Research ArticleNANOTECHNOLOGY

Room temperature detection of individual molecular physisorption using suspended bilayer graphene

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Science Advances  15 Apr 2016:
Vol. 2, no. 4, e1501518
DOI: 10.1126/sciadv.1501518
  • Fig. 1 Suspended strained graphene device.

    (A) Schematic of pulling a suspended graphene with electrostatic force onto the bottom electrode. Right panels are the side views before and after pull-in. The blue dashed box highlights the suspended graphene used for adsorption detection. (B) Atomic force microscopy image of the suspended BLG device [marked by the blue dashed box in (A)]. B, bottom; T, top. (C) Height profiles along the green and red lines in (B). The pink line highlights the suspended BLG. (D) Raman spectrum of the suspended graphene. The green lines are the Lorentzian subpeaks fitted to the 2D band. The blue dotted lines locate the G, 2D1A, and 2D1B bands of a pristine BLG, respectively. Red shadows mark stain-induced shifts in the 2D band. au, arbitrary units.

  • Fig. 2 Measurements of CO2 detection with the suspended BLG.

    (A) Gate modulations in a vacuum (left) and in a CO2 environment (right). (B) Resistance responses of BLG exposed to CO2 with Vg of 0 V (black dots), +15 V, and −15 V, respectively. The blue and green arrows highlight the positive and negative step-like changes in resistance, respectively. (C) Statistical distribution of the step-like change in resistance ΔR in BLG exposed to CO2 with a Vg of +15 V. The solid lines are Gaussian fits.

  • Fig. 3 Molecular dynamics simulations of CO2 motion over a graphene surface in an electric field.

    (A) Potential distribution on the graphene surface with the application of back-gate voltage. The area with high potential is located between the two dashed lines. (B and C) Molecular dynamics simulations of the trajectory of a free CO2 molecule near the graphene surface at 300 K from 0 to 4 ps without (B) and with (C) Vg. The arrow lines give the trajectory of the molecule.

  • Fig. 4 Schematics of the gate modulations of graphene before and after molecular physisorption.

    (A) When charge transfer dominates. (B) When impurity scattering dominates.

  • Fig. 5 Transport properties in the BLG affected by surface CO2 physisorption.

    (A to C) Cross-sectional charge density difference distribution along the CO2 molecule: in freestanding BLG, in BLG placed on a defective SiO2 surface, and in BLG placed on an ideal SiO2 surface, respectively. (D) Top view of the simulated charge density difference distribution in freestanding BLG with one CO2 adsorption event. Blue and red denote electron density enrichment and depletion with an isovalue of 6 × 10−6 e/Å3 in all simulations, respectively. (E) Coulomb potential energy distribution on the x axis on the BLG along a CO2 molecule. The blue dashed line indicates the thermal energy at room temperature. The thin dotted line marks the location of a CO2 molecule. (F) Schematic of partial conducting channel shutoff in BLG by Coulomb impurity scattering.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/4/e1501518/DC1

    fig. S1. Optical microscopic image of the as-fabricated double-clamped BLG device.

    fig. S2. Measurement showing BLG pulled into the bottom electrode.

    fig. S3. Relative changes in the resistance response of BLG plotted in Fig. 2B.

    fig. S4. Additional measurements of the resistance time revolution of current annealing regenerated the suspended BLG.

    fig. S5. Gate modulation of an additional suspended BLG in a CO2 environment.

    fig. S6. Simulated charge density difference distribution in freestanding BLG, with one CO2 adsorption event occurring in a large supercell.

    fig. S7. Model used in semiempirical molecular dynamics simulations.

    DFT calculations with vdW correction.

    References (32, 33)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Optical microscopic image of the as-fabricated double-clamped BLG device.
    • fig. S2. Measurement showing BLG pulled into the bottom electrode.
    • fig. S3. Relative changes in the resistance response of BLG plotted in Fig. 2B.
    • fig. S4. Additional measurements of the resistance time revolution of current annealing regenerated the suspended BLG.
    • fig. S5. Gate modulation of an additional suspended BLG in a CO2 environment.
    • fig. S6. Simulated charge density difference distribution in freestanding BLG, with one CO2 adsorption event occurring in a large supercell.
    • fig. S7. Model used in semiempirical molecular dynamics simulations.
    • DFT calculations with vdW correction.
    • References (32, 33)

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