This is the first reported instance of using hydrazine as the solvent. The graphene produced from the hydrazine solution is also a more efficient electrical conductor. Field-effect devices display output currents three orders of magnitude higher than previously reported using chemically produced graphene. Kaner and Kang's co-authors on the research were Vincent Tung, from Yang's lab, and Matthew Allen, from Kaner's lab.
"We have discovered a route toward solution processing of large-scale graphene sheets," Tung said. "These breakthroughs represent the future of graphene nanoelectronic research."
The coverage of graphene sheets can be controlled by altering concentration and composition of the hydrazine solution. The hydrazine method also preserves the sheets integrity, producing the largest-area graphene sheet yet reported, at 20 micrometers by 40 micrometers.
"These graphene sheets are by far the largest produced, and the method allows great control over deposition," says Allen. "Chemically converted graphene can now be studied in depth through a variety of electronic tests and microscopic techniques not previously possible."
"Interdisciplinary research of this sort is a benefit of collaborative institutes like the CNSI," said Kaner, also an associate director of the CNSI. "Graphene is a cutting-edge nanomaterial and one which has great potential to revolutionise electronics and many other fields."
There are two methods currently used for graphene production — a drawing method and a reduction method, each with drawbacks. In the drawing method, layers are peeled off graphite crystals until one is produced that is one-atom thick. When likely graphene suspects are identified from peeled layers, they must be extensively studied to conclusively prove their identity.
In the reduction method, silicon carbide is heated to 1100° C to reduce it to graphene. This process produces a small sample size, but is unlikely to be compatible with fabrication techniques for most electronic applications.
"This (hydrazine reduction) technology utilises a true solution process for graphene, which can dramatically simplify preparing electronic devices," said Yang, faculty director of the Nano Renewable Energy Center at the CNSI. "It thus holds great promise for future large-area, flexible electronics."