In-Situ SAXS and XAFS study of ultrathin gold nanowires first stages of formation

FERNANDO PSCHUNDER; GIOVANETTI, LISANDRO J; CRISTIAN HUCK-IRIART; CRISTINA HOPPE; REQUEJO, F. G.; JOSE MARTIN RAMALLO LOPEZ

Congreso; 29th RAU (Annual Users Meeting - LNLS/CNPEM); 2019

Ultrathin gold nanowires (AuNW) have attracted great interest due to their uniqueconductivity properties making them suitable candidates for a myriad of applications. Manyrelatively simple synthesis protocols have been reported using gold salts and surfactants, ingeneral HAuCl 4 . 3H 2 O and oleylamine (OAm), resulting in micrometer long wires with sub5 nm diameters [1] [2] .In order to gain control over the final product of the synthesis it is necessary tounderstand the different stages involved in the process, characterizing in detail thestructures generated along the way. In a recent report [3] we proposed a several stageprocess for the formation of AuNW at room temperature in hexane studying the oxidationstate and atomic coordination of gold by X-ray absorption fine structure (XAFS)spectroscopies at Au L 3 edge, and the shape and sizes of the nanostructures by small angleX-ray scattering (SAXS). However, the reaction velocity at room temperature does notallow a proper determination of the gold atomic environment in the early stages of thesynthesis, especially the Au coordination with Cl and OAm. Moreover, it is still not clearhow Au-OAm complexes form, through aurophilic interactions, the discs precursors of thenanowires.Herein we present an Au L 3 -edge EXAFS spectroscopy study (XAFS2 beamline atLNLS, Campinas, Brazil) performed at low temperature (~6 K) in order to decrease thereaction velocity and determine how Au coordination changes in the first moments of thesynthesis from Au +3 in the gold salt, coordinated with Cl atoms, to Au +1 in the Au-OAmcomplex, coordinated with N atoms. In addition, Cl K-edge XANES spectroscopyexperiments were performed at SXS beamline (LNLS, Campinas, Brazil) to clarify how Clcoordination evolves during the synthesis, and in-situ small angle X-ray scatteringexperiments were performed at SAXS1 beamline (LNLS, Campinas, Brazil) with 60 stemporal resolution to study how Au-OAm complexes interact and give rise to the initialstructures that generate the AuNW.References[1] N. Pazos-Pérez, D. Baranov, S. Irsen, M. Hilgendorff, L.M. Liz-Marzán, M. Giersig,Langmuir 24 (2008) 9855?9860.[2] H. Kura, T. Ogawa, Journal of Applied Physics 107 (2010) 074310.[3] F. Pschunder, J. Puig, L.J. Giovanetti, C. Huck-Iriart, F.G. Requejo, D. Buceta, C.E.Hoppe, J.M. Ramallo-López, J. Phys. Chem. C 122 (2018) 29051?29061.