Influence of assisting ion beam current on the microstructure and surface morphology of IBAD-MgO thin films for YBCO coated conductors

Abstract

MgO thin films were grown on Y2O3/Al2O3 buffered C276 tapes by ion beam assisted deposition (IBAD) method and the effects of assisting ion beam current on their microstructure and surface morphology were investigated. In order to evaluate the quality of IBAD-MgO thin films, CeO2 cap layer was deposited directly on the IBAD-MgO template and then YBCO superconducting layer was grown by pulsed laser deposition (PLD) method. Film characterization was performed by in-situ reflection high energy electron diffraction, X-ray diffraction, and atomic force microscopy. The critical current Ic of the YBCO film was measured by the conventional four-probe method. It was found that the orientation, texture degree and surface morphology of the IBAD-MgO thin films were very sensitive to assisting ion beam current. By optimizing the assisting ion beam current, IBAD-MgO thin films had pure (002) orientation, excellent biaxial texture and very smooth surface with a root mean square surface roughness of less than 1nm. The PLD-CeO2 layer had the best out-of-plane texture of Δω=1.6° and in-plane texture of Δφ=4.8° at 140mA of assisting ion beam current. Under optimized experimental condition, high quality YBCO coated conductor with the critical current density Jc of 4.5×106A/cm2 was fabricated at 77K and self field.