SCANNING TUNNELING MICROSCOPY OF PULSED-LASER-DEPOSITED YBA2CU3O7-DELTA EPITAXIAL THIN-FILMS - SURFACE MICROSTRUCTURE AND GROWTH-MECHANISM

Scanning tunneling microscopy suggests that epitaxial YBa2Cu3O7-delta thin films grow unit cell by unit cell, by a terraced-island-growth mode. Although films grown at low temperatures exhibit a spiral-growth surface microstructure, films with high critical current densities (grown at high temperatures on nearly-lattice-matched substrates) do not. The terraced microstructure explains the steps found in ultrathin YBa2Cu3O7-delta layers in YBa2Cu3O7-delta/PrBa2Cu3O7-delta superlattices. These steps may act as superconducting weak links, providing support for Josephson-coupled-array models of superconducting superlattices.