Optical properties of magnetron sputtered nanocrystalline gold nitride thin films

Abstract

The significance of this work is the direct synthesis of gold nitride films for surface plasmonic applications. Nanocrystalline gold nitride thin films were fabricated by reactive radio frequency (RF) magnetron sputtering on Phynox alloy substrates at room temperature and 250 °C for 1 and 2 h under a fixed power density of 0.3 W cm−2. The deposition rate is 50 nm h−1. X-ray diffraction (XRD) patterns reveal the formation of AuN2 phase with an orthorhombic crystal structure of gold nitride and was further confirmed and supported by Selected Area Electron Diffraction (SAED) patterns and High-Resolution Transmission Electron Microscopy (HR-TEM) images. Specular reflectance in the visible and near-infrared region is between 20 to 70%. Optical constants and dielectric functions of the films were obtained by employing the Drude-Lorentz model in the range of 1.37–4.1 eV. The real dielectric function crosses zero for values between 1.80–2.22 eV indicating that AuN2 films are suitable material for surface plasmonic applications. Field Emission Scanning Electron Microscopy (FE-SEM) images reveal the nano-porous microstructure of the films. Nanoindentation data show that films hardness values are in the range of 4–7 GPa, which are significantly higher compared with hardness values reported by others.