Crystallographic engineering of AlN films via N2/(Ar + N2) modulation: achieving hydrogen-resistant stability in high-pressure hydrogen systems

Abstract

Solving the operational stability of load sensors and other devices in high-pressure hydrogen environments is one of the key factors for the development of hydrogen energy. This study fabricated Cr/AlN bilayer films on 316L stainless steel via closed-field unbalanced magnetron sputtering ion plating (CFUBMSIP), systematically investigating the influence of N₂/(Ar + N₂) ratios on the microstructure evolution and high-pressure hydrogen resistance of AlN layers. The analysis of the research results shows that: (1) Nitrogen proportion critically governs AlN crystallographic characteristics – amorphous structure with elevated roughness (Ra = 19.6 nm) forms at 50 % N₂, while 33 % N₂ induces dense (100)-oriented crystallization with peak deposition rate (6.05 nm/min) and ultra-smooth surface (Ra = 2.5 nm). Further reducing N₂ to 25 % triggers (100) → (111) preferential orientation transition. (2) Under 12 MPa H₂ environment, both (100)- and (111)-oriented AlN films demonstrate exceptional insulation stability (≪3% resistance fluctuation), contrasting sharply with amorphous counterparts showing severe stability degradation due to hydrogen-induced defect state proliferation. By establishing quantitative correlations between gas composition, crystalline orientation, and functional performance, this work provides fundamental insights for engineering robust AlN insulating coatings in high-pressure hydrogen energy systems.