Structural, compositional, and plasmonic characteristics of Ti–Zr ternary nitride thin films tuned by the nitrogen flow ratio in magnetron sputtering

Ternary nitride gives high diversity and tunability of the plasmonic materials. In this work, highly crystallized ternary (Ti, Zr)N_x films were prepared by magnetron co-sputtering with different nitrogen gas flow ratio R_n. The structural and plasmonic properties of the films tuned by R_n were investigated. All the films are solid solutions of TiN_x and ZrN_x with a rocksalt structure and (111) preferred orientation. The films are nitrogen-overstoichiometric and the main defects are cation vacancies. Increased R_n reduces the zirconium content, and therefore leads to the reduction of lattice constant and enhancement of the crystallinity. As R_n increases, the screened plasma frequency decreases for the reduction of free electron density. The maximum of the energy loss spectra of (Ti, Zr)N_x films shifts to long-wavelength with R_n increasing. The calculated electronic structure shows that increased nitrogen content enhances the electronic density of states of nitrogen and reduces that of metal, and therefore elevates the energy level at which interband transition is exited. The results show that (Ti, Zr)N_x films give a relatively high plasmonic quality in the visible and near-infrared region, and the film properties can be significantly tuned by the nitrogen content.