New Insights Into the Growth Mechanism of Ultrathin Au Nanowires from Combined In-Situ EXAFS and SAXS Studies

摘要： The synthesis at room temperature of Au nanowires (NWs) in hexane solution of HAuCl4.3H2O, oleylamine and triisopropylsilane, was “in-situ” monitored by means of X-ray Absorption Fine Structure Spectroscopies and Small Angle X-Ray Scattering to determine, under identical synthesis conditions, both the changes of the oxidation state of gold atoms and the evolution of the size and shape of the objects involved in the formation of Au NWs. We propose a multi-stage process for the formation of the NWs: first, Au(III) atoms form a planar-square geometry complex that is continuously reduced to give Au(I) disc-like structures with diameters bigger than that of the final NWs. In a second stage, characteristic length/thickness ratio of these disc-like objects increases to form cylinders, presumably by aurophilic interactions between Au(I) centers and stacking of the discs. When most of the Au atoms have been reduced to Au(I), the reduction to Au(0) begins (third stage) and the NWs grow forming an hexagonal arrangement, separated by a bilayer of oleylamine molecules (fourth stage). Finally, a slow reduction leads the reaction to the final product, formed by bundles of long, ultrathin Au NWs.