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

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