Physical properties of a two-component system at the Fermi and Sharvin length scales

Previously, we have reported the measurement of various physical properties at the Fermi and Sharvin length scales in pure elements (1-component systems). In the present study, the evolution of physical properties is mapped in a 2-component system at these length scales, using Au-Ag alloys. These alloys are well known to have complete solubility in each other at all compositions in the bulk and an ideal system to vary the surface energy of the alloy simply by changing the alloy composition. At sample sizes where surface effects dominate (less than ∼2-3 nm), varying the alloy composition is found to cause dramatic changes in force required to rupture the bonds (strength) as well as atomic cohesion (modulus) and can be directly attributed to segregation of higher surface energy Au from the lower surface energy Ag. In other words, the Au-Ag system with complete solubility in the bulk exhibits segregation at these length scales. This breakdown of bulk solubility rules for alloying (the so-called Hume-Rothery rules) even in near-ideal solid solutions has consequences for future atomic-scale devices.