Re-evaporation effect on the surface morphology of GdxY1−xCa4O(BO3)3 films grown by combinatorial laser molecular-beam epitaxy

We have found unusual re-evaporation effect on the surface morphology of GdxY1−xCa4O(BO3)3 (GdxY1−xCOB) films grown by combinatorial laser molecular-beam epitaxy. The surface morphologies of the GdxY1−xCOB films grown on the atomically flat (0 1 0) GdCa4O(BO3)3 (GdCOB) substrates were strongly dependent on the deposition conditions such as substrate temperature and laser repetition rate. Decreasing the substrate temperature and/or increasing the laser repetition rate improved the surface morphology of the film since at such deposition conditions, re-evaporation which may make film surface rough could be effectively restrained. GdxY1−xCOB film grown at 500 °C and 4 Hz exhibited the ultra-smooth surface like that of the atomically smooth (0 1 0) GdCOB substrate. Under such conditions, intensity monitoring of reflection high-energy electron diffraction revealed the layer-by-layer growth of the film. Using this regulated growth behavior of the films we have successfully fabricated such nano-structured films as [GdCOB/YCa4O(BO3)3] superlattices.