Phase management in single-crystalline vanadium dioxide beams

Run Shi,Chun Cheng,Nan Shen,Zhuoqiong Zhang,Yong Chen,Xiangbin Cai,Qing Lian,Ning Wang,Abbas Amini

doi:10.1038/s41467-021-24527-5

Abstract

A systematic study of various metal-insulator transition (MIT) associated phases of VO2, including metallic R phase and insulating phases (T, M1, M2), is required to uncover the physics of MIT and trigger their promising applications. Here, through an oxide inhibitor-assisted stoichiometry engineering, we show that all the insulating phases can be selectively stabilized in single-crystalline VO2 beams at room temperature. The stoichiometry engineering strategy also provides precise spatial control of the phase configurations in as-grown VO2 beams at the submicron-scale, introducing a fresh concept of phase transition route devices. For instance, the combination of different phase transition routes at the two sides of VO2 beams gives birth to a family of single-crystalline VO2 actuators with highly improved performance and functional diversity. This work provides a substantial understanding of the stoichiometry-temperature phase diagram and a stoichiometry engineering strategy for the effective phase management of VO2.

Highlights

A systematic study of various metal-insulator transition (MIT) associated phases of VO2, including metallic R phase and insulating phases (T, M1, M2), is required to uncover the physics of MIT and trigger their promising applications
Compared to well-known metal-insulator transition (MIT) associated insulating phase and metallic phase, the other two insulating M2 and T phases have received little attention, despite their capability to lead to different phase transition behaviors and properties, because of their metastable structures and spatial phase inhomogeneity in film/bulk samples[1,2,3]
Zhang et al.[21] created an oxygen-rich reaction condition by injecting O2 flow to the vapor transport system during the first 15 min of heating, but only 15% of as-grown VO2 nanowires appeared to have stabilized M2/T phases by excessive oxygen at room temperature, implying the difficulty of the kinetics control of oxidation

Summary

Introduction

A systematic study of various metal-insulator transition (MIT) associated phases of VO2, including metallic R phase and insulating phases (T, M1, M2), is required to uncover the physics of MIT and trigger their promising applications. In recent years, controlled domain structures and phase transitions have been achieved in single-crystalline VO2 beams at the single domain level to decouple the effects of external factors These advancements have assisted to acquire relatively accurate phase diagrams for an in-depth understanding of MIT mechanism and various device applications[4,5,6,7,8]. Since either doping or strain causes remarkable structural distortion to VO2 lattices and varies their intrinsic properties and applications, an effective stoichiometric strategy is highly required for engineering the VO2 crystals with stabilized multi-phases. We report the stoichiometry engineering of singlecrystalline VO2 beams through an oxide inhibitor-assisted CVD method, which provides an empirical reaction phase diagram for the controllable fabrication of the structured insulating VO2 phases (M1, T, and M2) stabilized at room temperature. The outcomes indicate the powerful modulation capability of the proposed oxide inhibitor-assisted stoichiometry engineering strategy

Methods

Results

Conclusion