Ion implantation during film growth and its effect on the superconducting properties of niobium

Low-energy (?500 eV) Kr+ ion bombardment during film growth and its consequences on superconducting properties of Nb are studied in a triode glow discharge sputtering configuration. Tc is depressed from the bulk value at a rate of -0.19 °C/at.% dissolved in the lattice. The residual resistivity shows an increase of 3.4 μΩ cm/at.% Kr. It is shown that radiation damage due to ion bombardment dominates the superconducting properties up to 0.2 at.% dissolved, whereas above this Kr concentration, up to ∼2 at.% Kr, the noble-gas content dominates the transport properties. All films show a dilated lattice which is mainly caused by energetic bombardment during film growth rather than subsequent trapping of the Kr gas.