Research ArticlePHYSICAL SCIENCE

Quantum imaging of current flow in graphene

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Science Advances  26 Apr 2017:
Vol. 3, no. 4, e1602429
DOI: 10.1126/sciadv.1602429
  • Fig. 1 Graphene ribbons on a diamond imaging platform.

    (A) Schematic of the experiment. The diamond platform consists of a diamond chip hosting a layer of near-surface NV centers. The graphene devices are fabricated directly on the diamond chip, which is mounted on a coverslip equipped with an MW resonator. The NV centers’ PL under green laser and MW excitations is imaged on a camera to form the magnetic field image. (B) Optical micrograph of the final device. Apparent on the diamond are metallic contacts, and wire bonds, used for current injection in the graphene ribbons. (C) Bright-field image recorded with the camera, focused on a graphene ribbon (not visible). (D) PL image of the same area under laser excitation. The graphene ribbon is now visible because of PL quenching. (E) Line cut across the ribbon extracted from (D) (white dashed line). a.u., arbitrary units.

  • Fig. 2 Magnetic field imaging and reconstruction of the current density.

    (A) PL image of the graphene ribbon under study, defining the xyz reference frame. (B) ODMR spectrum of the NV centers in a single pixel near the graphene under a positive (red dots) or negative (blue dots) applied current. Solid lines are data fit to a sum of eight Lorentzian functions. Inset: Energy levels of the electron spin of a single NV center, showing the Zeeman splitting 2γeB between ms = ±1, where ms is the spin projection along the NV axis, B is the magnetic field projection, and γe is the electron gyromagnetic ratio. The two electron spin resonances are indicated by green arrows. The experimental spectrum comprises eight resonances in total due to the four possible crystallographic orientations, allowing vector magnetometry. (C) Maps of the Bx (top), By (middle), and Bz (bottom) components of the magnetic field produced by a total current I = 0.8 mA. (D) Maps of the Jx (top) and Jy (middle) components of the current density reconstructed from (C). The bottom panel shows the norm of the current density, Embedded Image. The black arrows represent the vector Embedded Image (length proportional to Embedded Image; threshold Embedded Image > 30 A/m). Scale bars, 10 μm (C and D).

  • Fig. 3 Current flow near defects in graphene.

    (A) Maps of the norm of the current density, Embedded Image, in two different graphene ribbons driven by a total current I = 0.8 mA. (B) Zooms of selected areas from (A). The black arrows represent the vector Embedded Image (length proportional to Embedded Image; threshold Embedded Image > 30 A/m). (C) PL images corresponding to the same areas as in (B). (D) Corresponding SEM images. Scale bars, 5 μm.

  • Fig. 4 Current flow near metallic contacts.

    (A and B) SEM images of two junctions between Ti/Au electrodes and a graphene ribbon. The insets show the corresponding PL images. (C and D) Maps of the norm of the current density, Embedded Image, under a total current I = 0.8 mA, corresponding to the two junctions shown in (A) and (B). The black dashed lines indicate the edges of the metallic electrodes, as extracted from the PL images. The black arrows represent the vector Embedded Image (length proportional to Embedded Image; threshold Embedded Image > 30 A/m). Scale bars, 10 μm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602429/DC1

    Supplementary Materials and Methods

    fig. S1. Raman spectroscopy.

    fig. S2. SEM imaging of graphene on diamond.

    fig. S3. Zeeman splitting as a function of magnetic field.

    fig. S4. Subtraction of the background magnetic field.

    fig. S5. Oersted magnetic field in the laboratory frame.

    fig. S6. Procedure to reconstruct the current density.

    fig. S7. Robustness of the reconstruction procedure.

    fig. S8. Oersted field as a function of probe distance.

    References (4852)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • fig. S1. Raman spectroscopy.
    • fig. S2. SEM imaging of graphene on diamond.
    • fig. S3. Zeeman splitting as a function of magnetic field.
    • fig. S4. Subtraction of the background magnetic field.
    • fig. S5. Oersted magnetic field in the laboratory frame.
    • fig. S6. Procedure to reconstruct the current density.
    • fig. S7. Robustness of the reconstruction procedure.
    • fig. S8. Oersted field as a function of probe distance.
    • References (48–52)

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