Local photochemical plasmon mode tuning in metal nanoparticle arrays

We report on the local modification of gold nanoparticle arrays by photochemical deposition of gold from solution. Our method allows to alter the localized surface plasmon resonance (LSPR) in a restricted area by exposure of gold salt (HAuCl4) to light, whereas the expansion of such sections depends on the illumination optics. The geometry parameters of the individual nanoparticles in the modified regions are characterized by SEM and AFM, while the optical properties of distinct array sections are analyzed by means of optical spectroscopy. A blueshift of the surface plasmon resonance wavelength is observed upon the deposition process. An explanation for the blueshift is found by performing calculations using an analytical dipolar interaction model (DIM), which allows us to distinguish the individual contributions of the particle geometry on the one hand and the changes in particle interaction on the other hand. The resulting simulated scattering spectra verify the blueshift of the LSPR, which can be attributed to an increase in aspect ratio of the particles during growth. Since plasmonically active nanoparticle arrays are known to be candidates for sensing applications, this method and the gained understanding can be exploited to fabricate large sensor substrates with local LSPR variations.