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.

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.

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.

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.

High-resolution transmission electron microscopy: A structural and chemical probe of semiconductor systems

1987 ◽  
Vol 45 ◽  
pp. 332-333
Author(s):  
A. Ourmazd
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Structural Information ◽  
Image Interpretation ◽  
Lattice Image ◽  
Semiconductor Interfaces ◽  
Transmission Electron ◽  
Lattice Images ◽  
The Individual

High Resolution Transmission Electron Microscopy (HRTEM) is now a powerful probe for the structural analysis of semiconductor systems. Lattice images can be obtained in a number of orientations, in at least three of which the individual atomic columns can be resolved. However, there exits an important class of problems, whose resolution requires chemical as well as structural information. The identification of individual atomic columns in compound semiconductors, and the atomic configuration of semiconductor/semiconductor interfaces are two important examples.In general, most reflection used to form a lattice image are not particularly sensitive to chemical changes in the sample. The information content of a typical lattice image is therefore strongly dominated by structural details. On the other hand, reflections such as the (200), which are normally forbidden in the diamond structure, come about in the zinc-blende system because of the chemical differences between the occupants of the two sublattices, and are thus highly chemically sensitive. In the “kinematical” thickness region, where simple image interpretation is possible, such reflections are relatively weak and their contribution to the lattice image is dominated by the stronger and chemically insensitive, allowed reflections.

Primitive clay precursors formed on feldspar

1987 ◽  
Vol 24 (3) ◽  
pp. 506-527 ◽  
Author(s):  
Kazue Tazaki ◽  
W. S. Fyfe
Keyword(s):  
Major Element ◽  
Depth Profiling ◽  
Original Structure ◽  
Lattice Image ◽  
Reactive Iron ◽  
Transmission Electron ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Clay Layers ◽  
Clay Formation

High-resolution transmission electron microscopy of clay formation on K-feldspar has revealed the existence of intermediate states between feldspar and crystalline clay products. During the earliest weathering stages of K-feldspar, a primitive clay precursor forms on the feldspar surface that is spotted by ion oxides. This reactive iron is incorporated into the primitive clay precursors, which have an ultrathin 150–200 Å (1 Å = 0.1 nm) circular form and 14–20 Å lattice images or long, curled fiber forms with varied lattice image spacings. The electron diffraction patterns of primitive clay precursors show diffuse rings at 2.65, 2.04, and 1.51 Å, suggesting low crystallinity, random orientation, and partial inheritance of the original structure. EDX step scanning analysis showed that the major-element concentrations of Si, Al, and K tend to decrease from unaltered parts to altered parts of precursors with substantial increase in Fe. Auger depth profiling showed the thickness of the primitive clay layers is 150–300 Å. The primitive clay precursors may well precede formation of spheroidal particles of halloysite, squat cylinders of halloysite or hexagonal crystalline, and tabuler halloysite (7 Å). SEM, XRD, SIMS, and SAM data support the TEM results.

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

Scanning Transmission Microscopy Applied to Thick Specimen

1972 ◽  
Vol 30 ◽  
pp. 452-453
Author(s):  
H. Koike ◽  
T. Matsuo ◽  
K. Ueno ◽  
M. Suzuki
Keyword(s):  
Psoas Muscle ◽  
Image Intensifier ◽  
Chromatic Aberration ◽  
Image Contrast ◽  
Transmission Microscopy ◽  
Crystalline Materials ◽  
Thick Specimen ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Microscope Image

Since the identification of single atoms was achieved by Crewe et al, scanning transmission microscopy has been put into pratical use. Recently they applied this method to the quantitative mass analysis of DNA.As pointed out previously the chromatic aberration which decreases the image contrast and quality, does not affect a scanning transmission image as it does a conventional transmission electron microscope image. Thus, the STEM method is advantageous for thick specimen. Further this method employs a high sensitive photomultiplier tube which also functions as an image intensifier. This detection method is effective for the observation of living specimens or easily damaged specimens. In this respect the scanning transmission microscope with high accelerating voltage is necessary.Since Uyeda's experiments of crystalline materials, many workers have been discussed how thick specimens can be observed by CTEM. With biological specimens, R. Szirmae reported on the decrease in the image contrast of rabbit psoas muscle sections at various accelerating voltages and specimen thicknesses.

Comparison of Techniques for EELS Mapping in Biology

1996 ◽  
Vol 54 ◽  
pp. 300-301
Author(s):  
R.D. Leapman ◽  
S.B. Andrews
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Image Data ◽  
Beam Current ◽  
Quantitative Information ◽  
Acquisition Time ◽  
Uniform Thickness ◽  
Electron Dose ◽  
Array Detectors ◽  
Transmission Electron

Elemental mapping of biological specimens by electron energy loss spectroscopy (EELS) can be carried out both in the scanning transmission electron microscope (STEM), and in the energy-filtering transmission electron microscope (EFTEM). Choosing between these two approaches is complicated by the variety of specimens that are encountered (e.g., cells or macromolecules; cryosections, plastic sections or thin films) and by the range of elemental concentrations that occur (from a few percent down to a few parts per million). Our aim here is to consider the strengths of each technique for determining elemental distributions in these different types of specimen.On one hand, it is desirable to collect a parallel EELS spectrum at each point in the specimen using the ‘spectrum-imaging’ technique in the STEM. This minimizes the electron dose and retains as much quantitative information as possible about the inelastic scattering processes in the specimen. On the other hand, collection times in the STEM are often limited by the detector read-out and by available probe current. For example, a 256 x 256 pixel image in the STEM takes at least 30 minutes to acquire with read-out time of 25 ms. The EFTEM is able to collect parallel image data using slow-scan CCD array detectors from as many as 1024 x 1024 pixels with integration times of a few seconds. Furthermore, the EFTEM has an available beam current in the µA range compared with just a few nA in the STEM. Indeed, for some applications this can result in a factor of ~100 shorter acquisition time for the EFTEM relative to the STEM. However, the EFTEM provides much less spectral information, so that the technique of choice ultimately depends on requirements for processing the spectrum at each pixel (viz., isolated edges vs. overlapping edges, uniform thickness vs. non-uniform thickness, molar vs. millimolar concentrations).

Flux-pinning-related defect structures in melt-processed YBa2Cu3O7-x

1993 ◽  
Vol 51 ◽  
pp. 936-937
Author(s):  
Z. L. Wang ◽  
R. Kontra ◽  
A. Goyal ◽  
D. M. Kroeger ◽  
L.F. Allard
Keyword(s):  
Volume Fraction ◽  
Local Density ◽  
Stacking Faults ◽  
Image Resolution ◽  
Defect Structures ◽  
Atomic Structures ◽  
Transmission Electron ◽  
Point Image ◽  
Related Defect ◽  
Point To Point

Previous studies of Y2BaCuO5/YBa2Cu3O7-δ(Y211/Y123) interfaces in melt-processed and quench-melt-growth processed YBa2Cu3O7-δ using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) have revealed a high local density of stacking faults in Y123, near the Y211/Y123 interfaces. Calculations made using simple energy considerations suggested that these stacking faults may act as effective flux-pinners and may explain the observations of increased Jc with increasing volume fraction of Y211. The present paper is intended to determine the atomic structures of the observed defects. HRTEM imaging was performed using a Philips CM30 (300 kV) TEM with a point-to-point image resolution of 2.3 Å. Nano-probe EDS analysis was performed using a Philips EM400 TEM/STEM (100 kV) equipped with a field emission gun (FEG), which generated an electron probe of less than 20 Å in diameter.Stacking faults produced by excess single Cu-O layers: Figure 1 shows a HRTEM image of a Y123 film viewed along [100] (or [010]).

Automatic analysis of Kikuchi diffraction patterns

1994 ◽  
Vol 52 ◽  
pp. 900-901
Author(s):  
H. Weiland ◽  
D. P. Field
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Spatial Resolution ◽  
Relevant Information ◽  
Crystalline Materials ◽  
Large Size ◽  
Transmission Electron ◽  
New Type ◽  
Diffraction Patterns ◽  
Orientation Determination

Recent advances in the automatic indexing of backscatter Kikuchi diffraction patterns on the scanning electron microscope (SEM) has resulted in the development of a new type of microscopy. The ability to obtain statistically relevant information on the spatial distribution of crystallite orientations is giving rise to new insight into polycrystalline microstructures and their relation to materials properties. A limitation of the technique in the SEM is that the spatial resolution of the measurement is restricted by the relatively large size of the electron beam in relation to various microstructural features. Typically the spatial resolution in the SEM is limited to about half a micron or greater. Heavily worked structures exhibit microstructural features much finer than this and require resolution on the order of nanometers for accurate characterization. Transmission electron microscope (TEM) techniques offer sufficient resolution to investigate heavily worked crystalline materials.Crystal lattice orientation determination from Kikuchi diffraction patterns in the TEM (Figure 1) requires knowledge of the relative positions of at least three non-parallel Kikuchi line pairs in relation to the crystallite and the electron beam.

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