title: Direct Imaging of Nanoscale Conductance Evolution in Ion-Gel-Gated Oxide Transistors.
abstract: Electrostatic modification of functional materials by electrolytic gating has demonstrated a remarkably wide range of density modulation, a condition crucial for developing novel electronic phases in systems ranging from complex oxides to layered chalcogenides. Yet little is known microscopically when carriers are modulated in electrolyte-gated electric double-layer transistors (EDLTs) due to the technical challenge of imaging the buried electrolyte-semiconductor interface. Here, we demonstrate the real-space mapping of the channel conductance in ZnO EDLTs using a cryogenic microwave impedance microscope. A spin-coated ionic gel layer with typical thicknesses below 50 nm allows us to perform high resolution (on the order of 100 nm) subsurface imaging, while maintaining the capability of inducing the metal-insulator transition under a gate bias. The microwave images vividly show the spatial evolution of channel conductance and its local fluctuations through the transition as well as the uneven conductance distribution established by a large source-drain bias. The unique combination of ultrathin ion-gel gating and microwave imaging offers a new opportunity to study the local transport and mesoscopic electronic properties in EDLTs.
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Ren
authors.affiliation: ‡Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States.|§SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025, United States.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Yuan
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Wu
authors.affiliation: ‡Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States.
authors.forename: Zhuoyu
authors.initials: Z
authors.lastname: Chen
authors.affiliation: ∥Quantum-Phase Electronics Center and Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.|⊥RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Iwasa
authors.affiliation: ‡Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States.|§SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025, United States.
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.affiliation: ‡Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States.|§SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, California 94025, United States.
authors.forename: Harold Y
authors.initials: HY
authors.lastname: Hwang
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Keji
authors.initials: K
authors.lastname: Lai
mesh_terms: D004553:Electric Conductivity; D004573:Electrolytes / Q000737:chemistry*; D004867:Equipment Design; D007477:Ions / Q000737:chemistry; D008853:Microscopy; D008872:Microwaves; D014173:Transistors, Electronic; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D007477:Ions; D015034:Zinc Oxide
keywords: Electric double-layer transistors; electrical imaging; metal−insulator transition; microwave impedance microscope; spatial inhomogeneity