Diffraction Channeling and the Production of Secondary Excitation

1999 ◽  
Vol 5 (S2) ◽  
pp. 688-689
Author(s):  
S.J. Pennycook
Keyword(s):  
Quantitative Description ◽  
Incident Beam ◽  
Diffraction Theory ◽  
Orientation Dependence ◽  
Contrast Imaging ◽  
Dynamical Diffraction ◽  
Efficient Detection ◽  
Annular Detector ◽  
Resolution Imaging ◽  
Z Contrast

The pivotal role played by Archie Howie in the development of many areas of electron microscopy is universary acknowledged.Here I would like to highlight his contribution to the quantitative description of secondary excitations, which was an important influence on the development of Z-contrast imaging in zone-axis crystals. Secondary excitations are those such as x-ray emission which occur following a primary scattering event, in this case excitation of inner shell electrons. The first important concept to be realized by Archie was that dynamical diffraction and channeling are different manifestations of the same physical effect, namely, the multiple scattering of electrons within a crystal. Second was the realization that processes which are localized within the unit cell will show a dependence on diffraction conditions, such as incident beam orientation, and could therefore be described quantitatively using dynamical diffraction theory. Precisely the same theory was used to describe the orientation dependence of cathodoluminescenceThe development of the STEM for high resolution imaging was of course due primarily to Crewe and coworkers, with an annular detector to allow efficient detection of elastic scattering over a wide angular range.

Z-Contrast Imaging of Heavy Metal Particles Supported in A Zeolitic Matrix Via High-Resolution Stem

1987 ◽  
Vol 45 ◽  
pp. 204-205
Author(s):  
J. H. Butler ◽  
G. M. Brown
Keyword(s):  
High Resolution ◽  
Incident Beam ◽  
Dark Field ◽  
Irradiation Damage ◽  
Contrast Imaging ◽  
Vacuum Oven ◽  
Annular Dark Field ◽  
Resolution Imaging ◽  
Beam Currents ◽  
Z Contrast

High resolution Imaging of zeolites is difficult because these materials are very susceptible to Irradiation damage. It is now well known that dehydrated samples are more stable under the electron beam. Thus the most successful high resolution studies of zeolites to date have been on samples which were freeze-fractured and subsequently dehydrated via heating in a vacuum oven. Electron microscopy was then performed using a combination of low Incident beam currents and sensitive detectors. One problem with this method is that zeolites fracture along cleavage planes and therefore are deposited on microscope grids In a particular orientation. This limits the range of viewing angles. Here we describe a method of sample preparation via ultramlctrotomy as well as the establishment of suitable FEG/STEM Imaging conditions which permit the observation of small (7-14 A diameter) Pt particles within Individual zeolite channels using the method of Z-contrast as applied with a high-angle annular dark field detector. This method allows observation over all crystalline orientations for relatively long exposures to the beam.

High-resolution z-contrast imaging of semiconductor interfaces

1989 ◽  
Vol 47 ◽  
pp. 468-469
Author(s):  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Phase Contrast ◽  
Contrast Imaging ◽  
Compositional Modulation ◽  
Semiconductor Interfaces ◽  
Complex Figure ◽  
Thin Region ◽  
Stem Image ◽  
Annular Detector ◽  
Z Contrast

Using a high-angle annular detector on a high-resolution STEM it is possible to form incoherent images of a crystal lattice characterized by strong atomic number or Z contrast. Figure 1 shows an epitaxial Ge film on Si(100) grown by oxidation of Ge-implanted Si. The image was obtained using a VG Microscopes' HB501 STEM equipped with an ultrahigh resolution polepiece (Cs ∽1.2 mm, demonstrated probe FWHM intensity ∽0.22 nm). In both crystals the lattice is resolved but that of Ge shows much brighter allowing the interface to be located exactly and interface steps to be resolved (arrowed). The interface was indistinguishable in the phase-contrast STEM image from the same region, and even at higher resolution the location of the interface is complex. Figure 2 shows a thin region of an MBE-grown ultrathin super-lattice (Si8Ge2)100. The expected compositional modulation would show as one bright row of dots from the 2 Ge monolayers separated by 4 rows of lighter Si columns. The image shows clearly that strain-induced interdiffusion has occurred on the monolayer scale.

Algorithms for determining the phase of RHEED oscillations

2015 ◽  
Vol 48 (6) ◽  
pp. 1927-1934 ◽  
Author(s):  
Zbigniew Mitura ◽  
Sergei L. Dudarev
Keyword(s):  
Experimental Data ◽  
Direct Method ◽  
Incident Beam ◽  
Diffraction Theory ◽  
High Energy ◽  
Angle Of Incidence ◽  
High Energy Electron ◽  
Dynamical Diffraction ◽  
Glancing Angle ◽  
Low Symmetry

Oscillations of reflection high-energy electron diffraction (RHEED) intensities are computed using dynamical diffraction theory. The phase of the oscillations is determined using two different approaches. In the first, direct, approach, the phase is determined by identifying the time needed to reach the second oscillation minimum. In the second approach, the phase is found using harmonic analysis. The two approaches are tested by applying them to oscillations simulated using dynamical diffraction theory. The phase of RHEED oscillations observed experimentally is also analysed. Experimental data on the variation of the phase as a function of the glancing angle of incidence, derived using the direct method, are compared with the values computed using both the direct and harmonic methods. For incident-beam azimuths corresponding to low-symmetry directions, both approaches produce similar results.

Computer Investigations of Features of RHEED Oscillations for GaAs and for Ge

2013 ◽  
Vol 203-204 ◽  
pp. 347-350
Author(s):  
Zbigniew Mitura
Keyword(s):  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Incident Beam ◽  
Diffraction Theory ◽  
Oscillation Phase ◽  
Dynamical Diffraction ◽  
Wide Range ◽  
Glancing Angle ◽  
Scattering Potential ◽  
Experimental Findings

During molecular beam epitaxy regular oscillations of the intensity of the specularly reflected beam often occur. The phenomenon of such oscillations is still theoretically explained only partially. For example it is not clear why usually the oscillation phase depends strongly on the glancing angle of the incident beam. However, quite recently interesting results were shown in the literature on the features of RHEED oscillations observed during the growth of Ge layers. The phase of oscillations practically stays constant for a wide range of angles. So in this paper, we show results of RHEED dynamical calculations for Ge. They are presented together with results of calculations for GaAs to make analysis executed more complete. It is concluded that experimental findings for Ge for off-symmetry azimuths can be explained using dynamical diffraction theory employing the proportional model (for which the scattering potential of the layer is determined as the potential of the completed layer multiplied by the coverage).

Z-Contrast Imaging in the Scanning Transmission Electron Microscope

1995 ◽  
Vol 1 (6) ◽  
pp. 231-251 ◽  
Author(s):  
S.J. Pennycook ◽  
D.E. Jesson ◽  
M.F. Chisholm ◽  
N.D. Browning ◽  
A.J. McGibbon ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Entropy Analysis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Annular Detector ◽  
Incoherent Imaging ◽  
Z Contrast

Z-contrast STEM using an annular detector can provide an intuitively interpretable, column-by-column, compositional map of crystals. Incoherent imaging reduces dynamical effects to second order so that the map directly reflects the positions of the atomic columns and their relative high-angle scattering power. This article outlines how these characteristics arise, presents some examples of the insights available from a direct image, and discusses recent developments of atomic-resolution microanalysis, direct structure retrieval by maximum entropy analysis, and Z-contrast imaging at 1.4 Å resolution using a 300-kV STEM.

scholarly journals Modeling Dislocation Contrasts Obtained by Accurate-Electron Channeling Contrast Imaging for Characterizing Deformation Mechanisms in Bulk Materials

2019 ◽  
Author(s):  
Hana Kriaa ◽  
Antoine Guitton ◽  
Nabila Maloufi
Keyword(s):  
Materials Science ◽  
Incident Beam ◽  
Sample Surface ◽  
Diffraction Theory ◽  
Contrast Imaging ◽  
Black Line ◽  
Electron Channeling ◽  
Theoretical Predictions ◽  
Deformation Defects ◽  
First Time

Electron Channeling Contrast Imaging (ECCI) is becoming a powerful tool in Materials Science for characterizing deformation defects. Dislocations observed by ECCI in Scanning Electron Microscope, exhibit several features depending on the crystal orientation relative to the incident beam (white/black line on a dark/bright background). In order to bring new insights concerning these contrasts, we report an original theoretical approach based on the dynamical diffraction theory. Our calculations led, for the first time, to an explicit formulation of the backscattered intensity as a function of various physical and practical parameters governing the experiment. Intensity profiles are modeled for dislocations parallel to the sample surface for different channeling conditions. All theoretical predictions are consistent with experimental results.

scholarly journals Modeling Dislocation Contrasts Obtained by Accurate-Electron Channeling Contrast Imaging for Characterizing Deformation Mechanisms in Bulk Materials

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1587 ◽  
Author(s):  
Hana KRIAA ◽  
Antoine GUITTON ◽  
Nabila MALOUFI
Keyword(s):  
Materials Science ◽  
Incident Beam ◽  
Sample Surface ◽  
Diffraction Theory ◽  
Contrast Imaging ◽  
Black Line ◽  
Electron Channeling ◽  
Theoretical Predictions ◽  
Deformation Defects ◽  
First Time

Electron Channeling Contrast Imaging (ECCI) is becoming a powerful tool in materials science for characterizing deformation defects. Dislocations observed by ECCI in scanning electron microscope exhibit several features depending on the crystal orientation relative to the incident beam (white/black line on a dark/bright background). In order to bring new insights concerning these contrasts, we report an original theoretical approach based on the dynamical diffraction theory. Our calculations led, for the first time, to an explicit formulation of the back-scattered intensity as a function of various physical and practical parameters governing the experiment. Intensity profiles are modeled for dislocations parallel to the sample surface for different channeling conditions. All theoretical predictions are consistent with experimental results.

scholarly journals Modeling Dislocation Contrasts Obtained by Accurate-Electron Channeling Contrast Imaging for Characterizing Deformation Mechanisms in Bulk Materials

2019 ◽  
Author(s):  
Hana Kriaa ◽  
Antoine Guitton ◽  
Nabila Maloufi
Keyword(s):  
Materials Science ◽  
Incident Beam ◽  
Sample Surface ◽  
Diffraction Theory ◽  
Contrast Imaging ◽  
Black Line ◽  
Electron Channeling ◽  
Theoretical Predictions ◽  
Deformation Defects ◽  
First Time

Electron Channeling Contrast Imaging (ECCI) is becoming a powerful tool in Materials Science such as for characterizing deformation defects. Dislocations observed by ECCI in Scanning Electron Microscope, exhibit several features depending on the crystal orientation relative to the incident beam (white/black line on a dark/bright background). In order to bring new insights concerning these contrasts, we report an original theoretical approach based on the dynamical diffraction theory. Our calculations led, for the first time, to an explicit formulation of the backscattered intensity as function of various physical and practical parameters governing the experiment. Intensity profiles are modeled for dislocations parallel to the sample surface for different channeling conditions. All theoretical predictions are consistent with experimental results.

Atomic structure determination of NIO-ZRO2(CaO) and NI-ZRO2(CaO) interfaces using Z-contrast imaging and EELS

1996 ◽  
Vol 54 ◽  
pp. 106-107
Author(s):  
E.C. Dickey ◽  
V.P. Dravid ◽  
P. Nellist ◽  
D.J. Wallis ◽  
N. D. Browning ◽  
...  
Keyword(s):  
Atomic Structure ◽  
Bulk Material ◽  
Interface Structure ◽  
Structure Property ◽  
Contrast Imaging ◽  
Spatially Resolved ◽  
Structure Property Relationships ◽  
Powerful Approach ◽  
Resolution Imaging ◽  
Z Contrast

Combining atomic-resolution imaging with spatially resolved electron energy loss spectroscopy (EELS) is a powerful approach to probing the geometric, chemical and electronic aspects of internal interfaces. By elucidating these interrelated constituents of interface structure, one can begin to understand the influence of the interface atomic structure on relevant bulk material properties, deducing atomic structure/property relationships. The combined Z-contrast and EELS approach was applied to two types of heterophase interfaces: oxide-oxide (NiO-ZrO2) and metal-oxide (Ni-ZrO2). The interface structure will be discussed in light of these experiments and compared to previous HREM results.

Nanometer-Scale Cathodoluminescent Properties Through Z-Contrast Scanning Transmission Electron Microscopy

2000 ◽  
Vol 6 (S2) ◽  
pp. 130-131
Author(s):  
H-J. Gao ◽  
G. Duscher ◽  
M. Kim ◽  
D. Kumar ◽  
R.K. Singh ◽  
...  
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Incident Beam ◽  
Dead Layer ◽  
Contrast Imaging ◽  
Tem Analysis ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast

Interest in rare earth-activated oxide-based phosphor thin films for high-resolution display devices has been growing in the last few decades. However, thin-film phosphors typically have a significantly reduced brightness compared to equivalent powder phosphor materials. Several possible explanations have been suggested for the lower brightness including internal reflection and the small interaction volume between the incident beam and the solid. In this report, we show another factor to be crucial to external radiative efficiency, the porosity of the films. Porosity creates internal surfaces that act as a "dead layer" which decreases the emission efficiency. Using Z-contrast imaging in the scanning transmission electron microscope (STEM) with simultaneous cathodoluminescence (CL) imaging, the dead layer is directly observed, and quantitative accounts for the reduction of luminescent efficiency.Eu activated Y2O3 thin films with thickness of about 200 nm were deposited on (001) LaAlO3 substrates by laser ablation. TEM analysis of the samples was conducted in a Philips EM-400 electron microscope operated at l00kV.

Sign in / Sign up

Export Citation Format

Share Document