Approaching the thermal emissivity limit with ultrathin MXene films

Control over thermal emission has garnered increasing attention, driven by the long-standing objective of achieving the theoretical limits of thermal emissivity in devices. However, conventional thermal emitters either approach the thermal emissivity limit at the cost of substantial thickness, or are ultrathin but fail to approach this limit due to impedance mismatch. In this work, we demonstrate that ultrathin MXene films (∼10nm) can effectively achieve impedance matching. A double-sided emitter, consisting of a suspended ultrathin MXene film, achieves a thermal emissivity limit of 0.5 in the 6–15 µm wavelength band. A single-sided emitter, formed by integrating the double-sided emitter within a resonator, attains emissivity close to unity at 10.8 µm based on Fabry–Perot resonance with critical coupling. This work paves the way for ultimate control of thermal emissivity in emitter design and has significant implications for energy harvesting and thermal management applications, including infrared imaging, light sources, and thermophotovoltaics.