Journal
ACTA MATERIALIA
Volume 61, Issue 14, Pages 5130-5143Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2013.04.062
Keywords
Gold-iron; Nanoparticles; Surface energy anisotropy; Phase transformations; Segregation
Funding
- Israel Science Foundation [775/10]
- Russell Berry Nanotechnology Institute at the Technion
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Sub-micrometer-sized particles of Au-Fe alloys were obtained by solid-state dewetting of single-crystalline Au-Fe bilayer films, deposited on c-plane sapphire (alpha-Al2O3) substrates. Depending on the annealing parameters, precipitation of an Fe-rich phase occurred on the side facets of the particles in an interface-limited reaction. Based on the literature values of surface and interface energies in the system, the precipitates were expected to grow inside the Au(Fe) particles, resulting in an (Fe) core-(Au) shell morphology. However, more complex, time-dependent precipitate morphologies were observed, with faceted Fe-rich precipitates attached to the parent faceted Au-rich particles of the same height being dominant at the last stages of the transformation. Our high-resolution transmission electron microscopy observations revealed a nanometric segregation layer of Au on the surface of Fe-rich particles and at their interface with sapphire. This segregation layer modified the surface and interface energies of the Fe-rich particles. A thermodynamic transformation model based on the concept of weighted mean curvature was developed, describing the kinetics of precipitations and morphology evolution of the particles during the dewetting process. Employing the values of surface and interface energies modified by segregation resulted in a good qualitative agreement between theory and experiment. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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