Pulsed laser deposition of YBa sub(2)Cu sub(3)O sub(7- delta ) and NdBa sub(2)Cu sub(3)O sub(7- delta ) thin films: A comparative study

摘要

Thin films of YBa sub(2)Cu sub(3)O sub(7- delta ) and NdBa sub(2)Cu sub(3)O sub(7- delta ) were grown by pulsed laser deposition. The statistical methods of experimental design and regression analysis were used to correlate the electrical and morphological properties of the films to the growth conditions. For optimized transition temperatures the deposition parameter settings of target-substrate distance, oxygen pressure and laser energy density were found to differ significantly for YBa sub(2)Cu sub(3)O sub(7- delta ) and NdBa sub(2)Cu sub(3)O sub(7- delta ). While the maximum transition temperatures obtained were similar (approximately 90 K) for the two materials, all NdBa sub(2)Cu sub(3)O sub(7- delta ) films had a roughness comparable to the c-axis unit cell dimension whereas the YBa sub(2)Cu sub(3)O sub(7- delta ) films had a surface roughness which varied between 5-17 nm depending on the growth conditions. In addition, there were differences in the average size and density of non-stoichiometric outgrowths on the two types of film. These differences we relate to a difference in growth mode. Our atomic force microscope and scanning tunnelling microscope studies suggest a 3D screw dislocation mediated growth for YBa sub(2)Cu sub(3)O sub(7- delta ) and a 2D layer-by-layer process for NdBa sub(2)Cu sub(3)O sub(7- delta ).