Currently, charge-coupled device (CCD) cameras are commonly used to capture these patterns with high speed rates -up to 3000 patterns per second-to produce phase and orientation maps based on the crystallography and crystallographic orientation of the different phases present in the analyzed material. At this time, the image was captured from a phosphorescent screen by means of an external camera. Later, in 1973, Venables and Hartland obtained similar patterns in spot mode when the specimen was highly tilted towards a phosphorescent screen, typically 60–70°. This type of pattern was later termed as an Electron Channeling Pattern (ECP) this led to the well-known electron channeling contrast imaging (ECCI). In 1967, Coates evidenced the channeling of BSEs by imaging a Kikuchi-like patterns from Ge and GaAs crystals when the electron beam was scanned over the surface of the specimens at low magnification. In the SEM, there are two ways of gathering the diffraction information carried by these electrons.
Electron backscatter diffraction free#
The depth resolution is of the order of the mean free path, but depends mostly on the energy-loss considered.īecause they interact with the crystal lattice of the specimen through diffraction processes, the BSEs carry information about the crystallinity in their emission volume, but mostly from the exit surface. These low-loss electrons suffer a small number of interactions, and originate from the close surrounding of the beam impact point on the surface. The energy distribution of these BSEs being material and SEM parameters dependent, energy filtration allows us to collect only high energy BSEs, i.e., those with low-loss of energy, which are associated with high spatial resolution and reduced interaction volume. Their emission depth and lateral distribution depend on the material characteristics and the primary beam accelerating voltage. These are called Backscattered Electrons (BSE), and are responsible for compositional contrast (also known as material or Z contrast), which is in fact related to the mean atomic number of the material interacting with them. In contrast, the primary electrons that are backscattered towards the surface due to the atoms’ Coulomb attraction forces retain sufficient energy to reach the exit surface with limited absorption, and carry information about the composition of the volume of material “seen” by these electrons. Note that these numbers are maximum values and that the emission depth and lateral distribution may be further reduced depending on the type of signal that is collected to generate the image. For example, the range of electrons/material interactions at E 0 = 20 kV in iron is roughly 1 µm, while it falls to 15 nm at E 0 = 1 kV. Thus, by varying the accelerating voltage (E 0) applied to the electron beam and the type of signal collected, one can obtain “bulk” information however, if lower voltages are used, the collected signals originate from the shallow surface layers. Because the mean free path of low energy electrons is dramatically smaller than that of X-rays, the technique is the missing link between high penetration depth techniques like X-ray-based systems and atomic level surface techniques like atomic force microscopy or scanning tunneling microscopy. It offers a spatial resolution in the sub-nanometer level when equipped with a cold-field emitter or a beam monochromator, and its design allows the analyst to observe the surface of a specimen from the nanometer to the centimeter range. This method, named dark-field electron backscatter diffraction imaging, is described in detail, and several application examples are given in reflection as well as in transmission modes.Īmong the characterization tools available to the materials scientist, the scanning electron microscope (SEM) is probably the most used and versatile. The method is becoming viable with the advent of new EBSD camera technologies, allowing acquisition speed close to imaging rates. This work shows preliminary and encouraging results regarding the non-conventional use of the EBSD detector. In this manuscript, we reviewed the benefits of this procedure regarding topographic, compositional, diffraction, and magnetic domain contrasts. When post-processing the diffraction patterns or the image captured by the EBSD detector screen which was obtained in this manner, specific imaging contrasts are generated and can be used to understand some of the mechanisms involved in several imaging modes. Among the available techniques in scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) is used to gather information regarding the crystallinity and the chemistry of crystalline and amorphous regions of a specimen. Scanning electron microscopy is widespread in field of material science and research, especially because of its high surface sensitivity due to the increased interactions of electrons with the target material’s atoms compared to X-ray-oriented methods.
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