Electron backscatter diffraction
Electron backscatter diffraction (EBSD), also known as backscatter Kikuchi diffraction (BKD) is a microstructural-crystallographic technique used to elucidate the crystallographic texture or preferred orientation of any crystalline or polycrystalline materials. EBSD can be used to index and identify the seven crystal systems, and as such it is applied to crystal orientation mapping, defect studies, phase identification, grain boundary and morphology studies, regional heterogeneity investigations, material discrimination, and using complimentary techniques, physico-chemical identification. Traditionally these types of studies have been carried out using x-ray diffraction (XRD), neutron diffraction and/or electron diffraction.
Experimentally EBSD is conducted using a scanning electron microscope (SEM) equipped with a backscatter diffraction camera. The diffraction camera is essentially a focal plane CCD coupled with a phosphor screen, which is inserted into the specimen chamber of the SEM at an angle greater than or equal to 90° to the pole piece. A flat/polished crystalline specimen is placed into the normal position in the specimen chamber, but is highly tilted (~70° from horizontal) towards the diffraction camera. When the electrons impinge on the specimen they interact with the atomic lattice planes of the crystalline structures, many of these interactions satisfy Bragg conditions and undergo backscatter diffraction. Due to the angle of the specimen these diffracted electrons are directed towards and impinge upon the phosphor screen of the diffraction camera causing it to fluoresce, this fluorescent light is then detected by the CCD. The diffracted electrons form an image termed a diffraction pattern on the diffraction camera. This pattern is unique to the microstructural-crystallographic properties of the material. And using computer aided interpretation can reveal a multitude of information. Each diffraction pattern will show several intersecting lines termed Kikuchi bands, these correspond to each of the lattice diffracting planes and can be indexed individually by the Miller indices of the diffracting plane which formed it.
EBSD when used together with other in-SEM techniques such as Cathodoluminescence (CL), Wavelength dispersive X-ray spectroscopy (WDS) and/or Energy dispersive X-ray spectroscopy (EDS) can provide a deeper insight into the specimens properties. For example, the minerals calcite (limestone) and aragonite (shell) have the same chemical composition - calcium carbonate (CaCO3) therefore EDS/WDS cannot tell them apart, but they have different microcrystalline structures so EBSD can differentiate between them.