scholarly journals High Resolution Imaging in Bright and Dark Field at High Voltages

1974 ◽  
Vol 32 ◽  
pp. 356-357
Author(s):  
L. J. Chen ◽  
K. Seshan
Keyword(s):  
Dark Field ◽  
High Resolution Imaging ◽  
Interband Transitions ◽  
Bragg Condition ◽  
Bright Field ◽  
Weak Beam ◽  
Powerful Means ◽  
Resolution Imaging ◽  
Field Imaging ◽  
Order Reflection

The weak beam dark field and high order bright field imaging(2) methods are powerful means for improving the resolution of images detected by diffraction contrast. However, at high voltages, many beam interactions become important as more interband transitions occur between different Bloch waves. At the exact Bragg condition, for any order reflection, usually more than two interband transitions are important for both weak beam and bright field images, and complicated images result.

scholarly journals A new technique for measuring the separation of closely spaced dislocations using residual-contrast conditions

1994 ◽  
Vol 52 ◽  
pp. 902-903
Author(s):  
J. E. Angelo ◽  
M. J. Mills
Keyword(s):  
Field Method ◽  
Dark Field ◽  
Foil Thickness ◽  
High Resolution Imaging ◽  
Bulk Materials ◽  
Weak Beam ◽  
Beam Method ◽  
True Position ◽  
Resolution Imaging ◽  
A New Technique

In order to measure the spacing of closely spaced dislocations, a method with sufficient spatial resolution must be used. High resolution imaging provides one method of determining the spacing of paired dislocations, but care must be taken since these authors have shown that thin film effects can give rise to structures not present in bulk materials. To date, the most widely used method of determining the spacing of paired dislocations is the weak-beam dark field method. This method has proved extremely useful in the study of many systems, see Cockayne3 for a review. One of the difficulties of the weak-beam method is that the observed peak positions do not generally correspond to the actual position of the partial dislocation cores. Correlation of the peak positions with the true position depends on the deviation parameter, foil thickness, and position of the dislocations within the foil.

Precipitation and dislocation decoration via extrinsic gettering of Co, Au and Pt by misfit dislocations in Si/Si-2%Ge epitaxy

1989 ◽  
Vol 47 ◽  
pp. 578-579
Author(s):  
D. M. Lee
Keyword(s):  
Imaging Techniques ◽  
Preceding Paper ◽  
Dark Field ◽  
Misfit Dislocations ◽  
Temperature Dependent ◽  
Bright Field ◽  
Dark Field Imaging ◽  
Weak Beam ◽  
Sample Structure ◽  
Field Imaging

Previous work on the gettering activity of a well defined array of buried interfacial misfit dislocations (MDs) showed that the amount of nickel gettered by MD is dominated by the strong temperature-dependent solubility. Precipitation occurs on or in the immediate vicinity of MDs due to nucleation enhancement by strain effects. High temperature 〈1000°C〉 diffusion of gold resulted in the planar colony precipitates on two {111} planes associated with stacking fault formation. In this contribution, we discuss our continuing research pertaining to cobalt, gold (at low temperature), and platinum gettering by MDs which involves studying the nature of dislocation decoration and impurity precipitation in the Si/Si-2%Ge epitaxial system.All the samples used in this study have a buried Si-2%Ge epitaxial layer of ∼ 2 μm thickness.Co, Au and Pt were deliberately diffused into the wafer. The details of the sample structure and preparation are described in a preceding paper. Two-beam bright field and weak-beam dark field imaging techniques were performed on cross-section TEM specimens.

Two Investigations into Grain Boundary Structure

1977 ◽  
Vol 35 ◽  
pp. 688-691
Author(s):  
P. Humble
Keyword(s):  
Grain Boundary ◽  
Dark Field ◽  
Boundary Structure ◽  
Boundary Dislocation ◽  
Bright Field ◽  
Intrinsic Structure ◽  
Weak Beam ◽  
Grain Boundary Structure ◽  
Independent Information ◽  
Diffraction Patterns

There has been sustained interest over the last few years into both the intrinsic (primary and secondary) structure of grain boundaries and the extrinsic structure e.g. the interaction of matrix dislocations with the boundary. Most of the investigations carried out by electron microscopy have involved only the use of information contained in the transmitted image (bright field, dark field, weak beam etc.). Whilst these imaging modes are appropriate to the cases of relatively coarse intrinsic or extrinsic grain boundary dislocation structures, it is apparent that in principle (and indeed in practice, e.g. (1)-(3)) the diffraction patterns from the boundary can give extra independent information about the fine scale periodic intrinsic structure of the boundary.In this paper I shall describe one investigation into each type of structure using the appropriate method of obtaining the necessary information which has been carried out recently at Tribophysics.

A Many-Beam Technique for Enhanced Resolution of Partial Dislocations

1972 ◽  
Vol 30 ◽  
pp. 646-647
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Field Method ◽  
Dark Field ◽  
Bright Field ◽  
Field Technique ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Enhanced Resolution ◽  
Nickel Base ◽  
Beam Technique

The “weak-beam” and systematic many-beam techniques are the currently available methods for resolution of closely spaced dislocations or other inhomogeneities imaged through strain contrast. The former is a dark field technique and image intensities are usually very weak. The latter is a bright field technique, but generally use of a high voltage instrument is required. In what follows a bright field method for obtaining enhanced resolution of partial dislocations at 100 KV accelerating potential will be described.A brief discussion of an application will first be given. A study of intermediate temperature creep processes in commercial nickel-base alloys strengthened by the Ll2 Ni3 Al γ precipitate has suggested that partial dislocations such as those labelled 1 and 2 in Fig. 1(a) are in reality composed of two closely spaced a/6 <112> Shockley partials. Stacking fault contrast, when present, tends to obscure resolution of the partials; thus, conditions for resolution must be chosen such that the phase shift at the fault is 0 or a multiple of 2π.

Spacings and Intensities of Weak-Beam Dark Field Thickness Fringes

1981 ◽  
Vol 39 ◽  
pp. 222-223
Author(s):  
M. Avalos-Borja ◽  
K. Heinemann
Keyword(s):  
Selection Criterion ◽  
Dark Field ◽  
Dynamical Theory ◽  
Bragg Condition ◽  
Weak Beam ◽  
Kinematical Theory ◽  
Equal Thickness

Weak-beam dark field (WBDF) TEM produces narrowly spaced equal-thickness fringes in wedge-shaped crystals. Using non-systematic diffraction conditions, we have shown elsewhere that simple 2-beam kinematical theory (KT) calculations yield average fringe spacings that are for most practical purposes as satisfactorily accurate as the average spacings obtained from optimized multibeam dynamical theory (DT) calculations, As Fig. 1 shows, this result holds for deviations from the Bragg condition as low as 2x10-1 nm-1, and the differences between the results from the two calculational methods become increasingly insignificant for larger excitation errors. (Unless otherwise noted, all results reported here are for gold crystals, using the 200 beam at 100 KV; the DT calculations were made for 74 beams, using the selection criterion D as discussed in ref. [3]).

The Dependence of Sample Thickness on Annular Bright Field Microscopy

2011 ◽  
Vol 5 (1) ◽  
Author(s):  
M.M.G. Latting ◽  
W. Walkosz ◽  
R.F. Klie
Keyword(s):  
Image Quality ◽  
Visual Information ◽  
Specific Property ◽  
Dark Field ◽  
Sample Thickness ◽  
Atomic Resolution ◽  
Imaging Method ◽  
Bright Field ◽  
Dark Field Imaging ◽  
Field Imaging

Annular Bright Field (ABF) is a relatively new method of Scanning Transmission Electron Microscopy (STEM) imaging that is desirable because of its ability to provide additional visual information in terms of showing lightweight atoms, whereas standard dark field imaging does not. In order to better understand the parameters necessary to perfect this method, this research article aimed to study a specific property of this imaging method: the dependence of sample thickness on image quality and atomic resolution. Multislice calculations were utilized to generate atomic potentials that were used to simulate different thicknesses of β-Si3N4. The resulting images were then examined to measure atomic full width at half-maximum (FWHM) in order to have a quantifiable value to support visual selection of the best ABF output image. Comparison of image quality/atomic resolution and FWHM values suggested that as a general trend, as sample thickness increases, atomic resolution and image quality deteriorate, citing Huygens' Principle of Classical Optics via the propagation of spherical electron waves through a vacuum. This study will bring a new awareness to the necessary precision required by researchers' sample preparation during Annular Bright Field imaging to yield the best image of their respective samples.

Ground scientific verification test for High Resolution Imaging Camera of China's First Mars Mission

2020 ◽  
Author(s):  
Wei Yan ◽  
Jianjun Liu ◽  
Xiaoxia Zhang ◽  
Dawei Liu ◽  
Donghao Liu
Keyword(s):  
High Resolution ◽  
Image Data ◽  
Image Motion ◽  
High Resolution Imaging ◽  
The Earth ◽  
Imaging Camera ◽  
Evaluation Test ◽  
Resolution Imaging ◽  
Verification Test ◽  
Field Imaging

&lt;p&gt;Mars is a planet in the solar system that is closer to the Earth and has the most similar natural environment to the Earth. It has always been the first choice for humans to go out of the Earth and Moon system for deep space exploration.&lt;/p&gt;&lt;p&gt;China&amp;#8217;s First Mars Mission (HX-1) will be launched in 2020 with an orbiter and a lander rover. One of the scientific goals of our mission is to study the morphology and geologic structure of the Mars. In order to achieve this purpose, the orbiter is equipped with a High Resolution Imaging Camera (HiRIC) to obtain the high-resolution morphology data of typical regions and to study the formation and evolution of geologic structure. HiRIC consists of three TDI CCD line-scan detectors and two COMS area-array detectors. Each TDI CCD detector covers 5 spectral bands. Its main working mode is the panchromatic TDI CCD push-scan imaging with a maximum spatial resolution of 0.5m.&lt;/p&gt;&lt;p&gt;Ground scientific verification test is an effective way to comprehensively evaluate the performance, data quality of HiRIC, and to fully verify its on-orbit detection process and data processing methods. In this study, contents and results of ground scientific verification test for HiRIC is introduced. The engineering model is used here for image motion compensation effect evaluation test, focusing effect evaluation test, and outdoor field imaging test. The results show that, 1) HiRIC can calculate the image motion compensation parameters and control the camera imaging correctly according to the platform parameters of orbiter; 2) Focus processing is effective, and HiRIC can adapt to the high-resolution imaging needs of different orbit altitudes; 3) Clear image data can be obtained according to the on-orbit detection process in the outdoor field imaging test, and image data processing was correct. Image data quality, compression quality, and TDI CCD stitching accuracy all meet the requirements of the verification test. This test fully evaluated HiRIC's ability to obtain high-resolution image data of the surface of Mars.&lt;/p&gt;

On Distinguishing between Small Vacancy and Interstitial Dislocation Loops Using a Non-Conventional Weak Beam Dark Field Technique

1975 ◽  
Vol 33 ◽  
pp. 166-167
Author(s):  
Wei-Kuo Wu
Keyword(s):  
Habit Plane ◽  
Dark Field ◽  
Dislocation Loops ◽  
Bright Field ◽  
Burgers Vector ◽  
Field Techniques ◽  
Field Technique ◽  
The Core ◽  
Weak Beam ◽  
Image Width

It is well known that both the burgers vector and the habit plane of dislocation loops are needed in order to determine their type, e.g. vacancy or interstitial. The conventional bright field and dark field techniques give a dislocation image width ⋍300Å or an image shift from the core position even larger than the true size of a small dislocation loop. This makes loop type determination very difficult.In this paper, the newly developed weak beam dark field technique, which decreases the effective extinction distance, ξg, has been used to reduce the dislocation image width (∽1/3 ξg), so that the shape (habit plane) and loop types of small dislocation loops (<500Å) can be determined unambiguously.

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