Strain‐Driven Thermal and Optical Instability in Silver/Amorphous‐Silicon Hyperbolic Metamaterials

Abstract

Hyperbolic metamaterials show exceptional optical properties, such as near‐perfect broadband absorption, due to their geometrically‐engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high‐temperature stability. In this work, Ag/a‐Si multilayers are examined as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations, and optical spectroscopy, the thermal and optical instability of the metamaterials is mapped. Although the thermal instability initiates at 300 °C, the hyperbolic dispersion persists up to 500 °C. Direct finite element simulations on tomographical data provide a route to decouple and evaluate interfacial and elastic strain energy contributions to the instability. Depending on stacking order the instability's driving force is either dominated by changes in anisotropic elastic strain energy due thermal expansion mismatch or by minimization of interfacial energy. These findings open new avenues to understand multilayer instability and pave the way to design hyperbolic metamaterials able to withstand high temperatures.

Optical Reflectance of Composites with Aligned Engineered Microplatelets

“…[10,11] Attempts to correlate the optical properties of plateletcontaining composite materials with their underlying microstructure have been made using established radiative transfer models, [7,18,19] including the well-known transfer-matrix approach. [20,21] The transfer matrix method [22] is a versatile analytical tool to study the propagation of quantum particles, such as electrons or photons, in arbitrary one-dimensional potentials or periodic media including metamaterials, [23] photonic crystals [24] and superlattices. [25] Current models for plateletcontaining composites show that, despite their overall disordered arrangement, platelets with thickness on the order of the incident wavelength cause optical interference effects that substantially enhance or reduce the optical reflectance of the composite, particularly at high filler concentrations.…”

Fabricating defogging metasurfaces via a water-based colloidal route

“…9 Usually, this challenge is met by applying high vacuum technique(s) like PVD, CVD, ALD, etc. [15][16][17][18] Faster, better scalable, and more affordable protocols need to be established to allow for a widespread application of metasurfaces in everyday life. Such protocols will aim at wafer-scale growth and they might imply the transfer of high-quality 2D materials to realize fabrication of metasurfaces in an industrially benign process.…”