Eur. Phys. J. Appl. Phys. 97, 56 (2022)
https://doi.org/10.1051/epjap/2022220027

Regular Article

Out-of-equilibrium supported Pt-Co core-shell nanoparticles stabilized by kinetic trapping at room temperature^★

¹ Interfaces, Confinement, Matériaux et Nanostructures, ICMN, Université d’Orléans, CNRS, 1B, rue de la Férollerie, 45071 Orléans Cedex, France
² Institut Néel, CNRS, Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France
³ Institut des Nanotechnologies de Lyon, CNRS, Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France
⁴ Conditions Extremes et Matériaux: Hautes Temperatures et Irradiations, CEMHTI, CNRS, 45071 Orleans Cedex, France

^a Present address: Département de Physique, Faculté des Sciences et des Sciences Appliquées, Université de Bouira, 10000, Algérie
^* e-mail: pascal.andreazza@univ-orleans.fr

Received: 6 February 2022
Received in final form: 18 April 2022
Accepted: 25 April 2022
Published online: 1 September 2022

Abstract

The chemical stability of supported CoPt nanoparticles in out-of-equilibrium core-shell configurations was investigated mainly by anomalous grazing incidence small angle X-ray scattering (AGISAXS) in association with combined transmission electron microscopy and X-ray absorption spectroscopy. CoPt nanoparticles were prepared at room temperature by ultrahigh vacuum atom beam deposition using two different routes: simultaneous deposition of the two metals (CoPt) or sequential deposition. In this last case, Co deposition on a Pt-core (Pt@Co) and the reverse configuration (Co@Pt) are explored. In the Pt@Co case, our experimental analysis of 2.5 nm particles shows the stability of a Pt rich-core (80% Pt) surrounded by a two-monolayers-thick Co shell. In the reverse case, the core-shell structure is also stabilized, while the codeposited sample leads to an alloyed structure. These results suggest that the growth kinetics can trap the thermodynamically non-favorable core-shell structure even for this system which has a high alloying tendency. Besides the lack of atom mobility at room temperature, this stabilization can also be associated with core strain effects. Post thermal treatment of core-shell samples induces a structural transition from the core-shell configuration to the equilibrium alloyed configuration. This study demonstrates that the element-selective scattering technique, AGISAXS is highly efficient for the extraction of chemical segregation information from multi-component supported nanoparticles, such as core-shell structures, up to ultimate small sizes.