Accommodation Of Lattice Mismatch Research Articles

Interfacial stability and electronic properties of YBCO/ABO3 heterostructures: A comparative DFT study

In this study, we utilized density functional theory (DFT) to analyze the interfacial properties of YBa2Cu3O7 (YBCO) with perovskite metal oxides LaAlO3 (LAO), KTaO3 (KTO), and SrTiO3 (STO). We focused on surface energies, lattice mismatches, strain energies, and adhesion energies to gauge the stability and compatibility of these interfaces. Our findings indicate that KTO exhibits the highest surface preference due to its lowest surface energy (0.054 eV/Å 2), suggesting superior surface stability. Moreover, LAO and STO show minor lattice mismatches with YBCO, implying effective interface integration, while YBCO/KTO interfaces experience significant strain due to extensive lattice mismatches. STO is distinguished by the lowest strain energy (0.07 eV), indicating minimal energy requirement for lattice mismatch accommodation, unlike KTO, which demonstrates high strain energy (0.42 eV) and potential structural distortions. The strongest interfacial bond, as indicated by an adhesion energy of −2.16 eV, was observed at YBCO/LAO, while the weakest was found at the YBCO/KTO interface, with an adhesion energy of −0.56 eV. Additionally, charge density difference (CDD) analysis highlighted electron density redistribution at the interfaces, predominantly around interfacial oxygen atoms, indicating a mix of ionic and covalent bonding. This study provides comparative insights into the interfacial characteristics of YBCO/ABO3 heterostructures, suggesting pathways for optimizing their design and performance.

Glass‐Like Through‐Plane Thermal Conductivity Induced by Oxygen Vacancies in Nanoscale Epitaxial La0.5Sr0.5CoO3−δ

AbstractUltrafast time‐domain thermoreflectance (TDTR) is utilized to extract the through‐plane thermal conductivity (ΛLSCO) of epitaxial La0.5Sr0.5CoO3−δ (LSCO) of varying thickness (<20 nm) on LaAlO3 and SrTiO3 substrates. These LSCO films possess ordered oxygen vacancies as the primary means of lattice mismatch accommodation with the substrate, which induces compressive/tensile strain and thus controls the orientation of the oxygen vacancy ordering (OVO). TDTR results demonstrate that the room‐temperature ΛLSCO of LSCO on both substrates (1.7 W m−1 K−1) are nearly a factor of four lower than that of bulk single‐crystal LSCO (6.2 W m−1 K−1). Remarkably, this approaches the lower limit of amorphous oxides (e.g., 1.3 W m−1 K−1 for glass), with no dependence on the OVO orientation. Through theoretical simulations, origins of the glass‐like thermal conductivity of LSCO are revealed as a combined effect resulting from oxygen vacancies (the dominant factor), Sr substitution, size effects, and the weak electron/phonon coupling within the LSCO film. The absence of OVO dependence in the measured ΛLSCO is rationalized by two main effects: (1) the nearly isotropic phononic thermal conductivity resulting from the imperfect OVO planes when δ is small; (2) the missing electronic contribution to ΛLSCO along the through‐plane direction for these ultrathin LSCO films on insulating substrates.

Formation of I2-type basal-plane stacking faults in In0.25Ga0.75N multiple quantum wells grown on a (101¯1) semipolar GaN template

In this work, I2-type basal-plane stacking faults (BSFs) were observed in In0.25Ga0.75N multiple quantum wells (MQWs) grown on a (101¯1) semipolar GaN template by high-resolution transmission electron microscopy. The structure and formation mechanisms of the I2-type BSFs at the GaN-InGaN interface were investigated in detail. The formation of the I2-type BSFs contributes to lattice mismatch accommodation within the InGaN QWs. Their density varies in different regions of the sample due to the inhomogeneous distribution of the In content in the InGaN layer. The relationship between the In content in the InxGa1-xN layer and the I2-type BSFs is discussed.

Selective area heteroepitaxy of GaSb on GaAs (001) for in-plane InAs nanowire achievement

The growth of in-plane GaSb nanotemplates on a GaAs (001) substrate is demonstrated combining nanoscale patterning of the substrate and selective area heteroepitaxy. The selective growth of GaSb inside nano-stripe openings in a SiO2 mask layer is achieved at low temperature thanks to the use of an atomic hydrogen flux during the molecular beam epitaxy. These growth conditions promote the spreading of GaSb inside the apertures and lattice mismatch accommodation via the formation of a regular array of misfit dislocations at the interface between GaSb and GaAs. We highlight the impact of the nano-stripe orientation as well as the role of the Sb/Ga flux ratio on the strain relaxation of GaSb along the [110] direction and on the nanowire length along the [1-10] one. Finally we demonstrate how these GaSb nanotemplates can be used as pedestals for subsequent growth of in-plane InAs nanowires.

Enhancement of order degree and perpendicular magnetic anisotropy of L10 ordered Fe(Pt,Pd) alloy film by introducing a thin MgO cap-layer

Fe50PtxPd50−x (at%, x=0–50) alloy films of 10nm thickness with and without 2-nm-thick MgO cap-layers are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200°C followed by high-temperature annealing at 600°C. The influences of MgO cap-layer on the structure and the magnetic properties are investigated. Fe50PtxPd50−x films epitaxially grow on the substrates at 200°C. The Fe50Pd50 and the Fe50Pt12.5Pd37.5 films are respectively composed of (001) single-crystals with disordered fcc-based (A1) and bcc-based (A2) structures. The films with x>25 consist of mixtures of A1 and A2 crystals. The volume ratio of A2 to A1 crystal decreases with increasing the x value from 25 to 50. The in-plane and out-of-plane lattices are respectively expanded and shrunk due to accommodation of lattice mismatch between film and substrate. When the films are annealed at 600°C, phase transformation to L10 ordered phase takes place. L10 phase transformation of Fe50PtxPd50−x film is promoted for a sample with MgO cap-layer and the order degree is higher than that without cap-layer. Furthermore, L10 ordering with the c-axis perpendicular to the substrate surface is enhanced for the film with cap-layer. The cap-layer is considered to be giving a tension stress to the magnetic film in lateral direction which promotes L10 ordering with the c-axis perpendicular to the substrate. Deposition of cap-layer is shown effective in achieving higher order degree and in enhancing perpendicular magnetic anisotropy with Fe(Pt,Pd) films.

Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.

Accommodation of Lattice Mismatch in a Thiol Self-Assembled Monolayer

The structure of self-assembled monolayers (SAMs) of 3-(4′-(methylthio)-[1,1′-biphenyl]-4-yl)propane-1-thiol (CH3S(C6H4)2(CH2)3SH) formed on Au(111)/mica has been investigated by scanning tunneling microscopy (STM), high-resolution X-ray photoemission spectroscopy (HRXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. A highly crystalline monolayer terminated by thioether moieties is formed, which adopts a structure that differs from the previously studied CH3 terminated analogue with its 2√3 × √3 unit cell. An oblique 2√3 × √61 chiral unit cell containing 8 molecules is proposed. Accommodation of the substantial mismatch between the lattices of the SAM and substrate is explained by molecular design. Serving as a buffer layer, the alkane spacer decouples the SAM lattice, defined by the functionalized aromatic moieties, from the substrate.

Epitaxial Si, SiGe and Ge on binary and ternary rare earth oxide buffers

AbstractLattice engineering by combining multilayer binary (Gd2O3 and La2O3) and ternary (ErxNd1‐x)2O3 rare earth oxide layers makes possible the accommodation of lattice mismatch between the silicon substrate and the grown semiconductor layer for semiconductor on insulator structures leading to a reduction of defect density. It also opens up the opportunity for stress engineering and the avoidance of the formation of structural defects and mechanical damages caused by different thermal‐mechanical properties of the substrate and the layers. In this work, some results of the development of epitaxial heterostructures with group IV semiconductors (Si, SiGe and Ge) on rare earth oxide buffer layers grown on Si(111) are desribed. Distributed Bragg reflectors designed with only three pairs exhibits 80% reflectivity for blue light. On ternary erbium neodymium oxide, SiGe layer grows with a 5x5 reconstructed surface and a roughness of 1.7 nm. We demonstrate a crack free 1 µm thick epitaxial single crystal Ge layer grown on a pseudomorphic cubic La2O3 layer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural Analysis of MgO/Fe Bi-Layer Films Epitaxially Grown on GaAs Single-Crystal Substrates with Different Orientations

MgO/Fe bi-layer films were prepared on GaAs single-crystal substrates of (100), (110), and (111) orientations by ultra-high vacuum radio-frequency magnetron sputtering. The effects of substrate orientation and substrate temperature on the film growth process and the crystallographic properties were investigated by reflection high energy electron diffraction and X-ray diffraction. Fe single-crystal layers of (100), (110), and (111) orientations epitaxially grow on GaAs substrates of (100), (110), and (111) orientations, respectively. MgO(100) single-crystal layers are obtained on the Fe(100) layers, whereas MgO layers epitaxially grow on the Fe(110) layers with two (111) variants whose orientations are rotated around the film normal by 180° each other. On the contrary, MgO polycrystalline layers are formed on the Fe(111) layers. The out-of-plane lattice spacing of MgO(100) layer is expanded, while the in-plane spacing is shrunk with respect to the lattice constant of bulk MgO crystal due to an accommodation of lattice mismatch with the Fe(100) layer. The strain in the MgO(100) layer decreases by employing a higher substrate temperature for thin film deposition.

Preparation of Co(0001)hcp and (111)fcc Films on Single-Crystal Oxide Substrates

Co thin film were prepared on oxide single-crystal substrates of Al2O3(0001)D51, MgO(111)B1, and SrTiO3(111)E21 by ultra high vacuum molecular beam epitaxy. Effects of substrate material and substrate temperate on the film growth and the crystallographic properties were investigated. Co epitaxial thin films of hcp(0001) and/or fcc(111) orientations are obtained on all the substrate. With increasing the substrate temperature, the volume ratio of hcp to fcc increases for the Co films grown on Al2O3 and MgO substrates, whereas the ratio decrease for the Co film grown on SrTiO3 substrate. The in-plane lattice strain is larger than the out-of-plane strain due to accommodation of lattice mismatch between the film and the substrate

Structure and magnetic properties of Fe epitaxial thin films prepared by UHV rf magnetron sputtering on GaAs single-crystal substrates

Fe thin films were prepared on GaAs single-crystal substrates of (100) B3 , (110) B3 , and (111) B3 orientations by ultra high vacuum rf magnetron sputtering. The effects of substrate orientation and substrate temperature on the film growth, the structure, and the magnetic properties were investigated. On GaAs(100) B3 substrates, Fe(100) bcc single-crystal films are obtained at 300 °C, whereas Fe films consisting of bcc(100) and bcc(221) crystals epitaxially grow at room temperature (RT). Fe(110) bcc and Fe(111) bcc single-crystal films are respectively obtained on GaAs(110) B3 and GaAs(111) B3 substrates at RT–300 °C. The in-plane lattice spacings of these Fe epitaxial films are 0–9% larger than the out-of-plane lattice spacings due to accommodation of lattice mismatch between the films and the substrates. The film strain is decreased by employing an elevated substrate temperature of 300 °C. The in-plane magnetization properties are reflecting the magnetocrystalline anisotropy of bulk bcc–Fe crystal.

Microstructures and interfaces in directionally solidified oxide–oxide eutectics

This article reviews different studies carried out on the microstructures and oxide–oxide interfaces encountered in directionally solidified eutectics. Depending on the phase diagram and preparation conditions, lamellar, fibrous or three-dimensional network microstructures can be obtained. Interfaces between refractory oxides with various structural types (corundum, fluorite, rocksalt, perovskite and garnet) are investigated. Orientation relations and interface planes are reported and general features of the structure of interfaces are discussed from high-resolution electron microscopy (HREM) studies. The accommodation of lattice mismatch at the interface is investigated by geometric phase analysis of HREM images.

Real-time characterization of GaSb homo- and heteroepitaxy

We examine the homo- and heteroepitaxial growth of moderately thick (∼700 nm) layers of GaSb with the objectives of optimizing growth conditions and determining the initial phase of heteroepitaxy on (001)GaAs. Real-time spectroscopic ellipsometry (RTSE) data show that the (001)GaSb surface degrades immediately in excess trimethylgallium (TMG), but both (001)GaSb and As-terminated (001)GaAs surfaces are stable in trimethylantimony (TMSb). The surface-dimer contribution to the optical-anisotropy (OA) signal of (001)GaSb is small and generally masked by structural (roughness) effects, hence it is not useful for determining surface stoichometry. However, we show that laser light scattering (LLS) data do allow the V/III ratio to be fine-tuned during growth to minimize macroscopic roughness. TEM micrographs show that our GaSb/GaAs heterointerface is relatively defect-free except for the necessary local accommodation of lattice mismatch. The initial phase of heteroepitaxy on (001)GaAs occurs here as a coexistence of separate regions of GaAs and GaSb.

Deposition of GaN films on (111) Si substrates by alternate supply of TMG and NH3

Abstract GaN films were grown on (1 1 1) Si substrates at 1000 °C by separate admittances of trimethylgallium (TMG) and ammonia (NH3). To achieve high quality GaN films, the optimization in growth temperature and layer thickness of AlN buffer layer between GaN film and Si substrate is required. Cross-sectional transmission electron microscopic observations of the GaN/(1 1 1)Si samples show a nearly parallel orientation relationship between the (0 0 0 1) planes of GaN film and the (1 1 1) planes of Si substrate. Room temperature photoluminescence spectra of high quality GaN films show a strong near band edge emission and a weak yellow luminescence. The achievement of high quality GaN films on (1 1 1) Si substrates is believed to be attributed to enhancement in surface mobilities of the adsorbed surface species and adequate accommodation of lattice mismatch between high temperature AlN buffer layer and Si substrate.

Growth and Properties of Ferromagnet-SemiconDuctor Hetero-Structures for Spin Injection

Molecular-beam epitaxial growth and interface formation is investigated and optimized for the material systems Fe-on-GaAs(001) and MnAs-on-GaAs(001), which represent model systems for the integration of magnetic materials with semiconductors and the investigation of spin injection. In view of interface reactions as a key problem for the first system and in order to optimize the surface morphology, the Fe films are grown at reduced temperature. For MnAs-on-GaAs, an abrupt interface with an anisotropic lattice-mismatch accommodation mechanism is observed, which explains the unexpected high quality of the films. It is shown that the phase transition between paramagnetic g MnAs and ferromagnetic f MnAs during cooling after growth plays an important role and leads, at appropriate conditions, to strain-mediated self-organized structures. Electrical injection of spin polarized electrons through the ferromagnet-semiconductor interfaces is observed by analyzing the electroluminescence signal of GaAs/(In, Ga)As light emitting diodes capped with Fe or MnAs.

Directional solidification and interface structure of BaTiO3-CoFe2O4 eutectic

The directional solidification and the interface structure of BaTiO3-CoFe2O4 eutectic grown by the floating zone melting method were investigated. The microstructure of the eutectic were found to consist grains of lamellar or fibrous morphology. Two types of crystal structures of BaTiO3 were observed for different growth conditions. The orientation relationships between BaTiO3 and CoFe2O4 (the spinel-type crystal structure) are a) hcp BaTiO3: (111) CoFe2O4 // (001) BaTiO3 and (110) CoFe2O4 // (110) BaTiO3, and b) tetra/cubic BaTiO3: (001) CoFe2O4 // (001) BaTiO3 and (100) CoFe2O4 // (100) BaTiO3. The interface has misfit dislocations due to the accommodation of lattice mismatch.

Kinetics of MnAs growth on GaAs(001) and interface structure

On different As-rich GaAs(001) templates, well characterized by reflectance difference spectroscopy, nucleation and growth of NiAs-type MnAs is investigated in real time by reflection high-energy electron diffraction. Using very high As4/Mn flux ratios and low growth rates, one of the two occurring azimuthal alignments of the (1̄100) orientation can be nearly suppressed even in the nucleation stage, and it vanishes completely with further growth. Annealing is found to be very effective in surface smoothing. In dependence on the As/Mn ratio the MnAs(1̄100) surface develops different reconstructions. This finding is important for further investigations in the growth of double heterostructures. High-resolution transmission electron microscopy of as-grown MnAs/GaAs samples reveals an abrupt interface. The lattice mismatch accommodation is anisotropic with regularly arranged misfit dislocations along the [1̄10] direction and less localized coherency strain in the [110] direction, consistent with a near-coincidence-site lattice model.

Lattice mismatch accommodation in perovskite films on perovskite substrates

Cubic perovskite films with different compositions were grown on perovskite substrates to investigate the influence of a large lattice mismatch on growth phenomena via the chemical solution deposition method, using toluene solutions of different 2-etyhlhexanoates and neodecanoates. The films were pyrolyzed to crystallize the perovskite of the desired composition and then heated to 1000°C to promote epitaxial grain growth. Pole figures obtained via X-ray diffraction as well as selected area diffraction (SAD) of TEM specimen with lattice mismatches of 2.5% (SrTi 0.5Zr 0.5O 3 on SrTiO 3), 5% (SrZrO 3 on SrTiO 3), 7.4% (BaZrO 3 on SrTiO 3) and 8.2% (SrZrO 3 on LaAlO 3) reveal only the epitaxial orientation [100](001) film ∣∣ [100](001) substrate. The XRD and TEM results also indicate increasing polycrystallinity with increasing lattice mismatch. High resolution electron microscopy (HREM) of films on SrTiO 3 demonstrated that an array of misfit dislocations is present at the interface. The misfit dislocations have line vectors 1 of 〈100〉 type and Burgers vectors b of 〈010〉 type. Dislocation separation distances obtained with HREM and XRD lattice parameter measurements show that the strain energy within the films, owing to lattice mismatch, is nearly fully relaxed. The mechanisms of epitaxial growth and dislocation formation are discussed.

The accommodation of lattice mismatch in Ag/Ni heterophase boundaries

The Ag/Ni system is chosen as a model system for metal/metal interfaces with a large lattice mismatch. This system is well suited for both experimental and theoretical studies, and Ag/Ni boundaries are among the best studied metal/metal heterophase interfaces. Simple embedded atom method (EAM) potentials have been shown to successfully predict boundary structures of Ag/Ni interfaces. In this paper, EAM potentials are used in a Monte Carlo (MC) scheme to study the equilibrium structures of various experimentally observed low-energy boundaries. The importance of faceting on the atomic scale is demonstrated for parallel oriented (cube-on-cube) interfaces as well as for misoriented interfaces like the (100) twist boundaries with twist angles 0‡ < θ < 10‡.

Silicium germanium heterodevices

Silicium germanium (SiGe) is a completely miscible alloy with a lattice mismatch to the Si substrate of up to 4.17%. Accommodation of lattice mismatch f causes elastic strain ε, and/or misfit dislocations and surface corrugations. Onset of misfit dislocation generation takes place above a critical thickness t c which is dependant on mismatch and growth temperature. Critical thicknesses are compared for equilibrium models (Matthews-Blakeslee, > 750°C) with fit curves for 550°C growth experiments (People-Bean). The most important factors for successful silicon based heterodevices are analyzed, and as attractive areas for future research are defined; heterobipolar transistors (HBT) for high frequency communication, complementary heterojunction field effect transistors (HFET) for digital logic, 1.3 μm waveguide receivers for opto/microelectronics integration and self assembled quantum dot devices for multifunctional long term applications. Treatment of surface corrugations, adatom behaviour, surfactant phenomena and surface passivation of devices will be an essential part of future device oriented research.