2D and 3D orientation mapping in nanostructured metals: A review

Nanostructured metals possess various excellent properties and offer the potential for a wide range of applications. Improvements in the properties and performance of nanostructured metal components motivate a complete characterization of the microstructures and crystallographic orientations of nanostructured metals with nanoscale spatial resolution. Two well developed orientation mapping techniques for such characterization are electron backscatter diffraction (EBSD) in the scanning electron microscope and precession electron diffraction (PED) using diffraction spots in the transmission electron microscope. However, these methods can only characterize the structure in two dimensions. It is still a great challenge to characterize grains in three dimensions, i.e. from the interior of the nanostructured metals. Recently, three-dimensional orientation mapping in the transmission electron microscope (3D-OMiTEM) was developed and further improvements of this technique are introduced in this paper. Utilization of these orientation mapping techniques for structural and orientational characterizations are demonstrated by examples of surface-deformed metals with gradient nanostructures, and a sputtered gold film of nano-islands containing nanograins. The merits and challenges of each of these techniques are discussed and suggestions for further developments are proposed.