Mapping the composition of materials at the atomic level

1992 ◽  
Vol 50 (2) ◽  
pp. 1474-1475
Author(s):  
A. Ourmazd ◽  
F.H. Baumann ◽  
Y. Kim ◽  
C. Kisielowski ◽  
P. Schwander
Keyword(s):  
Imaging Techniques ◽  
Atomic Level ◽  
Objective Lens ◽  
Lattice Imaging ◽  
Electron Microscopic ◽  
Lattice Image ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Lattice Images ◽  
Compositional Changes

This paper briefly outlines how transmission electron microscopic lattice imaging techniques can be used to map the composition of crystalline materials at the atomic level.Under appropriate conditions, a conventional lattice image is a map of the sample structure, because the dominant reflections used to form lattice images are relatively insensitive to compositional changes in the sample. Such reflections may be termed “structural”. In many cystalline materials, compositional changes occur by atomic substitution on a particular subset of lattice sites. In these systems, compositional changes are accompanied by the appearance of reflections, which we name “chemical”. Such reflections, for example the (200) in the zinc-blende structure, owe their existence to chemical differences between the various atomic species present on the different lattice sites. For fundamental reasons these reflections are often weak; they come about because of incomplete cancellation of out of phase contributions from different sublattices. “Chemical lattice imaging” exploits dynamical scattering to maximize the intensity of such reflections, and uses the objective lens as a bandpass filter to enhance their contribution to the image.

Chemical mapping of materials at the atomic level

1991 ◽  
Vol 49 ◽  
pp. 844-845
Author(s):  
A. Ourmazd ◽  
F. Baumann ◽  
M. Bode ◽  
Y. Kim ◽  
J.L. Rouviere
Keyword(s):  
Bandpass Filter ◽  
Objective Lens ◽  
Chemical Mapping ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Zinc Blende ◽  
Lattice Images ◽  
Sample Structure ◽  
Compositional Changes ◽  
Zinc Blende Structure

Under appropriate conditions, a conventional lattice image is a map of the sample structure, because the dominant reflections used to form lattice images are relatively insensitive to compositional changes in the sample. However, certain reflections, such as the (200) in the zinc-blende structure, owe their existence to chemical differences between the various atomic species present on the lattice sites. Such chemical reflections arc sensitive to compositional changes in the sample. For fundamental reasons such reflections are often weak; they come about because of incomplete cancellation of out of phase contributions from different sublattices. “Chemical lattice imaging” exploits dynamical scattering to maximize the intensity of such reflections, and uses the objective lens as a bandpass filter to enhance their contribution to the image.

7-beam lattice images of (110) oriented Ge

1978 ◽  
Vol 36 (1) ◽  
pp. 290-291
Author(s):  
J.R. Parsons ◽  
C.W. Hoelke
Keyword(s):  
Image Features ◽  
Objective Lens ◽  
Lattice Plane ◽  
Lattice Image ◽  
Crystalline Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Structural Aspects ◽  
Beam Lattice

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.

Measuring projected potential, thickness, and composition from lattice images

1994 ◽  
Vol 52 ◽  
pp. 732-733
Author(s):  
A. Ourmazd ◽  
P. Schwander ◽  
C. Kisielowski ◽  
F. H. Baumann ◽  
Y. Kim
Keyword(s):  
Quantitative Information ◽  
Image Features ◽  
Contrast Transfer Function ◽  
Lattice Image ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Highly Nonlinear ◽  
Lattice Images ◽  
Point To Point ◽  
Image Details

Lattice images obtained by Transmission Electron Microscopy (TEM) are routinely used to infer the subsurface microstructure of crystalline materials. In principle, a lattice image is a map of the sample (Coulomb) potential, projected along a zone axis (see, e.g., [1]). In practice, it is difficult to extract quantitative information from lattice images. This stems from two primary reasons. First, electrons are multiply scattered during their passage through crystalline samples of realistic thickness (>10Å). This results in a complex, highly nonlinear relationship between the sample potential and the characteristics of the lattice image. This relationship changes rapidly with the sample thickness, and thus from point to point over the sample. Second, electromagnetic lenses have severe aberrations. The image details thus depend sensitively on the (contrast) transfer function of the microscope, and hence the lens defocus. It is not possible to establish a general relationship between the sample potential and the image features.

Application of Lattice Imaging Techniques to Amorphous Films

1975 ◽  
Vol 33 ◽  
pp. 8-9
Author(s):  
S. R. Herd ◽  
P. Chaudhari
Keyword(s):  
Nearest Neighbor ◽  
Random Network ◽  
Imaging Techniques ◽  
Network Models ◽  
Accurate Method ◽  
Direct Transmission ◽  
Lattice Imaging ◽  
Transmission Electron ◽  
Lattice Planes ◽  
Nearest Neighbor Distances

Electron diffraction and direct transmission have been used extensively to study the local atomic arrangement in amorphous solids and in particular Ge. Nearest neighbor distances had been calculated from E.D. profiles and the results have been interpreted in terms of the microcrystalline or the random network models. Direct transmission electron microscopy appears the most direct and accurate method to resolve this issue since the spacial resolution of the better instruments are of the order of 3Å. In particular the tilted beam interference method is used regularly to show fringes corresponding to 1.5 to 3Å lattice planes in crystals as resolution tests.

Quantitative Investigations of Interfaces and Grain Boundaries by Phase Contrast Electron Microscopy with Ultra High Resolution

2001 ◽  
Vol 7 (S2) ◽  
pp. 288-289
Author(s):  
C. Kisielowski ◽  
J.M. Plitzko ◽  
S. Lartigue ◽  
T. Radetic ◽  
U. Dahmen
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Phase Contrast ◽  
Recent Progress ◽  
Image Interpretation ◽  
Present Contribution ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Contrast Microscopy ◽  
Lattice Images

Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission microscope'"". A reconstruction of the electron exit wave from a focal series of lattice images converts the recorded information into interpretable resolution. The present contribution illustrates some recent applications of this technique to interfaces.Fig. 1 shows a reconstructed electron exit wave of a heterophase interface between GaN and sapphire. The experiment takes advantage of three factors: First, we resolved the GaN lattice in projection, which requires at least 0.15 nm resolution. The projection eliminates the stacking fault contrast that usually obscures lattice images in the commonly recorded projection. Thus, image interpretation is drastically simplified. Second, all atom columns at the interface and in the sapphire are resolvable with a smallest projected aluminum - oxygen spacing of 85 pm in the sapphire.

Dislocations and related defects in niobium oxide structures

1977 ◽  
Vol 352 (1670) ◽  
pp. 303-323 ◽  
Keyword(s):  
Chemical Composition ◽  
Niobium Oxide ◽  
Shear Plane ◽  
Extended Defects ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Lattice Images ◽  
Crystallographic Shear ◽  
Third Dimension ◽  
Block Structures

Lattice images of the niobium oxides, structures based on the linkage of octahedral groups in continuous networks, occasionally contain features recognizable as dislocations. Since lattice imaging enables the micro-structure to be resolved in great detail, at the level of local structural organization, it is possible to determine the configuration, and also to infer the chemical composition, of dislocated areas. By treating the niobium oxide ‘block’ structures as superstructures of the ReO 3 (DO 9 ) type, the topology of dislocations can be expressed by relations between the insertion (or deletion) of one or more half-planes of cations, or of oxygen atoms only, changes in the number of crystallographic shear plane interfaces between blocks or columns, changes in (idealized) dimensions and any requisite distortion in the third dimension. Mapping the structure around a dislocation, from the lattice image, is directly equivalent to plotting the Burgers’ circuit. In this way, the precise nature of a dislocating perturbation and its implications for the local chemical composition of the crystal can be directly identified. The method is exemplified by analysis of dislocations and of related extended defects of several types, associated with twinning phenomena, semicoherent intergrowth between different ReO 3 -type superstructures and arrays building up a low angle boundary. The essential features of the analysis are not restricted to structures of the niobium oxide type, but can be extended to other types of polyhedron networks.

scholarly journals Lattice Image Contrast of Ordered Domains in Cu3Au

1974 ◽  
Vol 32 ◽  
pp. 500-501
Author(s):  
R. Sinclair ◽  
G. Thomas
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Crystal Lattice ◽  
Fine Scale ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Transmission Electron ◽  
Radiation Induced ◽  
Considerable Controversy ◽  
Lattice Planes

Although lattice Imaging was one of the first techniques in transmission electron microscopy of crystals, only with the improved resolution (≃2Å) of modern microscope has it become possible to obtain the lattice Image of metals as a matter of routine. To date fine-scale phenomena in alloys have been studied principally by relating the distortion of the fringe image to the defect in the crystal lattice ﹛e.g. dislocation, radiation induced damage, G-P zones etc. (2)﹜ but considerable controversy exists as to the validity of interpreting the fringes in terms of a one-to-one correspondence with the lattice planes in the specimen. One of the areas of research so Ear unexplored by this technique is the study of ordering reaction is alloy. The present paper demonstrates how it is particularly useful in this field especially in avoiding the controversy associated with the interpretation of fringe distortions.

Lattice Images at θ’ Precipitates in Al-3%Cu Alloy

1975 ◽  
Vol 33 ◽  
pp. 272-273
Author(s):  
V. A. Phillips
Keyword(s):  
Imaging Technique ◽  
Phase Identification ◽  
Lattice Imaging ◽  
Electron Microscopic ◽  
Cu Alloy ◽  
Solution Treated ◽  
Intermediate Phases ◽  
Resolution Electron ◽  
Slice Orientation ◽  
Lattice Images

As part of a high resolution electron microscopic study of the precipitation sequence at 130°C in aluminum - 3% copper alloy, we studied G. P. [1], G. P. [2] or θ”, and θ’ precipitates by the lattice imaging technique. This approach proved valuable for phase identification and distinction. Examples of cros sed-lattice and c-plane lattice images at θ’ platelets will be presented here.Slices were spark cut nearly parallel to {001} from a melt-grown single crystal of aluminum -3.0 wt. % copper, previously solution treated at540°C and water quenched. Slices were aged at 130°C in argon and hand ground. Discs were chemically, electrolytically or in one case ion thinned, and examined at 100 kV in a slightly modified Philips EM 300 microscope.In the aluminum-copper system, the intermediate phases (G. P. zones and θ’) separate parallel to cube matrix planes, so that the slice orientation chosen resulted in two sets of platelets being parallel and one set normal to the beam.

scholarly journals Optical Microdiffraction in Lattice Image Analysis

1976 ◽  
Vol 34 ◽  
pp. 494-495 ◽  
Author(s):  
R. Gronsky ◽  
R. Sinclair ◽  
G. Thomas
Keyword(s):  
Structural Transition ◽  
Optical Diffraction ◽  
Image Simulation ◽  
Optimum Conditions ◽  
Lattice Imaging ◽  
Lattice Image ◽  
Thin Foils ◽  
Transmission Electron ◽  
Metallurgical Analysis

Our applications of lattice imaging to the study of phase transformations in alloys have recently incorporated laser optical techniques to improve microdiffraction capabilities by three orders of magnitude over that attainable in conventional transmission electron microscopy (1). The method is based on optical diffraction from lattice image negatives which have been taken under optimum conditions dictated by computed image simulation. In this paper we present the optical microdiffraction data of two experiments to illustrate the role of this technique in metallurgical analysis.1)Recent observations (2) in Mg3 Cd have revealed the occurrence in thin foils of a structural transition: hexagonal DO19 →orthorhombic B19. In orientations where the Mg3Cd basal plane is parallel to the foil surface, selected area diffraction (S.A.D.) analysis fails to distinguish these phases.

Lattice Imaging of Grain Boundary Precipitation Reactions

1977 ◽  
Vol 35 ◽  
pp. 116-117
Author(s):  
R. Gronsky ◽  
G. Thomas
Keyword(s):  
Grain Boundary ◽  
Materials Science ◽  
Transformation Products ◽  
Lattice Imaging ◽  
Research Division ◽  
Transmission Electron ◽  
Boundary Precipitation ◽  
Compositional Changes ◽  
Grain Boundary Precipitation ◽  
Lattice Planes

Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Materials Science and Mineral Engineering, University of California, Berkeley, California 94720.Grain boundaries are known to catalyze a wide variety of solid state phase transformations which drastically affect metallurgical properties. The study of these reactions has traditionally required transmission electron microscopy, particularly when the transformation products are only partially developed. In the present paper, an application of lattice fringe imaging to the study of grain boundary reactions in Al-Zn alloys is described. The technique has proven to be far superior to conventional TEM methods in providing information on not only the detailed structural configuration of lattice planes at boundaries, but also the compositional changes, to within ∽10Å of the boundary plane, accompanying the transformations.

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