Using helium as background gas to avoid hydrogen brittleness for MgB2 film fabrication on niobium substrate by HPCVD

• Investigating the possibility of depositing MgB2 films on niobium substrates in other gases rather than hydrogen to suppress the hydrogen brittleness.
• Comparing the phase purity, surface morphology and superconducting properties of the MgB2 films prepared in hydrogen, helium, nitrogen and argon.
• The MgB2 film fabricated in helium shows similar properties with the film deposited in hydrogen and exhibits better ductility.

Magnesium diboride has shown potential as an alternative material for the application of superconducting RF cavities. However, if MgB2 films are fabricated on niobium substrates with HPCVD method, hydrogen brittleness will cause cracks on MgB2 film when it is bent. In this work, we have investigated the possibility of depositing MgB2 film on niobium in other background gases rather than hydrogen to avoid hydrogen brittleness. Though MgB2 films fabricated in nitrogen and argon have impurities and show poor superconducting properties, the MgB2 film fabricated in helium has similar morphology and superconducting properties of that prepared in hydrogen and no cracks are observed after bending. The problem of hydrogen brittleness can be solved by using helium as the background gas when fabricating MgB2 films on niobium substrates.