2, Universite de Toulouse, Toulouse, , France
Thin gold nanowires (NWs) represent ideal objects for fundamental studies as well as potential applications in sensing, catalysis, and electronic contacts for molecular devices. Various methods have been developed to grow and characterize thin Au NWs. Though exciting, the reported methods did not univocally address the questions of the nucleation and growth mechanism, which is of prime interest to tune the size of the NWs and thus their physicochemical properties. Furthermore, the atomic-scale structure of thin Au NWs is still under debate. We will present results of in situ high-energy XRD and atomic PDF studies on the nucleation, growth and 3D structure of Au NWs in solution. XRD data were taken in an interval of 5 min for up to 30 hours at room temperature. Gold clusters (size < 1 nm) are seen to nucleate fast and then continuously grow forming NWs with a diameter of < 2 nm and length of many tens of micrometers. A priori, one could anticipate that Au NWs of such a size would exhibit a weak tendency to depart from the bulk fcc structure, if at all. We find though that, due to competition between achieving optimal surface energy and atomic packing, the resulting Au NWs do not necessarily possess an fcc-type structure at atomic level. We elucidate how the unusual 3D structure of Au NWs evolves, including the unusually short Au-Au bonding distances, and show that the degree of its departure from the bulk fcc structure can be controlled through adjusting particular details in the synthesis protocol.