The formation of self-assembled structures is of great interest in the field of ferroelectric (FE)–ferromagnetic (FM) oxide interfaces with novel functionalities driven by the combination of strain relaxation and diffusion/segregation processes occurring during epitaxial growth of Mn-based heterostructures. In epitaxial bilayers and multilayers of La0.67Sr0.33MnO3 (LSMO)/BaTiO3 (BTO) on (001) SrTiO3, using the grazing-incidence small-angle X-ray scattering technique, self-assembled in-plane structural ordering with a repeated sequence of the bilayers has been found. This ordering has important magnetic consequences, as the materials show characteristics of a superparamagnetic type of behavior even with an increased number of bilayers. Transmission electron microscopy images reveal strain due to lattice mismatch between BTO and LSMO. This strain is greatly enhanced with the number of BTO and LSMO repetitions in a multilayer as an interdiffused columnar structure is formed. Electron energy loss spectra indicate a variation in oxygen environment from one monolayer to another within one LSMO layer. Reflectivity measurements with polarized neutrons prove that the LSMO layers are grown with sufficient periodicity but have a strongly reduced magnetic moment. This reduction is plausibly associated with interfacial strain and varying oxygen deficiencies within the layers or symmetry breaking effects which can turn the LSMO layer almost antiferromagnetic.
Self-assembled core-shelled hierarchical structures consisting of single-crystalline pyramid Zn microtip as a core, converted ZnO coating as the shell, and the grown ZnO nanowires as branches, have been prepared. Such ZnO hierarchical structures fabricated by a simple aqueous chemical growth method on Zn foil substrate are expected to be easily integrated into nanodevices. These self-organized structures are superior to both the random nanoarchitecture arrays formed in vapor system and the precipitated nanostructures suspended in the solution. Because of the easier transportation of electrons from the metallic core to ZnO branches, the self-assembled core-shelled hierarchical structures exhibit better field-emission characteristics.
ABSTRACTIn this letter we report the transition from self-assembled InAs quantum-wires to quantum-dots grown on (100) InP substrates. This transition is obtained when the wires are annealed at the growth temperature. Our results suggest that the quantum-wires are a metastable shape originated from the anisotropic diffusion over the InP buffer layer during the formation of the first InAs monolayer. The wires evolve to a more stable shape (dot) during the annealing. The driving force for the transition is associated with variations in the elastic energy and hence in the chemical potential produced by height fluctuations along the wire. The regions along the wires with no height variations are more stable allowing the formation of complex, self-assembled nanostructures such as dots interconnected by wires.
AbstractSelf-organized Ge-dots on (001)-oriented Si-substrates have been studied using two-dimensionally resolved high resolution x-ray diffraction and reflectivity. The degree of the vertical correlation of the dot positions ("stacking") has been derived as well as a lateral ordering of the dots in a (disordered) square array with main axes parallel to ]100] and ]010].
ABSTRACTCathodoluminescence wavelength imaging (CLWI) of InAs/GaAs self-assembled quantum dots (SAQDs) was performed to study the spatial variation in the spectral lineshape of the broadened quantum dot (QD) ensemble. The lineshape was found to vary on a scale of ∼μm, revealing attendant variations in the size distribution of SAQD clusters on this spatial scale. Energy variations in clusters of SAQDs are found to exhibit a spatial correlation with the efficiency of luminescence and the activation energy for thermal re-emission of carriers. A reduction in the energy variation of the QD clusters occurs when the thickness of the spacer layers in vertically self-organized samples is reduced or the number of stacks is increased. SAQDs were also prepared by punctuated island growth (PIG), in which deposition of the total desired amount is broken into two or more stages each separated by time delays. CLWI reveals a reduced variation in the energy of the dominant CL emission on a ∼μm spatial scale, correlating with a narrower size distribution of larger QDs for PIG, as measured in atomic force microscopy.
Hierarchical self-assembly: Self-organized nanostructures in a nematically ordered matrix of self-assembled polymeric chains
