Effects of Epitaxial Strain on the Growth Mechanism in YBa2Cu3O7-x Thin Films in YBa2Cu3O7-x /PrBa2Cu3O7 Superlattices

We report on the growth mechanism of YBa 2 Cu 3 O 7- x . Our study is based on an analysis of ultrathin YBa 2 Cu 3 O 7- x (YBCO) layers in c-axis-oriented YBa 2 Cu 3 O 7- x /PrBa 2 Cu 3 O 7 superlattices. We have found that the release of epitaxial strain in very thin YBCO layers triggers a change in the dimensionality of the growth mode. Ultrathin epitaxially strained YBCO layers with thickness below 3 unit cells grow in a block-by-block two-dimensional mode that is coherent over large lateral distances. Meanwhile, when the thickness increases and the strain relaxes, layer growth turns three-dimensional, resulting in rougher layers and interfaces.