Graphene, a layer of graphite just one atom thick, isn't called a wonder
material for nothing. The material is famed for its superlative
mechanical and electronic properties. Yet new computer simulations
suggest that the electronic properties of a little-known sister material
of graphene called graphyne may in some ways be better.
The simulations show that graphyne's conduction electrons should travel
extremely fast—as they do in graphene, but in only one direction. That
property could help researchers design faster transistors and other
electronic components that process one-way current, according to
researchers at the University of Erlangen-Nuremberg in Germany.
Electrically, graphene's structure has been considered unique. In most
materials, conduction electrons have an energy that depends on the
square of their momentum. Graphene's electronic energy levels, however,
stack into shapes called Dirac cones, which allow conduction electrons
to travel with an energy that is directly proportional to their
momentum. As a result, the electrons travel as though they were
massless, the way particles of light do - in other words, very fast.
Graphyne is similar to graphene in that it is also a two-dimensional
structure of carbon. Unlike graphene, though, graphyne contains double
and triple bonds and its atoms do not always have a hexagonal
arrangement. Indeed, there may be a vast number of possible graphynes,
each with the double and triple bonds in slightly different
arrangements. Theorists have been studying graphynes since the 1980s,
but little work has been devoted to their electronic properties.
The team have now examined these electronic properties in computer
simulations, using a technique called density functional theory. This is
standard for mapping the energy levels of different possible forms of
the material. The researchers discovered that in one particular graphyne
— so-called 6,6,12-graphyne - Dirac cones should still exist but in a
distorted, squashed form. As a result the material should conduct
electrons in a preferred direction, according to the team.