Fabrication and optical studies of monolayer assemblies of Au nanoparticles.

Two-dimensional nanoparticle self-assemblies provide a means of tuning the optical properties by manipulation of the fabrication parameters, thereby controlling the light-matter interaction. We report fabrication of self-assembled monolayers of colloidal gold nanoparticles on organosilane-coated substrates and a study of the linear and nonlinear optical properties. With increase in particle coverage of the gold monolayer self assemblies, an additional band in the absorption spectrum due to the collective particle surface plasmon resonance could be seen. The intensity and lambda(max) of this feature depends on the interparticle spacing and particle aggregation. Z-scan measurements show a saturable absorption behavior and a negative nonlinear refractive index of the monolayer films. A strong correlation between particle density and the linear and nonlinear optical properties is established.