Multiple scattering and displacive modulation in the YBa2Cu3O7-δ system

1991 ◽  
Vol 49 ◽  
pp. 1082-1083
Author(s):  
Yimei Zhu ◽  
M. Suenaga ◽  
A.R. Moodenbaugh
Keyword(s):  
Diffraction Pattern ◽  
Multiple Scattering ◽  
Diffuse Scattering ◽  
Incident Beam ◽  
High Symmetry ◽  
Diffuse Intensity ◽  
Modulated Structure ◽  
Transmission Electron ◽  
Scattering Effects ◽  
Structure Modulation

Using transmission electron microscopy, structure modulation associated with electron multiple scattering and diffuse scattering in oxygen reduced, and Fe and Co doped YBa2Cu3O7_δ has been studied. The modulated structure (tweed) exhibits [110] and roughly-periodic lenticular domain images (see Fig.l) and cross-shaped diffuse intensity in diffraction (see Fig.2). The overall diffraction pattern in the [001] zone has a 4-fold symmetry with diffraction intensity which falls off monotonically from one Brillouin zone to the next. Superimposed over each Bragg spot seem to be two cross-streaks of equal length in the [110] and directions.However, for a diffraction pattern in a high symmetry Laue case, one must consider the possibility of multiple scattering effects, whereby a diffracted electron beam acts as an incident beam. This can complicate diffuse scattering phenomena, even in a thin crystal. Careful inspection of Fig.2 reveals that the shapes of the diffuse scattering are not all identical at all diffraction spots.

An X-ray diffraction study of AgNbO3 and comparison with NaNbO3

1999 ◽  
Vol 14 (4) ◽  
pp. 253-257 ◽  
Author(s):  
C. N. W. Darlington
Keyword(s):  
Diffraction Pattern ◽  
Figure Of Merit ◽  
Parent Phase ◽  
Incident Beam ◽  
Large Error ◽  
High Symmetry ◽  
X Ray Diffraction ◽  
Beam Focusing ◽  
Low Symmetry

The powder diffraction pattern of the perovskite AgNbO3 has been measured using CuKα1 radiation with an incident beam focusing monochromator to eliminate the Kα2 component. Indexing the pattern shows that the multipartite cell is 2×2×4 times that of the pseudocubic subcell. Comparison is made with the diffraction pattern of NaNbO3, which has a similar multipartite unit cell. There are strong similarities, but close inspection shows that the structures are not isomorphous. The paper concludes with a discussion of the figure of merit FN for pseudosymmetric structures. It is suggested that two figures of merit be reported. The first should be the standard one using either all measured reflections or just the first 30. The proposed second figure of merit does not include any superlattice reflections. These superlattice reflections tend to be very weak, resulting in a low completeness factor and relatively large error in the measurement of their position. This effect produces an unrealistically low value of the standard figure of merit. By including only “main” reflections, i.e., those reflections that are common to both the low-symmetry and high-symmetry parent phase (if it exists), a much better estimate of the quality of the fitting of the measured diffraction pattern is obtained.

Transition from the incommensurately modulated structure to the lock-in phase in Co-åkermanite

2001 ◽  
Vol 57 (4) ◽  
pp. 443-448 ◽  
Author(s):  
Andreas K. Schaper ◽  
Michael Schosnig ◽  
Ali Kutoglu ◽  
Werner Treutmann ◽  
Helmut Rager
Keyword(s):  
Room Temperature ◽  
Domain Walls ◽  
Modulated Structure ◽  
Incommensurate Structure ◽  
Transmission Electron ◽  
Structure Modulation ◽  
Lock In ◽  
Highly Strained ◽  
Single Orientation

The adaptation of the incommensurate structure modulation in Ca2CoSi2O7 (dicalcium cobalt disilicate) single crystals to decreasing temperature has been examined using in situ high-resolution transmission electron microscopy and electron diffraction. The transition from the incommensurate to the commensurate lock-in phase of Co-åkermanite exhibits a pronounced hysteresis of a highly strained metastable state with a characteristic microdomain morphology. A network of domain walls surrounding single orientation domains develops out of the room-temperature tartan pattern, the domains increase in size and their alignment changes from crystallographic to random. At 100 K the phase transition becomes almost complete. In parallel, the evolution of the modulation structure can be described by a change from a loose arrangement of octagonal tilings into a close-packed configuration of overlapping octagons in the commensurate low-temperature lock-in phase. Thereby, the octagon represents the ordered distribution of low-coordinated Ca clusters within a nanodomain extending over 4 × 4 subunits, on average [Riester et al. (2000). Z. Kristallogr. 215, 102–109]. The modulation wavevector was found to change from q 1,2 = 0.295 (a* ± b*) at 300 K to q 1,2 = 0.320 (a* ± b*) at 100 K.

Disorder, structured diffuse scattering and the transmissionelectron microscope

2005 ◽  
Vol 220 (12) ◽  
Author(s):  
Ray L. Withers
Keyword(s):  
Electron Microscopy ◽  
Multiple Scattering ◽  
Solid Solutions ◽  
Diffuse Scattering ◽  
Disordered Materials ◽  
Diffuse Intensity ◽  
Modulation Wave ◽  
Distribution Shape ◽  
Flexible Framework ◽  
Diffuse Distribution

AbstractA review of the application of electron microscopy to disordered materials exhibiting sharp, highly structured diffuse intensity distributions is given from a modulation wave approach perspective. Structurally useful diffraction phenomena such as polarization, overall diffuse distribution shape and pseudo-extinction conditions are highlighted. The dangers of multiple scattering are emphasized before two particular such systems, substitutionally disordered solid solutions and inherently flexible framework structures are considered in more detail.

Development of an automatic electron diffraction pattern analyzing system

1983 ◽  
Vol 41 ◽  
pp. 400-401
Author(s):  
S. Moriguchi ◽  
T. Shinkawa ◽  
E. Watanabe ◽  
Y. Makita ◽  
S. Sakurai ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Electron Diffraction Pattern ◽  
Incident Beam ◽  
Light Level ◽  
Lattice Constants ◽  
Video Signals ◽  
Hardware System ◽  
Transmission Electron

The electron diffraction pattern has information on the crystal structure of samples, such as the crystal system, lattice constants and the orientation for the incident beam. Material can be identified by measuring the above characteristics and, in general principle by measuring their accurate lattice spacings. However, this measurement requires a lot of time and fundamental knowledge of the crystal structure.The present automatic analyzing system of the electron diffraction pattern makes the analysis ease. The outline of this system is described in this paper.The hardware system consists roughly of three components; a low-light-level TV device called the image carrier, a frame memory, and a minicomputer. The image carrier transforms the image formed on the flourescent screen of a transmission electron microscope (TEM) into video signals. The frame memory is provided with a memory plane of 512 x 512 pixels, each having 256 gray levels. It digitaizes video signals of the image and stores them in itself.

Dark-Field and Marginal Imaging with a Thin-Annular Detector in STEM

1996 ◽  
Vol 2 (1) ◽  
pp. 9-19
Author(s):  
R.-J. Liu ◽  
J.M. Cowley
Keyword(s):  
Diffraction Pattern ◽  
Amorphous Materials ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Imaging Mode ◽  
Annular Detector ◽  
Diffraction Patterns

The use of a thin annular detector in a scanning transmission electron microscope is shown, theoretically and experimentally, to allow several imaging modes that may be of value for the study of thin specimens. The diffraction pattern on the detector plane may be expanded or contracted by means of post-specimen lenses to vary the collection angle of the thin annular detector to form dark- or bright-field images. Dark-field images obtained from annuli of various radii in the diffraction pattern can selectively reveal different components of the sample, as illustrated in the case of a sample containing platinum crystallites, amorphous carbon, and carbon nanotubes. Amorphous materials of different composition can be distinguished by selecting the main maxima in their diffraction patterns. If the central beam is enlarged so that it just fills the inner aperture of the detector, the “marginal” imaging mode so achieved gives an image contrast that is proportional to the square of the differential of the projected potential distribution. Any deflection of the incident beam spot due to a change of the projected potential gives bright contrast in the image.

Dynamical scattering effects in electron scattering measurements of the Compton profiles of solids

1987 ◽  
Vol 409 (1836) ◽  
pp. 161-176 ◽  
Keyword(s):  
Crystal Structure ◽  
Compton Scattering ◽  
Multiple Scattering ◽  
Electron Scattering ◽  
Experimental Work ◽  
Incident Beam ◽  
Bragg Scattering ◽  
Dominant Contribution ◽  
Scattering Effects ◽  
Scattering Measurements

In electron scattering measurements of the Compton profiles of solids, multiple scattering events contribute strongly to the observed profile. The dominant contribution to the multiple scattering arises from events in which Bragg scattering is followed by Compton scattering. The Bragg scattering is calculated by using a multi-slice approach that allows for dynamical scattering, and each Bragg beam is then treated as a source of Compton scattering. In this paper, the dependence of multiple scattering on the energy of the incident beam and on the thickness, orientation, crystal structure and atomic number of the sample are investigated to determine the parameters that affect the multiple scattering most strongly, and to seek ways in which multiple scattering can be reduced in experimental work.

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 studies of the vacancy ordering in YSI2-X thin films

1991 ◽  
Vol 49 ◽  
pp. 562-563
Author(s):  
F.-R. Chen ◽  
T. L. Lee ◽  
L. J. Chen
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Thin Films ◽  
Diffraction Pattern ◽  
Annealing Temperature ◽  
Lattice Mismatch ◽  
Si Substrate ◽  
Metal Thin Films ◽  
Transmission Electron ◽  
Vacancy Ordering

YSi2-x thin films were grown by depositing the yttrium metal thin films on (111)Si substrate followed by a rapid thermal annealing (RTA) at 450 to 1100°C. The x value of the YSi2-x films ranges from 0 to 0.3. The (0001) plane of the YSi2-x films have an ideal zero lattice mismatch relative to (111)Si surface lattice. The YSi2 has the hexagonal AlB2 crystal structure. The orientation relationship with Si was determined from the diffraction pattern shown in figure 1(a) to be and . The diffraction pattern in figure 1(a) was taken from a specimen annealed at 500°C for 15 second. As the annealing temperature was increased to 600°C, superlattice diffraction spots appear at position as seen in figure 1(b) which may be due to vacancy ordering in the YSi2-x films. The ordered vacancies in YSi2-x form a mesh in Si plane suggested by a LEED experiment.

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.

On-line alignment and astigmatism correction using a TV and personal computer

1993 ◽  
Vol 51 ◽  
pp. 202-203
Author(s):  
F. Hosokawa ◽  
Y. Kondo ◽  
T. Honda ◽  
Y. Ishida ◽  
M. Kersker
Keyword(s):  
High Resolution ◽  
Personal Computer ◽  
Block Diagram ◽  
Incident Beam ◽  
Ccd Camera ◽  
Alignment Procedure ◽  
Astigmatism Correction ◽  
Transmission Electron ◽  
Alignment System ◽  
On Line

High-resolution transmission electron microscopy must attain utmost accuracy in the alignment of incident beam direction and in astigmatism correction, and that, in the shortest possible time. As a method to eliminate this troublesome work, an automatic alignment system using the Slow-Scan CCD camera has been introduced recently. In this method, diffractograms of amorphous images are calculated and analyzed to detect misalignment and astigmatism automatically. In the present study, we also examined diffractogram analysis using a personal computer and digitized TV images, and found that TV images provided enough quality for the on-line alignment procedure of high-resolution work in TEM. Fig. 1 shows a block diagram of our system. The averaged image is digitized by a TV board and is transported to a computer memory, then a diffractogram is calculated using an FFT board, and the feedback parameters which are determined by diffractogram analysis are sent to the microscope(JEM- 2010) through the RS232C interface. The on-line correction system has the following three modes.

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