S. Link et al., Simulation of the optical absorption spectra of gold nanorods as a function of their aspect ratio and the effect of the medium dielectric constant, J PHYS CH B, 103(16), 1999, pp. 3073-3077
Gold nanorods with different aspect ratios are prepared in micelles by the
electrochemical method and their absorption spectra are modeled by theory.
Experimentally, a linear relationship is found between the absorption maxim
um of the longitudinal plasmon resonance and the mean aspect ratio as deter
mined from TEM. It is shown here that such a linear dependence is also pred
icted theoretically. However, calculations also show that the absorption ma
ximum of the longitudinal plasmon resonance depends on the medium dielectri
c constant in a linear fashion for a fixed aspect ratio. Attempts to fit th
e calculations to the experimental values indicate that the medium dielectr
ic constant has to vary with the aspect ratio in a nonlinear way. Chemicall
y, this suggests that the structure of the micelle capping the gold nanorod
s is size dependent. Furthermore, comparison with the results obtained for
rods of different aspect ratios made by systematic thermal decomposition of
the long rods further suggests that the medium dielectric constant is also
temperature dependent. This is attributed to thermal annealing of the stru
cture of the micelles around the nanorods.