missing wedge (missing cone)

Fig. 1(a) Schematic of Missing Wedge for acquiring tilt-series images with the tilt-angle range of ±θ_max and the angle step of Δθ.
(b) Shapes of Missing Wedge for a uniaxial-tilt specimen holder. (c) Shapes of Missing Wedge for a double-tilt specimen holder.
When using a uniaxial-tilt specimen holder, the specimen images are taken by tilting the specimen only about the X axis. Whereas, when using the double-tilt holder, the images are taken by tilting the specimen about both of the X and Y axes.
Since the double-tilt holder achieves a smaller Missing Wedge than the uniaxial-tilt holder, the use of the double-tilt holder provides a 3D reconstructed structure with less artifacts.

Fig. 2 (a) Dark field-STEM image of a high-polymer specimen subjected to pillar-shaped milling.
(b) Artifacts due to the Missing Wedge appeared in the cross-sectional images of the structure obtained by 3D reconstruction from a uniaxial-tilt (about X-axis) series images of the specimen. As the tilt range becomes narrower, the resolution in the Z direction degrades. That is, the particles in the specimen are seen to elongate in the incidence direction of the electron beam (as indicated by the red arrow in each image (b)).
This degradation of resolution in the Z direction causes a decrease in accuracy of 3D metrological analysis (volume, surface area, aspect ratio).
(c) Schematic of the Missing Wedge indicated by blue color.

Fig. 3(a) Ordinary uniaxial-tilt specimen holder and (b) High-tilt specimen holder.