Collective and individual plasmon resonances in nanoparticle films obtained by spin-assisted layer-by-layer assembly

Nanoscale uniform films containing gold nanoparticle and polyelectrolyte multilayer structures were fabricated by the using spin-assembly or spin-assisted layer-by-layer (SA-LbL) deposition technique. These SA-LbL films with a general formula [Au/(PAH - PSS)_nPAH]_m possessed a well-organized microstructure with uniform surface morphology and high surface quality at a large scale (tens of micrometers across). Plasmon resonance peaks from isolated nanoparticles and interparticle interactions were revealed in the UV - visible extinction spectra of the SA-LbL films. All films showed the strong extinction peak in the region of 510 - 550 nm, which is due to the plasmon resonance of the individual gold nanoparticles redshifted because of a local dielectric environment. For films with sufficient density of gold nanoparticles within the layers, the second strong peak was consistently observed between 620 and 660 nm, which is the collective plasmon resonance from intralayer interparticle coupling. Finally, we suggested that, for certain film designs, interlayer interparticle resonance might be revealed as an independent contribution at 800 nm in UV - visible spectra. The observation of independent and concurrent individual, intralayer, and interlayer plasmon resonances can be critical for sensing applications, which involve monitoring of optomechanical properties of ultrathin optically active compliant membranes.