Ion implantation and mass transport in YBa 2Cu 3O 7−δ films and substrates

Abstract

This review discusses our previous work, covering the topic of keV–MeV ion implantation into YBa 2Cu 3O 7−δ (YBCO) thin film/substrate combinations and bulk oxide samples. This includes 50 keV 2H + implantation (10 12/cm 2 and 10 16/cm 2), 200 keV O + implantation (10 12 16O/cm 2, 5 × 10 14 18O/cm 2 and 5 × 10 16 18O/cm 2), 200 keV 20Ne + implantation (5 × 10 14 /cm 2), and 1.5 MeV 197Au + implantation (5 × 10 15 /cm 2 ) at room temperature. The experimental results show that the electrical properties of YBCO films are very sensitive to irradiation damage. Implantation at very low dose (i.e. a damage level up to 4.2 × 10 −4 dpa) can result in an increase of the critical current, J c, at lower temperatures. A damage level of about 0.06 dpa destroys the superconductivity in YBCO films, whereas a damage level of about 0.18 dpa renders a film amorphous. SIMS depth profiling was used to check the range data of the ion implantation and to obtain the diffusion coefficients of H, O, and Au in the YBCO films. The implanted 18O starts to migrate into the deeper undamaged layers of a YBCO film at a temperature between 250°C and 300°C. The apparent diffusion coefficient of oxygen, in the c-direction of a c-axis oriented film, is located between the c-axis value and the a- b plane value for a bulk single crystal. Short-circuit diffusion is thought to play an important role in determining this high mobility of oxygen. The ion implantation is shown to be a valuable method for determining the diffusion coefficient in YBCO thin films. Our studies have shown that the diffusion coefficients of implanted species follows the order H > O > Au.