Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

TL;DR

This study investigates the fabrication and properties of Nb3Sn superconducting films on sapphire and Nb substrates using magnetron sputtering, analyzing how annealing conditions affect their structural and superconducting characteristics.

Contribution

It presents a detailed analysis of Nb3Sn film properties post-annealing, highlighting improvements in superconducting temperature and microstructure evolution, which is novel for sputtered films from a single target.

Findings

Superconducting T_c improved after annealing at 800°C for 24 h.

RF surface resistance measured at 6-23 K shows enhanced superconducting performance.

Microstructural changes confirmed by Raman spectra after annealing.

Abstract

Superconducting Nb3Sn films were fabricated on sapphire and fine grain Nb substrates by magnetron sputtering from a single stoichiometric Nb3Sn target. The structural, morphological and superconducting properties of the films annealed for 24 h at temperatures of 800-1000 {\deg}C were investigated. The effect of the annealing time at 1000 {\deg}C was examined for 1, 12, and 24 h. The film properties were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The DC superconducting properties of the films were characterized by a four-point probe measurement down to cryogenic temperatures. The RF surface resistance of films was measured over a temperature range of 6-23 K using a 7.4 GHz sapphire-loaded Nb cavity. As-deposited Nb3Sn films on sapphire had a superconducting critical temperature of 17.21 K, which improved to 17.83 K when the film was annealed at 800 {\deg}C for 24 h. For the films annealed at 1000 {\deg}C, the surface Sn content was reduced to ~11.3 % for an annealing time of 12 h and to ~4.1 % for an annealing time of 24 h. The Raman spectra of the films confirmed the microstructural evolution after annealing. The RF superconducting critical temperature of the as-deposited Nb3Sn films on Nb was 16.02 K, which increased to 17.44 K when the film was annealed at 800 {\deg}C for 24 h.