Research ArticleAPPLIED PHYSICS

Thermionic transport across gold-graphene-WSe2 van der Waals heterostructures

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Science Advances  08 Nov 2019:
Vol. 5, no. 11, eaax7827
DOI: 10.1126/sciadv.aax7827
  • Fig. 1 Au-Gr-3WSe2-Gr-Au device.

    (A) Illustration of the cross-section of the Au-Gr-3WSe2-Gr-Au structure. The three layers of WSe2 flake are sandwiched by top and bottom graphene layers on a Si/SiO2 substrate, and contact metals (Ti/Au) are deposited on top and bottom graphene layers. (B) Optical microscope image of an Au-Gr-3WSe2-Gr-Au device. The three layers WSe2, top graphene, and bottom graphene are highlighted by red, white, and black dashed lines, respectively. Scale bar, 20 μm. (C) I-V curve of the fabricated Au-Gr-3WSe2-Gr-Au device.

  • Fig. 2 Seebeck measurement.

    (A) Schematic of the Seebeck measurement setup. (B) Seebeck voltage measured versus applied temperature difference. The measured Seebeck coefficient is 72 ± 12 μV/K.

  • Fig. 3 Electronic structure of Au/Pt-Gr-WSe2-Gr-Au/Pt.

    (A) Ball-stick model for the configuration of Au/Pt-Gr-WSe2-Gr-Au/Pt. The yellow, green, gray, and brown balls denote Au/Pt, Se, W, and C atoms, respectively. (B) Contour plot of the LDOS of the Au-Gr-WSe2-Gr-Au structure. The horizontal axis shows the positions of different layers. (C) Contour plot of the LDOS of the Pt-Gr-WSe2-Gr-Pt structure. The horizontal axis shows the positions of different layers.

  • Fig. 4 Transport properties of Au/Pt-Gr-WSe2-Gr-Au/Pt.

    (A) Electron transmission function in the cross-plane direction of gold structure (solid blue line) and platinum structure (red dotted line). (B) Calculated Seebeck coefficient (S, red line) and electrical conductance (G, blue line) versus temperature of both gold and platinum structure. The red circle is the experimentally measured Seebeck coefficient at room temperature. (C) Phonon transmission function in the cross-plane direction of gold structure (solid blue line) and platinum structure (red dotted line). (D) Calculated electronic thermal conductance (Ge, red line) and lattice thermal conductance (Gph, blue line) versus temperature of both gold and platinum structure.

  • Fig. 5 Thermal imaging of the Joule heating inside the structure and cooling curve.

    (A) Joule heating: 2D temperature map of the Au-Gr-WSe2-Gr-Au device under a relatively high-voltage 2 V obtained using the thermoreflectance method. Joule heating dominates in the Gr-WSe2-Gr junction and leaks through the graphene ribbon and gold contacts. (B) Cooling curve: Temperature difference between the substrate and top of the active device in Kelvin versus applied voltage at small applied voltages.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax7827/DC1

    Section S1. Series resistor model

    Section S2. Analysis of contact resistance

    Fig. S1. TDTR measurement.

    Fig. S2. Figure of merit (ZT) of Au-G-WSe2-G-Au structure and Pt-G-WSe2-G-Pt structure.

    Fig. S3. Repeatable cooling curve measurement.

    Fig. S4. Contact resistance measurement.

    Table S1. Two-probe resistance data for samples 1 and 2.

    Table S2. Four-probe resistance data for samples 1 and 2.

    Table S3. Contact resistances.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Series resistor model
    • Section S2. Analysis of contact resistance
    • Fig. S1. TDTR measurement.
    • Fig. S2. Figure of merit (ZT) of Au-G-WSe2-G-Au structure and Pt-G-WSe2-G-Pt structure.
    • Fig. S3. Repeatable cooling curve measurement.
    • Fig. S4. Contact resistance measurement.
    • Table S1. Two-probe resistance data for samples 1 and 2.
    • Table S2. Four-probe resistance data for samples 1 and 2.
    • Table S3. Contact resistances.

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