TEM orientation mapping on nanoscale using STEM mode
Péter Pekker(1), István Dódony(1,2), Norbert Hegman(1)
(1)Department of Nanotechnology, Bay Zoltán Foundation for Applied Research, Miskolc, Hungary
(2)Department of Mineralogy, Eötvös L. University, Budapest, Hungary
The crystallographic orientation mapping in STEM is a relatively new method for
textural studies of nanocrystalline materials (ASTAR system). Through this method
orientation of crystals, their shapes and relative orientations are subjects of
measurements.
The principle of orientation mapping is similar to that of backscattered electron
diffraction (EBSD), what is used in scanning electron microscopy. During the orientation
mapping measurements the electron beam is scanned through the selected area of interest
and a high speed CCD camera collects the electron diffraction patterns point by point.
The size of illuminating spot gives the spatial resolution of this method, what is usually
spanning the 1 to 10 nanometer range (depending on the parameters of applied
microscope). The crystallographic orientation for each measured spot is obtained by
matching the observed diffracted intensity distribution to the set of calculated diffraction
patterns of the investigated crystalline phases.
The result is a set of data on the crystal orientation assigned to each measured
spots in the scanned area relative to the illuminating electron beam. The crystallographic
orientations relative to the three orthogonal directions (parallel and perpendicular to the
electron beam) can be presented in colored maps (Figure 1.). These orientation data are
obtainable as a numerical dataset or can be visualized in stereographical projections too.
Maps are also created from the matching indices (fitting quality of the observed and the
calculated diffraction patterns) show the grain boundaries definitely, giving a good
opportunity to observe the sizes and shapes of the crystals (Figure 1.). Phase map shows
the different crystal phases in the material.
STEM orientation mapping is a powerful method to characterize texture of
nanocrystalline materials (see images of rolled aluminum sheet in the figures), to
determine relative orientation between crystals, preferred orientations, twinning and to
localize inclusions.
Figure 1.: Orientation mapping results on rolled alumina sheet sample. …