ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Superconducting NbN was produced on commercial carbon fibers and sapphire substrates by dc reactive magnetron sputtering. Uniform coating was achieved by spreading 9000 filaments into a strip located between two planar magnetrons facing each other. The conditions for B1 phase formation and homogeneous coating have been studied. Over a rather wide range of total pressures, pAr+pN2, the highest superconducting transition temperature was found for a nitrogen partial pressure pN2 of about 0.05 Pa. In addition, tensile or compressive strains were produced in the NbN film on the carbon fiber as a function of bias. The NbN grain size was controlled in the range between 10 and 25 nm. Without a bias, the usual (111) preferential orientation of the grains was observed in the NbN film on the carbon fiber. The intensity ratio I200/I111 could be controlled between 0.74 and 0.4. Under an increased bias, the lattice parameter grew from about 0.4385 to about 0.4395 nm. This behavior may be due to a variety of reasons. The superconducting critical currents jc in a self-magnetic field are about 105 A/cm2 for NbN on carbon fibers (C-NbN) and about 2×106 for NbN on sapphire (S-NbN). Various microstructures and, to some extent, also mechanical defects are thought to be responsible for this difference. At 13 T, the corresponding jc values are 2×104 and 105 A/cm2 for NbN films of 1-μm thickness. The extrapolated Bc2 (4K) values for C-NbN are about 30–35 T, for S-NbN about 25 T. The nucleation conditions for NbN depended strongly on the substrate; this was found to be true for the existence of the B1 phase with respect to gas composition, microstructure, and deposition rate. The analysis of the composition of the films, which was performed by Rutherford backscattering and scanning Auger depth profiling, revealed uniform compositions with approximately 1-at. % carbon and approximately 0.1-at. % oxygen contaminations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.334688
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