Monodisperse cobalt nanoparticles were synthesized by high-temperature reduction of solution-phase cobalt chloride in the presence of a pair of surfactants, oleic acid and triphenylphosphine. Highly ordered two-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. Analysis by X-ray diffraction, UV-vis absorption spectroscopy and transmission electron microscopy demonstrated that the size of the cobalt nanocrystals could be tuned by tailoring the concentration ratio of the two surfactants. In addition, the influence of different crystal sizes on magnetic properties of Co nanocrystals was also investigated.

Monodisperse cobalt nanoparticles are synthesized via a high-temperature thermal decomposition method in the presence of oleic acid and triphenylphosphine. The as-synthesized nanoparticles are stable against further deep oxidation when they are kept in heptane (C7H16). Time-dependent XPS studies indicate that oxidation of the as-synthesized cobalt nanoparticles in air is slow. The valence change of cobalt from the nanoparticle sample is not observed after it is kept in heptane under air for 90 days. The cobalt nanoparticles have a beta-manganese-type structure (also called epsilon-Co). Annealing the nanoparticles at 500degreesC under Ar (95%) + H-2 (5%) converts these particles from epsilon-Co to fcc-Co. Two-dimensional and three-dimensional self-assembled superlattices of the passivated cobalt nanoparticles are formed by slow evaporation of the carrier solvent. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles. Copyright (C) 2004 John Wiley Sons, Ltd.

Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles.

Long-chain n-octadecayl mercaptan (C18H37SH)-passivated palladium nanoparticles are synthesized and characterized. The palladium nanoparticles are successfully capped by n-octadecayl mercaptan. These palladium nanoparticles have the same face-centered cubic crystalline structure as Pd in the bulk phase. The size of the capped palladium nanoparticles varies in the range of 1.3–5.5 nm for various reaction conditions. These results show that the long-chain n-octadecayl mercaptan-capped palladium nanoparticles are more stable than alkanethiolate-capped Pd nanoparticles with a shorter chain.

Magnetic colloids of cobalt nanocrystals (NCs) were prepared by reducing solute cobalt chloride in the presence of stabilizing agents at a high temperature. The nanocrystalline samples were nearly monodisperse with narrow size distribution of about 7%. X-ray diffraction result showed that Co NCs had a third distinct crystal structure related to the beta phase of manganese. A red shift of the maximum absorption peak of the UV-visible spectra occurred with the increasing diameter of particles, which indicated that we could coarsely control average particle size by adjusting the concentration ratio of cobalt to surfactants. The size of these NCs samples was uniform enough to self-assemble into close-packed and ordered NCs

. Uniform gold nanowires were synthesized by electrodepositing the gold under a very low ac frequency in the pores of an anodic aluminum oxide (AAO) template. The surface of the Au/AAO composite is very even and appeared purplish red. Atomic force microscopy observation indicates that the template membranes we obtained have hexagonally close-packed nanochannels. The gold nanowire array is very orderly arranged after partially dissolving the aluminum oxide membrane. Gold nanowires were also characterized by transmission electron microscopy and the phase structure of the Au/AAO composite was proved by X-ray diffraction.

Hexagonally ordered microporous aluminum anoxic oxide (AAO) template was prepared by two-step anodization process. The thickness and diameter of the anodic alumina pore is proportional to the anodization voltage and the second time anodization. Au/AAO membrane was also characterized by X-ray diffraction (XRD). Gold nanowires array was prepared in AAO by a lower frequency AC electrodeposition. The deposition rate of gold nanoparticles under the lower frequency is slower than under the higher frequency, so the membrane surface of Gold/AAO is uniform. The morphology of the nanowires array uniformly filled in hexagonally ordered pore was also monitored by atomic force microscope (AFM) after dissolution parts of alumina film.