Near field heat transfer
Some of our work is aimed controlling heat transfer at the nanoscale using near-field thermal radiation. When objects that support an infrared surface polariton resonance (e.g., doped silicon, silicon dioxide, silicon carbide) are brought to submicron distances, they can exchange heat through coupling of their surface wave. This heat conduction channel presents unique features compared to conventional heat transfer. For example, even though the heat transfer still occurs through thermal radiation, it can overcome the black-body radiation limit by several orders of magnitude (see Fig. 1 left). Furthermore, this heat transfer channel field is concentrated on a very narrow frequency range (see Fig. 1 right), as opposed to usual heat transfer channels (i.e., physical contact with broadband phonon distribution). These unique features are expected to yield exciting new applications, such as efficient contact-free cooling or heating of nanostructures, or new types of devices for thermal control such as thermal rectifiers and thermal transistors.
We demonstrated near-field radiative cooling of thermally isolated nanostructures, without any physical contact, by several degrees through an oxidized probe that acts as a heat sink (Fig. 2). This method could, in principle, efficiently cool down localized hotspots by tens of degrees at submicrometer gaps, or be used for moving micro and nano structures (MEMS and NEMS) that cannot be touched.
We also demonstrated near-field heat transfer between two integrated nanobeams that are displaced relative to each other with an integrated MEMS actuator. This work demonstrates that near-field heat transfer can be the dominant heat conduction channel between nanostructures, even when these are integrated on a same substrate. We expect this platform to be a key enabler for the development of thermal control devices based on near-field heat transfer, such as thermal rectifiers and thermal transistors.