experimental solar absorptivity as small as 0.168. Our proposed design with high throughput, robustness, low cost, and high performance, therefore, shows great promise not only for space missions, but also for promoting environmentally friendly passive radiative cooling for our planet and thermal imaging in the field of security labeling.

Spectrally Tailored Light‐Matter Interaction in Lithography‐Free Functional Nanomaterials

“…Assembling in a suitable way layers with adequate (natural or effective) wavelength‐dependent dielectric functions is also useful to design planar structures with functionalities requiring multispectrally‐tuned optical properties. As a first example, nanostructured columnar ITO nanofilms with tailored effective optical properties were used to build ITO/dielectric/Ag mirror cavities with a high reflectance in the solar spectrum and a high absorbance and emissivity at longer wavelengths in the infrared . Such cavities can be useful to design solar reflectors with efficient radiative cooling properties.…”

Strong Light–Matter Interactions in Au Plasmonic Nanoantennas Coupled with Prussian Blue Catalyst on BiVO4 for Photoelectrochemical Water Splitting

“…Moreover, the simultaneous formation of small and large particles could excite both FP and LSPR modes to achieve both semiconductor light absorption enhancement and plasmonic hot electron injection. In recent studies, we developed a facial route based on oblique angle deposition to synthesize plasmonic nanostructures on a large scale. Moreover, we demonstrated that as a result of the cyanide chemistry, so‐called CoFe‐Prussian blue analog (PBA) is a strong and robust water oxidation catalyst (WOC), when connected to an organic chromophore .…”

Heavily Doped Semiconductor Metamaterials for Mid‐Infrared Multispectral Perfect Absorption and Thermal Emission

“…This is beneficial for the conventional metamaterial applications where a well‐defined absorption band is required, for example, for biochemical sensing applications or tailored thermal emission. TCOs are, due to their high losses and consequently their larger resonances, more adapted for broadband absorption and find their application, for example, as optical solar reflectors for thermal control of spacecraft and satellites, where they benefit moreover from their resistance to harsh environments …”