Structure, optical and magnetic properties of Ni@Au and Au@Ni nanoparticles synthesized via non-aqueous approaches

Although the combination of magnetic and noble metals in core-shell nanoparticles is very useful in many applications, the preparation of magnetic-noble bimetallic core-shell nanoparticles with uniform shells remains a great challenge due to large mismatch of crystal lattices between magnetic and noble metals. Herein we present non-aqueous methods for combing Au and Ni in nanoscale to form a core-shell structure. Ni@Au nanoparticles were prepared via an injection-quenching process in which Au precursors decomposed and formed closed shells on pre-formed Ni seeds synthesized in oleylamine, whereas Au@Ni nanoparticles were obtained in a one-step reaction involving a seed-catalyzed mechanism. The formed core-shell structure was confirmed by high-angle annular dark-field imaging along with the analyses of energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. UV-Visible absorption spectroscopy and superconducting quantum interference device magnetometer were used to characterize the optical and magnetic properties of the as-prepared bimetallic core-shell nanoparticles. Through the adjustment of growth conditions, Ni@Au and Au@Ni nanoparticles with different core or shell dimensions and morphologies were obtained, which offers an important means to tailor their optical and magnetic properties for multiple practical applications.