Control of T_c for Niobium by N Ion Implantation

概要

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Nitrogen ion implantation in niobium films and single crystals has been investigated as a novel method for controlling superconducting transition temperature (T_c) over a wide temperature range. T_c measurements and He ion backscattering measurements were done as a function of dose to characterize the implanted layer. Reflection electron diffraction (RHEED) was utilized to investigate the lattice structure in the implanted layer. T_c of films was found to decrease with increasing a dose up to 〜6×10^<16>N_2/cm^2 where T_c decreased below 4.2 K from the initial value of 9 K, but increased rapidly to 10〜11 K at a dose of 1×10^<17>N_2/cm^2. He ion channeling spectra of Nb single crystals also showed a sudden change at a dose of 6×10^<16>N_2/cm^2, a value above which a rapid increase in T_c was observed, which suggests that some change in structure occurs. The highest T_c of 12.9 K (4 K higher than the initial value) was observed for samples implanted at a dose of 3×10^<17>N_2/cm^2 and annealed at 900℃ for 10 min. RHEED pattern suggests that δ-NbN were formed in these implanted layers.
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1977-10-05