Infrared absorption spectra were measured at normal incidence of radiation for polymers on post-annealed silver films of 4-10 nm mass thicknesses that had been deposited in ultra high vacuum onto Si substrate surfaces. Results show that the polymer absorption intensity depends on the annealing temperature and the silver mass thickness. Results clarified that no simple relation existed, such as a negative correlation between reflectivity and the infrared absorption enhancement, even when the mass thickness was made constant and the silver particles' size and shape were changed. For infrared absorption intensity to become large, particles must be positioned discretely, but if the distance between particles is too large, absorption intensity decreases. Moreover, results verified that optimal thin-film morphology was different according to the wavelength region. (c) 2006 Elsevier B.V. All rights reserved.