Ion Beam Modification of the Bi-Sr-Ca-Cu-O Superconducting Thin Films

Abstract

Superconducting Bi-Sr-Ca-Cu-O thin films with thicknesses of 30nm and less than 10nm were synthesized by using single-target magnetron sputtering and optimizing the heat treatment conditions. Cross-sectional high-resolutional transmission electron microscopy revealed that a 4nm-thick thin film consisted of a set of half-unit-cell layers of the Bi 2223 (High-T_c) and Bi 2212 (Low-T_c) phases. These film specimens were irradiated with 100keV Ar, O and N ions at very low temperature (30K), and subsequently annealed at relatively low temperatures (1003-1117K). As a result, zero-resistance transition temperature (T_{c, 0}) increased for both 30nm-and 4nm-thick thin films. Especially, for the 4nm-thick thin film, the initial T_{c, 0} of 78K was improved to 88K, approaching the T_{c, 0} of high-T_c phase. And the introduction of the pinning center was confirmed by the Ar ion implantation for the 4nm-thick thin film. It was concluded that the modification mechanism by the ion beam is based on prior atomic displacement and channeling in the cascade with the volume which is equivalent to the unit cell of the Bi system superconducting phase.