Temperature dependence of thermal conductivity of VO₂thin films across metal–insulator transition

Abstract

Thermal conductivity of a 300-nm-thick VO 2 thin film and its temperature dependence across the metal-insulator phase transition (T MIT ) were studied using a pulsed light heating thermoreflectance technique. The VO 2 and Mo/VO 2 /Mo films with a VO 2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO 2 films were deposited by reactive rf magnetron sputtering using a V 2 O 3 target and an Ar-O 2 mixture gas at 645 K. The VO 2 films consisted of single phase VO 2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO 2 film decreased abruptly from 6.3 ' 10 %1 to 5.3 ' 10 %4 Ω cm across the T MIT of around 325-340 K. The thermal conductivity of the VO 2 film increased from 3.6 to 5.4 W m %1 K %1 across the T MIT . This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law.

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

“…Metal-insulator transitions: Metal-insulator transitions (MITs) dramatically change the electrical conductivity r. In the best-known example, r can increase by 5 orders of magnitude when vanadium dioxide crosses a MIT around T MIT ¼ 340 K. It is natural to suspect that the thermal conductivity of VO 2 may also show a large change across the MIT, since the standard single-electron Wiedemann-Franz (WF) law (Lorenz number L ¼ L 0 ¼ 2.44 Â 10 À8 WX/K 2 ) predicts that both electrons and phonons contribute significantly to k in the metallic state, while in the insulating state only the phonon k remains. Indeed, several experiments 22,23 have measured switch ratios as large as r ¼ 1.6 in polycrystalline VO 2 films. However, these experiments measured k in the cross-plane direction and r in the in-plane direction, so the WF law could not be quantitatively tested.…”

Thermal conductivity switch: Optimal semiconductor/metal melting transition

“…Also, VO 2 has a monoclinic structure at low temperature under 340 K, while it is tetragonal at higher temperatures 29,30 . During the structural transition of NbO 2 and VO 2 , their σ e increase undergoing semiconductor/metal (S/M) transition, increasing thermal conductivities as shown in Fig.…”

Switchable Friction across Insulator–Metal Transition in VO2

“…VO 2 is well known for its reversible insulator to metallic transition accompanied by structural phase transition. [22,23] To confirm our proposed approach, we have performed a thorough nanotribological characterization on VO 2 platelets by FFM and nanoindentation scratch tests. This phase transition in VO 2 can be achieved by a number of stimuli-like temperature, electrical current, or mechanical pressure.…”