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Revealing the secrets of anisotropic nanoalloy synthesis

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The synthesis of nanomaterials by chemical routes has long been developed empirically due to the lack of techniques to probe the dynamics of nano-objects in liquid media. In recent years, so-called "in-situ" approaches have emerged on all the techniques that allow probing matter at the atomic scale, with the aim of rationalizing the synthesis protocols of complex nanostructures. To meet this challenge, it is necessary to reveal their growth mechanisms and identify the action of each species involved in the reaction. However, such a study remains difficult to conduct, on the one hand because each in situ technique presents only partial or indirect information of the synthesis, and on the other hand because a single reagent can play several roles in this process.

Researchers from the MPQ laboratory, in collaboration with the Laboratoire de Physique des Solides (LPS, CNRS/Université Paris-Sud) and the SOLEIL synchrotron (SWING line) have combined three in situ techniques to probe in real time the growth of silver nanorods on gold bipyramids (see figure): UV-Visible Absorbance Spectroscopy (UV-Vis), Small Angle X-Ray Scattering (SAXS) and Transmission Electron Microscopy in Liquid Cells (Liquid TEM). Remarkably, this multimodal approach allows correlating indirect structural information obtained at the bench scale (SAXS and UV-Vis) with direct imaging of single-nanostructure growth (Liquid TEM). This multi-scale view of nanostructure dynamics in solution has highlighted an unexpected role of ascorbic acid, a reducing agent widely used in the synthesis of nanoparticles, in the formation of anisotropic nanostructures. These results are published in the Journal of Physical Chemistry Letters.

Time-resolved STEM images showing the anisotropic growth of silver nanorods on a gold bipyramid. Scale bar is 50 nm.

Damien Alloyeau (

Real-time in situ observations reveal a double role for ascorbic acid in the anisotropic growth of silver on gold, Kinanti Aliyah, Jieli Lyu, Claire Goldmann, Thomas Bizien, Cyrille Hamon, Damien Alloyeau, et Doru Constantin, J. Phys. Chem. Lett. 11, 2830 (2020)

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