Three-Dimensional Imaging in Aberration-Corrected Electron Microscopes
This article focuses on the development of a transparent and uniform understanding of possibilities
for three-dimensional ~3D! imaging in scanning transmission and confocal electron microscopes ~STEMs and
SCEMs!, with an emphasis on the annular dark-field STEM ~ADF-STEM!, bright-field SCEM ~BF-SCEM!, and
ADF-SCEM configurations. The incoherent imaging approximation and a 3D linear imaging model for
ADF-STEM are reviewed. A 3D phase contrast model for coherent-SCEM as well as a pictorial way to find
boundaries of information transfer in reciprocal space are reviewed and applied to both BF- and ADF-SCEM to
study their 3D point spread functions and contrast transfer functions ~CTFs!. ADF-STEM is capable of
detecting the depths of dopant atoms in amorphous materials but can fail for crystalline materials when
channeling substantially modifies the electron propagation. For the imaging of extended ~i.e., nonpointlike!
features, ADF-STEM and BF-SCEM exhibit strong elongation artifacts due to the missing cone of information.
ADF-SCEM shows an improvement over ADF-STEM/BF-SCEM due to its differential phase contrast eliminating
slowly varying backgrounds, an effect that partially suppresses the elongation artifacts. However, the 3D
CTF still has a cone of missing information that will result in some residual feature elongation as has been
observed in A. Hashimoto et al., J Appl Phys 160~8!, 086101 ~2009!.
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