|Created by AtomEye software, this image simulates the result of a nanoindentation experiment on a thin slice of copper.|
, say Ohio State University scientists. When forming tiny structures on integrated circuits and nanotechnology, aluminum endures mechanical stress more than 30% better than copper, which is usually considered to be the stiffer metal.
OSU scientists used quantum mechanical equations to model thin layers of aluminum and copper atoms under a condition called pure shear strain. The phenomenon arises when one layer of atoms slides over the other and is a common issue for tiny electronics where large temperature fluctuations make materials expand and contract. Tests showed aluminum atoms tended to hop across rather than slide over another layer. There were also related movements in the bottom layer of atoms as if they were somehow connected to those on top by an invisible set of hinges. One explanation is that aluminum atoms might form "directional" bonds with each other, says Ju Li, assistant professor of materials science and engineering. "Directional bonding is observed in ceramics and semiconductors such as silicon, but not in highly malleable metals such as aluminum. Aluminum showed a definite edge over copper in the simulations, enduring much larger shear strains before softening."
The research may prove important for nanoindentation experiments where scientists press a tiny diamond shard into material to gauge how it responds to extreme forces. The work also opens the door to a more accurate model of mechanical behavior in structures for nanotechnology.