Nov 12, 2010 14:40 GMT  ·  By
Graphene is one of the thinnest and strongest materials that were ever produced
   Graphene is one of the thinnest and strongest materials that were ever produced

Everyone is excited about graphene because it is a one-atom-thick sheet of carbon atoms densely packed in a honeycomb crystal lattice, but most of all, it's one of the thinnest and strongest materials that were ever produced.

The term graphene first appeared in 1987, when it was used for describing single sheets of graphite, and ever since, it captured scientists' interest.

They have made many experiments, but the one thing they did not manage to do, was to create a large graphene surface.

What they did do was stitch individual graphene sheets together, obtaining sheets large enough to try possible applications.

But as everything that's not made from a single piece, the large graphene sheet had to have weaknesses where individual patches met, some flaws that could weaken the 'grain boundaries', or at least this is what the engineers believed.

A more recent study carried out by engineers at Brown University and the University of Texas–Austin is contradicting this belief, and it adds that not only the grain boundaries do not compromise the material's strength, but they are so solid, that the sheets are almost as resistant as pure graphene.

All it takes is to stitch the individual sheets together at the right angle.

Vivek Shenoy, professor of engineering and the paper's corresponding author said that “when you have more defects, you expect the strength to be compromised, but here it is just the opposite.”

Graphene is a two-dimensional surface made of strongly bonded carbon atoms in an order nearly flawless, with the main unit of the lattice pattern consisting of six carbon atoms liked together chemically.

When joining two graphene sheets, some of these six-carbon hexagons become heptagons – seven-carbon bonds, and the places where they occur are called 'critical bonds'.

These critical bonds, formed along the grain boundaries, were considered to be the weak links in the material but Shenoy said that “it turned out that these grain boundaries can, in some cases, be as strong as pure graphene.”

The discovery was extraordinary, but the causes of the phenomenon remained a mystery, so the researchers wanted to find out more.

They used atomistic calculations and discovered that tilting the angle at which the sheets meet affected the overall resistance of the material.

They found out that the perfect angles for producing strong sheets were 28.7 degrees for sheets that had an armchair pattern and 21.7 degrees for sheets with a zigzag layout.

These grain boundaries are called large-angle grain boundaries, and they are stronger because the bonds in the heptagons are closer in length to those found in graphene.

Shenoy said that “it's the way the defects are arranged; the grain boundary can accommodate the heptagons better, [because] they're more relaxed.”

This discovery, presented in a paper published in Science, might boost the development of larger graphene sheets for use in electronics, optics and other industries.