D
Dirk Bruere at NeoPax
- Jan 1, 1970
- 0
http://www.physorg.com/news/2011-01-expitaxial-graphene-silicon-electronics.html
(PhysOrg.com) -- Move over silicon. There's a new electronic material in
town, and it goes fast. That material, the focus of the 2010 Nobel Prize
in physics, is graphene -- a fancy name for extremely thin layers of
ordinary carbon atoms arranged in a "chicken-wire" lattice. These
layers, sometimes just a single atom thick, conduct electricity with
virtually no resistance, very little heat generation -- and less power
consumption than silicon.
With silicon device fabrication approaching its physical limits, many
researchers believe graphene can provide a new platform material that
would allow the semiconductor industry to continue its march toward
ever-smaller and faster electronic devices -- progress described in
Moore's Law. Though graphene will likely never replace silicon for
everyday electronic applications, it could take over as the material of
choice for high-performance devices.
And graphene could ultimately spawn a new generation of devices designed
to take advantage of its unique properties.
Since 2001, Georgia Tech has become a world leader in developing
epitaxial graphene, a specific type of graphene that can be grown on
large wafers and patterned for use in electronics manufacturing. In a
recent paper published in the journal Nature Nanotechnology, Georgia
Tech researchers reported fabricating an array of 10,000 top-gated
transistors on a 0.24 square centimeter chip, an achievement believed to
be the highest density reported so far in graphene devices.
In creating that array, they also demonstrated a clever new approach for
growing complex graphene patterns on templates etched into silicon
carbide. The new technique offered the solution to one of the most
difficult issues that had been facing graphene electronics.
"This is a significant step toward electronics manufacturing with
graphene," said Walt de Heer, a professor in Georgia Tech's School of
Physics who pioneered the development of graphene for high-performance
electronics. "This is another step showing that our method of working
with epitaxial graphene grown on silicon carbide is the right approach
and the one that will probably be used for making graphene electronics."
Unrolled Carbon Nanotubes
For de Heer, the story of graphene begins with carbon nanotubes, tiny
cylindrical structures considered miraculous when they first began to be
studied by scientists in 1991. De Heer was among the researchers excited
about the properties of nanotubes, whose unique arrangement of carbon
atoms gave them physical and electronic properties that scientists
believed could be the foundation for a new generation of electronic devices.
Carbon nanotubes still have attractive properties, but the ability to
grow them consistently -- and to incorporate them in high-volume
electronics applications -- has so far eluded researchers. De Heer
realized before others that carbon nanotubes would probably never be
used for high-volume electronic devices.
But he also realized that the key to the attractive electronic
properties of the nanotubes was the lattice created by the carbon atoms.
Why not simply grow that lattice on a flat surface, and use fabrication
techniques proven in the microelectronics industry to create devices in
much the same way as silicon integrated circuits?
By heating silicon carbide -- a widely-used electronic material -- de
Heer and his colleagues were able to drive silicon atoms from the
surface, leaving just the carbon lattice in thin layers of graphene
large enough to grow the kinds of electronic devices familiar to a
generation of electronics designers.
That process was the basis for a patent filed in 2003, and for initial
research support from chip-maker Intel. Since then, de Heer's group has
published dozens of papers and helped spawn other research groups also
using epitaxial graphene for electronic devices. Though scientists are
still learning about the material, companies such as IBM have launched
research programs based on epitaxial graphene, and agencies such as the
National Science Foundation (NSF) and Defense Advanced Research Projects
Agency (DARPA) have invested in developing the material for future
electronics applications.
Georgia Tech's work on developing epitaxial graphene for manufacturing
electronic devices was recognized in the background paper produced by
the Royal Swedish Academy of Sciences as part of the Nobel Prize
documentation.
The race to find commercial applications for graphene is intense, with
researchers from the United States, Europe, Japan and Singapore engaged
in well-funded efforts. Since awarding of the Nobel to a group from the
United Kingdom, the flood of news releases about graphene developments
has grown.
"Our epitaxial graphene is now used around the world by many research
laboratories," de Heer noted. "We are probably at the stage where
silicon was in the 1950s. This is the beginning of something that is
going to be very large and important."
Silicon "Running Out of Gas"
A new electronics material is needed because silicon is running out of
miniaturization room.
"Primarily, we've gotten the speed increases from silicon by continually
shrinking feature sizes and improving interconnect technology," said
Dennis Hess, director of the National Science Foundation-sponsored
Materials Research Science and Engineering Center (MRSEC) established at
Georgia Tech to study future electronic materials, starting with
epitaxial graphene. "We are at the point where in less than 10 years, we
won't be able to shrink feature sizes any farther because of the physics
of the device operation. That means we will either have to change the
type of device we make, or change the electronic material we use."
It's a matter of physics. At the very small size scales needed to create
ever more dense device arrays, silicon generates too much resistance to
electron flow, creating more heat than can be dissipated and consuming
too much power.
Graphene has no such restrictions, and in fact, can provide electron
mobility as much as 100 times better than silicon. De Heer believes his
group has developed the roadmap for the future of high-performance
electronics -- and that it is paved with epitaxial graphene.
"We have basically developed a whole scheme for making electronics out
of graphene," he said. "We have set down what we believe will be the
ground rules for how that will work, and we have the key patents in place."
Silicon, of course, has matured over many generations through constant
research and improvement. De Heer and Hess agree that silicon will
always be around, useful for low-cost consumer products such as iPods,
toasters, personal computers and the like.
De Heer expects graphene to find its niche doing things that couldn't
otherwise be done.
"We're not trying to do something cheaper or better; we're going to do
things that can't be done at all with silicon," he said. "Making
electronic devices as small as a molecule, for instance, cannot be done
with silicon, but in principle could be done with graphene. The key
question is how to extend Moore's Law in a post-CMOS world."
Unlike the carbon nanotubes he studied in the 1990s, de Heer sees no
major problems ahead for the development of epitaxial graphene.
"That graphene is going to be a major player in the electronics of the
future is no longer in doubt," he said. "We don't see any real
roadblocks ahead. There are no flashing red lights or other signs that
seem to say that this won't work. All of the issues we see relate to
improving technical issues, and we know how to do that."
Making the Best Graphene
Since beginning the exploration of graphene in 2001, de Heer and his
research team have made continuous improvements in the quality of the
material they produce, and those improvements have allowed them to
demonstrate a number of physical properties -- such as the Quantum Hall
Effect -- that verify the unique properties of the material.
"The properties that we see in our epitaxial graphene are similar to
what we have calculated for an ideal theoretical sheet of graphene
suspended in the air," said Claire Berger, a research scientist in the
Georgia Tech School of Physics who also has a faculty appointment at the
Centre National de la Recherche Scientifique in France. "We see these
properties in the electron transport and we see these properties in all
kinds of spectroscopy. Everything that is supposed to be occurring in a
single sheet of graphene we are seeing in our systems."
Key to the material's future, of course, is the ability to make
electronic devices that work consistently. The researchers believe they
have almost reached that point.
"All of the properties that epitaxial graphene needs to make it viable
for electronic devices have been proven in this material," said Ed
Conrad, a professor in Georgia Tech's School of Physics who is also a
MRSEC member. "We have shown that we can make macroscopic amounts of
this material, and with the devices that are scalable, we have the
groundwork that could really make graphene take off."
Reaching higher and higher device density is also important, along with
the ability to control the number of layers of graphene produced. The
group has demonstrated that in their multilayer graphene, each layer
retains the desired properties.
"Multilayer graphene has different stacking than graphite, the material
found in pencils," Conrad noted. "In graphite, every layer is rotated 60
degrees and that's the only way that nature can do it. When we grow
graphene on silicon carbide, the layers are rotated 30 degrees. When
that happens, the symmetry of the system changes to make the material
behave the way we want it to."
Epitaxial Versus Exfoliated
Much of the world's graphene research -- including work leading to the
Nobel -- involved the study of exfoliated graphene: layers of the
material removed from a block of graphite, originally with tape. While
that technique produces high-quality graphene, it's not clear how that
could be scaled up for industrial production.
While agreeing that the exfoliated material has produced useful
information about graphene properties, de Heer dismisses it as "a
science project" unlikely to have industrial electronics application.
"Electronics companies are not interested in graphene flakes," he said.
"They need industrial graphene, a material that can be scaled up for
high-volume manufacturing. Industry is now getting more and more
interested in what we are doing."
De Heer says Georgia Tech's place in the new graphene world is to focus
on electronic applications.
"We are not really trying to compete with these other groups," he said.
"We are really trying to create a practical electronic material. To do
that, we will have to do many things right, including fabricating a
scalable material that can be made as large as a wafer. It will have to
be uniform and able to be processed using industrial methods."
Resolving Technical Issues
Among the significant technical issues facing graphene devices has been
electron scattering that occurs at the boundaries of nanoribbons. If the
edges aren't perfectly smooth -- as usually happens when the material is
cut with electron beams -- the roughness bounces electrons around,
creating resistance and interference.
To address that problem, de Heer and his team recently developed a new
"templated growth" technique for fabricating nanometer-scale graphene
devices. The technique involves etching patterns into the silicon
carbide surfaces on which epitaxial graphene is grown. The patterns
serve as templates directing the growth of graphene structures, allowing
the formation of nanoribbons of specific widths without the use of
e-beams or other destructive cutting techniques. Graphene nanoribbons
produced with these templates have smooth edges that avoid
electron-scattering problems.
"Using this approach, we can make very narrow ribbons of interconnected
graphene without the rough edges," said de Heer. "Anything that can be
done to make small structures without having to cut them is going to be
useful to the development of graphene electronics because if the edges
are too rough, electrons passing through the ribbons scatter against the
edges and reduce the desirable properties of graphene."
In nanometer-scale graphene ribbons, quantum confinement makes the
material behave as a semiconductor suitable for creation of electronic
devices. But in ribbons a micron or so wide, the material acts as a
conductor. Controlling the depth of the silicon carbide template allows
the researchers to create these different structures simultaneously,
using the same growth process.
"The same material can be either a conductor or a semiconductor
depending on its shape," noted de Heer. "One of the major advantages of
graphene electronics is to make the device leads and the semiconducting
ribbons from the same material. That's important to avoid electrical
resistance that builds up at junctions between different materials."
After formation of the nanoribbons, the researchers apply a dielectric
material and metal gate to construct field-effect transistors. While
successful fabrication of high-quality transistors demonstrates
graphene's viability as an electronic material, de Heer sees them as
only the first step in what could be done with the material.
"When we manage to make devices well on the nanoscale, we can then move
on to make much smaller and finer structures that will go beyond
conventional transistors to open up the possibility for more
sophisticated devices that use electrons more like light than
particles," he said. "If we can factor quantum mechanical features into
electronics, that is going to open up a lot of new possibilities."
Collaborations with Other Groups
Before engineers can use epitaxial graphene for the next generation of
electronic devices, they will have to understand its unique properties.
As part of that process, Georgia Tech researchers are collaborating with
scientists at the National Institute of Standards and Technology (NIST).
The collaboration has produced new insights into how electrons behave in
graphene.
In a recent paper published in the journal Nature Physics, the Georgia
Tech-NIST team described for the first time how the orbits of electrons
are distributed spatially by magnetic fields applied to layers of
epitaxial graphene. They also found that these electron orbits can
interact with the substrate on which the graphene is grown, creating
energy gaps that affect how electron waves move through the multilayer
material.
"The regular pattern of magnetically-induced energy gaps in the graphene
surface creates regions where electron transport is not allowed," said
Phillip N. First, a professor in the Georgia Tech School of Physics and
MRSEC member. "Electron waves would have to go around these regions,
requiring new patterns of electron wave interference. Understanding this
interference would be important for some bi-layer graphene devices that
have been proposed."
Earlier NIST collaborations led to improved understanding of graphene
electron states, and the way in which low temperature and high magnetic
fields can affect energy levels. The researchers also demonstrated that
atomic-scale moiré patterns, an interference pattern that appears when
two or more graphene layers are overlaid, can be used to measure how
sheets of graphene are stacked.
In a collaboration with the U.S. Naval Research Laboratory and
University of Illinois at Urbana-Champaign, a group of Georgia Tech
professors developed a simple and quick one-step process for creating
nanowires on graphene oxide.
"We've shown that by locally heating insulating graphene oxide, both the
flakes and the epitaxial varieties, with an atomic force microscope tip,
we can write nanowires with dimensions down to 12 nanometers," said
Elisa Riedo, an associate professor in the Georgia Tech School of
Physics and a MRSEC member. "And we can tune their electronic properties
to be up to four orders of magnitude more conductive."
A New Industrial Revolution?
Though graphene can be grown and fabricated using processes similar to
those of silicon, it is not easily compatible with silicon. That means
companies adopting it will also have to build new fabrication facilities
-- an expensive investment. Consequently, de Heer believes industry will
be cautious about moving into a new graphene world.
"Silicon technology is completely entrenched and well developed," he
admitted. "We can adopt many of the processes of silicon, but we can't
easily integrate ourselves into silicon. Because of that, we really need
a major paradigm shift. But for the massive electronics industry, that
will not happen easily or gently."
He draws an analogy to steamships and passenger trains at the dawn of
the aviation age. At some point, it became apparent that airliners were
going to replace both ocean liners and trains in providing first-class
passenger service. Though the cost of air travel was higher, passengers
were willing to pay a premium for greater speed.
"We are going to see a coexistence of technologies for a while, and how
the hybridization of graphene and silicon electronics is going to happen
remains up in the air," de Heer predicted. "That is going to take
decades, though in the next ten years we are probably going to see real
commercial devices that involve graphene."
Provided by Georgia Institute of Technology (news : web)
--
Dirk
http://www.neopax.com/technomage/ - My new book
http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show
(PhysOrg.com) -- Move over silicon. There's a new electronic material in
town, and it goes fast. That material, the focus of the 2010 Nobel Prize
in physics, is graphene -- a fancy name for extremely thin layers of
ordinary carbon atoms arranged in a "chicken-wire" lattice. These
layers, sometimes just a single atom thick, conduct electricity with
virtually no resistance, very little heat generation -- and less power
consumption than silicon.
With silicon device fabrication approaching its physical limits, many
researchers believe graphene can provide a new platform material that
would allow the semiconductor industry to continue its march toward
ever-smaller and faster electronic devices -- progress described in
Moore's Law. Though graphene will likely never replace silicon for
everyday electronic applications, it could take over as the material of
choice for high-performance devices.
And graphene could ultimately spawn a new generation of devices designed
to take advantage of its unique properties.
Since 2001, Georgia Tech has become a world leader in developing
epitaxial graphene, a specific type of graphene that can be grown on
large wafers and patterned for use in electronics manufacturing. In a
recent paper published in the journal Nature Nanotechnology, Georgia
Tech researchers reported fabricating an array of 10,000 top-gated
transistors on a 0.24 square centimeter chip, an achievement believed to
be the highest density reported so far in graphene devices.
In creating that array, they also demonstrated a clever new approach for
growing complex graphene patterns on templates etched into silicon
carbide. The new technique offered the solution to one of the most
difficult issues that had been facing graphene electronics.
"This is a significant step toward electronics manufacturing with
graphene," said Walt de Heer, a professor in Georgia Tech's School of
Physics who pioneered the development of graphene for high-performance
electronics. "This is another step showing that our method of working
with epitaxial graphene grown on silicon carbide is the right approach
and the one that will probably be used for making graphene electronics."
Unrolled Carbon Nanotubes
For de Heer, the story of graphene begins with carbon nanotubes, tiny
cylindrical structures considered miraculous when they first began to be
studied by scientists in 1991. De Heer was among the researchers excited
about the properties of nanotubes, whose unique arrangement of carbon
atoms gave them physical and electronic properties that scientists
believed could be the foundation for a new generation of electronic devices.
Carbon nanotubes still have attractive properties, but the ability to
grow them consistently -- and to incorporate them in high-volume
electronics applications -- has so far eluded researchers. De Heer
realized before others that carbon nanotubes would probably never be
used for high-volume electronic devices.
But he also realized that the key to the attractive electronic
properties of the nanotubes was the lattice created by the carbon atoms.
Why not simply grow that lattice on a flat surface, and use fabrication
techniques proven in the microelectronics industry to create devices in
much the same way as silicon integrated circuits?
By heating silicon carbide -- a widely-used electronic material -- de
Heer and his colleagues were able to drive silicon atoms from the
surface, leaving just the carbon lattice in thin layers of graphene
large enough to grow the kinds of electronic devices familiar to a
generation of electronics designers.
That process was the basis for a patent filed in 2003, and for initial
research support from chip-maker Intel. Since then, de Heer's group has
published dozens of papers and helped spawn other research groups also
using epitaxial graphene for electronic devices. Though scientists are
still learning about the material, companies such as IBM have launched
research programs based on epitaxial graphene, and agencies such as the
National Science Foundation (NSF) and Defense Advanced Research Projects
Agency (DARPA) have invested in developing the material for future
electronics applications.
Georgia Tech's work on developing epitaxial graphene for manufacturing
electronic devices was recognized in the background paper produced by
the Royal Swedish Academy of Sciences as part of the Nobel Prize
documentation.
The race to find commercial applications for graphene is intense, with
researchers from the United States, Europe, Japan and Singapore engaged
in well-funded efforts. Since awarding of the Nobel to a group from the
United Kingdom, the flood of news releases about graphene developments
has grown.
"Our epitaxial graphene is now used around the world by many research
laboratories," de Heer noted. "We are probably at the stage where
silicon was in the 1950s. This is the beginning of something that is
going to be very large and important."
Silicon "Running Out of Gas"
A new electronics material is needed because silicon is running out of
miniaturization room.
"Primarily, we've gotten the speed increases from silicon by continually
shrinking feature sizes and improving interconnect technology," said
Dennis Hess, director of the National Science Foundation-sponsored
Materials Research Science and Engineering Center (MRSEC) established at
Georgia Tech to study future electronic materials, starting with
epitaxial graphene. "We are at the point where in less than 10 years, we
won't be able to shrink feature sizes any farther because of the physics
of the device operation. That means we will either have to change the
type of device we make, or change the electronic material we use."
It's a matter of physics. At the very small size scales needed to create
ever more dense device arrays, silicon generates too much resistance to
electron flow, creating more heat than can be dissipated and consuming
too much power.
Graphene has no such restrictions, and in fact, can provide electron
mobility as much as 100 times better than silicon. De Heer believes his
group has developed the roadmap for the future of high-performance
electronics -- and that it is paved with epitaxial graphene.
"We have basically developed a whole scheme for making electronics out
of graphene," he said. "We have set down what we believe will be the
ground rules for how that will work, and we have the key patents in place."
Silicon, of course, has matured over many generations through constant
research and improvement. De Heer and Hess agree that silicon will
always be around, useful for low-cost consumer products such as iPods,
toasters, personal computers and the like.
De Heer expects graphene to find its niche doing things that couldn't
otherwise be done.
"We're not trying to do something cheaper or better; we're going to do
things that can't be done at all with silicon," he said. "Making
electronic devices as small as a molecule, for instance, cannot be done
with silicon, but in principle could be done with graphene. The key
question is how to extend Moore's Law in a post-CMOS world."
Unlike the carbon nanotubes he studied in the 1990s, de Heer sees no
major problems ahead for the development of epitaxial graphene.
"That graphene is going to be a major player in the electronics of the
future is no longer in doubt," he said. "We don't see any real
roadblocks ahead. There are no flashing red lights or other signs that
seem to say that this won't work. All of the issues we see relate to
improving technical issues, and we know how to do that."
Making the Best Graphene
Since beginning the exploration of graphene in 2001, de Heer and his
research team have made continuous improvements in the quality of the
material they produce, and those improvements have allowed them to
demonstrate a number of physical properties -- such as the Quantum Hall
Effect -- that verify the unique properties of the material.
"The properties that we see in our epitaxial graphene are similar to
what we have calculated for an ideal theoretical sheet of graphene
suspended in the air," said Claire Berger, a research scientist in the
Georgia Tech School of Physics who also has a faculty appointment at the
Centre National de la Recherche Scientifique in France. "We see these
properties in the electron transport and we see these properties in all
kinds of spectroscopy. Everything that is supposed to be occurring in a
single sheet of graphene we are seeing in our systems."
Key to the material's future, of course, is the ability to make
electronic devices that work consistently. The researchers believe they
have almost reached that point.
"All of the properties that epitaxial graphene needs to make it viable
for electronic devices have been proven in this material," said Ed
Conrad, a professor in Georgia Tech's School of Physics who is also a
MRSEC member. "We have shown that we can make macroscopic amounts of
this material, and with the devices that are scalable, we have the
groundwork that could really make graphene take off."
Reaching higher and higher device density is also important, along with
the ability to control the number of layers of graphene produced. The
group has demonstrated that in their multilayer graphene, each layer
retains the desired properties.
"Multilayer graphene has different stacking than graphite, the material
found in pencils," Conrad noted. "In graphite, every layer is rotated 60
degrees and that's the only way that nature can do it. When we grow
graphene on silicon carbide, the layers are rotated 30 degrees. When
that happens, the symmetry of the system changes to make the material
behave the way we want it to."
Epitaxial Versus Exfoliated
Much of the world's graphene research -- including work leading to the
Nobel -- involved the study of exfoliated graphene: layers of the
material removed from a block of graphite, originally with tape. While
that technique produces high-quality graphene, it's not clear how that
could be scaled up for industrial production.
While agreeing that the exfoliated material has produced useful
information about graphene properties, de Heer dismisses it as "a
science project" unlikely to have industrial electronics application.
"Electronics companies are not interested in graphene flakes," he said.
"They need industrial graphene, a material that can be scaled up for
high-volume manufacturing. Industry is now getting more and more
interested in what we are doing."
De Heer says Georgia Tech's place in the new graphene world is to focus
on electronic applications.
"We are not really trying to compete with these other groups," he said.
"We are really trying to create a practical electronic material. To do
that, we will have to do many things right, including fabricating a
scalable material that can be made as large as a wafer. It will have to
be uniform and able to be processed using industrial methods."
Resolving Technical Issues
Among the significant technical issues facing graphene devices has been
electron scattering that occurs at the boundaries of nanoribbons. If the
edges aren't perfectly smooth -- as usually happens when the material is
cut with electron beams -- the roughness bounces electrons around,
creating resistance and interference.
To address that problem, de Heer and his team recently developed a new
"templated growth" technique for fabricating nanometer-scale graphene
devices. The technique involves etching patterns into the silicon
carbide surfaces on which epitaxial graphene is grown. The patterns
serve as templates directing the growth of graphene structures, allowing
the formation of nanoribbons of specific widths without the use of
e-beams or other destructive cutting techniques. Graphene nanoribbons
produced with these templates have smooth edges that avoid
electron-scattering problems.
"Using this approach, we can make very narrow ribbons of interconnected
graphene without the rough edges," said de Heer. "Anything that can be
done to make small structures without having to cut them is going to be
useful to the development of graphene electronics because if the edges
are too rough, electrons passing through the ribbons scatter against the
edges and reduce the desirable properties of graphene."
In nanometer-scale graphene ribbons, quantum confinement makes the
material behave as a semiconductor suitable for creation of electronic
devices. But in ribbons a micron or so wide, the material acts as a
conductor. Controlling the depth of the silicon carbide template allows
the researchers to create these different structures simultaneously,
using the same growth process.
"The same material can be either a conductor or a semiconductor
depending on its shape," noted de Heer. "One of the major advantages of
graphene electronics is to make the device leads and the semiconducting
ribbons from the same material. That's important to avoid electrical
resistance that builds up at junctions between different materials."
After formation of the nanoribbons, the researchers apply a dielectric
material and metal gate to construct field-effect transistors. While
successful fabrication of high-quality transistors demonstrates
graphene's viability as an electronic material, de Heer sees them as
only the first step in what could be done with the material.
"When we manage to make devices well on the nanoscale, we can then move
on to make much smaller and finer structures that will go beyond
conventional transistors to open up the possibility for more
sophisticated devices that use electrons more like light than
particles," he said. "If we can factor quantum mechanical features into
electronics, that is going to open up a lot of new possibilities."
Collaborations with Other Groups
Before engineers can use epitaxial graphene for the next generation of
electronic devices, they will have to understand its unique properties.
As part of that process, Georgia Tech researchers are collaborating with
scientists at the National Institute of Standards and Technology (NIST).
The collaboration has produced new insights into how electrons behave in
graphene.
In a recent paper published in the journal Nature Physics, the Georgia
Tech-NIST team described for the first time how the orbits of electrons
are distributed spatially by magnetic fields applied to layers of
epitaxial graphene. They also found that these electron orbits can
interact with the substrate on which the graphene is grown, creating
energy gaps that affect how electron waves move through the multilayer
material.
"The regular pattern of magnetically-induced energy gaps in the graphene
surface creates regions where electron transport is not allowed," said
Phillip N. First, a professor in the Georgia Tech School of Physics and
MRSEC member. "Electron waves would have to go around these regions,
requiring new patterns of electron wave interference. Understanding this
interference would be important for some bi-layer graphene devices that
have been proposed."
Earlier NIST collaborations led to improved understanding of graphene
electron states, and the way in which low temperature and high magnetic
fields can affect energy levels. The researchers also demonstrated that
atomic-scale moiré patterns, an interference pattern that appears when
two or more graphene layers are overlaid, can be used to measure how
sheets of graphene are stacked.
In a collaboration with the U.S. Naval Research Laboratory and
University of Illinois at Urbana-Champaign, a group of Georgia Tech
professors developed a simple and quick one-step process for creating
nanowires on graphene oxide.
"We've shown that by locally heating insulating graphene oxide, both the
flakes and the epitaxial varieties, with an atomic force microscope tip,
we can write nanowires with dimensions down to 12 nanometers," said
Elisa Riedo, an associate professor in the Georgia Tech School of
Physics and a MRSEC member. "And we can tune their electronic properties
to be up to four orders of magnitude more conductive."
A New Industrial Revolution?
Though graphene can be grown and fabricated using processes similar to
those of silicon, it is not easily compatible with silicon. That means
companies adopting it will also have to build new fabrication facilities
-- an expensive investment. Consequently, de Heer believes industry will
be cautious about moving into a new graphene world.
"Silicon technology is completely entrenched and well developed," he
admitted. "We can adopt many of the processes of silicon, but we can't
easily integrate ourselves into silicon. Because of that, we really need
a major paradigm shift. But for the massive electronics industry, that
will not happen easily or gently."
He draws an analogy to steamships and passenger trains at the dawn of
the aviation age. At some point, it became apparent that airliners were
going to replace both ocean liners and trains in providing first-class
passenger service. Though the cost of air travel was higher, passengers
were willing to pay a premium for greater speed.
"We are going to see a coexistence of technologies for a while, and how
the hybridization of graphene and silicon electronics is going to happen
remains up in the air," de Heer predicted. "That is going to take
decades, though in the next ten years we are probably going to see real
commercial devices that involve graphene."
Provided by Georgia Institute of Technology (news : web)
--
Dirk
http://www.neopax.com/technomage/ - My new book
http://www.transcendence.me.uk/ - Transcendence UK
http://www.blogtalkradio.com/onetribe - Occult Talk Show
