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standard deviation (
) of 11% (Fig. 13.14a). A typical side-view image
of these superparticles shows that the height of the disks is about 56
nm, and the disks are single-layer assemblies of CdSe/CdS nanorods
(Fig. 13.14b). These superparticles possess a two-dimensional (2D)
structure. A typical TEM image shows that the superparticles exhibit
a superlattice-fringe pattern, which is the [00]-zone projection of a
p6 2D lattice structure with a lattice constant of 6.0
s
±
0.2 nm (Fig.
The [00] projection image displays the characteristic
hexagonal cross-fringes with a spacing of 5.2 nm, which can be
indexed as the (01), (10), and (11)
13.14c).
47
crystal lines in the 2D superlattice
(Fig. 13.14c). The interline spacing and angles obtained from the
TEM image are consistent with the corresponding small-angle ED
pattern (Fig. 13.14d). The ED pattern shows a sharp-spot array,
which demonstrates the perfection of the 2D superlattice.
Figure 13.14
TEM images of cylindrical superparticles: (a, b, and c) single-
layer disks and (e, f, and g) multilayer stacked-disk arrays.
(d) Small-angle ED pattern of the superparticle shown in (c).
(h) Wide-angle ED pattern of a bilayer superparticle shown
in (g). From Ref. [21] with permission.
The formation of cylindrical disks is likely driven by two major
forces: the anisotropic interparticle interactions between CdSe/
CdS nanorods, and the repulsive solvophobic interactions between
a superparticle and ethylene glycol/water solvent molecules.
The anisotropic interparticle interactions favor a hexagonally
close packing of CdSe/CdS nanorods along their c-axis inside
a superparticle; this packing characteristic can maximize the
volume free energy of this superparticle. The repulsive solvophobic
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