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Getting 'Kinky': Nanoscale Atomic Interfaces Have Serious Flaws

Scientists have long believed that the strength of a material lies in the way it is structured at the molecular level.
/ Source: TechNewsDaily

Scientists have long believed that the strength of a material lies in the way it is structured at the molecular level.

For example, shatter points and grain boundaries, found in substances like crystals and metals, are structural flaws in the way the compound's individual molecules or crystals hold themselves together. These flaws often become the site of fracturing, corrosion and weakness.

Using nanoscopic tools, scientists have found a way to correct these types of defects by changing the way the individual molecules or crystals interface with each other to form a structure.

The "perfect" means of structuring a crystal or metal, called a "coherent twin boundary," was discovered in 2004. Coherent twin boundaries were considered "perfect" because they appeared to be thin, perfectly flat planes of atoms.

Forming these coherent twin boundaries at the nanoscale in materials like gold and copper makes them not only stronger, but also more malleable and durable. The metals were also shown to become more conductive as well, greatly increasing their effectiveness in electronic hardware applications.

But a state-of-the-art microscope has put a dent in the coherent twin boundary's reputation — or rather, exposed a flaw that was always there. [See also: Crystal 'Flowers' Bloom in Harvard Nanotech Lab ]

Using a high-resolution electronic microscope, researchers at the University of Vermont researchers examined coherent twin boundaries in a sample of copper and saw, to their surprise, that the bonds weren't straight at all — in fact, the bonds had small kinks and curves that made them look more like rickety stairs than straight lines.

"We had no idea such defects existed. So much for the perfect twin boundary. We now call them defective twin boundaries," Frederic Sanzos, a University of Vermont engineer, said in a news release.

With their jagged lines and arbitrary angles, the coherent twin boundaries in copper may not be as pretty to look at anymore, but that doesn't mean they don't work. In fact, the researchers found that the strength of the coherent twin boundary is actually because of these "flaws," not in spite of them.

The discovery that the coherent twin boundaries in copper are "inherently defective" means that researchers will have to go back and re-examine coherent twin boundaries in other materials as well. It also opens up the question of why the so-called defects actually contribute to the material's strength.

"There are all manner of defects in nature… The point of this paper is that some defects make a material stronger," Sansoz said.

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