Highly efficient near-field thermal rectification between InSb and graphene-coated SiO2

We report a highly efficient thermal rectification model based on the near-field thermal radiation between InSb and graphene-coated SiO2, separated by nanoscale vacuum gaps. The results show that the introduction of graphene sheet enhances significantly near-field radiative heat flux and thermal rectification efficiency owing to the strong coupling of surface plasmon-polaritons between InSb and graphene. Specifically, under the same temperature bias, a rectification efficiency exceeding 80% is obtained at vacuum gaps varying from 10 nm to 100 nm for the graphene-coated SiO2 case, while such an efficiency requires a narrower gap between 10 nm to 20 nm for the bare SiO2 case. In addition, the introduction of graphene can lower greatly the emitter's temperature TH, e.g., an efficiency of 60% requires TH = 550 K in the bare SiO2 case, while it requires only the temperature around 400 K in the coated SiO2 case. The above results might be helpful in designing a highly efficient thermal diode with a wider vacuum gap and a lower operating temperature.