A metallic junction between two solids, when forced to vibrate at ambient temperature, inexplicably becomes liquid. This is what occurs in the nano-world according to some experimental observations. However, sometimes appearances are deceptive, as explained in a recent research study published in Nature Communications, conducted by a team of scientists at SISSA, ICTP, CNR-IOM in Trieste, and the École Normale Supérieure (ENS) in Paris. Thanks to computer simulations, the researchers found a surprising solution to this strange phenomenon, which up to now has remained without an explanation.
This new research shows that melting does not actually occur. If subjected to vibrations, the nanocontacts mimic the behaviour of a liquid, but remain solid from a structural perspective. Why is that? This happens because, in contrast to what occurs in macroscopic systems, nanoscale plastic deformations are reversible during oscillations, meaning they occur and then reverse in each cycle. More in detail, what happens during stretching is that two of the very small crystalline surfaces inside the nanocontact slide one over the other, as in standard macroscopic plastic deformation. In the second half of the cycle, however, they go back to their original state, and so on, until the next cycle, mimicking what a liquid would do but still maintaining the crystalline structure. This reversible rheological steady state, impossible in a system that was not of nanometric size, is at the origin of the apparent liquefaction of the junctions.
The results of this computational research, according to the authors, could have significant impact in applications in the nanotechnological sector.