Electron tomography is a technique to transform 2D images/projections into a full 3D representation of a sample. A series of images taken at different tilt angles are combined together with geometric knowledge to reconstruct the 3D structure. Conventional tomography specimen holders are designed to provide high tilt ranges. But, problematically, there is an angle range called the "missing wedge", where the holder, or even the sample support, physically obscures the region of interest from view.
Scientists from MML have surmounted the challenge posed by this missing data with a new specimen holder for tomography. The new holder allows for a full 360 degrees of rotational freedom, restoring access to all views of the sample. The holder is designed to have low "run-out" so that the sample stays in the field of view during rotation. Moreover, the holder accepts sample cartridges that allow for quick and easy exchange of pre-mounted specimens.
Experiments with the new holder are best accomplished using axially symmetric specimens. To make such samples, the scientists are using a focused ion beam instrument (FIB) to mill the material of interest into probes with a needle shape. These probes can be extracted by means of a nano-manipulator and attached to a cartridge stub. These probes can then be further FIB processed to create needle tips with thickness on the order of tens of nanometers. Scientists have employed this technique to examine materials such as nanostructured multilayer films and semiconductor interconnects.