Experimental Deformation Mechanics of Materials from their Near-Atomic-Resolution Defect Images

1991 ◽  
Vol 239 ◽  
Author(s):  
H. C. Choi ◽  
A. F. Schwartzman ◽  
K.-S. Kim
Keyword(s):  
Dislocation Core ◽  
High Resolution Electron Microscopy ◽  
Atomic Resolution ◽  
Lattice Image ◽  
Frank Loop ◽  
Mechanics Of Materials ◽  
Novel Approach ◽  
Resolution Electron ◽  
Experimental Deformation ◽  
Deformation Mechanics

ABSTRACTA novel approach to quantitative interpretation of high-resolution electron microscopy images of defects in materials has been developed. The emphasis of this paper is on the methodology, which has been named Computational Fourier Transform Moiré Analysis. The essential principle of this technique is to extract an accurate displacement field about a defect from its near-atomic-resolution picture using digital Fourier transformation procedures. From this data, the displacement gradient can be calculated which yields much information on the experimental deformation mechanics of the material under investigation. As a by-product, we produce the computational Moiré pattern without the need of an external perfect reference lattice image normally associated with the interference phenomena. This method is illustrated using a bounding Frank partial dislocation for a Frank loop of the vacancy type. Results are presented on its strain field, Burgers vector and dislocation core shape and dimensions. Further mention will be made on the types of J-integral calculations that can result from this experimental study.

scholarly journals Determination of the strain field from an HREM image of a Si lomer dislocation

1992 ◽  
Vol 50 (1) ◽  
pp. 144-145
Author(s):  
K.-H. Tsai ◽  
A. F. Schwartzman ◽  
R. Gallego ◽  
M. Ortiz ◽  
M. A. O'Keefe ◽  
...  
Keyword(s):  
Displacement Field ◽  
High Resolution Electron Microscopy ◽  
Hrem Image ◽  
Lattice Image ◽  
Novel Approach ◽  
External Reference ◽  
Resolution Electron ◽  
Strain Components ◽  
Defect Image ◽  
Deformation Mechanics

A novel approach to quantitative deformation characterization of high-resolution electron microscopy (HREM) defect images has been developed. The essential principle of this technique, called Computational Fourier Transform Deformation (CFTD) analysis, is to extract an accurate displacement field about a defect from its HREM image using Fourier transformation procedures. The methodology's unique feature is to digitize the defect image and compute the Moire pattern, from which the displacement field is obtained, without the need for an external reference lattice image, normally associated with the interference phenomena. Details of the image processing steps are described elsewhere. The motivation is that from this data, the displacement gradient can be calculated which yields much information on the experimental deformation mechanics of some solid undergoing a specific growth process or mechanical testing. One question that has arisen is whether different imaging conditions of the same defect affects the results of the CFTD analysis. We have studied this problem by analyzing the strain components of simulated images of a Lomer dislocation in Si and present our findings here.

Lattice Imaging of Twin, Lath and α/Martensite Boundaries in Duplex Low Carbon Steels

1977 ◽  
Vol 35 ◽  
pp. 118-119
Author(s):  
J. Y. Koo ◽  
G. Thomas
Keyword(s):  
High Resolution Electron Microscopy ◽  
Ferrite Matrix ◽  
Carbon Steels ◽  
Bright Field Image ◽  
Low Carbon ◽  
Lattice Imaging ◽  
Bright Field ◽  
Lattice Image ◽  
New Information ◽  
Resolution Electron

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

Electron crystallographic determination of the 3-D structure of staurolite at atomic resolution

1991 ◽  
Vol 49 ◽  
pp. 540-541
Author(s):  
Kenneth H. Downing ◽  
Hu Meisheng ◽  
Hans-Rudolf Went ◽  
Michael A. O'Keefe
Keyword(s):  
High Resolution ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Atomic Resolution ◽  
Dimensional Structure ◽  
Structure Information ◽  
Resolution Electron ◽  
Scattering Effects ◽  
High Resolution Images ◽  
Effects Of Radiation

With current advances in electron microscope design, high resolution electron microscopy has become routine, and point resolutions of better than 2Å have been obtained in images of many inorganic crystals. Although this resolution is sufficient to resolve interatomic spacings, interpretation generally requires comparison of experimental images with calculations. Since the images are two-dimensional representations of projections of the full three-dimensional structure, information is invariably lost in the overlapping images of atoms at various heights. The technique of electron crystallography, in which information from several views of a crystal is combined, has been developed to obtain three-dimensional information on proteins. The resolution in images of proteins is severely limited by effects of radiation damage. In principle, atomic-resolution, 3D reconstructions should be obtainable from specimens that are resistant to damage. The most serious problem would appear to be in obtaining high-resolution images from areas that are thin enough that dynamical scattering effects can be ignored.

The ultrastructure of coccoliths from the marine alga Emiliania huxleyi (Lohmann) Hay and Mohler: an ultra-high resolution electron microscope study

1983 ◽  
Vol 219 (1215) ◽  
pp. 111-117 ◽  
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Emiliania Huxleyi ◽  
Growth Patterns ◽  
Lattice Image ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Lattice Images ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns

The calcite coccoliths from the alga Emiliania huxleyi (Lohmann) Hay and Mohler have been studied by ultra-high resolution electron microscopy. This paper describes the two different types of structure observed, one in the upper elements, the other in the basal plate, or lower element. The former consisted of small, microdomain structures of 300-500 Å (1 Å = 10 -10 m) in length with no strong orientation. At places along these elements, and particularly in the junction between stem and head pieces, triangular patterns of lattice fringes were observed indicating multiple nucleation sites in the structure. In contrast, the lower element consisted of a very thin single crystalline sheet of calcite which could be resolved into a two dimensional lattice image, shown by a computer program that is capable of simulating electron diffraction patterns and lattice images to be a [421] zone of calcite. A possible mechanism for these growth patterns in the formation of coccoliths is discussed, together with the relevance of such mechanisms to biomineralization generally.

Micro-engineered Nanowire Electron Source for Atomic Resolution Imaging

2021 ◽  
Author(s):  
Han Zhang ◽  
Yu Jimbo ◽  
Akira Niwata ◽  
Akihiro Ikeda ◽  
Akira Yasuhara ◽  
...  
Keyword(s):  
Electron Beam ◽  
High Performance ◽  
Low Cost ◽  
High Resolution Electron Microscopy ◽  
Electron Source ◽  
Atomic Resolution ◽  
Angular Deviation ◽  
Resolution Electron ◽  
Emission Volume ◽  
Forming Efficiency

Abstract The size tunability and chemical versatility of nanostructures provide attractive engineering potential to realize an electron source of high brightness and spatial temporal coherence, which is a characteristic ever pursued by high resolution electron microscopy. (1–3) Regardless of the intensive research efforts, electron sources that have ever produced atomic resolution images are still limited to the conventional field emitters based on a bulk W needle. It is due to the lack of fabrication precision for nanostructured sources, that is required to align a nanometric emission volume along a macroscopic emitter axis with sub-degree angular deviation. (4) In this work, we produced a LaB6 nanowire electron source which was micro-engineered to ensure a highly collimated electron beam with perfect lateral and angular alignment. Such electron source was validated by installing in an aberration-corrected transmission electron microscope, where atomic resolution in both broad-beam and probe-forming modes were demonstrated at 60kV beam energy. The recorded un-monochromated 0.20eV electron energy loss spectroscopy (EELS) resolution, together with 20% probe forming efficiency and 0.4% probe current peak-to-peak noise ratio under a wide vacuum range, presented the unique advantages of nanotechnology and promised high performance low-cost electron beam instruments.

HREM imaging of screw dislocation core structures in bcc metals

2004 ◽  
Vol 839 ◽  
Author(s):  
B.G. Mendis ◽  
Y. Mishin ◽  
C.S. Hartley ◽  
K.J. Hemker
Keyword(s):  
Screw Dislocation ◽  
Dislocation Core ◽  
High Resolution Electron Microscopy ◽  
Core Region ◽  
Surface Relaxation ◽  
Hrem Image ◽  
The Core ◽  
Bcc Metals ◽  
Atomic Displacements ◽  
Resolution Electron

ABSTRACTQuantitative High Resolution Electron Microscopy (HREM) is used to characterize the in-plane displacements of atoms around a screw dislocation core in bcc molybdenum. The in-plane displacements have an important effect on the bulk mechanical properties of bcc metals and alloys. However, the largest displacements are predicted to be less than 10 pm, requiring that the atom positions in an HREM image be determined to sub-pixel accuracy. In order to calculate the displacements the positions of the atom columns in the undistorted crystal must be determined precisely from the information available in the HREM image. An algorithm for such a task is briefly discussed and the technique applied to several HREM images. It is seen that the atomic displacements are predominantly due to surface relaxation (i.e. Eshelby twist) of a thin TEM foil, thereby masking the finer displacements of the dislocation core. Nye tensor plots, which map the resultant Burgers vector at each point of a distorted crystal, are also used to characterize the core structure. Although the large displacements from the Eshelby twist were completely removed, no signal from the dislocation core region was observed.

Mixed partial dislocation core structure in GaN by high resolution electron microscopy

2006 ◽  
Vol 203 (9) ◽  
pp. 2156-2160 ◽  
Author(s):  
J. Kioseoglou ◽  
G. P. Dimitrakopulos ◽  
Ph. Komninou ◽  
Th. Kehagias ◽  
Th. Karakostas
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Partial Dislocation ◽  
Dislocation Core ◽  
High Resolution Electron Microscopy ◽  
Core Structure ◽  
Resolution Electron ◽  
Dislocation Core Structure

Nanoscale Measurement of Stress and Strain by Quantitative High-Resolution Electron Microscopy

2005 ◽  
Vol 482 ◽  
pp. 39-44 ◽  
Author(s):  
Martin J. Hÿtch ◽  
Jean-Luc Putaux ◽  
Jean-Michel Pénisson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Spatial Resolution ◽  
Strain Tensor ◽  
Dislocation Core ◽  
High Resolution Electron Microscopy ◽  
Stress And Strain ◽  
Fourier Space ◽  
Resolution Electron ◽  
Anisotropic Elastic

The geometric phase technique (GPA) for measuring the distortion of crystalline lattices from high-resolution electron microscopy (HRTEM) images will be described. The method is based on the calculation of the “local” Fourier components of the HRTEM image by filtering in Fourier space. The method will be illustrated with a study of an edge dislocation in silicon where displacements have been measured to an accuracy of 3 pm at nanometre resolution as compared with anisotropic elastic theory calculations. The different components of the strain tensor will be mapped out in the vicinity of the dislocation core and compared with theory. The accuracy is of the order of 0.5% for strain and 0.1° for rigid-body rotations. Using bulk elastic constants for silicon, the stress field is determined to 0.5 GPa at nanometre spatial resolution. Accuracy and the spatial resolution of the technique will be discussed.

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