How substrate temperature and oxygen flow rate affect surface quality and ring structure of HfO2 film on SiO2 substrate

• Suppressing microscopic defects in films and substrates improves optical performance. • Heating condition weakens densification of fused silica surface in deposition process. • Reduced compressive stress of films on substrates results in weaker Raman intensity. • Elevated oxygen flux inhibits small-ring formation by stabilizing hydroxyl groups. Designing low-absorption HfO 2 optical thin-film components (OTCs) on fused silica substrates (FSS) for high-power laser systems remains challenging. Electron beam evaporation (EBE) can introduce micro-defects in the HfO 2 films and simultaneously alter the amorphous network of FSS, compromising optical performance. This work investigates how substrate temperature ( T ) and oxygen flow rate ( Q ) control the relationship among process, structure and properties of OTCs, and how these relationships can be utilized to guide OTC design. Reactive EBE is conducted under controlled T (23 ∼ 100 °C) and Q (140 ∼ 190 sccm). Film surface quality is quantified by AFM roughness ( Sa ), while the nanoscale FSS network is assessed by Raman spectroscopy. The resulting structure changes are validated at the property level using optical constants and weak absorption ( β ) at the wavelength of 1064 nm. The novelty lies in a systematic cross-scale correlation that explicitly links film-induced stress and morphology with the evolution of the substrate ring structure during EBE. This aspect has not been widely explored for HfO 2 /fused-silica OTCs. Increasing T reduces the average compressive stress from 112 to 95 MPa, lowers Sa by 24.2%, decreases the Raman intensity by 21.6%, and reduces β by 41.2% from 6.92 to 4.07 ppm. Increasing Q further stabilizes hydroxyl-related structures and suppresses unfavorable ring conversion, leading to additional reductions of 11.8% in Sa , 11.1% in Raman intensity, and 29.2% in β . These results provide a critical process-parameter design guideline for co-optimizing film morphology, substrate network structure, and low- β performance in high-reliability OTCs