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- 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 deal-breaker 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]
Graphene Has a Fatal Flaw