Microstructure and properties of laser-deposited high-Tc superconducting thin films

We have experimentally and theoretically analyzed the evaporation and the physical phenomena involved in the interaction of high powered nanosecond excimer laser pulses with bulk targets resulting in evaporation, plasma formation and subsequent deposition of superconducting thin films. Based on the experimental results, a theoretical model for deposition of thin films by pulsed laser evaporation technique is developed. In this model, the laser generated plasma is treated as an ideal gas at high temperature and pressure, which is initially confined to small dimensions, and then is suddenly allowed to expand in vacuum. This model predicts most of the experimental features of laser evaporation and deposition of thin films by this technique. Excellent quality epitaxial YBa2Cu3O7 films were formed in-situ on various substrates in the temperature range of 500-650 degree C by XeCl laser ablation in the 0.2 torr oxygen ambient. By applying a dc bias voltage of + 300 V to an interposing ring, the substrate temperatures were reduced from 650 degree C to 500 degree C for obtaining epitaxial films. Reliable critical current density measurements have been successfully carried out on superconducting thin films which were in-situ patterned during the laser deposition process. Critical current densities (at zero magnetic field and 77 K) of 5.0 x 106 Amps/cm2 were obtained on films deposited at 650 degree C on (100) SrTiO3. Rutherford backscattering/channeling and other techniques showed excellent epitaxial quality thin films with best values of minimum ion channeling yield of 3.5% on (100) SrTiO3 substrates. Detailed microstructural analysis was carried out on superconducting films processed at low and high temperatures. The anisotropic twinning characteristics of epitaxial and textured YBa2Cu3O7 films were analyzed