Collective Surface Plasmon Modes in Multilayer Silver Nanoparticle Arrays

Serhiy Malynych Department of Polaritonic Optoelectronics, V.E. Lashkarev Institute of Semiconductors Physics NAS of Ukraine, Kyiv, Ukraine Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina, USA Department of Chemistry, Clemson University, Clemson, USA Oleg Yeshchenko Department of Physics, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine Illya Bondarchuk Department of Physics, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine Yuriy Galabura Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina, USA George Chumanov Department of Chemistry, Clemson University, Clemson, USA Igor Luzinov Department of Materials Science and Engineering, Clemson University, Clemson, South Carolina, USA

In present work we report on the extinction spectra of metal-dielectric composite consisting of stacked dense monolayers of silver nanoparticles. The nanostructures were fabricated employing layer-by-layer self-assembling technique that allows preparing of 2D array of randomly distributed nanoparticles. The average size of Ag nanoparticles used in experiments was 115 nm, while the distance between the nanoparticles within a plane and that between the planes was about 160 nm. Three types of samples with different number of layers (n = 1, 2 and 3) were considered. The extinction spectra were studied as a function of the angle incidence and polarization of the incident light. It was found that interaction between localized surface plasmon modes in adjacent nanoparticles results in the emerging of a collective plasmon mode, which manifests itself as a narrow band in the extinction spectra of 2D silver nanoparticle array.

Two distinct surface plasmon collective modes were identified for a single monolayer of the particles. The tangential T mode corresponds to induced dipoles parallel to the plane of nanoparticle layer, while normal P mode corresponds to dipoles normal to the plane of the layer. Blue and red spectral shift of the extinction bands with the incident angle was observed for T and P modes, respectively. More pronounced angular dependences for P mode band indicate the stronger coupling of dipoles for P mode than for T one. A new spectral band denoted as N was discovered for the sample comprised three Ag nanoparticle layers (n = 3). This new band was observed in the extinction spectra only for s-polarization. The angular dependence of the N band intensity resembles that of the P band. At the same time, the N band exhibits blue spectral shift with the increase of the angle of incidence, which is inherent for the tangential T band. The new N band originates from coupling between all the three layers of Ag nanoparticles. Our experimental findings might be of both fundamental and practical interest.

s.malynych@gmail.com