Effect of point defects on structure, hardness and plasmonic properties of ZrN thin films

Abstract

Zirconium nitride (ZrN) thin films combine high electrical conductivity, thermal stability, and chemical inertness with tunable optical and mechanical properties, making them ideal for cutting tools, wear-resistant coatings, and plasmonic devices. In this study, face-centered cubic ZrN films were grown at a substrate temperature of 723 K by reactive magnetron sputtering at nitrogen partial flow (RN2) = 0, 1.5, 2, 5, 10 and 12.5 %. X-ray diffraction confirmed that a single-phase ZrN starts to appear when the RN2 exceeds 2 % and well-crystalline phases appear for RN2 = 5 and 10 % samples. Raman spectroscopy measurements detected first-order modes indicative of intrinsic disorder in these samples. X-ray photoelectron spectroscopy was done to study the chemical state of samples. N and Zr K -edge x-ray absorption spectroscopy and Zr K -edge extended x-ray absorption fine structure evidenced local structural disorder and point defects in these ZrN samples which are enhanced with increasing RN2 from 5 to 12.5 %. Nanoindentation measurements showed a peak hardness of 29 GPa and elastic modulus of 245 GPa in RN2 = 2 % sample because of grain boundary hardening, with a secondary hardness maximum 26 GPa evidenced in RN2 = 10 % sample associated with the presence of point defects. Spectroscopic ellipsometry demonstrated a red-shift of the screened plasma energy from 3.57 to 2.27 eV as the RN2 increased, reflecting reduced free-electron density due to defect formation. These results establish that controlled nitrogen flow ratio enables a systematic tuning of point-defect concentration, thereby modulating the mechanical resilience and plasmonic response of ZrN thin films for advanced functional coatings. © 2026 Acta Materialia Inc.