Microdiffraction in Dedicated STEM

1981 ◽  
Vol 39 ◽  
pp. 356-357
Author(s):  
D.C. Houghton
Keyword(s):  
Diffraction Pattern ◽  
Crystal Orientation ◽  
Low Cost ◽  
Zone Axis ◽  
Phase Identification ◽  
Sequential Methods ◽  
Considerable Promise ◽  
Diffraction Patterns ◽  
Cu Foil

Microdiffraction in dedicated STEM instruments has shown considerable promise as a source of microanalytical information. A major problem has been the relatively inefficient sequential methods used to obtain the diffraction pattern. The apparatus shown schematically in Fig. 1 has facilitated parallel viewing and recording of diffraction patterns in the HB5 STEM. The equipment is robust, low cost and can be installed with no modifications to the microscope.A series of diffraction patterns were recorded under identical conditions at a (110) zone axis in an Al-4% Cu foil shown in Fig. 2(a) to allow direct comparison of sequential and parallel recording methods. The thickness in this part of the foil was ∼220 nm as measured from the projected widths of θ' plates. The selected area “rocking beam” images in Figs. 2(b) and (d) are clearly noisy, suffer from scan distortions and their usefulness for phase identification and crystal orientation is severely limited.

Determination of crystal orientation by a zone axis method application to grain boundaries

1978 ◽  
Vol 36 (1) ◽  
pp. 426-427 ◽  
Author(s):  
A. Rocher ◽  
C. Fontaine
Keyword(s):  
Crystal Orientation ◽  
Zone Axis ◽  
Coordinate Frame ◽  
In Situ Method ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
Diffraction Patterns ◽  
Better Than

Several methods (1 → 3) have been proposed in order to determine by transmission electron microscopy (TEM) the orientation relationship between the crystal and the electron beam. The same type of method (4) has been used to find the orientation of a bicrystal. The most accurate ones (better than 0.1°) are based on the measurement of the relative position of Kikuchi lines with respect to diffraction spots. Such analysis are performed on diffraction pattern micrographs. The aim of the present work is to develop for TEM an in situ method for determination of the crystal orientation with respect to the goniometer coordinate frame, avoiding any analysis of the diffraction micrographs. The diffraction patterns used for this characterization are associated to the zone axis of the crystal. The method consists in plotting on the same stereographic projection the coordinate frame of the goniometer stage and the <100> axis of the crystal. These axis are determined from experimental indexation of three zone axis.

Multislice calculation of Kikuchi patterns

1989 ◽  
Vol 47 ◽  
pp. 52-53
Author(s):  
G. Y. Fant
Keyword(s):  
Diffraction Pattern ◽  
Point Defects ◽  
Crystal Orientation ◽  
Spherical Wave ◽  
Forward Direction ◽  
Zone Axis ◽  
Crystal Symmetry ◽  
Line Pattern ◽  
Inelastic Event ◽  
Diffuse Background

The diffraction of the inelastically and pseudo-elastically scattered electrons in a crystal gives rise to the diffuse background in a diffraction pattern, including Kikuchi patterns as they are known, which are very sensitive to the direction of electron incidence relative to the crystal orientation. In the exact zone orientation, i.e., when the electrons are travelling along a major zone axis, a Kikuchi-band pattern is formed which reflects the crystal symmetry about that axis; otherwise, the pattern is known as Kikuchi-line pattern (thereafter collectively referred to as K-patterns).For localized inelastic events, such as interactions of incident electrons with shell electrons and various crystal point defects, in which intra-process coherence is negligible, the K-patterns can be simulated using the method described below.An inelastic event creates a spherical wave which, however, is strongly peaked in the forward direction of electron traveling, as given by the typical form f(θ)e-kr/r, where symbols have their usual meanings.

Automatic indexing of rotation diffraction patterns

1988 ◽  
Vol 21 (1) ◽  
pp. 67-72 ◽  
Author(s):  
W. Kabsch
Keyword(s):  
Diffraction Pattern ◽  
Crystal Orientation ◽  
Group Symmetry ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters ◽  
Initial Errors ◽  
Approximate Unit ◽  
Diffraction Patterns

A method is described which assigns indices to a set of single-crystal reflections recorded by the rotation-oscillation technique using a fixed X-ray wavelength. It is assumed that the space group and approximate unit-cell parameters are known. The unknown crystal orientation is determined directly from the observed diffraction pattern of one or several oscillation data records. A local indexing procedure is described which tolerates large initial errors in the parameters controlling the diffraction pattern. These parameters are refined subsequently, thereby satisfying the constraints imposed by the space-group symmetry.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

The Morphology and Crystallography of Diesel Particulate Emissions

1981 ◽  
Vol 39 ◽  
pp. 148-149
Author(s):  
R. Stevenson
Keyword(s):  
Diffraction Pattern ◽  
Carbon Films ◽  
Particulate Emissions ◽  
Diesel Particulate ◽  
Amorphous Carbon Films ◽  
Turbostratic Carbon ◽  
Diesel Particles ◽  
Tem Mode ◽  
Exhaust Stream ◽  
Diffraction Patterns

A study has been made of the morphology and crystallography of particulate emissions from indirect injection diesel engines. This particulate matter consists substantially of carbon (although hydrocarbons can be extracted with solvents). Samples were collected in a diluted exhaust stream on amorphous carbon films and examined in a JEM-200C electron microscope operated in the TEM mode with an accelerating voltage of 200 KV.The morphology of the diesel particles, as shown in Fig. 1, markedly resembles carbon blacks and consists of an agglomeration of quasispherical subunits arranged in chains or clusters. Only limited changes in morphology were observed as the number of subunits in the particle increased (although larger particles tended to be more cluster-like than the extended chain shown in Fig. 1). However, a dramatic effect of the number of subunits was observed on the character of the diffraction pattern. Smaller particles yielded a diffraction pattern consisting of very diffuse rings typical of turbostratic carbon; the diffraction patterns from the larger particles, however, although qualitatively similar, exhibited much sharper and less diffuse ring patterns.

TEM study of lanthanum aluminate

1990 ◽  
Vol 48 (4) ◽  
pp. 1060-1061
Author(s):  
C.Y. Yang ◽  
Z.R. Huang ◽  
Y.Q. Zhou ◽  
C.Z. Li ◽  
W.H. Yang ◽  
...  
Keyword(s):  
Domain Boundary ◽  
Point Group ◽  
Optical Microscope ◽  
Dark Field ◽  
Zone Axis ◽  
Superconducting Film ◽  
Ion Milling ◽  
Lanthanum Aluminate ◽  
Ring Diameter ◽  
Diffraction Patterns

Lanthanum aluminate(LaAlO3) single crystal as a substrate for high Tc superconducting film has attracted attention recently. We report here a transmission electron microscopy(TEM) study of the crystal structure and phase transformation of LaAlO3 by using Philips EM420 and EM430 microscopes. Single crystals of LaAlO3 were investigated first by optical microscope. Stripe-shaped domains of mm size are clearly seen(Fig.1a), and 90° domain boundary is also obvious. TEM specimens were prepared by mechanical grinding and polishing followed by ion-milling.Fig.lb shows μm size stripe domains of LaAlO3. Convergent beam electron diffraction patterns (CBED) from single domain were taken.Fig. 2a and Fig. 2c are [001] zone axis patterns which show a 4mm symmetry, and the (200) dark field of this zone axis gives 2mm symmetry(fig.2b). Therefore the point group of this crystal is either 4/mmm or m3m. The projection of the first order Laue zone(FOLZ) reflections on zero layer (fig. 2c) shows that the unit cell is face centered. A tetragonal unit ceil is chosen, with a=0.532nm and c=0.753nm, c being determined from the FOLZ ring diameter.

Determination of hydrogen ordering within the β-RH2+xphase (R= Ho, Y) using electron diffraction techniques

2000 ◽  
Vol 33 (5) ◽  
pp. 1246-1252 ◽  
Author(s):  
Elizabeth J. Grier ◽  
Amanda K. Petford-Long ◽  
Roger C. C. Ward
Keyword(s):  
Electron Diffraction ◽  
Neutron Scattering ◽  
Diffraction Pattern ◽  
Computer Simulations ◽  
Fluorite Structure ◽  
Long Range Order ◽  
Hydrogen Atoms ◽  
Ordered Structures ◽  
Diffraction Patterns

Computer simulations of the electron diffraction patterns along the [\bar{1}10] zone axes of four ordered structures within the β-RH2+xphase, withR= Ho or Y, and 0 ≤x≤ 0.25, have been performed to establish whether or not the hydrogen ordering could be detected using electron diffraction techniques. Ordered structures within otherRH2+x(R= Ce, Tb) systems have been characterized with neutron scattering experiments; however, for HoH(D)2+x, neutron scattering failed to characterize the superstructure, possibly because of the lowxconcentration or lack of long-range order within the crystal. This paper aims to show that electron diffraction could overcome both of these problems. The structures considered were the stoichiometric face-centred cubic (f.c.c.) fluorite structure (x= 0), theD1 structure (x= 0.125), theD1astructure (x= 0.2) and theD022structure (x= 0.25). In the stoichiometric structure, with all hydrogen atoms located on the tetrahedral (t) sites, only the diffraction pattern from the f.c.c. metal lattice was seen; however, for the superstoichiometric structures, with the excess hydrogen atoms ordered on the octahedral (o) sites, extra reflections were visible. All the superstoichiometric structures showed extra reflections at the (001)f.c.c.and (110)f.c.c.type positions, with structureD1 also showing extra peaks at (½ ½ ½)f.c.c.. These reflections are not seen in the simulations at similar hydrogen concentrations with the hydrogen atoms randomly occupying theovacancies.

scholarly journals Spatial Resolution in ACOM - What Will Come After EBSD

2008 ◽  
Vol 16 (1) ◽  
pp. 34-37 ◽  
Author(s):  
R.A. Schwarzer
Keyword(s):  
Grain Boundaries ◽  
Spatial Resolution ◽  
Crystal Orientation ◽  
High Sensitivity ◽  
Polycrystalline Materials ◽  
Phase Identification ◽  
Specific Level ◽  
Orientation Microscopy ◽  
Orientation Contrast ◽  
Phase Discrimination

Automated Crystal Orientation Microscopy (ACOM) on a grain specific level has proved to be an invaluable new tool for characterizing polycrystalline materials. It is usually based on scanning facilities using electron diffraction , due to its high sensitivity and spatial resolution, but also attempts have been made which rely upon X-ray or hard synchrotron radiation diffraction. The grain orientations are commonly mapped in pseudo-colors on the scanning grid to construct Crystal Orientation Maps (COM), which represent “images” of the microstructure with the advantage of providing quantitative orientation contrast. In a similar way, misorientations across grain boundaries, Σ values of grain boundaries, or other microstructural characteristics are visualized by mapping the grains in the micrograph with specific colors. The principal objectives are the determination of quantitative, statistically meaningful data sets of crystal orientations, misorientations, the CSL character (Σ) of grain boundaries, local crystal texture (pole figures, ODF, MODF, OCF) and derived entities, phase discrimination and phase identification.

Microstructure and Creep Properties of Selected Gravity Casting Magnesium Alloys

2016 ◽  
Vol 682 ◽  
pp. 372-379
Author(s):  
Tomasz Rzychoń
Keyword(s):  
Magnesium Alloys ◽  
Creep Resistance ◽  
Low Cost ◽  
Xrd Analysis ◽  
Phase Identification ◽  
Creep Tests ◽  
Gravity Casting ◽  
Creep Properties ◽  
Transmission Electron ◽  
Primary Crystals

In this paper microstructure and creep properties of Mg-Al-Ca-Sr, Mg-Zn-RE-Zr and Mg-Sn-Si gravity casting magnesium alloys are presented. The microstructure was characterized using light microscopy, scanning and transmission electron microscopy. Phase identification was made by SAED and XRD analysis. Creep tests were carried out in the temperature range from 180°C to 200°C at applied stress of 60 MPa. Microstructure of Mg-Al-Ca-Sr alloys composed of α-Mg grains and C36, C15 and C14 intermetallic compounds in the interdendritic regions. In case of Mg-Zn-RE-Zr alloys the dominant intermetallic compound is (Mg,Zn)12RE phase also located in the interdendritic regions. Microstructure of Mg-Sn-Si alloys after T6 heat treatment consists of plate-like precipitates of Mg2Sn phase, primary crystals of Mg2Si phase and globular Mg2Si phase. Among the alloys in this study, the low-cost Mg-5Al-3Ca-0.7Sr alloy has the best creep resistance. The other alloys, excluding the Mg-5Si-7Sn alloy, are characterized by a poorer creep resistance in compared to Mg-5Al-3Ca-0.7Sr alloy, however their creep resistance is better if compared to typical Mg-Al alloys. Creep resistance of Mg-5Si-7Sn alloy is very low.

Sign in / Sign up

Export Citation Format

Share Document