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Fe-Core/Au-Shell Nanoparticles: Growth Mechanisms, Oxidation and Aging Effects

Published online by Cambridge University Press:  26 February 2011

Kai Liu
Affiliation:
kailiu@ucdavis.edu, University of California - Davis, Physics Department, One Shields Avenue, Davis, CA, 95616, United States, 530-752-4109, 530-752-4717
Sung-Jin Cho
Affiliation:
sjcho@ucdavis.edu, University of California - Davis, Chemistry Department, United States
Susan M. Kauzlarich
Affiliation:
smkauzlarich@ucdavis.edu, University of California - Davis, Chemistry Department, United States
J. C. Idrobo
Affiliation:
jidrob1@uic.edu, University of California - Davis, Physics Department, United States
Joseph E. Davies
Affiliation:
Davies@physics.ucdavis.edu, University of California - Davis, Physics Department, United States
Justin Olamit
Affiliation:
Olamit@physics.ucdavis.edu, University of California - Davis, Physics Department, United States
N. D. Browning
Affiliation:
Nbrowning@ucdavis.edu, University of California - Davis, Department of Chemical Engineering and Materials Science, United States
Ahmed M. Shahin
Affiliation:
ashahin@ucalgary.ca, University of Missouri - Rolla, Chemistry Department, United States
Gary J. Long
Affiliation:
glong@umr.edu, University of Missouri - Rolla, Chemistry Department, United States
Fernande Grandjean
Affiliation:
fgrandjean@ulg.ac.be, University of Liëge, Physics Department, Belgium
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Abstract

We report the chemical synthesis of Fe-core/Au-shell nanoparticles (Fe/Au) by a reverse micelle method, and the investigation of their growth mechanisms and oxidation-resistant characteristics. The core-shell structure and the presence of the Fe and Au phases have been confirmed by transmission electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Mössbauer spectroscopy, and inductively coupled plasma techniques. Additionally, atomic-resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope have been used to study details of the growth processes. The Au-shells grow by nucleating on the Fe-core surfaces before coalescing. First-order reversal curves, along with the major hysteresis loops of the Fe/Au nanoparticles have been measured as a function of time in order to investigate the evolution of their magnetic properties. The magnetic moments of such nanoparticles, in the loose powder form, decrease over time due to oxidation. The less than ideal oxidation-resistance of the Au shell may have been caused by the rough Au surfaces. In a small fraction of the particles, off-centered Fe cores have been observed, which are more susceptible to oxidation. However, in the pressed pellet form, electrical transport measurements show that the particles are fairly stable, as the resistance and magnetoresistance of the pellet do not change appreciably over time. Our results demonstrate the complexity involved in the synthesis and properties of these heterostructured nanoparticles.

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Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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