Stable multilayer ultrathin film containing covalently attached colloidal Ag nanoparticles

Stable multilayer ultrathin films were constructed by alternate deposition of nitro-diazoresin (NDR) and Ag nanoparticles (Ag-NPs) followed by UV irradiation. The absorbance of the un-irradiated film at 385 and 412 nm, which is the characteristic absorption of -N-2(+) of NDR and Ag-NPs respectively, increases linearly with the fabrication cycle. This result shows that the layer-by-layer electrostatic deposition of NDR and Ag-NPs is successful and uniform. An atomic force microscopy image of the film with four deposition cycles demonstrates the presence of the close-packed Ag-NPs with the average roughness of 1.5 nm. Furthermore, the stability of the irradiated film toward polar solvents and salty liquids increases significantly, due to the formation of covalent bonds between the layers of the assembled film upon exposure to UV light.