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

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.

Air stable Fe and FeCo magnetic fluids—synthesis and characterization

“…16 For Fe nanoparticles we expect the same mechanism. Figure 1 shows the TEM image of the Fe nanoparticles after the 'smooth' oxidation.…”

Formation and Characterization of Pt Nanoparticle Networks

“…[34] Secondly, pre-stabilized Co nanoparticles were deposited on SiO x substrates from suspensions in toluene. [35] STM indicated that a closed layer of the particles was obtained. Figure 6 displays the MIES (a) and UPS (b) spectra of the surface-deposited, pre-stabilized Co nanoparticles as a function of surface temperature.…”

“…[35] For illustration, Figure 7 presents MIES and UPS (HeI) spectra for Pt colloids cross-linked by hydroquinone (left) and chlorohydroquinone (right) spacers. For the as-prepared films there is practically no emission for binding energies smaller than 3.5 eV.…”

Utilization of Screen Printed Low Curing Temperature Cobalt Nanoparticle Ink for Miniaturization of Patch Antennas

“…Magnetic nanoparticles are useful in various applications including electromagnetic devices [18], high-density storage media [19,20], ferrofluids [21], magnetic resonant imaging [22], drug delivery [23], and catalysts [24]. Magnetic metallic cobalt nanoparticles offer an interesting option as a raw material because using solid nanoparticles as a starting point instead of synthesizing them in situ simplifies the process substantially.…”