Digital direct electron imaging of energy-filtered electron backscatter diffraction patterns

In the present paper we demonstrate the use of electron backscatter diffraction (EBSD) for high resolution elastic strain determination. Here, we focus on analysis methods based on determination of small shifts in EBSD pattern with respect to a reference pattern using cross‐correlation algorithms. Additionally we highlight the excellent spatial and depth resolution of EBSD and introduce the use of simulated diffraction patterns based on dynamical diffraction theory for sensitivity estimation. Moreover the potential of EBSD for strain analysis of strained thin films with particular emphasis on appropriate target preparation which respect to occurring lattice defects is demonstrated.

The use of electron back-scattered diffraction to study the regrowth of amorphised silicon-based heterostructures

We demonstrate that the surface topography of a sample can be reconstructed from electron backscatter diffraction (EBSD) patterns collected with a commercial EBSD system. This technique combines the location of the maximum background intensity with a correction from Monte Carlo simulations to determine the local surface normals at each point in an EBSD scan. A surface height map is then reconstructed from the local surface normals. In this study, a Ni sample was machined with a femtosecond laser, which causes the formation of a laser-induced periodic surface structure (LIPSS). The topography of the LIPSS was analyzed using atomic force microscopy (AFM) and reconstructions from EBSD patterns collected at 5 and 20 kV. The LIPSS consisted of a combination of low frequency waviness due to curtaining and high frequency ridges. The morphology of the reconstructed low frequency waviness and high frequency ridges matched the AFM data. The reconstruction technique does not require any modification to existing EBSD systems and so can be particularly useful for measuring topography and its evolution during in situ experiments.

Electron backscatter diffraction (EBSD) is a powerful tool to automatically and quantitatively characterize the orientation of grains and phases of ceramic and composite materials [1]. EBSD ultra‐fast pattern acquisition, i.e., patterns streaming to hard disk (HD) and later pattern indexing, becomes an interesting technique to investigate a series of large‐scale ceramic, which can quickly provide phase distribution information for further improving ceramic production. However at the same time, it becomes more and more important to handle the huge offline EBSD raw data efficiently and correctly. In this project, we already reported the EBSD characterisation results of the polymorphs of a solid state sintered silicon carbide component based on Densitec 15, a ready to press powder‐made by Saint Gobain Ceramic Materials AS [2]. The pre‐sintered powder was produced using the Acheson process and would typically consist of the 4H‐ and 6H‐polytypes, with small amounts of 3C and sometimes traces of 15R. The offline EBSD raw data collection was carried out in a Hitachi SU‐6600 FESEM and the patterns were acquired by using NORDIF UF‐1100 EBSD detector and written directly to HD. The previous results only identified 4H‐ and 6H‐phases in the sample, consistent with the expected transformation of 3C‐crystals that takes place at temperatures significantly lower than the sintering temperature of 2110°C. In this abstract further detailed phase identification of silicon carbide 3C by the new developed NORDIF EBSD Extraction Software is carried out. Figure 1 is the overview for the new developed NORDIF EBSD Extraction Software, where the indexed phase map of the present silicon carbide sample shows partly on the right part of the figure. Offline EBSD indexing reveals that the content of the silicon carbide 3C phase is below 0.5% in the sample. By using the point analysis tool (+) in the program, the individual EBSD patterns from the silicon carbide 3C phase can be retrieved from HD with auto contrast and background subtraction corrections. Representative 3C‐SiC EBSD patterns shown in Fig. 2 together with the corresponding internal coordinations (x,y), where the pattern (6,59) is exactly the same retrieved pattern shown that in Fig. 1. Further detailed 3C‐SiC pattern indexing is performed. Under the system optimized calibration settings, the best confidence indexes (CIs) in Fig. 2 are all below 0.03, and the representative indexing result shows in Fig. 3. As checking back and comparing that in Fig. 1, it can be concluded that the indexed 0.5% 3C‐SiC phases are mostly located at the boundaries among different grains, phases and pores, which resulted those EBSD patterns mis‐indexed as 3C‐SiC phase. Offline EBSD together with its Extraction Software is hence an excellent tool to study not only the crystallographic texture and phase distribution, but also fully confirmed that the 3C‐SiC recrystallisation and phase transformations processes taking place during sintering of ceramic materials. It also reveals that the present EBSD Extraction Software is good practice to carefully view the offline EBSD raw data before applying further processing algorithms.

While electron backscatter diffraction (EBSD) patterns are often used to present two-dimensional information about a material microstructure, they are in fact a product of the three-dimensional electron interaction volume. Consequently, 3D spatial information exists in EBSD images, which is generally not accessed. Specifically, the inclination of the grain boundary plane may be observed in EBSD patterns taken near grain boundaries. If, at the same time, the shape of an electron interaction volume in the material is known, a grain boundary plane normal direction can be obtained from a sequence of EBSD images taken stepwise in a line crossing the grain boundary. Here, these two principles are used for demonstrating the determination of grain boundary normal vectors from EBSD images. Coherent twin boundaries and focused ion beam serial scan data are used for validation. Results indicate a mean error for this approach of 3 deg with a standard deviation of 3.8 deg.

Electron backscatter diffraction (EBSD) data yield plentiful information on microstructure and texture of natural as well as experimentally produced mineral and rock samples. For instance, the characterization of microstructures and textures by EBSD allows for the evaluation of phase equilibria. Furthermore, determination of the preferred orientations of crystals using EBSD yields constraints on deformation mechanisms and history of the minerals/rocks. The latter affects bulk-rock properites, for example, through the relation between lattice preferred orientation and electrical conductivity and seismic anisotropy. EBSD is also applied to advance our understanding of various phenomena such as seismic wave attenuation in the Earth deep interior and its relation to the presence of interfacial small degrees of melt fractions, or free fluid phases. In standard EBSD software solutions, the original EBSD patterns are rarely saved and indexing routines result in many artifacts, such as pseudo-symmetry or unindexed pixels at interfaces that may be misinterpreted as amorphous material, such as a melt. Here we report the first application of the dictionary indexing (DI) approach proposed by Chen et al. (2015), an alternative indexing routine, which we extended to be applicable to multiphase geologic materials. The DI method is independent of the EBSD system, and thus of the used detector/software. The DI routine generates simulated EBSD patterns for all possible crystal orientations, taking the sample composition and experimental setups into account. The resulting pattern database is called a dictionary. The experimental electron backscattering pattern (EBSP) images are indexed by comparing them to the dictionary using a dot-product algorithm. We evaluate the new DI method in comparison to standard routines and highlight advantages and disadvantages. To test and compare the DI’s reliability and performance, we apply the routine to two scientifically challenging samples: (1) A nominally anhydrous (“dry”) residual eclogite composed of garnet (cubic), clinopyroxene (monoclinic) and an amorphous melt, where the different degrees of hardness of the phases cause surface topology; and (2) a pure forsterite (olivine) polycrystalline sample produced by vacuum sintering. The acquired EBSD patterns are of low quality for the latter as a result of fast data acquisition to reduce the on-line machine time. We conclude that the new DI method is highly precise and surpasses the performance of previously available methods, while being computer time and computer memory consuming. We find that the DI method is free of pseudo-symmetry-related problems. Interpolation of data becomes obsolete and high reproducibility is obtained, which minimizes the operator impact on the final data set. The latter is often caused by applying several cleaning steps on EBSD maps with low indexing fraction. Finally, much higher scientific integrity is ensured by image collections as described above, which requires that all patterns are saved. This in turn allows later re-analyses if required. The DI routine will help to achieve more reliable information on interface properties of geological samples, including amorphous materials, and thus in the long run help to improve the accuracy of large-scale Earth mantle process models.

Electron backscattered diffraction (EBSD) is a widely used technique for both identifying the crystallographic phase and for mapping the orientation of crystalline materials on the micron length scale. Often the operating conditions necessary for phase identification are not suitable for orientation mapping and vice versa. In an effort to optimize the speed involved in the mapping technique, pattern quality is sacrificed and the wealth of information present in an EBSD pattern is compressed to basically 4 values: a matched phase and three Euler angles. However, ab initio identification of phases from EBSD patterns requires high quality patterns and fairly intense computation. Spectrum imaging is an analytical approach that may offer some solutions to the aforementioned problems. Spectrum imaging consists of collecting a whole spectrum at each pixel in a mapping style measurement. This large set of data is then analyzed using multivariate statistical analysis (MSA) techniques such as principle components analysis, multivariate curve resolution, or other least squares based techniques. The result of these calculations is a set of component spectral shapes with corresponding abundances that allow the analyst to extract the greatest amount of physically relevant information from an otherwise enormous data set. Spectrum imaging has been used successfullymore » in EDX microanalysis (both in the SEM and TEM), TOF-SIMS, WDS, and EELS. To examine the potential benefits of the spectrum imaging approach for EBSD data, a series of basic experiments and calculations were run. Test data sets (20 x 20 patterns in .jpeg format) on polycrystalline Al and on the directionally solidified eutectic oxide, CoO/ZrO{sub 2}(CaO), were collected using the HKL Channel 5 system with a Nordlys detector under normal mapping conditions. The data was collected on a FEI dual beam FIB (model DB235) and a Zeiss (Supra 55 VP) SEM at 20keV for Al and CoO/ZrO{sub 2}(CaO), respectively. The data sets were analyzed according to the schematic shown in Figure 1. Each EBSD pattern was hough transformed, unzipped into a 1-D vector of channels with intensities ranging from 0-255, and then added to an overall data matrix. A range of treatments (edge/no edge detection, spatial simplicity/spectral simplicity, etc.) were examined to determine the optimal way of treating the data. The multivariate analyses were performed using the AXSIA code developed at Sandia National Laboratories. The MSA techniques were able to correctly identify individual grains in the Al sample and individual phases in the CoO/ZrO{sub 2}(CaO) sample. For each component EBSD pattern identified from the Al data, a corresponding color map of abundance can be seen which clearly corresponds to a single grain (Figure 2). The success in the CoO/ZrO{sub 2}(CaO) sample is particularly notable due to both phases sharing the Fm-3m space group which would confuse most autoindexing routines. The range of analytical treatments identified two extremes in results: a minimal number of components (patterns) with only kikuchi line positions present or a larger number of components with full intensity information present. The further application of these results to phase mapping will be discussed.« less

High resolution electron back-scatter diffraction analysis of thermally and mechanically induced strains near carbide inclusions in a superalloy

A new approach to resolve the slight tetragonality ofL10-ordered γ-TiAl by electron backscatter diffraction (EBSD) is presented. The phase has ac/aratio of only about 2% larger than unity. The corresponding EBSD patterns therefore exhibit cubic pseudosymmetry. As a consequence, different order variants cannot be easily distinguished on the basis of their EBSD patterns. Automated orientation mapping results in frequent misindexing. In the past, either this problem was overcome by identifying order domains by relatively laborious transmission electron microscopy, or the order domain structure was ignored altogether by using a generic face-centered cubic structure to solve for the crystal orientations, accepting a significant loss of microstructural information. The presented approach is based on the detection of the minor tetragonal distortion of the diffraction patterns by an accurate measurement of backscatter Kikuchi band positions. To this end an accurate pattern center calibration together with high-accuracy parameters for pattern acquisition and indexing are required. Together with a modified indexing algorithm, the order domains in a lamellar microstructure of Ti–45.9Al–8Nb (at%) could be reliably identified. The occurrence of superlattice reflections in the Kikuchi patterns was used to validate the technique. The developed method was successfully applied to create a crystal orientation map of Ti–45.9Al–8Nb (at%) with a fully resolved domain microstructure.

The electron backscatter diffraction (EBSD) analytical technique is invaluable for determining the crystallography of bulk alloys, thin films, and nanoparticles. However, our physical understanding of EBSD pattern generation is incomplete, which hinders our ability to push the limits of EBSD analysis. Here, by using an energy filter with better than 10 eV resolution, an improvement in the spatial resolution of the EBSD pattern was experimentally demonstrated. A signal depth of less than 15 nm for an aluminum film was achieved by controlling the cutoff energy of the energy filter. Additionally, a two-fold improvement in the spatial resolution across a grain boundary was observed using the energy filter.

Orientation determination by EBSP in an environmental scanning electron microscope

Electron backscattering diffraction (EBSD) is a very useful technique for crystal orientation analysis by acquiring Kikuchi patterns formed by backscattered electrons [ 1 ]. Non-conductive materials under electron illumination are often suffering from charge-up effects which significantly hamper crystal orientation analysis. Surface coating by a vapour deposition of a conductive solid material is hence very often used to reduce charge-up. However, a special care should be taken to control the deposition thickness because too thick deposition would cause blurred and ambiguous EBSD patterns, whereas too thin deposition could be insufficient to reduce charge-up. A method compensating for charge-up by spraying an ionized gas onto the sample surface [ 2 ] is currently available, though it requires a particular equipment. Transmission EBSD (t-EBSD) is an alternative method to acquire Kikuchi patterns formed by forward-scattered electrons, which transmit through a thin sample like TEM [ 3 ]. In the present study we focus on the two characteristics of t-EBSD: the first one is that t-EBSD can acquire EBSD patterns of the sample even when its surface is contaminated on the side of electron incidence. The second one is that forward-scattered electron has a shorter average traveling path than that of backscattered electrons. Herein, we propose a method for crystal orientation analysis of non-conductive materials, to which t-EBSD is effectively applied with surface coating incorporated. We demonstrate that the surface coating on non-conductive samples exerts not only little influence on the clarity of t-EBSD patterns but also helps better identification of crystal orientation by reducing charge-up.

SummaryThe spatial resolution of electron diffraction within the scanning electron microscope (SEM) has progressed from channelling methods capable of measuring crystallographic characteristics from 10 μm regions to electron backscatter diffraction (EBSD) methods capable of measuring 120 nm particles. Here, we report a new form of low‐energy transmission Kikuchi diffraction, performed in the SEM. Transmission‐EBSD (t‐EBSD) makes use of an EBSD detector and software to capture and analyse the angular intensity variation in large‐angle forward scattering of electrons in transmission, without postspecimen coils. We collected t‐EBSD patterns from Fe–Co nanoparticles of diameter 10 nm and from 40 nm‐thick Ni films with in‐plane grain size 15 nm. The patterns exhibited contrast similar to that seen in EBSD, but are formed in transmission. Monte Carlo scattering simulations showed that in addition to the order of magnitude improvement in spatial resolution from isolated particles, the energy width of the scattered electrons in t‐EBSD is nearly two orders of magnitude narrower than that of conventional EBSD. This new low‐energy transmission diffraction approach builds upon recent progress in achieving unprecedented levels of imaging resolution for materials characterization in the SEM by adding high‐spatial‐resolution analytical capabilities.

In this paper we describe the use of electron backscatter diffraction (EBSD) mapping and electron channeling contrast imaging—in the scanning electron microscope—to study tilt, atomic steps and dislocations in epitaxial GaN thin films. We show results from epitaxial GaN thin films and from a just coalesced epitaxial laterally overgrown GaN thin film. From our results we deduce that EBSD may be used to measure orientation changes of the order of 0.02°, in GaN thin films. As EBSD has a spatial resolution of ≈ 20 nm, this means we have a powerful technique with which to quantitatively map surface tilt. We also demonstrate that channeling contrast in electron channeling contrast images may be used to image tilt, atomic steps and threading dislocations in GaN thin films.

Demonstrating the potential of accurate absolute cross-grain stress and orientation correlation using electron backscatter diffraction