Indexing Of Electron Diffraction Patterns Research Articles

A Denoising Autoencoder for Improved Kikuchi Pattern Quality and Indexing in Electron Backscatter Diffraction

The rapid collection and indexing of electron diffraction patterns as produced via electron backscatter diffraction (EBSD) has enabled crystallographic orientation and structural determination, as well as additional property-determining strain and dislocation density information with increasing speed, resolution, and efficiency. Pattern indexing quality is reliant on the noise of the collected electron diffraction patterns, which is often convoluted by sample preparation and data collection parameters. EBSD acquisition is sensitive to many factors and thus can result in low confidence index (CI), poor image quality (IQ), and improper minimization of fit, which can result in noisy datasets and misrepresent the microstructure. In an attempt to enable both higher speed EBSD data collection and enable greater orientation fit accuracy with noisy datasets, an image denoising autoencoder was implemented to improve pattern quality. We show that EBSD data processed through the autoencoder results in a higher CI, IQ, and a more accurate degree of fit. In addition, using denoised datasets in HR-EBSD cross correlative strain analysis can result in reduced phantom strain from erroneous calculations due to the increased indexing accuracy and improved correspondence between collected and simulated patterns.

Improvements in electron diffraction pattern automatic indexing algorithms

Accurate indexing of electron diffraction patterns (DPs) is a critical and enabling step in the nanostructure determination using electron diffraction. Here, we compare two automatic indexing algorithms for spot electron DPs from a known crystalline material, one is based on the normalized cross-correlation of simulated and experimental DPs and the other is based on Groth’s triangle algorithm. The Groth’s triangle algorithm offers better accuracy for indexing off zone axis DPs at the cost of significantly increased computer time. The comparison is made using electron DPs recorded from a nanostructured TiN thin-film sample.

Development of the DIFFRACALC program for analyzing the phase composition of alloys

The DiffraCalc software package is developed for automatic indexing of electron diffraction patterns. The program can operate with the existing base of X-ray diffraction data, containing information about the crystal structures of more than 100 thousands of materials. This information has been extracted from open sources. A compatibility with standard crystallographic files is implemented. In the indexing mode, the program automatically analyzes an experimental diffraction pattern, implementing a search for an appropriate phase from the list compiled by a user proceeding from the crystallographic database. The indexing mode algorithm is constructed using the method of pair reflections. In the simulation mode, the program calculates the electron diffraction pattern for a specified material, which is an additional way to verify the indexing results.

Is Pd2(DBA)3 a Feasible Precursor for the Synthesis of Pd Nanoparticles?

The organometallic reagent tris(dibenzylideneacetone) dipalladium(0) [Pd2(DBA)3] has been used as a reagent for synthesis of hexagonal microstructures ranging from 0.5−10 μm. We have shown elsewhere that Pd2(DBA)3 spontaneously forms hexagonal and cubic microstructures. The results obtained herein confirm that microstructures formed by spontaneous aggregation of Pd2(DBA)3 produce the same morphology and carbonaceous chemical composition as those produced with a process that has been called RNA-mediation by pyridyl-modified RNA (pmRNA). Synthesis products from both methods of preparation were analyzed using a combination of scanning transmission electron microscopy (STEM), electron energy loss spectroscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction. Indexing of electron diffraction patterns from hexagonal molecular crystals and metallic Pd nanoparticles combined with STEM Z-contrast imaging and X-ray dot maps were used to positively differentiate the two materials. On the...

On the reliability of fully automatic indexing of electron diffraction patterns obtained in a transmission electron microscope

Orientation maps similar to electron backscatter diffraction maps can be obtained in a transmission electron microscope. A method of such mapping by automatic indexing of electron diffraction patterns has been proposed recently. The procedure is relatively simple and fast but it does not avoid the 180° ambiguity. Using tests on simulated patterns, it is shown that under current practice automatic indexing may give a considerable fraction of erroneous solutions. Optimization of measurement conditions leading to a reduction of that fraction is considered.

Comments on`On the reliability of fully automatic indexing of electron diffraction patterns obtained in a transmission electron microscope'by Morawiec & Bouzy (2006)

The limitation of automatic indexing of electron diffraction patterns raised by Morawiec & Bouzy [(2006).J. Appl. Cryst.39, 101–103] is discussed. The theoretical problem related to the famous 180° ambiguity may be surmounted by adequate technical improvements. Three solutions to avoid misindexing are briefly described.

Icosahedrally related 1D quasicrystals

Taking a cut/section of a hyper lattice has proved a very elegant method of investigating the structure of incommensurate structures including the quasicrystals. We present here a method of generating a one dimensional incommensurate structure by distorting the six dimensional hypercubic lattice and the icosahedral basis vectors a long the 3 fold axis. Indexing of electron diffraction patterns of τ ∞ phase has been accomplished on this model and a structure for this phase having 3 symmetry a long the incommensurate direction and periodicity in planes normal to it has been proposed. The requirement of alternating Al and transition metal/vacancy layers in such structures can be satisfied by ordering the hyper unit cell a long three of the six directions.

Identifying characteristics of the fibrous cesium titanate Cs 2Ti 5O 11

Electron microscopic studies of the fibrous cesium titanate Cs 2Ti 5O 11 reveal characteristic features not readily apparent using standard methods of phase analysis (optical microscopy, X-ray diffraction). Its fibrous needle-like laths give characteristic diffuse scattering, complicating the indexing of electron diffraction patterns. The hydrated form Cs 2Ti 5O 11 · (1 + x)H 2O (0.5 < x < 1) is typically grossly distorted, resembling pyrolytic graphite. Cs 2Ti 5O 11 is unstable when stored under ambient conditions at room temperature for ∼1 year when disproportionation into Cs 2Ti 4O 9 and Cs 2Ti 6O 11 · nH 2O occurs. The structure of Cs 2Ti 5O 11 and intergrowth defects in the unstable forms have been studied by high-resolution electron microscopy. It is evident that these phases would be undesirable in titanate ceramics such as SYNROC, which are designed for immobilization of radioactive 137C s.

A computer program for unique indexing of electron diffraction patterns

A computer program for unambiguous and consistent indexing of a series of single-crystal diffraction patterns is discussed which allows determination of the unit triangle and therefore tilting of the specimen into any special orientation even if no Kikuchi patterns can be observed.

A method for the solution of electron diffraction patterns.

A simple aid to the indexing of electron diffraction patterns from multicomponent systems is described. An example of the method, which uses slide rule scales, is also given.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

A geometrical method for the determination and indexing of electron diffraction patterns

A geometrical method for the determination and indexing of electron diffraction patterns was developed by making use of descriptive geometry. This method is especially advantageous for noncubic structures. The general geometrical principles are presented, and a typical problem is solved in order to illustrate the procedures that can be followed to simplify the operations.

Complete indexing of electron diffraction patterns by computer

Complete indexing of electron diffraction patterns by computer

Indexing of diffracting planes using the Kikuchi pattern

Two types of ambiguity concerning indexing of electron diffraction patterns have been cleared up by making use of the Kikuchi lines. A convenient unambiguous method of uniquely indexing patterns is suggested assuming the beam is always along the viewing direction no matter how the picture is printed. It is shown that there are two completely equivalent ways of indexing the Kikuchi pattern, e.g., [111] or [1̄1̄1̄]. The method is also useful in interpreting dark-field pictures when top-bottom contrast is concerned.