Showing papers on "Electron backscatter diffraction published in 1992"

Automatic analysis of electron backscatter diffraction patterns

Abstract: The ability to measure lattice orientation in individual crystallites enables a more complete characterization of microstructure by combining lattice orientation with morphological features. Lattice orientation can be obtained by analyzing electron backscatter diffraction patterns (EBSPs). However, current computer-aided EBSP analysis techniques make it impractical to obtain the number of measurements needed for statistically reliable characterizations of microstructure. An effective fully automated technique for determining crystallographic orientation from EBSPs is described. Bands are identified by linear regions of correlation in the image intensity gradient direction. The most probable orientation is then found using the angles between the detected bands. The reliability of the technique was tested using a set of 1000 patterns obtained from annealed oxygen-free electrical grade (OFEC) copper. The orientation of each test pattern found using automatic indexing was checked against the corresponding orientation as determined by manual indexing. Ninety-nine percent of auto-indexed orientations were found to lie within 5 deg of the misorientation angle of the manual-indexed orientations. By simulating noise in the test patterns, it was found that image quality has a strong effect on the reliability of the technique. An image quality parameter is described which allows the reliability of the technique to be predicted for a pattern of given quality.

The Study of Surface Structures by Photoelectron Diffraction and Auger Electron Diffraction

Abstract: A knowledge of the atomic identities, positions, and bonding mechanisms within the first 3–5 layers of a surface is essential to any quantitative microscopic understanding of surface phenomena. This implies knowing bond directions, bond distances, site symmetries, coordination numbers, and the degree of both short-range and long-range order present in this selvedge region. A number of surface-structure probes have thus been developed in recent years in an attempt to provide this information.1 Each of these methods has certain unique advantages and disadvantages, and they are often complementary to one another.

Identification of a growth defect in solid C60 by electron diffraction

Abstract: The origin of an anomalous sawtooth-shaped feature in x-ray powder diffraction of solid C60 is explained via electron diffraction analysis Films sublimed on holey carbon crystallize with close-packed (111) planes parallel to the surface Rods of diffuse scattering are found along the 〈111〉 axis normal to the surface but not along other 〈111〉 axes Powder averaging of these rods, coupled with the x-ray form factor of spherical shells with 35 A radius, accounts for the sawtooth feature We attribute this phenomenon to planar defects parallel to close-packed layers, which form during the growth of solid C60 by sublimation A possibly related consequence of the growth mode is the observation of strong macroscopic (111) preferred orientation in films sublimed on a variety of substrates

The crystal structure analysis of deuterated benzene and deuterated nitromethane by pulsed-neutron powder diffraction: a comparison with single crystal neutron diffraction analysis

Abstract: The results of time-of-flight neutron powder diffraction analyses at 4.2 K are compared with those from steady-state neutron single-crystal analyses at 15 K for deuterated benzene, C 6 D 6 , and deuteronitromethane, CD 3 NO 2 .

Structural characterization of cadmium selenide thin films by X-ray diffraction and electron microscopy

Abstract: X-ray diffraction, transmission electron microscopy and transmission electron diffraction studies on cadmium selenide thin films deposited on glass substrates have been carried out. X-ray line profile analysis of the diffraction panems has been performed to study the microstructural parameters. The variation of different microstructural parameters. such as crystallite size, RMS strain. dislocation density and stacking fault probability with film thickness as well as substrate temperature is studied. The optimum growth condition is fixed to a film thickness of the order of 1 .Opm. The change of preferred orientation is observed for films deposited at and above 473 K. 0

Phase Transitions in C60 and the Related Microstructure : A Study by Electron Diffraction and Electron Microscopy

Abstract: The phase transition in C60 and (related) lattice defects are studied by low-temperature electron microscopy and electron diffraction. The microstructure of the room-temperature face-centered-cubic (fcc-a0) phase is very similar to that of a low stacking fault energy fcc alloy; micro twins and stacking faults on the {111} planes are the main defects. The phase transition fcc-a0 ⇒ simple cubic (sc) at 249 K, is confirmed by single-crystal diffraction and the space group of the sc phase was unambiguously determined from the systematic extinctions as Pa3¯. Moreover a second phase transition, sc ⇒ fcc-2a0, is discovered. It occurs at a slightly lower temperature. It is suggested that in the sc phase the molecules still have a rotational degree of freedom about their respective rotation axis, of which the orientation pattern is already fixed by the Pa3¯ space group. In the fcc-2a0 phase the rotation angle is found to be frozen in and to alternate between +φ and -φ along the directions. The domain structure of the sc phase consists of eight variants (four translation variants for each of the two orientation variants) present in rather ill-defined regions. As a consequence of the ease of rotation of the molecules, no sharp interfaces are formed between different orientation domains.

Crystalline modifications of lineartrans-quinacridone pigments

Abstract: Different crystalline structures of lineartrans-quinacridone were prepared and analysed by combination of X-ray diffraction, specific surface areas, optical and scanning electron microscopy, infrared spectroscopy, spectrophotometric analysis and differential thermal analysis. The lattice parameters of each crystalline phase were determined by X-ray diffraction. A new crystalline phase of this pigment was obtained and named theς-phase. Isothermal crystallization studies indicated that the crystallographic texture induced by pressure has a strong influence on the crystallization behaviour of this dyestuff.

Transmission electron microscopy study of order-disorder phenomena in non-stoichiometric LaNi5+x and LaNi6-xCux electrode materials

Abstract: High-energy electron diffraction, X-ray powder diffraction and high-resolution electron microscopy have been used to investigate the crystallographic properties of non-stoichiometric LaNi5+x (0≤ × ≤0.4) and LaNi6-xCux (0≤ × ≤3.0) electrode materials, which are based on the CaCu5 structure type. Structural aspects with respect to Ni/Cu rich deviations from the exact AB 5 stoichiometry are studied. X-ray powder diagrams show only the basic CaCu5 diffraction lines without any superstructure lines, and are therefore interpreted in terms of random substitutions of A atoms (La) by dumbbell pairs of B atoms (Ni/Cu) oriented along the c axis, thereby leading to a contraction and expansion of the lattice in the a and c direction, respectively. The observation of diffuse scattering in electron diffraction, which is located on a specific geometry in diffraction space, reveals that a large amount of the substitutions of A atoms by B 2 dumbbells occur in a partially ordered manner. High-resolution electron mi...

Structural properties of ZnSxSe1−x thin films on GaAs (1 1 0) substrate

Abstract: Deposition and structural characterization of lattice-matched ZnS x Se1−x (x=0.056) films on GaAs (1 1 0) and glass substrates by a new chemical growth technique have been investigated by transmission electron microscopy and X-ray diffraction, including low-angle X-ray diffraction, at different temperatures. Electron diffraction examination has revealed that ZnS x Se1−x films exhibit an amorphous nature when deposited at room temperature, and at 90 °C the films are polycrystalline with a large grain size. X-ray diffraction and morphology showed that the growth of the crystallite size increased with increasing solvent temperature. The chemical data from X-ray fluorescence confirm the enhancement of sulphur content at the interface and also establish the composition.

Structural study on C60 material

Abstract: The crystal structure and defect structures of C60 material have been studied by means of X-ray diffraction, high-resolution electron microscopy and electron diffraction. The diffraction measurements show that the C60 crystal has the face-centered cubic (fcc) structure with lattice parameter a=1.42 nm. High-resolution electron microscopy observations, combined with the analyses of selected area electron diffraction, indicate that the coherent twins situated in the {111} planes frequently appear in the C60 crystal. The disordered stacking along the 〈111〉 direction and other kinds of defects appearing in the new material have also been investigated. Upon in situ cooling and heating from 130 K to 700 K, the structural stability of the C60 crystal has been observed.

Medium-energy electron diffraction from Cu(100).

Abstract: We have investigated the polar-angle dependence of medium-energy electron diffraction (MEED) from a Cu(100) surface. It is observed that MEED is characterized by a combination of coherent and incoherent scattering, and the incoherent part is governed by the forward-scattering mechanism. The incoherent MEED pattern differs from that of x-ray photoelectron diffraction and Auger electron diffraction because of the angular distribution of the initial electron scattering. The asymmetry between the incident-beam and exit-beam diffraction is also observed and discussed.

Powder X-Ray Diffraction Data for Ca2Bi2O5and C4Bi6O13

Abstract: Single crystals and powder samples of Ca2Bi5O5and Ca4Bi6O13have been synthesized and studied using single crystal X-ray diffraction as well as X-ray and neutron powder diffraction. Unit cell dimensions were calculated using a least squares analysis that refined to a δ2θof no more than 0.03°. A triclinic cell was found with space group , a = 10.1222(7), b = 10.1466(6), c = 10.4833(7) A. α= 116.912(5), β= 107.135(6) and γ= 92.939(6)°, Z = 6 for the Ca2Bi2O5compound. An orthorhombic cell was found with space group C2mm, a = 17.3795(5), b = 5.9419(2) and c = 7.2306(2) A, Z = 2 for the Ca4Bi6O13compound.

An electron diffraction and microscopy investigation of quasi-periodic Ta-Al superlattices

Abstract: Quasi-periodic (Fibonacci sequence) Ta-Al multilayer films were fabricated by magnetron sputtering, and studied by electron and X-ray diffraction. Eleven orders of electron diffraction satellite spots were obtained. Their positions and intensities were in good agreement with the data from X-ray diffraction, and both were in excellent agreement with the theoretical positions predicted by the projection method, k = 2πD −1(n + mτ). Transmission electron microscope studies of the thin film cross-sections showed the well-formed layered structures of Fibonacci sequence Ta-Al superlattices. The films have textures with Ta [110] and Al [111] in the growth direction, and coherent stacking in the quasi-periodic multilayers.

Bragg-surface three-beam dynamical X-ray diffraction

Abstract: Three-beam diffraction with a symmetric Bragg reflection and a surface diffraction is studied based on the dynamical theory of X-ray diffraction. The difficulty involved in the boundary conditions for the surface diffraction is overcome by treating the Bragg–surface diffraction as either a Bragg–Laue or a Bragg–Bragg case with the inclination angle α between the crystal surface and the surface-diffracted beam being very small, about 10−5 rad. The geometry of the dispersion surface, the number of permitted modes of wave propagation, the linear absorption coefficient, the excitation of the beam and the diffracted intensity are calculated for the Ge (000) (222) (31\overline 1) Bragg–surface diffraction of Cu Kα1. It is found that the calculated relative integrated intensity ratio among the Bragg–surface 31\overline 1 case and the Bragg–Bragg 113 and 51\overline 1 cases is in good agreement with the integrated intensity ratio obtained experimentally.

High-resolution transmission electron microscopy of (1212) Bi-cuprate superconductor materials

Abstract: Powders as well as ion-thinned compressed powder specimens in the form of pellets are investigated by 300 keV high-resolution transmission electron microscopy and selected area electron diffraction techniques. They reveal, as the majority and superconducting phase, an oxide with the bulk composition Bi0.5Cu0.5Sr2Y0.8Cu2.2O6.9, as previously determined. High-resolution electron micrographs are compared with contrast simulation, based on the dynamical theory of electron diffraction. This comparison reveals the position of the metal atoms within the unit cell. The lattice parameters of the tetragonal unit cell, consistent with previous X-ray measurements, are a = 3.75 ± 0.08 A and c = 11.53 ± 0.2 A , as measured in selected area electron diffraction patterns. The crystal structure deduced from the high-resolution micrographs corroborates the 1212-structure type suggested on the basis of X-ray powder data (Ehmann et al., 1992). The material is virtually free of planar defects.

Superstructures in YBa2Cu3O6+x compounds by neutron and X-ray diffraction

Abstract: In a single crystal of YBa 2 Cu 3 O 6.35 we determined an oxygen superstructure with a 2√2 a X2√2 a cell by neutron diffraction. A 2√2 a X√2 a superstructure of a monodomain has been found by X-ray diffraction. In YBa 2 Cu 3 O 6.4 of T c =38K, we observed a short range ordered ortho-II structure by neutron single crystal diffraction.

Abnormal grain growth in textured FeAl intermetallics

Abstract: Abnormal grain growth has been observed in powder processed, hot extruded, B2 FeAl alloys which display significant wire textures. This study uses X-ray inverse pole figures and electron backscatter diffraction patterns to examine the relationship between the texture and this abnormal grain growth. Texture analysis has been performed on samples heat treated at various temperatures both above and below the critical temperature for abnormal grain growth initiation. The powder processed samples initially have a strong «111a wire texture which is generally retained after heat treatments of up to 1000 °C. At heat treatments of 1050 °C and higher this texture disappears and instances of abnormal grain growth are observed. In contrast to the powder alloys, abnormal grain growth has not been observed in cast and extruded FeAl alloys. Backscattered Kikuchi patterns have been used to determine the micro-texture of the alloys so that the relationship between the initial wire texture and the abnormal grain growth may be examined. The results of the texture and micro-texture analysis are discussed in light of current theoretical models for grain growth.

Neutron diffraction studies of the structure of PEEK

Abstract: Neutron fibre diffraction has been used to determine the orientation of phenyl rings with respect to the polymer backbone in poly (aryl-ether-ether-ketone) (PEEK). Results obtained from this study indicate that the orientation of the phenyl ring differs by 7° from the previously accepted value based on X-ray fibre diffraction studies.

Low-temperature neutron diffraction study of reh5(pphipr2)2(sihph2)2 and low-temperature x-ray diffraction study of reh5(pcyp3)2(sih2ph)2

Abstract: Crystals of bis[diisopropyl(phenyl)phosphine]bis(diphenylsilyl)pentahydridorhenium [ReHs(pPhipr2)2 (SiHPh2)2] (I) grow as transparent prisms from nhexane in the space group P1. Mr = 946.38, a = 11.879(1), b =16.754(1), c =12 .637(1)A, a 96.824(3), /3=116.169(3), y=87 .313(4 ) °, U = 2238.8 (6) ]k 3 (15 K), Z = 2, Dx = 1.41 g cm -3 (293 K), A = 1.3168 A (thermal neutrons; Ge monochromator), Iz = 2.74 cmi , F(000) = 208 × 1013 cm, R = 0.072 (3160 reflections used). Crystals of pentahydridobis(phenylsilyl)bis(tricyclopentylphosphine)rhenium [ReHs(PCyp3)E(SiHzPh)2] (II) grow from n-hexane as transparent prisms in the space group P212121. Mr = 882.38, a = 12.448 (2), b = 17.579 (4), c = 19.433 (4) A, U = 4252 (3)/k 3 (200 K~), Z = 4, Dx = 1 .36gcm -3 (293 K), A =0.71073 A (X-rays: Mo Ka; graphite monochromator), Iz = 30.2 cmi , F(000) = 1832.0, R=0.041 (6014 reflections used). For (I), the Re P bond lengths and P R e P bond angle are 2.444 (8), 2.444 (7)A and 141.2 (3) °, and the Re---Si bond lengths and Si--Re---Si bond angle are 2.500 (8), 2.510 (9) A and 117.9 (3) °. For (II), the corresponding lengths and angles are 2.439(1), 2.444 (1) A, 139.5 (1) ° and 2.501 (2), 2.490 (2) A, 97.9 (1) °. The closest intramolecular contact between hydride ligands in (I) is 2.002 (29)A, and that * Author to whom correspondence should be addressed. Present address: Department of Chemistry, University of Durham, Durham DHI 3LE, England. 0108-7681/92/040438-07506.00 between a hydride ligand and a silicon atom is 2.048 (13) A.