Monodisperse Co, Fe, and FeCo nanoparticles are prepared via thermal decomposition of metal carbonyls in the presence of aluminium alkyls, yielding air-stable magnetic metal nanoparticles after surface passivation. The particles are characterized by electron microscopy (SEM, TEM, ESI), electron spectroscopy (MIES, UPS, and XPS) and x-ray absorption spectroscopy (EXAFS). The particles are peptized by surfactants to form stable magnetic fluids in various organic media and water, exhibiting a high volume concentration and a high saturation magnetization. In view of potential biomedical applications of the particles, several procedures for surface modification are presented, including peptization by functional organic molecules, silanization, and in situ polymerization.

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Recently, magnetic nanoparticles and nanocomposite microspheres have attracted great interest for biomedical and technical application. Magnetic metal nanoparticles are of special interest due to their beneficial, size-dependent magnetic properties. Superparamagnetic metal nanoparticles and mesoscale nanocomposite particles (viz. Co nanoparticles, Co@SiO 2 , and Co@SiO 2 @TiO 2 particles) were obtained by a three-step synthesis, involving consecutive steps of thermolysis and sol-gel procedures. A high-resolution Schottky-type field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectrometer was used to characterize intermediate and final products at the successive stages of synthesis. The samples were deposited on carbon-coated transmission electron microscopy (TEM) grids (thin film technique) which afforded enhanced specimen contrast and reduced X-ray background contribution in microanalysis. The FESEM was equipped with a special mounting device for these grids with an appropriate detector beneath. By this method, the samples, covering sizes from the nanometer to micron scale, could be characterized and analyzed by several imaging modes, viz. with standard SE and BSE detection mode and supplementary with low-voltage scanning transmission mode (STEM-in-SEM) and fundamental information about particle size, morphology, and elemental distribution was obtained.