Highly uniform growth of monolayer graphene by chemical vapor deposition on Cu-Ag alloy catalysts.

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Highly Uniform Growth of Monolayer Graphene by Chemical Vapor Deposition on Cu-Ag Alloy Catalysts Hae-A-Seul Shin§a, Jaechul Ryu§b,c,d, , Sung-Pyo Chob, Eun-Kyu Leec, Seungmin Choc, Changgu Leed, Young-Chang Joo*a and Byung Hee Hong*b

Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x www.rsc.org/pccp

One of the major challenges for the practical application of graphene has been the synthesis of large scale and uniform films with higher quality at lower temperatures. Here, we demonstrate that the use of Ag-plated Cu substrates is very useful to synthesize high-quality graphene films via chemical vapor deposition (CVD) of methane gas at the temperature as low as 900 ℃. Various experimental analyses show that the plated Ag diffuses into Cu to form a uniform CuAg alloy that suppresses the formation of multilayer nucleation and decreases the activation energy of precursor formation, leading to the lower synthesis temperature with enhanced monolayer coverage. In addition, we also observed unusual Ag-assisted abnormal grain growth of Cu into cube texture with larger grain sizes and reduced grain boundaries, which is believed to provide homogeneous environment needed for uniform graphene growth.

Introduction Graphene, a one atom thick film composed of carbon atoms arranged in a regular hexagonal pattern, has received much attention from many researchers due to its fascinating electrical, mechanical, optical, and thermal properties1-6. Since the first discovery of graphene by mechanical exfoliation from graphite1, various industry-compatible methods for graphene synthesis have been investigated to fully realize its potentials. Among those, particularly, a CVD growth method using commercially available Ni or Cu foil7-8 as catalyst have shown great promises for mass and large-scale production of graphene. One can still find, however, a fundamental tradeoff between process temperature and uniformity control when using Cu and Ni; Cu enables the synthesis of highly uniform monolayer graphene owing to its self-limiting characteristics but it needs relatively high process temperatures about 1,000 ℃ . On the other hand, Ni allows lower process temperatures while it shows less control over number of graphene layers and hence with poor lateral uniformity. In an attempt to mitigate such tradeoff and thereby achieve uniform graphene growth at low temperatures, several new catalytic designs utilizing alloy metals such as Cu-Ni, Ni-Au, and Ni-Mo9-12 have been suggested. However, such Ni-based alloys usually result in limited uniformity and quality because carbon atoms precipitated from Ni are unfavorable to form a graphene film with high uniformity. In other point, there some trial of low temperature synthesis of graphene with other carbon precursors such as toluene or solid/liquid source13, 14.

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Synthesis of graphene flakes were achieved from these research however, synthesized graphene had limitation to form a uniform film. Thus, we propose a new binary Cu-based metal alloy with Ag plating and demonstrate that a highly uniform single layered graphene can be grown at considerably low temperature as low as 900 ℃. The electroplating of Ag on a Cu foil offers several advantages over conventional evaporation or sputtering methods, demonstrating its superior suitability for costeffective high-throughput manufacturing systems. In addition, the plating technique is readily roll-to-roll compatible and energy-efficient compared to the vacuum- and hightemperature-processed evaporation and sputtering techniques. It also provides well controlled thickness and composition along the length and width of the substrates. Moreover, the plating method can minimize the waste of deposit materials and protect the Cu surface from oxidation. The Ag-plated Cu can be homogeneously alloyed by annealing during the ramping up stage of the CVD process. The graphene synthesized by Cu-Ag alloys were carefully characterized by various analytical methods. Raman spectroscopy and transmission electron microscopy (TEM) analyses were conducted to confirm the structural properties of the synthesized graphene films. The behaviors of Ag adlayers were investigated using X-ray diffraction (XRD), dynamicsecondary ion mass spectrometry (D-SIMS) and electron backscatter diffraction (EBSD) measurements. Overall analysis results show that the use of Ag clearly enhances the uniformity and the quality graphene possibly due to microstructural

Phys. Chem. Chem. Phys., 2013, 00, 1-3 | 1

Physical Chemistry Chemical Physics Accepted Manuscript

Published on 06 December 2013. Downloaded by St. Petersburg State University on 18/12/2013 20:38:32.

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Physical Chemistry Chemical Physics

PCCP DOI: 10.1039/C3CP54748E

Figure 1 Raman spectra of graphene synthesized on (a) Cu and (b) Ag200Cu at 800 ℃, 900 ℃ and 1,000 ℃. Optical microscopic images of graphene synthesized on (c) Cu (d) Ag200Cu at 900 ℃ for 40 min. Uniform and complete graphene film was synthesized for Ag200Cu at 900 ℃.

changes (texture and grain sizes) in Cu-Ag allows as we will discuss in the later part our manuscript.

Experimental In this study, six different catalytic substrates for graphene synthesis were prepared by electroplating Ag with varying thickness of 50, 100, 200, 300, 500, and 1000 nm on 35 µm thick Cu foils (purity 98.85 %, Japan Energy Co.), which are labeled as Ag50Cu, Ag100Cu, Ag200Cu, Ag300Cu, Ag500Cu, and Ag1000Cu, respectively. The electroplating was performed using potassium silver cyanide as electrolyte with a deposition rate of 5.0 µm/min at a current density of 10 ASD (ampere per square decimeter). Ag plating were performed after removing Cu corrosion inhibitor layer by dipping the Cu foil in 5-10 % H2SO4 solution for 30-60 sec at 25-30 °C. The plating thickness after the process was confirmed using a common thickness measurement tool (Fischerscope MMS PC) that is capable of measuring variation of magnetic induction by thin films coated on metal substrates. Since the plating thickness linearly depends on the deposition time, the Ag deposition thickness of 50 nm~1,000 nm can be precisely controlled by switching the applied current within 0.6~12.0 sec. Overall, seven types of catalytic substrates were used in the experiments including bare Cu foils. Then, graphene was synthesized using a thermal CVD system with a 4 inch quartz tube (Graphene Square Inc.). Each of the seven types of catalytic substrates (5ｘ7 cm2 in size) was inserted inside of the quartz tube and then heated from room temperature to synthesis temperatures; 800 ℃ , 900 ℃ , and 1,000 ℃. The temperature of the CVD chamber was ramped up

2 | Phys. Chem. Chem. Phys., 2013, 00, 1-3

at the rate of 20 ℃ /min with flowing 8 sccm of H2. After reaching the target synthesis temperatures, CH4 gas was injected with flow rates of 35 sccm and H2 flow was maintained with 8 sccm at 1,000 mTorr for 40 min. Finally, the sample was cooled down to room temperature with flowing H2 at 70 mTorr. After the synthesis, the graphene on the catalytic substrate was protected by spin-coating poly methyl methacrylate (PMMA) and the underlying Cu was etched in aqueous (NH4)2S2O8 (APS; ammonium persulfate) 0.06 M solution. Additional etching of Ag was performed using dilute solution of nitric acid (HNO3) and sulfuric acid (H2SO4). The PMMA transferred onto a SiO2/Si substrate was removed using acetone.

Results and discussion Optical Analysis Using Raman spectroscopy, the qualities of graphene films synthesized on various catalytic substrates with different synthesis temperatures were compared. Fig. 1a and b show Raman spectra of graphene films transferred onto a SiO2/Si wafer, where the graphene films were synthesized on Cu and Ag200Cu at 800 ℃, 900 ℃ and 1,000 ℃, respectively. For the synthesis temperature of 1,000 ℃ , both Cu and Ag200Cu resulted in high quality graphene films; the intensity ratios of 2D to G Raman spectra peaks, I2D/IG, were 2.35 and 3.33, respectively. However, for 900 ℃ , the I2D/IG value differed from Cu and Ag200Cu; 2.25 vs. 3.66. D peak stood out in the Cu catalyst and it implies the increased defect in graphene. 900 ℃ is lower than the generally known synthesis temperatures of



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ARTICLE DOI: 10.1039/C3CP54748E 2b, and this result was similar for the graphene on pure Cu as shown in the Fig. 1c. On the other hand, for thicker Ag plating thickness above 100 nm, the synthesized graphene exhibited superior quality with complete coverage particularly for 200 nm and 300 nm.Ag500Cu and Ag1000Cu also show complete coverage with partial adlayer islands or multilayers, and more multilayers were observed for Ag1000Cu by an optical microscope. To evaluate the uniformity of synthesized graphene on Ag plated Cu, Raman G and 2D band mapping was employed to the graphene grown on Cu, Ag200Cu and Ag500Cu at 900 ℃ (see Supplementary Information). As shown in Fig. S1, the G band mapping results show the partial coverage for the Cu only case but complete coverage for Ag200Cu and Ag500Cu substrates. From these results, we achieved to synthesize the highly uniform graphene film with Ag plated Cu. In addition, the optimized thickness of Ag plating is found to be 200-300 nm for the growth of uniform and high-quality monolayer graphene from the results of Fig. 2 and Fig. S1. Taking into account of the cost effectiveness of plating process, the 200 nm plating thickness of Ag was selected for further study. Graphene Crystalline Quality Analysis

Figure 2 (a) Raman spectroscopy and (b) optical microscopic images of graphene synthesized on Ag50Cu, Ag100Cu, Ag200Cu, Ag300Cu, Ag500Cu, Ag1000Cu at 900 ℃for 40 min. Optimized thickness of Ag plating is suggested as 200-300 nm for the synthesis of uniform and firm monolayer graphene. 1,000-1,050℃ for Cu catalyst. As for Ag200Cu, the observed negligible D peak and high I2D/IG value indicated a graphene quality comparable to or higher than that of graphene synthesized on Cu at commonly reported temperatures, e.g., 1,000-1,050 ℃. In addition, an optical microscope observation (Fig. 1c and d) showed that an incomplete film was synthesized on Cu in contrast to a complete film devoid of adlayer islands on Ag200Cu. For 800℃, no graphene was formed on Cu, but graphene was formed on Ag200Cu. These results indicate that Ag can definitely reduce the growth temperature of CVD graphene, and Ag on Cu plays an important role in achieving uniform and complete graphene film at a low synthesis temperature. To find the optimum Ag thickness, various samples were compared. Fig. 2 shows the Raman spectra and optical images of graphene films synthesized on Ag plated Cu substrates with different Ag thickness, i.e., Ag50Cu, Ag100Cu, Ag200Cu, Ag300Cu, Ag500Cu and Ag1000Cu at 900 ℃. The values of I2D/IG are 1.10, 1.97, 3.66, 4.37, 2.38 (1.83) and 1.83 (0.60), respectively; the values in parentheses were measured from multilayer regions, if any. Graphene on Ag50Cu and Ag100Cu showed relatively incomplete film synthesis as shown in Fig.


The perfection of crystal lattice of the graphene films grown on various catalysts at 900 ℃ for 40 min were further investigated by TEM (JEOL JEM-2100 operating at 200 kV). The representative TEM images and selected area electron diffraction (SAED) patterns are shown in Fig. 3. For the graphene synthesis on Cu, incomplete film was grown on the overall area in the form of graphene islands as shown in Fig. 1d, and torn or undergrown regions were confirmed in the TEM images as shown in Fig. 3a. The SAED patterns obtained from the graphene synthesized on Cu (Fig. 3b, insets) show the six-fold symmetry feature of graphene. From the analysis of the intensity diffractions15, 16, the graphene synthesized on Cu was confirmed to be a monolayer with a high crystal quality. The average graphene domain sizes were 3-5 µm, 2-3 µm, and 1-2 µm for Cu, Ag200Cu, and Ag500Cu, respectively (Fig. 3). To measure the actual domain size of the complete graphene film, the domain boundary mapping of synthesized graphene film was carried out by putting together points with the identical SAED patterns, and it is denoted by white dotted lines in the TEM images. The average domain size of graphene on Cu was measured to be 3-5 µm. Next, as shown in Fig. 3c, the same TEM analysis also showed that graphene synthesized on Ag200Cu were also a monolayer and a high-quality crystal. The domain boundary of the synthesized graphene displayed by the white dotted line and their average size had 2-3 µm. Finally, the SAED patterns for Ag500Cu (Fig. 3d) indicated bilayer and monolayer graphene, respectively. These results show that monolayer domain graphene is formed overall areas of TEM sample but that multilayer domains exist on some parts of the sample. Also, the graphene synthesized on Ag500Cu had high crystalline quality. The average size of monolayer domain boundary represented by the white dotted line was determined to be 1-2 µm. From the TEM analysis, we demonstrated the



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PCCP DOI: 10.1039/C3CP54748E


Given the dependency of domain size and crystalline quality of synthesized graphene on the Ag thickness, the behavior of Ag layers during the heating process should be clearly identified. To investigate the mobility of Ag atoms with increasing temperature, surface study for Ag200Cu after annealing at 400 ℃, 600℃, 800℃ and 1,000 ℃ was conducted. All conditions such as temperature ramping rate, H2 gas flow rate and annealing time were identical with the conditions for graphene synthesis except CH4 was not used. Table 1 Surface atomic composition of Ag and Cu in Ag200Cu before annealing and after annealing at 400 ℃, 600 ℃, 800 ℃ and 1,000 ℃. Ag (at %)

Figure 3 TEM images of graphene synthesized at 900℃. The inserts show the SAED patterns of graphene. (a) Incomplete growth with the folded cluster of graphene and graphene hole was observed in graphene synthesized on Cu. (b) Graphene synthesized on Cu; monolayer. (c) Graphene synthesized on Ag200Cu; monolayer. (d) Graphene synthesized on Ag500Cu; monolayer and multilayer. high crystalline quality of graphene synthesis on Ag200Cu. Although identical synthesis conditions were applied, domain size and crystalline quality of synthesized graphene were varied with the addition of thin Ag layer. Graphene domain was smaller as the thickness of plated Ag was increased. This result is induced by the nucleation enhancement of graphene in Ag plated Cu, and the effect of Ag will be discussed further in detail.


Cu (at %)

Unannealed

99.70

0.30

400 ℃

99.78

0.22

600 ℃

78.85

21.15

800 ℃

0

100

1,000 ℃

0

100

Table 1 shows the surface atomic percent of Ag and Cu of Ag200Cu before and after annealing at 400 ℃, 600 ℃, 800 ℃ and 1,000 ℃ measured by energy dispersive x-ray spectrometer (EDS, equipped in SEM, HORIBA X-Max50 006) and Fig. 4a shows the scanning electron microscopic (SEM, Hitachi SU-70) images of Ag200Cu after annealing at each of the annealing temperatures. Because Ag was plated on Cu, Ag covered the surface of Cu foil and its atomic percentage measured by EDS was 99.70 % before annealing. The measured percentage of Ag was then found reduced to 78.85 % with annealing at 600 ℃, and, ultimately, the atomic percent of Ag was 0 % after annealing at 800 ℃ and 1,000 ℃. Such results were consistent with the SEM images of Cu surface after annealing. Some part of Cu foil surface was observed to be exposed over Ag layer and for annealing temperatures above 800 ℃, Ag layer became completely imperceptible against Cu foil. Two mechanisms, diffusion and evaporation, are supposed to be responsible for the movement of Ag. For Ag200Cu, the atomic percent of Ag can be calculated as 0.79 at% assuming that all of the plated Ag diffused in Cu foil with the increasing temperature; 0.19 at% for Ag50Cu, 0.39 at% for Ag100Cu, 0.79 at% for Ag200Cu, 1.18 at% for Ag300Cu, 1.97 at% for Ag500Cu and 3.94 at% for Ag1000Cu. Given the maximum solubility of Ag in Cu, 5% at 900 ℃, diffusion of 200nm thick Ag layer into 35 µm thick Cu foil is possible. The amount of diffusion and evaporation of Ag with 200 nm thick was calculated for 35 µm thick Cu foil during increasing temperature using diffusivity of Ag in Cu (Ref. 17) and evaporation rate of Ag (Ref. 18). Both of diffusivity and evaporation rate are exponential for temperature therefore diffusion and evaporation are very fast at 900 ℃. However diffusion rate is much faster than evaporation rate during



Alloying Behavior Analysis of Cu-Ag Catalyst



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Figure 4 Formation of Cu-Ag alloy during increasing temperature before graphene synthesis. (a) SEM images of annealed sample of Ag200Cu. Annealing temperature was 400 ℃, 600 ℃, 800 ℃ and 1,000 ℃. (b) D-SIMS depth profile of Ag and Cu for Ag200Cu after graphene synthesis at 900 ℃ for 40 min. (c) X-ray diffraction patterns of Ag200Cu after annealing at 400 ℃, 600 ℃, 800 ℃ and 1,000 ℃.

increasing temperature before synthesis; possible diffusion thickness of Ag is about 94 nm at 600℃ and 462 nm at 800 ℃ otherwise evaporation thickness of Ag is 1.9 nm at 600 ℃ and 31 nm at 800 ℃. For the temperature excursions in the synthesis process, most of Ag would diffuse in Cu foil before the vaporization. Taking into account of 0.5 to 1.0 percent limit resolution of EDS, the measured 0 at% of Ag after annealing at 800℃ and 1,000℃ may indicate the presence of Ag less than 1 % of Cu foils. Depth Analysis on Cu-Ag Alloying In-depth distribution analysis of Ag and Cu was conducted by D-SIMS (Cameca IMS 4FE7) on Ag200Cu after graphene synthesis at 900 ℃ for 40 min. Ag200Cu was sputtered by Cs+ ion and the graph in Fig.4b shows the secondary ion count rate of Ag and Cu as a function of time. During the 60 min of sputtering time, 3.8 µm depth of Cu was measured and 107Ag and 109Ag were found at the same concentration for every location from the surface to 3.8 µm sputter depth. The observed uniform concentration suggest that Ag diffusion was complete and it was well distributed all over the Cu foil due to the fast diffusivity of Ag in Cu17. Fig.4c shows the XRD (Bruker Miller Co., D8-Advance) patterns of Ag200Cu before annealing and after annealing at 400 ℃, 600 ℃, 800 ℃ and 1,000 ℃. Before annealing, Ag (111), (200), (220) and (311) peaks were shown


in the XRD results. These peaks were observed until 600 ℃and they disappeared for 800 ℃ and 1,000 ℃ . In addition, a shoulder appeared and increased gradually on the left side of Cu (200) peak for annealed samples with increasing annealing temperature. The shoulder is attributed to the presence of Ag at the substitutional sites in Cu foil due to the diffusion of Ag during annealing19. These results are consistent with the SEM results in Fig. 4a that surface was covered with Ag below 600 ℃ and Cu-Ag alloy was exposed at deposition temperature. Even though less than 0.79 % of Ag existed in Cu foil for Ag200Cu, these Ag atoms in Cu-Ag alloy must have affected the nucleation and growth of graphene. For the understanding of graphene growth, C-C interaction is necessary to be taken into account since C adatoms are known to form strong covalent bonds with one another when they nucleate to form graphene. In this regard, dimers are more stable than separate C adatoms by over 2 eV20. In addition, relatively weak C-Ag bonds are energetically more favorable than C-Cu or C-other metal since C dimers would weaken the C-metal bonding, and it has been reported that the weaker the C-metal interaction is, the more preferred are the C dimers20. Furthermore, because binding energy difference between a C dimer (∆Edimer) and two C monomers (2∆EC) is much more negative for Ag than Cu20, nucleation of dimers is preferred on Ag sites and this dimer nucleation promotes graphene synthesis in Cu-Ag alloy.



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PCCP DOI: 10.1039/C3CP54748E

Figure 5 EBSD orientation maps of Cu after graphene synthesis on Cu (a) and Ag200Cu (b) at 800 ℃, 900 ℃, 1,000 ℃; Scale bars, 200 µm. Misorientation angle distribution of Cu after graphene synthesis at 800 ℃, 900 ℃ and 1,000 ℃ on Cu (c) and Ag200Cu (d).

Texture Analysis It is also interesting that Cu texture of Ag plated Cu after graphene synthesis was significantly different with that of Cu after graphene synthesis. Fig. 5a and b show the electron backscatter diffraction (EBSD) results of Cu after graphene synthesis on Cu and Ag200Cu after graphene synthesis at 800 ℃, 900 ℃ and 1,000 ℃. The ratio of (100) texture in normal direction (ND; surface of the Cu foil on which graphene was synthesized) result are shown in table 2. The percentage of (100) increases with increasing temperature for both Cu and Ag200Cu, however the percentage of Ag200Cu is significantly larger than Cu for every temperature; 53-59 % for Cu and 90-98 % for Ag200Cu. Such dominance of (100) texture is also observed for other Ag plating thicknesses; the percentage is ~94 % for Ag500Cu after synthesis at 900℃ (Fig. S2a). We also found the significant grain growth of Cu to cube texture in case of Ag plated Cu during graphene synthesis. A detailed texture analysis revealed that most of the observed (100) texture in ND possess (100) texture in rolling direction


(RD) and transverse direction (TD) at the same time. Fig. S2b shows the texture analysis results in the ND, RD and TD for Ag200Cu after 1,000 ℃ graphene synthesis. This figure shows most of the Cu orientations are (100) however (110) and (111) textures are not observed, which indicates that the Cu texture is mostly (100), i.e., cube texture21.Generally cube texture is observed for heavily rolled or highly purified rolled Cu22-24. The addition of Ag may retard the development of cube texture from the point of purity of Cu. However cube texture was developed with the graphene synthesis in Ag admixed Cu and these conditions may induce the microstructural evolution and boundary characteristics in Cu. Table 2 Ratio of (100) texture in ND after graphene synthesis at 800 ℃, 900 ℃, 1,000 ℃ on Cu and Ag200Cu. Percentage of (100) in ND

Cu

Ag200Cu

Synthesis at 800 ℃

53.8 %

90.6 %

Synthesis at 900 ℃

54.9 %

92.7 %

Synthesis at 1,000 ℃

59.1 %

98.1 %




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For the in-depth discussion of Cu microstructural change the misorientation angle distribution of Cu after graphene synthesis on Cu and Ag200Cu at 800 ℃, 900 ℃ and 1,000 ℃ are shown in Fig. 5c and d. Both of The Cu and Ag200Cu exhibited different misorientation angle distributions. Both of Cu and Ag200Cu were not follow the Mackenzie plot which Therefore, the proportion of twin boundaries is found to decrease with the increase of both the synthesis temperature and proportion of cube texture. In other point, proportion of the randomly oriented grain boundaries decreased and low angle grain boundaries increased for Ag200Cu after graphene synthesis compared with the Cu. Because the portion of the misorientation angle in grain boundaries lower than 10° was high, these boundaries comprised the subgrain boundaries, and large grain with (100) texture was formed. For Ag200Cu after graphene synthesis at 1,000 ℃, one single grain almost filled the EBSD measurement area as shown in Fig. 5b and the measured grain size of one grain was over 1.05 mm2 reaching the upper limit of measurable grain size of the EBSD used in this study. In contrast, the average grain size of Cu after graphene synthesis at 1,000 ℃ was 56 µm2; for the grain size of Ag200Cu, more than 18,750 times larger than that of Cu.

Discussions Based on the various experimental analyses, the optimized thickness of Ag plating for the synthesis of uniform graphene film is found to be 200-300 nm. If Ag plating is too thin, the amount of Ag is too small to have an effect on graphene synthesis. On the other hand, if Ag plating is too thick, the dimer formation and nucleation is excessive at Ag sites resulting in non-uniform graphene synthesis. The dependence of domain size of graphene on Ag plating thickness, i.e., domains are larger for the synthesis on Cu and become smaller for increasing Ag thickness, can be explained as the followings; If the Ag plating thickness increases, the larger portion of Ag in Cu-Ag alloy leads to denser carbon dimers and hence more graphene nucleation sites. These results are consistent with the Raman and TEM results of graphene as shown in Fig. 2-3 and Fig. S1. The surface analyses of Cu-Ag alloys by SEM and EDS revealed that the Ag atoms show high mobility above 600℃, and the in-depth analyses by D-SIMS and XRD indicate that the Ag atoms are diffused into Cu to form a homogeneous CuAg alloys. In addition, the EBSD analysis of Cu-Ag alloy substrates shows that (100) cube texture development of Cu during graphene synthesis with the development of low angle subgrain boundaries and decrease of the twin boundaries are suggested to enhance the formation of large Cu grains with


showed the normally random grain boundaries. For Cu, first order twin boundaries represented by 58.5° - 60° misorientation angle was found to comprise 30-40 % by area. The percentage of twin boundaries for Ag200Cu after graphene synthesis was measured to be 17.2 %, 10.6 % and 4.8 % for synthesis temperature of 800 ℃, 900 ℃ and 1,000 ℃, respectively. one texture, and such Cu grain allowed for the uniform graphene synthesis by providing identical growth condition all over catalytic surface. In regard of characteristics of boundaries, twin boundaries are known to be more stable than normal grain boundaries against microstructural change, and it has been also reported that the twin boundaries suppress the abnormal microstructural change of Cu25, 26. Our results show that Ag in substitutional Ag-Cu alloys promotes the grain growth into the cube texture with reduced twin boundaries in Cu grains. We suppose that the graphene growth on Cu-Ag alloys and the abnormal grain growth into one texture are interacting each other, adding the formation of high-quality and uniform graphene films at lower temperature.

Conclusions We demonstrated a new method to synthesize a uniform highquality graphene film at low temperature by electroplating Ag layers conventional Cu catalysts. The thickness of Ag and the growth temperature were carefully optimized, which are found to be 200 nm and 900 ℃, respectively. The various surface and in-depth analyses show that the Ag atoms are mobile enough to diffuse into Cu at high temperature to form homogeneous CuAg alloys. In addition, the EBSD analysis implies that the abnormal grain growth of Cu-Ag alloys further assists the formation of uniform graphene films by providing identical growth environment across the whole catalytic surface.

Acknowledgements This work was supported by the National Core Research Center (NCRC) Program (2011-0006268), the Global Research Lab (GRL) Program (2011-0021972), the Global Frontier Research Program (2011-0031627), and the Basic Science Research Program (2009-0092950, 2012M3A7B4049807, 20110017587, 2013K000165) through the National Research Foundation of Korea (NRF) funded by the Korean government (MEST and MKE).

Notes and references




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a

Department of Materials Science & Engineering, Seoul National University, Seoul 151-744, Republic of Korea b Department of Chemistry, Seoul National University, Seoul 151-747, Republic of Korea c SAMSUNG TECHWIN Co., Ltd., Seongnam 463-400, Republic of Korea d SKKU Advanced Institute of Nanotechnology (SAINT) and Center for Human Interface Nano Technology (HINT), Sungkyunkwan University, Suwon 440-746, Republic of Korea

Corresponding Author *Byung Hee Hong ([email protected]) and *Young-Chang Joo ([email protected]). § These authors contributed equally. Electronic Supplementary Information (ESI) available: [Spectroscopic Raman mapping of graphene synthesized on Cu, Ag200Cu and Ag500Cu for the comparison of graphene coverage; Supplemental of EBSD results for Ag500Cu and EBSD maps of ND, RD and TD of Ag200Cu.]. See DOI: 10.1039/b000000x/

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ARTICLE


Chemical vapor deposition growth of crystalline monolayer MoSe2.

Controllable Growth of the Graphene from Millimeter-Sized Monolayer to Multilayer on Cu by Chemical Vapor Deposition.

Equilibrium chemical vapor deposition growth of Bernal-stacked bilayer graphene.

Transport properties of monolayer MoS2 grown by chemical vapor deposition.

High Quality Monolayer Graphene Synthesized by Resistive Heating Cold Wall Chemical Vapor Deposition.

Chemical vapor deposition of graphene single crystals.

Growth of millimeter-size single crystal graphene on Cu foils by circumfluence chemical vapor deposition.

Low Temperature Metal Free Growth of Graphene on Insulating Substrates by Plasma Assisted Chemical Vapor Deposition.

Large-Area Growth of Uniform Single-Layer MoS2 Thin Films by Chemical Vapor Deposition.

Contamination-free graphene by chemical vapor deposition in quartz furnaces.

Chemical Vapor Deposition Growth of Monolayer WSe2 with Tunable Device Characteristics and Growth Mechanism Study.

Cooperative island growth of large-area single-crystal graphene on copper using chemical vapor deposition.

Edge-controlled growth and kinetics of single-crystal graphene domains by chemical vapor deposition.

Ultrasmooth metallic foils for growth of high quality graphene by chemical vapor deposition.

Role of hydrogen in graphene chemical vapor deposition growth on a copper surface.

Controllable poly-crystalline bilayered and multilayered graphene film growth by reciprocal chemical vapor deposition.

Correction: Controllable poly-crystalline bilayered and multilayered graphene film growth by reciprocal chemical vapor deposition.

Quantum Chemical Simulation of Carbon Nanotube Nucleation on Al2O3 Catalysts via CH4 Chemical Vapor Deposition.

Low-temperature growth of highly crystalline β-Ga2O3 nanowires by solid-source chemical vapor deposition.

boron nitride film by chemical vapor deposition.

Effect of Growth Pressure on Epitaxial Graphene Grown on 4H-SiC Substrates by Using Ethene Chemical Vapor Deposition.

Direct fabrication of 3D graphene on nanoporous anodic alumina by plasma-enhanced chemical vapor deposition.

Synthesis and modeling of uniform complex metal oxides by close-proximity atmospheric pressure chemical vapor deposition.

Formation mechanism of overlapping grain boundaries in graphene chemical vapor deposition growth.