XRD Pole Figures Research Articles

Epitaxial ZnO piezoelectric layer on SiO2/Mo solidly mounted resonator fabricated using epitaxial Au sacrificial layer

In solidly mounted resonator (SMR) type of bulk acoustic wave resonator, it is difficult to fabricate single crystalline piezoelectric thin films in a bottom-up process due to the amorphous SiO2 in the low acoustic impedance layer of the acoustic Bragg reflector. In this study, single crystalline ZnO piezoelectric layer on amorphous SiO2/polycrystalline Mo acoustic Bragg reflector is fabricated using a wet etching process of the epitaxial Au sacrificial layer. Epitaxial growth of ZnO was confirmed by X-ray diffraction pole figure and transmission electron microscope electron diffraction pattern. Resonance frequency of 1.3 GHz of epitaxial ZnO SMR was observed using a network analyzer.

Comparative studies of nanoscale columnar AlxGa1-xN/AlN heterostructures grown by plasma-assisted molecular-beam epitaxy on cSi, porSi/cSi and SiC/porSi/cSi substrates

Problems of the growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on hybrid substrates involving porous silicon and silicon carbide layers by molecular beam epitaxy technique with plasma-activated nitrogen are discussed in this study. The epitaxial growth of nanoscale columnar AlxGa1-xN/AlN heterostructure is shown to be specified by the layer of silicon carbide, which is formed by atomic substitution technique, and a porous silicon sublayer predetermines the oriented growth of SiC. The performed complex of structural-spectroscopic analysis demonstrated that epitaxial growth of the nuclear AlN layer on all types of the substrates in N-enriched conditions resulted in the formation of AlxGa1-xN/AlN heterostructures with Ga-polar surface. At the same time it was found that the layer of ordered AlxGa1-xN alloy was formed only on the hybrid SiC/porSi/cSi substrate. The layer of AlxGa1-xN on the substrates of cSi and porSi/cSi is present in the state of disordered alloy with an excess content of gallium atoms. Nanocolumns of AlxGa1-xN/AlN grown on the hybrid SiC/porSi/cSi substrate have two types of preferential azimuthal orientation that affects not only their structural and optical properties but also the value of elastic deformation in the heterostructure nanoscale layers. For the first time, azimuthal dependence of intensity of E1(TO) and E2high photon modes was detected in the Raman spectra. The observed periodicity angle in micro-Raman scattering coincides with the characteristic swivel of nanoscale columns of AlxGa1-xN/AlN around c-axis according to the data of XRD pole figure measurements. Results obtained in our work show promising capabilities in the use of SiC/porSi/сSi substrates for integration of silicon technology and technology of synthesis of the nanoscale columnar AlxGa1-xN heterostructures by molecular-beam epitaxy with plasma-activated nitrogen.

Heteroepitaxial growth of β-Ga2O3 thin films on single crystalline diamond (111) substrates by radio frequency magnetron sputtering

In this work, we demonstrate the first achievement in heteroepitaxial growth of β-Ga2O3 thin films on single crystalline diamond (111) wafers using RF magnetron sputtering. A single monoclinic (β-phase) structure with a monofamily {01} plane was obtained. XRD pole figure shows (02) and (002) textures of the (01) β-Ga2O3 plane parallel to (111) diamond with six distinct rotational domains, confirming successful epitaxial growth. Collectively, this research provides valuable insights into the epitaxial growth of β-Ga2O3 on diamond via sputtering, paving the way for scalable β-Ga2O3/diamond heterostructures for future electronic and optoelectronic applications with not only high performance but also effective self-thermal management.

Corundum-structured α-Fe2O3 substrates for α-Ga2O3 epitaxial growth

The present study demonstrated the growth of α-Ga2O3 epitaxial thin films on α-Fe2O3 substrates via mist chemical vapor deposition. XRD analysis revealed that c-plane α-Ga2O3 thin films were epitaxially grown on a c-plane α-Fe2O3 substrate. The full width at half maximum for asymmetric diffraction (10–14) of α-Ga2O3 using α-Fe2O3 was lower than that obtained using α-Al2O3. Moreover, the XRD pole figure results revealed that α-Ga2O3 on α-Fe2O3 exhibited no in-plane rotations. We believe that α-Fe2O3 wafers with small lattice mismatches are promising substrates for α-Ga2O3 without rotational domains.

Real-time monitoring of plasma synthesis of functional materials by high power impulse magnetron sputtering and other PVD processes: towards a physics-constrained digital twin

Plasma synthesis of thin films by physical vapour deposition (PVD) enables the creation of materials that drive significant innovations in modern life. High value manufacturing demand for tighter quality control and better resource utilisation can be met by a digital twin capable of modelling the deposition process in real time. Optical emission spectroscopy (OES) was combined with process parameters to monitor all stages of both high power impulse magnetron sputtering and conventional magnetron sputtering processes to provide a robust method of determining process repeatability and a reliable means of process control for quality assurance purposes. Strategies and physics-based models for the in-situ real-time monitoring of coating thickness, composition, crystallographic and morphological development for a CrAlYN/CrN nanoscale multilayer film were developed. Equivalents to the ion-to-neutral ratio and metal-to-nitrogen ratios at the substrates were derived from readily available parameters including the optical emission intensities of Cr I, N2 (C–B) and Ar I lines in combination with the plasma diffusivity coefficient obtained from the ratio of substrate and cathode current densities. These optically-derived equivalent parameters identified the deposition flux conditions which trigger the switch of dominant crystallographic texture from (111) to (220) observed in XRD pole figures and the development of coating morphology from faceted to dense for a range of magnetron magnetic field configurations. OES-based strategies were developed to monitor the progress of chamber evacuation, substrate cleaning and preventative chamber wall cleaning to support process optimisation and equipment utilisation. The work paves the way to implementation of machine learning protocols for monitoring and control of these and other processing activities, including coatings development and the use of alternative deposition techniques. The work provides essential elements for the creation of a digital twin of the PVD process to both monitor and predict process outcomes such as film thickness, texture and morphology in real time.

Effect of graphene domains orientation on quasi van der Waals epitaxy of GaN

We demonstrate the growth features of III-nitrides on graphene buffer layers obtained by the CVD method on a copper catalyst with different dominant grain orientations. The reflection high-energy electron diffraction technique (RHEED) is used to map the 2D reciprocal space structures of graphene buffers and growing nitride layers. The RHEED reciprocal space pattern for the graphene layer grown on a (111) textured copper foil and transferred to a SiO2/Si substrate demonstrates the sixfold symmetry characteristic of a highly oriented material. In turn, graphene grown on a Cu (100) foil consists of two types of domains that are 30° rotated relative to each other. It has also been demonstrated that III-nitride films exactly repeat the texture of the 2D graphene buffers. The GaN sample grown over the highly textured substrate demonstrates a clear sixfold symmetry of the RHEED reciprocal space map as well as {101¯3} XRD pole figure, which is close to 2D surface morphology. In turn, the GaN film grown over the graphene buffer layer transferred from the Cu (100) textured foil has 12-fold axial symmetry, which is equivalent to the essentially two-domain in-plane orientation of the initial graphene.

Estimation of Phase Ratio in Bulk, Textured TWIP/TRIP Steels from Pole Figures.

The volume fraction of austenite (γ), ε martensite and α′ martensite is of key importance in the research of TWIP/TRIP steels. When mechanical loading is involved, the crystallographic texture also develops, which complicates X-ray diffraction-based phase ratio determination. The problem is more pronounced when only a couple, or only one Bragg-reflection can be measured. A solution for such cases is to determine the ratio of the phases based on the pole distribution function of a selected Bragg-reflection of the present phases. In this manuscript, this method is reconsidered for and applied to non-transmittable bulk specimens for the first time in the reflection mode of XRD pole figure measurements. First, the method was applied to a series of γ–α′ powder mixtures. The results were compared to those obtained by the Rietveld method. Afterwards, the technique was applied to strongly textured, bulk TWIP/TRIP steel specimens which were tensile tested at different temperatures. It was shown that the results of the presented method were close to those of the Rietveld technique in the case of powder mixtures. The results of the tensile-tested steels revealed that the α′ content increases with decreasing test temperatures, and the variation of the α′ ratio correlates very well with the ultimate tensile strength versus the temperature, confirming the contribution of the α′ content to the strength of TWIP/TRIP steels.

Atomic scale confirmation of ferroelectric polarization inversion in wurtzite-type AlScN

This work presents the first atomic scale evidence for ferroelectric polarization inversion on the unit cell level in a wurtzite-type material based on epitaxial Al0.75Sc0.25N thin films. The electric field induced formation of Al-polar inversion domains in the originally N-polar film is unambiguously determined by atomic resolution imaging using aberration-corrected scanning transmission electron microscopy (STEM). Anisotropic etching supports STEM results confirming a complete and homogenous polarization inversion at the film surface for the switched regions and the virtual absence of previous inversion domains in as-deposited regions. Local evidence of residual N-polar domains at the bottom electrode interface is observed and can be explained by both stress gradients and electric field deflection. The epitaxial relationship of the sapphire/AlN/Mo/AlScN multilayer stack is discussed in detail. Selected-area electron diffraction experiments and XRD pole figures reveal a Pitsch–Schrader type orientation relation between the Mo electrode and the AlScN film.

Effect of precursor stoichiometry on morphology, phase purity, and texture formation of hot filament CVD diamond films grown on Si (100) substrate

The effect of precursor stoichiometry is reported on morphology, phase purity, and texture formation of polycrystalline diamond films. The diamond films were deposited on 100-mm Si (100) substrates using hot filament chemical vapor deposition at substrate temperature 720–750 °C using a mixture of methane and hydrogen. The gas mixture was varied with methane concentrations 1.5% to 4.5%. Diamond film thickness and average grain size both increase with increasing methane concentration. Diamond quality was checked using surface and cross-section by ultraviolet micro-Raman spectroscopy. The data show consistent diamond properties across the surface of the film and along the cross-section. XRD pole figure analyses of the films show that 3.0% methane results in preferential orientation of diamond in the 〈111〉 direction, whereas films deposited with 4.5% methane showed texture along the 〈220〉 direction in addition to 〈111〉 which was tilted ~ 23° with respect to the surface normal.

Nonlinear optical absorption and asymmetric charge carrier conduction in chemical vapor deposited single-layer graphene

In this work, we report the nonlinear optical absorption and asymmetric charge carrier conduction in single layer graphene films deposited by chemical vapor deposition (CVD) technique on copper foils with pretreated surface. XRD texture and pole figure analysis of the substrate are utilized for the visualization of the effect of the pretreatment on the substrate. The synthesised graphene is employed as a channel layer in a back gated field-effect transistor and the asymmetric behavior of charge carriers is analyzed. Nonlinear optical response of graphene is recorded after transferring it onto a quartz substrate. Open aperture Z-scan technique yields a nonlinear absorption coefficient of 5.34 × 106 cm GW−1. The film exhibits saturable absorption in the visible range with a saturation intensity as low as 0.134 GW cm−2.

Improved Output Power Behavior of Ultraviolet GaN-Based Light-Emitting Diode By Using Agpdcu Reflector

GaN-based ultraviolet UVLEDs have attracted a great deal of interest because of their applications in water and air purification and solid-state lighting. These applications have stimulated the technological development of high-efficiency UVLEDs. On the one hand, UVLEDs exhibit relatively lower external quantum efficiencies (EQEs) than visible LEDs. In particular, high-power UVLEDs should have high light extraction and heat dissipation efficiencies. For the flip-chip (FC) LEDs, the fabrication of high-performance p-type reflector with low contact resistance and high reflectivity is reqyired. Silver (Ag) is a commonly adopted p-type reflector for near UV LEDs but suffers from thermal instability, namely, agglomerated when annealed in air above 300 °C. In addition, electromigration (EM) is one of the major failure mechanisms of electronic interconnect under high current density (> ~105 A/cm2) stressing in microelectronics devices. In this talk, we investigated the opto-electrical properties, and electromigration reliability of a Ag-Pd-Cu alloy (APC) reflector for near UV (385 nm)-LEDs as a function of temperature and compared with those of Ag only reflector. SEM results revealed that the Ag samples were less stable than the APC samples upon annealing. The contact resistivities of the Ag and APC contacts annealed at 500 °C were measured to be 2.59 × 10– 4 and 1.85 × 10–4 Wcm2, respectively. The Ga 2p core level for the APC sample shifted towards the lower binding-energies by 0.67 eV as compared to that of the as-deposited sample. The forward I-V properties of near UV LEDs fabricated with the Ag and APC reflectors were observe to be similar each other. Notably, the UV LEDs with the APC reflector produced 9.04% higher output at 100 mA than those with the Ag reflector. To investigate the device reliability, the EM behaviour of Ag and APC films were also characterised. The APC samples exhibited better EM resistance than the Ag samples. The APC samples yielded higher activation energies of the EM failures than the Ag sample. The better EM behaviour of the APC samples will be described and discussed on the basis of XRD pole figure and electron back scatter diffraction, phi scan, and inverse pole figures (IPFs) examination results.

Improved Light Output Power of Ultraviolet GaN-Based Light-Emitting Diode by Using AgPdCu Reflector

We investigated the output performance of UV LEDs with Ag-Pd-Cu (APC) and Ag-only reflectors. After annealing at 600°C, the Ag-only layer surface was seriously roughened, while the APC sample revealed a smooth surface with hillocks. The 600 °C-annealed APC and Ag samples gave reflectance of 84.9% and 70.9%at 385 nm. The contact resistivities of the Ag and APC contacts annealed at 500 °C were measured to be 2.59×10– 4 and 1.85×10– 4 Ωcm2, respectively. For the annealed APC sample, the Ga 2p core level was shifted towards the lower binding-energies by 0.67 eV as compared to that of the as-deposited sample. The UV LEDs with the annealed APC reflector yielded 9.04% higher output at 100 mA than those with the Ag reflector. Based on the XRD pole figure and SEM results, the better thermal property of the APC sample is described in terms of thermal stress and surface energy.

Texture characterization of powder-in-tube Ti/MgB2superconducting cables

Abstract The presence of texture in Ti sheathed MgB2 cables, induced by the manufacturing process, have been evaluated using XRD pole figures. Drawn monofilamentary and rolled multifilamentary cables have been compared in order to determine the effect of different deformation degrees arising from the thermo-mechanical treatments. Finally, the critical current density of the cables (Jc) was evaluated using a SQUID magnetometer. We found that MgB2 {10 1 - 0} planes align with the AD direction after drawing, while after rolling, this alignment is not present. The Jc ratio between parallel and perpendicular field is larger for the monofilamentary than for multifilamentary wires, which may be correlated with the differences in the MgB2 texture between these samples.

Cold spray deposition of Cr2AlC MAX phase for coatings and bond-coat layers

Highly pure Cr2AlC powders were synthesized and deposited for the first time by cold spray technology on stainless steel substrates. The Cr2AlC coatings were relative dense, up to 91%, and present high purity (> 98%) since only small traces of Cr2Al, Al2O3 and Cr2O3 were detected by XRD, SEM and EDX. The microstructure of the coatings is homogeneous, although some preferential orientation in the basal plane was observed by XRD pole figures. The adhesion between the coating and the substrate is strong, and compressive residual stresses up to 300 MPa in the coating were determined by XRD. Furthermore, a conventional YSZ Thermal Barrier Coating (TBCs) was deposited by Atmospheric Plasma Spray (APS) on top of the cold sprayed Cr2AlC coating in order to demonstrate the processing feasibility of Cr2AlC MAX phases as a bond-coat layer.

Yield locus prediction using statistical and RVE-based fast Fourier transform crystal plasticity models and validation for drawing steels

A methodology is presented to predict yield loci of drawing steels with virtual mechanical tests using (i) the statistical ALAMEL crystal plasticity model (VEF software of KU Leuven) and (ii) an approach based on representative volume elements (RVE’s) solved with a spectral numerical Fast Fourier Transform (FFT) technique (DAMASK software of MPIE). In the latter case, the RVE’s are defined in the form of a regular mesh of grid points in 3D-space with a crystal orientation assigned to each grid point. The experimental texture is derived from XRD pole figure measurements. Only tensile curves in the rolling direction are used to calibrate the hardening model included in the crystal plasticity models. For an interstitial free steel the predictions are compared to experimental yield loci, as obtained from uniaxial tests, plane strain tests, shear tests and through-thickness compression tests. Analytical FACET yield loci are calibrated to the crystal plasticity (CP) models and these are used in FE simulations of a square cup deep drawing process, validated by experiments.

Mechanical and microstructural characterization of magnesium single crystals

Abstract

Recrystallization in severely deformed Ag, Au, and Fe studied by positron‐annihilation and XRD methods

Positron‐annihilation studies of severely deformed samples of pure Ag, Au, and Fe are reported. The observed changes of the positron‐annihilation parameters during isochronal annealing are linked to the recrystallization process confirmed by measurements of the XRD patterns and pole figures. The latter, being sensitive to the crystallographic texture, change significantly during the recrystallization process for all three metals. The measured annihilation line‐shape parameter dependencies are described by a model that takes into account the boundary migration of the new defect‐free grains and positron diffusion inside these grains. The model fairly well describes the observed dependencies and allows us to determine the activation energy for grain‐boundary migration. The usefulness of the positron‐annihilation studies for determination of the recrystallization temperature in deformed metals and alloys is discussed.

Intrinsic Paramagnetic Defects in Zirconium and Hafnium Oxide Films

ABSTRACTThin films of zirconium oxide (ZrOx) and hafnium oxide (HfOx) were rf sputtered onto fused silica substrates in an oxygen rich argon environment. Pure zirconium and hafnium targets were used, and the oxygen partial pressure was varied to control the oxygen stoichiometry. Measurement of the EPR characteristics of the ZrOx films indicated two peaks corresponding to two orientations of the magnetic field. This anisotropic response suggested the films were polycrystalline with a preferred orientation. This was confirmed by XRD pole figures. The measured g-values for the ZrOx films were less than the free-spin g-value, indicating the defects corresponded to electron traps. It was further shown that the lower the oxygen partial pressure during deposition, the larger the EPR response, strongly suggesting the traps correspond to oxygen vacancies in ZrOx. Hafnium oxide thin films were also characterized by EPR. The EPR measurements indicated the presence of a single resonance peak, suggesting these films were polycrystalline without a preferred orientation or amorphous. XRD measurements confirmed that the HfOx films were amorphous. The g-value for these films was greater than that the free-spin value, indicating the presence of possibly self-trapped oxygen hole centers. These results will be discussed in the context of prior experimental and theoretical work on these systems.

Processing, texture quality, and piezoelectric properties of <001>C textured (1-x)Pb(Mg1/3Nb2/3)TiO3 - xPbTiO3 ceramics

This paper describes the link between texture quality and electromechanical properties for <001>C textured, 0.03(Na1/2Bi1/2)TiO3 - 0.97[0.715Pb(Mg1/3Nb2/3)TiO3 - 0.285PbTiO3] (0.03NBT-0.97[PMN-28.5PT]) ceramics with and without Mn-doping. Here, the subscript C denotes pseudocubic indices. Textured ceramics were prepared by templated grain growth of PMN-25PT on platelet-shaped 0.4(Na1/2Bi1/2)TiO3-0.6PbTiO3 (NBT-0.6PT) templates. Texture fractions of f = 0.92 (for undoped (1-x)Pb(Mg1/3Nb2/3)TiO3-xPbTiO3 (PMN-PT)) and f = 0.49 (for Mn-doped PMN-PT) were determined by fitting 002C XRD pole figures to the March-Dollase model, which was modified to account for symmetry-related 200C and 020C reflections. Using resonance methods, the elastic constants cij, sij, piezoelectric constants dij, eij, gij, hij, dielectric constants ɛij, and coupling coefficients kij of textured PMN-PT ceramics were characterized. It was found that the properties of textured PMN-PT approach the single crystal values along the texture axis (<001>C, also the poling axis), but not in transverse directions. In particular, the elastic compliance sE11 (perpendicular to <001>C) approaches an average of the single crystal sE11 and sE11(45°) coefficients, resulting in anomalous -sE12/sE11 ratios of − 0.01 and 0.04 in pure and Mn-doped textured PMN-PT, respectively. The 33-mode properties as measured by resonance-antiresonance methods were d33 = 852 pC/N, k33 = 0.83, ε33 = 3500, and mechanical quality factor Qm = 94 for undoped textured ceramics and d33 = 515, k33 = 0.76, ε33 = 2200, and Qm = 714 for Mn-doped textured ceramics.

Influence of growth rate on the epitaxial orientation and crystalline quality of CeO2 thin films grown on Al2O3(0001)

Growth rate-induced epitaxial orientations and crystalline quality of CeO2 thin films grown on Al2O3(0001) by oxygen plasma-assisted molecular beam epitaxy were studied using in situ and ex situ characterization techniques. CeO2 grows as three-dimensional (3D) islands and two-dimensional layers at growth rates of 1–7 Å/min and ≥9 Å/min, respectively. The formation of epitaxial CeO2(100) and CeO2(111) thin films occurs at growth rates of 1 Å/min and ≥9 Å/min, respectively. Glancing-incidence x-ray diffraction measurements have shown that the films grown at intermediate growth rates (2–7 Å/min) consist of polycrystalline CeO2 along with CeO2(100). The thin film grown at 1 Å/min exhibits six in-plane domains, characteristic of well-aligned CeO2(100) crystallites. The content of the poorly aligned CeO2(100) crystallites increases with increasing growth rate from 2 to 7 Å/min, and three out of six in-plane domains gradually decrease and eventually disappear, as confirmed by XRD pole figures. At growth rates ≥9 Å/min, CeO2(111) film with single in-plane domain was identified. The formation of CeO2(100) 3D islands at growth rates of 1–7 Å/min is a kinetically driven process unlike at growth rates ≥9 Å/min which result in an energetically and thermodynamically more stable CeO2(111) surface.