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概要

Graphene 2018: Large single crystal graphene production

James C Sung

Graphene has phenomenal properties, such as 100X of steel’s tensile strength and 100X of copper’s electrical Conductivity. However, such properties depend on intact honeycomb structure of carbon atoms that may be present in natural graphite across nanometer scales of la or lc. In order to expand defects less graphite crystals to micron sizes honeycomb area about one million times, we invented a metal catalytic process to regrow graphite. By heat treatment of nickel metal to saturate carbon atoms as solute, la can be enlarged with temperature and time as shown below. In addition to expand the single crystals of regrown graphite, we also exfoliate such single crystals by a liquid injection method with high pressure NMP that contains suspended graphite through a diamond nozzle. The supersonic speed of liquid can suddenly expand graphite to fewer layers. In the meantime, the defect ridden region of the regrown graphite is removed.

A new method to produce large, monolayer single-crystal-like graphene films more than a foot long relies on harnessing a "survival of the fittest" competition among crystals. The novel technique, developed by a team led by the Department of Energy's Oak Ridge National Laboratory, may open new opportunities for growing the high-quality two-dimensional materials necessary for long-awaited practical applications.

Producing Thin Layers of graphene and other 2D materials on a scale required for research functions is common, however they must be manufactured on much larger scale to be purposeful.

Graphene is acclaimed for its potential of unprecedented strength and high electrical conductivity and can be made through generic approaches: isolated flakes of graphite-the silvery soft material found in pencils-into one-atom-thick layers, or developing atom by atom on a catalyst from a gaseous precursor until ultrathin layers are formed.

Oak Ridge National Laboratory – led team utilized this method, acknowledged as chemical vapour deposition or CVD. In a study published in Nature Materials, they analyzed how localized control of CVD process allows evolutionary or self-choosing growth under optimal conditions, yielding a large, single-crystal-like Sheet of graphene. According to the researchers, Large single crystals are more mechanically robust and may have higher conductivity because of the deficiency arising from interconnections between individual domains in polycrystalline graphene are eliminated. The CVD method could be the key not only to improve large-scale manufacture of single-crystal graphene but to other 2D materials as well, which is necessary for their large-scale applications.

Mostly like the conventional CVD approaches to produce graphene., a gaseous mixture of hydrocarbon precursor molecules has been sprayed by the researchers onto a metallic, polycrystalline foil. Yet they carefully controlled the local deposition of the hydrocarbon molecules, bringing them directly to the corner of the emerging graphene film. According to substrate transferred underneath, the carbon atoms continuously meet as a crystal of graphene up to a foot in length.

As the hydrocarbons contact down the warm catalyst foil, they shape clusters of carbon atoms that develop over time into larger domains until coalescing to cover the total substrate. The research team has already located that at sufficiently high temperatures, the carbon atoms of graphene did now not correlate, or mirror, the substrate's atoms, allowing for nonepitaxial crystalline growth.

Considering the concentration of the gas mixture robustly influences how shortly the single crystal develops, Delivering the hydrocarbon precursor near the existing edge of single graphene crystal can promote its increase in extra effectiveness than the formation of new clusters.Research group stated that In such a managed environment, the fastest-growing orientation of graphene crystals overwhelms the others and gets 'evolutionarily selected' into a single crystal, even on a polycrystalline substrate, without having to suit the substrate's orientation, which normally takes place with preferred epitaxial growth.

The team’s theoreticians, led by Rice University provided a model analyzing which crystal orientations Possess the unique properties that make them fittest in the run for survival, and why the choice of a may depend on the substrate and the precursors. They also found that if Graphene or any 2D materials, similar to Czochralki’s method for silicon. They also noticed that manufactures could rest assured that when a large, wafer-size raw layer is cut for any device fabrication, each resulting piece will be a quality monocrystal. This potentially huge, impactful role motivates us to explore theoretical principles to be as clear as possible.

Practical scaling up of graphene the use of the team's technique stays to be seen, however the researchers consider their evolutionary choice single-crystal growth approach may want to also be applied to promising alternative 2D substances such as boron nitride, also recognized as "white graphene," and molybdenum disulfide.

The scalable growth of wafer-sized single-crystal graphene in an energy-efficient manner and well suited with wafer technique is critical for the killer functions of graphene in high-performance electronics and optoelectronics. Here, ultrafast epitaxial growth of single-crystal graphene wafers is realized on single-crystal Cu90Ni10.skinny films fabricated with the aid of a tailor-made two-step magnetron sputtering and recrystallization process. The minor nickel (Ni) content material extensively enhances the catalytic exercise of Cu, rendering the growth of a 4 in. single-crystal monolayer graphene wafer in 10 min on Cu90Ni10, 50 folds quicker than graphene growth on Cu. Through the carbon isotope labeling experiments, graphene increase on Cu90Ni10 is proved to be completely surface-reaction dominated, which is ascribed to the Cu surface enrichment in the CuNi alloy, as indicated via aspect in-depth profile. One of the first-class benefits of our protocol is the compatibility with wafer procedure and incredible scalability.

The single-crystal graphene wafers could grip great promising for high-performance electronics and optoelectronics that are suitable with wafer process. Polycrystalline graphene is formed by means of randomly oriented graphene islands, which limit its quality. Currently, scientists are capable to grow meter-sized polycrystalline graphene and smaller single-crystal graphene, ranging from 0.01 mm2 to a few Centimetres. Taking into the account of the short time for graphene synthesis (20 minutes) and the relatively low-cost experimental setup, the cost of a single-crystal graphene could be close to that of current polycrystalline graphene films which is lower than silicon.