Atomic resolution imaging using the real-space distribution of electrons scattered by a crystalline material

Abstract

We present an alternative atomic resolution incoherent imaging technique derived from scanning transmission electron microscopy (STEM) using detectors in real space, in contrast to conventional STEM that uses detectors in diffraction space. The images obtained from various specimens have a resolution comparable to conventional high-angle annular dark-field (HAADF) STEM with good contrast, which seems to be very robust with respect to thickness, focus and imaging conditions. The results of the simulations are consistent with the experimental results and support the interpretation of the real-space STEM image contrast as being a result of aberration-induced displacements of the high-angle scattered electrons.

The correction of electron lens aberrations

“…A related variant on the basic STEM imaging modes is being investigated by Joanne Etheridge and colleagues in Monash University [109,110,31] using an FEI Titan 300 kV microscope with double correction. In STEM, the source is conjugate to the specimen plane and the information used to form an image is retrieved in the far field.…”

Image formation in the scanning transmission electron microscope using object-conjugate detectors

“…The experimental images reported here and in our earlier works Lazar et al, 2011) were acquired using instruments equipped with both an aberration-corrected objective prefield and an aberration-corrected postfield. The experimental images reported here and in our earlier works Lazar et al, 2011) were acquired using instruments equipped with both an aberration-corrected objective prefield and an aberration-corrected postfield.…”

“…The experimental images reported here and in our earlier works Lazar et al, 2011) were acquired using instruments equipped with both an aberration-corrected objective prefield and an aberration-corrected postfield. For example, the upper solid curve applies to the instruments used here and in our previous works Lazar et al, 2011). On the other hand, correction of the postfield aberrations does not influence the resolution of the images and is not a requirement for the acquisition of R-STEM images.…”

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

“…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. Alternatively, if an annular detector or a very large disc detector is used, 2D incoherent, atomic resolution "R-STEM" images can be generated [31,36,37].…”

“…With future work a number of improvements can be made. For example, with small modifications to the intermediate lens series and/or location of the annular detector, a reference R-STEM image (an incoherent image with atomic number contrast [36,37]) could be recorded synchronously with the inelastic image, providing independent identification of atomic-column positions. Faster acquisition times would be expected if a high brightness gun were used.…”