Negative spherical aberration ultrahigh-resolution imaging in corrected transmission electron microscopy

Abstract

Aberration-corrected transmission electron microscopy allows us to image the structure of matter at genuine atomic resolution. A prominent role for the imaging of crystalline samples is played by the negative spherical aberration imaging (NCSI) technique. The physical background of this technique is reviewed. The especially high contrast observed under these conditions owes its origin to an enhancing combination of amplitude contrast due to electron diffraction channelling and phase contrast. A number of examples of the application of NCSI are reviewed in order to illustrate the applicability and the state-of-the-art of this technique.

Inclusion of radiation damage dynamics in high-resolution transmission electron microscopy image simulations: The example of graphene

“…For all three cases the quality of the imaging system was set to be the same; namely, correction of coherent aberrations provided a flat phase plate up to 20 mrad and incoherent aberrations resulted in a 4-nm focus spread. Among a variety of possible corrector settings [61][62][63] we have selected those used in experimental study: 5 positive value of spherical aberration (Cs = 10 μm) and defocus close to Scherzer 64 value (df = −8 nm for 80 kV and df = −6 nm for 200 kV). At these imaging conditions, resolution is determined by incoherent envelope, and the contrast of atoms does not change substantially at slight variation of Cs and df .…”

Defocus Polar rOse Estimation Method (POEM): A Fast Defocus Estimation Method for STEM

“…Due to astigmatism, electrons with different trajectory angles (measured in the x-y plane with respect to the x-axis) tend to be focused at different focal distances, thus giving the probe an elliptical (instead of circular) shape. Note that, although all three effects degrade the direct image interpretation (by blurring and deforming the images), they can also contribute to maximize the precision of imagebased measurements [10], [11], which motivates the need for both measuring and controlling them. In the sequel, however, the attention will be restricted to the defocus, and it will be assumed that the objective lens is astigmatism free and has a constant spherical aberration (which is the case in practice).…”

POEM: A fast defocus estimation method for scanning transmission electron microscopy

“…Due to astigmatism, electrons with different trajectory angles (measured in the − plane with respect to the −axis) tend to be focused at different focal distances, thus given the probe an elliptical (instead of circular) shape. Note that although all three effects degrade the direct image interpretation (by blurring and deforming the images), they can also contribute to maximize the precision of image-based measurements [6], [7], which motivates the need for both measuring and controlling them. In the sequel, however, the attention will be restricted to the defocus, and it will be assumed that the objective lens is astigmatism-free and has a constant spherical aberration (which is the case in practice).…”