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A Transmission Electron Microscopy Study of Fe-Co Alloy Nanoparticles in Silica Aerogel Matrix Using HREM, EDX, and EELS

Published online by Cambridge University Press:  16 March 2009

Andrea Falqui ,
Anna Corrias ,
Mhairi Gass  and
Gavin Mountjoy
Andrea Falqui
Affiliation:
Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato, Cagliari, Italy Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
Anna Corrias
Affiliation:
Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato, Cagliari, Italy
Mhairi Gass
Affiliation:
SuperSTEM, Daresbury Laboratory, Keckwick Lane, Daresbury, Cheshire WA4 4AD, UK
Gavin Mountjoy*
Affiliation:
Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato, Cagliari, Italy
*
Corresponding author. E-mail: g.mountjoy@kent.ac.uk
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Abstract

Magnetic nanocomposite materials consisting of 5.5 wt% Fe-Co alloy nanoparticles in a silica aerogel matrix, with compositions FexCo1−x of x = 0.50 and 0.67, have been synthesized by the sol-gel method. The high-resolution transmission electron microscopy images show nanoparticles consisting of single crystal grains of body-centered cubic Fe-Co alloy, with typical crystal grain diameters of approximately 4 and 7 nm for Fe0.5Co0.5 and Fe0.67Co0.33 samples, respectively. The energy dispersive X-ray (EDX) spectra summed over areas of the samples gave compositions FexCo1−x with x = 0.48 ± 0.06 and 0.68 ± 0.05. The EDX spectra obtained with the 1.5 nm probe positioned at the centers of ∼20 nanoparticles gave slightly lower concentrations of Fe, with means of ⟨x⟩ = 0.43 ± 0.01 and ⟨x⟩ = 0.64 ± 0.02, respectively. The Fe0.5Co0.5 sample was studied using electron energy loss spectroscopy (EELS), and EELS spectra summed over whole nanoparticles gave x = 0.47 ± 0.06. The EELS spectra from analysis profiles of nanoparticles show a distribution of Fe and Co that is homogeneous, i.e., x = 0.5, within a precision of at best ±0.05 in x and ±0.4 nm in position. The present microscopy results have not shown the presence of a thin layer of iron oxide, but this might be at the limit of detectability of the methods.

Keywords

Fe-Co alloynanoparticlesHREMEDXEELS
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 15 , Issue 2 , April 2009 , pp. 114 - 124
Copyright
Copyright © Microscopy Society of America 2009

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Footnotes

Permanent address: School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK

References

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