Initial Stage Nucleation and Growth of Epitaxial SrRuO₃ Thin Films on (0 0 1) SrTiO₃ Substrates

Abstract

We have investigated the initial stage nucleation and growth of epitaxial SrRuO₃ thin films grown on both polished (as received) and buffered HF (BHF) etched single crystal (0 0 1) SrTiO₃ substrates by 90° off-axis sputtering. Atomic force microscopy indicates a dramatic difference in the initial stage growth of SrRuO₃ films on the two substrates. The films on polished substrates nucleate as rectangular islands, which merge together to form a continuous film as the thickness increases. Complete coverage is obtained at film thickness of ∼20 nm. In contrast, the film on BHF etched substrate nucleates as finger-shaped islands at the step sites and continues to grow by adatom diffusion to the step sites. Complete coverage is obtained at a film thickness of ∼10 nm. This difference in the initial stage nucleation is attributed to the difference in surface morphology and termination layer of the two substrates. However, the thicker films on both as received and BHF etched substrates have identical surface morphologies. Such studies on the initial stage nucleation will also help us understanding the growth kinetics and development of surface morphology and interfaces in multilayered perovskite thin film heterostructures and devices.