Analyses
2.2.1. Transmission electron microscopy
The precipitated crystals were characterized by TEM on a Jeol 2010
F operated at 200 kV, coupled with an energy-dispersive X-ray spectrometer (EDX) chemical analyzer (PGT-PRISM 2000, associated with
IMIX software, with probe size of 1 nm, acquisition time of 300 s).
Samples were prepared by two methods leading to consistent results. In
the first method, a drop of the solution containing magnetite nanoparticles was directly deposited onto a copper mesh grid covered with a
carbon film. After 10 s, the drop was removed and the grid was allowed
to dry. In the second method, a solution containing precipitated magnetite particles was carefully washed after precipitation and evaporated
under vacuum the following night. Particles were then placed in ethanol, and a drop of this mixture was placed onto the copper mesh grid
for TEM analysis. The only difference observed between the two types
of preparation was the presence, in the first case, of sodium nitrate
crystals which were completely absent in the second case. Particle sizes
were analyzed using standard analytical software for processing digitized electron microscopy images (Gatan DigitalMicrograph, Scion
Image and CaRIne Cristallography [Monceau and Boudias, 1996]).
Additional measurements were carried out by electron energy-loss
spectroscopy (EELS) on a dedicated scanning transmission electron
microscope VG HB005 equipped with a cold field emission gun providing a high energy resolution (0.6 eV) and a high spatial resolution
(0.7 nm)
Analyses2.2.1. Transmission electron microscopyThe precipitated crystals were characterized by TEM on a Jeol 2010F operated at 200 kV, coupled with an energy-dispersive X-ray spectrometer (EDX) chemical analyzer (PGT-PRISM 2000, associated withIMIX software, with probe size of 1 nm, acquisition time of 300 s).Samples were prepared by two methods leading to consistent results. Inthe first method, a drop of the solution containing magnetite nanoparticles was directly deposited onto a copper mesh grid covered with acarbon film. After 10 s, the drop was removed and the grid was allowedto dry. In the second method, a solution containing precipitated magnetite particles was carefully washed after precipitation and evaporatedunder vacuum the following night. Particles were then placed in ethanol, and a drop of this mixture was placed onto the copper mesh gridfor TEM analysis. The only difference observed between the two typesof preparation was the presence, in the first case, of sodium nitratecrystals which were completely absent in the second case. Particle sizeswere analyzed using standard analytical software for processing digitized electron microscopy images (Gatan DigitalMicrograph, ScionImage and CaRIne Cristallography [Monceau and Boudias, 1996]).Additional measurements were carried out by electron energy-lossspectroscopy (EELS) on a dedicated scanning transmission electronmicroscope VG HB005 equipped with a cold field emission gun providing a high energy resolution (0.6 eV) and a high spatial resolution(0.7 nm)
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