Detailed Calculations of Thermal Diffuse Scattering

1997 ◽  
Vol 3 (S2) ◽  
pp. 1153-1154
Author(s):  
D.A. Müller ◽  
B. Edwards ◽  
E.J. Kirkland ◽  
J. Silcox
Keyword(s):  
Diffuse Scattering ◽  
Single Point ◽  
Scanning Transmission Electron Microscope ◽  
Diffraction Spot ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Einstein Model ◽  
Scanning Transmission ◽  
Convergent Beam ◽  
Thermal Diffuse

Convergent beam electron diffraction (CBED) produces a diffraction pattern from a single point on the specimen using a focused probe in the scanning transmission electron microscope (STEM). Because the incident wavefunction is a focused probe, each diffraction spot is enlarged to a disk the size of the objective aperture. Thermal vibration in the specimen reduces the intensity of the diffraction disks and introduces scattering in between the disk. This normally forbidden scattering between the diffraction disks is referred to as thermal diffuse scattering (TDS). The effects are most pronounced at large scattering angles, where TDS scattering can greatly reduce the intensity of the higher order Laue zone (HOLZ) lines. Previous work on modeling the TDS intensity involved the so-called frozen phonon method and the Einstein model of lattice vibration. The Einstein model assumes that each atom in the specimen vibrates independently of every other atom in the specimen and possible correlations among adjacent atoms are ignored.

Measurement of lattice parameter at the nanometer scale using convergent-beam microdiffraction from a thermal emission source

1993 ◽  
Vol 51 ◽  
pp. 690-691
Author(s):  
W. T. Pike
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Thermal Emission ◽  
Lattice Parameter ◽  
Scanning Transmission Electron Microscope ◽  
Emission Source ◽  
Device Structure ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Convergent Beam

With the advent of crystal growth techniques which enable device structure control at the atomic level has arrived a need to determine the crystal structure at a commensurate scale. In particular, in epitaxial lattice mismatched multilayers, it is of prime importance to know the lattice parameter, and hence strain, in individual layers in order to explain the novel electronic behavior of such structures. In this work higher order Laue zone (holz) lines in the convergent beam microdiffraction patterns from a thermal emission transmission electron microscope (TEM) have been used to measure lattice parameters to an accuracy of a few parts in a thousand from nanometer areas of material.Although the use of CBM to measure strain using a dedicated field emission scanning transmission electron microscope has already been demonstrated, the recording of the diffraction pattern at the required resolution involves specialized instrumentation. In this work, a Topcon 002B TEM with a thermal emission source with condenser-objective (CO) electron optics is used.

Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y Kotaka ◽  
T. Yamazaki ◽  
Y Kikuchi ◽  
K. Watanabe
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Contrast Imaging ◽  
High Spatial Resolution Image ◽  
Transmission Electron ◽  
Eigen Value ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam ◽  
Z Contrast

AbstractThe high-angle annular dark-field (HAADF) technique in a dedicated scanning transmission electron microscope (STEM) provides strong compositional sensitivity dependent on atomic number (Z-contrast image). Furthermore, a high spatial resolution image is comparable to that of conventional coherent imaging (HRTEM). However, it is difficult to obtain a clear atomic structure HAADF image using a hybrid TEM/STEM. In this work, HAADF images were obtained with a JEOL JEM-2010F (with a thermal-Schottky field-emission) gun in probe-forming mode at 200 kV. We performed experiments using Si and GaAs in the [110] orientation. The electron-optical conditions were optimized. As a result, the dumbbell structure was observed in an image of [110] Si. Intensity profiles for GaAs along [001] showed differences for the two atomic sites. The experimental images were analyzed and compared with the calculated atomic positions and intensities obtained from Bethe's eigen-value method, which was modified to simulate HAADF-STEM based on Allen and Rossouw's method for convergent-beam electron diffraction (CBED). The experimental results showed a good agreement with the simulation results.

The Characterization of Coal Structures for Coal Gasification Reactions Using Tem/Stem Techniques

1980 ◽  
Vol 38 ◽  
pp. 220-221
Author(s):  
J. A. Little ◽  
J. W. Evans ◽  
K. H. Westmacott
Keyword(s):  
Coal Gasification ◽  
Scanning Transmission Electron Microscope ◽  
Physical Parameters ◽  
Transmission Electron ◽  
Combined Use ◽  
Scanning Transmission ◽  
Gasification Reaction ◽  
Convergent Beam ◽  
Different Gases

The liquefaction and gasification of various coals are increasingly important technological utilizations of coal which are dependent upon its physical characteristics as well as its chemistry. In this respect, both the size and distribution of pores and the size, distribution and chemical identity of the submicron size minerals are physical parameters of great interest because of their probable influence in the coal conversion processes. In Berkeley, this study is proceeding by examination of such processes using an environmental cell in a high voltage microscope, by which the influence of different gases, temperatures and pressure upon the gasification reaction can be studied. An important first step in such a study is the primary characterization of the coals to be studied and the combined use of both transmission (TEM) and scanning transmission electron microscope (STEM) analyses utilizing both convergent beam methods and an energy dispersive X-ray analytical detector is thus a powerful tool in such a characterization.

Thermal diffuse scattering in transmission electron microscopy

2011 ◽  
Vol 111 (12) ◽  
pp. 1670-1680 ◽  
Author(s):  
B.D. Forbes ◽  
A.J. D'Alfonso ◽  
S.D. Findlay ◽  
D. Van Dyck ◽  
J.M. LeBeau ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Diffuse Scattering ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Thermal Diffuse

Structural studies on decagonal quasicrystals using the HAADF-STEM and CBED methods

2000 ◽  
Vol 215 (10) ◽  
Author(s):  
K. Saitoh ◽  
K. Tsuda ◽  
M. Tanaka ◽  
A.P. Tsai
Keyword(s):  
Structural Parameters ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Structural Studies ◽  
Space Groups ◽  
Decagonal Quasicrystals ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam

The applications of the high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and convergent-beam electron diffraction (CBED) methods to decagonal quasicrystals and its approximant are presented by giving some examples. The HAADF method can show the atomic arrangement mainly composed of transition metal (TM) atoms in Al-TM systems. The CBED method can determine the super point- and space-groups of quasicrystals, and furthermore can be used to refine the structural parameters.

Imaging dislocations with an annular dark-field detector

1992 ◽  
Vol 50 (2) ◽  
pp. 1224-1225 ◽  
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Supported Catalysts ◽  
Dark Field ◽  
Contrast Effects ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Active Research ◽  
Thermal Diffuse

High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) has been recently the subject of active research because of its successful applications to the characterization of supported catalysts, interface problems in MBE grown semiconductors, superconductors and X-ray multilayers. The characteristics of HAADF images are different from those of the TEM images. For perfect single crystals the HAADF signal is mainly generated from thermal diffuse scattering. HAADF technique has also been used to study dopant contrast effects in semiconductors and dislocations have also been observed with an ADF detector. In this paper we report a study of dislocation contrasts and their dependence on the inner collection angle of the ADF detector.The STEM instrument used for the observations was the HB5 from VG Microscopes, Ld., modified by the addition of an ultra-high resolution pole piece (Cs = 0.8 mm) and a two-dimensional detector system. Post specimen lenses and various beam stops were used to change the inner (α) and outer (β) collection angles of the ADF detector.

Atomic-focuser Imaging by Graphite Crystals in Carbon Nanoshells

2000 ◽  
Vol 6 (5) ◽  
pp. 429-436
Author(s):  
J.M. Cowley ◽  
J.B. Hudis
Keyword(s):  
High Resolution Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Diffraction Spot ◽  
Fourier Image ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Image Distance ◽  
Thin Crystal ◽  
Image Part

AbstractOne of the atomic-focuser modes for ultra-high resolution electron microscopy is described theoretically and illustrated by the observation of images formed within the diffraction spots of nanodiffraction patterns of carbon nanoshells. In this mode, the specimen is illuminated by the focused probe of a scanning transmission electron microscope and is followed by a thin crystal at a Fourier-image distance. The theory shows that each diffraction spot of the crystal contains a magnified image of the illuminated area of the specimen, having a resolution depending on the width of the intensity peak of electrons channeled along atomic rows in the crystal. A thin graphite crystal, contained within one wall of a carbon nanoshell, can act as an atomic focuser to image part of the other wall of the nanoshell, or tungsten atoms deposited on this wall. Simulations of the transmission of electrons through graphite crystals show that the images formed should have a resolution of about 0.06 nm. Experimental images suggest that this resolution has been attained in the imaging of tungsten atoms or clusters of tungsten atoms.

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