Gas-Flow-Driven Aligned Growth of Graphene on Liquid Copper

Abstract

S ingle crystalline graphene (SCG) has proven its potential as an ideal candidate toward high-performance electronic, spintronic, and optoelectronic devices owing to its extremely high intrinsic carrier mobility and significantly wavelengthindependent absorption. 1−4 By chemical vapor deposition (CVD), large-area SCG can be controllably prepared, which is promising to fulfill the industrial-level demands by top-down processing. Through controlling nucleation density on catalytic metal substrates, especially on Cu foil, large SCG up to centimeter-scale has been obtained so far. 5−7 However, the approaches employed to suppress graphene nucleation, such as long-time annealing, 8−10 prepolishing before growth, 11,12 and exquisite substrate design, 6,13−17 inevitably increase the fabrication period and complicate the preparation procedure.Recently, it has been reported that the utilization of single crystal metal substrate, for example, Cu(111), 18−21 high-index surfaces Cu(114) 22 or Ge(110), 23 could allow graphene domains aligning into the same orientation. Such behavior is very similar to the epitaxial growth of graphene on h-BN, in which the negligible lattice mismatch between the substrate and the two-dimensional (2D) material guides the 2D material nucleates with a fixed stacking orientation. 24,25 In addition, the different single crystal Cu substrates would endow graphene with specific properties, such as the unique pentagonal singlecrystal graphene domains formation on Cu(114) 22 and the strong interfacial coupling of the commensurate graphene on Cu(111) for anticorrosion. 26 More importantly, the stitching between aligned graphene domains is "boundary-free" to enable them coalesce into a single crystal. Thus, no extra treatment for nucleation control is required and large SCG with high crystallinity up to wafer-scale dimensions can be obtained in relative short duration. 18,20 However, the availability of single crystal metal, either directly purchased with high price or produced by repeated annealing process at high temperature, is still far from the request of industrial applications. In addition, the controllability and reliability of this strategy is reported to be challenging as single crystal substrate with high lattice perfection is difficult to obtain and remain in CVD system.Liquid copper, Cu foil in molten phase, is considered as an effective substrate to catalyze CVD graphene growth in recent years. 27−32 Compared with solid Cu, liquid Cu has advantages of higher surface uniformity, faster carbon precursor decomposition rate, and faster graphene growth rate; thus,

Ab Initio Thermodynamics of Hydrocarbons Relevant to Graphene Growth at Solid and Liquid Cu Surfaces

“…with the Helmholtz free energy, as in the differences of free energies considered here the small volume dependence of the pV term largely cancels out. CVD growth of graphene on both solid and liquid Cu is typically carried out at a temperature rather close to the melting temperature of Cu of 1358 K (solid Cu CVD typically at around 1300 K 4-9 and liquid Cu CVD typically at around 1370 K [10][11][12][13][14][15][16] ). For C 2 the diffusion and rotation barrier of 0.56 eV is significantly larger than k B T at the melting temperature of Cu (0.12 eV), while the CH diffusion barrier of 0.12 eV is of equal magnitude to k B T .…”

“…[4][5][6][7][8][9] Recent experimental evidence suggests that using a liquid Cu surface instead of a solid one enables the fast growth of large singlecrystalline and single-layered graphene flakes of very high structural quality. [10][11][12][13][14][15][16] While these findings are very promising for industrial-scale production of high-quality graphene samples, the reason for the improved catalytic properties of liquid Cu, and the catalytic properties of liquid metals in general, is still poorly understood.…”

Designed Growth of Large‐Size 2D Single Crystals

“…So far, various growth mechanisms for self‐aligned graphene grown on liquid Cu were studied. [ 41,72,73 ] In comparison, growth of self‐aligned hBN domains is more difficult but also realized not long ago. [ 74 ] The substrate of liquid gold was chosen for the low solubility of B and N, and high diffusion of adatoms on the surface.…”

Synthesis of Large-Area Single-Crystal Graphene

“…In addition, melted copper has been reported as the substrate for the growth of single-crystal SLG films. Fu and colleagues reported the seamless stitching of neighboring round graphene islands on liquid copper due to a self-rotation process on the smooth surface of liquid copper [80], while Yu and colleagues reported aligned hexagonal graphene islands grown in the temperature range 1083-1140°C, and theoretical calculations indicated that the aligned islands were driven by gas flow [81]. However, temperatures higher than the melting point of Cu, 1084.6°C, and tungsten foils, are needed to melt and support the copper.…”