The Effect of Molecular Adsorption On the Structural and Electrical Behavior of Elongating Gold Nanowires

Gold nanowire (AuNW) elongation is an important process in the field of nanoelectronics.  In some applications (e.g., the mechanically controllable break junction technique for generating metal-molecule-metal nanojunctions), AuNWs are coated with an adsorbate prior to elongation.  These adsorbates are likely to influence the structural, mechanical, and electrical properties of elongating AuNWs.  Using molecular dynamics (MD) simulations, we study the impact of physisorbing adsorbates on the structural and mechanical evolution of AuNWs undergoing elongation.  We find that an adsorbate interacting strongly with a AuNW enhances the mechanical properties of the wire by stabilizing high-energy structural motifs (e.g., monatomic chains and helices).  Conversely, a molecular species interacting weakly with a AuNW is found to worsen the stability of monatomic chains.  The atomic configurations we obtain from classical MD simulations are used as input for first-principles calculations of conductance through AuNWs and realistic metal-molecule-metal structures.  These results differ markedly from the conductance through ideal geometries.