Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition

Transcription

1 SUPPLEMENTARY INFORMATION Three-dimensional flexible and conductive interconnected graphene networks grown by chemical vapour deposition S1. Characterization of the graphene foam (GF) and GF/PDMS composites a b c f e d Figure S1. Photographs of the samples obtained in each step. (a) Ni foam; (b) Ni-G; (c) Ni-G-PMMA; (d) GF-PMMA; (e) GF; and (f) GF/PDMS. nature materials 1

2 supplementary information Figure S2. SEM images of the as-grown graphene films adhering to the surface of a nickel foam. Ripples and wrinkles of the graphene films are observed. 2 nature MATERIALS

3 supplementary information Figure S3. (a, b): Low- and high-magnification SEM images of one side of a GF. (c, d): Low- and high-magnification SEM images of the cross section of a GF. The cross section was obtained by cutting the GF with scissors. Figure S4. SEM images of a GF without a PMMA protection layer, showing that the GF collapses with severe distortion of graphene sheets. nature materials 3

4 supplementary information a b Thinkness (μm) Average number of layers Mass (mg) Density (mg/cm 3 ) Average number of layers Specific surface area (m 2 /g) Figure S5. (a) Thickness and mass of GFs as a function of the average number of graphene layers. (b) The density and specific surface area of GFs as a function of the average number of graphene layers. Figure S6. SEM images of (a, c) graphene films on nickel foams and (b, d) the resultant GFs. The nickel foams used in a and c have 95 and 115 pores per inch, respectively. All the scale bars are 250 μm. 4 nature MATERIALS

5 supplementary information Average number of layers CH 4 concentration (vol%) Figure S7. Average number of graphene layers in GFs as a function of CH 4 concentration used in CVD growth. Figure S8. SEM images of (a, b) graphene films grown on copper foams and (c, d) the resultant collapsed GFs. nature materials 5

6 supplementary information a b c d Figure S9. Photographs of a GF/PDMS composite under (a, b) bending, (c) stretching, and (d) twisting, showing its good flexibility. Thinkness (μm) Average number of layers Resistance (Ω) 6 nature MATERIALS

7 supplementary information Figure S10. Thickness and resistance of GFs and GF/PDMS composites as a function of the average number of graphene layers. From our Raman measurements, multi-layer graphene can show a single narrow 2D peak with a Lorentzian lineshape. This indicates that the graphene layers are randomly stacked, unlike in graphite with an ordered stacking (i.e., ABAB stacking). This result is consistent with those reported by other groups for CVD-grown graphene by using Ni as a substrate 1,2. The random stacking decouples the adjacent graphene layers so that their electronic properties are nearly identical to isolated graphene 3-5. As a result, the overall electrical conductivity of multi-layer graphene is proportional to the number of graphene layers 3,5. However, because of the lower shrinkage of the GF due to the increased stiffness of thicker graphene sheets, the resistance of the GFs and GF/PDMS is not inversely proportional to the average number of layers with a linear relation, as shown in Figure S10. Stress(MPa) Tensile modulus(mpa) 0.0 PDMS GF/PDMS PDMS GF/PDMS 0.0 Figure S11. Average tensile strength and tensile modulus of PDMS and GF/PDMS composites, which were calculated from the stress strain curves of five specimens for each sample, with error bars representing the standard deviation. nature materials 7

8 supplementary information a b c d e f Initial Bending Release Figure S12. Photographs of GF/PDMS (a c and a c ) and Ni foam/pdms (d f and d f ) composites before, under and after mechanical deformation. It can be found that the GF/PDMS composites have good elasticity and can recover to their initial form after releasing strain, while the Ni foam/pdms composites cannot recover but remain in bent or stretched forms. 8 nature MATERIALS

9 supplementary information 1.5 Stress (MPa) Strain (%) Figure S13. Typical stress strain curve of Ni foam/pdms composites, showing its plastic deformation under strain. The inset shows the breaking of a Ni foam/pdms composite after ~50% stretching. The Ni foam/pdms composites were synthesized by infiltrating free-standing Ni foams with PDMS prepolymer, a viscous mixture of base/curing agent (Sylgard 184, Dow Corning), followed by degassing in a vacuum oven for 30 min and thermally curing at 80 C for 4 h, the same as those for preparing GF/PDMS composites. The electrical conductivity and stretch measurements are the same as those for GF/PDMS composites. nature materials 9

10 supplementary information 30 max strain zero strain 50% ΔR/R 0 (%) % 0 10% Stretching cycles Figure S14. Electrical resistance change of GF/PDMS composites after 10, 30, and 50% stretching and then releasing for each cycle. It can be seen that an irreversible resistance change of the composites occurs in the first few cycles. Moreover, the irreversible resistance increase is larger for a larger maximum tensile strain, indicating that it can be intrinsically attributed to the partial breaking or cracking of the GF network. The cycle when the resistance change becomes stable has been marked. The number of cycles needed for GF/PDMS conductors becoming stable also depends on the degree of mechanical deformation. Under larger maximum deformation, more cycles are needed for the GF/PDMS conductors to become stable. 10 nature MATERIALS

11 supplementary information S2. Comparison of the electrical conductivity of GF/PDMS with CNT based composites. Table S1. Typical CNT composites and their electrical conductivity Conducting fillers/polymer Conducting filler content Electrical conductivity Reference SWNT/polyimide 0.5 vol% S/cm Ounaies, Z., et al. 6 SWNT/polystyrene 7 wt% S/cm SWNT/polyimide 0.2 vol% ~ S/cm Ramasubramaniam, R., et al. 7 McLachlan, D. S. et al. 8 SWNT/polystyrene 0.5 wt% ~ S/cm Grossiord, N et al. 9 SWNT/polystyrene 8.5 wt% S/cm Barraza, H.J et al. 10 MWNT/PVA 0.54 wt% S/cm Kilbride, B.E. et al. 11 SWNT/polyimide 0.2 vol% S/cm Park, C. et al. 12 SWNT/PMMA 1.3 wt% S/cm Haggenmueller, R et al. 13 GF/PDMS 0.5 wt% (0.22 vol%) 10 S/cm Our work S3. Evaluation of the specific surface area of GFs and their average number of graphene layers. Considering that a nickel foam is fully covered by graphene after CVD growth, the surface area of the GF (S GF ) is twice that of the nickel foam template used, which can be measured by nitrogen gas cryosorption (Micromeritics, ASAP2010M). Therefore, the specific surface area of GF and its average number of layers (N) of graphene sheets can be calculated as follows: nature materials 11

12 supplementary information S GF =2 (S Ni W Ni ) (1) S GF= S GF /W GF (2) N= S G /S GF (3) where S Ni and W Ni are the specific surface area and weight of the nickel foam template, respectively; S GF and W GF are the specific surface area and weight of the GF, respectively; S G 2600 m 2 /g 14, corresponds to the theoretical value of the specific surface area of a monolayer graphene. References 1. Reina, A. et al. Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition. Nano Lett. 9, (2009). 2. Alfonso Reina, S.T., Xiaoting Jia, Sreekar Bhaviripudi, Mildred S. Dresselhaus, Juergen A. Growth of large-area single- and bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces Nano Res. 2, (2009). 3. Bae, S. et al. Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nature Nanotechnol. 5, (2010). 4. Hass, J. et al. Why multilayer graphene on 4H-SiC(0001) behaves like a single sheet of graphene. Phys. Rev. Lett. 100, (2008). 5. Li, X.S. et al. Transfer of large-area graphene films for high-performance transparent conductive electrodes. Nano Lett. 9, (2009). 6. Ounaies, Z., Park, C., Wise, K.E., Siochi, E.J. & Harrison, J.S. Electrical properties of single wall carbon nanotube reinforced polyimide composites. Compos. Sci. Technol. 63, (2003). 7. Ramasubramaniam, R., Chen, J. & Liu, H.Y. Homogeneous carbon nanotube/polymer composites for electrical applications. Appl. Phys. Lett. 83, (2003). 8. McLachlan, D.S. et al. Ac and dc percolative conductivity of single wall carbon nanotube polymer composites. J. Polym. Sci., Part B: Polym. Phys. 43, (2005). 9. Grossiord, N., Loos, J. & Koning, C.E. Strategies for dispersing carbon nanotubes in highly viscous polymers. J. Mater. Chem. 15, (2005). 10. Barraza, H.J., Pompeo, F., O'Rear, E.A. & Resasco, D.E. SWNT-filled thermoplastic and elastomeric composites prepared by miniemulsion polymerization. Nano Lett. 2, (2002). 11. Kilbride, B.E. et al. Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films. J. Appl. Phys. 92, (2002). 12 nature MATERIALS

13 supplementary information 12. Park, C. et al. Dispersion of single wall carbon nanotubes by in situ polymerization under sonication. Chem. Phys. Lett. 364, (2002). 13. Haggenmueller, R., Gommans, H.H., Rinzler, A.G., Fischer, J.E. & Winey, K.I. Aligned single-wall carbon nanotubes in composites by melt processing methods. Chem. Phys. Lett. 330, (2000). 14. Stankovich, S. et al. Graphene-based composite materials. Nature 442, (2006). nature materials 13