Growth mode of epitaxial superlattices[BaCuO2+x]2/[CaCuO2]3on vicinal (001)SrTiO3substrates studied by x-ray diffraction

Abstract

Structural and morphological properties of $[{\mathrm{BaCuO}}_{2+x}{]}_{2}/[{\mathrm{CaCuO}}_{2}{]}_{3}$ superlattices with different thicknesses, grown on specially prepared vicinal (001) ${\mathrm{SrTiO}}_{3}$ substrates, are investigated. Using undulator radiation from a third-generation synchrotron we have performed x-ray-diffraction and diffuse scattering measurements, both in conventional and grazing-incidence geometries. We obtain detailed information about the role of the miscut of the substrate on the growth process of these superlattices. The critical thickness for pseudomorphic growth is found to depend on the miscut angle and, to a lesser extent on the film thickness. Thus the miscut of the substrate surprisingly influences the phase transition from the pseudomorphic, pseudotetragonal state to the orthorhombic state. Our results show that the interface morphology depends on the specific miscut of the substrate. Isotropic ripples, anisotropic ripples, and a fractal structure are formed upon slightly increasing the miscut angle from about 0.15\ifmmode^\circ\else\textdegree\fi{} up to angles less than 1\ifmmode^\circ\else\textdegree\fi{}. The ripples accompany the two-dimensional, layer-by-layer growth mode, which prevails for thin layers of the superlattices on well-oriented surfaces.