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Spontaneous Formation of Cluster Array of Gold Particles by Convective Self-Assembly
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posted on 2012-09-11, 00:00 authored by Satoshi Watanabe, Yasushi Mino, Yusuke Ichikawa, Minoru T. MiyaharaCluster arrays composed of metal nanoparticles are promising
for
application in sensing devices because of their interesting surface
plasmon characteristics. Herein, we report the spontaneous formation
of cluster arrays of gold colloids on flat substrates by vertical-deposition
convective self-assembly. In this technique, under controlled temperature,
a hydrophilic substrate is vertically immersed in a colloid suspension.
Cluster arrays form when the particle concentration is extremely low
(in the order of 10–6–10–8 v/v). These arrays are arranged in a hierarchically ordered structure,
where the particles form clusters that are deposited at a certain
separation distance from each other, to form “dotted”
lines that are in turn aligned with a constant spacing. The size of
the cluster can be controlled by varying the particle concentration
and temperature while an equal separation distance is maintained between
the lines formed by the clusters. Our technique thus demonstrates
a one-step, template-free fabrication method for cluster arrays. In
addition, through the direct observation of the assembly process,
the spacing between the dotted lines is found to result from the “stick-and-slip”
behavior of the meniscus tip, which is entirely different from the
formation processes observed for the striped patterns, which we reported
previously at higher particle concentrations. The difference in the
meniscus behavior possibly comes from the difference in colloidal
morphology at the meniscus tip. These results demonstrate the self-regulating
characteristics of the convective self-assembly process to produce
colloidal patterns, whose structure depends on particle concentration
and temperature.
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- Biophysics
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