Evolution of Insulator–Metal Phase Transitions in Epitaxial Tungsten Oxide Films during Electrolyte-Gating

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• 作者：Shinichi Nishihaya ; Masaki Uchida ; Yusuke Kozuka ; Yoshihiro Iwasa ; Masashi Kawasaki ; S. Nishihaya ; M. Uchida ; Y. Kozuka ; Y. Iwasa ; M. Kawasaki ; Y. Iwasa ; M. Kawasaki
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：August 31, 2016
• 年：2016
• 卷：8
• 期：34
• 页码：22330-22336
• 全文大小：531K
• 年卷期：0
• ISSN：1944-8252

文摘

An interface between an oxide and an electrolyte gives rise to various processes as exemplified by electrostatic charge accumulation/depletion and electrochemical reactions such as intercalation/decalation under electric field. Here we directly compare typical device operations of those in electric double layer transistor geometry by adopting A-site vacant perovskite WO₃ epitaxial thin films as a channel material and two different electrolytes as gating agent. In situ measurements of X-ray diffraction and channel resistance performed during the gating revealed that in both the cases WO₃ thin film reaches a new metallic state through multiple phase transitions, accompanied by the change in out-of-plane lattice constant. Electrons are electrostatically accumulated from the interface side with an ionic liquid, while alkaline metal ions are more uniformly intercalated into the film with a polymer electrolyte. We systematically demonstrate this difference in the electrostatic and electrochemical processes, by comparing doped carrier density, lattice deformation behavior, and time constant of the phase transitions.