Scientists from CNRS have studied the shape evolution of gold nano-tetrapods and revealed a two-step kinetics process: the four arms—initially sharp—quickly blunt, followed by a slow retraction towards an almost spherical final shape.
Deforming macroscopic metallic objects requires considerable force. At the nanoscale, however, things are quite different: surface forces alone are often sufficient to reshape nanoparticles, guiding them towards the most energetically favorable form. Understanding this “nano-metallurgy” is crucial not only for advancing fundamental knowledge but also for driving progress in nanotechnology. Yet, the processes involved are challenging to monitor in real-time.
A team of researchers from several French and European laboratories [1] recently published a detailed study in Nano Letters on the transformation pathway of metastable gold particles, initially featuring four sharp arms, into nearly spherical particles. Thanks to their well-defined geometry, these “nano-tetrapods” are easier to study than “nanostars,” which have similar characteristics but more varied morphologies. By combining electron microscopy, X-ray scattering, optical spectroscopy techniques, and advanced data processing, the researchers uncovered a complex kinetic process. This begins with a rapid flattening of the tips towards a {110} facet of gold’s crystalline lattice, followed by a slower reshaping phase into an isometric form.
Figure. Schematic representation of the temporal evolution (indicated by the arrow) of a nano-tetrapod, from its initial sharp state to a truncated form with arms defined by {110} facets, and finally to a rounded, quasi-spherical final state. This transformation was monitored in solution using small-angle X-ray scattering (SAXS) and UV-Vis optical absorption spectroscopy. Complementary studies using transmission electron microscopy (TEM) were conducted in the dry state.
Beyond the conceptual understanding of their evolution, this study will enable the use of these nano-objects in nonlinear optical applications [2], thanks to their unique shape, which lacks a center of inversion.
[1] Damien Alloyeau at Laboratoire Matériaux et Phénomènes Quantiques, (Université Paris Cité/CNRS), le Laboratoire de physique des solides (CNRS/Université de Paris-Saclay), Doru Constantin at l’Institut Charles Sadron (CNRS/Université de Strasbourg) and the European synchrotron ESRF (Grenoble).
[2] Jieli Lyu et al., Shape-Controlled Second-Harmonic Scattering from Gold Nanotetrapods, J. Phys. Chem. C 126, 9831-9835 (2022).
Reference
Jieli Lyu et al., Two-step reshaping of acicular gold nanoparticles, Nano Letters (2025).
DOI: 10.1021/acs.nanolett.4c05601
Contact : Cyrille Hamon