Edge-Catalyst Wetting and Orientation Control of Graphene Growth by

Aug 25, 2014 - Edge-Catalyst Wetting and Orientation Control of Graphene Growth by Chemical Vapor Deposition Growth. Qinghong Yuan,. †,‡,¶...
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Edge-Catalyst Wetting and Orientation Control of Graphene Growth by Chemical Vapor Deposition Growth Qinghong Yuan,†,‡,¶ Boris I. Yakobson,*,§ and Feng Ding*,†,§ †

Institute of Textiles and Clothing, Hong Kong Polytechnic University, Kowloon, Hong Kong 8523, People’s Republic of China Department of Physics, East China Normal University, Shanghai 200241, People’s Republic of China § Department of Mater Sci & NanoEngineering, Rice University, Houston, Texas 77005, United States ‡

S Supporting Information *

ABSTRACT: Three key positions of graphene on a catalyst surface can be identified based on precise computations, namely as sunk (S), step-attached (SA), and on-terrace (OT). Surprisingly, the preferred modes are not all alike but vary from metal to metal, depending on the energies of graphene-edge “wetting” by the catalyst: on a catalyst surface of soft metal like Au(111), Cu(111) or Pd(111), the graphene tends to grow in step-attached or embedded mode, while on a rigid catalyst surface such as Pt(111), Ni(111), Rh(111), Ir(111), or Ru(0001), graphene prefers growing as step-attached or on-terrace. Accordingly, as further energy analysis shows, the graphene formed via the S and SA modes should have orientations fixed relative to the metal crystal lattice, thus prescribing epitaxial growth of graphene on Au(111), Cu(111) and Pd(111). This conclusion indeed correlates well with numerous experimental data, also solving some puzzles observed, and suggesting better ways for growing larger-area single-crystalline graphene by making proper catalyst selections. SECTION: Surfaces, Interfaces, Porous Materials, and Catalysis

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practical applications. The approach (ii) requires the uniform alignment of all graphene islands on the catalyst surface, which have been shown possible by many experimental observations.16−19 Nevertheless, the causes of such alignment have not been understood due to the limited knowledge about the underlying mechanisms that govern the graphene formation on the catalyst substrate.20 Previous studies have shown that a graphene edge tends to be attached to a metal step during both nucleation and growth because of the decrease of edge formation energy on an existing step of the surface.11,21 Here, we call this growth mode a stepattached (SA) growth. However, for graphene growth on a flat terrace, there’s no existing metal steps. So, it is intuitive to assume that the graphene lays on a flat metal terrace with the edges bending toward the terrace for stronger passivation. We call this growth mode as an on-terrace (OT) growth hereafter. On the other hand, at the very high temperature of graphene growth (T ∼ 1000 °C), the reconstruction of the catalyst surface via the fast diffusion of metal atoms is possible. So, there exists a probability of the graphene being sunk into a basin of the catalyst surface during growth, and we classify this growth mode as sunk (S) growth. The illustration of the three growth modes is shown in Figure 1.

hemical vapor deposition (CVD) has been broadly regarded as a promising method toward the economic fabrication of high-quality, large-area graphene in large scale1−3 because a number of tunable experimental conditions (e.g., the type of catalyst, indexes of catalyst surface, type and partial pressures of the carbon feedstock, carrier gases, the temperature, etc.) ensure a large parameter space to improve the experimental design for the optimum graphene synthesis. So far, most CVD synthesized graphene are prone to be polycrystalline because numerous graphene islands with various orientations are simultaneously nucleated on the catalyst surface. The expansion of these islands on catalyst surface leads to numerous grain boundaries (GBs) between each pair of neighboring single crystalline domains like the sewing lines in a garment.4−6 The GBs in a polycrystalline graphene serve as carrier scattering centers7−9 and, thus, greatly degrade the electronic properties.8,10 To improve the quality of CVD graphene, it is crucial to suppress the concentration of GBs in the synthesized graphene by either (i) lowering the concentration of nuclei on the catalyst surface11−13 or (ii) avoiding the GB formation during the coalescence of graphene islands. The approch (i) can be achieved by reducing the carbon feedstock concentration/ activity to increase the graphene nucleation barrier,11−13 by pretreating the catalyst surface14 or by using preprepared graphene seeds to avoid the nucleation stage.7,15 However, the low concentration of carbon feedstock in approch (i) makes the growth time very long because macroscopic sized graphene islands, up to centimeters or inches, is required for many © XXXX American Chemical Society

Received: July 29, 2014 Accepted: August 25, 2014

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Figure 1. Illustration of the three modes of graphene growth: the stepattached (SA) mode, the on-terrace (OT) mode, and the sunk (S) mode.

In this article, motivated by the three potential modes of graphene CVD growth, we systematically investigate the graphene island formation on nine mostly used catalyst surfaces, Rh(111), Ru(0001), Ir(111), Ni(111), Pt(111), Pd(111), Cu(111), Cu(100), and Au(111). The calculation results demonstrated that on those metal surfaces which normally have higher step formation energies, including Ni(111), Rh(111), Ir(111) and Ru(0001), the SA + OT growth modes are preferrable; on those metal surfaces whose step formation energies are low, including Au(111), Cu(111), and Pd(111), the SA + S growth modes are common. For these growth modes, a strong correlation between the growth mode and the grown graphene is revealed. The graphene synthesized via the SA or S modes tends to be well aligned with θ = 0° or 30° because of the template effect of the metal step, whereas graphene synthesized via the OT mode is normally randomly aligned on the catalyst surface. Hence, avoiding graphene boundary formation during graphene coalescence and growing large-area crystalline graphene is expected via the SA or S growth on Cu(111), Au(111), and Pd(111) surfaces. On-Terrace (OT) Growth. For the OT graphene growth, the graphene sheet is laid flat on the metal surface and its edges are passivated by the metal surface. Because of the very large ratio of the graphene edge-catalyst interaction (∼1.5−2 eV/edge atom22) to the graphene wall−catalyst van der Waals interaction (∼0.03−0.1 eV/atom20,23,24), the graphene orientation is mainly determined by the graphene edge-catalyst interaction.20 Previous DFT calculations demonstrated the graphene orientation can be locked to various specific directions depending on the type of catalyst surface, the size and shape of the graphene islands, and so forth. As a consequence, it can be concluded that the orientation control of graphene during the OT growth is very unlikely.20,25 Step-Attached (SA) Growth Mode and the Role of Metal Step on Graphene Orientation Determination. An ideal metal substrate is a smooth surface without any defects, but in real experiments, a surface always has various metal steps and structural defects. It has been shown that graphene nucleation near a metal step is energetically more preferable than that on a flat terrace because of the low formation energy of the interface between the graphene and the metal step.2,21 Here, we explore a new mode of graphene growth, the SA growth mode. A step along the (011̅) direction of Cu(111) surface (Supporting Information Figure S2a) is chosen as a typical Cu step because of the lowest formation energy (Supporting Information SI-2). Different from that on a terrace, the matching between the graphene edge and the metal step plays a crucial role for the stability of the interface. For example, the structure of the most stable (011̅) step on the fcc(111) surface is characterized by all the step atoms aligned on a straight line. Among all potential graphene edges, only zigzag (ZZ) and armchair (AC) ones present the same characteristics. One can imagine that, an AC or ZZ type graphene edge is able to match a (011̅) step perfectly because all the atoms of the edge can bind with the metal step strongly (Figure 2b, θ = 0°, 30°).

Figure 2. (a) Formation energies of the interfaces between various graphene edge and (011̅) metal step on Cu(111) surface vs the graphene/Cu(111) misorientation angle θ. (b) The optimized geometries of the various graphene-metal step interfaces with θ = 0°, 12.2°, 19.1°, 23.41°, 27.0°, and 30°, respectively. (c) Illustration for various graphene edge binding at (011̅) metal step and the distance between graphene edge atoms and the metal step.

Once the edge is deviated from AC or ZZ, it is difficult for a kinky graphene edge to match the (011)̅ metal step and, thus, leads to some edge atoms are closer to the step than others (Figure 2c). This mismatching makes the strong binding of all edge atoms to the metal step impossible. So, we can anticipate that the AC and ZZ edges are the two types of edges that can form a more stable interface with the (011̅) metal step. As an example, the interfacial formation energy between various graphene edges and the (011̅) metal step on Cu(111) surface are calculated by the DFT method (Supporting Information SI-3 and Table S1) and the above analysis was validated. As shown in Figure 2a, θ = 0° (the ZZ edge − (011̅) step interface) and θ = 30° (the AC edge − (011̅) step interface) represent two minima of the potential energy surface. From Figure 2b, one can see the interface structures clearly: the ZZ-step interface (θ = 0°) shows a perfectly straight line; the AC-step interface (θ = 30°) is slightly curved and all others are heavily curved (θ = 12.2°, 19.1°, 23.4°, and 27°). Certainly, the distortion of a (011̅) step would lead to high interface formation energy and, thus, all these formation energies for non-AC or non-ZZ edges are above the linear interpolation line that connects the AC-step and ZZ-step interfaces. Among these interfaces, the one with θ = 19.1° is the most kinky one and, as a consequence, it has the highest formation energy. On the basis of the above analysis, one can conclude that graphene grown via the SA mode has two optimum orientations, which are θ = 0° + i × 60° and 30° + i × 60° (i = 0, 1, 2, 3, 4, 5), respectively. For graphene grown on a Cu(111) surface, the orientation of θ = 0° + i × 60° is more favorable than θ = 30° + i × 60°. It is worthwhile to note that this is in good agreement with many experimental observations. For example, Hu et al. reported that graphene flakes on a Cu(111) surface are mainly along the direction of θ = 0° and 30° under 900 °C and the orientation of graphene flakes were changed to dominantly 0° under a higher temperature of 1000 °C.17 Nie et al. also reported that the orientation of graphene flakes on a Cu(111) surface can be concentrated at 0° under high growth temperature.16 3094

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Table 1. ES(G), ET(G), EMS, and ΔE on different transition metal surfaces calculated by the DFT method. ET(G) is the formation energy of graphene edge on metal terrace, ES(G) is the formation energy of graphene edge at metal step, EMS refers to the formation energy of a (011̅) metal step, ΔE is the formation energy difference between the S and OT growth modes energy (eV/nm)

Au(111)

Pd(111)

Cu(111)

Cu(100)

Pt(111)

Ni(111)

Rh(111)

Ir(111)

Ru(0001)

ET (G) ES(G) EMS ΔE

7.52 4.37 1.03 -2.11

4.37 2.09 1.04 -1.24

4.73 3.08 1.16 -0.52

4.18 3.41 0.95 0.18

2.06 0.56 1.42 -0.08

2.29 0.78 1.65 0.14

1.48 1.01 1.62 1.16

2.32 1.04 2.15 0.87

1.80 1.09 2.19 1.48

Sunk (S) Growth. In the OT growth mode, the graphene edge bends toward the terrace for more stable passivation by the catalyst surface. Although the bending edge enhances the passivation, it is not sufficient because of (i) the elastic energy compensation existing near the bending edge and (ii) the small contact angle between graphene edge and the catalyst surface.21,22 As studied before, attaching a graphene edge onto a step of the catalyst surface would significantly reduce the formation energy.26 For a graphene island grown on a flat terrace, there is another potential growth mode: the island sinks into the flat terrace by kicking out metal atoms to form a basin (Figure. 1c). In such a basin, all edges of the graphene islands are passivated by metal steps and thus are very stable. However, on the other hand, creating such a basin on a terrace must increase the formation energy of the whole system. If the energy gained by attaching the graphene edge to a metal step is greater than that paid to create the metal steps, such a sunk (S) growth mode would be energetically more preferable than the OT growth mode. The S growth is competitive to the OT growth because both of them occurr on the metal terrace. To explore the feasibility of S growth, we define the formation energy difference between the S and OT growth modes as ΔE = ES(G) + EMS − E T(G)

Figure 3. Relationship between formation energy of metal step (EMS) and ΔE. For metals with small EMS (soft metals such as Au, Pd, and Cu), the S growth mode is preferred, whereas for metals with large EMS (hard metals such as Ni, Rh, Ru, and Ir) the OT growth mode dominates. ΔE is defined in eq 1.

In addition to the metal catalyst type, our calcualtion also indicates that the facet index of the metal surface also affects the growth mode of graphene. For example, S growth is energetically preferred on Cu(111) surface, whereas OT growth is preferred on Cu(100) surface. Based on the data shown in Figure 3 and taking the error of DFT calcualtions into account, the catalyst surfaces can be classified into three groups: (i) On the hard catalyst surfaces, such as Ru(0001), Ir(111), and Rh(111), graphene favors the OT growth. (ii) On the soft catalyst surfaces, such as Au(111), Cu(111), and Pd(111), graphene favors the S growth. (iii) On the catalyst surfaces with ΔE ∼ ± 0.2 eV/nm, such as Pt(111), Ni(111), and Cu(100), which mode is preferable is uncertain because of DFT calcualtion errors. For these catalyst surfaces, careful comparison with experimental data is required to determine the growth mode. It is important to note that the S growth is actually a special case of SA growth because all the edges of a graphene island are passivated by metal steps. Therefore, similar to what we discussed above, the graphene grown via the S mode also has two energetically preferred orientations, θ = 0° and 30°. Although the energetic preference of graphene S growth mode on soft metal surfaces is predicated, the initiation of the S growth mode largely depends on the route of realizing it and the corresponding barrier. Our further calculations demonstrated that graphene islands on the soft metal surface could sink easily from the very small size and thus the significant barrier of sinking a large graphene island can be avoided (see Supporting Information SI-5 for details).

(1)

where ET(G) and ES(G) are the formation energies of the graphene edge on the metal terrace and attached to a (011̅) metal step, respectively. EMS refers to the formation energy of a (011)̅ metal step. The definition and the details of the calculation of ES(G), ET(G), and EMS are availabe in Supporting Inforamtion SI-4 and Table S2. ES(G) + EMS can be considered as the formation energy of a sunk graphene edge because it requires the creation of both a metal step and the attachment of a graphene edge on it. ΔE < 0 indicates that the S growth is more favorable than the OT growth and vice visa. The calculated values of ET(G), ES(G), EMS, and ΔE on nine different transition metal surfaces are given in Table 1. It can be seen that both ET(G) and ES(G) of graphene on Au, Cu, and Pd surfaces are much higher than those on Pt, Ni, Rh, Ir, and Ru surfaces, demonstrating the weak graphene edge−Au/Cu/ Pd interaction and strong graphene edge−Pt/Ni/Rh/Ir/Ru interaction. A clear positive correlation between ΔE and EMS is shown in Figure 3. ΔE > 0 for most metal surfaces with EMS > 1.5 eV/nm (Ni(111), Rh(111), Ir(111), and Ru(0001)) and ΔE < 0 for those with EMS < 1.5 eV/nm (Au(111), Pd(111), Cu(111), Pt(111)). The Cu(100) surface is an exception, which has a small EMS and a positive ΔE. The EMS can be regarded as an indicator of the robusticity of the metal surface. The larger the EMS, the harder to create a metal step and the larger compensation of the S growth mode. On the basis of these calculated data, we conclude that the S growth is favorable on soft metal terraces and the OT growth is preferred on rigid ones. 3095

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should have many grain boundaries because of the uncontrolled orienation of graphene grown via the OT growth, whereas graphene grown via the SA + S modes may result in large area single-crystalline graphene due to the preferred orientation of the graphene islands, as shown in Figure 4b. It is also possible that the merging of graphene islands with same orientation leads to the formtion of one-dimensional toplogical defect because of the lattice mismatching.10 However, in most cases, the graphene islands can be seamlessly merged by forming a wrinkle. Therefore, a new route of growing large area single crystalline graphene quickly is revealed by using the single crystalline surface of soft catalysts (such as the Au(111) or Cu(111) surface), the graphene islands formed on it can be sewed perfectly into a large single crystalline one (Figure 4(b)). Experimentally, such a single-crystalline catalyst surface may be realized by sputtering very thin metal films on a highly orientated substrate such as MgO(111),29 Si(111),30,31 and so forth. Comparison with Experimental Results. Although great efforts have been paid for the experimental observation of graphene CVD growth, the in situ observations of graphene growth at high temperature are still rare. Although the growth mode can be inferred by some postgrowth measurements, for example, the measurement of graphene island’s height on a catalyst surface and the measurement of a graphene flake’s orientation in relative to that of the catalyst substrate. The height of the graphene island can be measured by atomic force microscopy (AFM) or scanning electron miscroscopy (SEM). And the orienation of CVD−graphene on a catalyst surface can be identified through the image of the moiré pattern or the low energy electron microscopy (LEEM) diffraction pattern. To verify our theoretical predictions, we compared our theoretical calculations with the two types of experimental measurements. Figure 5 summarizes the experimentally observed graphene height and its orientations on Pd, Pt, Ni, Ir, Ru, and Rh catalyst

We also would like to note that the high graphene growth temperature is another important driving force for achieving the graphene S growth. For example, the temperature of ∼1300 K is normally required to grow high quality graphene on various catalyst surfaces. At such high temperatures, the quick atomic migration, surface reconstruction, metal step flows have been broadly observed.27,28 Under that circumference, the S mode can be achieved by two routes: (i) by the removal of metal atoms beneath the graphene island or (ii) by adsorbing the fast migrated metal atoms around the graphene island to form a new atomic layer on the metal terrace. Although route (i) may experience a high barrier, route (ii) can be achieved easily because of the large amount of migrating atoms on the catalyst surface that accompanies the catalyst surface reconstruction. Summary of Graphene Growth Modes and Orientation Control. So far, we have identified three modes of graphene CVD growth: the SA growth near a metal step; the S growth on the soft metal terraces and the OT growth on the rigid metal terraces. Graphene grown via both SA and S modes has two energetically preferred orientations, 0° and 30°. Because one of the preferred orientations must be the global minimum of the potential energy surface, it is possible to further anneal the graphene grown via the SA or S mode to be along a specific direction, such as θ = 0° on Cu(111) surface as shown in Figure 2. However, graphene grown via the OT mode normally has no well controlled orientation and thus randomly orientated graphene islands may be simultaneously formed on a metal terrace.20 In real CVD experiments, perfect flat low index metal surfaces, such as the fcc(111) or hcp(0001), are hard to be achieved. Most surfaces are vicinal surfaces of the low index ones and thus the appearance of the metal steps is inevitable. Therefore, the SA growth is expected. So, graphene growth will adopt the combination of SA and OT modes on rigid catalyst surfaces (such as Ru, Rh, and Ir) or the SA and S modes on soft catalyst surface (such as Au, Cu, and Pd). As shown in Figure 4a, the large area graphene grown via the SA + OT modes

Figure 5. Height and orientation distribution of graphene islands on Pd(111), Pt(111), Ni(111), Ir(111), Ru(0001), and Rh(111) catalyst surfaces. The misorientation angle distribution on the six metal surfaces was summarized in the left-down columns and the graphene heigth distribution on the six metal surfaces was summarized in the right-up bars.

surfaces (details can be found in SI-6 of Supporting Information). It can be seen that the heights of graphene on Pt, Rh, and Ir are concentrated around 3.5 Å,32−37 indicating the weak interaction between graphene and the metal surface. In contrast, the graphene heights on a Ni surface are around 2.2

Figure 4. Illustration of the two potential combinations of graphene growth modes on different catalyst surface and the consequent large area graphene: (a) SA + OT growth on rigid catalyst surface and (b) SA + S growth on soft catalyst surface. 3096

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Å,38,39 which implies a strong metal−graphene interaction. It is interesting that the measured heights of graphene on a Ru(0001) surface varies over a large range from 1.5 to 3.0 Å,40−42 which can be viewed as a consequence of the moiré pattern. For graphene on Pd, the measured height is only ∼0.2 Å, which clearly indicates the S growth mode.43 It also can be seen that the graphene islands with heights of ∼2−3.5 Å have diverse orientation distributions, for example, graphene on Pt(111) surface has an even orientation distribution from 0° to 30°. This demonstrates that graphene islands cannot be constrained in a uniform orientation if they are floating on the metal surfaces. Another prominent feature of the orientation distribution is that about half of the measured graphene samples have a near zero orientation. This can be attributed to the predominant SA growth mode and the energy advantage of the 0° orientation graphene as mentioned before. It is a pity that only very limited experiments have been carried out to measure the graphene height on a Pd(111) surface, and there is even no graphene height measurements on Au(111) and Cu(111) surfaces to our best knowledge. So, although both data (height and orientation) measured on Pd(111) surface support our prediction, the correlation between graphene orientation and the S growth mode cannot be convincingly presented in these statistics. Graphene orientations on Au(111), Cu(111) and other catalyst surfaces have been broadly reported despite of the limited height measurements.13,16,18,24,29,44 Figure 6 shows the summarized orientation distribution of graphene on Cu(111), Cu(100), Ni(111), Pt(111), Ir(111), and Ru(0001) surfaces. We can see graphene flakes on Cu(111) surface are mainly 0° and 30° orientated, which is consistent with the SA + S growth modes. It was broadly reported that the graphene grown at a higher growth temperature of ∼1300 K are mostly 0° orientated,6,29,44 which is attributed to the energy advantage of 0° graphene over 30° graphene and the thermal activation. According to our theoretical predictions, 0° and 30° orientated graphene are the two local minima in the energy curve, and both of them can be observed at low growth temperature. However, at high temperature, the 30° orientated graphene can be annealed to 0° orientation because of its relatively higher formation energy (Figure 2a). Wofford et al. found over 95% of the graphene islands grown on Au(111) surface could be identically aligned with respect to each other and to the Au substrate.18 Given that the graphene film is only weakly coupled to the Au surface, graphene orientation locking on the lattice mismatched substrate is surprising. However, taking the S growth mode into account, such a puzzle can be well understood because of the strong orientation dependent graphene edge-metal step interaction. Although graphene grown on a Cu(100) surface are dominated by 0° and 30° orientations, there are a few other orientations, which is in consistent with the OT + SA growth mdoes.6,13,16,17,29,44 Similar results were observed on Ni(111), Pt(111), Ir(111) and Ru(0001) surfaces, where graphene islands were diversely orientated.30,45−47 For graphene grown on Pt(111) surface, where the orientation is evenly distributed, it is nearly impossible to achieve a graphene orientation control during CVD growth. In sumamry, most experimental observations support our theroetical prediction very well although the validation of some of them is still pending because the lack of the experimental

Figure 6. Mismatching angle distribution of graphene islands on Cu(111), Cu(100), Ni(111), Pt(111), Ir(111), and Ru(0001) surfaces. The numbers in vertical coordinate are the times of the graphene orientation appeared in the literature.

observations. We hope detailed experimental characterizations could fill these blanks in the near future. In conclusion, three modes of graphene CVD growth (step attached-SA, on terrace-OT and sunk-S) are explored by density functional calcualtions. Our study concluded that SA + S modes dominate the graphene growth on soft metal surfaces (Au(111), Cu(111), Pd(111),...), while the SA + OT modes control the graphene growth on hard metal surfaces (Ru(111), Ir(111), Rh(111), Pt(111), Ni(111), ...). Besides, our theoretical analysis showed that the growth mode largely influences the relative orientation of the grown graphene on the catalyst surface. Graphene grown via the SA or S modes can be constrained to the orientation of θ = 0° and 30° but graphene grown via the OT mode normally leads to many different orientations because of the lacking of catalyst steps. On the basis of this theoretical study, we propose a route that may lead to the fast growth of large-area single-crystalline graphene by choosing a proper catalyst on which the S growth is highly preferred. 3097

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(10) Lahiri, J.; Lin, Y.; Bozkurt, P.; Oleynik, I. I.; Batzill, M. An Extended Defect in Graphene as a Metallic Wire. Nat. Nanotechnol. 2010, 5, 326−329. (11) Gao, J. F.; Yuan, Q. H.; Hu, H.; Zhao, J. J.; Ding, F. Formation of Carbon Clusters in the Initial Stage of Chemical Vapor Deposition Graphene Growth on Ni(111) Surface. J. Phys. Chem. C 2011, 115, 17695−17703. (12) Kim, H.; Mattevi, C.; Calvo, M. R.; Oberg, J. C.; Artiglia, L.; Agnoli, S.; Hirjibehedin, C. F.; Chhowalla, M.; Saiz, E. Activation Energy Paths for Graphene Nucleation and Growth on Cu. ACS Nano 2012, 6, 3614−3623. (13) Wu, B.; Geng, D.; Guo, Y.; Huang, L.; Xue, Y.; Zheng, J.; Chen, J.; Yu, G.; Liu, Y.; Jiang, L.; et al. Equiangular Hexagon-ShapeControlled Synthesis of Graphene on Copper Surface. Adv. Mater. 2011, 23, 3522−3525. (14) Hao, Y.; Bharathi, M. S.; Wang, L.; Liu, Y.; Chen, H.; Nie, S.; Wang, X.; Chou, H.; Tan, C.; Fallahazad, B.; et al. The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper. Science 2013, 342, 720−723. (15) Wu, W.; Jauregui, L. A.; Su, Z. H.; Liu, Z. H.; Bao, J. M.; Chen, Y. P.; Yu, Q. K. Growth of Single Crystal Graphene Arrays by Locally Controlling Nucleation on Polycrystalline Cu Using Chemical Vapor Deposition. Adv. Mater. 2011, 23, 4898−4903. (16) Nie, S.; Wofford, J. M.; Bartelt, N. C.; Dubon, O. D.; McCarty, K. F. Origin of the Mosaicity in Graphene Grown on Cu(111). Phys. Rev. B 2011, 84, 155425. (17) Hu, B.; Ago, H.; Ito, Y.; Kawahara, K.; Tsuji, M.; Magome, E.; Sumitani, K.; Mizuta, N.; Ikeda, K.-i.; Mizuno, S. Epitaxial Growth of Large-Area Single-Layer Graphene Over Cu(111)/Sapphire by Atmospheric Pressure CVD. Carbon 2012, 50, 57−65. (18) Wofford, J. M.; Starodub, E.; Walter, A. L.; Nie, S.; Bostwick, A.; Bartelt, N. C.; Thuermer, K.; Rotenberg, E.; McCarty, K. F.; Dubon, O. D. Extraordinary Epitaxial Alignment of Graphene Islands on Au(111). New J. Phys. 2012, 14, 053008. (19) Nie, S.; Bartelt, N. C.; Wofford, J. M.; Dubon, O. D.; McCarty, K. F.; Thuermer, K. Scanning Tunneling Microscopy Study of Graphene on Au(111): Growth Mechanisms and Substrate Interactions. Phys. Rev. B 2012, 85, 205406. (20) Zhang, X.; Xu, Z.; Hui, L.; Xin, J.; Ding, F. How the Orientation of Graphene Is Determined during Chemical Vapor Deposition Growth. J. Phys. Chem. Lett. 2012, 3, 2822−2827. (21) Gao, J. F.; Yip, J.; Zhao, J. J.; Yakobson, B. I.; Ding, F. Graphene Nucleation on Transition Metal Surface: Structure Transformation and Role of the Metal Step Edge. J. Am. Chem. Soc. 2011, 133, 5009− 5015. (22) Yuan, Q.; Gao, J.; Shu, H.; Zhao, J.; Chen, X.; Ding, F. Magic Carbon Clusters in the Chemical Vapor Deposition Growth of Graphene. J. Am. Chem. Soc. 2011, 134, 2970−2975. (23) Vanin, M.; Mortensen, J. J.; Kelkkanen, A. K.; Garcia-Lastra, J. M.; Thygesen, K. S.; Jacobsen, K. W. Graphene on Metals: A van der Waals density functional study. Phys. Rev. B 2010, 81, 081408. (24) Wang, Q.; Wei, L.; Sullivan, M.; Yang, S. W.; Chen, Y. Graphene Layers on Cu and Ni (111) Surfaces in Layer Controlled Graphene Growth. Rsc Adv. 2013, 3, 3046−3053. (25) Wu, P.; Jiang, H.; Zhang, W.; Li, Z.; Hou, Z.; Yang, J. Lattice Mismatch Induced Nonlinear Growth of Graphene. J. Am. Chem. Soc. 2012, 134, 6045−6051. (26) Yuan, Q. H.; Hu, H.; Gao, J. F.; Ding, F.; Liu, Z. F.; Yakobson, B. I. Upright Standing Graphene Formation on Substrates. J. Am. Chem. Soc. 2011, 133, 16072−16079. (27) Kenjiro, H.; Shintaro, S.; Naoki, Y. Anisotropic Graphene Growth Accompanied by Step Bunching on a Dynamic Copper Surface. Nanotechnol. 2013, 24, 025603. (28) Lu, J.; Yeo, P. S. E.; Zheng, Y.; Xu, H.; Gan, C. K.; Sullivan, M. B.; Neto, A. H. C.; Loh, K. P. Step Flow Versus Mosaic Film Growth in Hexagonal Boron Nitride. J. Am. Chem. Soc. 2013, 135, 2368−2373. (29) Ogawa, Y.; Hu, B.; Orofeo, C. M.; Tsuji, M.; Ikeda, K.-i.; Mizuno, S.; Hibino, H.; Ago, H. Domain Structure and Boundary in

ASSOCIATED CONTENT

S Supporting Information *

Computation details for Cu step formation on Cu(111) surface, different orientated graphene on the (011) step of Cu(111) surface, graphene formation on metal terrace and metal step, C24 formation on Cu(111) and Ni(111) surfaces, as well as experimental results summary for graphene formation on different metal surfaces are included in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Present Address ¶

(Q.Y.) Currently at East China Normal University.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work in Hong Kong PolyU was supported by Hong Kong GRF research grant (G-YX4Q), NSFC grant (21273189), and the work in East China Normal University was supported by NSFC grant (21303056) and Shanghai Pujiang Program (13PJ1402600). Work at Rice was supported by the US Department of Energy, BES grant DE-SC0012547 (vertical modes assessment) and by the Air Force Office of Scientific Research grant FA9550-14-1-0107 (edge energies analysis).

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