Supplementary Information for Origin of New Broad Raman D and G Peaks in Annealed Graphene Jinpyo Hong, Min Kyu Park, Eun Jung Lee, DaeEung Lee, Dong Seok Hwang and Sunmin Ryu* Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi 446-71, Korea *E-mail: sunryu@khu.ac.kr Contents A. Presence of broad G peak, G ac B. Raman spectrum of carbon black in comparison with that of annealed graphene C. Effects of thermal annealing in CVD-grown graphene D. Raman spectrum of PMMA film E. Annealing-induced change in height profiles of 2L graphene F. Morphology analysis of ac layers on 1L graphene G. References 1
A. Presence of broad G peak, G ac 15 1 5 14 15 16 17 24 26 28 3 Raman shift (cm -1 ) Figure S1. Raman spectrum of exfoliated graphene annealed in Ar gas: T anneal = 4 o C, τ anneal = 3 min. With a Lorentzian function (green) for D ac, the G peak region is nicely fitted with two Lorentzian functions, respectively centered at 1587 and 163 cm -1. The former (red), G ac, is due to the amorphous carbons, whereas the latter (orange) originates from the graphene itself. The 2D peak, however, can be fitted with a single Lorentzian function, since the 2D ac peak with much smaller intensity and larger width overlaps 2D only slightly (see Fig. 1d). 2
B. Raman spectrum of carbon black in comparison with that of annealed graphene (a) 2 15 1 5 graphene, annealed at 4 o C carbon black (b) 25 2 15 1 5 D G 2D D+D' 1 15 2 25 3 35 Raman shift (cm -1 ) Figure S2. (a) Raman spectrum of carbon black powder (OCI, EG22) in comparison with that of exfoliated graphene annealed in Ar gas (T anneal = 4 o C, τ anneal = 3 min). (b) Expanded view of (a). The peak denoted by D+D is a combinational mode between D and D modes. 3
C. Effects of thermal annealing in CVD-grown graphene Deposition of ac was found to occur on CVD-grown graphene transferred onto SiO 2/Si substrates using poly(methyl methacrylate) (PMMA) supports. [1] Figure S3a presents an optical micrograph of a typical CVD graphene sample, entire region of which is covered by 1L graphene with multilayer dots (marked by arrows; diameter of ~1 μm) covering small fraction (< a few %) of the area. Raman spectra for as-prepared sample in Fig. S3b and S3c revealed D peak of noticeable intensity indicating that there is non-negligible amount of defects including the microscopic wrinkles and folds generated during the transfer process. [2] In addition to the D peak, there appear several sharp peaks in the range of 11 ~ 15 and 28 ~ 36 cm -1. The intensity of each peak varied from spot to spot and sample to sample suggesting high heterogeneity. Since removal of PMMA by acetone is known to be incomplete, [3, 4] these peaks are attributed to PMMA residues on graphene (see Fig. S4 for Raman spectrum of PMMA films). Upon annealing in Ar atmosphere which carbonizes hydrocarbons, however, most of the PMMA-derived peaks were converted into D ac, G ac, 2D ac and (D+D ) ac of much higher intensity than those of the exfoliated graphene. Thus, the ac-derived peaks were attributed to amorphous carbon generated from the PMMA residues. 4
a b 2 15 1 5 T anneal ( o C) pristine 3 4 5 6 7 c 6 1 μm 4 2 1 15 2 25 3 35 Raman shift (cm -1 ) Figure S3. The effects of thermal annealing in graphene grown by CVD. (a) Optical micrograph of single layer graphene transferred on to SiO 2/Si substrates. The entire area is covered by 1L graphene, whereas multilayer graphene, marked by yellow arrows, covers a small fraction of the whole area. (b) Raman spectra of CVD-grown graphene obtained before and after annealing for 2 hours at various temperatures in Ar gas. Separate samples were used for each of the annealing measurements. (c) Expanded view of (b). Raman peaks other than G, D and 2D from the pristine graphene (black) originate from residues of PMMA used as a support during etching and transfer processes. 5
D. Raman spectrum of PMMA film (a) 2 graphene PMMA 2D 15 1 5 G (b) 4 2 1 15 2 25 3 35 Raman shift (cm -1 ) Figure S4. (a) Raman spectrum of PMMA film drop-cast on SiO 2/Si substrates in comparison with that of CVD-grown graphene supported on SiO 2/Si substrates. (b) Expanded view of (a). 6
E. Annealing-induced change in height profiles of 2L graphene 8 6 t anneal = 8 hrs Height (nm) 4 2-2..5 1. 1.5 2. Position ( m) oxidized Figure S5. Height profiles of 2L graphene obtained along the white lines of Fig. 3b~3f, respectively from bottom to top. The vertical dotted line points to one of the 1L-deep pits in the white circle of Fig. 3b. 7
F. Morphology analysis of ac layers on 1L graphene a b c 1. Frequency (a.u.).8.6.4.2 Figure S6. Different surface morphology of amorphous carbon layers generated on 1L graphene by thermal annealing at 4 o C in low vacuum. (a) Non-contact AFM height images (2x2 μm 2 ) of exfoliated single layer graphene annealed for 3 min. (b) Non-contact AFM height images (2x2 μm 2 ) of exfoliated single layer graphene annealed for 8 hours. The right bottom corner of the image reveals the bare substrate. (c) Height distributions of (a) shown by red diamonds and (b) by black circles. While the latter is fitted well with a Gaussian function, the former was decomposed into two Gaussians (dash-dotted line and short dashed line). The samples are identical to those used in the Raman measurements to obtain Fig. 2b.. -1. -.5..5 1. Height (nm) G. References 1. Bae, S.; Kim, H.; Lee, Y.; Xu, X. F.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Kim, H. R.; Song, Y. I.; Kim, Y. J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S., Nat. Nanotechnol. 21, 5 (8), 574-578. 2. Ahn, G.; Kim, H. R.; Ko, T. Y.; Choi, K.; Watanabe, K.; Taniguchi, T.; Hong, B. H.; Ryu, S., ACS Nano 213, 7 (2), 1533-1541. 3. Lee, W. H.; Park, J.; Sim, S. H.; Lim, S.; Kim, K. S.; Hong, B. H.; Cho, K., J. Am. Chem. Soc. 211, 133 (12), 4447-4454. 4. Lin, Y. C.; Lu, C. C.; Yeh, C. H.; Jin, C. H.; Suenaga, K.; Chiu, P. W., Nano Lett. 212, 12 (1), 414-419. 8