A rendering shows two graphene nanocones. Photo by Rice University
HOUSTON, June 30 (UPI) -- Among scientists, it's a well established truth that graphene is a wonder material, but just how wonderful can it be? What's its potential -- specifically its electric potential?
Researchers at Rice University wanted to find out how graphene's conductivity might change depending on its shape. So scientists flexed and twisted sheets of graphene into different shapes -- a variety of nanotubes and nanocones -- and then ran an electric current through the material.
Flat and tubed graphene has balance that allows electricity to flow smoothly across the layer of atoms. Cone shapes, however, diminish the material's conductivity. By stretching the bonds between carbon atoms in some locations and condensing them in others, the cone shapes altered the electric dipole moments -- the mechanism that governs how polarized atoms interact with electricity.
"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," Boris Yakobson, lead researcher at the Rice labs where the experimentation took place, explained in a press release.
Using density functional theory to measure how the manipulations affected the cumulative flow of electricity, Yakobson and his colleagues found atoms along the edge also contribute electrically, but analyzing two cones docked edge-to-edge allowed them to cancel out, simplifying the calculations. Researchers were thus able to calculate graphene's electronic flexoelectric effect, and say the technique could be used to predict how more complex shapes, like wrinkled sheets, will influence conductivity.
The researchers' calculations are detailed in a new paper published in the Journal of Physical Chemistry Letters.
The strategic manipulation of the flow of electrons may improve graphene's use in the development of flexible touchscreens and other complex electronics.
"One possibly far-reaching characteristic is in the voltage drop across a curved sheet," Yakobson 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."
