Electron Backscatter Kikuchi Diffraction Research Articles

Kikuchi bandlet method for the accurate deconvolution and localization of Kikuchi bands in Kikuchi diffraction patterns

In order to retrieve crystallographic information from an electron backscatter Kikuchi diffraction pattern, its Kikuchi bands have to be localized. One of the main reasons for the limited precision of the present Kikuchi band localization methods is that the diffuse edges of a Kikuchi band are convoluted by many other Kikuchi bands that intersect them. To improve the localization accuracy, Kikuchi bands have to be deconvoluted. In this article, a new method for the deconvolution and localization of Kikuchi bands is presented. The deconvolution is based on the fact that, in a Kikuchi pattern, there are a number of Kikuchi bands that are not parallel to the bands that intersect them. It is performed in Fourier space. After deconvolution, localization is carried out by a quantitative shape analysis of the intensity profiles of the deconvoluted Kikuchi bands. Using the introduced method, for a real electron backscatter Kikuchi diffraction pattern with 45° half capture angle and 0.12° per pixel maximum scale factor, the characteristic hyperbolic features of the Kikuchi bands can be localized with a precision of better than 0.1° in reflection angle.

Review Electron backscatter Kikuchi diffraction in the scanning electron microscope for crystallographic analysis

The technique of electron backscatter Kikuchi diffraction patterns (BKDPs) in the scanning electron microscope is reviewed. The paper focuses mainly on the crystallographic applications of the technique, including discussions on point group and space group determination and strain analysis. Orientation microscopy is discussed but not reviewed. The geometrical configurations of BKDPs are reviewed in detail and the relationship between BKDPs and the technique of electron channelling patterns (ECPs) is explored briefly. Essential crystallography is discussed and methods of analysis of BKDPs to extract crystallographic information are analyzed in detail. Some important characteristics of diffraction contrast in BKDPs are analyzed with respect to the geometry of the technique, the dynamical theory of electron diffraction and crystallographic applications. Examples of the use of theoretical contrast in pattern interpretation are provided. Anomalous effects in BKDPs are analyzed in detail and ways of identifying anomalous contrast in practice are discussed. BKDPs included in the paper are zincblende (ZnS), silicon, germanium, GaAs, chalcopyrite (CuFeS2, TaTe4 and Er2Ge2O7.

EBSD of Zn-rich phases in Zn–Al-based alloys

Based on microstructure characterization, electron back-scatter Kikuchi diffraction (EBSD) methodology was used on a multi-phase alloy ZnAl4Cu11 (in wt.%). Electron back-scatter Kikuchi diffraction patterns (EBSDPs) were produced from the bulk Zn–Al-based alloy specimen using solely mechanical polishing instead of mechanical and electro-polishing. Both EBSDs of the Zn-rich hexagonal close-packed structure (hcp) phases of ε and η were distinguished for the first time using pre-determined lattice parameters of these phases as the computer database for the multi-phase alloy. These two procedures were practical developments of EBSD technology in the study of crystalline orientation and phase identification.

Texture formation and grain boundary networks in rolling assisted biaxially textured substrates and in epitaxial YBCO films on such substrates

Electron backscatter Kikuchi diffraction was used to study texture development and grain boundary networks in rolling-assisted-biaxially-textured-substrates, and the transfer of such a biaxial texture and preferential grain boundary network to epitaxial YBCO films grown on such substrates. It was found that the rolling texture in the Ni substrate is highly complicated, with most of the grains having orientations at and between the “B” and “S” orientations. No cube nuclei could be discerned in the etched, as-rolled sample. On recrystallization, a sharp {001}〈100〉, cube texture was imparted to the Ni substrate. It was found that the substrate was percolatively connected within 3°. Examination of epitaxial oxide layers on Ni showed that excellent epitaxy was obtained. At times, undesirable orientations nucleated during growth of the oxide layer, however, these were engulfed by the growing film (with correct orientation). Orientation image micrographs of an epitaxial YBCO film on a RABiT substrate with a Jc of 1.6MA/cm2 at 77K showed that most of the film was percolatively connected within 2°. A comparison of the spatially correlated and uncorrelated grain boundary misorientation distributions showed that local grain-to-grain correlations were present between the grains. Comparison of the data obtained for the YBCO film with those obtained for the underlying Ni substrate showed that both the macroscopic texture and the grain boundary networks were very similar in the two cases, implying excellent epitaxy of the multilayers.

Grain boundary studies of high-temperature superconducting materials using electron backscatter Kikuchi diffraction

Grain orientation and grain boundary misorientation distributions in high critical current density, high-temperature superconductors were determined using electron backscatter Kikuchi diffraction. It is found that depending on the type of superconductor and the processing method used to fabricate it, there exist different scales of biaxial texture from no biaxial texture, local biaxial texture, to complete biaxial texture. Experimentally obtained grain boundary misorientation distributions (GBMDs) were found to be skewed significantly to low angles in comparison to what is expected on the basis of macroscopic texture alone, suggesting that minimization of energy may be a driving force during the processing of high critical current density materials. In addition, a higher than expected fraction of coincident-site lattice boundaries is observed. Examination of maps of grain boundary misorientations in spatially correlated grains, i.e. the grain boundary mesotexture, suggests the presence of percolative paths of high critical current density. A combination of orientation measurements, theoretical modeling of GBMDs and modeling of percolative current flow through an assemblage of grain boundaries is performed to gain an insight into the important microstructural features dictating the transport properties of high-temperature superconductors. It is found that maximization of low energy, in particular, low-angle boundaries, is essential for higher critical currents. The combination of experimental and analytical techniques employed are applicable to other materials where physical properties are dominated by intergranular characteristics.

Grain boundary misorientations and percolative current paths in high-J c powder-in-tube (Bi,Pb)2Sr3Ca3Cu3Ox

Grain orientations and grain boundary misorientations in high-Jc, powder-in-tube (PIT) (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) were determined using electron backscatter Kikuchi diffraction and x-ray microdiffraction. Data collected from over 113 spatially correlated grains, resulting in 227 grain boundaries, show that over 40% of the boundaries are Σ1 or small angle (less than 15°). In addition, 8% of the boundaries are within the Brandon criterion for CSLs (sigma larger than 1 and less than 50). Grain boundary ‘‘texture maps’’ derived from the electron microscope image and orientation data reveal the presence of percolative paths between low energy boundaries.

Characterization of the near-interface region of chemical vapor deposited diamond films on silicon by backscatter Kikuchi diffraction

The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beam has been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the orientational arrangement of and among individual diamond crystallites in the near-interface region. A comparison with the orientation of the substrate has proved the existence of epitaxially nucleated grains. A high amount of twinned diamond has been deduced from the pole figures and verified by analysis of orientation correlations between neighboring crystallites. Moreover, the grain boundary maps have allowed us to monitor and quantify directly the occurring twin boundaries.

Texture Gradient Effects in Tantalum

The effects of inhomogeneities in texture on the mechanical response of a tantalum plate were investigated. Through-thickness compression samples exhibited an hourglass shape after deformation. The compression tests were modeled using a finite-element approach. A polycrystal plasticity model is embedded at each element of the mesh enabling the simulation to account for the spatial distribution of texture and its evolution. The texture was characterized using spatially specific individual lattice orientation measurements. The orientations were measured using automatic analysis of electron backscatter Kikuchi diffraction patterns. The influence of the spatially nonuniform distribution of texture on the experimental and simulated results is discussed. This work demonstrates the capability of currently available tools for characterizing inhomogeneous microstructures and modeling the effects of variations in texture on mechanical behavior.

A study of the breakdown of Friedel's law in electron backscatter Kikuchi diffraction patterns: application to zincblende-type structures

The breakdown of Friedel's law has been observed in backscatter Kikuchi diffraction patterns (BKDP) obtained in the scanning electron microscope (SEM) from a series of zincblende structures including GaAs, InP, GaSb, CdHgTe and the minerals sphalerite (ZnS), chalcopyrite (CuFeS2) and tetrahedrite (Cu12Sb4S13). Differences in intensities were observed between the reflections 51{\bar 1} and 5{\bar 1}{\bar 1} in InP, GaSb, CdHgTe and sphalerite, thus allowing the non-centrosymmetric point group {\bar 4}3m to be determined. In GaAs, differences in intensities were noted between {\bar 5}11 and {\bar 4}{\bar 1}. In chalcopyrite and tetrahedrite, non-equivalent intensities were observed between {\bar 2}15 and 2{\bar 1}{\bar 5} and between 3{\bar 1}{\bar 2} and 31{\bar 2}, respectively. In addition, BKDPs obtained from chalcopyrite revealed a small displacement at the point where the pair of equivalent reflections {\bar 4}06 and 460 intersect within the Kikuchi band 02{\bar 2}. The presence of this displacement together with observation of the breakdown of Friedel's law confirmed the tetragonal point group {\bar 4}2m for chalcopyrite. Although the point groups of GaAs, chalcopyrite and tetrahedrite were derived successfully using BKDPs, determination of their space groups proved unsuccessful. The superstructure reflections were invisible because the structure factors are very small. The behaviour of the invisible 200 reflection in GaAs is investigated using many-beam dynamical intensity profiles calculated across the h00 systematic row of reflections. Dynamical intensity profiles calculated across the h00 systematic rows of reflections for Ge, InP and sphalerite are also discussed.

Automated Lattice Orientation Determination From Electron Backscatter Kikuchi Diffraction Patterns

The ability to measure individual orientations from crystallites enables a more complete characterization of the microstructure. A primary obstacle to the use of single orientation measurements is the large investment of direct operator time necessary to obtain a statistically reliable data set. The most viable technique for obtaining individual orientation measurements is electron backscatter Kikuchi diffraction (BKD). Current technology requires an operator to identify a zone axis pair in a BKD pattern. This paper describes research in progress to automate the identification of lattice orientation from BKD patterns by identifying the planes associated with the bands that appear in the patterns. This work considered FCC crystal symmetry.