Issues of experimental apparatuses for electron tomography observation in crystalline materials

The author has contributed to developing sample holders for electron tomography (ET) [1, 2]. Based on the author’s experience of the holder development, there are distinctive issues of designing ET holders. Because ET usually needs high-angle sample tilt over 60 degrees, the information of a pole piece gap in a transmission electron microscope (TEM) is necessary and also unsatisfactory for designing sample holders capable of ET observation. Firstly, the eucentric height of a sample holder may not locate at the center of the pole piece gap. Secondly, there may not be an enough space (vertical and horizontal widths) outside the pole piece gap. These issues in the TEM sample chamber make the compatibility of high-angle tilt and desirable functions in an ET sample holder difficult. It is also an issue for ET that insertion of an objective aperture limits the maximal sample-tilt angle in modern TEMs of which the objective lens systems are optimized for high-resolution scanning transmission electron microscopy (STEM) as well as transmission electron microscopy (TEM). Therefore, using an objective aperture for diffraction contrast ET observation [3, 4] is not available in these modern TEMs. Alternative diffraction contrast ET observation methods without using an objective aperture have been reported [5, 6]. Fast tilt-series datasets acquisition for time-resolved ET [7] needs superior performances of a TEM goniometer system as well as an image acquisition system. Based on the author‘s experience of fast tilt-series datasets acquisition [8], the followings are issues of the goniometer system for high-resolution time-resolved ET imaging: controllable sample tilt speed at a user level; accurate readout of sample tilt angles synchronizing with image acquisition; (iii) a stable eucentric position of a field of view during sample tilt.