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Inqui r y I s sue
1
| 2016
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Inqui r y I s sue
1
| 2016
wo-dimensional materials are a bit of a
mind-bending concept. Humans live in a three-
dimensional world, after all, where everything
observed in our natural world has height, width,
and depth.
And yet when graphene—a carbon material unique
in its truly flat, one-atom-deep dimension—was first
produced in 2004, the mind-bending concept became
reality and an unexplored frontier in materials science.
Ames Laboratory scientists Pat Thiel and Michael
Tringides are explorers on that frontier, discovering the
unique properties of two-dimensional (2D) materials and
metals grown on graphene, graphite, and other carbon-
coated surfaces.
“Our work is somewhat of a miracle, if scientists
can talk about miracles,” said Tringides, who is also a
professor of physics at Iowa State University. “Only a few
decades ago, no one would have believed that we could
see individual atoms, but our capabilities now not only
allow us to see them, but manipulate them, like a child
building with Lego® bricks. We’re able to create these
materials from the bottom up, ones that could never
happen in nature.”
They’re created in a controlled laboratory setting, in
an ultra-high vacuum environment, and investigated with
the aid of scanning tunneling microscopy. After heating
the substrate to high temperature all impurities and
defects are removed. The substrate is cooled and atoms of
interest are deposited one by one from specially designed
sources. By tuning the temperature and deposition rate,
the researchers search for the Goldilocks-like condition:
atoms move not too fast and not too slow so a truly 2D
material forms.
While their research groups create a variety of surface
materials in their work, the fabrications methods all have
one thing in common: attempting to confine the assembly
of the atoms to the 2D plane. That’s difficult, because it’s
counter to what atoms naturally want to do under most
conditions, to assemble in three dimensions.
“Atoms are chaotic by nature; we are fighting this
randomness in everything we do,” said Tringides. “In our
work, atoms are precisely arranged on a highly reactive
surface in a vacuum. Every aspect of the environment is
controlled. Our work is to fabricate very small, very clean,
and very perfect. Working on materials in the nanoscale
demands it.”
T
2D MATERIALS REVEAL SURPRISING PROPERTIES
B Y L A U R A M I L L S A P S
Ultra-high vacuum equipment provides a clean, stable, and controllable environment for building 2D materials
and investigating them through scanning tunneling microscopy.
A scanning tunneling microscopy image of graphene.
Pat Thiel
Michael Tringides