Effect of polymer–metal interaction and substrate temperature on the properties of vacuum-evaporated silver nanoparticulate films

The structure and properties of vacuum-evaporated silver (Ag) nanoparticulate films on softened poly(1-vinylpyrrolidone-co-vinyl acetate) [P(VP-co-VAc)], containing pyrrolidone and acetate moieties are reported. The particulate films are characterized by optical spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and electrical resistance measurements. The broadening of the optical spectra, red-shift and increase in the intensity values of the plasmonic resonance peak with decrease in substrate temperatures has a strong dependence on the particle size, shape and inter-particle separation. Microscopy studies show smaller particles with larger gaps at higher temperatures. AFM studies indicate a reduction in the surface roughness with increase in substrate temperature. XRD studies indicate the formation of nanocrystallites of silver with preferred orientation. Lower thickness silver films and films deposited at higher substrate temperatures exhibit negative temperature coefficient of resistance indicating that these films are particulate. When the films are exposed to atmospheric air, the films show an irreversible increase in resistance with pressure. The extent of polymer–metal interaction caused by the strongly interacting amide group on the pyrrolidone moiety and the feebly interacting acetate moiety of the copolymer is discussed.