Kaustav Banerjee, a professor with the Electrical and Computer
Engineering department and Director of the Nanoelectronics Research Lab
at UCSB that has been studying carbon nanomaterials for more than seven
years, led the research team to perfect methods of growing sheets of
graphene, as detailed in a study to be published in the November 2011
issue of the journal Carbon.
"Our process has certain unique advantages that give rise to high
quality graphene," says Banerjee. "For the electronics industry to
effectively use graphene, it must first be grown selectively and in
larger sheets. We have developed a synthesis technique that yields high-
quality and high-uniformity graphene that can be translated into a
scalable process for industry applications."
UCSB researchers have successfully controlled the growth of a
high-quality bilayer graphene on a copper substrate using a method
called chemical vapor deposition (CVD), which breaks down molecules of
methane gas to build graphene sheets with carbon atoms.
Using adhesive tape to lift flakes of graphene from graphite,
University of Manchester researchers Geim and Novoselov were awarded the
2010 Nobel Prize in Physics for their pioneering isolation and
characterization of the material. To launch graphene into futuristic
applications, however, researchers have been seeking a controlled and
efficient way to grow a higher quality of this single-atom-thick
material in larger areas.
The discovery by UCSB researchers turns graphene production into an
industry-friendly process by improving the quality and uniformity of
graphene using efficient and reproducible methods. They were able to
control the number of graphene layers produced -- from mono-layer to
bi-layer graphene -- an important distinction for future applications in
electronics and other technology.
"Intel has a keen interest in graphene due to many possibilities it
holds for the next generation of energy- efficient computing, but there
are many roadblocks along the way," added Intel Fellow, Shekhar Borkar.
"The scalable synthesis technique developed by Professor Banerjee's
group at UCSB is an important step forward."
As a material, graphene is the thinnest and strongest in the world --
more than 100 times stronger than diamond -- and is capable of acting
as an ultimate conductor at room temperature. If it can be produced
effectively, graphene's properties make it ideal for advancements in
green electronics, super strong materials, and medical technology.
Graphene could be used to make flexible screens and electronic devices,
computers with 1,000 GHz processors that run on virtually no energy, and
ultra-efficient solar power cells.
Key to the UCSB team's discovery is their understanding of graphene
growth kinetics under the influence of the substrate. Their approach
uses a method called low pressure chemical vapor deposition (LPCVD) and
involves disintegrating the hydrocarbon gas methane at a specific high
temperature to build uniform layers of carbon (as graphene) on a
pretreated copper substrate. Banerjee's research group established a set
of techniques that optimized the uniformity and quality of graphene,
while controlling the number of graphene layers they grew on their
substrate.
According to Dr. Wei Liu, a post-doctoral researcher and co-author of
the study, "Graphene growth is strongly affected by imperfection sites
on the copper substrate. By proper treatment of the copper surface and
precise selection of the growth parameters, the quality and uniformity
of graphene are significantly improved and the number of graphene layers
can be controlled."
Professor Banerjee and credited authors Wei Liu, Hong Li, Chuan Xu
and Yasin Khatami are not the first research team to make graphene using
the CVD method, but they are the first to successfully refine critical
methods to grow a high quality of graphene. In the past, a key challenge
for the CVD method has been that it yields a lower quality of graphene
in terms of carrier mobility -- or how well it conducts electrons. "Our
graphene exhibits the highest reported field-effect mobility to date for
CVD graphene, having an average value of 4000 cm2/V.s with the highest
peak value at 5500 cm2/V.s. This is an extremely high value compared
with the mobility of silicon." added Hong Li, a Ph.D. candidate in
Banerjee's research group.
"Kaustav Banerjee's group is leading graphene nanoelectronics
research efforts at UCSB, from material synthesis to device design and
circuit exploration. His work has provided our campus with unique and
very powerful capabilities," added David Awschalom, Professor of
Physics, Electrical and Computer Engineering, and Director of the
California NanoSystems Institute (CNSI) at UCSB where Banerjee's
laboratory is located. "This new facility has also boosted our
opportunities for collaborations across various science and engineering
disciplines."
"There is no doubt graphene is a superior material. Intrinsically it
is amazing," says Banerjee. "It is up to us, the scientists and
engineers, to show how we can use graphene and harness its capabilities.
There are challenges in how to grow it, how to transfer or not to
transfer and pattern it, and how to tailor its properties for specific
applications. But these challenges are fertile grounds for exciting
research in the future."
Their research was supported by the National Science Foundation and
conducted at the California NanoSystems Institute (CNSI) and Materials
Research Laboratory (MRL) facilities at UC Santa Barbara.
From sciencedaily
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