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The experiment window consists of 5 panels.
If the chosen direction would need a chi angle larger than 100 degrees, you are notified through a dialog window, and asked whether it is OK to invert the direction.
The "Go here" button will position the goniometer to the displayed position. The colour of the "Go here" button will be green if positioning is possible, and red if positioning is impossible. "Minimize dx" will search for the minimal dx that can be obtained for the given position of the goniostat, leaving enough space for an omega scan.
Both these "view" windows can be manipulated with the mouse.
There is one additional button "Edit Faces", which will pop up a crystal face editor.
In the file name entry field, the name of a file that will contain the crystal description can be given (default absorb.ins).
To make a face-indexing description of the crystal, do the following: choose a reciprocal vector in the first panel of the main window, and select the direction "Along positive Y". Now press "Calculate". Make sure this position can be reached by the goniostat (otherwise possibly reposition the detector a bit), and press "Go Here" in the crystal face editor window. Now the face named by the vector you chose should be positioned vertical to the right of the center. Click "Add face facing right". A purple line will appear in the display showing the normal to the added face. In the table that will appear at the right of the window, you can change the length of that vector to match the size of the crystal. (You will need to press "enter" to activate any changes).
Now, check whether the anti-face (with the opposite index) also is present on the crystal (vertical at the left side). If it is, use the button "Add face facing left" to add the face to the list, and correct the length.
Do the same for all faces on the crystal.
If the faces on the crystal do not have nice indices, they can be found using a slightly different procedure. Rotate the crystal until one of the faces "disappears from view" (i.e. it is perpendicular to the view plane). Now click the "Add face" button and move the mouse to the face. Adjust the mouse position until the face cartoon touches the crystal at the right place. There, click the left mouse button.
Once the crystal description is closed, a cartoon of the crystal will be shown in the crystal face editor, as well as in any "Microscope View" and "Primary beam view" windows.
Please note that if you find any of the images too small, you can resize the window at will. As described above, the image itself can be rescaled by dragging the right mouse button over the image. Finally, the resolution of the crystal photo is determined by the size of the video window on the Windows computer, so verify that this window is as large as it can be.
Dragging with the left and middle mouse buttons pressed together can be used to translate the crystal drawing and not the microscope image. This can be used for face indexing if the alignment of the microscope is less than perfect.
The file for the crystal description contains one line for each of the crystal faces, each line contains the literal word "FACE", three indices h,k,l (separated by spaces) describing the face, and a distance "d" (in mm) for this face to the center of the goniometer. An alum crystal could have:
FACE 1 1 1 .2
FACE 1 1 -1 .2
FACE 1 -1 1 .2
FACE 1 -1 -1 .2
FACE -1 1 1 .2
FACE -1 1 -1 .2
FACE -1 -1 1 .2
FACE -1 -1 -1 .2
The cifin program will use this
file to define the crystal description fields of the cif file.
It is also the native format for face index absorption by the
platon program
by Dr. A.L. Spek.
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