Dislocation Tomography with the Mel-Build HATA tomography holder.
Dr Jonathan Barnard
Department of materials science and metallurgy
One of a series of weak-beam dark-field images of dislocations in silicon (left upper photography)
and a frame from a movie of the 3D reconstruction (right below tomography).
The movies show the dislocations, tomographically reconstructed, from a tilt series of weak-beam dark-field images of silicon
mounted in a Mel-Build High-Angle Triple-Axis (HATA) tomography holder.
The diffraction condition for weak-beam imaging is very sensitive to the crystal tilt and, with theHATA holder,
the diffraction condition can be held constant over the whole tilt range (-68o to 58o in 2o increments).
The tilt-series images were taken with the (220) reflection in a 200kV fieldz emission gun transmission electron microscope (FEGTEM) manufactured by FEI. With the possibility of tilting the crystal around the third axis, the deviation parameter, s220,
can be tuned to give images with good spatial resolution and image intensity.
Without this, the resolution and visibility is dependent on the sample preparation to give determine the diffraction condition .
The sample itself is of p-type silicon prepared, after indenting and annealing above the brittle/ductile transition temperature
(~550oC), to introduce plastic relaxation near the indent.
Using a focussed ion beam machine (FIB) and ion-beam milling, the near-indent region has been investigated.
The mechanism, by which, dislocations are generated in the stressed regions have been elaborated elsewhere .
The reconstruction of the dislocations was done using back-projection algorithms using the sequentially iterated reconstruction technique (SIRT) written in IDL?.
 Barnard J.S., Sharp J., Tong J.R. and Midgley P.A. (2006) Science 313 p319
 Higashida K., Narita N., Tanaka M., Morikawa T., Miura Y., Onodera R. (2002) Philosophical Magazine A82 p3263
Note: As for this 3D Tomography animation are only 40 frames that reduced for web-page. Original data is very smooth by 200 frames.
This paper is the first memorable Dark-Field 3D historically obtained using HATA-Holder by Dr Jonathan Barnard at 6 September 2007.