MICROSTRUCTURE AND GROWTH-MECHANISM OF THIN SPUTTERED FILMS OF YBA2CU3O7 ON MGO SUBSTRATES

The microstructures of very thin sputtered films of YBa2Cu3O7 deposited on (100) faces of single-crystal MgO, have been investigated using scanning tunneling and atomic force microscopies. By a thickness of 10 nm, the substrate is completely covered by a fine-grained layer of the superconductor. The average grain size is about 100 nm. Many of these grains show evidence of a spiral growth mechanism. In somewhat thicker films (20 nm), the grain size has increased considerably (to about 200 nm), and this trend continues as the thickness is increased. The small grain size close to the interface suggests a possible origin for widely observed ion-beam dechanneling in this region of the film.