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Image: Oak Ridge National Laboratory
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Atomic-level
defects in graphene could be a path forward to smaller and faster electronic
devices, according to a study led by researchers at the Department of Energy's
Oak Ridge National Laboratory (ORNL).
With unique
properties and potential applications in areas from electronics to biodevices,
graphene, which consists of a single sheet of carbon atoms, has been hailed as
a rising star in the materials world. Now, an ORNL study published in Nature Nanotechnology suggests that
point defects, composed of silicon atoms that replace individual carbon atoms
in graphene, could aid attempts to transfer data on an atomic scale by coupling
light with electrons.
"In this
proof-of-concept experiment, we have shown that a tiny wire made up of a pair
of single silicon atoms in graphene can be used to convert light into an
electronic signal, transmit the signal, and then convert the signal back into
light," said co-author Juan-Carlos Idrobo, who holds a joint appointment
at ORNL and Vanderbilt University.
An ORNL-led team
discovered this novel behavior by using aberration-corrected scanning
transmission electron microscopy to image the plasmon response, or optical-like
signals, of the point defects. The team's analysis found that the silicon atoms
act like atomic-sized antennae, enhancing the local surface plasmon response of
graphene, and creating a prototypical plasmonic device.
"The idea
with plasmonic devices is that they can convert optical signals into electronic
signals," Idrobo said. "So you could make really tiny wires, put
light in one side of the wire, and that signal will be transformed into
collective electron excitations known as plasmons. The plasmons will transmit
the signal through the wire, come out the other side and be converted back to
light."
Although other
plasmonic devices have been demonstrated, previous research in surface plasmons
has been focused primarily on metals, which has limited the scale at which the
signal transfer occurs.
"When
researchers use metal for plasmonic devices, they can usually only get down to
5 to 7 nm," said coauthor Wu Zhou. "But when you want to make things
smaller, you always want to know the limit. Nobody thought we could get down to
a single atom level."
In-depth
analysis at the level of a single atom was made possible through the team's
access to an electron microscope that is part of ORNL's Shared Research Equipment
(ShaRE) User Facility.
"It is the one
of only a few electron microscopes in the world that we can use to look at and
study materials and obtain crystallography, chemistry, bonding, optical, and
plasmon properties at the atomic scale with single atom sensitivity and at low
voltages," Idrobo said. "This is an ideal microscope for people who
want to research carbon-based materials, such as graphene."
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