Fabrication of high-performance ALD-Al2O3/SiO2 nanolaminate coating for atomic oxygen erosion resistance on polyimide

Abstract

Polyimide (PI), commonly used in space applications, is vulnerable to atomic oxygen (AO) erosion in low Earth orbit, causing performance degradation. Atomic layer deposition (ALD) of ultrathin films has great potential as AO protective coatings for aerospace materials. In this study, nanometer-thick plasma-enhanced atomic layer deposition (PEALD) SiO₂ films were deposited on in-situ oxygen plasma-activated PI surfaces. The nucleation and growth process of SiO₂ was systematically analyzed. A uniform and dense SiO₂ film was formed, providing limited resistance to AO erosion, but not sufficient for extreme environmental conditions. To further enhance AO resistance, we introduced thermal ALD-Al₂O₃ interlayers within the same processing window and alternately deposited conformal, continuous Al₂O₃/SiO₂ nanolaminates on the PI surface. The Al₂O₃ interlayer effectively reduced the film deposition roughness, forming a smoother, denser barrier layer and minimizing growth defects. This dense ALD-Al₂O₃/SiO₂ nanolaminate, with its inert Si-O-Al bonds, effectively prevents AO from penetrating the substrate, showing superior protection under long-term AO exposure. After AO irradiation, the surface remained smooth with no obvious defects or voids, effectively avoiding undercutting caused by AO. The synergistic effect of alumina and silica provides excellent AO protection while maintaining good optical transmittance.