Director Ruoff notes, “This pioneering breakthrough was due to many contributing factors, including human ingenuity and the ability of the CMCM researchers to reproducibly make large-area single-crystal Cu-Ni(111) foils, on which the graphene was grown by chemical vapor deposition (CVD) using a mixture of ethylene with hydrogen in a stream of argon gas.” Student Meihui Wang, Dr. Ming Huang, and Dr. Da Luo along with Ruoff undertook a series of experiments of growing single-crystal and single-layer graphene on such ‘home-made’ Cu-Ni(111) foils under different temperatures.
The team had previously reported single-crystal and adlayer-free films of graphene which were grown using methane at temperatures of ~1320 Kelvin (K) degrees on Cu(111) foils. Adlayers refer to small “islands” of regions that have another layer of graphene present. However, these films always contained long “folds” that are the consequence of tall wrinkles that form as the graphene is cooled from the growth temperature down to room temperature. This results in an undesirable reduction in the performance of graphene field effect transistor (GFET) if the “fold” is in the active region of the GFET. The folds also contain “cracks” that lower the mechanical strength of the graphene.
The next exciting challenge was thus eliminating these folds.
Importantly, the research team was able to achieve “scaling up” of graphene production using this method. The graphene was successfully grown on 5 foils (dimension 4 cm x 7 cm) simultaneously in a 6-inch diameter home-built quartz furnace. “Our method of growing fold-free graphene films is very reproducible, with each foil yielding two identical pieces of high-quality graphene films on both sides of the foil,” and “By using the electrochemical bubbling transfer method, graphene can be delaminated in about 1 minute and the Cu-Ni(111) foil can be quickly readied for the next growth/transfer cycle,” notes Meihui Wang. Ming Huang adds, “When we tested the weight loss of Cu-Ni(111) foils after 5 runs of growth and transfers, the net loss was only 0.0001 grams. This means that our growth and transfer methods using the Cu-Ni(111) can be performed repeatedly, essentially indefinitely.”
Such large-area fold-free single-crystal graphene film allows for the straightforward fabrication of integrated high-performance devices oriented in any direction over the entire graphene film. These single-crystal graphene films will be important for further advances in basic science, which will lead to new applications in electronic, photonic, mechanical, thermal, and other areas. The near-perfect graphene is also useful for stacking, either with itself and/or with other 2D materials, to further expand the range of likely applications. Given that the Cu-Ni(111) foils can be used repeatedly and that the graphene can be transferred to other substrates in less than one minute, the scalable manufacturing using this process is also highly promising.
A further interesting aspect of this article is that it includes Nature’s “Transparent Peer Review” document, so that readers may read through the reviewer comments and author rebuttals to also “observe” the process of scientific review. The paper went through two cycles of review and thus three revisions of the main text and the Supplemental Information document prior to being accepted. When the review process “works well”, reviewers offer useful comments and questions that the authors can then ponder and try to answer. Ruoff and Luo noted that “We dived back into our labs at the CMCM and really worked hard to respond to the reviewer comments and also to tackle other interesting aspects of the science during the 6-month time between our originally submitted manuscript to Nature, and its acceptance after 3 rounds of revision.” Ruoff further notes, “This was like a huge breath of fresh air for us— we got professional reviews and the entire review experience was professional in all regards. I think the “Transparent Peer Review” played a role in achieving this proper level of professionalism. Other journals might take note.”
This research was supported by the Institute for Basic Science and has been published in the journal Nature
Post credits to IBS Communication team