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

PSCHUNDER, FERNANDO; GIOVANETTI, LISANDRO J.; CRISTIÁN HUCK IRIART; CRISTINA E. HOPPE; FELIX G. REQUEJO; JOSE M. RAMALLO LÓPEZ

Campinas

Congreso; 29 RAU Annual User Meetings LNLS/CNPEM; 2019

CNPEM

Ultrathin gold nanowires (AuNW) have attracted great interest due to their unique conductivity properties making them suitable candidates for a myriad of applications. Many relatively simple synthesis protocols have been reported using gold salts and surfactants, in general HAuCl4.3H2O and oleylamine (OAm), resulting in micrometer long wires with sub 5 nm diameters [1] [2]. In order to gain control over the final product of the synthesis it is necessary to understand the different stages involved in the process, characterizing in detail the structures generated along the way. In a recent report, we proposed a several stage process for the formation of AuNW at room temperature in hexane studying the oxidation state and atomic coordination of gold by X-ray absorption fine structure (XAFS) spectroscopies at Au L3 edge, and the shape and sizes of the nanostructures by small angle X-ray scattering (SAXS) [3]. However, the reaction velocity at room temperature does not allow a proper determination of the gold atomic environment in the early stages of the synthesis, especially the Au coordination with Cl and OAm. Moreover, it is still not clear how Au-OAm complexes form, through aurophilic interactions, the discs precursors of the nanowires. Herein we present an Au L3-edge EXAFS spectroscopy study (XAFS2 beamline at LNLS, Campinas, Brazil) performed at low temperature (~6 K) in order to decrease the reaction velocity and determine how Au coordination changes in the first moments of the synthesis from Au+3 in the gold salt, coordinated with Cl atoms, to Au+1 in the Au-OAm complex, coordinated with N atoms. In addition, Cl K-edge XANES spectroscopy experiments were performed at SXS beamline (LNLS, Campinas, Brazil) to clarify how Cl coordination evolves during the synthesis and in-situ small angle X-ray scattering experiments were performed at SAXS1 beamline (LNLS, Campinas, Brazil), with 60 s temporal resolution, to study how AuOAm complexes interact and give rise to the initial structures that generate the AuNW. REFERENCES [1] N. Pazos-Pérez et al., Langmuir, vol. 24, pp. 9855?9860, 2008. [2] H. Kura and T. Ogawa, Journal of Applied Physics, vol. 107, pp. 074310, 2010. [3] F. Pschunder et al., J. Phys. Chem. C, vol. 122, pp. 29051?29061, 2018