Twisting Graphene Alters Its Electrical Properties

Illustration: Rice University

Graphene has developed quite a reputation as an alternative material for enabling flexible electronics, such as a replacement for indium tin oxide (ITO) as a transparent conductor in flexible displays.

But now researchers at Rice University have used computer models to demonstrate that graphene’s flexibility can be exploited in another way: by twisting it to alter its electrical properties.

In research published in the Journal of Physical Chemistry Letters, the Rice researchers, in collaboration with a scientist in Moscow, used computer models to show how to produce in graphene the so-called flexoelectric effect in which a material exhibits a spontaneous electrical polarization brought on by a strain.

It is well known that graphene is a great conductor when it is laid flat on a plane so that all of its atoms have a balanced electrical charge. However, if you put a curve in that plane of graphene, the electron clouds of the bonds on the concave side compress while on the convex side they stretch. This changes the electric dipole moment, which is a measure of the overall polarity and determines how polarized atoms interact with external electric fields.

The researchers determined how each possible curvature in graphene could impact its dipole moment. In so doing, they have provided a way to calculate how graphene’s electrical properties change in any given geometry.

“While the dipole moment is zero for flat graphene or cylindrical nanotubes, in between there is a family of cones, actually produced in laboratories, whose dipole moments are significant and scale linearly with cone length,” said Boris Yakobson, who led the research, in a press release.

Yakobson believes that this research could help with a number of engineering issues with graphene.

“One possibly far-reaching characteristic is in the voltage drop across a curved sheet,” he said. “It can permit one to locally vary the work function and to engineer the band-structure stacking in bilayers or multiple layers by their bending. It may also allow the creation of partitions and cavities with varying electrochemical potential, more ‘acidic’ or ‘basic,’ depending on the curvature in the 3-D carbon architecture.”

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
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