Graphene's Achilles Heel

Graphene is touted as being the supermaterial to beat all supermaterials -- but not so fast! Researcher have discovered a weakness that occurs in many sheets of graphene that renders it half as strong as we thought.

Formed from a single sheet of carbon atoms arranged in a hexagonal pattern, graphene is often celebrated for its disproportionate strength. But a team of scientists from Rice University ignored the hype and set to thinking about what happens at the very edge of the sheets. In fact, where the layer stops -- and it has to at some point -- the hexagons are interrupted and five-atom or seven-atom rings form.

While that might not sound like a big deal, think again: sheets of the stuff grown in a lab are almost never perfect arrays of hexagons. Instead, they're made up of a number of different islands of graphene called grains; where those grains meet, these flaws exist. And when placed under tension, those flaws start to cause problems. Boris Yakobson, one of the researchers, explains to Material Views:

"The details are complicated but, basically... the force is concentrated there, and that's where it starts breaking. Force on these junctions starts the cracks, and they propagate like cracks in a windshield. In metals, cracks stop eventually because they become blunt as they propagate. But in brittle materials, that doesn't happen. And graphene is a brittle material, so a crack might go a really long way."

The result? Imperfect sheets of graphene -- which essentially means most of them -- have about half the strength of pristine samples of the material. That's not a dealbreaker in terms of its potential uses, of course, but it serves as a good reminder that graphene might not necessarily solve all the world's problems. [Nano Letters via Materials Views]