Oxygen-plasma screening of ALD Al₂O₃ barriers on 3D-printed PLA for low-earth-orbit atomic-oxygen durability

Abstract

© 2026 The AuthorsAdditively manufactured polylactic acid (PLA) is a lightweight, low-cost material for spacecraft hardware but undergoes rapid oxidative erosion in the atomic oxygen (AO) environment of low-Earth orbit (LEO). This study evaluates the AO resistance of PLA coated with Al₂O₃ films deposited by low-temperature thermal atomic layer deposition (ALD) using 100–1000 ALD cycles. Samples were exposed to low-pressure oxygen plasma in a capacitively coupled RF reactor under two exposure regimes: (i) a radical-dominated plasma bulk rich in atomic oxygen (O) radicals (with background O₂), and (ii) an ion-assisted cathode-sheath region where positive oxygen ions enhance material removal, used here as an accelerated oxidative-erosion proxy for AO-driven degradation. Atomic oxygen (O) generation in the plasma was monitored by optical emission actinometry, and FTIR, SEM, EDS mapping, spectroscopic ellipsometry on co-deposited Si reference coupons, and gravimetric analysis assessed chemical, morphological, and mass changes. In the plasma bulk, even the 100-cycle coating suppressed mass loss below the detection limit. In the cathode sheath, performance was orientation-dependent: in the face-up configuration (coated face toward the plasma), a 100-cycle coating reduced the etch rate by a factor of 82; in the face-down configuration, the reduction was by a factor of 3.90 relative to uncoated PLA, consistent with lateral ingress through edges and/or localized coating defects. Increasing the ALD cycle count improved face-down protection, and at 1000 cycles no measurable mass variation was detected for either orientation, indicating erosion suppression below the detection limit under cathode sheath exposure. Elemental mapping showed that incomplete coverage of recessed print features was a key cause of reduced protection at low cycle counts, which was mitigated by increased ALD cycle count and geometry-aware fixturing. Applying 250 ALD cycles to both sides of a flat PLA panel increases the mass by 37.5 mg per 100 cm2, while providing effective protection against both oxygen-radical ingress and ion-assisted erosion.

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