198
J. Richardi et al.
A
B
C
Fig. 8.10 9.2 nm spherical cobalt nanoparticles with 6% polydispersity obtained by the
organometallic approach self-organized in a 2D and thin 3D assemblies as obtained by drop deposition on amorphous carbon. b and c Superlattices obtained by slow evaporation at room temperature
on graphite substrate
As mentioned above, this is due to the attractive Van der Waals interactions
between the metallic cores, the “chemical bonds” of self-assemblies resulting from
the interdigitation of the ligand molecules (OAm). It should be noticed that from
Fig. 8.10a, the deduced interparticle distance is 4.1 nm, which drastically limit the
interparticle interaction. As a consequence, no aggregation occurs in the solvent or
on the substrates during the deposition process. Indeed, the 2D patterns are purely
hexagonal patterns as well as in the thin 3D organization (Fig. 8.10). In case of
dipole–dipole interaction, non-close packed superlattices are often observed, which
is not the case here. Indeed we can claim that no aggregation occurs in solution due
to dipolar interaction.
8.6.1 3D Self-Organizations of Cobalt Nanoparticles
8.6.1.1 Control of the Mesoscopic Structure in 3D Assemblies of Co NPs
Dodecanoic acid coated Co NPs synthesized by micellar approach can be used as
building blocks to form 2D ordered arrays but also long-range 3D superlattices also
called supercrystals. For this aim, an HOPG substrate is horizontally immersed in
200 μl of a highly concentrated colloidal solution (5.5 × 10
–7 M) of 7.2 nm. The
solvent evaporates under nitrogen flux and the substrate temperature vary from 10 to
45 °C [59]. At 10 °C, TEM study shows the formation of a thin film with a smooth
surface (Fig. 8.11a). The diffractogram shows a broad and low intensity Bragg peak
indicating the absence of long-range ordering of NPs (Fig. 8.11b). By increasing the
temperature from 25 to 45 °C, the film appears cracked and the size of the resulting
isolated domains increases with increasing the substrate temperature (Fig. 8.11c,
J. Richardi et al.
A
B
C
Fig. 8.10 9.2 nm spherical cobalt nanoparticles with 6% polydispersity obtained by the
organometallic approach self-organized in a 2D and thin 3D assemblies as obtained by drop deposition on amorphous carbon. b and c Superlattices obtained by slow evaporation at room temperature
on graphite substrate
As mentioned above, this is due to the attractive Van der Waals interactions
between the metallic cores, the “chemical bonds” of self-assemblies resulting from
the interdigitation of the ligand molecules (OAm). It should be noticed that from
Fig. 8.10a, the deduced interparticle distance is 4.1 nm, which drastically limit the
interparticle interaction. As a consequence, no aggregation occurs in the solvent or
on the substrates during the deposition process. Indeed, the 2D patterns are purely
hexagonal patterns as well as in the thin 3D organization (Fig. 8.10). In case of
dipole–dipole interaction, non-close packed superlattices are often observed, which
is not the case here. Indeed we can claim that no aggregation occurs in solution due
to dipolar interaction.
8.6.1 3D Self-Organizations of Cobalt Nanoparticles
8.6.1.1 Control of the Mesoscopic Structure in 3D Assemblies of Co NPs
Dodecanoic acid coated Co NPs synthesized by micellar approach can be used as
building blocks to form 2D ordered arrays but also long-range 3D superlattices also
called supercrystals. For this aim, an HOPG substrate is horizontally immersed in
200 μl of a highly concentrated colloidal solution (5.5 × 10
–7 M) of 7.2 nm. The
solvent evaporates under nitrogen flux and the substrate temperature vary from 10 to
45 °C [59]. At 10 °C, TEM study shows the formation of a thin film with a smooth
surface (Fig. 8.11a). The diffractogram shows a broad and low intensity Bragg peak
indicating the absence of long-range ordering of NPs (Fig. 8.11b). By increasing the
temperature from 25 to 45 °C, the film appears cracked and the size of the resulting
isolated domains increases with increasing the substrate temperature (Fig. 8.11c,