Temperature dependent optical properties of silver from spectroscopic ellipsometry and density functional theory calculations

摘要

A detailed analysis of temperature dependence of optical constants of silver thin film measured by spectroscopic ellipsometry in the energy range 1.4 to 5 eV for temperatures ranging from 300 K to 650 K in steps of 50 K is presented in this paper. A microstructure modeling based on Bruggeman effective medium approximation is carried out on the temperature dependent optical constants. A red shift of ～300 meV accompanied by a broadening of the interband transition is observed and an additional weak absorption edge emerges from the lower energy side of main interband absorption transition at 550 K. Drude model is applied to perform the analysis of dielectric function in the low energy region. The energy loss function -Im(1/ε) shows large damping with increasing temperature and this is a consequence of increasing magnitude of ε_2 resulting from the composite transition in the region where ε_1 is very small. These experimental results are corroborated with first principles electronic structure calculations using the full potential linearized augmented plane wave method within the frame-work of density functional theory.