On the Occurrence of Stable and Metastable States in Metallic Core-shell Nanoparticles

O. A. OVIEDO; M. M. MARISCAL; E. P. M. LEIVA

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

RSC Editions

Año: 2010 vol. 12 p. 4580 - 4585

1463-9076

Following the framework established by Hill and Chamberlin [T. L. Hill and R. V. Chamberlin,Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 12779] to analyze the extension of thermodynamicsof small systems to metastable states, we have adopted the same basic ideas to study thethermodynamic stability of core-shell nanoparticles. For the first time we are able to address thequestion of whether or not core-shell nanoparticles have a limit of stability when they are underoversaturation conditions. By the latter, we mean the excess of chemical potential of theadsorbate (shell) atoms with respect to its bulk material, which is the driving force fornanoparticle growth. In this situation the probability density exhibits multiple local maximaassociated with different core-shell metastable states. The decrease of the free energy barriersfor the growth of the bulk phase of the shell material is analyzed for increasing oversaturation.At large positive oversaturations, the barrier disappears and the core-shell NP become unstablewith respect to the bulk deposit of the shell material. A brief discussion on the model is madeillustrating its application to a specific system by means of computer simulations using realisticinteratomic potentials. One of the most striking results of these specific studies is the occurrenceor not of a core-shell under undersaturation conditions depending on nanoparticle size.