Supplementary Figures Supplementary Figure 1

Transcription

1 Supplementary Figures Supplementary Figure 1 Optical images of graphene grains on Cu after Cu oxidation treatment at 200 for 1m 30s. Each sample was synthesized with different H 2 annealing time for (a) 1h, (b) 1h 30min and (c) 2hh 30min, respectively. Yellow circles present single graphene grain. (d) The number of grain per unit area as a function of H 2 annealing time.

2 Supplementary Figure 2 Graphene synthesis process for (a) 5 μm, and (b) 30~100 μm size domain. Domain size is confirmed by SEM image.

3

4 Supplementary Figure 3 SEM image of incompletely grownn graphene sheet with average (a) 5 μm, (b) 40 μm and (c)) 100 μm domain size on SiO 2 wafer w (300 nm). Each grain of graphene is marked with small alphabet letter. (d) Expanded image of (a). Each grain of Cu is marked with under-bar small alphabet letter and differentiated with w color inn magnified image.

5 Supplementary Figure 4 Optical microscope image of incompletely grown graphene sheet of which average domain size is (a) 5 μm, (b) 40 μm and (c) 1000 μm on copper foil.

6 Supplementary Figure 5 2D mapping image of Raman spectra for large size graphene

7 a) SAED mapping patterns of 100 μm graphene domain

8 b) Magnified SAED patterns and overlapped pattern Supplementary Figure 6 (a) SAED mapping patterns of 100 μm graphene sheet on TEM grid, (b) Magnified images off SAED pattern measured from 144 different points in a graphene domain and overlapped image. Intensityy of diffraction from white w dot, suspended graphene (number 5, 6 and 8) are much stronger than those from SiN membrane area.

9

10 Supplementary Figure 7 Alignment of LC on incomplete grown graphene of (a) 5 μm (b) 40 μm and (c) 100 μm domains which is wet transferred on glass. Cross polarizer is represented with cross arrows. Each grain of graphene and copper is marked with small alphabet letter and under-bar small s alphabet letter, respectively..

11 Supplementary Figure 8 POM images of graphene (~100 μmm in domain size) coated with 'A' LC molecules without a cover substrate with alignment layer. The quality of image is not as good as that with alignment layer to improve LC alignment.

12 Supplementary Figure 9 POM imagess of graphene before (a) and after (b) LC alignments. Red box region of graphene don t contain a PMMA residue (c). Bright dots in purple box indicate PMMA residues (d). In case of PMMA residues with relatively r small size and height (e and g, red line), there is nott clear difference in alignment of LCs between residue and pure graphene regions. On the other hand, in case of PMMA residues with relatively large size and height over 1.3 μm and 88 nm (e, f, blue line), the PMMAA domain exhibited different luminance compared to surrounding area, indicating different alignment a off LCs on the region from that on the pure graphene. However, since the residual PMMA domains populated sparsely, these didd not influence the overall LC alignment on graphene domainss or Cu domains, although the PMMA domains were indicated as defects.

13 Supplementary Figure 10 SEM (a) and AFM (b) images of a representative graphene sheet printed on glass. The surface profile images of c and d indicate that printed graphene sheet contains ripples and wrinkles withh the height of 7~8 nm. In addition, in some cases, a graphene sheet which is well transferred present very flat surface profile without t a ripple or a wrinkle as shown in Supplementary Figure 9c.

14 Rubbed polyimide : strong anchoring A A Rubbing direction A A Glass : weak anchoring Graphene : strong anchoring Supplementary Figure 11 Schematic illustration of LC alignment on a glass substrate coated with graphene islands. LC molecules on a glass substrate are aligned just along the upper rubbing polyimide layer. On the other hand, those on a graphene island with strong anchoring energy can be aligned as twisted structure.

15 Supplementary Figure 12 (top) Optical images of graphene synthesized by incomplete growth process on Cu foil (left: graphenee with domain of ~10 μm, μ middle: : ~20 μm and right: ~30 μm. (bottom) POM images of LC coated graphene films after a complete growth process. LC molecules with different orientations on the graphene domain exhibit various birefringent colors. The patterns of LC alignment are correspondent with that of Cu domains.

16 Supplementary Figure 13 Optical image of graphene domains (5 μm in size) with different orientation on different crystal planes of Cu. Right box indicatess the boundaries of crystal planes of Cu.

17 Supplementary Figure 14 POM images of graphene (100 μm in size) coated with 5CB single component LC molecules a function of time. Phase transition from nematic to smectic is not observed before all molecules are absorbed into PDMS.

18 a) b) Residual molecule compare to initial amount (%) 100% 80% 60% 40% 20% MIX. A 0hr MIX. A 6hr 0% Molecular weight Residual molecule compare to initial amount (%) 100% 80% 60% 40% 20% MIX. B 0hr MIX. B 6hr 0% Molecular weight Supplementary Figure 15 Molecular weight distribution and composition change of mixture A (a) and B (b) on PDMS.

19 a) 5 μm Gr. domain using mixture A LC b) 40 μm Gr. domain using mixture A LCC c) 100 μm Gr. domain using mixture A LC

20 d) 5 μm Gr. domain using mixture B LC e) 40 μm Gr. domain using mixture B LCC f) 100 μm Gr. domain using mixture B LCC

21 g) 5 μm Gr. domain using mixture A LC stretching (0.1% / min.) test h) 5 μm Gr. domain using mixture B LC stretching (0.1% / min.) test Supplementary Figure 16 LC phase transition as a functionn of time. Intrinsic pinhole or defect of graphenee with grain size of 5 μm, 40 μm and 100 μm induce the mixture LC A (a-c) and B (d-f) phase transition; Nematic LC mixture A and B show difference time scale and shape of smectic phase. (g, h) On 5 μm grain graphene, visualization of crack initiation throughh phase transition of LC mixture A and B with increasingg strain value of 0.1%/min.

22 Supplementary Figure 17 Calculation of the ratio of phase transition with image processing program. LC'A'-coated graphene sheet with 5 μm domain d on PDMS is stretched s by external strain of 2.25%.

23 Supplementary Figure 18 Raman measurement and opticall image of overlapped domain boundaries for graphene sheets with large domain size over 100 μm. Raman spectra exhibits clearly G/2D peak ratio similar to that of bilayer graphene, verifying that the overlapped boundary is composed of bilayer. Each peak was normalized with respect to G peak.

24 Supplementary Figure 19 Phase transition ratios vs. time for the LC mixture A on variety of graphene sheets: (a) with various domain sizes, or (b) transferred using different transferr processes. (c) The variations inn the phase transition ratio on the graphene/pdms substrate during stretching of the graphene/pdms substrate (green triangle) or in the absence of stretching (red square), and POM images of the LC phase transition.

25 *(R-R 0 ) / Ro (%) % Strain (%) d[100*(r-ro)/ro]/ d[strain] Supplementary Figure 20 Electric resistance of (5 μm domain) graphene sheet for strain stretching

26 Supplementary Figure 21 Optical images of 'A' LC alignments on graphene with domain size of 100 μm by utilizing cover substrate with vertical alignment layer (a) without stretching (b-c) with stretching. Although the cover substrate with vertical alignment layer can provide clearerr birefringence image than that with parallel layer, it is difficult to observe clearly the domain boundariess of phase when the phase transition from nematic to smectic or crystal begins to appear.

27 Supplementary Notes Supplementary Note 1. LC alignment on incomplete Gr. grain which transferred on glass. Nematic LC mixture A (JNC Chisso, IAN-5000XX T1) on the 40 μm, 100 μm size of graphene grain is well aligned following the single crystal graphene as shown in Supplementary Figure 7b-c. 17 In high magnification image, the monochrome color of LC domain on single graphene grain means that all LCs are well aligned in the one direction on each single grain. On the contrary, the LC domain on 5 μm size of graphene grain (Supplementary Fig. 7a) shows uneven color differently from 40 μm and 100 μm graphene grain in high magnification image, but, interestingly, uneven LC domain seems to follow copper domain from the macroscopic viewpoint of low magnification image owing to affection of the underlying copper crystal orientation. 21,41 Graphene seeds cannot avoid having a predominant direction. Thus, the director of LC also shows predominant direction. Supplementary Note 2. PMMA residues effect of LCs alignment. It is nearly impossible to remove PMMA residue perfectly after transfer process. Small amount of PMMA residue is always remained on top of graphene. As shown in magnified POM image of Supplementary Figure 7c, it is found that small black dots exist in graphene grain. These dots seem to be created by PMMA residues or dust particles. To check the effect of PMMA residues on LC alignment, AFM measurements were performed as shown in Supplementary Fig. 9. Supplementary Note 3. Surface roughness of graphene transferred to substrates. Graphene sheets grown by CVD method include ripples and wrinkles on the surface due to the difference in thermal conductivity between metal catalyst and graphene. Many of these ripples or wrinkles can be flattened during transfer process of graphene sheets to a flat substrate. To check the surface roughness of graphene sheets, AFM measurements were performed as shown in Supplementary Fig. 10. Supplementary Note 4. Optical image of graphene domains with different orientation on different crystal planes of Cu. In order to study clearly the distribution of graphene domains with different orientation on different crystal planes of Cu, we directly observe graphene

28 domains on Cu foil without transfer after light oxidation process for enhancing the contrast. As shown in Supplementary Fig. 13, Cu planes with different crystal orientation show distinct color, which help us to distinguish each plane. It is found that graphene domains with a specific orientation and shape are confined in a Cu domain. Supplementary Note 5. LCs alignment tendency by grain size of graphene. 10, 20 and 30 μm domains show the similar tendency with 5 μm one (Supplementary Fig. 12). Graphene domains in the range from 5 to 30 μm tended to grow within the Cu grains without moving far over the Cu grain boundary. Therefore, it is found that the grain size between 30 and 40 μm is the resolution of this method. In addition, Supplementary Fig. 13 shows clearly the distribution of graphene domains with different orientation on different crystal planes of Cu. Supplementary Note 6. Electric resistance measurement of 5 μm domain graphene sheet during stretching. The experimental result of visualization of crack initiation represents that graphene can endure the strain up to 2.20% (Fig. 4c). To verify our conclusion, the change of resistance is measured (left blue axis in Supplementary Fig. 20) while the strain is applied on the graphene, and the data was converted as change ratio of resistance for strain (right red axis in Supplementary Fig. 20). Interestingly, the change ratio of resistance as function of strain, which is maintained as a constant before 2.18% strain, abruptly increased exponentially after 2.18% strain value. Supplementary Methods The control of graphene grain size by suppressing the initiation of seed. The characteristics of graphene domains which grow on a Cu foil by CVD method can be affected by surface roughness and impurity particles of Cu foil, and crystal orientation and size of Cu grains Therefore, in order to increase the size of graphene domain, it is necessary to reduce initial seed density of graphene domains, which can be achieved by increasing the size of Cu grains and the surface flatness, and decreasing the number of impurity particles that can work as a nucleation site of graphene. 14,19,36-37 The size of Cu grain and the surface flatness, and many of impurity particles on top of Cu foil can be improved and removed, respectively, and the initial growth of seeds can be suppressed by high temperature annealing process under hydrogen environment before feeding hydrocarbon sources for graphene growth

29 Thus, this process can effectively reduce the number of nucleation sites and as a result, the seed density. 37,40 In addition, some of impurity particle that cannot be removed by H 2 annealing can be removed by acid treatment of Cu foil before CVD growth step. This pretreatment can also reduce the surface roughness of Cu foil. To see the dependency of graphene domain size on H 2 annealing time, graphene sheets were grown by an identical growth condition after different H 2 annealing time. As a result, it is found that the number of nucleated seeds is decreased as H 2 annealing time (Supplementary Fig. 1). Graphene, which has a limitation of grain size below 5 μm domain, was synthesized with conventional process (Supplementary Fig. 2a), Graphene with bigger grain size was prepared with the process as shown in Supplementary Fig. 2b, of which concept has been previously reported. 21 In order to suppress the density of graphene grain seed, copper foil was enclosed prior to insertion in the furnace. All the variables including temperature (1035 C), ratio of methane and hydrogen, and growth time, were fixed except for only hydrogen annealing time. As the annealing time increased, the graphene with bigger grain size up to 100 μm is synthesized as shown in bottom graph of Figure 2b. Observation of incomplete graphene having various grain size. The SEM images of incompletely grown graphene having various grain size, transferred on SiO 2 wafer (300 nm), present much information as well as the size of grain. Unlike the 5 μm graphene domain, the overlapping suspected dark line is observed from 40 and 100 μm domain graphene at the boundary of adjoining grains (Supplementary Fig. 3a-c). And, in the expanded image of 5 μm graphene domain, each Cu domain is clearly perceived from the shape of graphene domain. Comparison of graphene domain with that of Copper. To observe the domain of graphene and copper with reflective optical microscope, copper foil covered with incompletely grown graphene was oxidized by annealing (200 C for 1min) on the hot plate. 35 The grain boundaries of copper and graphene were obviously distinguished owing to their different reflectivity (Supplementary Fig. 4). Each grain of graphene and copper is marked with small alphabet letter and under-bar small alphabet letter, respectively. From the fact that graphene with the grain size of 40 μm and 100 μm is lies on two domains of Cu, it is betrayed that the growth of grain of graphene is not confined into the underlying Cu domain.

30 Characterization of large size graphene. The SAED mapping pattern was performed across the graphene sheets with 100 μm domain sizes and 14 different points. Graphene was transferred on SiN membrane TEM grid for measurement. For observation of a domain shape, graphene was prepared as a form of an island (Supplementary Fig. 6). These SAED patterns had very similar orientations, indicating that large size graphene domains form a singlecrystalline lattice structure. Although overlapped patterns exhibit a slight distortion, it resulted from the accidental folding of a sheet introduced during the transfer. Raman mapping images in Supplementary Fig. 6 of D-band for 100 μm domains show uniform color distribution inside of domains without detecting the disordered region between domains with different orientation, indicating each domain is composed of single domain with an orientation. The edge regions and overlapped boundaries exhibit the enhanced intensity. Gas Chromatography-mass spectrometry of mixture A and B. As shown in Supplementary Fig. 15, we measured the Gas Chromatography-mass spectrometry (GC-mass) to characterize the composition and the absorption rate of A and B LC mixtures into PDMS. According to GC result, mixture A is composed of four kinds of single molecules with relatively light molecular weight and mixture B is composed of nine kinds of molecules with relatively wide weight distribution and heavy weight. The slow phase change of mixture B on PDMS may result from slight change in composition and heavy weight of constituent molecules. Supplementary References 34. Bhaviripudi, S. et al. Role of kinetic factors in chemical vapor deposition synthesis of uniform large area graphene using copper catalyst. Nano Lett.10, (2010) 35. Han, G. H. et al. Influence of Copper Morphology in Forming Nucleation Seeds for Graphene Growth. Nano Lett.11, (2011) 36. Luo, Z. et al. Effect of Substrate Roughness and Feedstock Concentration on Growth of Wafer Scale Graphene at Atmospheric Pressure. Chem Mater. 23, (2011)

31 37. Shanshan Chen. et al. Millimeter Size Single Crystal Graphene by Suppressing Evaporative Loss of Cu During Low Pressure Chemical Vapor Deposition. Adv. Mater. 25, (2013) 38. Li, X. et al. Evolution of graphene growth on Ni and Cu by Carbon Isotope Labelling. Nano Lett. 9, (2009) 39. Li, X. et al. Graphene films with large domain size by a two step chemical vapor deposition process. Nano Lett. 10, (2010) 40. Ajmal, M. et al. Fabrication of the Best Conductor from Single Crystal Copper and the Contribution of Grain Boundaries to the Debye Temperature. Cryst Eng Comm. 14, (2012) 41. Wood, J. D. et al. Effects of Polycrystalline Cu Substrate on Graphene Growth by Chemical Vapor Deposition. Nano Lett. 11, (2011)