Initial stage nucleation and growth of epitaxial SrRuO3 thin films on (001) SrTiO3 substrates

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 degrees 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 similar to 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 similar to 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.