N. Waldöfner

A size-selective synthesis of air stable colloidal magnetic cobalt nanoparticles

A novel, size-selective preparation route leads to air stable ‘monodisperse’ colloidal cobalt nanoparticles via the thermolysis of Co2(CO)8 in the presence of aluminum alkyls. X-ray absorption near edge structure measurements have proved that this preparation pathway provides long term stable zerovalent magnetic Cobalt particles. In addition, these measurements show that the chemical nature of the surfactant used exerts a significant influence on the stability and the local electronic and geometric structure of the analyzed nanoparticles.

Interaction between core and protection shell of N(butyl)4Cl- and N(octyl)4Cl-stabilized Pd colloids

Abstract We present X-ray absorption near edge structure (XANES) measurements on N(butyl)4Cl- and N(octyl)4Cl-stabilized Pd colloids at both the Pd LIII- and the Cl K-edge. Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (HeI) results for these colloids, deposited on silica substrates, are also shown. The results provide detailed insight into the mechanism of bonding between the protection shell and the colloidal core. Both XANES and MIES suggest that the chlorine is present on the inside of the protection shell, located between palladium core and N(alkyl)4 groups forming the protection shell. Moreover, the XANES results suggest a dependence of the equilibrium position of the chlorine between the metal core and the alkyl chain on the length of the alkyl chains. The possible motivation for such an effect is discussed on the basis of different models. MIES, in addition, provides information on the thermal stability of the shell-stabilized Pd colloids.

Three-dimensional Pt-nanoparticle networks studied by anomalous small-angle X-ray scattering and X-ray absorption spectroscopy

Anomalous small-angle X-ray scattering (ASAXS) experiments with synchrotron radiation were performed to study the three-dimensional nanostructures of metal/organic hybrids formed by crosslinking aluminium-organic-stabilized platinum nanoparticles with various bifunctional organic spacer molecules. The advantage of ASAXS is the possibility of separating the particle scattering from that of the organic components, thus providing unbiased information about particle size distributions and interparticle correlation. In order to obtain the structural information from the scattering data, a model function based on Vrijs analytical solution for a multicomponent system of hard spheres is proposed. The model is applied to three different samples and the results are compared with those obtained from the application of Fourier methods (characteristic function) and X-ray absorption measurements.

From Pt molecules to nanoparticles: in-situ (anomalous) small-angle X-ray scattering studies

Anomalous small angle X-ray scattering was employed to monitor in situ the formation of colloidal Pt particles by the reaction of Pt(acac)2 and Al(CH3) 3 in solution. An intermediate complex molecule was found to decompose to form stable Pt particles of 1.2 nm diameter with a monomodal particle size distribution. A network like correlation in the particle positions tends to build up by organic spacer molecules between stabilizing aluminum-organic shells.