Bruker D8 Discover Research Articles

Effects of indium composition on the surface morphological and optical properties of InGaN/GaN heterostructures

PurposeThis study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures.Design/methodology/approachThe InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368 sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples.FindingsThe InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements.Originality/valueIt can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.

In-situ strain- and temperature-control X-ray micro-diffraction analysis of nickel–titanium knitted architectures

The reversible phase transformation between B2 austenite phase and B19’ martensite phase is the governing mechanism behind the exciting active and passive capabilities of Nickel–Titanium (NiTi) knitted architectures. NiTi knitted architectures are manufactured from a monofilament fiber of originally-straight NiTi wire that is bent into an interlocking network of adjacent loops. Depending on the thermo-mechanical load path, NiTi knitted architectures can provide excellent isothermal energy-absorption using the superelastic effect (SE) or function as large-deformation actuators that respond to thermal inputs using the shape memory effect (SME). The magnitude of NiTi knitted architecture characteristic performance metrics is dependent on the ability of the knitted architecture to undergo the reversible phase transformation, which is a function of the material stresses, strains, and temperature. This research quantifies the NiTi knitted architecture austenite phase fraction of the highly stressed filament surface in X-ray diffraction experiments as a function of the measurement position on the knitted loop and applied thermo-mechanical loading conditions. A Bruker D8 Discover 2D micro-diffractometer was equipped with a custom tensile straining- and temperature-control device. The Direct Comparison Method was employed to derive the austenite phase fraction from the X-ray diffraction patterns. This research establishes novel in-situ strain- and temperature-control X-ray micro-diffraction experiments and provides understanding of the governing deformation modes in NiTi knitted architectures.

Microstructure and Residual Stresses of AA2519 Friction Stir Welded Joints under Different Heat Treatment Conditions.

The aim of this research was to investigate the effect of different heat treatment conditions of AA2519 friction stir welded joints on their microstructure and residual stresses. The following welding parameters have been used: 500 rpm tool rotation speed, 150 mm/min tool traverse speed, tool tilt angle 2°, pressure force 17 kN. The welded material was investigated in three different configurations: HT0, HT1, and HT2. The first type of weld (HT-0) was made using AA2519 alloy in non-precipitation hardened state and examined in such condition. The second type of weld (HT-1) has been performed on AA2519-T62, that corresponds to precipitation hardening condition. The last type of weld (HT2) was performed on annealed AA2519 and the obtained welds were subjected to the post-weld precipitation hardening process. The heat treatment was carried out in two stages: solution heat treatment (530 °C/2 h + cooling in cold water) and aging (165 °C/1 0 h). Residual stresses were measured using X-Ray diffraction patterns obtained from Bruker D8 Discover X-ray diffractometer utilizing the concepts of Euler cradle and polycapillary primary beam optics. The conducted research indicates that the best material properties: homogenous microstructure and uniform distribution of microhardness and compressive state of residual stresses were obtained for the HT-2 series samples subjected to heat treatment after the friction stir welding (FSW) process.

Microstructure Evolution and Texture Development in a Cu-8.5%AT. AL Material Subjected to Hydrostatic Extrusion

AbstractThe aim of the present paper was to investigate microstructure and texture evolution of two single crystals and polycrystal of Cu-8.5%at.Al material. All of mentioned samples were deformed by HE to achieve true strain ε = 1.17. For microstructure analyzes observations by transmission electron microscope (STEM) were done. Crystalline size for samples after SPD were determine using XRD method. The global texture measurements were done using Bruker D8 Discover diffractometer equipped in Cr radiation. Microstructure investigations revealed nanocrystalline structure in single crystals with initial orientations <110> and <100> and polycrystalline Cu-8.5%at.Al material after SPD. The global texture measurements have shown the stability of initial orientation of <100> Cu-8.5%at.Al single crystal after HE, whereas the same SPD process strongly brakes up the orientation <110> Cu-8.5%at. Al single crystal.

On the use of an external reference sample in the X-ray diffraction analysis of epitaxial layers

The differences in the high-resolution X-ray patterns for measurement of the crystal-lattice constant with and without the use of an external reference sample are discussed. The calculation procedures in the measurement of the lattice constant are compared. The results of the measurements of a Si(111) test crystal using a Bruker D8 Discover diffractometer are presented, and the examples of the use of this crystal as an external reference are described.

Application of a pseudomorphous layer on a vicinal substrate as a test sample for high-resolution X-ray diffractometry

A procedure whereby a pseudomorphous layer on a vicinal substrate is used as a test sample for high-resolution X-ray diffractometry is discussed. An algorithm for calculating the angles between the layer- and substrate-induced peaks according to the substrate-cut deviation and the sample composition, which are known under mechanical-equilibrium conditions of the system, is proposed and illustrated by examples. It is demonstrated that the given sample enables us to control the accuracy of the measured angles of reflection from the layer to within 0.0005°. Two examples are investigated in detail. The first is an AlGaAs/GaAs(001) + 2.5° layer for which the calculations are compared with published experimental data. The second is a GaAs:Te/GaAs(001) + 4° structure measured by means of a Bruker D8 Discover diffractometer.

Grain size measurement from two-dimensional micro-X-ray diffraction: Laboratory application of a radial integration technique

Two-dimensional X-ray diffraction data contain information about not only the type of mineral phases present in an assemblage, but also the textural or grain size relationships between minerals in a sample. For minerals within a certain grain size range, ~0.1 to 100 μm, the appearance and characteristics of a Debye ring can reveal the mean grain size of a sample. In this contribution, using mineral and rock samples of known grain size ranges, we investigate the applicability of calculating the grain size of a material using a two-dimensional X-ray diffraction crystallite size analysis method for micrometer-sized materials. A radial integration technique was used to derive the number of grains contributing to produce diffraction spots in the Debye ring. Monomineralic pyroxene and magnetite samples of known grain size ranges were analyzed, and the calculated grain size was observed to broadly correlate with the sample size except at the upper and lower extremes. To evaluate the technique on broader geological materials, polymineralic basalt samples with known grain size ranges were analyzed, and the calculated grain sizes did not correlate with the size of the rock fragments, but did correlate closely with the size of the individual mineral grains. Using a Bruker D8 Discover X-ray diffractometer with a 300 μm nominal incident beam diameter, the effectiveness of the applied method appeared limited to the grain size range of ~15–63 μm for monomineralic samples. The method is further limited by several complicating factors and assumptions, including the requirement for the crystallite size to correlate with the sample grain size. The effective range of this method will vary with different instrumental and experimental conditions. When applying this method to calculate the grain size of geological materials, the calculated result should be interpreted as a minimum estimate of the grain size.

Temperature Dependent Magnetic and Structural Properties of Ni-Mn-Ga Heusler Alloy Glass-Coated Microwires

In last years, Ni-Mn-X Heusler alloys have attracted significant attention because of number of their functional properties. Ni-Mn-Ga glass-coated microwires (MWs) have a good prospects for new generation technical applications [1]. We investigated magnetic and structural properties of the Ni-Mn-Ga MWs fabricated by Tailor-Ulitovsky method. MWs with total diameter of 54.6 and 24.7 µm and the diameter of metallic core of 26.7 and 8.3 µm, respectively, were obtained. Energy dispersive spectrometer (Oxford Instr. X-Act) was used to detect composition of the metallic core of as-cast and annealed MWs. Magnetic moment versus temperature (-196-77 C) measurements and hysteresis loops were obtained by VSM (Lakeshore 7400 system). X-Ray diraction (using Bruker D8 Discover in temperature range of -100-350 C) and magnetic temperature measurements reveal martensitic transition in the samples near the room temperature.

A temperature-controlled sample stage for in situ micro-X-ray diffraction: Application to Mars analog mirabilite-bearing perennial cold spring precipitate mineralogy

A temperature-controlled sample stage with an operational range of ~60 °C above or below ambient laboratory temperature (~ −35 to 85 °C) was constructed for in situ X-ray diffraction of minerals and materials using a Bruker D8 Discover diffractometer with θ-θ geometry. The stage was primarily designed for characterizing mirabilite-bearing samples from a Mars analog High Arctic perennial cold spring at an in situ temperature. Operation of the stage was demonstrated through the analysis of a synthetic sample of the hydrated sodium sulfate, mirabilite (Na 2 SO 4 ·10H 2 O). Mirabilite was held at −25 °C for approximately two hours without significant dehydration and then incrementally warmed to ambient laboratory temperature at 5 °C intervals, during the acquisition of in situ diffraction data. At ambient laboratory temperature, the mirabilite dehydrated and only polycrystalline thenardite (Na 2 SO 4 ) remained. Preliminary analysis of the cold spring precipitates demonstrates that when mirabilite is present in the sample the dehydration reaction is occurring between collection and analysis at ambient laboratory temperature. This temperature-controlled stage was designed for versatility and ease of X-ray access, with applications that can extend to many geological and planetary settings, including Mars analog environments.

An Estimate of the Uncertainty of Measurements of Lattice Spacings in Silicon Single Crystals Using a Laboratory x-Ray Diffractometer

An estimate of the uncertainty of the results of measurements of the lattice spacing in silicon using the Bruker D8 DISCOVER laboratory diffractometer and a standard NIST SRM-2000 sample is given.

Microstructure and Deposition Relations in Alumina Particle Strengthened Ni-W Matrix Composites

The nanostructured Ni-W/Al2O3 composite coatings were prepared by electrodeposition technique on ferritic steel substrates from aqueous electrolyte solutions containing ultrafine alumina particles in suspension. The effects of plating parameters like current density, inert particle concentration in plating bath and ultrasonic field frequency on the incorporation of α-Al2O3 particles (TM-DAR Taimicron) into an Ni-W matrix were investigated. The MMC coatings microstructure, phase and chemical composition were studied by means of scanning (E-SEM FEI XL-30) and transmission (TECNAI G2 SuperTWIN) electron microscopies, as well as XRD measurements (Bruker D8 Discover). SEM and TEM observations of composite cross-section microstructure showed that the presence of ultrasounds considerably reduces the particles agglomeration and enables a uniform distribution of particles in the Ni-W matrix. The electron diffraction pattern analysis revealed that the composite metallic matrix consists of an α-Ni(W) solid solution. The matrix was characterized by quasifibrous, nanocrystalline grains of an average size about 10 nm.

XRD characterisation of composite Ni-based coatings prepared by electrodeposition

The present work is aimed at XRD investigation of structural parameters that influence the functional properties of Ni–W/Al2O3 electrodeposit coatings. The relationship between electrodeposition parameters and structural properties of the coatings deposited on steel substrates has been determined. XRD investigations were performed on a Bruker D8 Discover diffractometer equipped with a position-sensitive linear detector. The modified sin2ψ X-ray diffraction method was used to determine the macroscopic residual stresses of deposits. The crystallite size and lattice strain of the coatings were evaluated by analysis of X-ray diffraction patterns (Rietveld analysis). The crystallographic texture was analysed using the orientation distribution function (ODF) calculated from the incomplete pole figures. It was shown that the structural properties of the deposits were strongly correlated with chemical composition. X-ray diffraction patterns of all Ni–W coatings exhibit mainly the fcc phase structure of the Ni–W solid solution with a lattice parameter intermediate between those of Ni and W, which rises when the tungsten content increases. At the same time the crystallite dimension (the size of the coherent domains) was gradually reduced. It was found that Ni–W coatings containing about 40wt.% W revealed the tensile residual stresses (2300–1200MPa), depending on deposition conditions.

1 + 1 = 3: Coupling μ-XRD2 and DTA New insights in temperature-dependent phase transitions

The article shows how additional information can be obtained from coupling a self constructed DTA-system with a commercially available BRUKER D8 DISCOVER GADDS XRD2-microdiffractometer. The dehydration process of gypsum to anhydrite in the temperature range from room temperature up to 723 K is used as an example. Due to the short measurement times of 10 s for each diffraction pattern the three phase transformations from gypsum to anhydrite (anhydrite II) via the hemihydrate bassanite, a water-free bassanite structure (γ-anhydrite, anhydrite III) were resolved in detail by recording the thermal signal and the diffraction pattern simultaneously. To the best of our knowledge, this is the first observation of a completely reversible dehydration/rehydration process of the bassanite/γ-anhydrite-structure around 373 K which is studied by coupled XRD and differential thermal analysis (DTA) measurements.

XRD Investigation of Residual Stresses in Electron Beam Deposited Pt-V Coatings

Platinum and platinum alloys, due to their good electrical and mechanical properties, are commonly used in fields such as jewellery, catalysis and electronics. In this work, a two-layer system of Pt and V, deposited on Si substrates by electron beam deposition technique, were investigated amongst others for residual stress development in the coating. The investigation was carried out using diffraction techniques employing laboratory X-rays on the BRUKER D8 Discover instrument equipped with a High Star detector and analyzed with LEPTOS v6 software. The results showed the stress state to be tensile, relaxing significantly on annealing. In addition, complementary results of phase composition, and coating morphology will also be presented.

Fast XRD2 Microdiffraction with Focusing X‐Ray Microlenses

AbstractThe advantages using specially designed X‐ray‐polycapillary microlenses with spot sizes of 50 μm to 200 μm in a commercially available BRUKER D8 DISCOVER GADDS XRD2‐microdiffractometer with a standard sealed X‐ray tube instead of a microfocus source are shown and compared to commercially available pin hole collimators or monocapillary optics.The application of a focusing X‐ray microlens instead of a monocapillary optic with similar spot size leads to an increase of the primary beam flux by a factor of approximately 10 to larger than 100 depending on the additional pinhole used at the exit of the microlens. This additional pinhole can be used to optimize the beam geometry for a better peak profile without additional changes on the setup. Therefore the use of a focusing X‐ray microlens instead of a mono capillary optic reduces the measurement time by at least a factor of 10. A factor up to 200 is possible by simple changing the diameter of the exit pinhole – for the price of a wider peak profile. Due to the similar housing the focusing X‐ray microlens fits in the standard collimator support enabling switching between collimators, mono‐capillaries and the microlens without realignment. This is why no time consuming modification of the microdiffractometer is needed.

New statistical calibration approach for Bruker AXS D8 Discover microdiffractometer with Hi-Star detector using GADDS software

An additional statistical calibration for the Bruker D8 Discover microdiffractometer is necessary to obtain accurate reproducible 2θ data for cell-refinement work. This new approach uses a graphical mapping method of the 2θ error versus the location of a selected diffraction peak on the detector surface to describe the separate roles of different calibration procedures (rebiasing, flood field, and spatial corrections) and parameters (sample-to-detector distance, x-y center coordinate) in minimizing the error. Optimized parameters are used to obtain the lowest achievable Δ2θ with this setup. Intensity error relative to the position of the diffracted line on the detector was found to be consistent at up to 20% and could not be reduced using any of the investigated techniques and parameters.

Micro X-ray diffraction (µXRD): a versatile technique for characterization of Earth and planetary materials

Recent developments in laboratory-based micro X-ray diffraction (µXRD) have extended X-ray examination of geomaterials to the microscopic level (50–500 µm), greatly expanding the applicability of XRD to mineralogy, petrology, materials, environmental, and planetary sciences. Laboratory-based µXRD has been accomplished using a Bruker™ D8 Discover diffractometer, having a sealed-tube Cu source, theta–theta geometry, Gobel mirror parallel optics with 50–500 µm collimation, and general area detector diffraction system (GADDS). A wide range of samples, including polished thin sections, electron probe microanalysis (EPMA) mounts, rock slabs, whole rocks, and powders have been examined with µXRD using a remote-controlled XYZ sample stage, with imaging by optical microscope monitor and charge-coupled device (CCD) camera. Individual grains in heterogeneous samples have been examined in situ, with little or no sample preparation. The two-dimensional GADDS preserves textural and crystallinity information (e.g., bioapatite) and easily discriminates between multiple phases of utility for synthetic or natural samples (e.g., mine tailings). In situ µXRD of minerals preserves spatial relationships, enabling study of orientational phenomena, such as strain-related mosaicity (giving “streaked” diffraction lines). Examples include strained quartz (La Malbaie quartzite, Quebec) and shocked clinopyroxenes (Shergottite NWA 3171). Mineral mapping has been demonstrated by reproducing exsolution textures of kamacite from taenite (Widmanstätten pattern) in the Toluca iron meteorite. Diffraction data obtained from single crystals (by the omega scan method) have enabled grain-by-grain correlation between unit cell (µXRD) and chemical composition (EPMA), as demonstrated by kimberlite indicator garnets. The examples shown herein demonstrate the breadth of information that can be obtained by µXRD of Earth and planetary materials.

Rietveld refinement of LaB6: data from µXRD

The Rietveld method of crystal structure refinement was an important breakthrough, allowing crystal structural information to be obtained from powder diffraction data. One remaining challenge is to collect Rietveld-quality data for polycrystalline mineralsin situ, using laboratory-based micro X-ray diffraction (µXRD) techniques. Here a new data collection method is presented, called `multiframes', which produces high-quality data, suitable for Rietveld refinement, using the Bruker D8 DISCOVER micro X-ray diffractometer. 91 frames of two-dimensional X-ray diffraction data were collected for powdered NIST SRM 660 LaB6standard material, using a general area-detector diffraction system (GADDS), at intervals of 0.8° 2θ. For each frame, only the central 1° 2θ was integrated and merged to produce a diffraction profile from 17 to 90° 2θ. Rietveld refinement of this data usingTOPAS2gave a unit-cell parameter (ao) and atomic position of boron (x) for LaB6of 4.1549 (1) Å and 0.1991 (9), respectively (Rwp= 4.26,RBragg= 3.21). The corresponding La—B bond length was calculated to be 3.0522 Å. These parameters are in good agreement with the literature values for LaB6. These encouraging results suggest that Rietveld-quality micro X-ray diffraction data can be collected from the Bruker D8 DISCOVER diffractometer, provided that the GADDS detector is stepped in small increments, for each frame only the central 1° 2θ is integrated at constant arc length, and counting time is sufficient to yield adequate intensity (∼10 000 counts).