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

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.

SUBMITTER: Hamaoui G

PROVIDER: S-EPMC6584564 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Publications

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

Hamaoui Georges G Horny Nicolas N Gomez-Heredia Cindy Lorena CL Ramirez-Rincon Jorge Andres JA Ordonez-Miranda Jose J Champeaux Corinne C Dumas-Bouchiat Frederic F Alvarado-Gil Juan Jose JJ Ezzahri Younes Y Joulain Karl K Chirtoc Mihai M

Scientific reports 20190619 1

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 prope ...[more]

PMID: 31217509

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Project description:Fenestration elements that enable spectrally selective dynamic modulation of the near-infrared region of the electromagnetic spectrum are of great interest as a means of decreasing the energy consumption of buildings by adjusting solar heat gain in response to external temperature. The binary vanadium oxide VO2 exhibits a near-room-temperature insulator-metal electronic transition accompanied by a dramatic modulation of the near-infrared transmittance. The low-temperature insulating phase is infrared transparent but blocks infrared transmission upon metallization. There is considerable interest in harnessing the thermochromic modulation afforded by VO2 in nanocomposite thin films. However, to prepare a viable thermochromic film, the visible-light transmittance must be maintained as high as possible while maximizing thermochromic modulation in the near-infrared region of the electromagnetic spectrum, which necessitates the development of high-crystalline-quality VO2 nanocrystals of the optimal particle size embedded within the appropriate host matrix and refractive index matched to the host medium. Here, we demonstrate the preparation of acrylate-based nanocomposite thin films with varying sizes of embedded VO2 nanoparticles. The observed strong size dependence of visible-light transmittance and near-infrared modulation is explicable on the basis of optical simulations. In this article, we elucidate multiple scattering and absorption mechanisms, including Mie scattering, temperature-/phase-variant refractive-index mismatch between VO2 nanocrystals and the encapsulating matrix, and the appearance of a surface plasmon resonance using temperature-variant absorptance and diffuse transmittance spectroscopy measurements performed as a function of particle loading for the different sizes of VO2 nanocrystals. Nanocrystals with dimensions of 44 ± 30 nm show up to >32% near-infrared energy modulation across the near-infrared region of the electromagnetic spectrum while maintaining high visible-light transmission. The results presented here, providing mechanistic elucidation of the size dependence of the different scattering mechanisms, underscore the importance of nanocrystallite dimensions, refractive-index matching, and individualized dispersion of particles within the host matrix for the preparation of viable thermochromic thin films mitigating Mie scattering and differential refractive-index scattering.

Dataset Information

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

Publications

Thermophysical characterisation of VO<sub>2</sub> thin films hysteresis and its application in thermal rectification.

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