Dielectric function of polycrystalline <i>α</i>-Ag2S by spectroscopic ellipsometry

Abstract

Complex optical properties (ε=ε1+iε2) of polycrystalline bulk α-Ag2S are investigated by spectroscopic ellipsometry from 0.5 to 8.5 eV at room temperature. The acanthite structure (monoclinic) of α-Ag2S is confirmed by structural analysis. Multilayer analysis with Tauc-Lorentz dispersion model is applied to draw out ε from ellipsometric data. Ag2S shows absorption in the entire range of the visible spectrum with onset band gap of 1.07 eV; furthermore, six other interband transitions are identified whose energy positions accurately obtained by standard lineshape analysis of second-energy-derivative of point-by-point fit determined ε. Finally, we compared our data with reported theoretically calculated data, and origin of the main optical structures is discussed.