8 Magnetic Self-Assembling of Spherical Co Nanoparticles …
197
Fig. 8.9 TEM images of a monolayer (a) and a multilayer (b) of solution-phase annealed 7.1 nm
hcp-Co single crystals obtained by the micellar approach. TEM images of a monolayer (c) and a
multilayer (d) of 7.0 nm hcp-Co single crystals obtained by dry annealing of a native monolayer
and multilayer of fcc-Co polycrystals
8.6 2D Self-Organizations of Cobalt Nanoparticles
Synthesized by Organometallic Approach
The self-assembly process is not dependent of the route used to synthesize the
cobalt NPs. As presented above, the 9.2 nm spherical Co NPs coated by oleylamine
(OAm) are characterized by low size dispersity (0.6%). By simply depositing a drop
of a colloidal solution of these NPs dispersed in toluene, onto amorphous carbon
substrates, they self-organize in a long-range 2D hexagonal ordering (Fig. 8.10a)
and thin 3D assemblies. When a concentrated solution is allowed to slowly evaporate on graphite substrate, well-developed supercrystals sitting on their larger flat
facets are observed. (Fig. 8.10b, c). This is characteristic of the formation of the
so-called supercrystals resulting from 3D periodic arrangement of the NPs either in
fcc or hcp organization.
197
Fig. 8.9 TEM images of a monolayer (a) and a multilayer (b) of solution-phase annealed 7.1 nm
hcp-Co single crystals obtained by the micellar approach. TEM images of a monolayer (c) and a
multilayer (d) of 7.0 nm hcp-Co single crystals obtained by dry annealing of a native monolayer
and multilayer of fcc-Co polycrystals
8.6 2D Self-Organizations of Cobalt Nanoparticles
Synthesized by Organometallic Approach
The self-assembly process is not dependent of the route used to synthesize the
cobalt NPs. As presented above, the 9.2 nm spherical Co NPs coated by oleylamine
(OAm) are characterized by low size dispersity (0.6%). By simply depositing a drop
of a colloidal solution of these NPs dispersed in toluene, onto amorphous carbon
substrates, they self-organize in a long-range 2D hexagonal ordering (Fig. 8.10a)
and thin 3D assemblies. When a concentrated solution is allowed to slowly evaporate on graphite substrate, well-developed supercrystals sitting on their larger flat
facets are observed. (Fig. 8.10b, c). This is characteristic of the formation of the
so-called supercrystals resulting from 3D periodic arrangement of the NPs either in
fcc or hcp organization.