X-ray photoelectron spectrum in surface interfacing of gold nanoparticles with polymer molecules in a hybrid nanocomposite structure

In situ Au3+ -> Au reaction and dispersion of the resulting gold in the form of nanoparticles (NPs) in a reactive polymer medium, such as poly(vinyl alcohol) (PVA) molecules in hot water, are explored to devise a composite Au-PVA structure of self-standing films. The Au-NPs (0-2 wt%) tailor a violet to purple to a yellowish color of films from a colorless base polymer. A distinct surface interface (of thickness 2-5 nm) from the core (20-30 nm diameter) is resolved in transmission electron microscope images. The x-ray photoelectron spectrum (XPS) in the 81-91 eV range accounts for the effect which causes asymmetric shapes of the 4f(7/2) and 4f(5/2) Au bands. In a model structure, the asymmetry arises in the contribution of the surface Au atoms, which extend a chemical bridging with surface O atoms from the PVA molecules in a surface layer. A similar asymmetry also arises in C 1s and O 1s bands in the counterpart PVA molecules at 287.79 and 532.35 eV, respectively. At Au content as large as 2 wt%, no separate XPS band arises on a negligibly small fraction of surface Au atoms when Au-NPs have been grown in thin laminates (or cuboids and prisms).