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Ultrathin thermoresponsive self-folding 3D graphene

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Science Advances  06 Oct 2017:
Vol. 3, no. 10, e1701084
DOI: 10.1126/sciadv.1701084
  • Fig. 1 Surface functionalization and patterning of monolayer graphene.

    (A) Schematic illustration of the surface functionalization process of graphene. In the first step, dopamine was self-polymerized on the surface of graphene to form a thin layer of PD, and then, the amine-terminated PNIPAM chains were grafted on the PD. (B) Schematic illustration of the fabrication and folding process of graphene microstructures. First, a patterned Al sacrificial layer was deposited. Then, monolayer graphene was transferred onto the substrate and functionalized using PD and PNIPAM. The functionalized graphene layer was patterned using photolithography and plasma etching. Finally, folding was induced by heating above the LCST of PNIPAM.

  • Fig. 2 Characterization of the functionalized graphene.

    (A) Raman spectra of graphene and functionalized graphene with PD and PNIPAM. PDx and PNIPAMx denote self-polymerization times of PD and grafting times of PNIPAM for x hours, respectively. a.u., arbitrary unit. (B) Representative AFM line scans of the graphene and functionalized graphene measured from the AFM images (insets). (C and D) XPS spectra (solid line) and peak fitting (dotted line) of graphene and functionalized graphene at the (C) C1s and (D) N1s binding energy regions.

  • Fig. 3 Temperature-induced self-folding.

    Optical microscope snapshots of the self-folding of ultrathin graphene microstructures with different geometries: (A to C) flower, (D to F) dumbbell, and (G to I) box. The first column is at room temperature and before folding, the second column is a folding intermediate, and the third column is the folded structure after heating to 45°C. All the optical images were taken in an aqueous environment. Yellow dash lines indicate the pinned down area. Scale bars, 100 μm. The dimension of the rigid SU8 hinge in (G) has a length of 200 μm and a width of 25 μm.

  • Fig. 4 Selective folding, reversibility, and live cell encapsulation.

    (A to D) Selectivity of self-folding in graphene microstructures induced by heating. (A) Optical microscope image of a dumbbell with only its right circle functionalized and (C) a flower with alternating three petals functionalized. (B and D) Optical images of folded structures indicating that only the functionalized regions self-fold on heating. (E and F) Reversibility of the temperature-induced self-folding. The sequence in (E) shows the folding and unfolding of a functionalized graphene flower, whereas the sequence in (F) shows the folding and unfolding of a flower with rigid SU8 petals, with better stability and reversibility but with increased thickness. (G and H) Encapsulation of live breast cancer cells within the functionalized graphene flowers. (G) Bright-field and (H) corresponding fluorescence image of encapsulated cells. Cells were stained with a live/dead (calcein AM/ethidium homodimer-1), and green fluorescence indicates viability. Insets in (G) and (H) show the encapsulation of a single breast cancer cell with a 60-μm flower. Scale bars, 50 μm, except for (G) and (H), which are 10 μm.

  • Fig. 5 Multiscale modeling of the temperature-driven self-folding of the functionalized graphene.

    (A) Top view of the aggregation of an array of PNIPAM brushes with increasing temperatures in full atomistic MD simulations (cyan, C; red, O; blue, N; white, H). (B) A representative mesoscale coarse-grained model of the flower-shaped functionalized graphene. (C) Simulation snapshots of the coarse-grained model during the folding process of the functionalized graphene flower. The first row is the side view, and the bottom row is the top view. (D) Plot of the height versus the overall initial radius of the flower pattern over time. (E and F) Flat and folded states of the dumbbell and box shaped graphene from simulation. The top row is the side/tilted view, and the bottom row is the top view. The coarse-grained structure is colored according to different materials: blue for the PNIPAM layer and red for the PD-graphene layer. A certain region of the bottom layer of coarse-grained beads is fixed by adapting the same boundary condition as in the experiments.

  • Fig. 6 Graphene-based nonlinear resistors and creased transistor devices.

    (A) Optical images and circuit diagrams of the measured resistor devices in the flat (top) and folded (bottom) states. (B) Representative I-V curves of a graphene dumbbell before and after folding. (C) R-V curves of the same samples as shown in (B). (D) Optical images and circuit diagrams of the measured graphene FETs in the flat (top) and folded (bottom) states. (E) The transfer curves of the functionalized graphene FET as a function of back-gate voltage in the flat (black line) and folded (red line) states. (F) Output curves of the functionalized graphene FET in the folded state as a function of drain voltage with varying gate voltages.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/10/e1701084/DC1

    Additional experimental details

    Raman spectra of the functionalized graphene

    AFM characterization of the functionalized graphene

    XPS characterization of functionalized graphene

    Optical and SEM imaging of the self-folding graphene structures

    Raman spectra of folded graphene

    Cell encapsulation and Raman analysis

    Full atomistic modeling of the folding behaviors

    Electrical properties of folded graphene structures

    fig. S1. Raman spectra of PD with different thickness (self-polymerization for 2 and 4 hours) on the Si substrate.

    fig. S2. Surface morphology of graphene and functionalized graphene.

    fig. S3. Chemical composition of functionalized graphene studied by XPS.

    fig. S4. High-resolution O1s XPS spectra and peak fitting (dotted lines) of graphene, G-PD, and G-PD-PNIPAM.

    fig. S5. Effect of the rigid hinge on the self-folding of functionalized graphene box.

    fig. S6. Characterization of the self-folding graphene microstructures using SEM.

    fig. S7. Highly parallel self-folding of ultrathin 3D graphene microstructures.

    fig. S8. Control experiments of self-folding on pristine graphene and G-PD.

    fig. S9. Self-folding of functionalized graphene with 5 nm thickness.

    fig. S10. The folding process of half-functionalized graphene dumbbell with increasing temperature.

    fig. S11. Raman spectra of a graphene flower in the flat and folded regions.

    fig. S12. Cell viability with the live/dead assay.

    fig. S13. Single cell encapsulation and Raman study.

    fig. S14. Initial configuration of the PNIPAM-water system in the MD model.

    fig. S15. Top view of the aggregation behavior of an array of (36 chains in total) PNIPAM brushes at different temperatures in MD simulations.

    fig. S16. Comparison between the coarse-grained MD model and the experiment results for a functionalized graphene flower with different size.

    fig. S17. The effect of mechanical properties of the two layers on self-folding.

    fig. S18. Electrical measurements on pristine graphene and functionalized graphene dumbbell.

    fig. S19. Dimension of the folding crease measured by AFM.

    fig. S20. Output and transfer curves of the pristine and functionalized graphene FET.

    table S1. XPS data analysis of graphene, G-PD, and G-PD-PNIPAM at the C1s, N1s, and O1s peaks.

    table S2. Tensile test results of PNIPAM from the MD simulations.

  • Supplementary Materials

    This PDF file includes:

    • Additional experimental details
    • Raman spectra of the functionalized graphene
    • AFM characterization of the functionalized graphene
    • XPS characterization of functionalized graphene
    • Optical and SEM imaging of the self-folding graphene structures
    • Raman spectra of folded graphene
    • Cell encapsulation and Raman analysis
    • Full atomistic modeling of the folding behaviors
    • Electrical properties of folded graphene structures
    • fig. S1. Raman spectra of PD with different thickness (self-polymerization
      for 2 and 4 hours) on the Si substrate.
    • fig. S2. Surface morphology of graphene and functionalized graphene.
    • fig. S3. Chemical composition of functionalized graphene studied by XPS.
    • fig. S4. High-resolution O1s XPS spectra and peak fitting (dotted lines) of graphene, G-PD, and G-PD-PNIPAM.
    • fig. S5. Effect of the rigid hinge on the self-folding of functionalized graphene box.
    • fig. S6. Characterization of the self-folding graphene microstructures using SEM.
    • fig. S7. Highly parallel self-folding of ultrathin 3D graphene microstructures.
    • fig. S8. Control experiments of self-folding on pristine graphene and G-PD.
    • fig. S9. Self-folding of functionalized graphene with 5 nm thickness.
    • fig. S10. The folding process of half-functionalized graphene dumbbell with increasing temperature.
    • fig. S11. Raman spectra of a graphene flower in the flat and folded regions.
    • fig. S12. Cell viability with the live/dead assay.
    • fig. S13. Single cell encapsulation and Raman study.
    • fig. S14. Initial configuration of the PNIPAM-water system in the MD model.
    • fig. S15. Top view of the aggregation behavior of an array of (36 chains in total) PNIPAM brushes at different temperatures in MD simulations.
    • fig. S16. Comparison between the coarse-grained MD model and the experiment results for a functionalized graphene flower with different size.
    • fig. S17. The effect of mechanical properties of the two layers on self-folding.
    • fig. S18. Electrical measurements on pristine graphene and functionalized graphene dumbbell.
    • fig. S19. Dimension of the folding crease measured by AFM.
    • fig. S20. Output and transfer curves of the pristine and functionalized graphene FET.
    • table S1. XPS data analysis of graphene, G-PD, and G-PD-PNIPAM at the C1s, N1s, and O1s peaks.
    • table S2. Tensile test results of PNIPAM from the MD simulations.

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