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Moreover, colloidal gold superparticles synthesized according to
Zhong's method exhibit a very narrow size-distribution (<8%, Fig.
13.4A
28
This method also allows the control of superparticle
sizes, which was achieved by varying the amount of thioether
mediators: The larger the amount of mediators, the smaller the size
of superparticles, and vice versa.
C).
28
A larger amount of thioether
mediators causes a faster formation rate of active species, while the
superparticle growth rate is not significantly affected by the amount
of the mediators in the synthesis. Therefore, the size-control effect in
this superparticle synthesis is also consistent with the prediction of
Eq. 13.10: A faster active species formation results in a larger number
of nuclei and thus a smaller final size of superparticles. Furthermore,
the resulting colloidal superparticles exhibit interesting size-
dependent surface plasmon bands, which are introduced by the
interparticle coupling of their building blocks. Larger superparticles
exhibit a larger red shift of their surface plasmon band as compared
with that of their dispersed building blocks, and vice versa (Fig.
13.5).
28
Figure 13.4
TEM images for samples
obtained
from solutions of
2
/Au] = 100 (A), 25
(B), and 10 (C)) after one cleaning treatment. Each image has
the same scale bar. The corresponding size distributions (A)
133
-mediated assemblies of
1
/Au (
r
= [
2
]/[
1
±
±
±
11 nm are based
on 30 counts of the assemblies in each case. (
10 nm, (B) 176
7 nm, and (C) 195
±
1
/Au = 5.3
1.0
nm). From Ref. [28] with permission.
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