Use Of Electron Backscatter Diffraction Research Articles

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

Electron back-scattered diffraction (EBSD) patterns are produced by inelastically scattered electrons and are intimately related to the local crystal orientation and quality. Analysis of the EBSD patterns is a rapid, non-destructive technique, which we have used to follow the regrowth of amorphised silicon-based heterostructures. The effective spatial resolution is 80nm, and we show that the technique can detect buried amorphous and oxide layers. Cross-sectional transmission electron microscopy (XTEM) studies confirm the EBSD results. A gas source MBE-grown Si1−xGex (x=14.5%) multi-quantum-well structure with good optical properties was implanted with an amorphising dose of either Si or Er, or Si followed by Er. The structure was annealed at 560°C under flowing N2 and regrowth was monitored at intervals by EBSD. It was found that structures implanted only with Er regrew faster than those implanted only with Si. As expected, the sample implanted with both Si and Er showed regrowth kinetics in between the two.

Quantitative metallography by electron backscattered diffraction.

Although electron backscattered diffraction (EBSD) in the scanning electron microscope is used mainly to investigate the relationship between local textures and microstructures, the technique has now developed to the stage where it requires serious consideration as a tool for routine quantitative characterization of microstructures. This paper examines the application of EBSD to the characterization of phase distributions, grain and subgrain structures and also textures. Comparisons are made with the standard methods of quantitative metallography and it is shown that in many cases EBSD can produce more accurate and detailed measurements than the standard methods and that the data may sometimes be obtained more rapidly. The factors which currently limit the use of EBSD for quantitative microstructural characterization, including the speed of data acquisition and the angular and spatial resolutions, are discussed, and future developments are considered.

Phase Identification Using EBSD in the SEM: What Can be Done Today and What we Hope to do Tomorrow

Phase identification using electron backscatter diffraction (EBSD) in the SEM has become a useful and important tool for the characterization of crystalline materials. Phase identification is accomplished using EBSD in the following manner. First, a high quality camera must be added to the SEM. Suitable cameras use slow scan CCD imagers coupled either by a lens or a fiber optic bundle to a phosphor screen that is situated near the sample. A EBSD pattern is collected and EDS or WDS is used to determine qualitatively the chemistry of the area. An automated routine is then used to extract the positions and widths of the lines in the pattern followed by a calculation of the unit cell volume. This information coupled with the chemistry of the sample is then used to search a database of crystal structures. Currently, the ICDD's Powder Diffraction file of over 100,000 compounds is used. Once a list of potential matches is found the patterns are indexed and then simulated to demonstrate that the phase has been identified. This paper will demonstrate use of EBSD for phase identification and then will speculate on future developments.A particularly nice application of EBSD is the use of the technique for the identification of phases that form in welds. Figure 1a is an EBSD pattern obtained from a acicular phase in a superalloy weld. The phase was determined to be primarily Ti and Ni. Analysis of the patterns showed that the phase is Ni3Ti. Figure 1b shows the simulation for Ni3Ti overlaid on the experimental pattern demonstrating that the phase has been identified.

An investigation into the use of electron back scattered diffraction to measure recrystallised fraction

The Electron Back-Scattered Diffraction (EBSD) technique is in its infancy and is a highly promising area of development. Use of EBSD has been predominantly for the determination of crystallographic textures. Other applications have also been considered, which include: crystal structure determination, phase determination, grain boundary studies and both elastic and plastic deformation measurement. Although it has been acknowledged that an important use of the EBSD could be in the measurement of recrystallization and its kinetics there are a number of inherent problems with such measurements using EBSD. These problems include the ability of the system to index deformed microstructures even those on a fine scale, the difficulties of analyzing patterns in the region of grain boundaries and the problems of sample preparation which is critical in the quality of the diffraction patterns obtained. The aim of the present study is to determine whether it is possible to measure the volume fraction recrystallized using EBSP of partially recrystallized stainless steel. This has been done by investigation of the quality of matching between the observed and calculated diffraction patterns, and the quality of the observed patterns measured in terms of their contrast. The material used was stainless steel 316L.

Crystallographic preferred orientations and misorientations in some olivine rocks deformed by diffusion or dislocation creep

The development of crystallographic preferred orientations (CPO) and grain misorientation distributions (MOD) in fine-grained (0.5–30 μm) olivine rocks, experimentally deformed by diffusion creep and dislocation creep has been investigated. The use of electron back-scattered diffraction (EBSD), in a scanning electron microscope (SEM), has enabled the measurement of CPO in rocks which are too fine-grained to be measured by conventional U-stage methods. Our objective is to study the influence of deformation and recrystallisation mechanisms on the CPO and MOD. The olivine rocks studied were deformed in uni-axial compression, in a gas-medium apparatus, to 17–24% strain at temperatures of 1200–1300°C and 300 MPa confining pressures. The samples show a trend of weaker CPO with lower flow stress which may be related to an increasing component of grain boundary sliding and diffusion creep. In the diffusion creep regime the CPO and MOD are weak to random, whereas in the dislocation creep regime the CPO and MOD are non-random but the MOD is principally controlled by the CPO. These results confirm the idea, based on studies from metals, that the CPO and MOD in olivine are characteristic of the deformation mechanism. Dynamic recrystallisation during dislocation creep results in the occurrence of more intermediate-angle (10–40°) grain boundaries than expected from the CPO. In local areas of complete recrystallisation the MOD is controlled by the CPO which implies that the statistical MOD retains no signature of the initial recrystallisation process. In the dislocation creep regime small grains have a weaker CPO compared to large grains. This result is consistent with predictions from deformation mechanism maps which indicate that the fine recrystallised grains deform by a combination of dislocation creep and grain boundary sliding. The grain boundaries found in the deformed olivine polycrystals are predominately high-angle boundaries with misorientations between 60 and 117°. No obvious evidence has been found for the occurrence of preferred misorientation, or special, grain boundaries.

Plastic deformation of metamorphic pyrite: new evidence from electron-backscatter diffraction and forescatter orientation-contrast imaging

Application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods. Specifically, use of forescatter solid-state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images, which map the distribution of deformation domains within grains. Use of electron-backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images. Combination of these techniques shows that the pyrite studied deforms by slip on {100} and more rarely {110} systems. Slip is often associated with distributed rotation of up to 20° about and more rarely axes. Pyrites may have simple histories involving rotation about a single axis, or more complex histories involving rotation about different axes, and more rarely , in different domains of the same pyrite grain, or sequential rotations about quite different systems, typically distributed rotation about followed by discrete rotation about a non-crystallographic axis.