Issue 19, 2013 - Balliol College - University of Oxford

college features
Science and progress:
growing synthetic graphene
By JAmie wArner (JUNIOR RESEARCH FELLOW IN MATERIAL SCIENCE)
Growing a synthetic version has
allowed an Oxford team to study
the fundamental atomic structure
of a material, using the University’s
electron microscope.
For the majority of our existence, humans have
looked to the stars for an understanding of our
universe. the philosophical aspects that drive
us to contemplate the vast enormity and size
scale of our universe also help point us towards
the smaller scale with a view to unravelling
the fundamental building blocks of matter.
scientific studies in the early 18th and the 19th
centuries started to provide physical evidence
that matter was comprised of atoms and, later,
revealed sub-atomic particles. However, it
wasn’t until the development of the electron
microscope in the 1930s and thereafter that
the tools for imaging the atomic structure
of materials became available. in the normal
optical microscope we are familiar with, light
(photons) is used to form an image of the
sample, but these types of optical microscopes
are generally limited to resolving micron-sized
features due to the fundamental physics related
to the long wavelength of light. the electron
microscope works in a very similar manner to
an optical microscope, with lenses to focus a
beam and a detector for acquiring an image,
but uses electrons instead of photons. the
photograph opposite shows a state-of-the-art
electron microscope based in the Department
of Materials at oxford, which is used by my
team and me. An electron gun (1) sits at the
very top and emits a beam of electrons that
are accelerated to a velocity close to the
speed of light. electromagnetic lenses (2)
focus the electron beam on to the sample
(3), and after the electrons pass through the
sample, further lenses (4) form an image on
to a CCD detector below.
Quantum physics tells us that electrons
can act as waves and have a wavelength that
decreases with increasing energy and which
can be many orders of magnitude smaller
than light. therefore, by using electrons as
the ‘illuminating’ source for imaging, pictures
of materials can be obtained with structure
revealed all the way down to the atomic level.
in a solid material, atoms are typically
arranged in a periodic crystalline stack, or
are randomly distributed (amorphous), or
form small crystal clusters that are randomly
orientated within a larger structure. the
way atoms assemble strongly influences
the electronic, chemical, magnetic and
mechanical properties of a material. A great
example of this is carbon, which can adopt
a metallic form as graphite, be insulating
as in diamond, or be semiconducting as in
a carbon nanotube. All materials are made
solely from carbon, but differ in the way their
atoms are bonded together and assemble in
3D. this extraordinary diversity of carbon
materials has generated substantial research
interest. With the natural progression of
science towards designed materials, and in
particular nanomaterials, the ability to image
the size, shape, crystallinity and elemental
composition, using electron microscopy, has
been critical to the rapid development of
nanotechnology.
new materials hold great promises for
changing technology and consequently
quality of life. in 2010, two British physicists
(Professor sir Kostya novoselov and
Professor sir Andre Geim) were awarded the
nobel Prize in physics for their work on the
2D material graphene. Graphene is made of
carbon and is a single sheet of graphite. it
is only one atom thick, much like a sheet of
paper the size of ten football fields, and the
carbon atoms are arranged in a hexagonal
pattern, like a honeycomb. the charge
carriers in graphene move at remarkable
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