Crystal structure of YBa 2Cu 3O 7− x thin films prepared by pulsed laser deposition with substrate bias voltage

Abstract

The crystal structure of YBa 2Cu 3O 7− x thin films has been investigated by cross-section transmission electron microscopy. The samples were deposited on MgO (100) substrates at 670°C 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 YBa 2Cu 3O 7− x system, so extra cationic layers are inserted in the YBa 2Cu 3O 7− x intrinsic stacking sequence. For the case of −300 V, rotated domains were dominant 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 YBa 2Cu 3O 7− 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.