Preparation of anisotropic transition metal phosphide nanocrystals: the case of nickel phosphide nanoplatelets, nanorods, and nanowires.

We have synthesized anisotropic nickel phosphide nanocrystals, including triangular/hexagonal nanoplatelets, nanorods and nanowires, via a solution-phase synthetic method that uses nickel(II) acetylacetonate as a metal precursor and trioctylphosphine as a phosphorus source. Nickel phosphide nanoplatelets have been prepared from a one-pot reaction, and their dimensions in the length mostly vary from 20 to 50 nm, while their thicknesses are in a narrow range of 7-9 nm. Nickel phosphide nanorods with a width of approximately 6 nm and a typical length of 25-32 nm can be synthesized from either the one-pot reaction or the multi-injection approach, although the latter can generate nanorods with a much higher uniformity. A continuous injection approach has been used to synthesize nanowires that have a typical width of approximately 6 nm and a length ranging from tens of nanometers up to several hundred nanometers. Major factors that influence the growth of nickel phosphide nanocrystals have been investigated, and a multi-surfactant system is found to be essential for the formation of anisotropic nanostructure. Magnetic studies have revealed paramagnetic characteristics for all the synthesized samples.

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.

Size- and structure-controlled synthesis and characterization of nickel nanoparticles.

Nearly monodisperse face-centered cubic (fcc) and hexagonal close-packed (hcp) nickel nanoparticles have been prepared via the thermal decomposition of nickel organometallic precursors in a reaction mixture containing alkylamine, and characterized by powder X-ray diffraction, transmission electron microscopy and magnetic measurement. The employed alkylamine can serve as both solvent and reducing agent. The as-synthesized nickel nanoparticles are air-stable, and their sizes can be readily tuned by the variation of surfactant concentration and reaction temperature. The crystalline phase control was achieved by adjusting alkylamine concentration, heating rate and reaction temperature. Magnetic measurements showed that hcp Ni nanoparticles have quite different magnetic properties compared to fcc Ni nanoparticles.