Ever since graphene was discovered in 2004, this one-atom thick, super strong,
carbon-based electrical conductor has been billed as a "wonder material"
that some physicists think could one day replace silicon in computer chips.
But graphene, which consists of carbon atoms arranged in a honeycomb lattice,
has a major drawback when it comes to applications in electronics – it
conducts electricity almost too well, making it hard to create graphene-based
transistors that are suitable for integrated circuits.
In August’s Physics World, Kostya Novoselov - a condensed-matter physicist
from the Manchester University
group that discovered graphene -- explains how their discovery of graphane,
an insulating equivalent of graphene, may prove more versatile still.
Graphane has the same honeycomb structure as graphene, except that it is "spray-painted"
with hydrogen atoms that attach themselves to the carbon. The resulting bonds
between the hydrogen and carbon atoms effectively tie down the electrons that
make graphene so conducting. Yet graphane retains the thinness, super-strength,
flexibility and density of its older chemical cousin.
One advantage of graphane is that it could actually become easier to make the
tiny strips of graphene needed for electronic circuits. Such structures are
currently made rather crudely by taking a sheet of the material and effectively
burning away everything except the bit you need. But now such strips could be
made by simply coating the whole of a graphene sheet – except for the
strip itself - with hydrogen. The narrow bit left free of hydrogen is your conducting
graphene strip, surrounded by a much bigger graphane area that electrons cannot
go down.
As if this is not enough, the physicists in Manchester have found that by gradually
binding hydrogen to graphene they are able to drive the process of transforming
a conducting material into an insulating one and watch what happens in between.
Perhaps most importantly of all, the discovery of graphane opens the flood
gates to further chemical modifications of graphene. With metallic graphene
at one end and insulating graphane at the other, can we fill in the divide between
them with, say, graphene-based semiconductors or by, say, substituting hydrogen
for fluorine?
As Professor Novoselov writes, "Being able to control the resistivity,
optical transmittance and a material’s work function would all be important
for photonic devices like solar cells and liquid-crystal displays, for example,
and altering mechanical properties and surface potential is at the heart of
designing composite materials. Chemical modification of graphene – with
graphane as its first example – uncovers a whole new dimension of research.
The capabilities are practically endless."
Posyed July 31st, 2009
