Retrieval of the projected potential by inversion from the scattering matrix in electron–crystal scattering

1999 ◽  
Vol 55 (2) ◽  
pp. 105-111 ◽  
Author(s):  
L. J. Allen ◽  
H. Leeb ◽  
A. E. C. Spargo
Keyword(s):  
Simulated Data ◽  
Incident Beam ◽  
Scattering Matrix ◽  
High Energy ◽  
Crystal Potential ◽  
Transmission Electron ◽  
S Matrix ◽  
General Data ◽  
Limiting Case

The retrieval of a unique crystal potential from the scattering matrix {\cal S} in high-energy transmission electron diffraction is discussed. It is shown that, in general, data taken at a single orientation are not sufficient to determine all the elements of {\cal S}. Additional measurements with tilted incident beam are required for the determination of the whole {\cal S} matrix. An algorithm for the extraction of the crystal potential from the {\cal S} matrix measured at a single energy and thickness is presented. The limiting case of thin crystals is discussed. Several examples with simulated data are considered.

Kinematic Approximations in TED and RHEED Analysis of Reconstructed Surfaces

1990 ◽  
Vol 48 (2) ◽  
pp. 396-397
Author(s):  
L. -M. Peng ◽  
M. J. Whelan
Keyword(s):  
Electron Diffraction ◽  
Kinematic Analysis ◽  
Incident Beam ◽  
High Energy ◽  
Energy Electron ◽  
Great Success ◽  
High Energy Electron ◽  
Kinematic Approximation ◽  
Reconstructed Surfaces

In recent years there has been a trend in the structure determination of reconstructed surfaces to use high energy electron diffraction techniques, and to employ a kinematic approximation in analyzing the intensities of surface superlattice reflections. Experimentally this is motivated by the great success of the determination of the dimer adatom stacking fault (DAS) structure of the Si(111) 7 × 7 reconstructed surface.While in the case of transmission electron diffraction (TED) the validity of the kinematic approximation has been examined by using multislice calculations for Si and certain incident beam directions, far less has been done in the reflection high energy electron diffraction (RHEED) case. In this paper we aim to provide a thorough Bloch wave analysis of the various diffraction processes involved, and to set criteria on the validity for the kinematic analysis of the intensities of the surface superlattice reflections.The validity of the kinematic analysis, being common to both the TED and RHEED case, relies primarily on two underlying observations, namely (l)the surface superlattice scattering in the selvedge is kinematically dominating, and (2)the superlattice diffracted beams are uncoupled from the fundamental diffracted beams within the bulk.

High-Efficiency Three-Dimensional Visualization of Complex Microstructures via Multidimensional STEM Acquisition and Reconstruction

2020 ◽  
Vol 26 (2) ◽  
pp. 240-246 ◽  
Author(s):  
Kevin G. Field ◽  
Benjamin P. Eftink ◽  
Chad M. Parish ◽  
Stuart A. Maloy
Keyword(s):  
High Efficiency ◽  
3D Visualization ◽  
Accurate Determination ◽  
Three Dimensional ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
Chromium Steel ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractComplex material systems in which microstructure and microchemistry are nonuniformly dispersed require three-dimensional (3D) rendering(s) to provide an accurate determination of the physio-chemical nature of the system. Current scanning transmission electron microscope (STEM)-based tomography techniques enable 3D visualization but can be time-consuming, so only select systems or regions are analyzed in this manner. Here, it is presented that through high-efficiency multidimensional STEM acquisition and reconstruction, complex point cloud-like microstructural features can quickly and effectively be reconstructed in 3D. The proposed set of techniques is demonstrated, analyzed, and verified for a high-chromium steel with heterogeneously situated features induced using high-energy neutron bombardment.

A Critical Comparison of the Techniques used to Characterize the Crystallography of an Interface: Pd on mbe “Rown GaAs(100)

1984 ◽  
Vol 37 ◽  
Author(s):  
I. P. Delrue ◽  
M. Wittmer ◽  
T. S. Kuan ◽  
R. Ludeke
Keyword(s):  
Electron Diffraction ◽  
High Energy ◽  
Hexagonal Structure ◽  
Ex Situ ◽  
Epitaxial Relationship ◽  
Ion Channeling ◽  
Transmission Electron ◽  
Pronounced Reduction

AbstractIn situ Reflection High Energy Electron Diffraction and ex-situ Transmission Electron Diffraction and Ion Channeling have been applied to a reacted Pd-GaAs interface and the results obtained are critically compared. The investigation has been done on the stabilized c(2×8) surface obtained by MBE on GaAs(100) substrates. Smooth surface epitaxial growth has been observed by RHEED as soon as a few monolayers of Pd are deposited at a substrate temperature of about 325°C. TEM diffraction studies indicate the presence of an intermetallic hexagonal structure similar to the orthorhombic Pd5Ga2 but with slightly different lattice parameters due to the possible incorporation of As. A less abundant phase was also identified as an hexagonal structure similar to Pd8As2. Ion Channeling indicates pronounced reduction in scattering yield when the [100] axis of the substrate was aligned with the impinging beam, thus supporting the RHEED analysis. The three techniques listed above were found to be useful for the determination of the epitaxial relationship between the identified phases and the substrate.

Advances in image simulation for high-resolution TEM

1995 ◽  
Vol 53 ◽  
pp. 38-39
Author(s):  
Michael A. O'Keefe
Keyword(s):  
High Resolution ◽  
Structure Determination ◽  
Incident Beam ◽  
Hrtem Image ◽  
Image Simulation ◽  
Lattice Image ◽  
Transmission Electron ◽  
High Resolution Tem ◽  
Projection Approximation

The original high-resolution transmission electron microscope (HRTEM) image simulation program was written as a tool to confirm interpretation of HRTEM images of niobium oxides. Thorough testing on known structures showed that image simulation could reliably duplicate the imaging process occurring in the HRTEM, and could thus be confidently used to interpret images of unknown structures. Mainstream application of image simulation to routine structure determination by HRTEM was ushered in by the establishment of the wide applicability of the SHRLI (simulated high-resolution lattice image) programs. Structure determination of the mineral takéuchiite by HRTEM and image simulation was the first such determination accepted by the KJCr without x-ray data. Of course, once the reliability of image simulation had been established, it was realized that the technique could be put to work for applications other than structure determination. Early on, simulations were used to explore various HRTEM imaging parameters, including specimen ionicity, validity of the projection approximation, and the resolutionlimiting effects of incident-beam convergence. Since the inception of HRTEM image simulation, its range of uses has continued to expand, and so has the number of programs available; distribution of the SHRLI code spawned improved versions as well as some new programs.

Local determination of the components of the deflection of the vertical using gravitational potential parameters at a neighboring point

2020 ◽  
Author(s):  
Gerassimos Manoussakis ◽  
Romylos Korakitis
Keyword(s):  
Gravitational Potential ◽  
Simulated Data ◽  
Deflection Of The Vertical ◽  
Neighboring Point ◽  
Geodetic Coordinates ◽  
S Matrix ◽  
Local Determination ◽  
Derivatives Of ◽  
Potential Parameters

<p>We present a method for the estimation of the components ξ and η of the deflection of the vertical using several parameters of the gravitational potential. Specifically, we assume that we know the geodetic coordinates (φ, λ, h), the magnitude of gravity g, the components ξ, η and the second partial derivatives of the gravitational potential (elements of the Eötvös matrix) at a point P. Knowing only the geodetic coordinates of a neighboring point A (at a distance up to several kilometers from P), we estimate the components ξ and η at A. The proposed method is evaluated with simulated data at several points in Greece. The results show that it may be used for the densification of a given astrogeodetic net.</p>

Resolution Attainable With the Present Day STEM

1973 ◽  
Vol 31 ◽  
pp. 230-231 ◽  
Author(s):  
J. S. Wall ◽  
J. P. Langmore ◽  
H. Isaacson ◽  
A. V. Crewe
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Aperture Size ◽  
Magnetic Lens ◽  
Peak Intensity ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Half Angle

The scanning transmission electron microscope (STEM) constructed by the authors employs a field emission gun and a 1.15 mm focal length magnetic lens to produce a probe on the specimen. The aperture size is chosen to allow one wavelength of spherical aberration at the edge of the objective aperture. Under these conditions the profile of the focused spot is expected to be similar to an Airy intensity distribution with the first zero at the same point but with a peak intensity 80 per cent of that which would be obtained If the lens had no aberration. This condition is attained when the half angle that the incident beam subtends at the specimen, 𝛂 = (4𝛌/Cs)¼

Transmission Electron Microscopy of Protein Macromolecules

1971 ◽  
Vol 29 ◽  
pp. 424-425
Author(s):  
Henry S. Slayter
Keyword(s):  
Biological Systems ◽  
Metal Vapor ◽  
Resolving Power ◽  
Electron Microscopic ◽  
Chemical Methods ◽  
Molecular Weights ◽  
The Past ◽  
Physical Chemical ◽  
Transmission Electron

Electron microscopic methods have been applied increasingly during the past fifteen years, to problems in structural molecular biology. Used in conjunction with physical chemical methods and/or Fourier methods of analysis, they constitute powerful tools for determining sizes, shapes and modes of aggregation of biopolymers with molecular weights greater than 50, 000. However, the application of the e.m. to the determination of very fine structure approaching the limit of instrumental resolving power in biological systems has not been productive, due to various difficulties such as the destructive effects of dehydration, damage to the specimen by the electron beam, and lack of adequate and specific contrast. One of the most satisfactory methods for contrasting individual macromolecules involves the deposition of heavy metal vapor upon the specimen. We have investigated this process, and present here what we believe to be the more important considerations for optimizing it. Results of the application of these methods to several biological systems including muscle proteins, fibrinogen, ribosomes and chromatin will be discussed.

Determination of the phase structure of polymerblends by electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 492-493
Author(s):  
Dr. G. Kaemof
Keyword(s):  
Screw Extruder ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Single Screw Extruder ◽  
Transmission Electron ◽  
The Matrix ◽  
Twin Screw ◽  
Special Case ◽  
Microscopic Investigations

A mixture of polycarbonate (PC) and styrene-acrylonitrile-copolymer (SAN) represents a very good example for the efficiency of electron microscopic investigations concerning the determination of optimum production procedures for high grade product properties.The following parameters have been varied:components of charge (PC : SAN 50 : 50, 60 : 40, 70 : 30), kind of compounding machine (single screw extruder, twin screw extruder, discontinuous kneader), mass-temperature (lowest and highest possible temperature).The transmission electron microscopic investigations (TEM) were carried out on ultra thin sections, the PC-phase of which was selectively etched by triethylamine.The phase transition (matrix to disperse phase) does not occur - as might be expected - at a PC to SAN ratio of 50 : 50, but at a ratio of 65 : 35. Our results show that the matrix is preferably formed by the components with the lower melting viscosity (in this special case SAN), even at concentrations of less than 50 %.

Void-Lattice Formation in Natural Fluorite by Electron Irradiation

1976 ◽  
Vol 34 ◽  
pp. 614-615 ◽  
Author(s):  
L.E. Murr
Keyword(s):  
Electron Microscope ◽  
Electron Irradiation ◽  
Heavy Ion ◽  
High Energy ◽  
Stoichiometric Ratio ◽  
Direct Observations ◽  
Transmission Electron ◽  
Anion Vacancies ◽  
Cation And Anion Vacancies ◽  
Lattice Formation

The production of void lattices in metals as a result of displacement damage associated with high energy and heavy ion bombardment is now well documented. More recently, Murr has shown that a void lattice can be developed in natural (colored) fluorites observed in the transmission electron microscope. These were the first observations of a void lattice in an irradiated nonmetal, and the first, direct observations of color-center aggregates. Clinard, et al. have also recently observed a void lattice (described as a high density of aligned "pores") in neutron irradiated Al2O3 and Y2O3. In this latter work, itwas pointed out that in order that a cavity be formed,a near-stoichiometric ratio of cation and anion vacancies must aggregate. It was reasoned that two other alternatives to explain the pores were cation metal colloids and highpressure anion gas bubbles.Evans has proposed that void lattices result from the presence of a pre-existing impurity lattice, and predicted that the formation of a void lattice should restrict swelling in irradiated materials because it represents a state of saturation.

A General Method for Spectrometer Design in the Scoff Approximation

1976 ◽  
Vol 34 ◽  
pp. 538-539
Author(s):  
J. R. Fields
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Energy Analysis ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Chemical Identification ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
General Method

The energy analysis of electrons scattered by a specimen in a scanning transmission electron microscope can improve contrast as well as aid in chemical identification. In so far as energy analysis is useful, one would like to be able to design a spectrometer which is tailored to his particular needs. In our own case, we require a spectrometer which will accept a parallel incident beam and which will focus the electrons in both the median and perpendicular planes. In addition, since we intend to follow the spectrometer by a detector array rather than a single energy selecting slit, we need as great a dispersion as possible. Therefore, we would like to follow our spectrometer by a magnifying lens. Consequently, the line along which electrons of varying energy are dispersed must be normal to the direction of the central ray at the spectrometer exit.

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