Francoeur Receives UURF to Demonstrate Near-Field Radiation Mediated Thermal Rectification

January 1, 2016

For his research, Experimental Demonstration of Near-field Radiation Mediated Thermal Rectification for Heat Flow Regulation in Micro/Nanoscale, mechanical engineering assistant professor Mathieu Francoeur received a one-year $32,700 UURF (University of Utah Research Fund) grant.

The objective of this research is to experimentally demonstrate near-field radiation
mediated thermal rectification at an efficiency larger than 80% via a thermal diode consisting
of two terminals separated by a nanosize vacuum gap. Rectification efficiency will be
evaluated by measuring radiative heat flux between the terminals for positive and negative
temperature gradients. Understanding thermal rectification is crucial for the development of
thermal diodes and transistors enabling effective cooling of micro/nanoscale devices.
Thermal rectification is a phenomenon in which heat flows preferentially along one direction.
Devices capable of achieving thermal rectification, such as thermal diodes and transistors,
could greatly facilitate thermal management of micro/nanoscale devices, computers and
buildings. Recently, a thermal rectification paradigm based on near-field radiation has been
proposed. More specifically, it has been theoretically shown that high rectification is
achievable via thermal diodes made of dissimilar materials separated by a nanosize vacuum
gap. In such thermal diodes, the asymmetric heat flux is due to the dissimilar temperature
dependence of the optical properties (i.e., dielectric functions) of the materials. In particular,
rectification efficiency, quantifying the asymmetry of heat transfer with respect to the sign of
the temperature gradient, larger than 80% is expected with materials supporting surface
polariton resonances in the infrared. This is due to the fact that the strength, spectral location
and spectral width of these resonances, dominating radiation transfer in the near field, are
strongly dependent on the temperature. While several groups investigated numerically the
possibility of regulating heat transfer with near-field radiation mediated thermal rectification,
no experimental verification of this phenomenon has been reported so far in the literature. The proposed research is radically different from the state-of-the-art, as near-field radiation
mediated thermal rectification will be experimentally demonstrated for the first time. In Task
1 of the proposed research activities, thermal diodes made of doped silicon will be fabricated
and tested for gap thicknesses ranging from 50 to 500 nm. The nanosize gap between the two
terminals constituting the thermal diode will be maintained via polystyrene spacers.
Experimental data of near-field radiative flux and rectification efficiency will be compared
against numerical predictions. In Task 2, thermal diodes maximizing rectification efficiency
will be designed by considering various materials supporting surface polariton resonances in
the infrared, namely silicon carbide, silica, boron nitride and doped silicon. These diodes will
be fabricated and experimentally tested for gap thicknesses ranging from 50 to 500 nm. It is
expected that rectification efficiency larger than 80% will be measured.
Experimental demonstration of thermal rectification is crucial for the future development of
near-field radiation based thermal transistors that would allow rectifying, switching,
modulating and amplifying the heat transferred between a heat source and sink, thus enabling
effective cooling of micro/nanoscale devices. The overarching goal of this proposal is to
develop a novel, externally-funded research thrust on heat flow regulation for thermal
management of micro/nanoscale devices. The results obtained from this research will enable
the PI to submit competitive proposals to the DoD, NSF and DoE.

To learn more about Dr. Francoeur and his research visit the Radiative Energy Transfer Lab.