Influence Of Lattice Mismatch Research Articles

Influence of Lattice Mismatch on Structural and Functional Properties of Epitaxial Ba0.7Sr0.3TiO3 Thin Films.

Substrate-induced strains can significantly influence the structural properties of epitaxial thin films. In ferroelectrics, this might lead to significant changes in the functional properties due to the strong electromechanical coupling in those materials. To study this in more detail, epitaxial Ba0.7Sr0.3TiO3 films, which have a perovskite structure and a structural phase transition close to room temperature, were grown with different thicknesses on REScO3 (RE-rare earth element) substrates having a smaller lattice mismatch compared to SrTiO3. A fully strained SrRuO3 bottom electrode and Pt top contacts were used to achieve a capacitor-like architecture. Different X-ray diffraction techniques were applied to study the microstructure of the films. Epitaxial films with a higher crystalline quality were obtained on scandates in comparison to SrTiO3, whereas the strain state of the functional layer was strongly dependent on the chosen substrate and the thickness. Differences in permittivity and a non-linear polarization behavior were observed at higher temperatures, suggesting that ferroelectricity is supressed under tensile strain conditions in contrast to compressive strain for our measurement configuration, while a similar reentrant relaxor-like behavior was found in all studied layers below 0°C.

Fabrication and Growth Orientation Control of NaBH4 Epitaxial Thin Films Using Infrared Pulsed-Laser Deposition

Complex hydrides are well-known reducing agents and hydrogen storage materials and have recently attracted attention as ionic conductors. To expand the application scope of complex hydrides, physically well-defined epitaxial films that can investigate intrinsic properties and interfacial effects are essential. However, fabricating the epitaxial films of complex hydrides is difficult because of the difficulty in maintaining [BH4]− complex anions during deposition. Herein, we present the fabrication and growth orientation control of NaBH4 epitaxial thin films, whereby an infrared pulsed laser was used to evaporate [BH4]− complex anions. We obtained NaBH4(100) and (111) epitaxial thin films on MgO(100) and CaF2(100) substrates, respectively, with the assistance of H2 gas. This is the first example of the growth orientation control of complex hydride thin films. The influence of lattice mismatch at the interface and stacking sequence along the out-of-plane direction on the growth orientation control is comparatively discussed. This study provides a basis for the advanced investigation of complex hydrides and their surface and interfacial phenomena.

EFFECT OF LATTICE MISMATCH ON THE MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF LaNiO3 CONDUCTIVE FILMS

In this work, we prepared LaNiO3 (LNO) and Au-LaNiO3 (Au-LNO) films using sol–gel multilayer coating method. The effects of lattice mismatch on the microstructure and electrical properties of the films were investigated by choosing different single-crystal substrate. XRD, SEM, and AFM results showed the high quality of LNO and Au-LNO films, indicating the successful epitaxial growth of the films on the single-crystal substrates. The room temperature resistivity of LNO films increased with the increase of lattice mismatch while different tendency was observed in Au-LNO films, suggesting that different mechanisms prevailed in the LNO and Au-LNO films. Both the transport behavior and the residual resistivity ratio were checked to explore the relationship between the lattice mismatch and the electrical properties of the films. Strain and defect concentration were proposed as the predominating factors for the changes in the resistivity of LNO and Au-LNO films under the influence of lattice mismatch.

Energy Gaps in BN/GNRs Planar Heterostructure.

Using the tight-binding approach, we study the band gaps of boron nitride (BN)/ graphene nanoribbon (GNR) planar heterostructures, with GNRs embedded in a BN sheet. The width of BN has little effect on the band gap of a heterostructure. The band gap oscillates and decreases from 2.44 eV to 0.26 eV, as the width of armchair GNRs, , increases from 1 to 20, while the band gap gradually decreases from 3.13 eV to 0.09 eV, as the width of zigzag GNRs, , increases from 1 to 80. For the planar heterojunctions with either armchair-shaped or zigzag-shaped edges, the band gaps can be manipulated by local potentials, leading to a phase transition from semiconductor to metal. In addition, the influence of lattice mismatch on the band gap is also investigated.

Substrate influence on the structure and properties of YbFeO3 films

Herein, YbFeO3 films are synthesized by using radio frequency magnetron sputtering and influence of substrate on film quality and magneto-optical properties is systematically investigated by depositing YbFeO3 films on different substrates, such as quartz glass, sapphire(0001), MgO(111), YSZ(111), SrTiO3(STO)(100) and SiO2(0001). The crystal structure, surface morphology, magnetic behavior and magnetic circular dichroism are characterized by using x-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and magnetic circular dichroism spectrometer. The crystallinity of films has been enhanced by thermal annealing at elevated temperatures. The results reveal that highly crystalline YbFeO3 films can be obtained after annealing at 800 °C. Moreover, the influence of lattice mismatch between substrate and film on film quality, growth orientation and surface morphology has been discussed in detail. The results reveal that large degree of lattice mismatch led to the formation of surface cracks and hindered the preferred growth orientation of film. Furthermore, it has been demonstrated that the choice of substrate significantly affected the optical, magnetic and magneto-optical properties of the YbFeO3 films, which exhibited obvious magnetic anisotropy, excellent coercivity of ∼882 Oe and significant magneto-optical anisotropy.

Effect of Coherent Lattice Mismatch on the Morphology and Kinetics of Ordered Precipitates

The morphological evolution and precipitation kinetics of ordered precipitates under the influence of lattice mismatch were studied by using the phase field model. The variation of the average aspect ratio of the precipitates and their distributions was investigated quantitatively, and the relationship of particles shape and particles fraction with the variation of the aspect ratio was determined. As the lattice mismatch increases, the coarsening rate constants and the particles number density decrease, the particles size distribution (PSD) becomes narrower, and the peak value of the PSD becomes lower than the value obtained by the Lifshitz–Slyozov–Wagner theory, while it is close to the value obtained by the Brailsford–Wynblatt theory. The change rate of the particles number density shows four-stage characteristics and decreases as the lattice mismatch and time increase, indicating that the precipitation and coarsening are retarded for a large lattice mismatch and that a large lattice mismatch results in fewer particles being dispersed in the matrix phase. The morphology and the particles number density show that a suitable lattice mismatch can enhance the mechanical properties of the alloys.

Influence of Lattice Mismatch in Preparation of the SmBiO3 Buffer Layer by a CSD Method

SmBiO 3 (SBO) buffer layers have been prepared via a rapid chemical solution deposition (CSD) method on different substrates, such as LaAlO 3 (LAO), yttrium-stabilized zirconium (YSZ), and NiO-buffered NiW (NiO/NiW). The SBO buffer layers deposited on LAO, YSZ, and NiO/NiW substrates have strong SBO (200) peaks and smooth surface. The SBO buffer layer is difficult to grow on the MgO substrate. The lattice mismatches between SBO buffer layers and different substrates have great influence on the epitaxial films quality. With the increase in lattice mismatch, the optimum texture temperature ranges become narrower, also the texture degrees of SBO epitaxial films decrease, and the SBO buffer layers become rougher.

Phase-field modeling the effect of misfit on the precipitation of the second-phase particles and grain coarsening

Abstract A modified phase-field model has been used to study the precipitation of the second-phase particles and the coarsening of grains under the influence of lattice mismatch. The elastic strain energy caused by misfit is taken into account, and the force equilibrium equation is solved using the iterative-perturbation method. The simulations show that the morphology of the second-phase particles is significantly influenced by the misfit, and the elastic stress blocks the precipitation of the particles. With the increase of the elastic modulus, the process of grain coarsening changes, and the morphology of the second-phase particle gradually transforms from globular to square and rod. The interactions between solute concentration and the misfit are cooperative, which together control the size of grains.

Flexural deformation and bending mode of magnetoelectric nanobilayer

A model is discussed for magnetoelectric (ME) coupling in a nanobilayer of ferromagnetic and piezoelectric phases on a substrate. The theory is applied to a specific case, nickel ferrite and lead zirconate titanate bilayer on strontium titanate substrate. Both low-frequency coupling and ME interactions at frequencies corresponding to bending oscillations have been considered. The influence of lattice mismatch between the substrate and piezoelectric and piezomagnetic layers on material parameters has been estimated using the Landau–Ginsburg–Devonshire phenomenological thermodynamic theory. At low frequencies, the model predicts a maximum in the ME coupling strength when the substrate is of the same thickness as the bilayer. The ME voltage coefficient drops with further increase in substrate thickness due to clamping effects. The bending oscillations in nanobilayers are expected to occur at ultralow frequencies (<5 Hz) compared to longitudinal acoustic modes at 100–200 kHz for bilayers of nominal dimensions. The mode frequency shows an increase with increasing substrate thickness, and the resonance value of the ME coefficient is predicted to show a minimum when the substrate-to-bilayer thickness ratio is 0.3.

Orientated nano grain growth and effect of annealing on grain size in LiTaO 3 thin films deposited by sol–gel technique

This paper reports the deposition of lithium tantalate (LiTaO 3) thin films by sol–gel process. Thin films were deposited on three different substrates, viz. Pt–Si [Pt(1 1 1)/TiO 2/SiO 2/Si(1 0 0)], Si(1 1 1), and sapphire(0 0 6) by spin coating. The influence of lattice mismatch and packing structure of atoms on the orientation of the film was investigated. In order to study the influence of annealing temperature on crystallinity, microstructure, grain size, and roughness, the films were first annealed at 650 °C, and subsequently annealed at 1000 °C. From XRD and AFM pictures it is confirmed that nano-oriented grain growth occurs only on sapphire substrate at the annealing temperature 650 °C, and the grain size increases from 50 to 200 nm when the annealing temperature is increased to 1000 °C. The surface roughness of the film increases when the annealing temperature increases. In the case of the Pt–Si substrate, prominent grain growth occurs at 1000 °C, but the grains are randomly oriented due to the lattice mismatch and packing structure of atoms. But in case of silicon substrate, packing structure of atoms plays an important role, rather than the lattice mismatch.

The influence of lattice mismatch and film thickness on the growth of TiO 2 on LaAlO 3 and SrTiO 3 substrates

Titanium dioxide, in both anatase and rutile phases, is of interest for many industrial applications and, when doped with cobalt, as a room temperature ferromagnet. Although the metastable anatase forms of TiO 2 are difficult to produce in bulk, they can be grown in thin film form by the choice of an appropriate lattice-matched substrate. We present the thickness dependence of lattice strain and crystalline quality for thin films of (0 0 1) oriented anatase grown on (0 0 1) LaAlO 3 and (0 0 1) SrTiO 3 substrates by pulsed laser deposition. For films on (0 0 1) LaAlO 3 the crystalline quality decreases as the film thickness increases. However, for films grown on (0 0 1) SrTiO 3, the film quality improves as the film thickness increases due to the lattice strain being relieved. We also show the epitaxial growth of TiO 2 on both SrTiO 3 (0 1 1) and (1 1 1) substrates. On (0 1 1) SrTiO 3, anatase grows (0 1 2) oriented with an in-plane orientation of [0 1 0] anatase ∥[1 0 0]SrTiO 3. On (1 1 1) SrTiO 3, single phase (1 0 0) oriented epitaxial rutile films are obtained, with an in-plane orientation of [0 0 1] rutile ∥ [01 1 ̄ ] SrTiO 3.

Lateral modulations in InAlAs/InP and InGaAs/InP systems

The influence of different technological parameters on the development of compositional and morphological instabilities in InAlAs and InGaAs layers grown on InP substrates is studied in the present work by transmission electron microscopy (TEM). Results show that substrate misorientation plays a decisive role in the decomposition of strained layers. It is illustrated that the modulation of composition due to the layer morphological instability is a thermally activated process. The influence of lattice mismatch on composition modulation has been assessed by introducing changes of composition in the InGaAs layers. In this case, a change of the propagation direction in the modulation is found.

Determining the crystal symmetry of epitaxial Tl-2201 thin films by X-ray diffraction

The crystal symmetry of epitaxial Tl-2201 films on LaAlO 3 and SrTiO 3 substrates is investigated by X-ray diffraction. In the case of Tl 1.85Ba 2CuO 6 film, a φ-scan of the (1 1 10) reflection showed four diffraction peaks separated by 90.00±0.02°. A 2 θ-scan of the same reflection exhibited a single peak. 2 θ− ω- and φ-scans of the corresponding reflection in Tl 2.04Ba 2CuO 6 show splitting and broadening of the diffraction peaks indicating an orthorhombic distortion. The effect of errors in film alignment on the φ-scan and 2 θ− ω-scans is discussed. A periodic function, δ= a+ bsin( β− φ), was used to correct the φ-scan measurements. The influence of lattice mismatch between film and substrate on the structural symmetry of the films is discussed.

Influence of Lattice Mismatch and Growth Rate on the Decay of RHEED Oscillation in the Case of InGaAs/GaAs Growth

The intensity decay of the oscillation of the reflection high-energy electron diffraction pattern's specular beam is analysed during the molecular beam epitaxy of strained InGaAs/GaAs heteroepitaxial structures. The oscillations' amplitude was found to decrease exponentially with time during the InGaAs growth. Further, the decay time constant decreases with InAs mole fraction, indicating that the lattice strain increases islanding during growth. A simple semi-quantitative model based on the growth front roughening is formulated to explain the results. Assuming that the oscillation decay is related partly to the strain and partly due to kinetic effects during growth, a decay component that is solely due to strain can be separated; we find that the onset of increased roughening due to the misfit strain component roughly corresponds to the equilibrium critical layer thickness for misfit dislocation generation.

Influence of lattice mismatch on magnetization-induced optical second harmonic generation from a magnetic film on a nonmagnetic substrate

The optical second harmonic generation from a thin magnetic film on a nonmagnetic substrate is theoretically investigated for both s- and p-polarized incident light. The contributions of lattice misfit strain as well as of misfit dislocation strain to the second-order nonlinear optical susceptibility are described using a nonlinear photoelastic tensor, together with the contribution of magnetization described by a nonlinear magneto-optical tensor.

Effects of lattice mismatch due to partially relaxed buffer layers in InGaAs/AlGaAs strain balanced quantum well modulators

This letter describes the performance of electro-absorption optical modulator structures, based on strain-balanced InGaAs/AlGaAs p-i-n multiple quantum wells (MQWs). It specifically considers the influence of lattice mismatch with the graded InGaAlAs buffer arising from unrelaxed material forming the substrate upon which the p-i-n structure is grown. We have shown that to achieve a lattice constant corresponding to the average for the MQW region, it is necessary to grade the buffer up to a higher indium concentration than the average indium concentration of the MQW. We have found that mismatched samples exhibit poorer modulation on the long wavelength side of the exciton peak as a result of a greater reduction in the exciton peak with applied field, and we attribute this to screening and nonuniform fields resulting from the ionization of defects at high fields. We have also shown that the similar effect induced by going to lower barrier potentials is relatively less important.

Influence of lattice mismatch on the crystalline quality of metastable GaAsSb grown by metalorganic chemical vapor deposition

GaAs 1-x Sb x layers covering an immiscible compositional range (0.14 < x < 0.74) are grown either on GaAs or InP substrates by low-pressure metalorganic chemical vapor deposition. Although the controllability of the solid-phase composition is independent of the substrate material, the full-width at half-maximum (FWHM) of the X-ray diffraction rocking curve is found to depend strongly on the lattice mismatch between the epi-layer and the substrate. A very small FWHM of 50 arcsec is obtained in closely lattice-matched GaAsSb layers grown on InP substrate, showing the importance of lattice matching in obtaining high crystalline quality epi-layers of metastable materials.

Influence of Lattice Mismatch on the Electrical and Structural Properties of HgCdTe Epilayers

The influence of lattice mismatch on the electrical and structural properties of HgCdTe epilayers grown on CdZnTe substrates has been investigated. A slight lattice mismatch of the order of less than ±0.1% between the epilayer and the substrate brings about a conductivity-type conversion of HgCdTe layers, which is related to the presence of misfit dislocations. It is considered that the conductivity-type conversion is caused by diffusion of impurities from the substrate to the epilayer due to the high interface dislocation density. This work emphasizes the importance of minimizing the interactions between the epilayer and its substrate by the precise lattice-matching.

Assessment of some crystallographic, electrical and optical properties of MOVPE-grown GaInAs(P)/InP heterostructures

Some characterisation results for GaxIn1-xAsyP1-y/InP heterostructures grown by atmospheric pressure MOVPE are presented. Hall effect, double-crystal X-ray diffraction, low-temperature photoluminescence and Shubnikov-de Haas effect were used. Very high mobilities in GaInAs/InP heterostructures have been recorded: 10750, 92000 and 153000 cm2 V-1 s-1 at 300, 77 and 10 K respectively for a residual doping level of 2*1015 cm-3. These record figures have been related to the presence of a two-dimensional electron gas which is shown to have two populated sub-bands with a total sheet density of ns=2.9*1011 cm-2 and a mobility of 250000 cm2 V-1 s-1 at 2.17 K. GaInAsP has also been grown with a low residual doping level (3.5*1015 cm-3) along with high mobilities mu (300 K)=4800 cm2 V-1 s-1, mu (77 K)=31000 cm2 V-1 s-1. A single photoluminescence line has been recorded at 0.887 eV with a full width at half maximum of 8 meV at 4 K. Finally, the influence of lattice mismatch on GaInAs/InP heterostructures has been investigated: morphology, Hall mobility and electrical properties were studied. In particular, the band gap shift is well interpreted by assuming the breaking of valence band gap degeneracy at k=0 induced by the biaxial strain.

Influence of lattice mismatch on photoluminescence from liquid phase epitaxial grown InGaP on GaAs substrates

InGaP layers were grown on GaAs substrates by liquid phase epitaxial (LPE) growth using a temperature difference growth technique under controlled phosphorus vapor pressure. Mirror-like surfaces were obtained with a lattice mismatch ranging from 0 to 0.2%. In these mismatch ranges, the photoluminescence half widths associated with the band-to-band transition were small and nearly constant for layers on both (111)B and (100) substrates. It was found that the photoluminescence band, which was observed at nearly 1.9 eV at 80 K, strongly correlates with the amount of lattice mismatching between the InGaP layer and the GaAs substrate. The intensity of this band becomes weak for lattice match at the growth temperature.