Synthesis, metal–insulator transition, and photoresponse characteristics of VO2 nanobeams via an oxygen inhibitor-assisted vapor transport method

Abstract

Vapor-transport technique is comprehensively employed method for synthesizing monoclinic VO₂ nanostructures to exploit the intrinsic metal–insulator transition (MIT) of VO₂. However, the precise control of growth characteristics, such as morphology and surface density, remains a challenge. Here, we present a modified vapor-transport technique for annealing V₂O₅ powder and for growing high-quality VO₂ crystals with controlled shape and density through merely regulating the O₂ flow. A transition from quasi-2D microplates or thin films to high-density nanobeams (NBs) was observed by introducing a small amount of O₂ gas; however, a notable reduction in NBs density was realized at high levels of O₂. In order to qualitatively elucidate the growth behavior, a prospective model based on the oxygen-inhibiting effect is offered in combination with findings on the morphological and structural evolutions of the intermediate phases. To further examine the MIT behavior and photoresponse, a two-terminal device based on VO₂ NBs was fabricated. The results showed that NBs not only displayed a significant shift in resistance by around 5 orders of magnitude, but also a high MIT temperature and significant hysteresis across the MIT as a result of the significant substrate-induced strain. Our photodetector device performed well when compared to previously reported VO₂-based photodetectors due to its high responsivity and fast response speed under both 532 and 1550 nm laser excitations. This study reveals the significance and efficacy of oxygen in the modulation of VO₂ crystal growth, including the compatibility of narrow-bandgap VO₂ NBs for application in multispectral photodetectors.