Three-Dimensional Imaging in Aberration-Corrected Electron Microscopes

Abstract

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).

Advanced semiconductor characterization with aberration corrected electron microscopes

“…angles greater than 15 mrad) one should take care of the reduced depth of field of HR-STEM images [37]. On the other hand, this limited depth of field can be used for depth sectioning, that is to say, 3D reconstructions [37]. We noticed that in FIB prepared samples or in samples having some amorphous layers at the surface of the TEM lamella, the best images are not obtainable from the thinnest areas of the samples.…”

“…However, when working with high convergence angles (i.e. angles greater than 15 mrad) one should take care of the reduced depth of field of HR-STEM images [37]. On the other hand, this limited depth of field can be used for depth sectioning, that is to say, 3D reconstructions [37].…”

High‐Resolution Scanning Transmission Electron Microscopy (HRSTEM) Techniques: High‐Resolution Imaging and Spectroscopy Side by Side

“…[71] Theoretical studies, [72,73] supported by image simulation procedures and experiments using different imaging modes, on STEM regime [74,75] indicate that the SCEM technique can provide spatial resolution up to 1 nm along the zone axis and can unveil depth localization of heavy atoms (Bi) on a lighter matrix (Si). State-of-the-art SCEM presents high-resolution depth profile analysis for nanocrystals [75,76] by the use of STEMoptimized optical systems, including Cs correction. Further advances are expected by the use of novel Cc correction hardware and improved analysis methods.…”

Fast Imaging with Inelastically Scattered Electrons by Off-Axis Chromatic Confocal Electron Microscopy

“…1(a) and compared with on-axis SCEM [Fig 1(b)]. On-axis SCEM has been developed to improve the axial resolution in 3D electron imaging [20][21][22][23][24][25][26][27][28][29][30][31] and more recently its use for 3D imaging with inelastically scattered electrons has been demonstrated [32][33][34][35]. In both cases, a point detector or equivalent is used to omit electrons that are not focused precisely on the detector plane, in analogy with confocal optical microscopy.…”