Tailoring Thermal Emission with Ultrathin Films

The thermal spectrum of hot bodies is well-known and described by Planck’s law for blackbody emission. However, for many modern technologies, it is desirably to have significant deviations from this law to achieve directional or wavelength-controlled emission. Many approaches exist, yet difficulties arise due to thermal compatibility of materials at high temperatures, as well as stability of nanostructures when metasurfaces are employed. Here we present an alternative route involving single-layer, ultrathin films. We explored >100 materials that are stable above 2000°C and found combinations that allow for significant tunability of thermal emission throughout the near-infrared frequency range. We have fabricated and tested several material combinations at high temperature and show that the spectrum can be significantly modified using this simple configuration. Using these structures, we optimize the emission spectra of such emitters to match five common thermophotovoltaic cells and show that efficiencies in excess of 45% are achievable at moderate temperatures.