THE GROWTH OF YBA2CU3O7-X THIN-FILM

We have investigated several factors affecting the growth of YBa2Cu3O7 -x(YBaCuO) thin films; (1) lattice mismatch on the crystallinity and s urface morphology of c-axis films, (2) substrate surface roughness on the density of outgrowth, and (3) deposition temperature on the oxygen contents of a-axis films. (1) We have studied the influence of the su bstrate lattice mismatch and substrate surface roughness on the growth of c-axis YBaCuO thin films deposited by laser ablation. For the stud y of lattice mismatch, high quality ultra-thin films of thickness from 50 to 150 angstrom were deposited on the SrTiO3 and NdGaO3 which have 2 % and 0.2 % mismatch with YBaCuO respectively. The DELTAomega of th e (005) peaks were less than 0.11-degrees for all the ultra-thin films , and this showed the high crystallinity of the films. Mosaic texture was observed on the surface of the ultra-thin films on SrTiO3 but not on the ultra-thin films on NdGaO3. This shows that ultra-thin films gr ow on the 2 % lattice mismatch SrTiO3 under strain and stress. (2) For the study of the substrate surface roughness, different degree of rou ghness were introduced to the surface of the substrates by annealing, HCI or oxygen plasmas etching. For SrTiO3, a substrate surface roughne ss of peak-valley height of 10-20 angstrom was found to increase the d ensity of outgrowths but a roughness of 50 angstrom increased the dens ity tremendously. This indicates that 20 angstrom is the substrate rou ghness limit in which the growth of YBaCuO films is less affected. (3) A-axis films with very good crystallinity usually have very low T(c). The main reason is still unclear but should be related to the oxygen contents and ordering. We have determined the oxygen content of a-axis films with good crystallinity by resonant Rutherford backscattering s pectrometry using 3.05 MeV He++. The oxygen contents were found to be determined by the deposition temperature.