BRONZE FORMATION AND THE MOTION OF MESOSCOPIC TIN CLUSTERS ON A COPPER SURFACE

Abstract

To study the dynamics of alloy phase transformations, we deposited submonolayer amounts of Sn onto Cu(111) surfaces. The subsequently observed formation of bronze alloy was found to be surprisingly complex. First, the Sn forms 2D clusters with a 2×2 structure and typical diameters of the order of 100 nm. Then the Sn clusters move across the Cu surface and shrink in size, leaving dilute bronze in their wake. The curious motion of the Sn clusters can be interpreted as an example of chemomechanical energy transduction on a surprisingly small length scale. Thus the Sn clusters are microscopic engines and one can discuss their fundamental mechanical properties. A speculative comparison of the self-propelled motion of the Sn clusters with other isothermal engines, such as molecular biological machines, is considered.