EFFECT OF AN OXYGEN-PRESSURE ON CRYSTAL-GROWTH OF ALPHA-AXIS ORIENTED YBA2CU3O7-X FILMS PREPARED BY PULSED LASER DEPOSITION

The effect of an oxygen partial pressure on the growth of a-axis oriented YBa2Cu3O7-x films has been investigated by cross-section transmission electron microscopy and scanning electron microscopy. The samples were deposited on SrTiO3 (100) substrates at 700-degrees-C and oxygen partial pressures of 20, 50 and 100 mTorr. Under 20 mTorr, a-axis and c-axis oriented domains equally grow over the whole substrate, resulting in the alternate structure of both with a separation of about 150 angstrom in TEM images. The alternate structure continues from the substrate to the film surface. At 50 and 100 mTorr, the a-axis oriented domain becomes dominant above a thickness of 40 and 100 angstrom, respectively. A disordered layer is observed between the a-axis oriented domain and substrate for 50 mTorr and the c-axis oriented domain grows on the substrate for 100 mTorr. The surface morphology is improved with decreasing the c-axis oriented domain.