Nanoparticle spectroscopy: Plasmon coupling in finite-sized two-dimensional arrays of cylindrical silver nanoparticles

This study provides new data for interpreting plasmon coupling in finite two-dimensional arrays, which are important in plasmonic devices and sensing applications. Finite square arrays of cylindrical silver nanoparticles with two different nanoparticle diameters (339 and 163 nm) and two different interparticle spacings (400 and 450 nm) were fabricated by e-beam lithography. The plasmonic properties of these arrays were obtained by UV-visible-near-IR extinction spectroscopy and compared with isolated particle spectra. In the case of the large-diameter particle arrays, the semi-infinite array resonance is quite blue-shifted from the isolated particle resonance; the resonant wavelength of the 2 x 2 particles and successively larger blocks keeps blue-shifting relative to the isolated particle resonance and converges to that of a semi-infinite array. For the small-diameter particle arrays, the semi-infinite resonance is red-shifted from the isolated particle resonance; the resonant wavelength of the 2 x 2 particles and successively larger blocks keeps red-shifting and converge's to the semi-infinite array. The experimental resonances for progressively increasing array sizes show systematic resonance shifts consistent With increasing numbers of particles, and the bandwidth trends require models and more experiments to obtain better insight into trends.