Disparate effects of an O₂ internal impurity on the elongation and quantum transport of gold and silver nanowires

In this work, we investigated the effects of an internal O₂ impurity on the conductance of elongated gold and silver nanowires (NWs) using density functional theory calculations. We found that the O₂ interacts with these metallic NWs very differently. In the case of gold NWs, the presence of an internal oxygen molecule locally strengthens the wire, therefore, forcing the phase transformations connected to the thinning process (3D to 2D and 2D to single atom chain) to occur far from the oxygen. As a consequence, towards the end of the elongation, the internal O₂ is located far from the main conductance channel and therefore has little influence on the conductance of the NW. In contrast, in silver NWs, the presence of an internal oxygen molecule involves a larger charge transfer from the metallic atoms to the oxygen, therefore, weakening the Ag-Ag binding. During the initial stages of the elongation, several metallic bonds adjacent to the impurity break, so that in most simulations the NW thinning takes place near the O₂. This thinning mechanism places the O₂ near the main conductance channel, therefore, significantly reducing the conductivity of the elongated silver NWs. For both metals, our findings agree well with the published experimental results.