Abstract
We present the optical absorption spectra of metal nanoparticles prepared by thermal annealing of the ultra thin metal films evaporated on polycrystalline ZnO films. The surface morphology, particle size and density were monitored by the atomic force microscopy (AFM) and scanning electron microscopy (SEM). ZnO films with the surface roughness about 10βnm rms deposited on sapphire and immersed in the transparent liquid show negligible optical reflectance, interferences and light scattering and are transparent at wavelengths above 400βnm. The optical absorption of ZnO film in UV region allows to calibrate the photothermal deflection spectra (PDS) both with and without metal nanoparticles and to estimate with high precision the optical absorptance of metal nanoparticles in the visible and near infrared region. The optical absorptance spectra of gold nanoparticles embedded in the nonβabsorbing medium can be simulated by effective medium approximationβEMA (MaxwellβGarnett model). The maximum of the localized plasmon resonance shifts to longer wavelengths (red shift) when the metal nanoparticles are more tightly packed in the matrix, whereas the size of the nanoparticles determinate the width of the resonance peak. The electron scattering cross section of Au nanoparticles observed by SEM is about two times larger than their diameter.