Large-angle Convergent-beam Electron Diffraction Research Articles

An analysis of elementary dislocations in icosahedral Al-Pd-Mn by Large Angle Convergent-Beam Electron Diffraction (LACBED)

Large Angle Convergent Beam Electron Diffraction (LACBED) experiments on dislocations located in the mirror planes of icosahedral AlPdMn single grains show that – as previously inferred from standard image contrast technique – the direction of the Burgers vector is perpendicular to the mirror plane of movement, thus confirming the fact that climb should be an important process for the plasticity mechanisms in icosahedral quasicrystals.

Stress fields near interfaces of aluminium-based metal-matrix composites

Abstract Large-angle convergent-beam electron diffraction (LACBED) is used to investigate the interfacial strain fields in a short-fibre-reinforced Al-based metal-matrix composite. LACBED patterns are simulated using the dynamic scattering theory with local variations in the scattering vectors caused by lattice distortions. Comparison of experimental and simulated patterns permits local strains to be estimated. Thermal strains and surface relaxation of the thin foil for transmission electron microscopy are considered. Long-range thermal strains caused by the fibre overlapping with localized high strains produced by spinel grains at the fibre boundary are analysed. In Al grains, local stress concentrations are reduced by the emission of dislocations. In Si precipitates, high stresses at the Si-fibre interfaces are maintained. Short-range stresses from inhomogeneities at the Si-fibre interfaces and not the long-range thermal stresses from the whole fibres dominate in Si precipitates.

Stress fields near interfaces of aluminium-based metal-matrix composites

Abstract Large-angle convergent-beam electron diffraction (LACBED) is used to investigate the interfacial strain fields in a short-fibre-reinforced Al-based metal-matrix composite. LACBED patterns are simulated using the dynamic scattering theory with local variations in the scattering vectors caused by lattice distortions. Comparison of experimental and simulated patterns permits local strains to be estimated. Thermal strains and surface relaxation of the thin foil for transmission electron microscopy are considered. Long-range thermal strains caused by the fibre overlapping with localized high strains produced by spinel grains at the fibre boundary are analysed. In Al grains, local stress concentrations are reduced by the emission of dislocations. In Si precipitates, high stresses at the Si-fibre interfaces are maintained. Short-range stresses from inhomogeneities at the Si-fibre interfaces and not the long-range thermal stresses from the whole fibres dominate in Si precipitates.

Polarity determination of III–V compound semiconductors by large-angle convergent beam electron diffraction

The large-angle convergent beam electron diffraction (LACBED) technique is used for determining the crystal polarity of GaP and GaAs single crystals from 〈1 1 0〉 cross-sectional samples. The method which is based on an earlier approach using convergent beam electron diffraction (CBED) evaluates the polarity-sensitive contrast of high odd-index Bragg-lines in {0 0 2} dark-field patterns. The polarity is determined by application of a simple contrast rule as well as by direct comparison with dynamical simulations. For the two materials the ranges of applicability are determined by a detailed analysis of the Bragg-line contrast as a function of the sample thickness. The coexistence of the Bragg-line pattern and the of shadow image of the defect in correct rotational relationship to each other makes the analysis straightforward and free from possible sources of errors. As an example, the crystal polarity of GaP is related to the morphology of facetted voids. The LACBED method is shown to be suitable for relating the analysis of extended crystal defects. The advantages and the disadvantages of the LACBED method are discussed in comparison with the corresponding CBED method and with a recent method based on the analysis of bend contours.

Lattice strain and static disorder in hydrogen-implanted and annealed single-crystal silicon as determined by large-angle convergent-beam electron diffraction

The large-angle convergent-beam electron-diffraction technique, available in a conventional transmission electron microscope, has been employed in order to characterize the defective layer present in heavily damaged high-dose hydrogen-implanted and low-temperature annealed $(T<~500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ single-crystal silicon in terms of lattice strain and static disorder. These quantities have been measured to determine the mean relaxation volume and atomic concentration of defect clusters present in the implanted layers in order to investigate the structural features causing the reverse annealing phenomena observed in ion channeling measurements. In particular, the mean relaxation volume detected in the 300 \ifmmode^\circ\else\textdegree\fi{}C 2-h annealed sample (0.1 ${\mathrm{nm}}^{3}$) results in a factor three times higher than that measured in the as-implanted sample; on the contrary the mean atomic concentration of clusters does not vary appreciably after this thermal treatment. This experimental evidence suggests a nonconservative growth of clusters in the low-temperature annealing regime. After annealing at 500 \ifmmode^\circ\else\textdegree\fi{}C for 2h, an increase of the relaxation volume and a significant decrease of the mean concentration is found, thus suggesting that only after this thermal treatment, producing in the meantime intrinsic defects with extended internal surfaces, defects seem to follow a conservative ripening.

TEM characterisation of defects, strains and local electric fields in AlGaN/InGaN/GaN structures

This paper describes how transmission electron microscopy (TEM) can be used to study the structure and electronic properties of threading defects in GaN structures. A combination of TEM and large angle convergent beam electron diffraction (LACBED) is used to examine dislocations and nanopipes, and to show that migration of dislocations in epitaxially overgrown material is correlated to local shear strains and grain rotations. It is shown how electron holography (EH) can be used to examine in-plane electric fields, and, in particular, the charge on threading edge dislocations.

Dislocations and Slip Systems of Mantle Minerals

Research Article| January 01, 2002 Dislocations and Slip Systems of Mantle Minerals Patrick Cordier Patrick Cordier Laboratoire de Structure et Propriétés de l’Etat Solide (ESA CNRS 8008), Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq-Cedex, France Search for other works by this author on: GSW Google Scholar Author and Article Information Patrick Cordier Laboratoire de Structure et Propriétés de l’Etat Solide (ESA CNRS 8008), Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq-Cedex, France Publisher: Mineralogical Society of America First Online: 03 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2002) 51 (1): 137–179. https://doi.org/10.2138/gsrmg.51.1.137 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Patrick Cordier; Dislocations and Slip Systems of Mantle Minerals. Reviews in Mineralogy and Geochemistry 2002;; 51 (1): 137–179. doi: https://doi.org/10.2138/gsrmg.51.1.137 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search This chapter focuses on dislocations and slip systems that are responsible for the plastic flow of high-pressure mantle minerals. After briefly introducing some basic concepts on crystal plasticity, we describe some recent experimental advances of the last decade that have contributed to our understanding of the rheology of mantle minerals. Among them, we describe some progress in the achievement of deformation experiments under high pressure. A more detailed review is presented by Durham et al. (this volume). We present then a novel Transmission Electron Microscopy (TEM) technique: Large Angle Convergent Beam Electron Diffraction (LACBED), which is very well adapted to... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Strain fields at interfaces of Al-based metal matrix composites

Owing to the different thermal expansion coefficients of the phases involved, stresses are induced in metal matrix composites (MMCs). In the present study, the strain fields in MMCs consisting of an Al-based alloy containing 12wt.% Si and 4wt.% (Cu, Mg, Ni, Fe), reinforced by Fiberfrax® short fibers, are investigated by large-angle convergent beam electron diffraction (LACBED). Strain fields used to simulate the LACBED patterns are adjusted to experimental LACBED images. For these simulations the dynamical scattering theory is used. While thermally induced stresses in the Al matrix are reduced by a large number of dislocations near the fibers, these stresses are maintained in the Si precipitates. The strain fields are not homogeneously distributed around the fibers. Inhomogeneities near the fiber–matrix interfaces, 10–50 nm in extent, cause local stress concentrations. These inhomogeneous internal stresses can lead to plastic deformation of the Al matrix, to cracking of the fibers and to detachment at the matrix–fiber interfaces. The sign of the strains in the Si precipitates depends on the properties and the arrangement of the surrounding phases, whereas compressive strains perpendicular to the fiber interfaces prevail in the Al grains.

LACBED measurement of the chemical composition of a thin In xGa 1− x As layer buried in a GaAs matrix

Large angle convergent beam electron diffraction (LACBED) observations are used to determine the x indium content of a thin In x Ga 1− x As quantum well buried in a GaAs matrix. The method consists in a quantitative analysis of the Bragg line intensities lying in the central disc of any LACBED pattern. This analysis makes it possible to determine the displacement vector R introduced, between the two parts of the GaAs matrix, by the deformation of the quantum well and consequently to determine the x indium content. This indium content is found to be consistent with the value expected from the molecular beam epitaxy growth conditions.

HOLZ line analysis of lattice parameters in magnesium alloys.

A method of refining lattice parameters from deficit higher-order Laue zone (HOLZ) line data from large angle convergent beam electron diffraction (LACBED) data is presented, relying on distances between nearest neighbour intersections alone in order to minimize effects of distortion over the field of view. Use is made of a dynamical correction deltak to the fast electron wavevector k for kinematic analysis. This correction term is shown to depend on the specific HOLZ beam under consideration, as well as the zone axis and eigenvalue associated with the branch index of the relevant dispersion surface. This method is applied to analysis of data from magnesium alloys, where momentum filtering induced by the LACBED method facilitates HOLZ contrast from a relatively low index zone axis (where contrast is not detectable with conventional CBED), and contrast is enhanced at elevated temperatures from a higher index zone axis. Although the accuracy of refined lattice parameters from these sets of data is shown to be no better than 0.1%, it is felt that issues arising out of the analysis may be of some interest, particularly since these are non-ideal specimens. Full eigen-state analysis of the fast electron wavefunction is presented, and issues related to the influence of the dispersion surface on deficit HOLZ line behaviour are discussed.

Higher‐order Laue zone line contrast in large‐angle convergent‐beam electron diffraction around a dislocation

The physical picture of higher-order Laue zone (HOLZ) line contrast in a large-angle convergent-beam electron diffraction pattern around a dislocation, which is used for determining the Burgers vector, was examined. To evaluate the analytical expression of diffracted wave amplitude, we introduced an approximate form of the atomic displacement field of a dislocation. We showed that the four features of the HOLZ line contrast, that is, splitting, fading, bending and periodical contrast can be explained by analysis of the atomic displacement field. The localized lattice plane bending around a dislocation core made a HOLZ line split, fade and bend. However, we found that the periodical contrast of a HOLZ line was produced by the change of phase difference of the atomic displacement field between the crystals above and below the slip plane across the dislocation line.

Anaysis of Lacbed Patterns from A Microtwin in Cobalt

Recently LACBED (Large Angle Convergent Beam Electron Diffraction) studies for identifying the nature of stacking faults has been reported in [1,2]. Here we report the LACBED study for a microtwin whose images are usually similar to those of an intrinsic or an extrinsic stacking faults (for this discussion, see [3]).Observations: Thin foils of cobalt with the thickness of about 180 nm (f.c.c phase, a=0.354 nm) were examined by a Philips CM200. Fig. 1 shows strong beam dark field images of microtwins or stacking faults. Fig. 2 shows the bright field LACBED pattern taken near the area marked as a circle in fig. 1. The specimen height, from the convergent point of beams, was about 0.0586 mm and the convergent angle was 0.615 degrees.Calculations and analysis: Analysis of fig. 1 alone indicates the encircled fault an extrinsic stacking fault.

A study of interfacial residual stress field in a K 2O · 6TiO 2 w/Al composite by LACBED and 3-D finite element method

The interfacial residual stress field in a K 2O · 6TiO 2 w /Al composite was studied by large angle convergent-beam electron diffraction (LACBED) technique. The diffraction lines near the interface between the Al matrix and the K 2O · 6TiO 2 whisker became split and twisted when the interface was within the illuminated area. The splitting and shifting of diffraction lines provided information about spatial variation of the residual strain field in the vicinity of whisker. The displacement field near the interface, which was essential to simulation of the LACBED patterns, was calculated with three-dimensional finite element method (3D-FEM) in which the initial strain was one of the adjustable parameters. The initial strain was then determined by fitting the dynamically simulated LACBED patterns to the experimental patterns. The residual stress field in bulk specimen of K 2O · 6TiO 2 w /Al composite was calculated with the obtained initial strain, and compared with that in thin foil specimen. The factors influencing the accuracy in determining the strain/stress field with this method were discussed.

AFM, SEM, EDX and HRTEM study of the crystalline growth rate anisotropy-induced internal stress and surface roughness of YBaCuO thin film

The influence of the anisotropy of the crystalline growth rate on the microstructure and morphology of YBaCuO thin film deposited by laser ablation has been studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy dispersive X-ray (EDX) analysis. The results obtained from high resolution lattice imaging and large angle convergent beam electron diffraction (LACBED), together with the investigations of the thin film surface morphology, show the strong influence of the different crystalline growth rates on both the internal stress present in the YBaCuO film and the roughness of the outer surface. These results should be of prime importance for the superconducting properties. This is essential in tailoring these thin films for device applications.

Epitaxial stress study by large angle convergent beam electron diffraction and high-resolution transmission electron microscopy Moiré fringe pattern

Epitaxial stresses are studied by means of large angle convergent beam electron diffraction (LACBED) and Moiré fringe patterns obtained by high-resolution transmission electron microscopy in pulsed laser deposited thin films of Y–Ba–Cu–O on MgO substrate. Grains with their c-axis parallel to the interface grow from the substrate up to the outer surface of the film. These grains, embedded in the c-axis normal to the interface host matrix, are studied in cross-sectional samples, by both LACBED performed on the MgO substrate just beneath the different orientations of the thin film, and by the Moiré fringe patterns obtained by tilting the interface of the sample. The broadening of the Bragg lines present in the LACBED disk together with the direction of the Moiré fringes, clearly indicate that the c //-oriented grains embedded in a c ⊥-oriented Y–Ba–Cu–O matrix are under stress.

Measurement of charge of Cu and O in YBa 2Cu 3O y by energy-filtering convergent-beam electron diffraction

Large-angle convergent-beam electron diffraction (CBED) patterns were observed from small areas in nanometer scale in YBa 2Cu 3O y (Y123), using a new transmission electron microscope (TEM) JEM-2010FEF. An energy filter of omega type was used to subtract background intensities caused by inelastically scattered electron. Specimens were cooled with a liquid nitrogen stage to suppress thermal diffuse scattering that cannot be eliminated well by the energy filter. In order to measure specimen thickness, electron energy loss spectra were also measured from the same areas where CBED patterns were recorded. Charges of Cu and O on CuO chains and CuO 2 planes, and charge of O on Ba–O planes were determined by analyzing the intensities of CBED patterns with the dynamical theory of electron diffraction. The obtained values are Cu 2.0+ and O 1.65− on CuO chains, Cu 2.2+ and O 1.98− on CuO 2 planes and O 2.0− on BaO planes. The present results indicate that the energy-filtering CBED technique is useful for determination of charge distribution along the z-direction in Y123.

Characterization of grain-boundary dislocation networks by a combination of large-angle convergent-beam electron diffraction and weak-beam techniques

The Burgers vector of very close intrinsic dislocations in a near-Σ = 11,{311} grain-boundary in nickel is identified using a geometrical method based on local and accurate measurements of the angular deviation from perfect coincidence Σ = 11 by large-angle convergent-beam electron diffraction and of the dislocation spacing from weak-beam images of the grain boundary.

Dislocations in meteoritic and synthetic majorite garnets

Shock veins in the Acfer 90072, L5/6 (S6) chondrite contain polycrystalline fragments constituted of ringwoodite and majorite. The dislocation microstructures of the majorite crystals have been characterised by transmission electron microscopy and large-angle convergent-beam electron diffraction. Most of the dislocations form sub-grain boundaries organised in cells. Some free dislocations can be found in the cells. Dislocations with 1/2 and Burgers vectors have been characterised. These microstructures compare well with those observed in majorite synthesised from a glass in multi-anvil experiments. These observations suggest that the dislocation microstructures observed in both synthetic and meteoritic majorite result from imperfect growth.

Dynamical simulation of LACBED patterns in cross-sectioned heterostructures

The Large Angle Convergent Beam Electron Diffraction (LACBED) technique has been applied to determination of the tetragonal mismatch in coherent Si/Si 1− x Ge x /Si heterostructures. Two-dimensional (2D) dynamical simulation of the LACBED patterns has been performed and compared with the corresponding experimental ones. A good agreement is found in the whole simulated area, particularly as regards the splitting of the Bragg contours, due to the strain field present in the TEM cross-sections.

Large angle convergent beam electron diffraction strain measurements in high dose helium implanted silicon

Large angle convergent beam electron diffraction (LACBED) technique has been applied to <110> TEM cross section of silicon samples implanted with 2×1016 cm−2 He ions at an energy of 20 KeV in order to evaluate the stress/strain field in the implanted layer. The stress/strain field depends on the mismatch between the lattice of the silicon substrate and the one of the defective layer which contains clusters of point defects and small He bubbles. Lattice mismatch causes changes in the spacing and inclination of diffraction planes producing a shift and a rotation of diffraction intensity lines (Bragg contours (BC)) visible in LACBED patterns. In particular, when the electron beam is parallel to the rotation axis, the BC simply rotate. This is the case of mismatches observed with (333) BC when the electron beam is incident on the sample along a direction close to <110> zone axis. Measurements show a peak of the stress/strain field (intensity 1.5 GPa) at a depth close to the helium projected range, where small bubbles occasionally form aggregate oriented along <011> direction.