Highly Conducting Graphene Sheets and. Langmuir-Blodgett Films

Transcription

1 Highly Conducting Graphene Sheets and Langmuir-Blodgett Films Xiaolin Li, Guangyu Zhang, Xuedong Bai, Xiaoming Sun, Xinran Wang, Enge Wang, Hongjie Dai * Department of Chemistry and Laboratory for Advanced Materials, Stanford University, Stanford, CA 94, USA Institute of Physics, Chinese Academy of Sciences, Beijing 0080, China * Correspondence to hdai@stanford.edu Supplementary Information with Supplementary Figures (1) Several control experiments of the preparation of single layer GS High yield GS suspension (Fig. S1a) was obtained by grinding exfoliated graphite with NaCl crystallites, oleum treatment and TBA insertion. We did various control experiments and found TBA insertion is key to the formation of high-yield single-layer high quality GS. We obtained very low yield of single layer GS without the TBA insertion step (Fig. S1b). Oleum treatment was important. We almost couldn t obtain any single layer GS if we skip the oleum treatment and only did the grinding with NaCl crystallites and TBA insertion (Fig. S1c). Grinding with NaCl crystallites was important too. We could get some single layer GS but the concentration of the suspension was low if we skip the grinding with NaCl crystallites and only did the oleum treatment and TBA insertion (Fig. S1d). 1

2 (a) (b) (c) (d) Figure S1. Photograph of the graphene sheet suspension and some control experiments. (a) Regular graphene sheet suspension obtained by grinding with NaCl crystallites, oleum treatement, and TBA insertion. (b) Suspension obtained without TBA insertion. (c) Suspension obtained without oleum treatment. (d) Suspension obtained without grinding with NaCl crystallites. (2) Histogram of GS size and topographic height We measured the size and height of >0 graphene sheets. Fig. S2a and Fig. S2b showed the size and topographic height histogram. Based on the AFM results, about 90% of the samples are single layer graphene sheets. The rest of the sample are two- or multilayer graphene sheets. These single layer GS have an average size of about nm (Fig. S2a) and height of about 1nm (Fig. S2b and Fig. S3). The height measurement of our single layer graphene was also consistent with the reported AFM results on few-layer graphene sheets, where the single layer graphene is always ~1nm (1, 2). 1 Novoselov, K. S., Geim, A. K., Morozov, S.V., Jiang, D., Zhang, Y., Dubonos, S. V., Grigorieva, I. V., Firsov, A. A. Science 6, 666 (04). 2 Gupta, A., Chen, G., Joshi, P., Tadigadapa, S., Eklund, P. C. Nano Lett. 6, 2667 (06). 2

3 Percentage (%) (a) R1 Percentage (%) L (nm) (b) R Height (nm) Figure S2: (a): Size (topographic size from AFM data) histogram of GS measured over 0 sheets. (b): Height (topographic height from AFM data) histogram of GS measured over 0 sheets nm 0.963nm 3

4 1.08nm 1.081nm Figure S3. Topographic height profiles of several GS. The height of these GS is ~ 1.0nm. In each row, the left image is a zoom-in image of the GS, with which topographic analysis is done. (3) LB equipment and isothermal curve GS LB films were made using a commercial KSV-Minimicro 00 LB trough (Fig. S4). About 1.2mL of GS/DCE suspension was added to a water subphase in the LB trough. A platinum plate was used to monitor the surface tension during compression of the GS on the water subphase by moving the two opposing barriers towards each other. 4

5 The isothermal curve was recorded during the compressing procedure to a target ~27mN/m pressure (Fig. S) prior to film transfer. Figure S4. Making Langmuir-Blodgget Films of GS. A photograph of the LB trough used equipped with two movable Teflon barriers, pressure measurement plate and dipper for film transfer onto solid substrates. Isothermal curve Surface tension (mn/m) Barrier position (mm) Figure S. Isothermal curve recorded during the compressing procedure to reach a targeted 27mN/m pressure prior to film transfer.