Ion Beam Modification of BiSrCaCuO Ultrathin Films of Nearly Three Half-Unit-Cell Thickness

The effects of ion irradiation on superconducting BiSrCaCuO ultrathin films were examined. Superconducting ultrathin films with a nearly three half-unit-cell thickness of ∼50 Å were prepared by rf magnetron sputtering and a precisely controlled multistep heat treatment. The 100 keV Ar ion irradiation followed by short-time annealing of these ultrathin films was found to improve the zero-resistance critical temperature T c,0 in a significant manner. The T c,0 improvement was marked in the case of low-T c,0 multiphase films. The ion beam modification of ultrathin films was interpreted in terms of Ar-ion-induced atomic mixing and reordering within a specific volume containing superconducting phases and nonsuperconducting impurity phases.