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A Transmission Electron Microscopy Study of CoFe2O4 Ferrite Nanoparticles in Silica Aerogel Matrix Using HREM and STEM Imaging and EDX Spectroscopy and EELS

Published online by Cambridge University Press:  04 March 2010


Andrea Falqui
Affiliation:
Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato, Cagliari, Italy Istituto Italiano di Technologia, 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, I-09042 Monserrato, Cagliari, Italy
Peng Wang
Affiliation:
SuperSTEM, Daresbury Laboratory, Keckwick Lane, Daresbury, Cheshire WA4 4AD, UK
Etienne Snoeck
Affiliation:
CEMES, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France
Gavin Mountjoy
Affiliation:
Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, I-09042 Monserrato, Cagliari, Italy
Corresponding
E-mail address:

Abstract

Magnetic nanocomposite materials consisting of 5 and 10 wt% CoFe2O4 nanoparticles in a silica aerogel matrix have been synthesized by the sol-gel method. For the CoFe2O4-10wt% sample, bright-field scanning transmission electron microscopy (BF STEM) and high-resolution transmission electron microscopy (HREM) images showed distinct, rounded CoFe2O4 nanoparticles, with typical diameters of roughly 8 nm. For the CoFe2O4-5wt% sample, BF STEM images and energy dispersive X-ray (EDX) measurements showed CoFe2O4 nanoparticles with diameters of roughly 3 ± 1 nm. EDX measurements indicate that all nanoparticles consist of stoichiometric CoFe2O4, and electron energy-loss spectroscopy measurements from lines crossing nanoparticles in the CoFe2O4-10wt% sample show a uniform composition within nanoparticles, with a precision of at best than ±0.5 nm in analysis position. BF STEM images obtained for the CoFe2O4-10wt% sample showed many “needle-like” nanostructures that typically have a length of ∼10 nm and a width of ∼1 nm, and frequently appear to be attached to nanoparticles. These needle-like nanostructures are observed to contain layers with interlayer spacing 0.33 ± 0.1 nm, which could be consistent with Co silicate hydroxide, a known precursor phase in these nanocomposite materials.


Type
Materials Applications
Copyright
Copyright © Microscopy Society of America 2010

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A Transmission Electron Microscopy Study of CoFe2O4 Ferrite Nanoparticles in Silica Aerogel Matrix Using HREM and STEM Imaging and EDX Spectroscopy and EELS
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