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We report on the unusual nanoscale kinetics of the layer-by-layer deposition of complex oxide heterostructures composed of a unit-cell thick correlated metal LaNiO3 and dielectric LaAlO3. The ultrathin multilayers demonstrate extremely good crystallinity and surface morphology maintained over the large number of layers, as confirmed by combination of AFM, RHEED, and synchrotron x-ray diffraction. To elucidate the physics behind the growth, the temperature of the substrate and the deposition rate are varied over a wide range and the results are treated in the framework of a two-layer model. The results demonstrate that, in addition to temperature and vapor supersaturation, modulated flux can be employed as a powerful kinetic handle for the fine-tuned manipulation of sub-monolayer growth regimes of multicomponent materials. [ABSTRACT FROM AUTHOR]

Unlike widely explored complex oxide heterostructures grown along [001], the study of [111]- oriented heterointerfaces is very limited thus far. One of the main challenges is to overcome the polar discontinuity that hinders the epitaxy of atomically sharp interfaces. Here, by taking LaCoO3/ SrTiO3(111) as a prototype, we show that the reconstruction, which effectively compensates the surface polarity, can stabilize the epitaxy of the heterostructure with polar discontinuity. A reconstructed substrate surface is prepared, while the growth is controlled to form reconstruction on the film surface. To suppress the chemical diffusion across the interface, the growth is interrupted between each unit cell layer to allow the lattice relaxation at a lowered temperature. In this way, high quality two-dimensional growth is realized and the heterointerfaces exhibit sharpness at the atomic scale. Our work provides a path to precisely control the growth of complex oxide heterostructures along polar orientations that exhibit emergent quantum phenomena. [ABSTRACT FROM AUTHOR]

High quality (111)-oriented CoCr2O4/Al2O3 heterostructures were synthesized on the sapphire (0001) single crystal substrates by pulsed laser deposition. The structural properties are demonstrated by in-situ reflection high energy electron diffraction, atomic force microscopy, X-ray reflectivity, and X-ray diffraction. X-ray photoemission spectroscopy confirms that the films possess the proper chemical stoichiometry. This work offers a pathway to fabricating spinel type artificial quasi-two-dimensional frustrated lattices by means of geometrical engineering. [ABSTRACT FROM AUTHOR]

High quality (111)-oriented CoCr2O4/Al2O3 heterostructures were synthesized on the sapphire (0001) single crystal substrates by pulsed laser deposition. The structural properties are demonstrated by in-situ reflection high energy electron diffraction, atomic force microscopy, X-ray reflectivity, and X-ray diffraction. X-ray photoemission spectroscopy confirms that the films possess the proper chemical stoichiometry. This work offers a pathway to fabricating spinel type artificial quasi-two-dimensional frustrated lattices by means of geometrical engineering. [ABSTRACT FROM AUTHOR]

We report on the fabrication of high quality (1 1 1)-oriented ferrimagnetic normal spinel CoCr2O4 epitaxial thin films on single crystal Al2O3 substrates. The structural, electronic, and magnetic properties were characterized by in-situ reflection high energy electron diffraction, atomic force microscopy, X-ray diffraction, X-ray photoemission spectroscopy, dc magnetization measurement, and element resolved resonant X-ray magnetic scattering. The comprehensive characterization reveals that no disorder in the cation distribution or multivalency issue is present in the samples. As a result, Kagome and triangular layers are naturally formed via this specific growth approach. These findings offer a pathway to fabricate two dimensional Kagomé heterostructures with exotic quantum many-body phenomena by means of geometrical design. [ABSTRACT FROM AUTHOR]

Depth-resolved cathodoluminescence spectroscopy of atomically flat TiO2-terminated SrTiO3 single crystal surfaces reveals dramatic differences in native point defects produced by conventional etching with buffered HF (BHF) and an alternative procedure using HCl–HNO3 acidic solution (HCLNO), which produces three times fewer oxygen vacancies before and nearly an order of magnitude fewer after pure oxygen annealing. BHF-produced defect densities extend hundreds of nanometers below the surface, whereas the lower HCLNO-treated densities extend less than 50 nm. This “Arkansas” HCLNO etch and anneal method avoids HF handling and provides high-quality SrTiO3 surfaces with low native defect density for complex oxide heterostructure growth. [ABSTRACT FROM AUTHOR]

We report on the epitaxial stabilizationeffect of strain on thegrowth of ultrathin heterostructures of a correlated metal LaNiO3(10 unit cells, ∼3.84 nm; u.c. hereafter) grown ona series of perovskite oxide substrates with both tensile and compressivestrain. An unusual polynomial dependence of the activation energyfor surface relaxation processes in terms of the lattice misfit wasobserved. Our experimental investigations further demonstrate theinfluence of strain relaxation on the self-ordering of complex oxidecompounds in the perovskite structure during high supersaturationmonolayer (interrupted layer-by-layer) deposition. [ABSTRACT FROM AUTHOR]

An optical study of the effects of strain and heterostructuring on nickelates is presented. The optical conductivity data obtained for a series of ultrathin films of NdNiO3 with varying amounts of strain reveal that two mechanisms, each associated with a different energy scale, are responsible for the tuning of the Drude-like spectral weight as a function of strain. Additionally, the optical properties of the LaNiO3 layers in a LaNiO3/LaAlO3 superlattice are investigated, showing that the coherent Drude transport associated with strained LaNiO3 is suppressed due to the presence of the LaAlO3 interlayers. [ABSTRACT FROM AUTHOR]

Depth-resolved cathodoluminescence spectroscopy of atomically flat TiO2-terminated SrTiO3 single crystal surfaces reveals dramatic differences in native point defects produced by conventional etching with buffered HF (BHF) and an alternative procedure using HCl–HNO3 acidic solution (HCLNO), which produces three times fewer oxygen vacancies before and nearly an order of magnitude fewer after pure oxygen annealing. BHF-produced defect densities extend hundreds of nanometers below the surface, whereas the lower HCLNO-treated densities extend less than 50 nm. This “Arkansas” HCLNO etch and anneal method avoids HF handling and provides high-quality SrTiO3 surfaces with low native defect density for complex oxide heterostructure growth. [ABSTRACT FROM AUTHOR]