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Iron-Gold core-shell nanocrystals : A question of balance

Published in Nanoletters

par Evelyne Prevots - publié le

The nature and the stress state of the exposed facets determine the capacity of nanocrystals to bind to or dissociate a target molecule. They can be mastered by transposing the island growth conditions on a crystalline substrate to core-shell nanocrystals. This has just been demonstrated by a CEMES team and collaborators in Gold-Iron (Fe @ Au) nanoparticles. This work is published in Nanoletters.

The iron-gold nanocrystals were prepared by physical growth in an ultrahigh vacuum sputtering device. An amorphous alumina layer serves as substrate and cover layer for the nanocrystals. The growth conditions were optimized to promote the epitaxial growth of gold on iron nanocrystals, which form in the first place and act as nano-substrates.

Through a detailed analysis by transmission electron microscopy, CEMES researchers, in collaboration with a researcher from the LMA-INA (Zaragoza, Spain), managed to accurately determine the original morphology of these nanocrystals, formed of iron nanocubes surrounded by six gold truncated pyramids. This morphology is all the more remarkable that i) the size of the nanocrystals is only 13 nm ; ii) the gold pyramids provide a complete coverage of the core ; iii) this morphology allows to control the nature of the exposed gold facets, thus promoting the binding of target molecules. If its stability is ensured, such a morphology should be particularly well suited for many applications in medical biology.

The stability of this morphology, in particular the possible benefit of its evolution toward a Janus geometry in which a gold pyramid grows at the expense of the others, was analyzed by calculating the evolution of the various volume and surface energy contributions with the geometry and composition of the nanocrystals. The researchers were able to demonstrate the unusual stability of the core-shell geometry for a wide size range in this system. They attribute this stability to the low elastic contribution associated with the small lattice mismatch at the iron-gold interface compared to the contribution of the surface energy.

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Distribution cœur @coquille dans un nanocristal Fe-Au observé en STEM-HAADF – les spectres EDX bleu et rouge correspondent aux régions bleue et rouge indiquées sur l’image.
© CEMES-CNRS

 

Contact

Dr Marie-Jose Casanove : casanove chez cemes.fr

 

Reference

Fully Crystalline Faceted Fe–Au Core–Shell Nanoparticles - C. Langlois †, P. Benzo †, R. Arenal ‡§, M. Benoit †, J. Nicolai †, N. Combe †, A. Ponchet †, and M. J. Casanove* †, Nano Lett., 2015, 15 (8), pp 5075–5080.

DOI : 10.1021/acs.nanolett.5b02273