TEM-Induced Structural Evolution in Amorphous Fe Oxide Nanoparticles
journal contributionposted on 04.10.2006, 00:00 authored by Andrew H. Latham, Mark J. Wilson, Peter Schiffer, Mary Elizabeth Williams
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 γ-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 γ-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.
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transmission electron microscopynanocrystalline Fe oxide shellselectron energy loss spectroscopyenergy electron beamEPR spectroscopyFe oxide nanoparticlesFe oxide particlesTEM changesSQUID magnetometryBET surface analysisEELStrioctylphosphine oxide surfactants2Oheterostructured nanoparticlesAmorphous Fe Oxide NanoparticlesExposuremorphology changeelectron beamAmorphous Fe oxide nanoparticles