Skip to main content Accessibility help

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

  • Andrea Falqui (a1) (a2), Anna Corrias (a1), Peng Wang (a3), Etienne Snoeck (a4) and Gavin Mountjoy (a1)...


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.


Corresponding author

Corresponding author. E-mail:


Hide All
Abeles, B. (1976). Granular metal films. In Applied Solid State Science, Wolfe, R. (Ed.), pp. 1117. New York: Academic Press.
Ammar, S., Helfen, A., Jouini, N., Fievet, F., Rosenman, I., Villain, F., Molinie, P. & Danot, M. (2001). Magnetic properties of ultrafine cobalt ferrite particles synthesized by hydrolysis in a polyol medium. J Mater Chem 11, 186192.
Brinker, C.J. & Scherer, G.W. (1990). Sol-Gel Science. San Diego, CA: Academic Press.
Cannas, C., Casula, M.F., Concas, G., Corrias, A., Gatteschi, D., Falqui, A., Musinu, A., Sangregorio, C. & Spano, G. (2001). Magnetic properties of gamma-Fe2O3-SiO2 aerogel and xerogel nanocomposite materials. J Mater Chem 11, 31803187.
Carta, D., Casula, M.F., Corrias, A., Falqui, A., Loche, D., Mountjoy, G. & Wang, P. (2009). Structural and magnetic characterization of Co and Ni silicate hydroxides in bulk and in nanostructures within silica aerogels. Chem Mater 21, 945953.
Carta, D., Corrias, A., Mountjoy, G. & Navarra, G. (2007a). The structure of highly porous nanocomposite aerogels. J Non-Cryst Solids 353, 17851788.
Carta, D., Mountjoy, G., Navarra, G., Casula, M.F., Loche, D., Marras, S. & Corrias, A. (2007b). An X-ray absorption investigation of the formation of cobalt ferrites nanoparticles in an aerogel silica matrix. J Phys Chem C 111, 63086317.
Casas, L.I., Roig, A., Molins, E., Greneche, J.M., Asenjo, J. & Tejada, J. (2002). Iron oxide nanoparticles hosted in silica aerogels. Appl Phys A 74, 591597.
Casu, A., Casula, M.F., Corrias, A., Falqui, A., Loche, D. & Marras, S. (2007). Magnetic and structural investigation of highly porous CoFe2O4-SiO2 nanocomposite aerogels. J Phys Chem C 111, 916922.
Casula, M.F., Loche, D., Marras, S., Paschina, G. & Corrias, A. (2007). Role of urea in the preparation of highly porous nanocomposite aerogels. Langmuir 23, 35093512.
Cliff, G. & Lorimer, G.W. (1975). The quantitative analysis of thin specimens. J Microsc 103, 203207.
Congiu, F., Concas, G., Ennas, G., Falqui, A., Fiorani, D., Marongiu, G., Marras, S., Spano, G. & Testa, A.M. (2004). Magnetic properties of nanocrystalline CoFe2O4 dispersed in amorphous silica. J Magn Magn Mater 272-276, 15611562.
Egerton, R.F. (1996). Electron Energy-Loss Spectroscopy in the Electron Microscope, pp. 210216. New York: Plenum Press.
Ennas, G., Casula, M.F., Falqui, A., Gatteschi, D., Marongiu, G., Piccaluga, G., Sangregorio, C. & Pinna, G. (2001). Nanocrystalline iron-cobalt alloys supported on a silica matrix prepared by the sol-gel method. J Non-Cryst Solids 293-295, 19.
Falqui, A., Corrias, A., Gass, M. & Mountjoy, G. (2009). A transmission electron microscopy study of Fe-Co alloy nanoparticles in silica aerogel matrix using HREM, EDX and EELS. Microsc Microanal 15, 114124.
Gich, M., Casas, Li., Roig, A., Molins, E., Sort, J., Suriñach, S., Baró, M.D., Muñoz, J.S., Morellon, L., Ibarra, M.R. & Nogués, J. (2003). High-coercivity ultralight transparent magnets. Appl Phys Lett 82, 43074309.
Haefeli, U., Schuett, W., Teller, J. & Zborowski, M. (1997). Scientific and Clinical Applications of Magnetic Carriers. New York: Plenum Press.
Husing, N. & Schubert, U. (1998). Aerogels airy materials: Chemistry, structure, and properties. Angew Chem, Int Ed 37, 2245.
Hutlova, A., Niznansky, D., Rehspringer, J.-L., Estournes, C. & Kurmoo, M. (2003). High coercive field for nanoparticles of CoFe2O4 in amorphous silica sol-gel. Adv Mater 15, 16221625.
Kryder, M.H. (1996). Ultrahigh-density recording technologies. MRS Bull 21, 1722.
Moreno, E.M., Zayat, M., Morales, M.P., Serna, C.J., Roig, A. & Levy, D. (2002). Preparation of narrow size distribution superparamagnetic gamma-Fe2O3 nanoparticles in a sol-gel transparent SiO2 matrix. Langmuir 18, 49724978.
Pierre, A.C. & Pajonk, G.M. (2002). Chemistry of aerogels and their applications. Chem Rev 102, 42434265.
Raj, K., Moskowitz, B. & Casciari, R. (1995). Advances in ferrofluid technology. J Magn Magn Mater 149, 174180.
Wang, P., Bleloch, A.L., Falke, U. & Goodhew, P.J. (2006). Geometric aspects of lattice contrast visibility in nanocrystalline materials using HAADF STEM. Ultramicroscopy 106, 277283.
Williams, D.B. & Carter, C.B. (1996). Transmission Electron Microscopy, vol. 4, pp. 608611. New York: Plenum Press.



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed