Controlling Nitrogen Plasmas for Thin Film Synthesis of Complex Semiconductor, Superconductor and Magnetic Materials

Inorganic nitrides are recognized as highly functional materials for several applications, such as semiconducting GaN, superconducting NbN, and magnetic Fe₁₆N₂. Unfortunately, the stability of the N₂ molecule makes metal-nitride synthesis difficult, which precludes the functionalization of many predicted and promising nitride materials. One approach to the experimental realization and optimization of novel nitrides is to use nitrogen plasmas to either vibrationally excite N₂ or even rend the dinitrogen molecule into N* radicals, which are far more reactive. Over the last several years, our group has used this concept for the synthesis and optimization of several new nitride materials. This talk will introduce our work using nitrogen plasmas for the synthesis of new ternary metal-metal-nitride semiconductors and magnetic materials, as well as the optimization of nitride superconductors. Our work is based on reactive co-sputtering processes, where we use plasma parameters to control the nitrogen chemical potential both to realize novel phases as well as optimize known materials. We establish general rules where nitrogen activation enables the synthesis of nitrogen-rich nitrides (e.g., ZnTiN₂), which are required for semiconducting applications, but we also find that activation of dilute nitrogen concentrations enables the synthesis and optimization of metal-poor nitride materials needed for superconducting and magnetic applications (e.g., Mn₃GeN). We will also discuss our recent efforts to establish an autonomous synthesis assistant that is guided by in-situ monitoing of plasma emission spectra to optimize the composition of ZnTiN₂, an emerging ternary nitride material with promising properties as a CO₂ reduction photoanode.