scholarly journals Electron Microscopy of Bubbles and Dislocations in Helium Implanted Metals

2021 ◽  
Author(s):  
◽  
Kevin John Stevens
Keyword(s):  
Electron Diffraction ◽  
Bubble Radius ◽  
Gas Bubbles ◽  
Foil Thickness ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Imaging Parameters ◽  
Transmission Electron ◽  
Wide Range ◽  
Isotropic Elasticity

<p>The theoretical contrast in transmission electron microscope of a superlattice of helium gas bubbles in copper is computed using the two-beam and many-beam dynamical theories of electron diffraction with the aim the aim of measuring the density and size of dislocation loops associated with the bubble array. A wide range of parameters (foil thickness, diffraction vector, excitation error, defocus, and depth, radius, and strain-field of the bubble) is considered to considered to construct a library of theoretical images and intensity profiles for a single, isolated bubble. Various criteria are applied to obtain a measurement of the bubble radius from the simulations but the results are inaccurate because of the sensitive dependence of the intensity profile on the imaging parameters. A better measurement is profiles from a single stack of bubbles are modeled and electron diffraction from superlattices simulated. The results obtained suggest that the bubble ordering is of limited extent. A library is made of the theoretical contrast when imaging a system of dislocation loops punched out along the <110> directions by the growth of gas bubbles ordered on a superlattice aligned with the host fcc matrix. These image simulations use the displacement fields surrounding loops and bubbles predicted by isotropic elasticity theory. For a variety of structures involving loops and bubbles, the following imaging parameters were investigated: beam direction, foil normal, diffracting vector, excitation error, number of beams, and defocus, These simulations indicate that it should be possible to image the small dislocations at high density thought to be present in the bubble lattice, provided well focused micrographs taken under strong two-beam conditions can be obtained. In Practice it proved difficult to tilt specimens containing superlattices to strong two-beam conditions because of the deterioration in crystallinity resulting from the implantation. However, the lower concentrations by low dose implantations.</p>

scholarly journals Electron Microscopy of Bubbles and Dislocations in Helium Implanted Metals

2021 ◽  
Author(s):  
◽  
Kevin John Stevens
Keyword(s):  
Electron Diffraction ◽  
Bubble Radius ◽  
Gas Bubbles ◽  
Foil Thickness ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Imaging Parameters ◽  
Transmission Electron ◽  
Wide Range ◽  
Isotropic Elasticity

<p>The theoretical contrast in transmission electron microscope of a superlattice of helium gas bubbles in copper is computed using the two-beam and many-beam dynamical theories of electron diffraction with the aim the aim of measuring the density and size of dislocation loops associated with the bubble array. A wide range of parameters (foil thickness, diffraction vector, excitation error, defocus, and depth, radius, and strain-field of the bubble) is considered to considered to construct a library of theoretical images and intensity profiles for a single, isolated bubble. Various criteria are applied to obtain a measurement of the bubble radius from the simulations but the results are inaccurate because of the sensitive dependence of the intensity profile on the imaging parameters. A better measurement is profiles from a single stack of bubbles are modeled and electron diffraction from superlattices simulated. The results obtained suggest that the bubble ordering is of limited extent. A library is made of the theoretical contrast when imaging a system of dislocation loops punched out along the <110> directions by the growth of gas bubbles ordered on a superlattice aligned with the host fcc matrix. These image simulations use the displacement fields surrounding loops and bubbles predicted by isotropic elasticity theory. For a variety of structures involving loops and bubbles, the following imaging parameters were investigated: beam direction, foil normal, diffracting vector, excitation error, number of beams, and defocus, These simulations indicate that it should be possible to image the small dislocations at high density thought to be present in the bubble lattice, provided well focused micrographs taken under strong two-beam conditions can be obtained. In Practice it proved difficult to tilt specimens containing superlattices to strong two-beam conditions because of the deterioration in crystallinity resulting from the implantation. However, the lower concentrations by low dose implantations.</p>

Investigations of Defective β-NiAl by Transmission Electron Microscopy

1981 ◽  
Vol 39 ◽  
pp. 58-59 ◽  
Author(s):  
H. C. Liu ◽  
E. Chang ◽  
T. E. Mitchell
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
Defect Structures ◽  
Transmission Electron ◽  
Nial Phase ◽  
Wide Range ◽  
Diffraction Patterns ◽  
B2 Structure

The β-NiAl phase, which is an ordered B2 structure, covers a wide range of compositions extending from ∼46 at.% Ni to ∼60 at.% Ni. For non-stoichiometric β-NiAl, studies (1,2) have shown that, for compositions below 50 at.% Ni, structural vacancies are introduced on the Ni sublattice (denoted as VNi), but for compositions above 50 at.% Ni,excess Ni atoms replace A1 atoms on the A1 sublattice (denoted as NiAl). In this work, defect structures in compositions of 45, 45.5, 46, 47, 50, 55, 58 and 60 at.% Ni were studied by electron diffraction techniques in a Siemens 102 TEM.Figs. 1 and 2 show selected area diffraction patterns at the exact [011] and [001] zone axes respectively.

The Application of Electron Diffraction in the Study of Biocrystals

1982 ◽  
Vol 40 ◽  
pp. 570-571
Author(s):  
DoSuk D. Lee
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Transmission Electron Microscope ◽  
Interdisciplinary Studies ◽  
Atomic Configuration ◽  
Naturally Occurring ◽  
Transmission Electron ◽  
Wide Range ◽  
Potential Applications

The transmission electron microscope (TEM) is employed in a wide range of interdisciplinary studies related to the ultrastructure of the synthetic and naturally occurring calcified crystals. However, the use of electron diffraction in studying the orientation, atomic configuration and defects of these crystals has been given little attention. This paper will examine the potential applications of electron diffraction in the study of these biominerals.

Transmission Electron Diffraction Analysis by Computer

1970 ◽  
Vol 28 ◽  
pp. 40-41
Author(s):  
R.A. Ploc ◽  
G.H. Keech
Keyword(s):  
Electron Diffraction ◽  
Input Data ◽  
Reciprocal Lattice ◽  
Computer Programme ◽  
Transmission Electron Diffraction ◽  
Usual Procedure ◽  
Transmission Electron ◽  
Complex Shapes ◽  
Computer Input ◽  
Diffraction Effects

An unambiguous analysis of transmission electron diffraction effects requires two samplings of the reciprocal lattice (RL). However, extracting definitive information from the patterns is difficult even for a general orthorhombic case. The usual procedure has been to deduce the approximate variables controlling the formation of the patterns from qualitative observations. Our present purpose is to illustrate two applications of a computer programme written for the analysis of transmission, selected area diffraction (SAD) patterns; the studies of RL spot shapes and epitaxy.When a specimen contains fine structure the RL spots become complex shapes with extensions in one or more directions. If the number and directions of these extensions can be estimated from an SAD pattern the exact spot shape can be determined by a series of refinements of the computer input data.

Annealing Of Radiation Damage in Tungsten

1970 ◽  
Vol 28 ◽  
pp. 412-413
Author(s):  
Robert C. Rau ◽  
John Moteff
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radiation Damage ◽  
Thermal Annealing ◽  
Neutron Fluence ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Polycrystalline Tungsten ◽  
Transmission Electron ◽  
Radiation Induced

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in polycrystalline tungsten. Specimens were taken from cylindrical tensile bars which had been irradiated to a fast (E > 1 MeV) neutron fluence of 4.2 × 1019 n/cm2 at 70°C, annealed for one hour at various temperatures in argon, and tensile tested at 240°C in helium. Foils from both the unstressed button heads and the reduced areas near the fracture were examined.Figure 1 shows typical microstructures in button head foils. In the unannealed condition, Fig. 1(a), a dispersion of fine dot clusters was present. Annealing at 435°C, Fig. 1(b), produced an apparent slight decrease in cluster concentration, but annealing at 740°C, Fig. 1(C), resulted in a noticeable densification of the clusters. Finally, annealing at 900°C and 1040°C, Figs. 1(d) and (e), caused a definite decrease in cluster concentration and led to the formation of resolvable dislocation loops.

Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

TEM Analysis of Long-Period Polytypes in SiC—S

1976 ◽  
Vol 34 ◽  
pp. 630-631
Author(s):  
S. Shinozaki ◽  
J. W. Sprys
Keyword(s):  
Electron Diffraction ◽  
Isothermal Annealing ◽  
Tem Analysis ◽  
Long Period ◽  
Transmission Electron ◽  
Average Grain Size ◽  
High Resolution Tem ◽  
Structural Lattice ◽  
The Stability ◽  
Continuous Curves

In reaction sintered SiC (∽ 5um average grain size), about 15% of the grains were found to have long-period structures, which were identifiable by transmission electron microscopy (TEM). In order to investigate the stability of the long-period polytypes at high temperature, crystal structures as well as microstructural changes in the long-period polytypes were analyzed as a function of time in isothermal annealing.Each polytype was analyzed by two methods: (1) Electron diffraction, and (2) Electron micrograph analysis. Fig. 1 shows microdensitometer traces of ED patterns (continuous curves) and calculated intensities (vertical lines) along 10.l row for 6H and 84R (Ramsdell notation). Intensity distributions were calculated based on the Zhdanov notation of (33) for 6H and [ (33)3 (32)2 ]3 for 84R. Because of the dynamical effect in electron diffraction, the observed intensities do not exactly coincide with those intensities obtained by structure factor calculations. Fig. 2 shows the high resolution TEM micrographs, where the striped patterns correspond to direct resolution of the structural lattice periodicities of 6H and 84R structures and the spacings shown in the figures are as expected for those structures.

Luminescence from individual dislocations in II-VI and III-V semiconductors

1991 ◽  
Vol 49 ◽  
pp. 834-835
Author(s):  
J W Steeds
Keyword(s):  
Group Iv ◽  
Luminescence Properties ◽  
Carrier Recombination ◽  
Transmission Electron ◽  
Wide Range ◽  
Basic Physics ◽  
Semiconducting Compounds ◽  
Diamond Group ◽  
Non Destructive ◽  
Technological Significance

There is a wide range of experimental results related to dislocations in diamond, group IV, II-VI, III-V semiconducting compounds, but few of these come from isolated, well-characterized individual dislocations. We are here concerned with only those results obtained in a transmission electron microscope so that the dislocations responsible were individually imaged. The luminescence properties of the dislocations were studied by cathodoluminescence performed at low temperatures (~30K) achieved by liquid helium cooling. Both spectra and monochromatic cathodoluminescence images have been obtained, in some cases as a function of temperature.There are two aspects of this work. One is mainly of technological significance. By understanding the luminescence properties of dislocations in epitaxial structures, future non-destructive evaluation will be enhanced. The second aim is to arrive at a good detailed understanding of the basic physics associated with carrier recombination near dislocations as revealed by local luminescence properties.

An Interactive Minicomputer Program for the Indexing and Simulation of Electron Diffraction Patterns

1976 ◽  
Vol 34 ◽  
pp. 542-543
Author(s):  
R.P. Goehner ◽  
W.T. Hatfield ◽  
Prakash Rao
Keyword(s):  
Electron Diffraction ◽  
Real Time ◽  
Pattern Analysis ◽  
Flow Diagram ◽  
Hard Copy ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Transmission Electron ◽  
One Step ◽  
Diffraction Patterns

Computer programs are now available in various laboratories for the indexing and simulation of transmission electron diffraction patterns. Although these programs address themselves to the solution of various aspects of the indexing and simulation process, the ultimate goal is to perform real time diffraction pattern analysis directly off of the imaging screen of the transmission electron microscope. The program to be described in this paper represents one step prior to real time analysis. It involves the combination of two programs, described in an earlier paper(l), into a single program for use on an interactive basis with a minicomputer. In our case, the minicomputer is an INTERDATA 70 equipped with a Tektronix 4010-1 graphical display terminal and hard copy unit.A simplified flow diagram of the combined program, written in Fortran IV, is shown in Figure 1. It consists of two programs INDEX and TEDP which index and simulate electron diffraction patterns respectively. The user has the option of choosing either the indexing or simulating aspects of the combined program.

Theory and Errors in Stereo Electron Microscopy

1968 ◽  
Vol 26 ◽  
pp. 336-337
Author(s):  
J. M. Pankratz
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plane Wave ◽  
Focal Length ◽  
Foil Thickness ◽  
Points Of Interest ◽  
Transmission Electron ◽  
Vertical Spacing ◽  
Illuminating System

It is often desirable in transmission electron microscopy to know the vertical spacing of points of interest within a specimen. However, in order to measure a stereo effect, one must have two pictures of the same area taken from different angles, and one must have also a formula for converting measured differences between corresponding points (parallax) into a height differential.Assume (a) that the impinging beam of electrons can be considered as a plane wave and (b) that the magnification is the same at the top and bottom of the specimen. The first assumption is good when the illuminating system is overfocused. The second assumption (the so-called “perspective error”) is good when the focal length is large (3 x 107Å) in relation to foil thickness (∼103 Å).

Sign in / Sign up

Export Citation Format

Share Document