Properties of Superconducting Niobium Films Made by Asymmetric ac Sputtering
作者:
R. Frerichs,
C. J. Kircher,
期刊:
Journal of Applied Physics
(AIP Available online 1963)
卷期:
Volume 34,
issue 12
页码: 3541-3543
ISSN:0021-8979
年代: 1963
DOI:10.1063/1.1729254
出版商: AIP
数据来源: AIP
摘要:
Superconducting films of niobium can be made by asymmetrical ac sputtering. This modification of the conventional sputtering process uses a reverse sputtering current to bombard the film as it deposits, thus dislodging gaseous impurities to obtain pure films. The deposition conditions to yield the purest films have been established using cylindrical geometry, that is, Vycor tubing substrates which are heated internally and surrounded by a large niobium cathode. At substrate temperatures of 500°C and with a sputtering to reverse sputtering current density ratio of 4:1, films with &bgr;=R300°K/R10°Kas large as 4.7 have been obtained from bulk material of &bgr;=14. Films so made have critical temperatures between 8.9° and 9.2°K; the bulk material critical temperature is 9.25°K. The critical temperature of the films is a strong function of &bgr;, falling below 4.2°K for &bgr;<1.25.
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