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absorption in the transparent region and preserve welldefined optical bandgaps, indicating that any nanocrystalline or defect-state contributions remain minimal and do not compromise optical performance.
The results of both HfO 2 thin films conclusively confirm that PEALD enables the fabrication of optically dense HfO 2 layers with properties suitable for advanced optical designs, including applications in ultraviolet meta-optics.
5 Conclusion
In summary, we have presented a comprehensive optical characterization of hafnium oxide thin films deposited by plasma-enhanced atomic layer deposition. By combining spectroscopic ellipsometry and spectrophotometry across a wide spectral range, reliable optical constants from the infrared to the vacuum ultraviolet were obtained. The films exhibit high refractive indices, low surface roughness, and excellent optical homogeneity. These findings underscore the suitability of ALD-grown HfO 2 for demanding optical applications, particularly in the ultraviolet spectral range and in nanostructured meta-optical systems. The presented dataset provides a valuable reference for optical modeling and design and supports the further development of HfO 2-based optical components.
Funding
The research has been supported by the Deutsche Forschungsgemeinschaft( DFG)( Emmy-Noether-Project SZ253 / 1-1, 287542364 and Collaborative Research Center( CRC / SFB) 1375), the European Space Agency( ESA)( Contract No. 4000109161 / 13 / NL / RA), under Grant No. 13 N16897 GRADI- ENT, and BMFTR, Förderprogramm Fusion2040 – Forschung auf dem Weg zum Fusionskraftwerk, FKZ: 13F1009I, SHARP and ATIQ( Fkz: 13N16116), Cluster of excellence QuantumFrontiers( ExC-2123-390837967) as well as from the EMPIR programme 20IND04 ATMOC.
Conflicts of interest
The authors declare that they have no competing interests to report.
Data availability statement
The data that support the findings of this study will be made publicly available in the refractiveindex. info database( https:// refractiveindex. info /) upon publication.
Author contribution statement
Thomas Siefke contributed to writing( original draft), formal analysis, funding acquisition, and resources. Kristin Gerold contributed to writing( original draft), visualization, formal analysis, and investigation. Svetlana Shestaeva contributed to writing( review and editing), formal analysis, and investigation. Pallabi Paul contributed to formal analysis, and investigation. Shawon Alam contributed to formal analysis, and investigation. Daniel Franta contributed to formal analysis and investigation. Adriana Szeghalmi contributed to funding acquisition and writing( review and editing). Sven Schröder contributed to writing( review and editing). Stefanie Kroker contributed to funding acquisition and writing( review and editing).
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