Near-field Heat Transfer

Broadband thermal radiation sources are critical for various applications including spectroscopy and electricity generation. However, due to the difficulty in simultaneously achieving high absorptivity and low thermal mass these sources are inefficient. Our platform has the potential to enable development of ideal blackbody sources operating at substantially lower heating powers.

Near field heat transfer

Schematics of device

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. 

SEM picture of device

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.