Houde She

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.

A nonaqueous approach to the preparation of iron phosphide nanowires.

Previous preparation of iron phosphide nanowires usually employed toxic and unstable iron carbonyl compounds as precursor. In this study, we demonstrate that iron phosphide nanowires can be synthesized via a facile nonaqueous chemical route that utilizes a commonly available iron precursor, iron (III) acetylacetonate. In the synthesis, trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) have been used as surfactants, and oleylamine has been used as solvent. The crystalline structure and morphology of the as-synthesized products were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The obtained iron phosphide nanowires have a typical width of ~16 nm and a length of several hundred nanometers. Structural and compositional characterization reveals a hexagonal Fe2P crystalline phase. The morphology of as-synthesized products is greatly influenced by the ratio of TOP/TOPO. The presence of TOPO has been found to be essential for the growth of high-quality iron phosphide nanowires. Magnetic measurements reveal ferromagnetic characteristics, and hysteresis behaviors below the blocking temperature have been observed.

Preparation and magnetic properties of size-monodispersed Fe-Co alloy nanoclusters

Fe₇₀Co₃₀ alloy clusters were prepared by a plasma-gas-condensation-type cluster deposition technique. By adjusting the deposition parameters, size-monodispersed Fe₇₀Co₃₀ alloy clusters were obtained and their average sizes can be changed from 8.6 to 14.3 nm. The structural and magnetic properties of these alloy nanoclusters were studied. The as-obtained Fe₇₀Co₃₀ clusters have a body-centered-cubic alpha-(Fe,Co) structure although a very weak oxide phase ((Fe,Co)₃O₄ or gamma-(Fe,Co)₂O₃) was also detected because the cluster assemblies have to be exposed to the ambient atmosphere for transmission electron microscopy (TEM) observation and magnetic measurement. Based upon the magnetic measurement results, we compared and discussed the magnetic differences between Fe₇₀Co₃₀ alloy clusters and pure Fe and Co clusters.