Alloying process at the interface of silver nanoparticles deposited on Au(1 1 1) substrate due to the high-temperature treatments

Abstract

X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to study the silver nanoparticles (AgNPs) deposited on Au(1 1 1). It is found out that the AgNPs form a layer which covers most of the Au surface. XPS has been used to observe the changes in the core levels of the AgNPs due to a high-temperature treatment. The XPS investigations clearly show that annealing of the AgNPs films at 620 K results in decreasing of the Ag 3d peaks intensity. At 770 K it is not possible to detect silver signal in the XPS spectra. However, after soft Ar + sputtering of the sample silver is again detectable. Our results show that during annealing of the AgNPs deposited on Au(1 1 1), the hydrocarbon-based ligands decompose and at higher temperatures diffusion of silver cores into gold substrate takes place. In the theoretical part of the work the Ag diffusion has been studied using a mean field theory for minimizing the mixing free energy with respect to the atomic configuration and local spatial relaxation. The present approach searches for energetically the most favorable equilibrium structure of the surface region described in terms of random-alloy within the Valenta model of the inhomogeneous systems. As a result, the layer resolved atomic configuration in the surface region in different temperatures has been obtained. Both results, experimental and theoretical, are consistent.