Experiments on near-field radiative heat transfer: A review

Near-field radiative heat transfer (NFRHT) has been demonstrated to exceed the blackbody limit due to the coupling effect of evanescent waves in the near-field regime, opening the door to application in active thermal control, thermophotovoltaics, and nanoscale imaging. Although the theoretical studies on NFRHT have been investigated exhaustively, the experimental measurement of NFRHT has been stagnant due to the challenges in controlling gap distance at the nanoscale. Remarkable progress has been greatly boosted until the 21st century to overcome the nanoscale controlling and measurement of NFRHT, benefiting from the advances of micro-nanofabrication techniques and materials science. This review examines an in-depth discussion of the experimental development of NFRHT. According to the structure of the emitter and receiver, the experimental devices are divided into three different categories: plate-to-plate structure, tip-to-plate structure, and sphere-to-plate structure. Existing experimental setups and methodology of NFRHT between metals, semiconductors, two-dimensional materials, and hyperbolic metamaterials are thoroughly explored and analyzed in detail. Finally, the remarks on outstanding challenges at the nanoscale and promising advances in applications are briefly concluded in the measurements of NFRHT.