Showing papers on "Electron backscatter diffraction published in 1995"

A powder neutron diffraction determination of the structure of sr6co5o15, formerly described as the low-temperature hexagonal form of srcoo3-x

Abstract: The structure of Sr6Co5O15 is determined by Rietveld analysis of powder neutron diffraction data and identified as the low-temperature hexagonal form of SrCoO3–x.

Refinement of crystal structure parameters using convergent-beam electron diffraction: the low-temperature phase of SrTiO3

Abstract: The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.

Structural study of the close-packed two-dimensional phases of pb on ge(111) and si(111)

Abstract: The close-packed two-dimensional structures of Pb on Ge(111) and Si(111) have been studied with scanning tunneling microscopy (STM), reflection high-energy electron diffraction, and low-energy electron diffraction. Several closely-related commensurate and incommensurate phases were observed. For both adsorbate systems, schematic phase diagrams are derived and compared to the predictions of the domain-wall theory for commensurate-incommensurate phase transitions. A complex structural model is presented which describes the various incommensurate phases and is in good agreement with the STM data.

X-ray diffraction investigations of magnetron sputtered TiCN coatings

Abstract: X-ray diffraction measurements were performed on titanium carbonitride coatings produced in an electron enhanced, unbalanced magnetron system. The films were deposited onto AISI 316 stainless steel substrates with an argon background pressure in the range of 0.1 Pa. A gas mixture of nitrogen and acetylene was introduced in different ratios, which alters the carbon-to-nitrogen ratio in the coating. The composition of the film was determined by glow discharge optical emission spectroscopy and wavelength-dispersive X-ray analysis. The morphology of the films was determined by scanning electron microscopy. The peak positions, integral breadths and shape parameters were determined by X-ray diffraction, and the composition influence on these parameters was investigated. The applied X-ray diffraction methods were conventional Bragg-Brentano diffraction and also parallel beam low angle diffraction. Morphological and microstructural features are found which indicate that an increased carbon content in the film gives similar results to a decrease in bias voltage.

Texture development in Al-1.8 wt% Cu depending on the precipitation state—II. Recrystallization textures

Abstract: The development of the recrystallization texture of the alloy Al-1.8 wt% Cu was investigated by analysis of orientation distribution functions (ODF) determined by X-ray diffraction, supported by metallography and EBSD local texture analysis. In dependence on the degree of deformation, the annealing temperature and, in particular, on the precipitation state a large variety of recrystallization textures was found which could be subdivided into four characteristic types. The differences between these recrystallization texture types could be attributed to differnces in the nucleation and growth behaviour. From the present results general conclusions about the various recrystallization mechanisms occurring in aluminium alloys can be drawn.

Quantification of partially recrystallized polycrystals using electron backscatter diffraction

Abstract: A new experimental method of determining the volume fraction of recrystallized structure in a polycrystalline material has been developed. This method is based upon the comparison of electron backscatter diffraction patterns from adjacent locations in a polycrystal. Positions along a line are tested to determine whether adjacent points have the same crystal lattice orientation indicating that no dislocation structure exists between the two locations. If the distance between the two positions is relatively small, it is assured that the two points lie within a region of essentially defect-free lattice. Scanning through a region of material in this manner yields the lineal fraction of recrystallized material which directly correlates with the volume fraction. This automatic measurement eliminates the subjectivity and human error always associated with the quantitative determination of fraction recrystallized in a material.

Mosaic dislocation structures in aluminium crystals deformed in multiple slip at 0.5 to 0.8TM

Abstract: Deformation microstructures are characterised in high purity aluminium crystals deformed in multiple slip by channel die compression up to strains of 1.5, temperatures of 473 to 773 K, and strain rates of 10 −1 to 10 −3 s −1 . Four single crystal orientations are examined: three orientations corresponding to the stable rolling texture components of polycrystalline f.c.c. metals, C {112} , S {421} , and B {110} and one recrystallisation component {001} . The deformation microstructures are investigated by different techniques over a wide range of scales and the local orientations have been measured by EBSD (electron back scattered diffraction) and by CBED (convergent beam electron diffraction). The deformation microstructures are subdivided by dislocation boundaries which bound cell blocks oriented at ± 30° to ± 55° with respect to the rolling direction. The dislocation boundaries are regularly spaced in two families creating a regular structure of cell blocks whose size is very strain rate and temperature dependent. Such cell blocks are also characterised by lattice rotations of alternating sign (often about the transverse axis). For all crystals, the misorientations between adjacent blocks are of the order of 5° to 10° at e = 0.2. At strains of the order of unity, certain orientations, e.g. C and S, develop local regions of very large misorientations whereas in the B orientation the misorientations do not exceed 10°. The microstructural evolution is analysed within the framework of the LEDS hypothesis and compared to that observed at room temperature. The stability of the mosaic dislocation wall pattern is confirmed by post-deformation anneals

RMC: modelling neutron diffraction, X-ray diffraction and EXAFS data simultaneously for amorphous materials

Abstract: The simultaneous modelling of neutron diffraction, X-ray diffraction and extended X-ray absorption fine structure (EXAFS) data for a disordered material has been developed with the reverse Monte Carlo (RMC) method. The details of this technique are described and its power is highlighted by modelling four sets of experimental data simultaneously for the multi-component, amorphous fast-ion conductor (AgI)x(AgPO3)1 - x. From the resultant structural models, it is proposed that the first sharp diffraction peak observed in the diffraction data at Q ⋍ 0.7 A −1 is related to the density distribution of the phosphate network; pathways through the structure which favour Ag+ ion conduction are highlighted and a structural explanation for the material's glass formation limit at x ≈ 0.58 is proposed.

Anisotropic thermal displacements of adsorbed atoms and molecules on surfaces studied by low-energy electron diffraction

Abstract: We present a detailed account of the concept of ``split positions'' in low-energy electron diffraction (LEED). This allows us to study the dynamics of adsorbate particles on surfaces in addition to structural information usually provided by LEED. Enhanced lateral movements of adsorbed atoms and molecules are simulated by displacing them from their equilibrium position by an amount respresenting the mean-square deviation. Within the harmonic-oscillator approximation, the mean-square deviation is closely related to the eigenfrequencies of the vibrational modes which can be compared to values obtained by (standard) spectroscopic techniques. Several examples of adsorbate overlayers on metal and semiconductor surfaces will demonstrate the merits and potentiality of this approach.

Method and apparatus for identification of crystallographic defects

Abstract: An imaging apparatus (10) includes a scanning electron microscope (12) which is controlled to bombard numerous points (62) of a material sample (24) with an electron beam (18). Backscatter diffraction patterns are collected by an image collection system (26) which may include both a slower responding video camera (32) and a faster responding diode array (40). For a baseline point (62), an electron backscatter diffraction pattern collected at the video camera (32) is analyzed to identify representative pixels which reside along Kikuchi bands (78). Backscatter images from subsequent points (62) are rapidly compared (98) with the baseline to detect changes. When changes are not detected, EBSPs are not analyzed. When changes are detected, EBSPs are analyzed to generate new baselines. The resulting collection of analyzed EBSPs are processed (104) to identify microstructure attributes and to characterize defects (64).

High Resolution Low Energy Electron Diffraction Study of Flattening on the TiO 2 (110) Surface

Abstract: We investigate the thermal annealing of a ${\mathrm{TiO}}_{2}$ surface on atomic length scales using high resolution low energy electron diffraction (spot profile analysis) to measure the interface width and the lateral correlation length of a surface height function. In particular, we find the correlation length (similar to average terrace size) increases with time during annealing as ${t}^{1/4}$ at temperatures above 800 K, in agreement with predictions derived for continuous macroscopic surfaces.

Influence of the Initial Grain Size on the Rolling and Recrystallization Textures in the Alloy Al-1.8% Cu

Abstract: The influence of the initial grain size prior to deformation on the rolling and recrystallization textures is investigated in the alloy Al-l.8wt%Cu by X-ray macrotexture analysis. Two different particle stages are examined: (i) Small shearable precipitates give rise to shear band formation and, during annealing, to nucleation of recrystallization at shear bands. (ii) Large particles cause particle stimulated nucleation of recrystallization (PSN). The microstructural evolution, particularly during recrystallization nucleation, is elucidated by metallographical investigations supported by EBSD local texture analysis.Both the initial grain size and the precipitation state strongly influence the evolution of the rolling textures. The results are interpreted with the help of Taylor-type deformation models. The recrystallization textures of Al-alloys emerge from a superposition of the orientations stemming from the various nucleation sites, i.e. Cube-bands, shear bands and particles. An increase of the initial grain size prior to deformation substantially shifts the recrystallization texture from the Cube-orientation towards the orientations being attributed to the other nucleation sites (shear bands, particles) which is interpreted by the spatial density of the various nucleation sites.

Crystallization of colonies of locally aligned grains during thallination of spray-pyrolyzed tlba2ca2cu3ox thick films

Abstract: Recent microstructural studies of high‐Jc, Tl‐1223, spray‐pyrolyzed thick films have shown that the high‐Jc and reduced weak‐link behavior can be ascribed to the presence of a unique microstructure, wherein the film is divided into ‘‘colonies’’ of biaxially aligned regions In an effort to understand the nucleation and growth of Tl‐1223 as well as the formation of the colony microstructure, several sets of films quenched from various stages of the high‐temperature thallination process were examined using electron microscopy, x‐ray diffraction and electron backscatter diffraction (EBSD) It is found that the crystallization of the 1223 phase is associated with formation of a liquid phase which contains significant amounts of all oxides Furthermore, it is found that the film nucleates at the substrate on the side closest to the thallium source The growth front then moves up through the thickness and along the length of the film X‐ray microdiffraction measurements show that local biaxial alignment or the

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111): In situ observation by reflective high energy electron diffraction

Abstract: Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111) has been studied by in situ observation of reflective high energy electron diffraction combined with ex situ Auger electron spectroscopy depth profile analysis. The direct phase formed at the top surface after iron coverage has been determined to be mixture Fe3Si and Fe5Si3, FeSi, and β‐FeSi2, respectively, according to the results of different deposit temperature. Diffraction patterns as well as the depth profile for the Fe/Si ratio have been discussed.

Electron Diffraction Intensity Analysis of Amorphous Pd75Si25 Alloy Thin Film with Imaging-Plate Technique

Abstract: Atomic pair distribution function (PDF) analysis for an amorphous Pd 75 Si 25 alloy thin film has been made by means of electron diffraction intensity measurement with the help of imaging-plate (IP). This is aimed for developing a structural analysis technique using electron diffraction, which is complementary to high resolution electron microscopy (HREM) in studying amorphous alloy structures. In the diffraction intensity measurement, an intensity correction to omit the inelastic part of intensity has been performed by taking advantage of electron energy loss spectroscopy. In the PDF a subpeak for the Pd-Si correlation at the distance of 0.24 nm was clearly observed near the first mainpeak for the Pd-Pd correlation. Availability of IP in precise electron diffraction intensity measurement, therefore, has been proved. In accordance with the observed strong Pd-Si correlation and the Pd-Pd coordination number close to that of Pd 3 Si, a Pd 3 Si-like medium range order structure was clearly observed by HREM. A structure model based on the PDF and the HREM result was constructed and examined.