Dielectric function of polycrystalline gold films: Effects of grain boundary and temperature

The experimental data of the dielectric function of gold films are vital in metal optics since optical and optoelectronic properties depend sensitively on the dielectric function. Even though significant discrepancies of the dielectric function exist among the measurements in the past 60 years, the contribution of the grain boundary is less studied. In this work, we measured the dielectric function of three different gold films using two ellipsometers covering the spectral range from 200 nm to 25 μm. Based on the Drude model and the Mayadas-Shatzkes model of the electron-grain boundary scattering, we find that electronic reflection coefficient at the grain boundary is a vital factor to influence the dielectric function of the polycrystalline gold films. Furthermore, the temperature dependent dielectric function of gold is measured from 300 K to 800 K. Performing extended Drude analysis with a frequency dependent relaxation rate, we get a deviation of relaxation rate from the Fermi liquid theory at energies below 0.1 eV from 300 K to 800 K.