Growth of niobium thin films on C-plane and R-plane sapphire substrates for superconducting devices

Nb thin films were sputtered by heating C-plane and R-plane sapphire substrates to 800°C with a SiC heater and depositing the films via DC magnetron sputtering. XRD measurements confirmed that the films exhibited epitaxial growth, reflecting the crystal growth directions of Nb and sapphire. AFM revealed that triangular-shaped grains were present on the Nb thin films on the C-plane sapphire substrates and rectangular-shaped grains were present on the Nb thin films on the R-plane sapphire substrates. Resistivity-temperature measurements revealed that the RRR of Nb thin films on C-plane and R-plane sapphire substrates were 25.6 and 53.36, respectively. The RRR of Nb thin films on R-plane sapphire substrates was approximately twice higher than that of Nb thin films on C-plane sapphire substrates. Nb thin films on R-plane sapphire substrates can be used as materials for superconducting devices because they can form thin films with good crystallinity.