Effect of Precursor on the Electronic and Geometric Properties of Cobalt Nanoparticles Investigated by Co-K XANES and EXAFS

By varying techniques and parameters in wet-chemical synthesis Co-nanoparticles different crystallographic structures (hcp, fcc and epsilon) can be synthesized. Co-K XANES and EXAFS spectra are very powerful tools to distinguish between those structures. In this study we are investigating for the first time the effect of the precursor molecule used for the synthesis on the electronic and geometric properties of cobalt nanoparticles. As precursors two organometallic cobalt complexes were used: alkyne-bridged dicobalthexacarbonyl [(Co2(mu-HCCH)(CO)6] (ADH) and the well known dicobalt octacarbonyl [Co2(CO)8] (DCO). Both precursors were thermally decomposed under identical reaction conditions. Besides, effect of the precursor on the Co NPs was also investigated when two different types of surfactants are utilized in the reaction, oleic acid and n-trioctylphosphine. When only oleic acid was used as the surfactant, the XAFS analysis showed formation of fcc structure with ADH and hcp with DCO. When a combination of oleic acid and TOP were used, the crystal structure of CO NPs obtained is currently being analyzed.