[Paper Review] Tuning near field radiative heat flux through surface excitations with a metal insulator transition

P. J. van Zwol, L. Ranno+1 more|arXiv (Cornell University)|Jan 24, 2012

Thermal Radiation and Cooling Technologies2 references12 citations

TL;DR

This study experimentally demonstrates that tuning the near-field radiative heat flux in vanadium dioxide (VO2) across its metal-insulator transition enables significant modulation of heat transfer via surface excitations. The phase transition alters surface polariton states, resulting in heat flow contrasts larger than those achievable in the far field, with the Derjaguin approximation accurately predicting near-field transfer despite underestimating far-field limits.

ABSTRACT

The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new oppor-tunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experi-mentally that the phase transition of VO2 entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the farfield limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in farfield.

Motivation & Objective

• To investigate how phase transitions in VO2 affect near-field radiative heat transfer.
• To explore the role of surface excitations, particularly surface polaritons, in modulating heat flux.
• To determine whether heat flow contrasts in the near field can surpass those in the far field.
• To validate the Derjaguin approximation for near-field radiative transfer in the context of tunable materials.

Proposed method

• Experimental measurement of near-field radiative heat transfer across a vacuum gap between a VO2-coated substrate and a probe.
• Leveraging the metal-insulator transition in VO2 to dynamically tune surface polariton states.
• Using the Derjaguin approximation to model and compare theoretical predictions with experimental data.
• Analyzing heat flux variations as a function of temperature across the VO2 phase transition.
• Comparing near-field and far-field heat transfer limits to assess modulation contrast.
• Employing spectroscopic and thermal characterization to correlate electronic and thermal responses.

Experimental results

Research questions

• RQ1 How does the metal-insulator transition in VO2 influence near-field radiative heat flux through surface excitations?
• RQ2 Can heat flow modulation in the near field exceed that achievable in the far field?
• RQ3 To what extent does the Derjaguin approximation accurately predict near-field radiative transfer in this system?
• RQ4 What is the role of surface polaritons in mediating the enhanced heat transfer during the phase transition?
• RQ5 How does the temperature-dependent electronic structure of VO2 affect the spectral and spatial characteristics of heat transfer?

Key findings

• The metal-insulator transition in VO2 induces a significant change in surface polariton states, leading to a strong modulation of near-field radiative heat flux.
• Heat flow contrasts in the near field exceed those observed in the far field, demonstrating superior tunability.
• The Derjaguin approximation accurately predicts near-field heat transfer but underestimates the far-field limit.
• The experimental results confirm theoretical predictions that surface excitations can be exploited to control radiative heat flow.
• The observed heat flux modulation is directly linked to the change in dielectric response across the VO2 phase transition.
• The study establishes VO2 as a promising material for active thermal management devices based on near-field radiative control.