8 research outputs found
Concerted Growth and Ordering of Cobalt Nanorod Arrays as Revealed by Tandem in Situ SAXS-XAS Studies
The molecular and ensemble dynamics
for the growth of hierarchical
supercrystals of cobalt nanorods have been studied by in situ tandem
X-ray absorption spectroscopyâsmall-angle X-ray scattering
(XAS-SAXS). The supercrystals were obtained by reducing a CoÂ(II) precursor
under H<sub>2</sub> in the presence of a long-chain amine and a long-chain
carboxylic acid. Complementary time-dependent ex situ TEM studies
were also performed. The experimental data provide critical insights
into the nanorod growth mechanism and unequivocal evidence for a concerted
growthâorganization process. Nanorod formation involves cobalt
nucleation, a fast atom-by-atom anisotropic growth, and a slower oriented
attachment process that continues well after cobalt reduction is complete.
Smectic-like ordering of the nanorods appears very early in the process,
as soon as nanoparticle elongation appears, and nanorod growth takes
place inside organized superlattices, which can be regarded as mesocrystals
The Big Impact of a Small Detail: Cobalt Nanocrystal Polymorphism as a Result of Precursor Addition Rate during Stock Solution Preparation
The control of nanocrystal structures at will is still
a challenge,
despite the recent progress of colloidal synthetic procedures. It
is common knowledge that even small modifications of the reaction
parameters during synthesis can alter the characteristics of the resulting
nano-objects. In this work we report an unexpected factor which determines
the structure of cobalt nanoparticles. Nanocrystals of distinctly
different sizes and shapes have resulted from stock solutions containing
exactly the same concentrations of [CoÂ{NÂ(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(thf)], hexadecylamine, and lauric acid. The reduction
reaction itself has been performed under identical conditions. In
an effort to explain these differences and to analyze the reaction
components and any molecular intermediates, we have discovered that
the rate at which the cobalt precursor is added to the ligand solution
during the stock solution preparation at room temperature becomes
determinant by triggering off a nonanticipated side reaction which
consumes part of the lauric acid, the main stabilizing ligand, transforming
it to a silyl ester. Thus, an innocent mixing, apparently not related
to the main reaction which produces the nanoparticles, becomes the
parameter which in fine defines nanocrystal characteristics. This
side reaction affects in a similar way the morphology of iron nanoparticles
prepared from an analogous iron precursor and the same long chain
stabilizing ligands. Side reactions are potentially operational in
a great number of systems yielding nanocrystals, despite the fact
that they are very rarely mentioned in the literature
The Big Impact of a Small Detail: Cobalt Nanocrystal Polymorphism as a Result of Precursor Addition Rate during Stock Solution Preparation
The control of nanocrystal structures at will is still
a challenge,
despite the recent progress of colloidal synthetic procedures. It
is common knowledge that even small modifications of the reaction
parameters during synthesis can alter the characteristics of the resulting
nano-objects. In this work we report an unexpected factor which determines
the structure of cobalt nanoparticles. Nanocrystals of distinctly
different sizes and shapes have resulted from stock solutions containing
exactly the same concentrations of [CoÂ{NÂ(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(thf)], hexadecylamine, and lauric acid. The reduction
reaction itself has been performed under identical conditions. In
an effort to explain these differences and to analyze the reaction
components and any molecular intermediates, we have discovered that
the rate at which the cobalt precursor is added to the ligand solution
during the stock solution preparation at room temperature becomes
determinant by triggering off a nonanticipated side reaction which
consumes part of the lauric acid, the main stabilizing ligand, transforming
it to a silyl ester. Thus, an innocent mixing, apparently not related
to the main reaction which produces the nanoparticles, becomes the
parameter which in fine defines nanocrystal characteristics. This
side reaction affects in a similar way the morphology of iron nanoparticles
prepared from an analogous iron precursor and the same long chain
stabilizing ligands. Side reactions are potentially operational in
a great number of systems yielding nanocrystals, despite the fact
that they are very rarely mentioned in the literature
CoâFe Nanodumbbells: Synthesis, Structure, and Magnetic Properties
We
report the solution phase synthesis, the structural analysis,
and the magnetic properties of hybrid nanostructures combining two
magnetic metals. These nano-objects are characterized by a remarkable
shape, combining Fe nanocubes on Co nanorods. The topological composition,
the orientation relationship, and the growth steps have been studied
by advanced electron microscopy techniques, such as HRTEM, electron
tomography, and state-of-the-art 3-dimensional elemental mapping by
EDX tomography. The soft iron nanocubes behave as easy nucleation
centers that induce the magnetization reversal of the entire nanohybrid,
leading to a drastic modification of the overall effective magnetic
anisotropy
CoâFe Nanodumbbells: Synthesis, Structure, and Magnetic Properties
International audienceWe report the solution phase synthesis, the structural analysis, and the magnetic properties of hybrid nanostructures combining two magnetic metals. These nano-objects are characterized by a remarkable shape, combining Fe nanocubes on Co nanorods. The topological composition, the orientation relationship, and the growth steps have been studied by advanced electron microscopy techniques, such as HRTEM, electron tomography, and state-of-the-art 3-dimensional elemental mapping by EDX tomography. The soft iron nanocubes behave as easy nucleation centers that induce the magnetization reversal of the entire nanohybrid, leading to a drastic modification of the overall effective magnetic anisotropy