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HRSTEM Imager

The HRSTEM Imager loads a HAADF Object Intensity image (Fig. 2c) and performs a convolution with the Optical Transfer Function of the microscope (Fig. 2b). The HRSTEM imager uses the metric and geometry stored in the HAADF intensity image. This makes possible to control the probe shape (Fig. 2b) by introducing lens Aberrations up to order 8 (Figures 3a, 3b).

Figure1

Figure 1 HAADF imager, object intensity loaded (graphene).

The HAADF image, Probe and Object intensity tabs display the HAADF image (Fig. 2a), the Probe shape (Fig. 2b) and the Object intensity (Fig. 2c) respectively.

The slider controlling the HAADF gain is placed on the Imaging pane (2d).

Figure2a Figure2b
Figure 2a HAADF image. Figure 2b Probe image and profile.
Figure2c Figure2d
Figure 2c Object intensity. Figure 2d Imaging controls.

The imaging parameters controls, optical Aberrations, coherence, drift, ... are grouped in several panes:


The toolbar contains tool buttons to:

Figure3a Figure3b
Figure 3a Sliders to set Aberrations. Figure 3b Table of Aberrations.
Figure3c Figure3d
Figure 3c Coherence controls. Figure 3d Drift and noise controls.

The HADDF intensity map approximates the inverse Fourier transform of power spectrum of the High Angle Annular Dark Field inelastically scattered electrons.

A popup menu is attached to each figure. It allows to change the color lookup table, to tabulate the image values or to display the image in 3-D (Figures 4, 5).

Figure4a Figure4b
Figure 4a Microscope controls set 1. Figure 4b Microscope controls set 2.
Figure5a Figure5b
Figure 5a Popup menu attached to the HAADF intensity image. Figure 5b Popup menu attached to the Probe intensity image.
Figure5c Figure5d
Figure 5c 3-D view of the probe. Figure 5d Popup menu attached to the object intensity.

Notes

The Aberrations coeeficients can be changed either using sliders (on the left) or directly in the text fields on the right. When selected the text field background color is yellow. When the text field is selected (yellow color) using the:

The formula text field displays the mathematical description of the aberration in orthogonal coordinates.

The notation adopted for the optical Aberrations coefficent follows either the notation of Krivanek and Haider, as well as a notation describing the wavefront aberration (Wnm). The wavefront aberration is simpler to remember since n provides the power of the spatial frequency and m the rotational symmetry. For example W40 is the spherical aberration coefficient C30 or C3 that describes the deformation of the wavefront:

w40 (no angular dependence).

As another example three fold astigmatism W23 (Krivanek) or A2 (Haider) is labelled W33 with formula:

w33

that clearly shows that this aberration scales as the third power of the spatial frequency (u3) and has a rotational symmetry 3.

HAADF image is pretty sensitive to focus changes (6a, 6b).

A larger defocus completey blur the HAADF image (6c, 6d).

It is not possible to simulate images with a very large defocus since under such a condition the probe will extend farther than the Nyquist limit and consequently the HAADF images will contains many artefacts.

Figure6a Figure6b
Figure 6a HAADF image intensity. Figure 6b Probe image.
Figure6c Figure6d
Figure 6c HAADF image intensity. Figure 6d Probe image.