Revealing the nature of the graphene on-off control of the electrolyte gating effect in WO3 film phase transition

Abstract

Electrolyte gating-induced metallization has been broadly observed in various transition metal oxides for decades, while the gating mechanism is still under debate. In this work, we realize the Insulator-Metal Transition (IMT) control of WO3 film by inserting a few-layer graphene. It's found that a sharp IMT process in WO3 film emerges if applying an electrolyte gating treatment, while this IMT behavior will be strikingly suppressed if inserting a graphene layer between the WO3 film and ionic liquid. Interestingly, the pronounced IMT behavior can be always observed if substituting the ionic liquid by acid solution, regardless of graphene layer insertion or not. According to the first-principles calculations, the diffusion energy barriers for the hydrogen or oxygen propagating graphene layer are extracted, and then the mechanism of electrolyte gating in WO3 films is proposed. Moreover, the roles of hydrogen and oxygen vacancy on the WO3 IMT process are further discussed based on the band structure calculations. Our current study will boost the development of electrolyte gating technique and bring deeper understanding of the electrolyte gating treatment for other transition metal oxides.