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The atomic resolution Z-contrast images
show individual silicon atoms bonded differently in graphene.
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Electron microscopy at the Department of Energy's Oak Ridge National Laboratory is providing unprecedented views of the individual atoms in graphene, offering scientists a chance to unlock the material's full potential for uses from engine combustion to consumer electronics.
Graphene crystals were first isolated
in 2004. They are two-dimensional (one-atom in thickness), harder
than diamonds and far stronger than steel, providing unprecedented
stiffness, electrical and thermal properties. By viewing the atomic
and bonding configurations of individual graphene atoms, scientists
are able to suggest ways to optimize materials so they are better
suited for specific applications.
"We have used new experimental and
computational tools to reveal the bonding characteristics of
individual impurities in graphene. For instance, we can now
differentiate between a non-carbon atom that is two-dimensionally or
three-dimensionally bonded in graphene. In fact, we were finally able
to directly visualize a bonding configuration that was predicted in
the 1930s but has never been observed experimentally," said ORNL
researcher Juan-Carlos Idrobo. Electrons in orbit around an atom fall
into four broad categories - s, p, d and f - based on factors
including symmetry and energy levels.
"We observed that silicon d-states
participate in the bonding only when the silicon is two-dimensionally
coordinated," Idrobo said. "There are many elements such as
chromium, iron, and copper where the d-states or d-electrons play a
dominant role in determining how the element bonds in a material."
By studying the atomic and electronic
structure of graphene and identifying any impurities, researchers can
better predict which elemental additions will improve the material's
performance.
Slightly altering the chemical makeup
of graphene could customize the material, making it more suitable for
a variety of applications. For example, one elemental addition may
make the material a better replacement for the platinum catalytic
converters in cars, while another may allow it to function better in
electronic devices or as a membrane.
Graphene has the potential to replace
the inner workings of electronic gadgets people use every day because
of its ability to conduct heat and electricity and its optical
transparency. It offers a cheaper and more abundant alternative to
indium, a limited resource that is widely used in the transparent
conducting coating present in almost all electronic display devices
such as digital displays in cars, TVs, laptops and handheld gadgets
like cell phones, tablets and music players.
Researchers expect the imaging
techniques demonstrated at ORNL to be used to understand the atomic
structures and bonding characteristics of atoms in other
two-dimensional materials, too.
The authors of the paper are Wu Zhou,
Myron Kapetanakis, Micah Prange, Sokrates Pantelides, Stephen
Pennycook and Idrobo.
This research was supported by National
Science Foundation and the DOE Office of Science. Researchers also
made use of Oak Ridge National Laboratory's Shared Research Equipment
User Facility along with Lawrence Berkeley National Laboratory's
National Energy Research Scientific Computing Center, both of which
are also supported by DOE's Office of Science.
ORNL is managed by UT-Battelle for the
Department of Energy's Office of Science. DOE's Office of Science is
the single largest supporter of basic research in the physical
sciences in the United States, and is working to address some of the
most pressing challenges of our time. For more information, please
visit http://science.energy.gov.
Jennifer Brouner
Communications and Media Relations
865-241-9515
Communications and Media Relations
865-241-9515
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