Sustainable ion-beam regulation of multi-scale defects in electron-beam deposited Ta₂O₅ films

Ta₂O₅ films prepared by ion-assisted electron beam evaporation (IEBD) are irreplaceable optical elements in high-power laser systems. However, this process is highly parameter-sensitive and involves coupled multi-physics across scales, making it prone to the formation of microscopic defects. This work addresses this challenge by elucidating how ion-beam energy field governs the formation of micro-pores and atomic defects. The aim is to enable more sustainable fabrication of defect-free films. For micro-pores, increasing Ar⁺ proportion broadens the incident-angle distribution via gas-phase collisions, reducing shadowing effects and surface roughness ( Sa ). When argon flow rate ( f _a) > 25 sccm, intensified re-sputtering causes a rise in Sa . Increasing ion flux can make film surfaces smooth by enhancing ion-bombardment-driven migration. As beam current ( I _i) > 850 mA, film growth becomes roughening-dominated. Quantitatively, Sa decreases from 0.38 nm to 0.20 nm when f _a increases from 5 sccm to 25 sccm, indicating that collision-induced incident-angle redistribution weakened the shadowing effect and improved valley filling. However, Sa increases to 0.33 nm at f _a = 30 sccm due to enhanced Ar⁺-induced re-sputtering and re-deposition. With increasing I _i, Sa decreases to 0.31 nm at 960 mA, while excessive ion flux caused slight surface re-roughening. For atomic defects, PL intensity exhibits a non-monotonic evolution, reflecting the competition among collision-induced energy loss, reactive oxygen compensation, Ar⁺-dominated preferential sputtering, and bombardment damage. The lowest weak absorption ( A ) of 1.81 ppm is obtained at I _i = 850 mA, whereas A increases to 4.86 ppm at I _i = 960 mA. Correlation analysis further revealed that Sa is weakly correlated with A for micro-pores ( r = 0.14–0.20), whereas PL intensity showes a strong positive correlation with A for atomic defects ( r = 0.67–0.84). These results demonstrate that A in IEBD-prepared Ta₂O₅ films is mainly governed by atomic defect states rather than surface micro-pores, providing mechanistic guidance for defect-controlled fabrication of low-absorption oxide optical films.