title: TEM-induced structural evolution in amorphous Fe oxide nanoparticles.
abstract: Exposure to the high energy electron beam of a TEM changes the morphology of amorphous Fe oxide nanoparticles from solid spheres to hollow shells. Amorphous Fe oxide nanoparticles prepared via high-temperature methods using hexadecylamine and trioctylphosphine oxide surfactants were compared to crystalline gamma-Fe2O3 particles of similar size. Both sets of particles are fully characterized via SQUID magnetometry, X-ray powder diffraction, BET surface analysis, EPR spectroscopy, high-resolution transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Time-resolved TEM images reveal that the amorphous Fe oxide particles evolve from solid spheres into hollow shells in <2 min, whereas crystalline gamma-Fe2O3 are unaffected by the electron beam. The resulting nanocrystalline Fe oxide shells bear striking resemblance to core-shell nanocrystals, but are a result of a morphology change attributed to restructuring of particle voids and defects induced by quasi-melting in the TEM. These results thus imply that caution is necessary when using TEM to analyze nanoparticle core-shell and heterostructured nanoparticles.
authors.affiliation: Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Latham
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Wilson
authors.forename: Peter
authors.initials: P
authors.lastname: Schiffer
authors.forename: Mary Elizabeth
authors.initials: ME
authors.lastname: Williams