X-ray Diffraction Pole Figure Analysis Research Articles

Thermal conductivity across the van der Waals layers of α-MoO3 thin films composed of mosaic domains with in-plane 90° rotations

α-Molybdenum trioxide (α-MoO3) is a typical two-dimensional metal oxide material, in which the covalently bonded layers are bonded by van der Waals forces. Herein, the thermal conductivities across the van der Waals layers of α-MoO3 thin films with nominal thicknesses of 50, 100, and 125 nm were investigated. The α-MoO3 thin films were fabricated on the (100) plane of a single-crystalline SrTiO3 substrate heated up to 400 °C by DC reactive magnetron sputtering using a Mo metal target. The b-axis-oriented α-MoO3 thin films epitaxially grown on the SrTiO3 (100) plane were confirmed by x-ray diffraction and x-ray pole figure analyses. Electron diffraction patterns and plane-view transmission electron micrographs revealed that the α-MoO3 thin films were composed of mosaic domains with a diameter of ∼2 nm, with each domain rotated in-plane by 90° with respect to the neighboring one. The mean thermal conductivity across the van der Waals layers of the three α-MoO3 thin films was evaluated to be 1.2 ± 0.3 W m−1 K−1, which is comparable to the reported thermal conductivities of layered cobalt oxide thin films. The reduced thermal conductivity is mainly due to phonon scattering at domain boundaries lying in the in-plane direction.

Size dependent strengthening in high strength nanotwinned Al/Ti multilayers

Mechanical behavior of metallic multilayers has been intensively investigated. Here we report on the study of magnetron-sputtered highly textured Al/Ti multilayer films with various individual layer thicknesses (h = 1–90 nm). The hardness of Al/Ti multilayers increases monotonically with decreasing layer thickness without softening and exceeds 7 GPa, making it one of the strongest light-weight multilayer systems reported to date. High-resolution transmission electron microscopy and X-ray diffraction pole figure analyses confirm the formation of high-density nanotwins and 9R phases in Al layers. The density of nanotwins and stacking faults scales inversely with individual layer thickness. In addition, there is an HCP-to-FCC phase transformation of Ti when h ≤ 4.5 nm. The high strength of Al/Ti multilayers primarily originates from incoherent layer interfaces, high-density twin boundaries, as well as stacking faults.

High-performance ambipolar benzodifurandione-based donor-acceptor copolymer with balanced hole and electron mobility

Well-balanced ambipolar benzodifurandione (BDO) donor–acceptor copolymers were synthesized by tuning its intramolecular charge transfer nature by expanding the volumetric portion of the donor moiety, i.e., by using thiophene copolymerized with thiophene vinylene thiophene (TVT) or selenophene vinylene selenophene (SVS). Photophysical analyses revealed that BDO-SVS formed highly aggregated states in the solution state compared with BDO-TVT, facilitating a well-ordered self-assembled crystalline structure in the solid state. Using two-dimensional grazing incident X-ray diffraction and quantitative pole figure analyses, we established that the molecular orientation and degree of crystallinity was higher in BDO-SVS than in BDO-TVT. The morphological features identified by atomic force microscopy also showed a higher crystalline nature of SVS derivative, implying that SVS can strengthen intermolecular charge transport. This improved environment for charge transport, was revealed by the performance of organic field-effect transistors: BDO-SVS had superior performance than that of BDO-TVT for both hole and electron mobilities. This research shows that BDO, with a strong acceptor moiety, renders high-performance ambipolar characteristics when copolymerized with an expanded and aggregating donor moiety, such as SVS.

Strong texturing of lithium metal in batteries

Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO3 and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. This understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.

Interface layer to tailor the texture and surface morphology of Al-doped ZnO polycrystalline films on glass substrates

A 10-nm-thick radio frequency magnetron-sputtered aluminum-doped zinc oxide (AZO) showing a texture with a preferential (0001) orientation on amorphous glass substrates was used as an interface layer for tailoring the orientation of 490-nm-thick polycrystalline AZO films subsequently deposited by direct current (DC) magnetron sputtering at a substrate temperature of 200°C. Wide-angle X-ray diffraction pole figure analysis showed that the resulting 500-nm-thick AZO films showed a texture with a highly preferential c-axis orientation. This showed that DC-magnetron-sputtered AZO films grew along with the orientation matching that of the interface layer, whereas 500-nm-thick AZO films deposited on bare glass substrates by DC magnetron sputtering exhibited a mixed orientation of the c-plane and other planes. The surface morphology was also improved while retaining the lateral grain size by applying the interface layer as revealed by atomic force microscopy.

Orientation epitaxy of Ge1−xSnxfilms grown on single crystal CaF2substrates

Ge1−xSnx films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge1−xSnx(111) films are grown on CaF2(111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 °C. This is the first report of (111) oriented Ge1−xSnx grown on a (100) oriented CaF2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. Additionally, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.

Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and 〈10〉CdTe//〈10〉Ge// in the in-plane direction. The I–V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ∼η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.

Heteroepitaxial growth of diamond films on 3C-SiC/Si substrates with utilization of antenna-edge microwave plasma CVD for nucleation

Antenna-edge microwave plasma chemical vapor deposition was utilized for heteroepitaxial nucleation of diamond on 3C-SiC(001)/Si(001) substrates. A diamond grain density of 3 × 109 cm−2 was obtained after 2 h of growth under the 〈001〉 preferential growth conditions. A two-step growth process led to a highly-oriented diamond films by suppressing the growth of non-aligned grains. Sharply-defined reflection high energy electron diffraction patterns of diamond were observed. The crystalline quality of the diamond films were investigated by X-ray diffraction pole figure analysis and micro-Raman spectroscopy. After 30 h of growth, heteroepitaxial diamond films were obtained with a full width at half-maximum of 3.8° in the X-ray diffraction polar angle and 7 cm−1 in the diamond Raman peak. The surface of diamond films was observed by atomic force microscopy. Flat domain surfaces with a root mean square roughness of 0.45 nm in 1 × 1 µm2 were obtained.

Directed Branch Growth in Aligned Nanowire Arrays

Branch growth is directed along two, three, or four in-plane directions in vertically aligned nanowire arrays using vapor-liquid-solid glancing angle deposition (VLS-GLAD) flux engineering. In this work, a dynamically controlled collimated vapor flux guides branch placement during the self-catalyzed epitaxial growth of branched indium tin oxide nanowire arrays. The flux is positioned to grow branches on select nanowire facets, enabling fabrication of aligned nanotree arrays with L-, T-, or X-branching. In addition, a flux motion algorithm is designed to selectively elongate branches along one in-plane axis. Nanotrees are found to be aligned across large areas by X-ray diffraction pole figure analysis and through branch length and orientation measurements collected over 140 μm(2) from scanning electron microscopy images for each array. The pathway to guided assembly of nanowire architectures with controlled interconnectivity in three-dimensions using VLS-GLAD is discussed.

High quality Y-type hexaferrite thick films for microwave applications by an economical and environmentally benign crystal growth technique

Thick barium hexaferrite Ba2Zn2Fe12O22 (i.e., Zn2Y) films having thicknesses of ∼100 μm were epitaxially grown on MgO (111) substrates using an environmentally benign ferrite-salt mixture by vaporizing the salt. X-ray diffraction pole figure analyses showed (00l) crystallographic alignment with little in plane dispersion confirming epitaxial growth. Saturation magnetization, 4πMs, was measured for as-grown films to be 2.51 ± 0.1 kG with an out of plane magnetic anisotropy field HA of 8.9 ± 0.1 kOe. Ferromagnetic resonance linewidth, as the peak-to-peak power absorption derivative at 9.6 GHz, was measured to be 62 Oe. These properties demonstrate a rapid, convenient, cost-effective, and nontoxic method of growing high quality thick crystalline ferrite films which could be used widely for microwave device applications.

Physical Properties of ZnSe Thin Films Depending on the Process Parameters

ZnSe thin films were grown by a co-evaporation method with various Se/Zn flux ratios. In order to characterize ZnSe thin films, we performed an investigation that utilized X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Ultra Violet–Visible-Near InfraRed (UV-VIS-NIR) measurements of the structural, optical, and morphological properties. XRD pole-figure analysis confirmed that the orientation of the ZnSe cubic (111) plane has been widely distributed throughout the ψ axis with respect to process conditions, flux rate of Se. It has been found that as long as the Se/Zn flux ratio is larger than 1.43, stable, single-phase, ZnSe thin films can be grown. Additional experimental data revealed that optical properties strongly depend on the substrate temperature and have correlation with crystallinity.

Reduced twinning efficiency and tri-dimensional crack structure in melt-textured NdBa2Cu3O7−δ bulk samples fragmentation process

Here we report on a detailed investigation on NdBa2Cu3O7−δ (Nd123) crack generation achieved by an extensive morphological and structural study on 1 cm diameter top-seeded melt-textured grown pellets, where crack development stops at an earlier stage, and on the parallelepiped fragments resulting from the spontaneous breaking of larger (3 and 5 cm diameter) pellets. In this way complementary information on the process is obtained. Sample morphology was investigated by polarized light optical microscopy, scanning electron microscopy, and atomic force microscopy, confirming that microscopic fissures and macroscopic cracks act as preferential oxygenating channels. This fact suggests that mechanical stress, generated locally by an oxygenation induced tetragonal–orthorhombic transition, is the driving mechanism for fissure evolution into cracks and their further growth. Our observations reveal that Nd123 fissure bundles have a tri-dimensional character, lying not only along the a–b plane, but also along two a–b out-of-plane perpendicular directions. Twin and fissure bundle orientations appear to differ by 45°, thus suggesting that fissures lie along a–c and/or b–c crystallographic planes. This observation was confirmed by θ–2θ x-ray diffraction and x-ray pole figure analysis (XPFA) performed on the parallelepiped fragments, which revealed that samples are single domain, with edges oriented along the principal crystallographic planes. XPFA detected a–b axes twinning in the domain on the global scale. A remarkable result achieved by electron backscattered diffraction (EBSD) is the evidence that cracking along b–c plane is preferred with respect to a–c, acting in this way as a second preferential cleavage direction. Indeed EBSD measurements show long-range ordering of a and b axes, suggesting that twinning is less effective in releasing in-plane mechanical stress in Nd123 than in parent compounds. Results are discussed on the basis of the identification of Nd–Ba cationic substitutions as the main competing relaxation mechanism. The superconducting properties of the analysed samples were studied by measuring the fragments superconducting parameters by vibrating sample magnetometry.

Biaxial texture development in aluminum nitride layers during off-axis sputter deposition

Polycrystalline aluminum nitride (AlN) layers were deposited by pulsed-dc reactive magnetron sputtering from a variable deposition angle α = 0°–84° in 5 mTorr pure N2 at room temperature. X-ray diffraction pole figure analyses show that layers deposited from a normal angle (α = 0°) exhibit fiber texture, with a random in-plane grain orientation and the c-axis tilted by 42° ± 2° off the substrate normal, yielding wurtzite AlN grains with the {101¯2} plane approximately parallel (±2°) to the substrate surface. However, as α is increased to 45°, two preferred in-plane grain orientations emerge, with populations I and II having the c-axis tilted toward and away from the deposition flux, by 53° ± 2° and 47° ± 1° off the substrate normal, respectively. Increasing α further to 65° and 84°, results in the development of a single population II with a 43° ± 1° tilt. This developing biaxial texture is attributed to a competitive growth mode under conditions where the adatom mobility is sufficient to cause intergrain mass transport, but insufficient for the thermodynamically favored low energy {0001} planes to align parallel to the layer surface. Consequently, AlN nuclei are initially randomly oriented and form a kinetically determined crystal habit exposing {0001} and {112¯0} facets. The expected direction of its highest growth rate is 49° ± 5° tilted relative to the c-axis, in good agreement with the 42°–53° measured tilt. The in-plane preferred orientation for α > 0° is well explained by the orientation dependence in the cross section of the asymmetric pyramidal nuclei to capture directional deposition flux. The observed tilt is ideal for shear mode electromechanical coupling, which is maximized at 48°.

Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents

High quality 1 μm thick a-plane MgxZn1−xO layers were produced by molecular beam epitaxy with Mg contents higher than 50%. Resonant Rutherford backscattering spectrometry combined with ion channeling revealed a uniform growth in both composition and atomic order. The lattice-site location of Mg, Zn and O elements was determined independently, proving the substitutional behaviour of Mg in Zn-sites of the wurtzite lattice. X-Ray diffraction pole figure analysis also confirms the absence of phase separation. Optical properties at such high Mg contents were studied in Schottky photodiodes.

An approach to (103) oriented YBa 2Cu 3O 7–δ thin films epitaxially grown on (100) MgO substrates

The preferred growth orientations of YBa2Cu3O7–δ (YBCO) thin films on (100) MgO substrates produced by pulsed laser deposition are reported. In particular, (103) perpendicular oriented films were successfully demonstrated. The crystallographic properties of the oriented films were examined by transmission electron microscopy and X-ray diffraction pole figure analyses, indicating a 45° tilt of the superconducting CuO2 planes relative to the substrate surface. This work provides a unique pathway to realizing the growth of (103) oriented YBCO films on highly valued electronic and microwave (100) MgO substrates.

Compression Behavior and Texture Development of Polymer Matrix Composites Based on NiMnGa Ferromagnetic Shape Memory Alloy Particles

Deformation behavior and texture development of NiMnGa ferromagnetic shape memory alloy (FSMA) particles embedded polymer composites were investigated by compression tests and X-ray diffraction pole-figure analysis (XRD-PF). Both the NiMnGa/silicone and NiMnGa/epoxy composites exhibited a characteristic three-stage deformation which is often seen in shape memory alloys due to martensite variant reorientation. XRD-PF revealed that (004) texture was developed in the compressed NiMnGa/silicone due to the retention of martensite variant reorientation. On the other hand, significant texture change was not recognized in the compressed NiMnGa/epoxy. Rearranged martensite variants was kept after unloading in silicone matrix having low Young's modulus, but reverse reorientation occurred in epoxy matrix with high Young's modulus. The rearrangement behavior of martensite variants is strongly affected by elastic properties of matrix.

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr1−xSixN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N2/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200°C and post-deposition annealing up to 1000°C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200°C growth temperature. After the annealing treatment, films with Si content x<0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x>0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000°C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100nm thick films have an average roughness <2nm, except for Si content near x=0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV–visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x>0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x<0.15), there is no band gap and the films are highly conductive.

Comparative Studies of Crystalline Orientation and Morphology of Injection Molded Polyolefin Parts

Abstract We have studied the structural characteristics of the cross-sections of injection molded parts of various crystalline polyolefins including polyethylene (PE), isotactic polypropylene (PP), isotactic poly(butene-1) (PB1) and isotactic poly(4-methylpentene-1) (P4MP1). Polarized light microscopy, birefringence and wide angle x-ray diffraction pole figure analysis were used to investigate the samples. In most cases, high orientations were observed near the mold wall and isotropic molded part cores were found. However, highly oriented mold core regions were found in P4MP1. Significantly different types of crystalline orientation near the mold wall were observed among the various polyolefins. We represent the development of these differences through the components of a crystalline orientation tensor which represent changes in the state of orientation between melts in the mold prior to crystallization and the final crystalline molded part.

Anisotropy of Longitudinal Wave Velocity and Hydroxyapatite Orientation in Bovine Cortical Bone

The anisotropy of longitudinal wave velocity and the hydroxyapatite (HAp) crystallite orientation in bovine cortical bone were experimentally investigated in detail. A ring-shaped cortical bone sample was obtained from the midshaft of a 32-month-old bovine femur. Four cylindrical specimens (diameter 11 mm) were taken from the ring-shaped cortical bone specimen along the radial direction. Velocity was measured by a conventional ultrasonic pulse system, by rotating the specimen in the axial-tangential plane. The direction of the fastest wave velocity observed was inclined 5–10° from the axial direction. The HAp crystallite orientation in the specimen was also investigated by X-ray diffraction pole-figure analysis. We observed a strong intensive peak of (0002), indicating HAp crystallite c-axis alignment along the bone axis. However, the pole-figure also revealed a small tilt in the HAp crystallite orientation from the axial direction. Comparing the velocity and X-ray diffraction peak at each angle of the axial-tangential plane, a significant correlation between the velocity and the HAp orientation was observed.

Texture formation in Ag thin films: Effect of W–Ti diffusion barriers

Pure Ag films were deposited on SiO2/Si with and without introduction of W0.7Ti0.3 barrier layers. The films were annealed in vacuum for 1 h at temperatures up to 650 °C. X-ray diffraction pole figure analysis was used to investigate the texture information in as-deposited and annealed films. After annealing, the {111} texture in Ag films increased; however, the degree of increase was significantly higher in Ag/W–Ti/SiO2. In Ag/SiO2 structures, the {200} texture also increased. In Ag/W–Ti/SiO2 structures, no significant increase in {200} texture was observed; however, {111} twin related {511} texture evolved. In as-deposited samples, {111} pole figure revealed that {111} absolute intensity was higher in Ag/SiO2 than in Ag/W–Ti/SiO2. After annealing, Ag {111} intensity was always higher in Ag/W–Ti/SiO2. Sources for the texture evolution were discussed in detail. Field emission scanning electron microscope showed the presence of twins and abnormal grain growth. After annealing at 650 °C, both the roughness and resistivity of Ag increased significantly.