On the indexing of a selected area diffraction pattern

1978 ◽  
Vol 46 (4) ◽  
pp. 429-429
Author(s):  
W. F. Lewis
Keyword(s):  
Diffraction Pattern ◽  
Selected Area Diffraction Pattern

Using the TEM Condenser Lens to Switch between Image and Diffraction Modes

2013 ◽  
Vol 21 (2) ◽  
pp. 40-40
Author(s):  
Lydia Rivaud
Keyword(s):  
Electron Microscope ◽  
Diffraction Pattern ◽  
Transmission Electron Microscope ◽  
Condenser Lens ◽  
Selected Area Diffraction Pattern ◽  
Transmission Electron ◽  
Set Up ◽  
Convergent Beam ◽  
Beam Diffraction ◽  
Convergent Beam Diffraction

Central to the operation of the transmission electron microscope (TEM) (when used with crystalline samples) is the ability to go back and forth between an image and a diffraction pattern. Although it is quite simple to go from the image to a convergent-beam diffraction pattern or from an image to a selected-area diffraction pattern (and back), I have found it useful to be able to go between image and diffraction pattern even more quickly. In the method described, once the microscope is set up, it is possible to go from image to diffraction pattern and back by turning just one knob. This makes many operations on the microscope much more convenient. It should be made clear that, in this method, neither the image nor the diffraction pattern is “ideal” (details below), but both are good enough for many necessary procedures.

TEM Observation of the Polytype Transformation of Bulk SiC Ingot

2008 ◽  
Vol 600-603 ◽  
pp. 365-368 ◽  
Author(s):  
Masahiko Aoki ◽  
Megumi Miyazaki ◽  
Taro Nishiguchi ◽  
Hiroyuki Kinoshita ◽  
Masahiro Yoshimoto
Keyword(s):  
Raman Spectroscopy ◽  
Diffraction Pattern ◽  
Growth Direction ◽  
Selected Area Diffraction Pattern ◽  
Polytype Transformation

This article describes the analysis of the polytype transformation of SiC ingot. We analyzed the sample by Raman spectroscopy and TEM observation. The result of the analysis shows the polytype is transformed from 4H-SiC to 6H-SiC, and then returned to 4H-SiC. We found that the direction of the c-axis is not the same as the growth direction of the ingot. And also we found the existence of 8H-SiC at the interface between 6H-SiC and 4H-SiC region by the selected area diffraction pattern and confirmed it by HR-TEM observation.

New phases in the Al-Co-Cu alloy system : Marked variations from the “true” decagonal phase

1992 ◽  
Vol 50 (1) ◽  
pp. 32-33
Author(s):  
Atul S. Ramani ◽  
Lucille A. Giannuzzi ◽  
Altaf H. Carim ◽  
William R. Bitler ◽  
Paul R. Howell
Keyword(s):  
Single Crystal ◽  
Diffraction Pattern ◽  
Alloy System ◽  
Fivefold Symmetry ◽  
Decagonal Phase ◽  
Cu Alloy ◽  
Selected Area Diffraction Pattern ◽  
The One ◽  
Pentagonal Symmetry ◽  
Incommensurate Phases

The decagonal phase in the Al-Co-Cu alloy system was first discovered by He et al. We shall call this phase the “true” decagonal phase (TD) phase because it is the one most commonly observed in the Al-Co-Cu alloy system. It is well known that quasicrystalline phases such as the TD phase contain the phason defect peculiar to incommensurate phases that causes subtle variations from perfect decagonal symmetry. In this paper we report on the existence of new phases in the Al-Co-Cu alloy system, that are related to the TD phase but yet show marked variations from the TD phase. These variations are too drastic to be caused by phason defects alone.Figure 1(a) is a selected area diffraction pattern (SADP) recorded from a TD phase single “crystal” showing near perfect decagonal (tenfold) symmetry. This SADP agrees very well with the first published SADP of the TD phase in Al-Co-Cu that also shows almost perfect decagonal symmetry. In a previous paper we have reported several kinds of deviations from perfect decagonal symmetry, but none of these deviations involved the observation of perfect pentagonal (fivefold) symmetry. Figure 1(b) is an SADP recorded from a phase in Al-Co-Cu that exhibits perfect pentagonal symmetry instead of the expected decagonal symmetry. This breakdown of true tenfold symmetry into true fivefold symmetry is caused by unequal intensities of equal and opposite reflections. This example is a clear violation of Friedel's law, which states that the intensities of equal and opposite diffraction vectors must be equal.

Analysis of electron-diffraction intensity profiles using a photodiode-array detection system

1983 ◽  
Vol 41 ◽  
pp. 322-323
Author(s):  
J. B. Warren
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Detection System ◽  
High Energy ◽  
Photographic Emulsion ◽  
Diffraction Intensity ◽  
Silicon Photodiode ◽  
Photodiode Array Detection ◽  
Analog To Digital ◽  
Photodiode Array

Electron diffraction intensity profiles have been used extensively in studies of polycrystalline and amorphous thin films. In previous work, diffraction intensity profiles were quantitized either by mechanically scanning the photographic emulsion with a densitometer or by using deflection coils to scan the diffraction pattern over a stationary detector. Such methods tend to be slow, and the intensities must still be converted from analog to digital form for quantitative analysis. The Instrumentation Division at Brookhaven has designed and constructed a electron diffractometer, based on a silicon photodiode array, that overcomes these disadvantages. The instrument is compact (Fig. 1), can be used with any unmodified electron microscope, and acquires the data in a form immediately accessible by microcomputer.Major components include a RETICON 1024 element photodiode array for the de tector, an Analog Devices MAS-1202 analog digital converter and a Digital Equipment LSI 11/2 microcomputer. The photodiode array cannot detect high energy electrons without damage so an f/1.4 lens is used to focus the phosphor screen image of the diffraction pattern on to the photodiode array.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

Electron Diffraction Analysis of Microtwin Structures in Regrown (III) Silicon

1982 ◽  
Vol 40 ◽  
pp. 460-461
Author(s):  
P. Ling ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
Electron Diffraction ◽  
Ion Implantation ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Direct Consequence ◽  
The Other ◽  
Electron Diffraction Analysis ◽  
Defect Microstructures ◽  
Ion Implanted

The defect microstructures of Si arising from ion implantation and subsequent regrowth for a (111) substrate have been found to be dominated by microtwins. Figure 1(a) is a typical diffraction pattern of annealed ion-implanted (111) Si showing two groups of extra diffraction spots; one at positions (m, n integers), the other at adjacent positions between <000> and <220>. The object of the present paper is to show that these extra reflections are a direct consequence of the microtwins in the material.

Video-Enhanced Microscopy--Better Visibility of Plant Cell Structures

1982 ◽  
Vol 40 ◽  
pp. 182-185
Author(s):  
N.S. Allen ◽  
R.D. Allen
Keyword(s):  
Diffraction Pattern ◽  
Theoretical Basis ◽  
Numerical Aperture ◽  
Gain Control ◽  
Control Unit ◽  
Camera Control ◽  
Variable Gain ◽  
Contrast Method ◽  
Fine Detail ◽  
Cell Structures

Various methods of video-enhanced microscopy combine TV cameras with light microscopes creating images with improved resolution, contrast and visibility of fine detail, which can be recorded rapidly and relatively inexpensively. The AVEC (Allen Video-enhanced Contrast) method avoids polarizing rectifiers, since the microscope is operated at retardations of λ/9- λ/4, where no anomaly is seen in the Airy diffraction pattern. The iris diaphram is opened fully to match the numerical aperture of the condenser to that of the objective. Under these conditions, no image can be realized either by eye or photographically. Yet the image becomes visible using the Hamamatsu C-1000-01 binary camera, if the camera control unit is equipped with variable gain control and an offset knob (which sets a clamp voltage of a D.C. restoration circuit). The theoretical basis for these improvements has been described.

Convergent Beam Electron Diffraction

1978 ◽  
Vol 36 (3) ◽  
pp. 304-315
Author(s):  
G. Lehmpfuhl
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Crystal Surface ◽  
Diffraction Spot ◽  
Crystal Thickness ◽  
Large Area ◽  
Electron Microscopic ◽  
Additional Information ◽  
Microscopic Investigations

Introduction In electron microscopic investigations of crystalline specimens the direct observation of the electron diffraction pattern gives additional information about the specimen. The quality of this information depends on the quality of the crystals or the crystal area contributing to the diffraction pattern. By selected area diffraction in a conventional electron microscope, specimen areas as small as 1 µ in diameter can be investigated. It is well known that crystal areas of that size which must be thin enough (in the order of 1000 Å) for electron microscopic investigations are normally somewhat distorted by bending, or they are not homogeneous. Furthermore, the crystal surface is not well defined over such a large area. These are facts which cause reduction of information in the diffraction pattern. The intensity of a diffraction spot, for example, depends on the crystal thickness. If the thickness is not uniform over the investigated area, one observes an averaged intensity, so that the intensity distribution in the diffraction pattern cannot be used for an analysis unless additional information is available.

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