Structural and Low Temperature Transport Properties of PBBI Thin Films Fabricated by Rapid Solidification Technique

Abstract

In this work, 500 nm thick superconducting α-phase PbBi thin-films were grown by thermal evaporation and quench-condensation mechanism in a vacuum chamber. Thermally-evaporated lead-bismuth vapor condensed on the silicon substrate which was cooled to 77 K by liquid nitrogen (LN2). Titanium-sublimation and a homemade LN2 cold-trap station were utilized to further improve the vacuum conditions. Structural and elemental analyses were conducted using scanning electron microscopy and energy dispersive x-ray spectroscopy techniques. The alloy content of the resulting PbBi film (78.22 at% Pb and 21.78 at% Bi) was found similar to that of the source alloy (82 at% Pb and 18 at% Bi) as the vapor pressure of bismuth lies close to that of lead. To reveal the transport characteristics of superconducting PbBi film, low temperature DC transport measurements were conducted by means of a four-probe method in a closed cycle dry cryostat cryogenics system. It was revealed that the superconductivity transition temperature of PbBi film decreased from 7.74 K to 5.95 K under increasing H-fields from 0 kOe to 7 kOe, respectively. Based on the R-T measurements, the electrical resistivity of quench-condensed PbBi film was calculated at different temperatures of 300 K, 77 K and 7.74 K, which were found as 9.11 × 10-7 ohm · m, 4.43 × 10-7 ohm · m and 1.95 × 10-7 ohm ·m, respectively. The residual resistance ratio value, which gives a rough estimation about the quality and performance of the superconducting film, was calculated as 4.65 indicating a reasonably quality film formation. © 2017 IOP Publishing Ltd.