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Formation Energies of Antiphase Boundaries in GaAs and GaP: An ab Initio Study  [PDF]
Oleg Rubel,Sergei D. Baranovskii
International Journal of Molecular Sciences , 2009, DOI: 10.3390/ijms10125104
Abstract: Electronic and structural properties of antiphase boundaries in group III-V semiconductor compounds have been receiving increased attention due to the potential to integration of optically-active III-V heterostructures on silicon or germanium substrates. The formation energies of {110}, {111}, {112}, and {113} antiphase boundaries in GaAs and GaP were studied theoretically using a full-potential linearized augmented plane-wave density-functional approach. Results of the study reveal that the stoichiometric {110} boundaries are the most energetically favorable in both compounds. The specific formation energy γ of the remaining antiphase boundaries increases in the order of γf113g ≈ γf112g < γf111g, which suggests {113} and {112} as possible planes for faceting and annihilation of antiphase boundaries in GaAs and GaP.
Antiphase magnetic boundaries in iron-based superconductors: A first-principle density-functional theory study  [PDF]
Z. P. Yin,W. E. Pickett
Physics , 2009, DOI: 10.1103/PhysRevB.80.144522
Abstract: Superconductivity arises in the layered iron-pnictide compounds when magnetic long range order disappears. We use first principles density functional methods to study magnetic arrangements that may compete with long range order near the phase boundary. Specifically, we study the energetics and charge density distribution (through calculation of the electric field gradients) for ordered supercells with varying densities of antiphase magnetic boundaries. We quantify the amount by which Fe atoms with low spin moments at the antiphase boundaries have higher energies than Fe atoms with high spin moments away from the antiphase boundaries. These disruptions in magnetic order should be useful in accounting for experimental data such as electric field gradients and hyperfine fields on both Fe and As atoms.
Electronic properties of structural twin and antiphase boundaries in materials with strong electron-lattice couplings  [PDF]
K. H. Ahn,T. Lookman,A. Saxena,A. R. Bishop
Physics , 2003,
Abstract: Using a symmetry-based atomic scale theory of lattice distortions, we demonstrate that elastic textures, such as twin and antiphase boundaries, can generate intricate electronic inhomogeneities in materials with strong electron-lattice coupling, as observed in perovskite manganites and other functional materials.


中国物理 B , 1995,
Abstract: In this paper the nucleation and growth processes of GaAs(001) molecular-beam epitaxy were studied by Monte Carlo simulation, The density of islands and the density of isolated Ga adatoms were obtained for different growth temperatures, and the island size distribution at low coverage, as well as the correlation function between atoms and its relation with the temperature were studied in detail.
Low-energy, planar magnetic defects in BaFe2As2: nanotwins, twins, antiphase and domain boundaries  [PDF]
S. N. Khan,Aftab Alam,D. D. Johnson
Physics , 2013, DOI: 10.1103/PhysRevB.88.184515
Abstract: In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study using density-functional theory the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated $nano$twins (twin nuclei) - spin excitations proposed and/or observed. These nanoscale defects have very low surface energy ($22$-$210$~$m$Jm$^{-2}$), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries -- making a uniform-moment picture inappropriate for long-range magnetic order in real samples. {\it{Nano}}twins explain features in measured pair distribution functions, so should be considered when analyzing scattering data. All these defects can be weakly mobile and/or have fluctuations that lower assessed "ordered" moments from longer spatial and/or time averaging, and should be considered directly.
TiO2 as an electrostatic template for epitaxial growth of EuO on MgO(001) by reactive molecular beam epitaxy  [PDF]
A. G. Swartz,Jared J. I. Wong,I. V. Pinchuk,R. K. Kawakami
Physics , 2012, DOI: 10.1063/1.4704685
Abstract: We investigate the initial growth modes and the role of interfacial electrostatic interactions of EuO epitaxy on MgO(001) by reactive molecular beam epitaxy. A TiO2 interfacial layer is employed to produce high quality epitaxial growth of EuO on MgO(001) with a 45{\deg} in plane rotation. For comparison, direct deposition of EuO on MgO, without the TiO2 layer shows a much slower time evolution in producing a single crystal film. Conceptual arguments of electrostatic repulsion of like-ions are introduced to explain the increased EuO quality at the interface with the TiO2 layer. It is shown that ultrathin EuO films in the monolayer regime can be produced on the TiO2 surface by substrate-supplied oxidation and that such films have bulk-like magnetic properties.
Microscopical derivation of Ginzburg-Landau-type functionals for alloys and their application to studies of antiphase and interphase boundaries  [PDF]
V. G. Vaks
Physics , 2002, DOI: 10.1134/1.1510065
Abstract: The earlier-described cluster methods are used to generalize the Ginzburg-Landau gradient expansion for the free energy of an inhomogeneous alloy to the case of not small values of order parameters and variations of composition. The results obtained reveale a number of important differences with the expressions used in the phenomenological phase-field approach. Differential equations relating the local values of concentration and order parameters within the antiphase or interphase boundary (APB or IPB) are derived. These equations are applied to study the segregation at APBs near the phase transition lines; the structure of APBs and IPBs near tricritical points; pre-wetting and wetting APBs in phases with single and several order parameters; and also some effects of anisotropy of APBs under L1$_0$ and L1$_2$-type orderings.
Atomic ordering in self-assembled Ge:Si(001) islands observed by X-ray scattering  [PDF]
A. Malachias,T. U. Schulli,G. Medeiros-Ribeiro,M. Stoffel,O. G. Schmidt,T. H. Metzger,R. Magalhaes-Paniago
Physics , 2004,
Abstract: X-ray diffuse scattering in the vicinity of a basis-forbidden (200) Bragg reflection was measured for a sample with uncapped self-assembled Ge islands epitaxially grown on Si(001). Our results provide evidence of atomically ordered SiGe domains in both islands and wetting layer. The modeling of x-ray profiles reveals the presence of antiphase boundaries separating the ordered domains in a limited region of the islands where the stoichiometry is close to Si0.5Ge0.5.
Quantitative strain-field measurement of 1:1 B-site cation ordered domains and antiphase boundaries in Pb(Sc1/2Ta1/2)O3 ceramics by high-resolution transmission electron microscopy  [PDF]
Cheuk. W. Tai,Y. Lereah
Physics , 2009, DOI: 10.1063/1.3079412
Abstract: Quantitative strain measurements of the 1:1 B-site cation ordered domains, antiphase boundaries and dislocations in a highly ordered Pb(Sc1/2Ta1/2)O3 ceramic have been carried out by high-resolution transmission electron microscopy and geometric phase analysis. A phase shift of PI between two adjacent ordered domains across an antiphase boundary are determined unambiguously. The maximum in-plane strain and lattice rotation induced by a dislocation are 9.5% and 5.4deg, respectively. In a defect-free antiphase boundary, the maximum in-plane strain and lattice rotation are 1.8% and 0.9deg, respectively. The strain mainly concentrates inside the antiphase boundary.
Fabrication of superconducting MgB2 thin films by magnetron co-sputtering on (001) MgO substrates  [PDF]
Savio Fabretti,Patrick Thomas,Markus Meinert,Andy Thomas
Physics , 2010,
Abstract: We fabricated superconducting MgB2 thin films on (001) MgO substrates. The samples were prepared by magnetron rf and dc co-sputtering on heated substrates. They were annealed ex-situ for one hour at temperatures between 450{\deg}C and 750{\deg}C. We will show that the substrate temperature during the sputtering process and the post annealing temperatures play a crucial role in forming MgB2 superconducting thin films. We achieved a critical onset temperature of 27.1K for a film thickness of 30nm. The crystal structures were measured by x-ray diffraction.
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