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Characterisation of core@shell nanoparticles

Characterisation of Co@Fe₃O₄ core@shell nanoparticles using advanced electron microscopy

Benjamin R. Knappett, Pavel Abdulkin, Emilie Ringe, David A. Jefferson, Sergio Lozano-Perez, T. Cristina Rojas, Asuncion Fernandez and Andrew E. H. Wheatley

Nanoscale 2013, Vol. 10, 5765-5772

ICMS

As part of the Al-Nanofunc EU Project, researchers from the Universities of Cambridge and Oxford (UK), and the Materials Science Institute of Seville have used statistically refined EFTEM and a calibrated EELS analysis to probe the core and shell phases of nanoparticles formed from the sequential decomposition of Co and Fe carbonyls, with organic capping agents present. The presence of a carbonaceous layer of capping ligand residues separating the core and shell of the particles has been identified, shedding light on the possible mechanisms of particle formation and suggesting potential new routes to the synthesis of core@ shell particles.

 

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

 

The AL-NANOFUNC project has been designed to install and fully develop at the Materials Science Institute of Seville (ICMS, CSIC-Univ. Seville) an advanced laboratory for the Nano-analysis of novel functional materials. More info: www.al-nanofunc.eu/

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