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Nanoparticles of nickel have been obtained in solution through reaction of an organometallic precursor, Ni(COD)[sub 2] (COD=cycloocta-1,5-diene), with dihydrogen, in the presence of various stabilizing agents. X-ray diffraction studies evidence a face-centered-cubic structure for all samples. Spherical isolated superparamagnetic nanoparticles (d∼4.5 nm) are produced in the presence of poly(N-vinylpyrrolid-2-one). They display a magnetization value comparable to that of bulk nickel, as determined from superconducting quantum iinterference device (SQUID) measurements. Exposure of the surface of the nanoparticles to CO, leading to CO coordination as monitored by infrared spectroscopy, or to methanol, strongly reduces their magnetization. This reduction corresponds respectively to one or two magnetically inactive layers of nickel atoms at the nanoparticles surface. The production of elongated nanoparticles was favored when either trioctylphosphineoxide or hexadecylamine (HDA) were used as stabilizing agents. In this case, SQUID measurements show that only HDA preserves the magnetization of the surface. This stabilizing agent was selected for the production of nickel nanorods. The influence of ligands on the effective anisotropy is discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Composition (metal or metal oxide core and organic coating), size, shape and structure are the main parameters governing the properties of nano-objects. Driven by their huge potential for application in fields as diverse as catalysis, energy, environment, electronics and medicine much research effort has been dedicated to the control of these parameters over the past 30 years. Namely, the use of concepts and techniques of molecular chemistry has provided remarkable advances in the growth of well-defined nanostructures by pointing out the key roles played by both the metal precursors and stabilizing agents (polymers, dendrimers, ionic liquids, ligands, etc .) during the three main steps of the formation of nanostructures: release of metal atoms, nucleation and growth. It is now currently admitted that interaction between the precursor and stabilizing agent may generate intermediate complexes in the reacting medium which may change the course of the reaction. Also, coordination of the ligand on the growing seeds is recognized as an important factor influencing the growth of nanostructures. Finally, coordination of the ligand at the surface of nanostructures may induce a change in their physical and chemical properties by tuning electronic density and steric hindrance at their surface. To illustrate these points, this review will focus on metal nanostructures synthesized in organic solutions from molecular metal complexes as metal sources and stabilized by coating ligands, short chain molecules with headgroups able to coordinate onto the metal surface. Recent advances will be described highlighting the incidence of coordination chemistry through a selection of relevant examples from the literature. [ABSTRACT FROM AUTHOR]

Nanoparticles can be synthesized from metal-organic or organometallic precursors, either by classical thermal decomposition, ultrasound activation, photolysis as well as hydrogenation or hydrolysis reactions. The size, size distribution and more importantly surface state of these nanoparticles are much better controlled than when they are produced by chemical or electrochemical reduction of metal salts. Hence, metal or oxide nanoparticles can be obtained that are suitable for fundamental physics at the nanoscale, especially for magnetic studies. This is currently of particular interest as many applications require systems of still smaller sizes, the properties of which are not yet fully understood. [ABSTRACT FROM AUTHOR]

Review: 313 refs. [ABSTRACT FROM AUTHOR]

Stable iron nanoparticles have been synthesised by the decomposition of {Fe(N[Si(CH3)3]2)2}2 under dihydrogen pressure. Those conditions lead to a system of monodisperse and metallic nanoparticles which diameter is less than 2 nm and stabilized by HN[Si(CH3)3]2. The magnetization is found to be MS=1.92μB/at., i.e., 10% lower than the bulk value. The Mössbauer spectrum is fitted by two contributions of metallic iron. The magnetic anisotropy energy constant increases up to 5.2×105 J/m3, i.e., ten times the bulk one. [ABSTRACT FROM AUTHOR]

A porous Ru nanomaterial exhibits high electrocatalytic performance and excellent durability for the hydrogen evolution reaction (HER) under both acidic and neutral conditions. It displays a low overpotential of 83 mV at a current density of 10 mA cm−2 and an excellent durability up to 12 h in 0.5 M H2SO4. [ABSTRACT FROM AUTHOR]

Abstract: Oxide free core–shell nanoparticles with an average diameter of about 2nm were wet-chemically synthesised with two different morphologies: either with Rh-rich or an Fe-rich core. The magnetic properties of these nanoparticles were investigated between 5 and 290K by ferromagnetic resonance and superconducting quantum interference device magnetometry. The magnetic anisotropy field varied by a factor of 2 in this temperature range. The nanoparticles with Rh-rich core were found to have a higher anisotropy field of at 5K as compared to the nanoparticles with Fe-rich core (). Multifrequency ferromagnetic resonance (4–24GHz) was used to determine the g-factor. It was determined that the g-factor of nanoparticles with Fe-rich core is higher () compared to nanoparticles with Rh-rich core , being close to the value for iron bulk. [Copyright &y& Elsevier]

Fe[subx] Rh[sub100-x] (x = 50, 80) nanoparticles (NPs) with an average diameter of ∼2 nm were prepared by simultaneous decomposition of stoichiometric quantities of Fe[N(Si(CH[sub3])[sub3])[sub2]][sub2] and Rh(C[sub3] H[sub5] )[sub3] using two different routes: 1) a standard hydrogenation procedure and 2) a new one based on use of amino-borane as a reducing agent. All samples were found to be superparamagnetic with a blocking temperature below 10 K. Results of X-Ray magnetic circular dichroism (XMCD) experiments at the Fe K-edge and the Rh L[sub2,3] edges have shown that not only iron but also rhodium atoms are magnetic as a result of hybridization of Fe 3d states with 4d states of Rh. The total induced magnetic moment of Rh atoms as well as its spin and orbital contributions are shown to depend on chemical composition of NP[subs] and the preparation method. [ABSTRACT FROM AUTHOR]

Monodisperse FeCo nanoparticles were synthesized via thermal decomposition of appropriate organometallic complexes in heated toluene containing surfactants, aiming to a soft magnetic nanomaterial with a high metal percent. The particles were characterized by X-ray powder diffraction, electron microscopy, and static magnetometry techniques. The effect of air exposure on the structural and magnetic properties was examined. Portions of the dried nanoparticles were mixed with additional surfactants or polyvinylpyrrolidone, followed by redispersion into tetrahydrofuran, so as to study arrangement features in the first case, while the use of polyvinylpyrrolidone intended to the expansion of the interparticle distances in order to get more "isolated" nanoparticles. [ABSTRACT FROM AUTHOR]

CoRh alloy nanoparticles (NPs) show nontrivial correlations between chemical and magnetic order that lead to a remarkable nonmonotonous dependence of the magnetic anisotropy energy as a function of composition. Combining experiment and theory we demonstrate how the induced 4d moments and the 3d-4d interfaces control the magnetoanisotropic behavior. New possibilities of tailoring the magnetic characteristics of NPs are thus opened. [ABSTRACT FROM AUTHOR]

The magnetism of bimetallic CoxM1-x (M: Ru and Rh) clusters has been investigated on systems of nanoparticles with diameters smaller than 2 nm embedded in a polymer obtained by means of organometallic synthesis. Whatever the composition (up to x=0.75), the investigation of magnetism evidence a ferromagnetic behavior. As a consequence of size reduction, both CoRh and CoRu systems display enhanced magnetic moments and anisotropy compared to bulk values. [Copyright &y& Elsevier]

The magnetic remanent states of 4-nm-diameter single-crystalline Co nanowires are characterized using off-axis electron holography. Measurements are obtained from isolated wires, as well as from bundles of wires and "multibranch" wires joined by 15-nm-diameter nodes of Co. The fraction of magnetically active moments in a single 4-nm-diameter wire is measured to be 1.01±0.19, indicating that, to within experimental error, the wire is fully magnetized throughout its diameter. [ABSTRACT FROM AUTHOR]

Ultrafine cobalt particles have been reproducibly synthesized by decomposition of an organometallic precursor in the presence of a stabilizing polymer. The size of the stable monodisperse colloids thus obtained is seen to strongly depend on the nature of the polymer: around 4.2 nm diameter in polyphenylenoxide (PPO) and around 1.4 nm diameter in polyvinylpyrrolidone (PVP). Investigations by wide angle x-ray scattering (WAXS) and high-resolution transmission electron microscopy (HRTEM) give evidence for a size dependence of the structural organization, and hence for a close relationship between structure and synthesis conditions. Co/PPO particles exhibit a hexagonal compact structure with the metal-metal bond length of the bulk material while Co/PVP ones display an original structure. We show that the unusual features of the experimental data in Co/PVP clearly point to a nonperiodic polytetrahedral structure. Successful simulations of the HRTEM and WAXS results have been obtained using models built on the basis of a polytetrahedral arrangement. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]