Substrate effects on the ordering nanostructure for La_(2/3)Ca_(1/3)MnO_3 ultrathin films

摘要

Ultrathin La_(2/3)Ca_(1/3)MnO_3 (LCMO) films grown on (001) SrTiO_3 (STO), (001) yttrium stabilized ZrO_2 (YSZ) and (001) LaAlO_3 (LAO) single crystal substrates have been studied by means of synchrotron radiation and atomic force microscopy (AFM). LCMO films oriented along (00l) (l = 1,2,3) are formed on STO and LAO substrates compared to only (hh0) (l = 1,2) reflections that are present on YSZ substrate. Rocking curve studies reveal that the surface inhomogeneity appears in LCMO films grown on YSZ substrate. Ordered nanostructures are observed in the surface, which may be driven by the lattice strain induced by the lattice mismatch. With thickness increasing, films undergo dramatic surface evolution: starting with a relative flat surface separated by many pinholes and grooves, followed by improved crystallite quality but 2D-island morphology in LCMO/STO; from typical layer-by-layer growth to hatched morphology, which could be seen as the onset of 3D island structure in LCMO/LAO; in contrast, in the most mismatched LCMO/YSZ system, initially quasi-1D rod feature is dominant and ends with growing island-like structure in thicker films. The driving forces for morphology instabilities have been discussed by calculating the work of adhesion based on the first principle calculations.