Centre d’Élaboration de Matériaux et d’Etudes Structurales (UPR 8011)

Accueil > Recherche > SINanO : Surfaces, Interfaces et Nano-Objets > Thématiques de Recherche

Nanoparticles : formation mechanisms, size effects, properties

SINanO Highlights - The names of the team members are in blue

Prediction of Co nanoparticle morphologies

stabilized by ligands : towards a kinetic model

Van Bac Nguyen, Magali Benoit, Nicolas Combe and Hao Tang

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Cobalt nanoparticles (NPs) synthesized in liquid environments present anisotropic shaped nanocrystals such as disks, plates, rods, wires or cubes. Though the synthesis parameters (precursor, reducing agent, stabilizing ligands, concentration, temperature or rate of precursor injection) controlling the final morphologies are experimentally well controlled, little is known concerning the growth mechanisms at the atomic scale. In this work, we intend to predict the morphology variation of hcp cobalt NPs as a function of the ligand concentration. To this aim, we consider two well-established thermodynamic models and develop a new kinetic one. These models require the knowledge of the adsorption behaviors of stabilizing molecules as a function of surface coverage on preferential facets of NPs. To this end, density functional theory (DFT) calculations were performed on the adsorption of a model carboxylate ligand CH3COO on different Co crystalline surfaces. The shapes of the Co NPs obtained by these models are compared to experimental morphologies and other theoretical results from the literature. While thermodynamic models are in poor agreement with experimental observations, the variety of shapes predicted by the kinetic model is much more promising. Our study confirms that the morphological control of NPs is mostly driven by kinetic effects.

Modeling Iron–Gold Nanoparticles Using a

Dedicated Semi-Empirical Potential :

Application to the Stability of Core–Shell Structures

F. Calvo, N. Combe, J. Morillo, and M. Benoit

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Core–shell nanoparticles made from iron embedded in gold have a strong potential interest in nanomedicine, the Au shell providing an efficient biocompatible coating for the magnetic Fe core. With the aim of determining theoretically the equilibrium morphologies of Fe–Au nanoparticles in a broad size range and with different compositions, a semiempirical many-body Fe–Au potential was designed combining well-established models for the pure metals and introducing dedicated contributions for the interactions involving mixed elements. The potential was parametrized against various energetic properties involving impurities, intermetallics, and finite clusters obtained using density functional calculations in the generalized gradient approximation. The potential was tested to investigate Fe–Au nanoparticles near equiconcentration containing about 1000–2000 atoms at finite temperature using parallel tempering Monte Carlo simulations initiated from the core–shell structure. The core–shell nanoparticles are found to be thermally stable up to about 800 K, at which point the gold outer layer starts to melt, with the iron core remaining stable up to approximately 1200 K. In contrast, the alternative potential developed by Zhou and co-workers (Zhou, X. Z. ; Johnson, R. A. ; Wadley, H. N. G. Phys. Rev. B, 2004, 69, 144113) predicts a strong tendency for mixing, the core–shell structure appearing energetically metastable. The two models also predict significantly different vibrational spectra.


Magnetism and morphology in faceted

B2-ordered FeRh nanoparticles

M. Liu, P. Benzo, H. Tang, M. Castiella, B. Warot-Fonrose, N. Tarrat, C. Gatel, M. Respaud, J. Morillo and M. J. Casanove

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Whereas the bulk equiatomic FeRh alloy with B2 structure is antiferromagnetic (AFM) below 370K, we demonstrate that the surface configuration can stabilize the low temperature ferromagnetic (FM) state in FeRh nanoparticles in the 6–10 nm range. The most stable configuration for FM nanoparticles, predicted through first-principles calculations, is obtained in magnetron sputtering synthesized nanoparticles. The structure, morphology and Rh-(100) surface termination are confirmed by aberration-corrected (scanning) transmission electron microscopy. The FM magnetic state is verified by vibrating sample magnetometry experiments. This combined theoretical and experimental study emphasizes the strong interplay between surface configuration, morphology and magnetic state in magnetic nanoparticles. EPL, 116 27006 (2016).


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. Casano

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