title: A transmission electron microscopy study of Fe-Co alloy nanoparticles in silica aerogel matrix using HREM, EDX, and EELS.
abstract: Magnetic nanocomposite materials consisting of 5.5 wt% Fe-Co alloy nanoparticles in a silica aerogel matrix, with compositions Fe(x)Co(1-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 Fe(0.5)Co(0.5) and Fe(0.67)Co(0.33) samples, respectively. The energy dispersive X-ray (EDX) spectra summed over areas of the samples gave compositions Fe(x)C(o1-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 approximately 20 nanoparticles gave slightly lower concentrations of Fe, with means of x = 0.43 +/- 0.01 and x = 0.64 +/- 0.02, respectively. The Fe(0.5)Co(0.50) 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.
authors.affiliation: Dipartimento di Scienze Chimiche and INSTM, Università di Cagliari, S.P. Monserrato-Sestu Km 0.700, 09042 Monserrato, Cagliari, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Falqui
authors.forename: Anna
authors.initials: A
authors.lastname: Corrias
authors.forename: Mhairi
authors.initials: M
authors.lastname: Gass
authors.forename: Gavin
authors.initials: G
authors.lastname: Mountjoy
mesh_terms: D000497:Alloys / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry / Q000648:ultrastructure*; D046529:Microscopy, Electron, Transmission / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry*; D046590:Spectroscopy, Electron Energy-Loss; D013057:Spectrum Analysis; D014965:X-Rays
chemical_list: D000497:Alloys; D003035:Cobalt; D012822:Silicon Dioxide; D007501:Iron