Uniform hexagonal graphene flakes and films grown on liquid copper surface

Abstract

Unresolved problems associated with the production of graphene materials include the need for greater control over layer number, crystallinity, size, edge structure and spatial orientation, and a better understanding of the underlying mechanisms. Here we report a chemical vapor deposition approach that allows the direct synthesis of uniform single-layered, large-size (up to 10,000 μm 2 ), spatially self-aligned, and single-crystalline hexagonal graphene flakes (HGFs) and their continuous films on liquid Cu surfaces. Employing a liquid Cu surface completely eliminates the grain boundaries in solid polycrystalline Cu, resulting in a uniform nucleation distribution and low graphene nucleation density, but also enables self-assembly of HGFs into compact and ordered structures. These HGFs show an average two-dimensional resistivity of 609 AE 200 Ω and saturation current density of 0.96 AE 0.15 mA∕μm, demonstrating their good conductivity and capability for carrying high current density.atomic crystal | electronic materials G raphene has attracted considerable attention because of its extraordinary physical properties and potential electronic and spintronic applications (1-3). It is critical to find ways of precisely controlling the graphene layer number (4-6), crystallinity, size, edge structure, and even spatial orientation. The chemical vapor deposition (CVD) approach is a powerful and cost-effective technique for the production of high-quality and large-scale graphene films. In spite of the complexity of CVD procedures involving different catalysts, carbon sources, and other variables, the physical principles underlying this method are relatively simple. It is widely accepted that CVD mainly involves either surface catalytic reaction (7,8) or bulk carbon precipitation onto the surface during cooling (9, 10) for catalysts with low-carbon and high-carbon solubility, respectively. In both cases, graphene nucleation on a catalyst surface is one of the critical steps in the growth process. Various factors affect the initiation of the graphene nucleation process, including the type (11, 12) or surface microstructure of the catalyst, carbon source (13), carbon segregation from metal-carbon melts (14), processing history, and parameters in CVD growth (15)(16)(17). In general, nucleation densities on substrates such as Cu or Ni are nonuniform. This nonuniformity causes a large dispersion of both nucleus density and size distribution of graphene, representing a general problem in graphene CVD growth systems.It has been found that low-pressure CVD synthesis of graphene on Cu foil provides a good way of fabricating uniform single-layer graphene films (7). Studies have shown that the continuous films were formed by connecting randomly oriented, irregular-shaped, and micrometer-sized graphene flakes, resulting in the presence of a large amount of both low-and high-angle grain boundaries composed of pentagons and heptagons, which leads to a dramatic degradation in electronic properties compared with those of pristine graphene (7...

The Way towards Ultrafast Growth of Single‐Crystal Graphene on Copper

“…In addition, the inhomogeneities influence the growth rate slightly by affecting the diffusion process 53, 54, 55, 56, 57. Proper surface treatment technique, like long‐time annealing,65 polishing,56, 68, 87 melting and resolidification,72, 73, 74 and the above mentioned special Cu stacking configuration can accelerate the graphene growth by minimizing surface roughness.…”

“…The growth of large‐area high‐quality graphene films is fundamental for the upcoming graphene applications. Chemical vapour deposition (CVD) method offers good prospects to produce large‐size graphene films due to its simplicity, controllability and cost‐efficiency 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75. Many researches have verified that graphene can be catalytically grown on metallic substrates, like ruthenium (Ru),13, 14 iridium (Ir),15, 16 platinum (Pt),17, 18, …”

Molecular dynamics simulation of graphene on Cu (1 0 0) and (1 1 1) surfaces

“…However, we can well imagine that in experiments a narrow temperature window exists where the presence of graphene permanently tips the Cu surface from molten to solid. Graphene can be grown on molten Cu [6].…”

“…While early experiments used mechanical exfoliation with Scotch tape to produce single or few layer thick graphene samples, this process is not well suited for industrial production. issues are the role of hydrogen in the gas mixture [2,3,4], the interaction of graphene with Cu under different orientations [5], the influence of temperature on growth [6] and the diffusion of C atoms and clusters during graphene growth. [7].…”

Electromagnetic induction heating for single crystal graphene growth: morphology control by rapid heating and quenching

“…In general, nucleation densities on polycrystal Cu substrates are nonuniform, representing a key problem in high quality graphene film synthesis. Recently it has been found that uniform nucleation distribution, low nucleation density and highly ordered single crystal graphene films can be obtained by using liquid Cu film as catalytic, which is possibly due to the elimination of Cu grain boundaries 21,22 . However, the direct insight of single crystal graphene growth and its corresponding domain shape evolution during the growth process are still lacking.…”