196
J. Richardi et al.
Table 8.3 Structural characteristics of 2D ordered arrays presented in Figs. 8.5 and 8.6 and obtained
by deposition of Co NPs characterized by an average diameter D and a size distribution σ . D c-c ;
center-to-center nanoparticle distance; D i-p : inter-particle distance
Sample
D (nm)
σ (%)
D c-c (nm)
D i-p (nm)
Co fcc (S1)
3.9 ± 0.1
12
5.9 ± 0.1
2.1 ± 0.1
Co fcc (S3)
4.6 ± 0.1
11
6.9 ± 0.1
2.3 ± 0.1
Co fcc (S6)
7.7 ± 0.1
12
9.3 ± 0.1
1.6 ± 0.1
Co fcc (S7)
9.3 ± 0.1
15
10.5 ± 0.1
1.4 ± 0.1
Co hcp (S ann 1)
7.1 ± 0.2
8
9.8 ± 0.2
2.7 ± 0.2
Co hcp (S ann 2)
7.0 ± 0.2
10
10.3 ± 0.2
3.3 ± 0.2
(2) Similarly to the native fcc-Co polycrystals, the deposition of solution-phase
annealed 7.1 nm hcp-Co single crystals (Fig. 8.9a and Table 8.3) gives rise to
2D long-range ordered arrays characterized by center-to-center distance and
interparticle gap of 9.8 nm and 2.7 nm, respectively (Sample Sann 1) [58]. The
increase in the D i-p of around 1 nm compared to the arrays composed of similar
size native NPs is attributed to the presence of larger amount of coating agent,
related to the annealing protocol. By slightly increasing the concentration of the
colloidal solution, ordered multilayers can also be obtained (Fig. 8.9b).
(3) 2D arrays of hcp-Co single crystals can also result from dry annealing at 350 °C
of 2D ordered arrays of as-synthesized Co polycrystals. Such 2D arrays are
characterized by NP diameter, D c-c and D i-p values equal to 7.0, 10.3 and 3.3 nm,
respectively (Fig. 8.9c, Table 8.3). The D i-p increases after annealing, while the
D c-c remains almost unchanged [23, 58]. NP size decrease is partly attributed
to the structural transition of the NPs from the poorly crystalline phase to the
hcp-Co single-crystalline phase. As shown in Fig. 8.9d, when the dry annealing
is performed on ordered multilayers of Co polycrystals, the assembly keeps
their integrity.
Whatever the protocol used is, 2D and thin 3D arrays of Co NPs can be obtained.
We show that the characteristics of these organizations can be tuned by varying the
mean diameter and the nanocrystallinity of the Co NPs, as well as the mean centerto-center distance between particles and interparticle gap. The high stability of these
assemblies, especially in the dry and solution-phase annealing cases, is due to the
high thermal stability of dodecanoic acid coating agent.
J. Richardi et al.
Table 8.3 Structural characteristics of 2D ordered arrays presented in Figs. 8.5 and 8.6 and obtained
by deposition of Co NPs characterized by an average diameter D and a size distribution σ . D c-c ;
center-to-center nanoparticle distance; D i-p : inter-particle distance
Sample
D (nm)
σ (%)
D c-c (nm)
D i-p (nm)
Co fcc (S1)
3.9 ± 0.1
12
5.9 ± 0.1
2.1 ± 0.1
Co fcc (S3)
4.6 ± 0.1
11
6.9 ± 0.1
2.3 ± 0.1
Co fcc (S6)
7.7 ± 0.1
12
9.3 ± 0.1
1.6 ± 0.1
Co fcc (S7)
9.3 ± 0.1
15
10.5 ± 0.1
1.4 ± 0.1
Co hcp (S ann 1)
7.1 ± 0.2
8
9.8 ± 0.2
2.7 ± 0.2
Co hcp (S ann 2)
7.0 ± 0.2
10
10.3 ± 0.2
3.3 ± 0.2
(2) Similarly to the native fcc-Co polycrystals, the deposition of solution-phase
annealed 7.1 nm hcp-Co single crystals (Fig. 8.9a and Table 8.3) gives rise to
2D long-range ordered arrays characterized by center-to-center distance and
interparticle gap of 9.8 nm and 2.7 nm, respectively (Sample Sann 1) [58]. The
increase in the D i-p of around 1 nm compared to the arrays composed of similar
size native NPs is attributed to the presence of larger amount of coating agent,
related to the annealing protocol. By slightly increasing the concentration of the
colloidal solution, ordered multilayers can also be obtained (Fig. 8.9b).
(3) 2D arrays of hcp-Co single crystals can also result from dry annealing at 350 °C
of 2D ordered arrays of as-synthesized Co polycrystals. Such 2D arrays are
characterized by NP diameter, D c-c and D i-p values equal to 7.0, 10.3 and 3.3 nm,
respectively (Fig. 8.9c, Table 8.3). The D i-p increases after annealing, while the
D c-c remains almost unchanged [23, 58]. NP size decrease is partly attributed
to the structural transition of the NPs from the poorly crystalline phase to the
hcp-Co single-crystalline phase. As shown in Fig. 8.9d, when the dry annealing
is performed on ordered multilayers of Co polycrystals, the assembly keeps
their integrity.
Whatever the protocol used is, 2D and thin 3D arrays of Co NPs can be obtained.
We show that the characteristics of these organizations can be tuned by varying the
mean diameter and the nanocrystallinity of the Co NPs, as well as the mean centerto-center distance between particles and interparticle gap. The high stability of these
assemblies, especially in the dry and solution-phase annealing cases, is due to the
high thermal stability of dodecanoic acid coating agent.