Strain Induced Modifications of Valence Band Features in Fe3O4 Epitaxial Heterostructures

We report systematic investigations of lattice mismatch strain and the strain relaxation induced modifications on the valence band electronic structure of the epitaxial Fe3O4/Si (100) and Fe3O4/MgO (100) heterostructures. The Fe3O4 films on Si (100) and MgO (100) substrates were investigated though the angle-integrated photoemission spectroscopy (AIPES) at room temperature in the energy range 45-65 eV. Depending on the strain state of the films, the Raman modes and the Verwey transition temperature show deviations from the corresponding bulk values. The valence band feature at 2.7 eV (3.5 eV) shifts towards (away) the Fermi level with an increase (decrease) in strain resulting in decrease (increase) of density of states (DOS) of the minority spin Fe(A) 3d-eg band (majority spin Fe(B) 3d-t2g band). The effect is more pronounced in the case of films on MgO (100) substrate in comparison to the films on Si (100) substrate.

Analysis of Functionally Graded Quantum-Dot Systems with Graded Lattice Mismatch Strain

The production methodology of alloyed quantum-dot (QD) structures introduced a new design degree of freedom for QD arrays which is the grading of the material composition in the QD growth direction. This enables QDs of same size to generate different colors when exposed to blue light based on the grading of each QD. The grading of the material composition affects the material properties as well as the lattice mismatch strain between the QDs and the host matrix. Previous studies modeled graded QDs by just considering graded lattice mismatch strain while the material properties were kept uniform. Because these previous studies were seeking analytical solutions, including a graded material property model would have complicated the solutions. In this paper, a fully-coupled thermo-electro-mechanical finite element model of a cylindrical functionally graded QD (FGQD) in a host piezoelectric matrix is developed with both graded material properties and graded lattice mismatch strain. Different cases are considered corresponding to separately increasing and decreasing the strength of the lattice mismatch strain and the material properties in the QD thickness direction. The grading function is expressed using the power law that enables fractional exponents. The results show the effect of grading on the electromechanical quantities and demonstrate the flexibility that grading can add to the design of QD arrays. This work contributes to the development of quantum dots with "grading-dependent color" rather than the traditional "size-dependent color." The model can be easily extended to other cases such as different shapes of QDs, addition of wetting layer, and any applied thermo-electro-mechanical loads.

Effect of Lattice Mismatch Strain Grading on the Electromechanical Behavior of Functionally Graded Quantum Dots

A fully coupled thermo-electro-mechanical models of cylindrical and truncated conical GaN/AlN Functionally Graded Quantum Dot (FGQD) systems with and without WL are analyzed in this study to determine the effect of lattice mismatch strain grading on the electromechanical behavior of the FGQD system. This has a technological and fundamental importance because the production methodology adopted for manufacturing QDs enables the composition of the QD material to be graded in the growth direction, so the material properties as well as the induced mismatch strain between the QD and the carrier matrix are accordingly graded. The power law is used to describe the grading function. Based on the obtained results, grading of material properties and lattice mismatch strain have significant effect on the distribution of the electromechanical quantities inside the QD and can be used as another tuning parameter in the design of QD systems.

Molecular Dynamics Simulations of CdTe / CdS Heteroepitaxy - Effect of Substrate Orientation

<p class="1Body">Molecular dynamics simulations were used to catalogue atomic scale structures of CdTe films grown on eight wurtzite (wz) and zinc-blende (zb) CdS surfaces. Polytypism, grain boundaries, dislocations and other film defects were detected. Dislocation lines were distributed in three distinct ways. For the growths on the wz {0001} and zb {111} surfaces, dislocations were found throughout the epilayers and formed a network at the interface. The dislocations within the films grown on the wz {1100}, wz {1120}, zb {110}, zb {010}, and zb {1/10 1 1/10} surfaces formed an interface network and also threaded from the interface towards the film’s surface. In contrast, the growth on the zb {112} surface only had dislocations localized to the interface. This film exhibited a different orientation from the substrate to reduce the lattice mismatch strain energies, and therefore, its misfit dislocation density. Our study indicates that the substrate orientation could be utilized to modify the morphology of dislocation networks in lattice mismatched multi-layered systems.</p>

Surface-growth-mode-induced strain effects on the metal–insulator transition in epitaxial vanadium dioxide thin films

The surface growth mode can induce the anomalous compressive strain in thicker VO2/Al2O3 epitaxial films, which can't be explained by conventional epitaxial lattice-mismatch. Strain may be an effective tool for manipulating MIT of the VO2 films.

Defect and Interfacial Structure of Heteroepitaxial Fe3O4/BaTiO3 Bilayers

The defect and interfacial structure in a Fe3O4/BaTiO3 heteroepitaxial bilayer was investigated by scanning transmission electron microscopy. The results show that the Fe3O4 film grew epitaxially on BaTiO3. The orientation relationship between Fe3O4, BaTiO3 and MgO is [100]Fe3O4//[100]BaTi3O//[100]MgO and (010)Fe3O4//(010)BaTiO3//(010)MgO. An initial interfacial nucleation layer was formed that partially accommodated the lattice mismatch strain between BaTiO3 and MgO. This investigation indicates that the formation of this buffer layer provides a high-quality BaTiO3 surface for subsequent Fe3O4 growth, resulting in a semicoherent interface. The Fe3O4 surface is nearly atomically abrupt (roughness Rrms = 0.78 nm). The Fe3O4 film exhibits magnetic domains with a diameter in the range of 0.4–2 μm.

Stacking Faults around the Hetero-Interface Induced by 6H-SiC Polytype Transformation on 3C-SiC with Solution Growth

6H-SiC hetero-epitaxially grown on a (111) 3C-SiC was observed with TEM. High-density stacking faults were formed around the hetero-interface, and the density of stacking faults decreased with increasing distance from interface. On the other hand, when 3C-SiC was homo-epitaxially grown on a 3C-SiC, any stacking faults did not exist at the interface between the grown crystal and the seed crystal. Thus, the stacking faults formation started from the 6H/3C hetero-interface. Considering the lattice-mismatch strain between 3C-SiC and 6H-SiC, the strain energy is equivalent to the stacking fault energy of 6H-SiC. This similarity suggests that the stacking faults formation could be caused by the relaxation of the lattice-mismatch strain.