Thermophysical characterisation of VO2 thin films hysteresis and its application in thermal rectification

Georges Hamaoui,Frederic Dumas-Bouchiat,Corinne Champeaux,Karl Joulain,Cindy Lorena Gomez-Heredia,Younes Ezzahri,Mihai Chirtoc,Nicolas Horny,Juan Jose Alvarado-Gil,Jorge Andres Ramirez-Rincon,Jose Ordonez-Miranda

doi:10.1038/s41598-019-45436-0

Abstract

Hysteresis loops exhibited by the thermophysical properties of VO2 thin films deposited on either a sapphire or silicon substrate have been experimentally measured using a high frequency photothermal radiometry technique. This is achieved by directly measuring the thermal diffusivity and thermal effusivity of the VO2 films during their heating and cooling across their phase transitions, along with the film-substrate interface thermal boundary resistance. These thermal properties are then used to determine the thermal conductivity and volumetric heat capacity of the VO2 films. A 2.5 enhancement of the VO2 thermal conductivity is observed during the heating process, while its volumetric heat capacity does not show major changes. This sizeable thermal conductivity variation is used to model the operation of a conductive thermal diode, which exhibits a rectification factor about 30% for small temperature differences (≈70 °C) on its terminals. The obtained results grasp thus new insights on the control of heat currents.

Highlights

Where qF and qB are the heat fluxes in the forward and backward configurations of the TDs, respectively
VO2 thin films were deposited on r-sapphire and silicon (100) covered by an amorphous native oxide layer substrates through pulsed laser deposition (PLD)
Taking into account that the sapphire substrate and VO2 films are semi-transparent to the visible light, a 30 nm-thick Ti layer was deposited on top of the VO2 films of both samples

Summary

Introduction

Where qF and qB are the heat fluxes in the forward and backward configurations of the TDs, respectively. Optical[13,35,36] and electrical[37,38,39,40] properties of VO2 exhibit a hysteresis behaviour (i.e., do not yield the same values during the heating and cooling processes at a given temperature within the MIT), its thermal properties are expected to present this thermal hysteresis. This phenomenon has not yet been experimentally neither observed nor quantified on the thermophysical properties of VO2. The obtained k are applied to model the operation of a conductive TD and to estimate its rectification factor

Methods

Results

Discussion

Conclusion