High resolution TEM images of graphene nanoribbons encapsulated in SWNTs, simulated structures of flat and helical nanoribbons inside of nanotubes and scheme of chemical reaction which results in formation of nanoribbons from coronene and perylene molecules. Image: Umea University |
Physicists from Umeå
University and Finland have
found an efficient way to synthesize graphene nanoribbons directly inside of
single-walled carbon nanotubes. The result was published in Nano Letters.
Graphene
has a wide range of unusual and highly interesting properties. As a conductor
of electricity it performs as well as copper. As a conductor of heat it
outperforms all other known materials. There are possibilities to achieve
strong variations of the graphene properties by making graphene in the form of
belts with various widths, so called nanoribbons. These nanoribbons are now the
real focus of attention in physics and an extremely promising material for electronics,
solar cells, and many other things. However, it is has not been easy to make
such ribbons.
Associate
professor Alexandr Talyzin and his research group at the Department of Physics,
Umeå University,
have together with colleagues from Professor Esko Kauppinen´s group, Aalto University
in Finland,
discovered a way to use the hollow space inside carbon nanotubes as a 1D
chemical reactor to make encapsulated graphene. An intriguing property of this
space is that chemical reactions occur differently here compared to under bulk
3D conditions.
“We
used coronene and perylene, which are large organic molecules, as building
blocks to produce long and narrow graphene nanoribbons inside the tubes. The
idea of using these molecules as building blocks for graphene synthesis was
based on our previous study,” says Alexandr Talyzin.
This
study revealed that coronene molecules can react with each other at certain
conditions to form dimers, trimers, and longer molecules in a bulk powder form.
The result suggested that coronene molecules can possibly be used for synthesis
of graphene but need to be somehow aligned in one plane for the required
reaction. The inner space of single-walled carbon nanotubes seemed to be an
ideal place to force molecules into the edge-to-edge geometry required for the
polymerization reaction.
In
the new study, the researchers show that this is possible. When the first
samples were observed by electron microscopy by Ilya Anoshkin at Aalto University,
exciting results were revealed: all nanotubes were filled inside with graphene
nanoribbons.
“The
success of the experiments also depended a lot on the choice of nanotubes.
Nanotubes of suitable diameter and in high quality were provided by our coauthors
from Aalto University,” says Alexandr Talyzin.
Later
the researchers found that the shape of encapsulated graphene nanoribbons can
be modified by using different kinds of aromatic hydrocarbons. The properties
of nanoribbons are very different depending on their shape and width. For
example, nanoribbons can be either metallic or semiconducting depending on
their width and type. Interestingly, carbon nanotubes can also be metallic,
semiconducting, or insulating when chemically modified.
“This
creates an enormous potential for a wide range of applications. We can prepare
hybrids that combine graphene and nanotubes in all possible combinations in the
future,” says Alexandr Talyzin.
For
example, metallic nanoribbons inside insulating nanotubes are very thin
insulated wires. They might be used directly inside carbon nanotubes to produce
light thus making nano-lamps. Semiconducting nanoribbons can possibly be used
for transistors or solar cell applications and metallic-metallic combination is
in fact a new kind of coaxial nano-cable, macroscopic cables of this kind are
used e.g. for transmitting radio signals.
The
new method of hybrid synthesis is very simple, easily scalable, and allows
obtaining almost 100% filling of tubes with nanoribbons. The theoretical
simulations, performed by Arkady Krasheninnikov in Finland, also show that the
graphene nanoribbons keep their unique properties inside the nanotubes while
protected from the environment by encapsulation and aligned within bundles of
single-walled nanotubes.
“The
new material seems very promising, but we have a lot of inter-disciplinary work
ahead of us in the field of physics and chemistry. To synthesize the material
is just a beginning. Now we want to learn its electric, magnetic and chemical
properties and how to use the hybrids for practical applications,” says
Alexandr Talyzin.
