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

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.

Meeting Name

2005 Materials Research Society Fall Meeting (2005: Nov. 28-Dec. 1, Boston, MA)

Department(s)

Chemistry

Keywords and Phrases

Aging Of Materials; Crystal Growth; Energy Dispersive Spectroscopy; Iron Compounds; Transmission Electron Microscopy; X Ray Diffraction Analysis; Aging Effects; First-order Reversal Curves; Oxidation-resistant Characteristics; Nanostructured Materials

International Standard Book Number (ISBN)

978-1558998414

International Standard Serial Number (ISSN)

0272-9172

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2006 Materials Research Society (MRS), All rights reserved.

Publication Date

01 Jan 2006

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