The
localized surface plasmon resonances of gold nanoparticles
have been widely studied at visible and near-infrared frequencies
but less so in the ultraviolet. The spectral extinction measurements
of gold nanospheres at UV wavelengths reported here closely match
calculated spectra down to 200 nm using the measured dielectric function
of gold. The nanosphere volume attenuation coefficient, αv, is size-dependent in the 200–300 nm wavelength range
where the dielectric function follows the Drude free electron model
(as it does for wavelengths larger than 500 nm). In the interband
transition region, the extinction is more closely proportional to
mass and therefore has a value of αv that is largely
independent of size. Gold nanorod solutions exhibit very strong UV
extinction below 220 nm due to charge transfer to solvent (c.t.t.s.)
excitations of the bromide counterion to the cationic surfactant.
The gold nanorod UV properties depend on the alignment between the
optical polarization and nanorod structure. For polarization along
each major axis, the spectral extinction is similar to that of a sphere
of nanorod size in that dimension.
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