Synthesis of Large-Area Single-Crystal Graphene

Abstract

There have been breakthroughs in the mass production of graphene by chemical vapor deposition (CVD) and its practical applications have also been identified. Grain boundaries are typically present in 'CVD graphene' and adversely impact its properties. We summarize recent progress in growing large-area singlecrystal graphene. Centimeter-scale single-crystal, truly single-layer graphene (SLG) films have been reportedly achieved on single-crystal Cu(111) foils by CVD growth, while meter-scale single-crystal SLG films have been reportedly produced with assistance of a roll-to-roll technique. The growth of uniform single crystals of bilayer or multilayer graphene over a large area remains an exciting challenge. Layer-by-layer transfer and the stacking of single-crystal SLG is considered a promising route to making new types of 'single' crystals or quasicrystals with specific numbers of layers and different stacking angles. Structure and Properties of Single-Crystal GrapheneGraphene, a single layer of carbon atoms arranged in a honeycomb lattice (Figure 1A), has attracted worldwide attention due to its unique 2D structure and excellent physical properties [1][2][3][4][5]. When two graphene layers are stacked on top of each other, the properties of the bilayer material [6] depend on the stacking angle (Figure 1B,C) [7,8]. AB-stacked bilayer graphene (BLG) (see Glossary) reportedly has a continuously tunable bandgap of up to 250 meV when a vertical electrical field is applied, which enables the fabrication of semiconductor devices [9][10][11]. An AB-stacked BLG film was reportedly converted to an ultra-thin 'diamond' film (F-diamane) by fluorine chemisorption [12]. In addition, twisted bilayer graphene (tBLG) reportedly presents θ-dependent interfacial conductivity [13], van Hove singularities [14], and particular electronic structures [15] that are reported to have potential for use in ultra-sensitive sensors and ultra-thin capacitors. A Mott insulator and unconventional superconductivity with a critical temperature up to 1.7 K was reported for a twist angle of 1.1 o in BLG [10,11]. Compared with AB-stacked BLG, tBLG reportedly has a higher chemical reactivity, which was said to be due to distinct variations in the density-of-states distribution in the gap region [16]. Among various synthesis methods, chemical vapor deposition (CVD) has shown to be the most promising for the scalable production of large-area high-quality graphene films [17]. Ruoff and colleagues first reported the preparation of a centimeter-scale single-layer graphene (SLG) film on a commercial Cu foil by CVD in 2009 [18]. Unlike Ni with high carbon solubility (~0.9 at.% at 900°C [19]), Cu has a much lower carbon solubility, even up to 1000°C (7.4 at. ppm at 1020°C [20]), which is believed to predominantly contribute to the surface-mediated mechanism of graphene growth and good uniformity of the number of layers of the as-grown graphene [21]. As a result, Cu-based foils or films are the most common substrates for studying the behavior of graphene growt...

The Wet‐Oxidation of a Cu(111) Foil Coated by Single Crystal Graphene

“…The epitaxial growth of single crystal graphene on a single crystal metal substrate, especially a single crystal Cu(111) foil, has been reported. [ 15,29–32 ] Since both graphene and the Cu substrate are single crystals, the influence by defects and GBs in both graphene and Cu can be minimized, thus this single crystal graphene‐coated Cu(111) is a good platform to investigate whether it is possible to minimize or even eliminate oxidation of the Cu using graphene as a barrier. Xu et al.…”

“…The epitaxial growth of single crystal graphene on a single crystal metal substrate, especially a single crystal Cu(111) foil, has been reported. [15,[29][30][31][32] Since both graphene and the Cu substrate are single crystals, the influence by defects and GBs in both graphene and Cu can be minimized, thus this single crystal graphene-coated Cu(111) is a good platform to investigate whether it is possible to minimize or even eliminate oxidation of the Cu using graphene as a barrier. Xu et al reported that asgrown single crystal graphene islands on a Cu(111) foil protect the Cu surface from wet-oxidation by preventing water and/or O 2 from diffusing to the graphene/Cu(111) interface when exposed to humid air (relative humidity > 80%) at 50 °C.…”

Towards Repeatable, Scalable Graphene Integrated Micro-Nano Electromechanical Systems (MEMS/NEMS)

“…Mass production schemes discussed in this section includes graphene transfer process using roll-to-roll (R2R) processing, graphene growth and MEMS device fabrication on transition metal thin films for transfer-free process, controlled graphene growth on single-crystalline films, strain engineering on the substrate, and other approaches. [183][184][185]. Two data points with asterisks represent CVD growth of graphene by accelerated growth technique [186,187].…”

“…Cu (111) and graphene have 4% lattice mismatch, and as temperature is highly elevated during graphene growth, the domains connect with each other creating seamless boundaries. It has been reported merging of grain boundaries is critical to electrical quality of graphene as electron scattering is observed near grain boundaries and wrinkles [5,184,214]. [209].…”

“…(a) Mobility by graphene growth time on different growth metal layer. (b) Grain sizes by graphene growth time on different growth metal layer[183][184][185]. Two data points with asterisks represent CVD growth of graphene by accelerated growth technique[186,187].…”