Mixing gold and iron in nanoparticles by electrical discharges in liquid: A new approach

Abstract

The possibility to create homogeneous nanoparticles containing iron and gold by nanosecond-pulsed discharges in liquids, without any laser assistance, is demonstrated. Thanks to a new kind of electrode where elements are coated by PVD on a silicon plate, AuFe nanoparticles, ranging from 10 to 50 nm, are synthesized. Depending on their residence time in the discharge, the structure of the homogeneous nanoparticles evolves to become a core–shell structure, either nested or not. Larger submicrometric particles (from 100 to 500 nm) are specifically formed with the present process by the ejection of liquid droplets from the molten pool created by the discharge on electrode surfaces. These larger particles are produced by solidification of a AuFe shell on a silicon core. This new mechanism can be used to create core–shell particles with a shell containing several, possibly immiscible, elements. Thermal post-treatment performed in situ in a TEM microscope shows the AuFe shell, where Au and Fe separate, turning either into a Janus structure or into a SiFe core facetted by gold pyramids.