Simulating the fine structure in HRTEM images of defects

1990 ◽  
Vol 48 (4) ◽  
pp. 448-449
Author(s):  
M. J. Mills
Keyword(s):  
Structural Information ◽  
Memory Capacity ◽  
Atomic Scale ◽  
Formation Theory ◽  
Crystalline Defects ◽  
Essential Step ◽  
Transmission Electron ◽  
Properties Of Materials ◽  
Image Simulations ◽  
Image Formation Theory

The macroscopic properties of materials are often determined by the atomic structure of crystalline defects. High resolution transmission electron microscopy (HRTEM) enables the study of internal defects on the atomic scale. Image simulations represent an essential step in these studies since it is generally not possible to deduce the atomic positions near defects directly from the image intensities. Fortunately, image simulations which employ the multislice method and incorporate image formation theory for partially coherent illumination offer an accurate means of simulating images. With the availability of faster computers with larger memory capacity, the routine calulation of images of aperiodic defects is now feasible. This discussion will focus on the use of image simulations to extract structural information at defects, and to account for the artifacts which are frequently encountered in these studies.

Trends in Atomic Resolution Electron Microscopy

1994 ◽  
Vol 332 ◽  
Author(s):  
David J. Smith ◽  
M.R. Mccartney
Keyword(s):  
Electron Microscopy ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Operating Conditions ◽  
Atomic Scale ◽  
Irradiation Damage ◽  
Image Recording ◽  
Exit Surface ◽  
Resolution Electron ◽  
Image Simulations

ABSTRACTStructural information on the atomic scale is readily accessible from thin samples using the technique of high-resolution electron microscopy. Electron micrographs recorded under well-defined operating conditions can be directly interpreted in terms of atomic arrangements around defects of interest such as dislocations and interfaces. Digital image recording with slow-scan CCD cameras and quantitative comparisons with image simulations based on structural models are starting to lead to improved accuracy and reliability in structure determinations. Techniques based upon holographic methods are utilizing the superior illumination coherence of the field emission electron source to enhance resolution beyond the conventional extended Scherzer limit. Innovative methods for combining image and diffraction pattern information are also leading to improved levels of resolution for periodic objects. Care is needed to ensure that electron irradiation damage and surface cleanliness do not impose unnecessary restrictions on the details that can be extracted from recorded micrographs. It is proposed that the complex wavefunction emerging from the exit-surface of the sample should be considered as a basis for comparing the differences between experimental micrographs and image simulations.

Plasticity at Crack Tips in Zr-Based Bulk Metallic Glasses

2000 ◽  
Vol 644 ◽  
Author(s):  
Jing Li ◽  
Xiaofeng Gu ◽  
Li-Qian Xing ◽  
Ken Livi ◽  
T. C. Hufnagel
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Metallic Glasses ◽  
Fourier Transforms ◽  
Structural Information ◽  
Dark Field ◽  
Atomic Scale ◽  
Partial Explanation ◽  
Transmission Electron

AbstractWe have examined the structure of plastic deformation zones ahead of the tips of microcracks in Zr-based bulk metallic glass Zr57Ti5Cu20Ni8Al10. We have used an axially aligned dark field transmission electron microscopy technique, with the objective aperture placed to form images using electrons from several different areas of the diffraction patterns. We also compared Fourier transforms of the high resolution transmission electron microscopy images of deformed and undeformed regions to extract additional structural information. The plastic zones produce enhanced low-angle scattering of electrons and an apparent broadening of the amorphous halo, suggesting increased disorder and the presence of voids in the deformed zones. These results are consistent with an increased degree of atomic-scale disorder and enhanced free volume in highly deformed regions, which may provide a partial explanation of the manner in which plastic deformation occurs in metallic glasses.

scholarly journals Effects of He-D Interaction on Irradiation-Induced Swelling in Fe9Cr Alloys

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6669
Author(s):  
Haibiao Wu ◽  
Zhen Wang ◽  
Te Zhu ◽  
Qiu Xu ◽  
Baoyi Wang ◽  
...  
Keyword(s):  
Nuclear Energy ◽  
Positron Annihilation Spectroscopy ◽  
Atomic Scale ◽  
Nanometer Scale ◽  
Energy Materials ◽  
Helium Bubbles ◽  
Helium Atoms ◽  
Vacancy Clusters ◽  
Transmission Electron ◽  
Properties Of Materials

The atomic-scale defects such as (deuterium, helium)-vacancy clusters in nuclear energy materials are one of the causes for the deterioration of the macroscopic properties of materials. Unfortunately, they cannot be observed by transmission electron microscopy (TEM) before they grow to the nanometer scale. Positron annihilation spectroscopy (PAS) has been proven to be sensitive to open-volume defects, and could characterize the evolution of the size and concentration of the vacancy-like nanoclusters. We have investigated the effects of He-D interaction on the formation of nanoscale cavities in Fe9Cr alloys by PAS and TEM. The results show that small-sized bubbles are formed in the specimen irradiated with 5 × 1016 He+/cm2, and the subsequent implanted D-ions contribute to the growth of these helium bubbles. The most likely reason is that helium bubbles previously formed in the sample captured deuterium injected later, causing bubbles to grow. In the lower dose He-irradiated samples, a large number of small dislocations and vacancies are generated and form helium-vacancy clusters with the helium atoms.

Quantitative HREM analysis of planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 720-721
Author(s):  
Hong Zhang ◽  
L. D. Marks ◽  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
...  
Keyword(s):  
High Pressure ◽  
Atomic Scale ◽  
Structure Model ◽  
Hrem Image ◽  
Ion Milling ◽  
Planar Defects ◽  
Infinite Layer ◽  
Transmission Electron ◽  
Best Fit ◽  
Image Simulations

Planar defects in the infinite-layer (Sr1-xCax)1-yCuO2 structure (planar CuO2 sheets separated by single Sr and Ca cations) have been suggested to be responsible for superconductivity with Tc up to about 110K. It is therefore important to understand the details of these defects at the atomic scale. In this work, we have used high resolution transmission electron microscopy to identify these defects and χ2 minimizations to best fit the experimental images; an optimized structure model from these studies is proposed.Thin samples of the infinite layer superconductor with the nominal chemical formula (Sr1-xCax)1-y CuO2 (x=0 and 0.3; y=0.9, 1.0 and 1.1) synthesized by high pressure treatment were prepared using a combination of mechanical polishing, dimpling and ion milling techniques. Through focal (10 nm steps) [100] HREM images of the defects (Fig. 1) were obtained on a 300kV Hitachi H-9000 microscope. HREM image simulations were carried out using NUMIS software and these were quantitatively compared against the experimental images using conventional χ2 minimizations with SEMPER software.

An Ultra-High-Resolution Objective Lens for a 200-kV TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 132-133
Author(s):  
J.G. Bakker ◽  
P.E.S. Asselbergs
Keyword(s):  
High Resolution ◽  
Structural Information ◽  
Spherical Aberration ◽  
Atomic Scale ◽  
Objective Lens ◽  
High Resolution Imaging ◽  
X Ray ◽  
Transmission Electron ◽  
High Resolution Tem ◽  
Resolution Imaging

High resolution TEM imaging has been well established as superb technique for obtaining structural information about materials on an atomic scale. Trends in equipment for high resolution imaging have progressed to the stage where point resolutions below 2 Å can be obtained at 200 kV. This paper describes such a new objective lens for the Philips CM20 Transmission Electron Microscope.In designing a new objective lens, several parameters have to be taken into account. Not only should the coefficient of spherical aberration of the objective lens be minimised, the lens should also allow considerable tilting of the specimen in two directions. The lens should be compatible with X-ray analysis. And last but not least, the design of lens must ensure that the heat transfer of the lens to the specimen environment is minimised.

Metallurgical Effects of Grain Boundary Ledges

1977 ◽  
Vol 35 ◽  
pp. 126-129
Author(s):  
L.E. Murr
Keyword(s):  
Grain Boundary ◽  
Quantitative Data ◽  
Mechanical Treatment ◽  
Unit Length ◽  
Physical And Mechanical Properties ◽  
Direct Observations ◽  
Transmission Electron ◽  
Properties Of Materials ◽  
Thermo Mechanical Treatment ◽  
Ledge Density

Ledges in grain boundaries can be identified by their characteristic contrast features (straight, black-white lines) distinct from those of lattice dislocations, for example1,2 [see Fig. 1(a) and (b)]. Simple contrast rules as pointed out by Murr and Venkatesh2, can be established so that ledges may be recognized with come confidence, and the number of ledges per unit length of grain boundary (referred to as the ledge density, m) measured by direct observations in the transmission electron microscope. Such measurements can then give rise to quantitative data which can be used to provide evidence for the influence of ledges on the physical and mechanical properties of materials.It has been shown that ledge density can be systematically altered in some metals by thermo-mechanical treatment3,4.

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.

Automated electron tomography: from data collection to image processing

1995 ◽  
Vol 53 ◽  
pp. 26-27
Author(s):  
Weiping Liu ◽  
Jennifer Fung ◽  
W.J. de Ruijter ◽  
Hans Chen ◽  
John W. Sedat ◽  
...  
Keyword(s):  
Image Processing ◽  
Data Collection ◽  
Structural Information ◽  
Imaging Technique ◽  
Electron Tomography ◽  
Ccd Camera ◽  
Automated Data Collection ◽  
Full Control ◽  
Transmission Electron ◽  
Amorphous Structures

Electron tomography is a technique where many projections of an object are collected from the transmission electron microscope (TEM), and are then used to reconstruct the object in its entirety, allowing internal structure to be viewed. As vital as is the 3-D structural information and with no other 3-D imaging technique to compete in its resolution range, electron tomography of amorphous structures has been exercised only sporadically over the last ten years. Its general lack of popularity can be attributed to the tediousness of the entire process starting from the data collection, image processing for reconstruction, and extending to the 3-D image analysis. We have been investing effort to automate all aspects of electron tomography. Our systems of data collection and tomographic image processing will be briefly described.To date, we have developed a second generation automated data collection system based on an SGI workstation (Fig. 1) (The previous version used a micro VAX). The computer takes full control of the microscope operations with its graphical menu driven environment. This is made possible by the direct digital recording of images using the CCD camera.

Structural studies of small amorphous volumes by electron diffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 122-123
Author(s):  
Pierre Moine
Keyword(s):  
Electron Diffraction ◽  
Born Approximation ◽  
Structural Information ◽  
Fundamental Relation ◽  
X Rays ◽  
Structural Studies ◽  
Diffraction Experiment ◽  
Transmission Electron ◽  
Amorphous Structures ◽  
Diffraction Patterns

Qualitatively, amorphous structures can be easily revealed and differentiated from crystalline phases by their Transmission Electron Microscopy (TEM) images and their diffraction patterns (fig.1 and 2) but, for quantitative structural information, electron diffraction pattern intensity analyses are necessary. The parameters describing the structure of an amorphous specimen have been introduced in the context of scattering experiments which have been, so far, the most used techniques to obtain structural information in the form of statistical averages. When only small amorphous volumes (< 1/μm in size or thickness) are available, the much higher scattering of electrons (compared to neutrons or x rays) makes, despite its drawbacks, electron diffraction extremely valuable and often the only feasible technique.In a diffraction experiment, the intensity IN (Q) of a radiation, elastically scattered by N atoms of a sample, is measured and related to the atomic structure, using the fundamental relation (Born approximation) : IN(Q) = |FT[U(r)]|.

Probing vacancies and structural distortions at individual defects in ceramics using EELS

1996 ◽  
Vol 54 ◽  
pp. 678-679
Author(s):  
D. J. Wallis ◽  
N. D. Browning
Keyword(s):  
Structural Information ◽  
Core Loss ◽  
Nearest Neighbors ◽  
Ceramic Materials ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Atomic Scale ◽  
Structure Property ◽  
Scanning Transmission ◽  
Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

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