Continuous Tuning of Phase Transition Temperature in VO₂ Thin Films on c-Cut Sapphire Substrates via Strain Variation

Abstract

Vanadium dioxide (VO) thin films with controlled thicknesses are deposited on c-cut sapphire substrates with Al-doped ZnO (AZO) buffer layers by pulsed laser deposition. The surface roughness of AZO buffer layers is varied by controlling oxygen pressure during growth. The strain in the VO lattice is found to be dependent on the VO thickness and the VO/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO thin films are characterized and the transition temperature (T) is successfully tuned by the VO thickness as well as the VO/AZO interface roughness. It shows that the T of VO decreases with the decrease of film thickness or VO/AZO interface roughness. Other SMT properties of the VO films are maintained during the T tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning T of VO continuously.

The Control of Transition Behavior of VO2 Film Deposited on Sapphire (0001) Substrate by the Organic Polymer‐Assisted Thermal Deposition

“…This reflection seems no relationship with the sapphire itself because no diffraction plane of the sapphire can be observed around this position. The slight peak position shift of the VO 2 film on a substrate can be related to stress and strain of the lattice …”

“…As shown in Figure (a), the matching unit in sapphire (0001) plane are about 2 times larger than the matching unit in the (020) plane of monoclinic VO 2 , 4.570 × 2.851 Å 2 . Therefore, the VO 2 film would be preferred deposited in rutile (011) axis on the sapphire (0001) plane during the thermal deposition process and then became monoclinic (020) axis preferred phase, as reported . This type of lattice matching may be applied to explain the preferred growing of monoclinic (−211) axis near 37.5°.…”

“…For VO 2 granules, larger particles show wider and sharp phase transition, for VO 2 nanorods, bigger rods show decreased hysteresis at the phase transition. The (020) ordered VO 2 thin films (<200 nm) deposited on sapphire (0001) surface with controlled strain determine transition temperature from 338.2 to 320.8 K . The transition behavior of VO 2 could be modulated more easily by doping of impurity metal or controlling of oxidation state of vanadium.…”

“…12 For VO 2 granules, larger particles show wider and sharp phase transition, 12,13 for VO 2 nanorods, bigger rods show decreased hysteresis at the phase transition. 12 The (020) ordered VO 2 thin films (<200 nm) deposited on sapphire (0001) surface with controlled strain determine transition temperature from 338.2 to 320.8 K. 14 The transition behavior of VO 2 could be modulated more easily by doping of impurity metal or controlling of oxidation state of vanadium. The most well-studied impurity for the T c control of VO 2 is W. [15][16][17][18] The temperature decreases near room temperature by W doping (up to~−40 K/W% within~1% of W doping) 18 Also, the controlled oxygen level by the oxygen annealing in VO 2 film controls the transition temperature down to 313.7 K. [19][20][21] Even though there are many variations to make VO 2 smart film, most popular methods are physical vapor deposition, 22 dip coating, 23 and direct thermal decomposition.…”

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

“…It was concluded that the in-plane tensile strain induced by the interfacial lattice mismatch could modify the electronic structure of VO 2 and the strain relaxed gradually when increased the thickness of the VO 2 film. [30,32,225,226] The local modulation such as atomic defects also affects τ c . Taking the W dopant as an example, it was directly observed on an atomically resolved strain map to induce the anisotropic localized stress in the M phase by the aberration-corrected scanning TEM.…”