title: A transmission electron microscopy study of CoFe2O4 ferrite nanoparticles in silica aerogel matrix using HREM and STEM imaging and EDX spectroscopy and EELS.
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.
authors.affiliation: Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, Monserrato, Cagliari, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.forename: Anna
authors.initials: A
authors.lastname: Corrias
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.forename: Etienne
authors.initials: E
authors.lastname: Snoeck
authors.forename: Gavin
authors.initials: G
authors.lastname: Mountjoy