Supporting Information Metallization of epitaxial VO2 films by ionic ...
Supporting Information
Metallization of epitaxial VO2 films by ionic liquid gating through initially insulating TiO2 layers Donata Passarello §,†, Simone G. Altendorf †, Jaewoo Jeong§, Mahesh G. Samant§, and Stuart S. P. Parkin*,§,† §
†
IBM Research - Almaden, San Jose, California 95120, USA. Max Plank Institute for Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
Characterization of TiO2 / VO2 / TiO2 heterostructures
Figure S1. In situ RHEED patterns of (a) TiO2 (001) single crystal before deposition and (b) 5 nm TiO2 on 10 nm VO2/ TiO2 (001) measured in situ right after growth. Incident beam is along the crystallographic direction of TiO2. (c) Atomic force microscopy image of the same TiO2 / VO2 / TiO2 heterostructure after growth. The root mean square (RMS) roughness of the films is about 0.2 nm. S1
Fitting of ex situ x-ray diffraction measurements before gating
Figure S2. Fitting of the θ-2θ patterns of ex situ x-ray diffraction measurements for the data shown in Figures 1a and 3 of the main text of the pristine 2.5 nm (a), 5 nm (b) and 10 nm (c) TiO2 thin films on 10 nm VO2 (001) and a bare VO2 (001) film (d). The fitting was performed with the Bruker Leptos 7.03 software program. A VO2 c-axis lattice parameter of 2.832 Å, 2.833 Å, 2.833 Å and 2.831 Å and a TiO2 c-axis lattice parameter of 2.958 Å, 2.959 Å, 2.958 Å was derived from the fits for 2.5 nm, 5 nm and 10 nm TiO2 thin films on 10 nm VO2 (001) and for bare VO2, respectively. The fitted thicknesses were the same as the nominal thicknesses within experimental error.
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Fitting of ex situ x-ray diffraction measurements after gating
Figure S3. Fitting of θ-2θ patterns of ex situ x-ray diffraction measurements for the data shown in Figure 3 of the main text of the gated 2.5 nm (a), 5 nm (b) and 10 nm (c) TiO2 thin films on 10 nm VO2 (001) and a bare VO2 (001) film (d). The fitting was performed with the Bruker Leptos 7.03 software program. A VO2 c-axis lattice parameter of 3.003 Å, 3.019 Å, 2.914 Å and 2.950 Å was derived from the fits for 2.5 nm, 5 nm and 10 nm TiO2 thin films on 10 nm VO2 (001) and for bare VO2 respectively. The TiO2 c-axis lattice parameter does not change from that of the
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pristine state. The fitted thicknesses were the same as the nominal thicknesses within experimental error.
Gating response of single layer TiO2 films and TiO2 / VO2 (001) on TiO2 (001) single crystals
Figure S4. (a) Sheet resistance at 100 K and 150 K for devices fabricated from 0 nm, 2.5 nm, 5 nm and 10 nm TiO2 films deposited on TiO2 (001) single crystal substrates that were annealed in oxygen for 30 minutes at 450 °C. (b) Source-drain current ISD and gate current IG versus time for a device fabricated from a 20 nm thick TiO2 film deposited on a TiO2 (001) single crystal substrate.
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Figure S5. (a) Time evolution of c-axis parameter change upon IL gating for 2.5 nm, 5 nm and 10 nm thick TiO2 films on 10 nm VO2 (001). The lattice constant is extracted from fitting of XRD patterns. Time evolution of source-drain current ISD after IL gating (full circles) and reverse gating (empty circles). Sheet resistance vs temperature for 2.5 nm (b), 5 nm (c) and 10 nm (d) thick TiO2 films on TiO2 (001) single crystals after gating.
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Figure S6. In situ θ-2θ x-ray diffraction patterns for a 10 nm thick TiO2 film grown on TiO2 (001) single crystals. XRD measurements were performed at Stanford Synchrotron Radiation Laboratory (SSRL). XRD was performed in pristine state and after gating at VG = 2.6 V.
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Metallization of epitaxial VO2 films by ionic liquid gating through initially insulating TiO2 layers Donata Passarello §,†, Simone G. Altendorf †, Jaewoo Jeong§, Mahesh G. Samant§, and Stuart S. P. Parkin*,§,† §
†
IBM Research - Almaden, San Jose, California 95120, USA. Max Plank Institute for Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
Characterization of TiO2 / VO2 / TiO2 heterostructures
Figure S1. In situ RHEED patterns of (a) TiO2 (001) single crystal before deposition and (b) 5 nm TiO2 on 10 nm VO2/ TiO2 (001) measured in situ right after growth. Incident beam is along the crystallographic direction of TiO2. (c) Atomic force microscopy image of the same TiO2 / VO2 / TiO2 heterostructure after growth. The root mean square (RMS) roughness of the films is about 0.2 nm. S1
Fitting of ex situ x-ray diffraction measurements before gating
Figure S2. Fitting of the θ-2θ patterns of ex situ x-ray diffraction measurements for the data shown in Figures 1a and 3 of the main text of the pristine 2.5 nm (a), 5 nm (b) and 10 nm (c) TiO2 thin films on 10 nm VO2 (001) and a bare VO2 (001) film (d). The fitting was performed with the Bruker Leptos 7.03 software program. A VO2 c-axis lattice parameter of 2.832 Å, 2.833 Å, 2.833 Å and 2.831 Å and a TiO2 c-axis lattice parameter of 2.958 Å, 2.959 Å, 2.958 Å was derived from the fits for 2.5 nm, 5 nm and 10 nm TiO2 thin films on 10 nm VO2 (001) and for bare VO2, respectively. The fitted thicknesses were the same as the nominal thicknesses within experimental error.
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Fitting of ex situ x-ray diffraction measurements after gating
Figure S3. Fitting of θ-2θ patterns of ex situ x-ray diffraction measurements for the data shown in Figure 3 of the main text of the gated 2.5 nm (a), 5 nm (b) and 10 nm (c) TiO2 thin films on 10 nm VO2 (001) and a bare VO2 (001) film (d). The fitting was performed with the Bruker Leptos 7.03 software program. A VO2 c-axis lattice parameter of 3.003 Å, 3.019 Å, 2.914 Å and 2.950 Å was derived from the fits for 2.5 nm, 5 nm and 10 nm TiO2 thin films on 10 nm VO2 (001) and for bare VO2 respectively. The TiO2 c-axis lattice parameter does not change from that of the
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pristine state. The fitted thicknesses were the same as the nominal thicknesses within experimental error.
Gating response of single layer TiO2 films and TiO2 / VO2 (001) on TiO2 (001) single crystals
Figure S4. (a) Sheet resistance at 100 K and 150 K for devices fabricated from 0 nm, 2.5 nm, 5 nm and 10 nm TiO2 films deposited on TiO2 (001) single crystal substrates that were annealed in oxygen for 30 minutes at 450 °C. (b) Source-drain current ISD and gate current IG versus time for a device fabricated from a 20 nm thick TiO2 film deposited on a TiO2 (001) single crystal substrate.
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Figure S5. (a) Time evolution of c-axis parameter change upon IL gating for 2.5 nm, 5 nm and 10 nm thick TiO2 films on 10 nm VO2 (001). The lattice constant is extracted from fitting of XRD patterns. Time evolution of source-drain current ISD after IL gating (full circles) and reverse gating (empty circles). Sheet resistance vs temperature for 2.5 nm (b), 5 nm (c) and 10 nm (d) thick TiO2 films on TiO2 (001) single crystals after gating.
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Figure S6. In situ θ-2θ x-ray diffraction patterns for a 10 nm thick TiO2 film grown on TiO2 (001) single crystals. XRD measurements were performed at Stanford Synchrotron Radiation Laboratory (SSRL). XRD was performed in pristine state and after gating at VG = 2.6 V.
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