Zack’s co-authored paper was published at Surface and Coatings Technology!
The first author, Moishe Y.E. Azoff-Slifstein, was a UConn alumnus and also my advisee!
Many Congratulations!
Moishe Y.E. Azoff-Slifstein, Anshuman Thakral, Sadiq S. Nishat, Zachary S. Arenella, Seok-Woo Lee, Daniel Gall, “Hardness Enhancement in MoN/MoC Superlattices,” 133627 Surface and Coatings Technology (2026) [PDF][web]
Abstract:
1.2-μm-thick molybdenum nitride/carbide coatings with nominal modulation periods Λ = 1.9 to 30 nm are deposited on MgO(001) substrates by reactive magnetron sputtering in alternating Ar/N2 and Ar/CH4 gas mixtures at 800 °C. X-ray diffraction patterns show a single set of rock-salt structure peaks, indicating a polycrystalline microstructure with 111- and 001-oriented grains and coherency across compositional modulations. Pure nitride and carbide films have compositions corresponding to MoN0.5 and MoC0.5, while the composition modulated films exhibit an overall stoichiometric (1:1) cation-to-anion ratio but approximately four times more carbon than nitrogen. The films exhibit hardness H and elastic modulus E values which are low in comparison to existing literature. This is attributed to a significant surface roughness and an under-dense, columnar microstructure with intra- and inter-columnar pores. H and E of the films increase from H = 3 GPa and E = 135 GPa for Λ = 1.9 nm to maxima H = 12 GPa and E = 255 GPa at Λ = 15 nm, followed by a decrease to H = 7 GPa and E = 170 GPa for Λ = 30 nm. The hardness maximum is 471% and 50% larger than the measured H = 2.1 and 7.9 GPa of pure MoN and MoC films, respectively. This change in mechanical properties as a function of compositional modulation is attributed to both variations in the under-dense columnar microstructure and dislocation pinning caused by the compositional modulation that leads to local strain fields and bond strength variations.