Abstract
Vanadium dioxide (VO2) is a promising phase-change material (PCM) in controlling radiative heat transfer because of the large permittivity contrast between the phases and the moderate metal-insulator transition temperature of 340 K. Widely adopted bare VO2 films on a dielectric substrate permit more radiative heat in the insulating state compared to that in the metallic state. In this paper, we present PCM-insulator-metal metasurfaces that invert the thermal radiative contrast, which means that the radiative heat flux is more promoted in the metallic state. The metasurfaces exhibit similar but broader resonance compared to conventional metal-insulator-metal metamaterials based on localized gap-plasmons when VO2 is in the metallic state. The broad resonance facilitates to maximize the radiative thermal exchange and is explained by the damping of the gap-plasmon mode dominated by the optical loss of VO2. The measured electromagnetic response of the fabricated metasurfaces agrees well with numerical simulations, and it also demonstrates that the resonant wavelength is tuned by the temperature. High emission or absorption contrast at a specific temperature is numerically obtained by geometrical optimization albeit lossy amorphous silicon or alumina is employed as the insulating layer to satisfy the fabrication requirement. We believe that the presented metasurface design contributes to intelligent thermal management systems with flexibility.
Highlights
Tunable photonic responses by utilizing phase-change materials[1,2,3,4] have enormous impacts in the fields of optical communication, sensing, and thermal management
Radiative heat transfer is promoted when VO2 is at low temperatures and is in the insulating state, while it is suppressed when VO2 is at high temperatures and is in the metallic state
We present phase-change material (PCM)-insulator-metal metasurfaces with inverted thermal radiative contrast between the phases
Summary
Tunable photonic responses by utilizing phase-change materials[1,2,3,4] have enormous impacts in the fields of optical communication, sensing, and thermal management. Electromagnetic thermal properties of a body embedded with VO2 are largely switched by the transition,[3,4] and it has been employed to realize thermal radiative rectifiers,[5,6,7] thermal transistors,[8,9,10] thermal memories,[11,12] and near-field thermal switches.[13] In these devices, radiative heat transfer is promoted when VO2 is at low temperatures and is in the insulating state, while it is suppressed when VO2 is at high temperatures and is in the metallic state This intrinsic thermal radiative contrast between the phases can be utilized for thermochromic windows and intentional thermal runaway,[14] and the case in the far-field is explained by the increase in the reflectance according to the screening of electromagnetic waves by induced free electrons
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