TEMStrain    

Orientation

An orientation must be specified for each pattern by clicking on “Settings” command button and by selecting “Orientation” tab.

There are two ways to specify the orientation:

1. By providing Euler angles. Their definition is the same as in crystallographic texture analysis (see, e.g. A.Morawiec, Orientations and rotations, Springer, Berlin, 2004), except that the standard in textures is to provide the orientation with respect to the sample coordinate system; here it must be given  with respect to the microscope coordinate system, i.e. tilt angles have no influence on these orientation parameters. The third axis (z) of the microscope coordinate system is parallel to the microscope optical axis and directed from the detector towards the foil; its first axis is parallel to the holder tilt axis. The first angle of the three Euler angles (fi1) corresponds to the rotation about the microscope optical axis. Because of the magnetic rotation, the correct value of this angle can be established based on comparison of the experimental pattern with kinematically simulated HOLZ line diagram.

2. By specifying the zone axis parallel to the microscope optical axis. This is equivalent to providing two of three orientation parameters. The third one  is the rotation about the microscope optical axis; it can be determined using the command button marked by a circle in the "Fine-tuning" frame box in the main (TEMStrain) window of the program.

If multiple patterns are used, the orientations must be specified in a consistent way; they must be linked to holder tilts for which they were obtained. The symmetrical equivalence of orientations cannot be used because, with arbitrary strain tensor, the symmetry is broken. For instance, if the zone axes are [001], [011] and [010] (tilt about x), one cannot use [001], [110] and [010] or [001], [011] and [0-10]. The same warning applies to orientations given by Euler angles. If orientation and tilt angles of a given pattern are not consistent (2deg limit) with orientations and tilt angles of all remaining patterns, a flash (located near the "Settings" button) blinks. 

Orientation can be fine-tuned using the “arrow and circle” buttons in the “Fine tuning”  frame box.

If the orientation is not known, it can be determined using a Kikuchi pattern recorded with known and sufficiently small camera length. If the camera length is smaller than 10 times the physical dimension of the detector (=512 * Pixel size), a button marked by 'O' appears in the “Fine tuning”  frame box. The pattern can be solved by carefully marking more than three pairs of Kikuchi lines, and by clicking on 'O'. In simple cases this function may work based on automatically detected lines. It is important to set the "Maximal Miller index" ("Minimal intensity ratio") in "Settings/Simulation/Kinematic Simulation"  to a reasonably small (large) number.