The growth and morphology of epitaxial multilayer graphene

Hass, Joanna; Heer, Walt A. de; Conrad, E. H.

doi:10.1088/0953-8984/20/32/323202

Cited by 757 publications

(868 citation statements)

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“…Developing methods for synthesizing largearea and uniform layers is an important step for applications such as wafer-scale fabrication of electronic devices and flexible, transparent optoelectronics. As previously demonstrated for graphene, the development of wafer-scale synthesis methods via chemical vapour deposition (CVD) on metal substrates 66 and epitaxial growth on SiC substrates 67 has enabled large-scale device fabrication [68][69][70] .…”

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

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“…17,[30][31][32] This method takes into account particularly the π -π interactions since the corresponding overlaps are the dominant effect in this weakly interacting system. The underlying SiC buffer [33][34][35][36][37] layer was neglected, since the expected energy contribution to the C 60 total energy due to the vdW interaction is at least an order of magnitude lower than the contribution due to the presence of SLG, 18 considering the large separation of SLG and the buffer layer. 38 In the calculations we used more than 20 different adsorption geometries of C 60 /SLG in a 4 × 4 periodicity.…”

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van der Waals interactions mediating the cohesion of fullerenes on graphene

et al. 2012

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Fullerenes on single-layer epitaxial graphene are a model system to study very faint interactions at a molecular level. By a variable temperature scanning tunneling microscope we have been able to study ordered fullerene layers at 40 K, exclusively bound by van der Waals interactions. The experimentally determined adsorption geometry of the molecules is computationally confirmed only if van der Waals interactions are included in the calculation formalism. The relative orientation of fullerenes in their close-packed arrangement is found to be the crucial factor for determining the total energy. Observation of collective movements of fullerene islands points out the weak coupling to the substrate and the important role of the van der Waals cohesion forces within. Mechanical stability, friction, or adhesion are among the physical properties that strongly depend on van der Waals (vdW) interactions. This is also true for the nanoscale. The nucleation and growth of molecular surface structures involve dynamic processes such as diffusion, molecular rotations, or conformational changes, which rely also on vdW intermolecular interactions. 1,2 Moreover, self-assembly and adsorption studies focus on determining the preferred adsorption site and configuration, the adsorbate-adsorbate interaction, and the distance between the adsorbate and substrate (e.g., Ref. 3).There is an increasing interest in the role of vdW interactions of organic molecules on graphite and other surfaces. 4,5 Generally, long-distance forces as vdW are not described by the most widely used functionals of the density-functional theory (DFT). Thus, in many of the works performed until now they are simply not included. However, when planar systems of carbon-based materials are in question, they require a different approach to the interplay between intermolecular (lateral) and adsorbate-substrate (vertical) interactions in determining the properties of ordered molecular structures. To evidence the important role of the vdW interactions in adsorption processes we have chosen a system of a very weakly interacting substrate and adsorbate, single-layer graphene (SLG) 6 and fullerenes (C 60 ). 7 The fact that both materials consist exclusively of carbon atoms arranged in an atomically thin planar mesh without H or any other atoms inside the atomic structure that could lead to long-range H-bond interactions makes this system a good prototype for a demonstration of the effect of these forces at a molecular level.Thus, we consider the C 60 on SLG grown on 6H-SiC(0001) 8-10 as a model system to test the strength of the vdW forces and mutual interactions that occur between neutral inert nanostructures. C 60 adsorbed on surfaces generally tend to form hexagonal close-packed arrangements 11 in order to optimize their lateral interactions. In very recent studies of C 60 molecules deposited on SLG epitaxially grown on metal, 12,13 it has been shown that the interaction between the molecules and the substrate, and consequently the molecular arrangement, is ruled by the m...

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“…We discuss how to reconcile these findings with transport properties which appear to be identical to those of single-layer graphene. Finally, we show how the bandstructure of freestanding bilayer graphene grown on the carbon face of SiC differ from those of bilayer graphene grown on the silicon face of SiC, in order to demonstrate the impact of the substrate on the electronic properties.Samples were grown on the C-terminated face of SiC substrate as previously reported [6,9]. High-resolution ARPES data were taken at BL12.0.1 of the Advanced Light Source at a temperature of 15 • K after annealing samples to 1300 • K using photon energies from 42eV to 80eV.…”

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Quasifreestanding multilayer graphene films on the carbon face of SiC

et al. 2010

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The electronic band structure of as-grown and doped graphene grown on the carbon face of SiC is studied by high-resolution angle-resolved photoemission spectroscopy, where we observe both rotations between adjacent layers and AB-stacking. The band structure of quasi-freestanding ABbilayers is directly compared with bilayer graphene grown on the Si-face of SiC to study the impact of the substrate on the electronic properties of epitaxial graphene. Our results show that the C-face films are nearly freestanding from an electronic point of view, due to the rotations between graphene layers.One of the most substantial problems that the graphene community is faced with is a choice of substrate that preserves the unique properties of the Dirac charge carriers in graphene. Most substrates require tradeoffs between ease of large-scale sample growth and the strength of the substrate interaction. One of the earliest forms of graphene was grown on transition metal substrates like nickel [1,2], where the growth process itself is straightforward but the interaction with the substrate is very strong [3,4]. More recently, free-standing graphene has been isolated through mechanical exfoliation [5], but the process is time-consuming and unreliable. The ideal graphene system for the purposes of both scientific studies and industrial applications would be one where large-scale sample growth is simple and efficient, and the graphene is relatively free-standing. Graphene grown on the carbon face of SiC, SiC(0001) [6] might be one such system. Despite the large number of graphene layers, the different orientations between adjacent layers (most commonly ±2 • and 30 • rotation with respect to the substrate) [7][8][9] causes them to decouple from one another, resulting in a system whose transport and electronic properties closely match those of freestanding monolayer graphene [6,[10][11][12][13]. On the other hand, recent magnetospectroscopy and localization measurements suggest a more complicated role of the interlayer interaction [14] and the possible presence of AB-stacked (Bernal or rhombohedral) domains [15]. In addition, X-ray measurements of C-face graphene indicate an average lattice spacing that lies between that of AB-stacked graphene and of fully rotationally disordered films [8]. This is completely different from the case of graphene grown on the Si-face of SiC, where all adjactent layers are coupled due to the AB-stacking [16][17][18].To shed light on the role of the interlayer interaction and to fully characterize the electronic structure of these samples, it is of fundamental importance to directly measure their band structure and in particular to study the π bands near the Dirac point. Angle-resolved photoemission spectroscopy (ARPES) is the ideal tool to directly measure the electronic band structure of graphene and determine the number of AB-stacked layers by measuring the number of π bands. The thickness of AB-stacked films can be verified by measuring the variation in photoemission intensity of these bands along the k...

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The growth and morphology of epitaxial multilayer graphene

Cited by 757 publications

References 147 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

van der Waals interactions mediating the cohesion of fullerenes on graphene

Quasifreestanding multilayer graphene films on the carbon face of SiC

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