Study of the structure and stability of cobalt nanoparticles for ferrofluidic applications

✍ Scribed by S. Rudenkiy; M. Frerichs; F. Voigts; W. Maus-Friedrichs; V. Kempter; R. Brinkmann; N. Matoussevitch; W. Brijoux; H. Bönnemann; N. Palina; H. Modrow

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 234 KB
• Volume: 18
• Category: Article
• ISSN: 0268-2605
• DOI: 10.1002/aoc.760

✦ Synopsis

Abstract

We present X‐ray absorption spectroscopy (XAS) data, ultraviolet photoelectron spectra (HeI) and metastable impact electron spectra (MIES) of cobalt nanoparticles (typically 4 to 10 nm), prepared by Co~2~(CO)~8~ thermolysis and pre‐stabilized by smooth oxidation. We find that the particles consist of a core–shell system with a dominantly f.c.c. core and a shell in which CoC and CoO coordination is likely to occur. This corresponds well to the results from electron spectroscopy, that stabilization occurs via formation of (CoCO~x~) and (CoO) groups formed during the oxidation procedure and appears sensitive to the reaction conditions. Peptization of the pre‐stabilized particles with KorantinSH surrounds the particles with a dense organic shell, stable up to about 250°C. The carbonic acid molecules of the shell are oriented predominantly perpendicular to the surface of the particles, their carboxyl functional group linking the shell with the cobalt particles. This result is also supported by the XAS data, where it is observed that, during peptization, CoC coordination is partly replaced by CoO coordination. In order to arrive at these statements, auxiliary measurements on bare and gas‐exposed cobalt films, also reported here, were required. Copyright © 2004 John Wiley & Sons, Ltd.