Ion irradiation and annealing studies of NbC thin films

Single-phase NbC thin films, prepared by reactive RF sputtering, have been irradiated with 600 keV Ar ions and 200 keV He ions at room temperature in the fluence range from 0.01 to 100 dpa. With the preservation of the B1 structure, the lattice parameter, a₀, increases at the first stage of the irradiation and then decreases down to a saturation value for higher fluences. The superconducting transition temperature, T_c, decreases continuously from 11.2 K to 4 K and saturates in the fluence range of a⁰ saturation. The effects of both ion species irradiations on the changes of the lattice parameter and T_c depressions are nearly the same at a given dpa. Isochronal annealing processes of the sample that has the maximum lattice parameter have revealed a few recovery stages of the lattice parameter and T_c. The recovery stage at 700°C coincides with the recovery of the displacements of the metal atoms.