Structure and Metal‐to‐Insulator Transition of VO 2 Nanowires Grown on Sapphire Substrates

Single‐crystalline VO 2 nanowires exhibit interesting growth phenomena along three equivalent <1 $\bar {1}$ 00> directions of the C‐planes of the sapphire substrates. Under certain growth conditions, VO 2 nanowires form V‐shaped twining structures with uniform morphologies and interfaces. Due to the strong elastic stress at the interfaces, the metal‐to‐insulator transition (MIT) of individual VO 2 nanowires grown directly on sapphire substrates were observed to display distinct electrical hysteresis loops relative to VO 2 nanowires dispersed on sapphire substrates. The distinctive characteristics in the hysteresis loops, exhibited in the process of MIT, are shown to be correlated with the nucleation and growth of periodic/random domain structures in the nanowires during the heating and cooling processes. The periodic domain structures observed in the directly grown nanowires can be explained under the framework of a modified stress‐induced elastic energy model that was first developed for ferroelectric systems.