OIM - new analytical tool

OIM - Orientation Imaging Microscopy and, more generally, EBSD - Electron Backscatter Diffraction are techniques utilising the possibility to invoke electron diffraction in the SEM chamber, and thus to obtain information about the crystallographic identity or - if this is known - about the orientation distribution in a sample. Electron diffraction in the SEM relies on tilting the sample to a very steep angle between the sample surface and the electron beam; typical slopes are 60° to 75° from the horizontal. Such a high tilt is necessary to enable the primary electrons to penetrate under the sample surface, subsequently undergoing diffraction leading to EBSD pattern formation. The processes of diffraction are similar to those producing Kikuchi lines in TEM: first multidirectional inelastic scattering and then elastic scattering on appropriately oriented crystallographic planes. The difference from the TEM arrangement is that the diffracted electrons emanate back out of the primary beam specimen side, and then they impinge the phosphor screen forming the diffraction pattern. The pattern image is subsequently recorded with the CCD camera and grabbed into the computer for indexing.