Optical Properties of Au-Doped Titanium Nitride Nanostructures: a Connection Between Density Functional Theory and Finite-Difference Time-Domain Method

In this paper, we present a computational method to investigate optical properties of materials using a combination of density functional theory (DFT) calculations and finite-difference time-domain (FDTD) method. We show our method in the framework of an example for analyzing the effect of Au doping on optical transmission behavior of TiN compounds with a given geometry. First, DFT is employed based on generalized gradient approximation (GGA) exchange-correlation potential to investigate the electronic properties as well as dielectric function of TiN with respect to different percentages of doped Au. Our results reveal a growth in the imaginary part of dielectric function for energies below 4 eV by increasing Au doping level due to compression of Ti(1-x)Aux(N) DOS into the Fermi energy. In order to clarify the impact of Au doping on the optical behavior of Ti1-xAuxN with a given geometry, the optical dielectric function calculated from DFT was used as an input data for FDTD method to simulate a perforated surface plasmon system originated from Ti1-xAuxN-dielectric configuration via Optiwave package. It is observed that an increase in the Au level decreases the transmission intensity of excited modes of the perforated surface plasmon system, which is in agreement with the observed behavior for the imaginary part of dielectric function from DFT calculations. This implies that an enhanced imaginary part of dielectric function leads to more energy dissipation and finally less transmitted wave. The proposed method enables us to simulate optical properties of a wide range of compounds with arbitrary geometries and material-specific properties.