Investigation of ion-beam-sputtered Nb-Ti thin films by complementary use of backscattering and nuclear-reaction microanalysis

The composition of superconducting Nb-Ti films deposited by ion-beam sputtering has been studied. Both MeV 4He backscattering and direct observation of nuclear reactions on nitrogen and oxygen were used to determine the composition of the deposits. The films appear to have a uniform composition with depth. The stoichiometry of the Nb-Ti alloy is independent of beam intensity and is equal to that of the target. The oxygen and nitrogen content decrease with the background pressure inside the sputtering chamber and with deposition rate; oxygen contents as low as 0.6 at.% have been obtained. Irrespective of deposition conditions, the argon inclusion was very low. The various mechanisms of incorporation of argon and of the reactive species into ion-beam-sputtered films are discussed taking these results into account