Near-field radiative modulator based on a-MoO3 films

Near-field radiative heat transfer (NFRHT) has great potential in thermal management and energy harvesting due to the giant radiative heat flux. Modulation of NFRHT is another important research direction, where relative rotation between the emitter and receiver is a typical method. However, the enhancement of modulation contrast (MC) is mainly concerned in previous works, while large heat flux is not taken into account. In this work, we investigate the heat transfer coefficient (HTC) between & alpha;-MoO3 films along different crystal directions of & alpha;-MoO3. We take account of the modulator with high heat flux and high MC. The results show that the HTC and MC can reach 223.2 W/(m2 & BULL;K) (36 times of blackbody limit) and 6.33 at a gap distance of 100 nm when NFRHT is along [010] crystal direction of & alpha;-MoO3, respectively. These are attributed to the excitation and mismatch of hyperbolic phonon polaritons (HPhPs). Furthermore, when NFRHT is along [100] and [001] crystal directions of & alpha;-MoO3, MCs reach 5.84 and 2.38, respectively. The results are strongly related to the crystal direction. In addition, the impact of film thickness on the MC for different crystal directions is investigated. This work is conducive to the applications of hyperbolic materials in non-contact thermal modulators.