Self-assembled multilayer films based on a Keggin-type polyoxometalate and polyaniline

Multilayer ultrathin films were fabricated from partially doped polyaniline (PAN) and a Keggin-type polyoxometalate [α-SiW₁₂O₄₀]^4- (α-SiW₁₂) in aqueous solution via the layer-by-layer self-assembly technique and characterized by UV-vis, FTIR, and X-ray photoelectron spectra (XPS), ellipsometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). UV-vis spectroscopy shows that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of PAN/α-SiW₁₂ bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. FTIR and XPS spectra confirm the incorporation of α-SiW₁₂ and PAN into the films. Ellipsometric measurements show that the PAN/α-SiW₁₂ bilayer thickness increases with the increasing PAN solution concentration. SEM and AFM images indicate that the film surface is relatively uniform and smooth. In addition, the electrical conductivities of the multilayer films doped with hydrochloric acid were also measured.