Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning

Abstract

Screw dislocations play an important role in materials' mechanical, electrical and optical properties. However, imaging the atomic displacements in screw dislocations remains challenging. Although advanced electron microscopy techniques have allowed atomic-scale characterization of edge dislocations from the conventional end-on view, for screw dislocations, the atoms are predominantly displaced parallel to the dislocation line, and therefore the screw displacements are parallel to the electron beam and become invisible when viewed end-on. Here we show that screw displacements can be imaged directly with the dislocation lying in a plane transverse to the electron beam by optical sectioning using annular dark field imaging in a scanning transmission electron microscope. Applying this technique to a mixed [a+c] dislocation in GaN allows direct imaging of a screw dissociation with a 1.65-nm dissociation distance, thereby demonstrating a new method for characterizing dislocation core structures.

4D-Data Acquisition in Scanning Confocal Electron Microscopy for Depth-Sectioned Imaging

“…3. While a similar depth-sectioning technique has been reported in the literature [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54], we note that all the Co particles in the view field are observed irrespective of the used defocus values.…”

3D elemental mapping with nanometer scale depth resolution via electron optical sectioning

“…Once such a 3D OTF is calculated it can be sectioned parallel to the beam direction (vertically in Figure 4) for any given spatial frequency to yield the transfer function corresponding to sample features with the corresponding lateral spacing. We extract a depth resolution of 9 nm for the 0.28 nm minimum transverse spacing of the Zr lattice, only a couple of nanometers more than the 7 nm depth of field [10]. For the larger 0.39 nm Ti-Ti and Sr-Sr spacings we calculate the depth resolution to be 11 nm.…”

“…With just a few nanometers in optimal focus at a time, three dimensional information can be obtained by observing which features are in focus as the probe is focused to different depths. Such optical sectioning has previously been used with Z-contrast imaging in STEM to identify and determine the three dimensional positions of individual dopant atoms [2,3,4,5,6,7], and to image the core structure and inclination of dislocations [8,9,10]. However, Z-contrast imaging suffers from an inability to differentiate heavier elements of similar atomic number and very light elements can be obscured by the strong scattering of nearby heavy elements.…”

From Dose to Response: In Vivo Nanoparticle Processing and Potential Toxicity

“…Much work remains to be done in determining the in vivo properties of the many different types of nanoparticles and how variables such as particle morphology, size, surface treatments, and composition effect in vivo processing. The application of aberration corrected electron microscopes to the study of in vivo processing would most likely be very fruitful [65, 86]. These microscopes have the resolution to determine if a cloud surrounding a nanoparticle is composed of single molecules or very small clusters as in the silica examples above.…”