W Doping and Voltage Driven Metal–Insulator Transition in VO₂ Nano-Films for Smart Switching Devices

A correct understanding of the effects of dopants and the electric field on the metal–insulator transition of VO2 remains a challenge. Herein, theoretical and experimental studies are performed to elucidate the role of W dopants and the electric field on the transition. W dopants are found to introduce additional localized electrons in d bands, which induce the splitting of d// orbitals and the V–V dimerization of local V ions in W-doped R-VO2. The experiments on electric-field-driven MIT of VO2 nanofilms indicate that the conductivity of W-doped R-VO2 increases with increasing applied voltage; however, for the pure R-VO2, the conductivity is independent of applied voltages. The phenomena evidence that the electric field would excite the localized d electrons to the conduction band and result in the closure of the d// orbital splitting. This work gives an insight into electric-field-driven MIT and doping engineering of VO2, which would offer opportunities for improving and promoting the applications of VO2 nanofilms in smart electrical switching devices.