Oct 15, 2009
Graphene feels the strain
Graphene is a highly conducting material and is thus ideal for electronic applications. However, its extreme conductivity can also be a problem because devices remain conducting even when switched off. Strain engineering could help overcome this challenge, according to new work by scientists in Spain and the UK.
Graphene consists of a planar single sheet of carbon arranged in a honeycombed lattice. It is the thinnest elastic material known and has attracted the attention of scientists and engineers alike since it was discovered in 2004 thanks to its unique electronic and mechanical properties. The material could even replace silicon as the electronic material of choice in the future thanks to the fact that electrons travel ballistically through it at extremely high speeds.
However, there is a problem: integrated circuits should not consume electricity when they are switched off, but devices made from graphene continue to conduct even in their best off state.
Researchers have proposed various schemes to overcome this problem – for example, by using nanoscale ribbons or quantum dots, or chemically modifying graphene to make it semiconducting. Although both schemes work in principle, opening a band gap in graphene also damages the material so much that finished devices no longer show either ballistic transport or high electron mobilities.
Strain engineering, on the other hand, involves just smoothly deforming the material and strained graphene would be a semiconductor that has a sufficiently large energy gap while keeping its other unique characteristics," team member Paco Guinea of the Material Science Institute in Madrid told nanotechweb.org.
The team, led by Andrei Geim from Manchester University, suggests applying forces to graphene to induce the required strains. This could be done by suspending a graphene flake over a triangular hole and then applying pressure or stretching it in three directions.
The researchers say that strain induces strong fields that effectively act as uniform magnetic fields of over 10 T. The strained material becomes a "topological insulator" – that is, semiconducting in the bulk but metallic at the edges. This new class of material is fundamentally interesting.
"The strain can be described as a shear deformation," explained Guinea. "There are also regions where the graphene lattice compresses or expands. Here charge carriers (electrons and holes) pile up."
Geim and colleagues are now trying to observe the effect in experiments. "The plan is to bend nanoribbons and open up a 'bend' gap – no pun intended."
Although it seems straightforward in theory, such results may take up to two years to arrive, and we did not want to keep our present findings hidden for so long, said Geim.
The work was reported in Nature Physics.
About the author
Belle Dumé is contributing editor at nanotechweb.org