Radiative heat transfer between objects can increase dramatically at sub-wavelength scales. Radiative heat transfer in low-dimensional systems - microscopic mode Our work illustrates the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nanodevices. These structures are widely used to measure the thermal transport through nanowires and low-dimensional systems and can be employed to test our predictions. In particular, we illustrate this phenomenon in the case of suspended pads made of polar dielectrics like SiN or SiO2. Guided by this relation, and making use of state-of-the-art numerical simulations, we show that the far-field radiative heat transfer between highly anisotropic objects can largely overcome the black-body limit when some of their dimensions are smaller than the thermal wavelength. To guide the search for super-Planckian far-field radiative heat transfer, we make use of the theory of fluctuational electrodynamics and derive a relation between the far-field radiative heat transfer and the directional absorption efficiency of the objects involved. We present here a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. Super-Planckian far-field radiative heat transferįernández-Hurtado, V. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres.
For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4-6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Kim, Kyeongtae Song, Bai Fernández-Hurtado, VÃctor Lee, Woochul Jeong, Wonho Cui, Longji Thompson, Dakotah Feist, Johannes Reid, M T Homer GarcÃa-Vidal, Francisco J Cuevas, Juan Carlos Meyhofer, Edgar Reddy, Pramod Radiative heat transfer in the extreme near field.
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