"In-situ" XAFS and SAXS study of the growth kinetics of Au nanowires

JOSÉ M. RAMALLO-LÓPEZ; CRISTINA. HOPPE; LISANDRO J. GIOVANETTI; CRISTIÁN HUCK-IRIART; FELIX REQUEJO

Quebec

Congreso; XIII International Conference on Nanostructured Materials (NANO 2016); 2016

International Committee on Nanostructured Materials (ICNM)

Recently, ultrathin gold nanowires (NWs), which exhibit a mean diameter in the range 1.5−2 nm and a micrometer length, attracted lots of interest due to their size homogeneity and their potential application as SERS probes, lightweight foldable optoelectronic membranes, or elastic coiled springs.[1] Their unique 1D feature confers them remarkable conductivity properties, such as quantum phenomena at room temperature, opening innovative routes in nanoelectronics. Two main strategies have been followed to synthesize these NWs. In the first one, a gold salt (HAuCl4 or AuCl) is reduced in pure oleylamine (OY)[1], whereas in the second one, reaction is carried out in a solution containing OY and an additional reducing agent.[2] Self-assembly of these ultrathin nanowires into very nice parallel arrays was observed on the TEM carbon grids,[1] opening perspectives for artificially designed nanomaterials. Though exciting, the reported synthesis did not univocally address the question of the growth mechanism, which is of fundamental importance to control their size and physical properties. If the presence of OY was reported consensually as crucial for the 1D growth, no clear evidence of the steps responsible for the formation and unidirectional growth of Au NWs has been provided. Hadler et al. proposed an oriented attachment and ripening process of small seeds,[2] while Pazos-Pérez et al. invoked a micellar growth.[3]. But till now there is no conclusive evidence of the reduction path of Au precursors, which could help to understand the synthesis mechanism. In this work we studied the kinetics of growth of Au NWs by means of ?in situ? studies using X-ray Absorption Fine Structure (XAFS) Spectroscopy at the Au L3 edge and Small Angle X-ray Scattering (SAXS).