2025/12/15 by David R. Boris, Michael J. Johnson, Virginia D. Wheeler +5 · 1 voice
Materials Science · Engineering · #Anodic Oxide Films and Nanostructures #Plasma Diagnostics and Applications #Optical Coatings and Gratings
paper · doi:10.1116/6.0004993
openalex publication_date 2025/12/15 · openalex created_date 2025/12/15 · openalex updated_date 2026/07/31
In this work, electron beam generated plasmas in Ar/SF6 and Ar/NF3 mixtures are used to form ion-ion plasmas from which one can extract F− ions. These negative ions are used to controllably fluorinate the surface of an aluminum substrate with nanoscale precision. To understand this process, the ion-ion plasmas are characterized with Langmuir probes and optical emission spectroscopy, and the resulting AlF3 layer is characterized using in situ spectroscopic ellipsometry and ex situ x-ray photoelectron spectroscopy with depth profiling. This combination of plasma and material characterization indicates that the fluoride layer formation process is similar to plasma anodization. Here, the flux of negative ions delivered to the surface combined with an applied bias that promotes the migration of F− ions into the substrate where they react to form AlF3, enabling the growth of thick fluoride layers. The minimum thickness of the resulting AlF3 layer is determined by the thickness of the resident native oxide layer on the aluminum surface, as the conversion of this layer from oxide to fluoride is necessary for the production of stoichiometric AlF3 films. It is found that converting the native oxide layer into a fluoride results in an expansion of the surface passivation layer thickness by about a factor of 2. It is also found that NF3 produces significantly higher densities of atomic F and F− compared to SF6, leading to more rapid growth of the AlF3 layer.