Cluster-derived structures and conductance fluctuations in nanowires

Understanding the variation of a material's properties with size, form of aggregation and dimensionality is becoming important in the face of increasing miniaturization of electronic and mechanical devices. Experimental studies have focused on the preparation and characterization of solid-state nanometre-scale structures such as metal and semiconductor nanocrystals1,2,3, surface-supported structures and quantum dots4 and nanoscale junctions or wires5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22. It has emerged that these nanostructures can often be fruitfully described using concepts and methodologies developed in the contexts of gas-phase atomic clusters and atomic nuclei23,24,25. Here we make this connection explicitly through first-principle molecular dynamics simulations22,26 which show that, as nanowires of sodium metal are stretched to just a few atoms in diameter, the structures formed by metal atoms in the neck can be described in terms of those observed in small gas-phase sodium clusters27. We find that the electronic spectral and conductance characteristics of these atomic-scale contacts exhibit dynamical thermal fluctuations on a sub-picosecond timescale, owing to rearrangements of the metal atoms, which will significantly affect the transport properties of such nanowires.