Crystal structure of YBa2Cu3O7-x thin films prepared by pulsed laser deposition with substrate bias voltage

The crystal structure of YBa2Cu3O7-x thin films has been investigated by cross-section transmission electron microscopy. The samples were deposited on MgO (100) substrates at 670degC with substrate bias voltages of ±300 V. For the unbiased case, c-axis, a-axis and (103) oriented domains normal to the substrate surface were observed. In this film, the c-axis oriented domains are dominant, but the crystal often exhibits a longer c-lattice constant than that of the YBa2Cu3O7-x system, so extra cationic layers are inserted in the YBa2Cu3O7-x intrinsic stacking sequence. For the case of -300 V, rotated domains were dominated in the entire film; however, c-axis oriented domains also grow from the substrate surface. Small-angle semicoherent grain boundaries between them were observed. In the case of +300 V, all the grains show c-axis oriented YBa2Cu3O7-x. The degree of preferential orientation of the grains is reduced at negative bias voltage of -300 V and the structure defects are reduced by applying a positive bias of +300 V. (orig.)