Gold wire thick is enough to hold in your hand bends and stretches, making it useful in electronics equipment. But stretch gold too thin—to less than 20 nanometers in diameter—and it becomes brittle , researchers report this month in Advanced Functional Materials. When the team zoomed in for a closer look at the single-crystal gold wires it had been stretching, it found that the brittle-broken single crystals hadn't been so single when they snapped. They had spontaneously "twinned." Twin crystals share some atoms but their overall crystal structures are offset from each other (as shown by the yellow lines in the picture above). When the gold wires stretch, entire groups of atoms slip into different positions to relieve the stress and create twins. As the gold wire stretches more and more, it twins again and again. It eventually breaks, in a brittle way, along a plane between twins. This discovery may force engineers to treat gold wires in nanoelectronics more gingerly, or substitute a different material entirely.
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