LabAdviser/314/Microscopy 314-307/SEM/Nova/Transmission Kikuchi diffraction: Difference between revisions

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 Typically from 3 to 9 detected bands are used for automatic indexing in
 commercial softwares.
+= Orientation Imaging Microscopy =
+The necessity to obtain large data sets of crystal orientations and crystallographic
+phases in polycrystalline materials, the development of electron
+microscopy, together with the perfecting of automated Kikuchi pattern indexing,
+led in the last 20 years to the development of a powerful new form
+of microscopy, the so-called Orientation Imaging Microscopy (OIM) [29, 30].
+OIM generally refers to techniques for the reconstruction of micro- and
+nanostructures based on the spatially resolved measurement of individual
+crystal orientations and crystallographic phases. Electron di�raction techniques
+are particularly suited for such analysis because they allow (i) unambiguous
+orientation determination, (ii) orientation and phase determination
+for all crystal systems, (iii) high spatial resolutions and (iv) high automatization.
+OIM can be performed using both SEM and TEM instruments; a
+schematic representation of an OIM system inside a SEM is shown in Fig.
+.5.
+In an OIM scan the beam is stepped across the sample surface in a regular
+grid. The user typically programs an array of positions, specifying the spatial
+range and step size of sampling points. At each point the Kikuchi pattern
+is captured and automatically indexed in real time and the orientation and
+other information recorded.
+The acquired OIM data are usually plotted in the form of an inverse pole
+�gure (IPF) orientation map, an example of which is shown in Fig. 3.6.
+While a pole �gure represents a crystal direction or plane normal of a
+material within the sample reference system, an inverse pole �gure displays a
+speci�c sample direction within the crystal system. Due to the symmetry of
+the crystal system, in most cases the inverse pole �gure can be reduced, for
+example it is a standard triangle in the case of cubic materials. Thus, IPF
+coloring of OIM data shows which crystal direction is parallel to the sample
+direction to which the IPF is assigned to. Using the common color-code for
+cubic materials, [100] points parallel to the assigned sample direction are
+colored red, [110] green and [111] blue, while mixtures of orientations are
+colored in mixed colors.
+The �rst-developed and most popular SEM OIM technique is the electron
+backscatter di�raction (EBSD) [31, 32, 33, 34, 35, 36]. In the TEM the main
+techniques used are the transmission Kikuchi pattern (TKP) technique, the
+small-angle convergent beam di�raction (SCBED) and the precession enhanced
+di�raction (PED) method [30, 37, 38, 39].