PHOTON FREQUENCY-DEPENDENT ELECTRON RELAXATION-TIME IN NOBLE-METALS -EFFECT OF VOIDS

Optical properties of noble metals at frequencies below the interband transitions are well described by a simple Drude model of the free ele ctron gas. However, a photon frequency dependent electron relaxation t ime tau(omega)(-1)=tau(0)(-1)+beta omega(2) has been reported frequent ly for experimental data. Also, the parameters of the Drude model of s ilver were found to be influenced by fluids (H. Gugger et al., Phys. R ev. B, 30 (1984) 4189). On the other hand, thin silver films condensed on cold substrates contain a large amount of voids with elongated sha pe, which cause a strong absorption around lambda approximate to 450 n m. Borensztein et al. (Surf. Sci., 211/212 (1989) 775) modelled this a bsorption band with an effective medium theory (EMT), taking into acco unt the shape of the voids. In the present work it is shown that both the frequency-dependent relaxation time and the effects of fluids can be explained by this EMT.