Shell effects in alkali metal nanowires

Abstract

After making a cold weld by pressing two clean metal

surfaces together, and gradually separating the two pieces, a metallic nanowire is formed,

which is progressively thinning down to a single atom before the contact is lost. We show

evidence that the radii of such nanowires are influenced by electronic shell filling

effects, in analogy to electronic shell structure in metal clusters. A modulation of the

shell effect, known as supershell structure, is clearly observed. For sodium and potassium

at larger diameters there is a crossover to crystalline facets with shell-closings

corresponding to the completion of an additional atomic layer. We conclude that a complete

analogy exists between shell structure in metallic clusters and nanowires.