Superconducting Tin Films of Low Residual Resistivity

Abstract

Evaporated tin films of low residual resistivity have been produced by using very high deposition rates in a conventional vacuum system. The substrates were cooled with liquid nitrogen. After the film edges are removed by mechanical trimming or chemical etching, these films show sharp magnetic and temperature transitions from the superconducting to the normal state, a critical field- temperature characteristic which is close to a modified version of the London theory, a transition temperature very close to the value of bulk tin, and a reversible resistance - critical current characteristic. These characteristics are compared with those of films deposited on substrates at room temperature using low deposition rates. Evidence is presented to indicate that the edge effect in the temperature transition of films is caused by a concentration of impurities in the edges. The low-temperature mean free path, rather than the resistivity ratio, is suggested as a figure of merit for estimating film purity because the size effect limits the resistivity ratio for thin films.