Análise das propriedades ópticas e elétricas em ligas de AgxAu1−x utilizando a teoria do funcional da densidade.

Abstract

The use of metallic alloys is crucial for several applications as plasmonic materials due to their superb optical response. The alloys extend the application range with their tunable plasmonic resonances. Hence, in the present work, we applied the Density

Functional Theory to pure gold and silver structures and their alloys to analyze optoe- lectronic properties. We obtained the wave functions and the charge densities using

Non-local Norm-Conserving pseudopotentials. To evaluate the role of the structural compositions of the periodic bulk structures, we analyzed their band structures, the density of states, the dielectric function, the refraction and extinction indexes, and the birefringence. We applied the exchange-correlation functional within the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) parametrization. The results showed an accumulation of states below the Fermi Level (around -6eV and -2eV), predominantly related to the d orbital. Analyzing the real and imaginary parts of the dielectric function, we observed the rise of an anisotropy in the optical response for the Ag0,50Au0,50 alloy. All other concentrations did not show such behavior. The anisotropy can be related to the charge accumulation around the gold atoms. This leads to a non-symmetric contribution for the projection of the density of state for the dxy orbital against the dxy e dyz ones. In comparison to the experimental results, we did not find works reporting anisotropic optical responses to alloys with 50% gold and 50% silver. We claim that the divergencies between the experimental optical results may be associated with this anisotropy. Since the geometry of the excitation may change within the different experiments, the anisotropy may lead to inconsistent results for the same kind of structure. From the theoretical point of view, the majority of the works with such systems perform interpolations of the optical responses from the pure structures. We do not expect their results to present any anisotropy, since it is not present in the pure counterparts. The findings here described open up the perspective for new applications such as birefringent plasmonic devices.