Crystallographic Orientation Maps Obtained from Ion and Backscattered Electron Channeling Contrast.
Clément LAFOND1, Cyril LANGLOIS1, Thierry DOUILLARD1, Sébastien DUBAIL2, Sophie CAZOTTES1
1. MATEIS laboratory – INSA Lyon, Lyon, France.
2. Axon Square Ltd, Sciez, France.
several years now, new directions have been explored to obtain
orientation maps by other means than the classical Electron Back
Scattered Diffraction (EBSD) method, or to modify it aiming at improved
information. Particularly, the channeling contrast may be used to
obtain orientation maps, with the following approach, called Channeling
Orientation Determination (CHORD) [1,2]. The main idea is to acquire an
electron or ion image series when rotating a pre-inclined
polycrystalline sample with respect to the beam (Figure 1). Along such
image series, each (X,Y) pixel of the region of interest undergoes an
intensity variation due to the channeling effect, that can be plotted
as a function of the rotation angle. Such intensity profiles can be
theoretical predicted for a given orientation of a crystal. The
indexation procedure then relies on a search in a database of
theoretical profiles obtained by simulating intensity profiles for a
large set of orientations. The principal issue is to model
quantitatively the channeling effect observed in such image series.
ion-induced electron images (iCHORD image series), an intensity loss is
observed when the ion beam arrives parallel to some low index
crystallographic planes of a crystal. Therefore, if the atomic
structure of the crystal is projected onto a surface perpendicular to
the ion beam, an intensity loss will corresponds to large “free spaces”
between the atomic projections, which are quantified by summing the
grey levels of the projection pixels. An efficient model of the
channeling effect is then obtained following this principle (Figure 2)
provided precautions to avoid projection artefacts.
back scattered electron image series, the similarity between the eCHORD
and Electron Channeling Patterns (ECP) acquisitions is used to model
quantitatively the experimental electron channeling effect. The eCHORD
intensity profiles are then simulated by extracting the intensity along
a circle from simulated ECPs (Figure 3) .
resulting orientation maps, the angular resolutions are both under 1°,
with slightly better performances using electrons (around 0.3°)
compared to ions (0.8°). More generally, the main advantage is that no
extra detector is needed to carry out the experiment, opening
orientation mapping capability potentially on any SEM and FIB machine.
Moreover, acquisition times are comparable to EBSD technique. The
geometry of acquisition, simpler than the EBSD one, could be also a
critical advantage when turning to 3D orientation mapping.
Figure 1. Experimental CHORD setup
Figure 2. a) Atomic brightness function as a function of the distance toward the projection plane (black line on
the top); b) Projection plane on which atoms are projected c) Concordance between experimental (blue) and
theoretical (brown) intensity profiles.
Figure 3. a) ECP simulated at 15 kV for aluminum: in red, circle corresponding to the beam path at 10°;
b) comparison between the theoretical profile extracted from the ECP in (a) and the experimental profile after denoising.
 C. Langlois et al., Ultramicroscopy 157 (2015), p. 65
 C. Lafond et al., Ultramicroscopy 186 (2018), p. 146
 S. Singh and M. De Graef, Microscopy & Microanalysis, 23 (2017), p. 1