Chemical Vapor Deposition Graphene Grown on Peeled- Off Epitaxial Cu(111) Foil: A Simple Approach to Improved Properties

Transcription

1 Supplementary information Chemical Vapor Deposition Graphene Grown on Peeled- Off Epitaxial Cu(111) Foil: A Simple Approach to Improved Properties Hak Ki Yu 1,2, Kannan Balasubramanian 3, Kisoo Kim 4, Jong-Lam Lee 4, Manisankar Maiti 5, Claus Ropers 5, Janina Krieg 3#, Klaus Kern 3 and Alec M. Wodtke 1,2 * 1 Institute for Physical Chemistry, University of Göttingen, Göttingen, Germany 2 Max Planck Institute for Biophysical Chemistry, Göttingen, Germany 3 Max Planck Institute for Solid State Research, Stuttgart, Germany 4 Department of Materials Science and Engineering and Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang, Korea 5 IV. Physical Institute, University of Göttingen, Göttingen, Germany # Current address: GSI Helmholtz Center for Heavy Ion Research, Darmstadt, Germany * alec.wodtke@mpibpc.mpg.de

2 Figure S1. Domain mismatch in Cu/C-Al 2 O 3 system. a, Table for domain mismatch between Cu and C-Al 2 O 3. The 12/11 matching structure has the lowest domain mismatch at about nm. b, Schematic diagram of postulated atomic arrangement for Cu (111) projection to C-plane sapphire substrate based on 12/11 matching. In Fig. 1b, the X-ray diffraction of epitaxially grown Cu films (50 nm thick on c-al 2 O 3 ) exhibit 6-fold azimuthal symmetry despite the fact that Cu(111) is three fold symmetric. We attribute this to the six-fold symmetric Moiré pattern formed by Cu(111) on c-al 2 O 3.

3 Figure S2. Electron backscatter diffraction (EBSD) of Cu foils. Kikuchi band images of peeled-off Cu foil surface (measured by CCD camera in EBSD machine) a, from the green pixel in Fig. 2a b, from the orange pixel in Fig. 2a. There were only these two kinds of Kikuchi bands. The area fraction for green is 64 % and orange is 36%. c, EBSD map of normal Cu foil. This map clearly shows the polycrystalline Cu surface. d, Corrected pole figures of normal Cu foil obtained by EBSD.

4 Figure S3. O 1s XPS spectra of several Cu foils. This is related to the decrease of oxygen on peeled-off Cu surface compare to normal Cu foils. This tendency is coincident with Cu 2p signal in Fig. 2c.

5 Figure S4. Graphene growth on epitaxial Cu (111)/C-sapphire without plating and peeling off. Optical microscope images after graphene growth on epitaxial Cu film/csapphire substrate with respect to different growth temperature and time for the case of a, thin Cu (100 nm) and b, thick Cu (500 nm) films. The Cu films were easily evaporated from sapphire substrate although we used low growth temperature (until 850 o C) and short growth time (3 min). If we use thick epitaxial Cu film (500 nm) on C-sapphire, we can reduce these kinds of evaporation and migration problems. However, in this case (low temperature graphene growth to reduce Cu migration and evaporation), the solubility of carbon in Cu matrix is lower than high temperature growth, resulting in island growth of graphene as shown in c, SEM images after graphene growth on epitaxial Cu (500 nm)/csapphire at the condition of 850 o C, 3min CH 4 flow.

6 Figure S5. Pre-reduction of normal Cu foil removal of native oxide by acetic acid. a, SEM images after graphene growth on Cu foil using reductive annealing with hydrogen at 1000 o C for 30 min. No wet chemical reduction was employed. b, same as Fig. S2a but with additional acetic acid pre-reduction (acetic acid ~99.7% was used without further purification, dipping 10 min at 30 o C). The impurity particles are composed of copper and oxygen. The graphene folding structure is distorted by the copper oxide nanoparticles. There is a significant decrease in the size of impurity particles from acetic acid treatment. c, Elemental analysis of impurity particles and graphene obtained by area resolved energy dispersed X-ray spectroscopy (EDX). d, Schematic view of pre-reduction treatment for normal Cu foil in (NH 4 ) 2 S 2 O 8 solution.

7 Figure S6. Pre-reduction of normal Cu foil removal of native oxide by ammonium persulfate. Surface morphology of several Cu foils by SEM a, before graphene growth and b, after graphene growth. The effect of pre-reduction (middle panel) is to reduce or indeed nearly eliminate impurity copper oxide particles. Notice that the graphene folding pattern is much more uniform when the copper oxide nanoparticles are removed. Moreover, the graphene grown on peeled-off Cu foil (lower panel) also shows the clean and uniform folding patterns. c, Carbon 1s X-ray photoemission spectra (XPS) from the Cu foil surfaces after graphene growth and its dependence on pre-reduction with (NH 4 ) 2 S 2 O 8 solution. XPS spectra of graphene grown without pre-reduction (lower panel) show the presence of substantial sp 3 carbon as well as carbon-oxygen covalent bonding. The effect of pre-reduction (upper panel) is to reduce chemical oxidation of the graphene.

8 Figure S7. EBSD results of peeled-off Cu foil after graphene growth. Although the crystallinity was degraded after growth, it still shows the Cu (111) distribution.

9 Figure S8. High carrier mobility derived from Drude model fit to field effect measurements. For the graphene grown on the peeled-off Cu, the derived Dirac point (0.027 V) and intrinsic charge concentration cm -2 reflect a high quality graphene sample with high carrier mobility. The contact resistance is found to be kω and the gate capacitance is µf cm -2. For reference graphene, we find the charge carrier mobility is 5,000 cm 2 V -1 sec -1, with a Dirac point of 0.18 V and an intrinsic charge concentration of cm -2. The contact resistance is kω and the gate capacitance is µf cm -2.

10 Figure S9. Step-terrace of Cu foils after graphene growth. Surface morphology of Cu foils after graphene growth by AFM; a, b normal Cu foil and c, d peeled-off Cu foil. The both Cu foils have step-terrace structure after graphene growth. However, the stepterrace of peeled-off Cu surface shows the paralleled structure compare to that of normal Cu foil surface which shows a lot of curvatures. This means that the step-terrace structure of peeled-off Cu surface have an advantage of carrier mobility if the carrier moves the direction of without nano-ripples.

11 Figure S10. High carrier mobility derived from Hall bar measurements. a, 4-probe resistance of a graphene (on peeled-off Cu foil) Hall-bar as a function of the liquid gate voltage. b, Mobility and charge carrier concentration as a function of the liquid gate voltage. c, d, 4-probe resistance and mobility as a function of charge carrier concentration. Negative values on X-axis denote holes, while positive values denote electrons. We derive an electron mobility of 10,100 cm 2 V -1 sec -1 at an electron concentration of 4.7 x cm -2