| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1986: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1985: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
Preparation of NbN is usually carried out by reactive sputtering with controlling the N2 gas partial pressure( <P_N2> ). In the present investigation, besides <P_N2> , the <N_2> gas flow-rate( <Gf_N2> ) and the Ar gas flow-rate( <Gf_Ar> ) were controlled, and also the relationship between the plasma temperature(Tp) and the discharge current( <I_p> ) was clarified. In this way, the preparation condition of Bl-type NbN was obtained.
NbN was deposited onto carbon fibers(fiber diameter of 7 <micro> m, Toray, Japan) by DC reactive magnetron sputtering with two opposed Nb-plate targets, under <P_N2> =2.4mTorr, <Gf_N2> =2.5cc/min, <Gf_(Ar)> =4.0cc/min, and <I_p> =350-600mA. X-ray diffraction analysis showed that these samples have the Bl-type crystal structure. Morphology of NbN-coated carbon fiber filaments was observed by a scanning electron microscope. The dependence of the superconducting transition temperature(Tc) on <I_p> was investigated. Under <P_N2> =2.2mTorr and <Gf_N2> =2.5cc/min, it was found that Tc increases with increasing <I_p> . In the region of <I_p> =500-600mA, Bl-type NbN films with Tc(middle point)=17K were formed on carbon fibers. A Tc of 17K is the highest Tc in NbN films deposited onto carbon fibers.
The critical current became larger for the samples prepared at higher <I_p> . This result corresponds to the fact that Bl-type NbN with higher Tc was formed at higher <I_p> . The dependence of the critical current density(Jc) on the transverse external magnetic field(Hex) was obtained at 4.2K. For example, Jc=9x <10^4> A/ <cm^2> at Hex=0, or Jc=4x <10^4> A/ <cm^2> at Hex=10T. These Jc values are about one tenth of those of NbN films deposited onto sapphire substrates. The origin of this result is thought to be due to inhomogeneity and microstructure in the samples. It was found that Bl-type NbN was synthesized in the presence of N2 (excited N2 molecule) in a plasma.
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