Monitoring Gold Nanorod Synthesis
J. Phys. Chem. B, Vol. 110, No. 45, 2006 22327
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in eq 4. Such a model may better fit the data in Figure 5b rather
than the asymptotic expressions derived from the Gibbs-
Thomson effect.40 Alternatively, it has also been suggested that
the CTAB micelles regulate nanorod growth by acting as a
carrier of Au ions during the reaction. The CTAB micelles are
selectively drawn to the nanorod tips due to the enhanced electric
field at regions of high curvature. Such a model would certainly
predict a size dependent growth rate that could be compared to
the data in Figure 5b.
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Conclusion
Here we have demonstrated a simple spectroscopic method
to determine the microscopic length and diameter of gold
nanorods during synthesis by comparing their plasmon resonant
extinction spectra to those calculated by Gans’ theory for prolate
spheroids. Nanorod length and diameter were monitored to
follow the kinetics of seed mediated, surfactant directed gold
nanorod synthesis. The nanorod structure could be detected and
analyzed by extinction for sizes as small as 6 nm diameter and
20 nm length. In contrast to constant growth rates from TEM
observations, we find that the nanorod length rate decelerates
throughout the initial growth phase. The size dependence of
the growth rate did not follow simple reaction-limited or
diffusion-limited growth kinetics.
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Acknowledgment. The authors acknowledge the Robert A.
Welch Foundation for support (Grant no. C-1556).
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