We have examined the novel heteroepitaxy of magnetic oxide thin films on ultra-smooth sapphire substrates by laser MBE for fabrication of low-dimensional structures. Employing the atomically controlled substrate surfaces with atomic steps and terraces, we demonstrate the deposition of magnetic oxide nanowires (~0.5 nm high and ~20 nm wide) and nanodots of (Mn, Zn) ferrite, Fe3O4 and NiO.
Atomic-scale surface/termination of single-crystal oxide substrates were examined by coaxial impact collision ion scattering spectroscopy (CAICISS) and atomic force microscopy (AFM). CAICISS enabled us to determine the terminating atomic species and their arrangements of single crystal oxide substrates and epitaxial oxide films. Through thermal-annealing of the single crystal oxide substrates, atomically flat terrace and stepped structures were developed on the surface. The molecular layer-by-layer growth was verified by in situ monitoring of reflection high energy electron diffraction (RHEED) intensity oscillation. The atomic-scale substrate engineering made it possible to attain the novel heteroepitaxial growth such as step-decoration epitaxy resulting in the nanowire structures and diamond epitaxy on the ultrasmooth sapphire substrate. The diamond films could be grown epitaxially only on the atomically flat sapphire substrates by pulsed laser ablation of graphite. The novel application of the ultrasmooth sapphire substrate to the AFM observation stage for DNA molecules was also presented.
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