Jason Armstrong, Susan Hua and Harsh Chopra from the University of Buffalo published last month an interesting paper on Physical Review B. They probed a gold surface with a a gold tip of a cantilever forming a neck atomic-sized of decreasing diameter, until to create a single line of gold atoms. UB’s researchers measured the Young’s modulus, and so the stiffness of the shaped gold wire and found two kind of transitions or crossovers in deformation modes with increasing contact diameter:
- crossover due to rearrangement of the atomic layers with defect-mediated deformations;
- crossover due to surface- to volume-dominated deformation.
The first result was already investigated in a previous work. The relevant finding is that in the second case the stiffness is twice than that of bulk gold. Indeed when the gold wire is very thin – at the atomic size – they arrive to stress directly single bonds of surface atoms that are stiffer than bulk atoms.
This result is in some way counter-intuitive, because you don’t expect that an ultra-very thin wire is stronger than a bulk wire, but it is in agreement with theory at all!