Heer, who helped discover many properties of carbon
nanotubes over the past decade, believes their primary
value has been in calling attention to the useful
properties of graphene. Continuous graphene circuitry
can be produced using standard microelectronic processing
techniques, potentially allowing creation of a "road
map" for high-volume graphene electronics manufacturing,
"Nanotubes are simply graphene that has been rolled
into a cylindrical shape," de Heer explained. "Using
narrow ribbons of graphene, we can get all the properties
of nanotubes because those properties are due to
the graphene and the confinement of the electrons,
not the nanotube structures."
De Heer envisions using the graphene electronics
for specialized applications, potentially within
conventional silicon-based systems. Graphene systems
could also be used as the foundation for molecular
electronics, helping resolve resistance issues that
now affect such systems.
"There is a huge advantage to making a system out
of one continuous material, compared to having different
materials with different interfaces – and large contract
resistances to cause heating at the contacts," he
De Heer and collaborators Claire Berger, Nate Brown,
Edward Conrad, Zhenting Dai, Rui Feng, Phillip First,
Joanna Hass, Tianbo Li, Xuebin Li, Alexei Marchenkov,
James Meindl, Asmerom Ogbazghi, Thomas Orlando, Zhimin
Song, Xiaosong Wu of Georgia Tech and Didier Mayou
and Cecile Naud of CNRS start with a wafer of silicon
carbide, a material made up of silicon and carbon
atoms. By heating the wafer in a high vacuum, they
drive silicon atoms from the surface, leaving a thin
continuous layer of graphene.
Next, they spin-coat onto the surface a photo-resist
material of the kind used in established microelectronics
techniques. Using optical lithography or electron-beam
lithography, they produce patterns on the surface,
then use conventional etching processes to remove
"We are doing lithography, which is completely familiar
to those who work in microelectronics," said de Heer. "It's
exactly what is done in microelectronics, but with
a different material. That is the appeal of this
Using electron beam lithography, they've created
feature sizes as small as 80 nanometers – on the
way toward a goal of 10 nanometers with the help
of a new nanolithographer in Georgia Tech's Microelectronics
The graphene circuitry demonstrates high electron
mobility – up to 25,000 square centimeters per volt-second,
showing that electrons move with little scattering.
The researchers have also shown electronic coherence
at near room temperature, and evidence of quantum
interference effects. They expect to see ballistic
transport when they make structures small enough.
So far, they have built an all graphene planar field-effect
transistor. The side-gated device produces a change
in resistance through its channel when voltage is
applied to the gate. However, this first device has
a substantial current leak, which the team expects
to eliminate with minor processing adjustments.
The researchers have also built a working quantum
interference device, a ring-shaped structure that
would be useful in manipulating electronic waves.
The key to properties of the new circuitry is the
width of the ribbons, which confine the electrons
in a quantum effect similar to that seen in carbon
nanotubes. The width of the ribbon controls the material's
band-gap. Other structures, such as sensing molecules,
could be attached to the edges of the ribbons, which
are normally passivated by hydrogen atoms.
De Heer and collaborators began working on graphene
in 2001 and received support from Intel in 2003.
They later received a Nanoscale Interdisciplinary
Research Team (NIRT) award from the U.S. National
Science Foundation. They have filed one patent for
their methods of fabricating graphene circuitry.
De Heer and his colleagues expect to continue improving
their materials and fabrication processes, while
producing and testing new structures. "We have taken
the first step of a very long road," de Heer said. "Building
a new class of electronics based on graphene is going
to be very difficult and require the efforts of many
Technical Contacts: Walt de Heer (404-894-7880);
E-mail: ( email@example.com )
or Phil First (404-894-0548); E-mail: ( firstname.lastname@example.org ).