Layer-controlled single-crystalline graphene film with stacking order via Cu–Si alloy formation

Luo

et al. 2021

Trends in Chemistry

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...

Section: Single-crystal Blg Grown From Multiple Nucleimentioning

confidence: 99%

Section: Single-crystal Blg Grown From Multiple Nucleimentioning

confidence: 99%

See 1 more Smart Citation

Synthesis of Large-Area Single-Crystal Graphene

Luo

et al. 2021

Trends in Chemistry

“…[ 11–14 ] While the intrinsic physical properties of polycrystalline films have been comprehensively investigated in terms of micrometer‐scale grains, its inhomogeneity in a wafer scale limits application to integration challenges associated with structural defects such as grain boundaries and disorder. [ 15 ] The growth of single‐crystal (SC) monolayer and multilayer graphene films on SC Cu (111) and Cu–Si (111) surfaces has been demonstrated in a wafer scale, [ 16,17 ] whereas the growth of diatomic 2D SC film such as hBN and TMdCs remains still complicated due to their non‐centrosymmetric structures. [ 18 ] Recently, the self‐collimation of hBN grains on liquid Au substrate has been proposed for growing diatomic hBN SC film in a wafer scale but further study is required to grow other 2D vdW materials.…”

Section: Figurementioning

confidence: 99%

Epitaxial Single‐Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface

et al. 2021

Self Cite

Growth of 2D van der Waals layered single‐crystal (SC) films is highly desired not only to manifest the intrinsic physical and chemical properties of materials, but also to enable the development of unprecedented devices for industrial applications. While wafer‐scale SC hexagonal boron nitride film has been successfully grown, an ideal growth platform for diatomic transition metal dichalcogenide (TMdC) films has not been established to date. Here, the SC growth of TMdC monolayers on a centimeter scale via the atomic sawtooth gold surface as a universal growth template is reported. The atomic tooth‐gullet surface is constructed by the one‐step solidification of liquid gold, evidenced by transmission electron microscopy. The anisotropic adsorption energy of the TMdC cluster, confirmed by density‐functional calculations, prevails at the periodic atomic‐step edge to yield unidirectional epitaxial growth of triangular TMdC grains, eventually forming the SC film, regardless of the Miller indices. Growth using the atomic sawtooth gold surface as a universal growth template is demonstrated for several TMdC monolayer films, including WS2, WSe2, MoS2, the MoSe2/WSe2 heterostructure, and W1−xMoxS2 alloys. This strategy provides a general avenue for the SC growth of diatomic van der Waals heterostructures on a wafer scale, to further facilitate the applications of TMdCs in post‐silicon technology.

“…The detachment of graphene edges from growth substrate promotes the diffusion of active carbon species into the interface for the formation of bilayer graphene with a yield of 99%; [ 82 ] 2) the designs of high Ni concentration (23%) in Cu−Ni alloy and long growth time for the isothermal growth of bilayer graphene with a yield of 99.4%; [ 83 ] 3) the use of large‐area single‐crystal Cu/Ni(111) alloy with Ni concentration of 16.6% for the formation of bilayer graphene with a yield of almost 100%; [ 84 ] 4) the introduction of ultra‐low‐limit methane concentration (0.01, 0.03, 0.06, and 0.1%) on Cu–Si alloy to produce a SiC layer, achieving the control of graphene layer number from mono‐, bi‐, tri‐, and tetralayer graphene after the sublimation of Si atoms, respectively. [ 85 ] Drawing on these strategies, the uniform tBLG was expected to be formed.…”

Section: The Manufacturing Techniques Of Tblgmentioning

confidence: 99%

Fabrication Strategies of Twisted Bilayer Graphenes and Their Unique Properties

Cai

2021

Advanced Materials

Therefore, graphene becomes a rising star on the horizon of materials science. Since the first report of centimeter-scale single-crystal graphene by Ruoff group showed high electrical quality, [9] great achievements have been made in the fabrication of high-quality graphene for the application in electronic devices, including single-crystalline graphene flakes, [10,11] super-ordered graphene structures, [12,13] super-clean graphene films, [14-16] and ultra-flat graphene films. [17] However, the zero-bandgap feature for monolayer graphene has limited its potential applications in semiconductors. In addition, the negligible mass, low yield, and high production costs of graphene are insurmountable bottlenecks for the practical application in energy conversion and storage. In particular, the absence of killer applications leads to the increased difficulty in graphene commercialization. [18,19] Nevertheless, it is undeniable that the unique structure of graphene has sparked intense interest in condensed matter physics, such as fractional quantum Hall effects, [17] proton permeation, [20] and plasmons. [21] More interestingly, twisted bilayer graphene (tBLG), which is similar to the van der Waals heterostructures, has a dramatic effect on the electronic properties. [22,23] The relative rotating graphene layers become a powerful model to study topological physical properties, including ferromagnetism, [24] Mott insulating behavior and superconducting behaviors, [25,26] topological valley transport, [27] van Hove singularities, [28] and tunable bandgap. [29] Consequently, the twisted structure of tBLG has triggered tremendous enthusiasm, even inspiring the formation of a new field for twisted 2D materials. Currently, production methods of tBLG contain chemical vapor deposition (CVD) on metal catalysts; [30] epitaxial growth on SiC substrate; [31] folding monolayer graphene, [32] and stacking monolayer graphene. [33] These methods are divided into two categories: direct growth and manual assembly. Generally, the direct growth of tBLG undergoes an in situ rearrangement of carbon atoms in the non-equilibrium state at high temperatures, whereas the ex situ vertical overlap of monolayer graphene by transfer process is the basic principle for manual assembly. The completely different preparation processes give rise to the distinctive advantages and disadvantages, but precise control over twist angle and super-clean interface are the ultimate pursuits for any preparation method. Recent progress in Twisted bilayer graphene (tBLG) exhibits a host of innovative physical phenomena owing to the formation of moiré superlattice. Especially, the discovery of superconducting behavior has generated new interest in graphene. The growing studies of tBLG mainly focus on its physical properties, while the fabrication of high-quality tBLG is a prerequisite for achieving the desired properties due to the great dependence on the twist angle and the interfacial contact. Here, the cutting-edge preparation strategies and challenges of tBLG fabrica...