Assembly and optical properties of metal nanoparticles

In this paper, the deposition and optical properties of charge-stabilized gold nanoparticles on silicon oxide substrates is studied, which have been derivatised with (aminopropyl) triemethoxysilane. Monodispersed charged-stabilized colloidal gold nanoparticles with diameters between 20-150 nm were prepared and their self-assembly and optical properties on silica substrates is studied. Atomic force microscopy (AFM) is employed to investigate the nanoparticle monolayers ex situ. Analysis of AFM images provide evidence that the formation of the colloidal nanoparticle monolayers is governed by random sequential adsorption. The results indicate that the ionic strength of the suspension influences the spatial distribution of the nanoparticles. For all sizes of the Au nanoparticles tested, optical simulations of extinction coefficients made by finite-difference time domain (FDTD) indicate a resonance peak in the range of 510-600 nm wavelength of the visible range of the electromagnetic spectrum. The results indicate a simple and inexpensive approach of assembly of plasmonic nanostructures that can find applications in metamaterials and light waveguides.