Supporting Information for. Patterning and Electronic Tuning of Laser. Scribed Graphene for Flexible All-Carbon Devices

Transcription

1 Supporting Information for Patterning and Electronic Tuning of Laser Scribed Graphene for Flexible All-Carbon Devices Veronica Strong, Sergey Dubin, Maher F. El-Kady,, Andrew Lech, Yue Wang, Bruce H. Weiller, and Richard B. Kaner,, Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, USA., Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt, Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California at Los Angeles, Los Angeles, California 90095, USA., Micro/Nano Technology Department, Space Materials Laboratory, The Aerospace Corporation, Los Angeles, California 90009, and Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California To whom correspondence should be addressed Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, USA. Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California at Los Angeles, Los Angeles, California 90095, USA. Micro/Nano Technology Department, Space Materials Laboratory, The Aerospace Corporation, Los Angeles, California Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California

2 Supplemental A common infrared laser that fits inside a CD/DVD optical drive unit, is shown to be a powerful tool in the efficient production of laser scribed graphene (LSG) conducting films, with results comparable to chemically converted graphene acquired through other methods. Although, graphite oxide has a minimal absorption in the infrared region as shown in Figure S1 a focused 788 nm infrared laser with a minimum power output of 5 mw provides enough energy to produce laser scribed graphene. The inexpensive infrared laser which emits at 788 nm not only generates large areas of highly reduced laser scribed graphene (hr-lsg) film, but can easily pattern complex and conducting images on different substrates with precision, all within a single step. Here we take advantage of LightScribe software, a program that allows users to create any image on the surface of a LightScribed enabled compact or digital video disc (CD/DVD) to effective reduce and pattern graphite oxide. The typical LightScribe enabled commercially available CD/DVD optical drive combines the specialized dye coating mixture on CD/DVD media to generate images.? Essentially, as the disk rotates concentrically, the 788 nm laser pulses up and down, causing the dye coating mixture to chemically alter and produce visible changes in the film. These visible changes make up the high quality image on the disk, which can be re-patterned many times without shifting the initially inscribed image. Unlike other expensive lithography methods, the typical investment for this process is below $30.00, which includes a LightScribe compatible DVD drive (LG drive model GH24LS50), LightScribe enabled media (DVD/CD), and printing software. Scanning electron microscopy (SEM) is used to understand the effects a low energy infrared laser has on the structural properties of GO film by comparing the morphological differences between highly reduced laser scribed graphene and un-treated graphite oxide film. Figure S2a illustrates the infrared laser s effect on graphite oxide film; prior to laser treatment, the GO film appears flat (right side of image) in contrast to the aligned, stacked laser reduced graphite oxide that occurs immediately after contact with the infrared laser 2

3 Figure S1: UV-vis absorbance spectra of graphite oxide shown in black. Inset: A magnified view of the boxed area showing the absorbance of graphite oxide with respect to the 788 nm infrared laser ( -) in the 650 to 850 nm region. (left-side of image). The image not only gives a clear definition between laser scribed graphene and un-treated GO regions, but also demonstrates the level of precision possible when using this method as a means to pattern and reduce graphite oxide. The regions of stacked and reduced graphitic carbon, which result from the laser treatment, can be further analyzed through cross-sectional SEM. The cross-sectional view shown in Figure S2b is of a free-standing film of laser treated and un-treated GO, which shows a significant difference between film thicknesses. In fact, laser scribed graphene increases in thickness by approximately 10 times that of un-treated GO film, as indicated by the blue brackets in Figure 2b. The increased thickness stems from rapid degassing of gases generated and released during laser treatment, similar to thermal shock, which effectively cause the reduced graphite oxide s expansion and exfoliation as these gases rapidly pass through the film. In addition, the film does not suffer any detrimental effects even after several irradiation cycles, and the film thickness remains consistent and stable even after several months in ambient conditions. Figure S2c is a cross-sectional image of a single laser scribed graphene stack, which clearly shows a porous and expanded structure. By magnifying a selected area within the stacked region in Figure 2c, the thickness of the expanded sheets can be calculated to be between 5-10 nm (Figure S2d). Additionally, transmission electron 3

4 Figure S2: Scanning electron microscope (SEM) images of laser scribed graphene (LSG). a) Top-view of GO before laser treatment (right) and after laser treating (left). Laser treating GO film results in large domains of stacked laser scribed graphene. b) Cross-sectional view of a free standing film, which compares the expanded and exfoliated laser scribe graphene film with that of graphite oxide film. An increase in film thickness is clearly visible for laser scribed graphene. c) A higher magnification cross-sectional view. d) Selective area magnification of LSG demonstrating the large open network, which results from the laser reduction process. 4

5 Figure S3: A transmission electron microscope (TEM) image of few layer laser scribed graphene deposited on lacy carbon TEM grids. Scale bar = 200 nm. 5

6 microscopy (TEM) was taken of the expanded and exfoliated laser scribed graphene film in order to fully characterize the film. As clearly visible by the highly transparent sheet shown in Figure S3, the laser irradiation of graphite oxide results in the generation of large thin sheets of few-layer laser scribed graphene, which is consistent with SEM analysis. Although irradiation from an infrared laser is only marginally absorbed by graphite oxide, with enough power and focus, it can cause sufficient thermal energy to efficiently reduce, deoxygenate, expand, and exfoliate graphite oxide film. Figure S4: Powder X-ray Diffraction of a) graphite, b) graphite oxide, and c) highly reduced laser scribed graphene. A powder X-ray diffraction (XRD) pattern of highly reduced laser scribed graphene is 6

7 compared to both graphite and graphite oxide diffraction patterns (Figure S4). A typical XRD pattern for graphite, shown in Figure S4a, displays the characteristic peak of 2θ = 27.8 with a d-spacing of 3.20 Å. An XRD pattern for graphite oxide, on the other hand, exhibits a single peak at 2θ = 10.76, which corresponds to an interlayer d-spacing of 8.22 Å(Figure S4b). The increased d-spacing in graphite oxide is due to the oxygen containing functional groups in graphene oxide sheets, which trap water molecules between the basal planes and the sheets which then expand and separate. 1 4 The XRD pattern of hr-lsg shows the presence of both GO ( θ) and a broad graphitic peak at θ associated with a d-spacing of 3.43 Å(Figure S4c). The GO presence in LSG is expected since the laser has an optimum penetration depth, which will result in the reduction of only the top portion of the film with the bottom layer being unaffected by the laser. The small presence of GO is more prominent in thicker films, but begins to diminish in thinner films. In addition, one can also observe a partially obstructed peak at θ, which shows a similar intensity to the broad θ peak. Both of these peaks, considered graphitic peaks, and are associated to two different lattice spacing between basal planes. It has been previously shown that the immobilization of carbon nanotubes (CNTs) on glassy carbon electrodes will result in a thin porous CNTs film, which directly affects the voltammetric behavior of the CNT modified electrodes. 5 In a ferro/ferrocyanide redox couple, the voltammetric current measured at the CNT modified electrode will likely have two types of contributions. The thin layer effect is a major type of contribution that stems from the oxidation of ferrocyanide ions, which get trapped between the nanotubes. The other contribution results from the semi-infinite diffusion of ferrocyanide towards the planar electrode surface. Unfortunately, the mechanistic information is not easily de-convoluted and requires knowledge of the film thickness. In our case, on the other hand, no thin layer effect is observed since a plot of log 10 of peak current versus log 10 of the applied voltammetric scan rate (Figure S5) is linear with a slope of 0.53 (the average of three measurements). A value that is very close to the theoretical value calculate using the 7

8 Figure S5: Electron transfer kinetics. Dependence of the peak current (i p ) of [Fe(CN)6 ]3 /4 redox couple on the applied scan rate (υ) for hr-lsg electrode. The peak currents were obtained from the cyclic voltammograms of hr-lsg electrode in 5 mm K3 [Fe(CN)6 ]/K4 [Fe(CN)6 ] (1:1 molar ratio) dissolved in 1.0 M KCl solution and run at scan rates 0.01 to 0.4 V/s. The plot is linear with a slope of 0.53 indicating a semi-infinite diffusion mechanism. 8

9 semi-infinite diffusion model as governed by the Randles-Sevcik equation: 6 i p = AC o Do ν(nf) 3 RT (1) The fact that graphene-based modified electrodes have no thin layer effect is similar to previous observations of other research groups. 7,8 References 1. Dikin, D. A.; Stankovich, S.; Zimney, E. J.; Piner, R. D.; Dommett, G. H. B.; Evmenenko, G.; Nguyen, S. T.; Ruoff, R. S. Preparation and Characterization of Graphene Oxide Paper. Nature 2007, 448, Park, S.; Lee, K.-S.; Bozoklu, G.; Cai, W.; Nguyen, S. T.; Ruoff, R. S. Graphene Oxide Papers Modified by Divalent Ions-Enhancing Mechanical Properties via Chemical Cross- Linking. ACS Nano 2008, 2, Buchsteiner, A.; Lerf, A.; Pieper, J. Water Dynamics in Graphite Oxide Investigated with Neutron Scattering. J. Phys. Chem. B 2006, 110, Lerf, A.; Buchsteiner, A.; Pieper, J.; Schöttl, S.; Dekany, I.; Szabo, T.; Boehm, H. P. Hydration Behavior and Dynamics of Water Molecules in Graphite Oxide. J. Phys. Chem. Solids 2006, 67, Streeter, I.; Wildgoose, G. G.; Shao, L.; Compton, R. G. Cyclic Voltammetry on Electrode Surfaces Covered with Porous Layers: An Analysis of Electron Transfer Kinetics at Single-Walled Carbon Nanotube Modified Electrodes. Sensors and Actuators B 2008, 133, Zoski, C. G., Ed. Handbook of Electrochemistry, 1st ed.; Elsevier: Radarweg 29, P.O. Box 211, 1000 AE Amsterdam. The Netherlands,

10 7. Hallam, P. M.; Banks, C. E. Quantifying the Electron Transfer Sites of Graphene. Electrochem. Commun. 2011, 13, Ambrosi, A.; Bonanni, A.; Pumera, M. Electrochemistry of Folded Graphene Edges. Nanoscale 2011, 3,