ION-BEAM MODIFICATION OF BISRCACUO ULTRATHIN FILMS OF NEARLY 3 HALF-UNIT-CELL THICKNESS

The effects of ion irradiation on superconducting BiSrCaCuO ultrathin films were examined. Superconducting ultrathin films with a nearly thr ee half-unit-cell thickness of similar to 50 Angstrom were prepared by rf magnetron sputtering and a precisely controlled multistep heat tre atment. The 100 keV Ar ion irradiation followed by short-time annealin g of these ultrathin films was found to improve the zero-resistance cr itical temperature T-c,T-0 in a significant manner. The T-c,T-0 improv ement was marked in the case of low-T-c,T-0 multiphase films. The ion beam modification of ultrathin films was interpreted in terms of Ar-io n-induced atomic mixing and reordering within a specific volume contai ning superconducting phases and nonsuperconducting impurity phases.