Chromium-based coating–substrate systems for ceramic data storage media

Sustainable long-term data storage is increasingly important, as most stored data is “cold”, rarely accessed or modified. Conventional solutions, such as HDDs and SSDs, rely on energy-intensive server farms to maintain data integrity. This study investigates Cr-based coatings—Cr, CrN, Cr 2 O 3 , CrB 2 , and (Al,Cr)N—deposited on sapphire and polycrystalline Al 2 O 3 via magnetron sputtering as potential ceramic data carriers. X-ray diffraction confirmed the expected crystal structures, while nanoindentation revealed hardness values ranging from 11.4 ± 0.2 GPa (Cr) to 30.0 ± 0.6 GPa ((Al,Cr)N), with indentation moduli from 379 ± 5 GPa (Cr) to 495 ± 24 GPa (CrB 2 ). Surface roughness measurements showed R a = 1–3 nm for most coatings, with CrB 2 being rougher (R a = 9 nm), highlighting the influence of surface quality on laser ablation. Femtosecond laser experiments at wavelengths of 343, 515, and 1030 nm identified CrN on sapphire as the most promising system. The 25-nm-thin film exhibited the lowest ablation threshold of 114 mJ/cm 2 at λ = 343 nm with a single pulse, increasing nearly linearly with thickness and remaining lower than for polycrystalline Al 2 O 3 . Ablation thresholds decreased with increasing pulse number (power-law exponent k = −0.276 to −0.360), enabling lower-power lasers or higher writing speeds. CrN on sapphire combines low ablation threshold, smooth surface, and high mechanical stability, allowing fast, energy-efficient data writing. Once written, the data requires virtually no energy to maintain, offering a sustainable, durable alternative to conventional storage media.