Tailoring near-field thermal radiation between metallo-dielectric multilayers using coupled surface plasmon polaritons

Abstract

Several experiments have shown a huge enhancement in thermal radiation over the blackbody limit when two objects are separated by nanoscale gaps. Although those measurements only demonstrated enhanced radiation between homogeneous materials, theoretical studies now focus on controlling the near-field radiation by tuning surface polaritons supported in nanomaterials. Here, we experimentally demonstrate near-field thermal radiation between metallo-dielectric multilayers at nanoscale gaps. Significant enhancement in heat transfer is achieved due to the coupling of surface plasmon polaritons (SPPs) supported at multiple metal-dielectric interfaces. This enables the metallo-dielectric multilayers at a 160-nm vacuum gap to have the same heat transfer rate as that between semi-infinite metal surfaces separated by only 75 nm. We also demonstrate that near-field thermal radiation can be readily tuned by modifying the resonance condition of coupled SPPs. This study will provide a new direction for exploiting surface-polariton-mediated near-field thermal radiation between planar structures.

Fig. 1

Experimental setup for measuring near-field thermal radiation between MD multilayers. a Schematic of an integrated platform consisting of the MEMS-based microdevices and the three-axis nanopositioner. b Three-dimensional schematic of the experimental setup. The position of the emitter part is controlled by the displacement of the picomotor actuators. The receiver part is fixed on the heat sink. c Photo of emitter part taken by digital single-lens reflex (DSLR) camera. The width and length of the MD emitter are 720 μm and 14.3 mm, respectively. The area excluding the MD emitter is coated with Au film to suppress far-field radiation. d DSLR image of the receiver part. The width of the MD receiver is 540 μm. The length of one segment of the MD receiver is 3.44 mm. e Three-dimensional schematic of emitter part of MEMS-fabricated microdevice. MD-emitter-capacitor electrode, Au film for suppressing far-field radiation, and MD-emitter-capacitor-soldering pads are described. f As in e, except for the receiver part. MD-receiver-capacitor electrodes (d_1–4 capacitor electrodes), MD-receiver-capacitor-soldering pads (d_1-4 capacitor-soldering pads), and calibration-heater-soldering pads are depicted

Fig. 2

Measurement of vacuum gap distance between MD emitter and MD receiver. a Schematic cross-sectional view of aligned MD emitter and MD receiver. The four local vacuum gaps can be estimated from the measured capacitances between the MD emitter and each of the divided MD receiver segments. b Measurement of four local vacuum gaps and a fitted curve when d = 200 nm. c Upper panel: measured average vacuum gap displacement between MD emitter and MD receiver while reducing vacuum gap distance. In order to conduct steady-state measurement, the vacuum gap distance is slowly reduced by about 0.125 nm per second. Lower panel: measured dissipation factors for four segments, obtained simultaneously with results from the upper panel. The inset shows the scenario of physical contact between MD emitter and fourth MD receiver segment

Fig. 3

Heat transfer analysis with experimental setup. a Schematic of enlarged cross-sectional view of MEMS-device-integrated platform showing heat flow. The radiative heat flux from the MD emitter to the MD receiver Q_e→r can be estimated from the measured temperature difference between the backside temperature sensor and the thermocouple on the heat sink. b Equivalent thermal circuit for experimental platform

Fig. 4

Manipulation of near-field radiation by modifying surface condition with MD multilayers. a Measured near-field radiative heat flux between MD multilayers (f = 0.1, 3 Ti/MgF₂ unit cells) with respect to the submicron vacuum gap distance (emitter temperature: 400 K and receiver temperature: 300 K). Theoretical results of near-field thermal radiative heat flux between multilayered structures that are computed considering multiple reflections in multilayer (i.e., exact computation) or effective medium theory (EMT), as well as between bulk Ti media, are plotted. The inset shows the near-field radiative heat flux plotted on log scale. Calculated near-field radiative heat flux between bulk MgF₂ media and far-field radiative heat flux between Ti/MgF₂ multilayers are also plotted. b Near-field radiative heat flux between MD multilayers (f = 0.1, 3 Ti/MgF₂ unit cells) as a function of emitter temperature. The inset is a graph of radiative heat transfer coefficient h_R for all measured data. c Enhanced near-field radiative heat flux between MD multilayers (f = 0.1) with different numbers of unit cells. Emitter temperature is set to 370 K. d Tuning of near-field radiative heat flux by changing of volume filling ratio of MD multilayer, f (3 Ti/MgF₂ unit cells). The near-field radiative heat flux is measured at an emitter temperature of 370 K. The error bars in a–d represent the combination of the measurement uncertainty and standard deviation of multiple measurements (Supplementary Note 11)

Fig. 5

Investigation of manipulated near-field radiative heat flux by modifying surface condition with MD multilayers. a Computed spectral heat flux between Ti/MgF₂ multilayers (f = 0.1 and 0.23) and bulk Ti media (f = 1) at vacuum gap distance of 400 nm. The temperatures of the emitter and receiver are set to 370 K and 300 K, respectively. b, c As in a, but for p-polarized and s-polarized spectral heat flux, respectively. d Computed $S_{\beta ,\omega }^p$ between bulk Ti media for vacuum gap distance of 400 nm and temperature of emitter and receiver conditions described in a. A larger value of $S_{\beta ,\omega }^p$ is observed along the plotted SPP dispersion curve. e, f As in d, but between MD multilayers, which have volume filling ratios of 0.1 and 0.23