Tem Diffraction Pattern Analysis Software

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Practical approaches for in-situ and environmental transmission electron microscopy. Gatan Microscopy Suite software. Diffraction analysis package to. Please tell me about some software to analyze TEM diffraction images and fringe patterns? I need some software to analyze TEM. The SAED pattern analysis software?

Selected area diffraction (SAD) is a TEM technique to obtain diffraction patterns that result from the electron beam scattered by the sample lattice. Obeying the bragg’s law, the electrons are scattered elastically by the lattice, therefore, we can index the diffraction spots in the pattern and identify the phases in the sample and study their structures. Typically, the area size of the sample been selected by SAD aperture is 0.5-1 μm, so the microstructure of the sample could be fine selected and tested.
From an SAD pattern the material scientists can obtain structural information of the sample, like crystalline symmetry, unit cell parameter and space group etc. While the metallurgists can learn the information about phase separation, texture, precipitation and some other microstructure features in their samples.
Instrument:
The SAD test is one of the most conventional experiments that are conducted by TEM. Almost all the TEM machines with a parallel electron beam source are capable of SAD tests. The world-famous TEM machine producers are listed as follows: Zeiss, FEI/Philips, JEOL, and Hitachi. The photo on the left shows the Morgagni 268(D)[1] TEM produced by FEI company.
In the imaging system of a TEM , an SAD aperture is inserted in the image plane of the low object lens to limit the sample volume that contributes to the diffraction pattern. In the figure on the right, we can find the SAD aperture on the image plane is equivalent to a virtual aperture close to the specimen which functions as a diffraction area selector.
The diffraction pattern could be analyzed by software. After inputting test parameters such as TEM machine brand, voltage, zone axis, a simulated diffraction pattern can be drawn according to the kinematical theory of electron diffraction. The intensity of the spots is just proportional to their structure factor.
There are many softwares for SAD pattern analysis. Digital Micrograph is an advanced image aquisition and analysis software provided by Gatan in TEM labs, but it is very expensive. Electron direct methods is a set of programs by L. Marks & R. Kilaas to combine various aspects of imaging processing and manipulation of HRTEM images and diffraction patterns as well as direct methods. Java electron crystallography package developed by X. Z. Li can be used for stereographic projection, simulation and analysis of electron patterns. Process diffraction by J. Labar allows to obtain quantitative structural information from SAD patterns. JEMS student edition developed by P. Stadelmann is the swiss army knife for simulation of HRTEM images and diffraction patterns, the photo below shows the simulation of the SAD pattern of Al alloy by JEMS student edition.
Analysis:
The SAD technique in TEM test is a powerful tool for material characterization. Its capability includes identification of the material species, determination of unit cell parameters etc.
To analyze the SAD patterns, we combine the Bragg's equation and geometric relationship in the reciprocal space[2]
tan2θ = D/L (geometric relationship in reciprocal space)
where d is spacing between planes, λ is the wavelength of the electron beam, θ is the diffraction angle, D is the distance between spots on the SAD pattern, L is camera length for the TEM machine. For a very small diffraction angle θ, 2sinθ equals to tan2θ, therefore, we can calculate the d-spacings for the spots on the SAD pattern by
Every spot in the SAD pattern corresponds to lattice planes of a certain miller index in single crystal. All the spots on the pattern could be indexed. Every ring in SAD pattern corresponds to a group of lattice planes of the same miller index family in the polycrystalline sample. If we fix the electron beam and rotate the sample, some spot/ring will be activated, other spot /ring may die away, all of which is based on the diffraction condition stated above.
Since the SAD pattern is only 2D projection of reciprocal lattice, tilting test technique should be applied to determine 3D parameters in a unit cell. Systematic extinction in the diffraction pattern can be used to determine space group for an unknown crystal.
Some examples are provided below to explain the application of SAD pattern in the research of material science:
From the principle of electron diffraction, the diffraction pattern is completely dependent on the d-spacing and composition of the crystal being analyzed. In other words, the diffraction pattern could be regarded as a finger print for a certain crystal.
In figure on the right[3], the fundamental diffraction pattern corresponds to the B2-structure NiAl in [111] zone axis, while around the fundamental bright spots there are also weak diffraction spots which may result from Ni4Ti3 particles precipitated in the NiAl matrix after heat treatment. Obviously, we can investigate and identify the phases in the sample, even if the amount of some phase is quite small.
Typically, a pattern of diffraction spots results from the electron beam diffracted by a single crystal, while the sample containing large number of small randomly distributed grains results in continuous rings. That is because these grains all contribute to the formation of the diffraction pattern. The radii of the rings are inversely proportional to the interplanar spacings dhkl of a lattice planes of crystals, which obeys the relationship that mentioned above:
SAD patterns of B2 structure NiAl (b)before annealing, (d) after 10hr at 400 ℃ and (f) 100hr at 400℃

Diffraction Grating

The rings turn from continuous to dotty as the grain size of the polycrystalline material increases. The figures[3] above show this trend clearly. These figures correspond to the SAD pattern of B2 structure NiAl before annealing, after 10hr at 400 and after 100hr at 400 respectively. The grain sizes of the specimens are 20nm, 30nm and 70 nm respectively.
When it comes to the case that the grain size is extremely small or the material is totally amorphous, the feature of concentric rings disappears but only left a halo around the bright spot in the center, which indicates that the electrons are diffracted randomly by the material of amorphous structure. The photo on the left is the SAD pattern[4] of as-deposited GeSi film.
If the grains in the sample oriented in a favored direction, the SAD pattern turns out to be many partial rings, as shown in the right figure[5]. The texture featured diffraction pattern can be regarded as a intermediate case between the diffraction in single crystal and in polycrystalline. The researchers usually study the textured alloy by analyzing these SAD patterns.

References:

[1] http://www.fei.com/products/transmission-electron-microscopes/morgagni.aspx
[2] David B. Williams C. Barry Carter Transmission Electron Microscopy A Textbook for Materials Science Springer Science Business Media, LLC 1996, 2009
[3] Prokofiev, E.A., et al., Suppression of Ni(4)Ti(3) Precipitation by Grain Size Refinement in Ni-Rich NiTi Shape Memory Alloys. Advanced Engineering Materials, 2010. 12(8): p. 747-753.
Tem
[4] Z. W. Xu & A. H. W. Ngan (2004): TEM study of electron beam-induced crystallization of amorphous GeSi films, Philosophical Magazine Letters, 84:11, 719-728
[5] Mogilevsky, P., et al., Evolution of Texture in Rhabdophane-Derived Monazite Coatings. Journal of the American Ceramic Society, 2003. 86(10): p. 1767-1772.

Selected area (electron) diffraction (abbreviated as SAD or SAED), is a crystallographic experimental technique that can be performed inside a transmission electron microscope (TEM).

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In a TEM, a thin crystalline specimen is subjected to a parallel beam of high-energy electrons. As TEM specimens are typically ~100 nm thick, and the electrons typically have an energy of 100–400 kiloelectron volts, the electrons pass through the sample easily. In this case, electrons are treated as wave-like, rather than particle-like (see wave–particle duality). Because the wavelength of high-energy electrons is a few thousandths of a nanometer,[1] and the spacing between atoms in a solid is about a hundred times larger, the atoms act as a diffraction grating to the electrons, which are diffracted. That is, some fraction of them will be scattered to particular angles, determined by the crystal structure of the sample, while others continue to pass through the sample without deflection.

Double

As a result, the image on the screen of the TEM will be a series of spots—the selected area diffraction pattern, SADP, each spot corresponding to a satisfied diffraction condition of the sample's crystal structure. If the sample is tilted, the same crystal will stay under illumination, but different diffraction conditions will be activated, and different diffraction spots will appear or disappear.

SADP of a single austenite crystal in a piece of steel

SAD is referred to as 'selected' because the user can easily choose from which part of the specimen to obtain the diffraction pattern. Located below the sample holder on the TEM column is a selected area aperture, which can be inserted into the beam path. This is a thin strip of metal that will block the beam. It contains several different sized holes, and can be moved by the user. The effect is to block all of the electron beam except for the small fraction passing through one of the holes; by moving the aperture hole to the section of the sample the user wishes to examine, this particular area is selected by the aperture, and only this section will contribute to the SADP on the screen. This is important, for example, in polycrystalline specimens. If more than one crystal contributes to the SADP, it can be difficult or impossible to analyze. As such, it is useful to select a single crystal for analysis at a time. It may also be useful to select two crystals at a time, in order to examine the crystallographic orientation between them.

As a diffraction technique, SAD can be used to identify crystal structures and examine crystal defects. It is similar to X-ray diffraction, but unique in that areas as small as several hundred nanometers in size can be examined, whereas X-ray diffraction typically samples areas several centimeters in size.

Diffraction

A diffraction pattern is made under broad, parallel electron illumination. An aperture in the image plane is used to select the diffracted region of the specimen, giving site-selective diffraction analysis. SAD patterns are a projection of the reciprocal lattice, with lattice reflections showing as sharp diffraction spots. By tilting a crystalline sample to low-index zone axes, SAD patterns can be used to identify crystal structures and measure lattice parameters. SAD is essential for setting up dark-field imaging conditions. Other uses of SAD include analysis of: lattice matching; interfaces; twinning and certain crystalline defects.[2]

SAD is used primarily in material science and solid state physics, and is one of the most commonly used experimental techniques in those fields.

Polycrystalline materials[edit]

Single slit diffraction pattern

Single spots appear only when the beam is diffracted by a single crystal. In many materials there are many crystals with different orientations. This is the case for typically made metals as well as powders. SAD of polycrystalline materials gives ring patterns analogous to those from X-ray powder diffraction,[3] and can be used to identify texture and discriminate nanocrystalline from amorphous phases.[2]

References[edit]

  1. ^David Muller Introduction to Electron Microscopy. p. 13
  2. ^ abSAD. CIME. Retrieved on 2011-11-22.
  3. ^Williams, David; Carter, C. (2009). Transmission Electron Microscopy: A Textbook For Materials Science. New York, USA: Springer. p. 35. ISBN978-0-387-76500-6.
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