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To Core-Shell

To Core-Shell allows to model a core-shell spherical particle. As an example a Si core will be embeded in a Ge. First the Si crystal struture is loaded and the ToCoreShell menu item of menu Miscellany is selected.

Figure1

Figure 1 To core-shell window.

By default a core of diameter 0.192 nm is defined. Use the Duplicate sliders to make it larger. A 12 × 12 × 12 precipitate is displayed in Fig. 2. & Figure 3:

Figure2

Figure 2 Duplicating the core 12 × 12 × 12 produces a core of diameter 2.304 nm.

Figure3

Figure 3 Si core, diameter 2.304 nm and 2516 atoms.

Select the Shell pane, load the Ge structure and duplicate it 20 × 20 × 20 (Fig.4).

Figure4

Figure 4 Load Ge and duplicate it 20 × 20 × 20.

Figure5

Figure 5 Ge spherical shell from unit cell duplicated 20 × 20 × 20.

Figure5

Figure 6 List of atoms of the Si-Ge core-shell spherical spherical particle.

Figure7

Figure 7 Si-Ge Core-shell model.

The orientation relationship between the Si core and the Ge shell is defined using the Core pane Direction (Figures 8a, 8b).Note that the directions are specidied with respect to the cell sides.

Figure8a Figure8b

Figure 8a Si-Ge [uvw]=[111] core direction along Oz ZoneAxisGeometry.

Figure 8b Si-Ge [uvw] rotation of [uvw]=[111] axis, i.e. of Oz .

Figure9

Figure 9 Si [111], 60o-Ge Core-shell model.

Figure10a Figure10b

Figure 10a Si-Ge core-shell slices (56 slices of 0.2nm).

Figure 10b Si-Ge slice number 30.

The whole model is loaded (Fig. 11) and simple SAED, projected potential, HAADF and WPOA images calculated (Figures 12a, 12b, 12c, 12d). Indeed to perform accurate dynamical calculations it is necessary to introduce the slices into the Multislicer procedure.

Figure11

Figure 11 Si-Ge model.

Figure12a Figure12b

Figure 12a Si-Ge model SAED.

Figure 12b Si-Ge model projected potential.

Figure12c Figure12d

Figure 12c Si-Ge model HAADF image.

Figure 12d Si-Ge slice WPOA image.

Since the model is pretty thick it is necessary to slice it in ~0.2 nm thick slices. The model can be sliced directly with the To CoreShell window or saved and sliced with the To Slices window.

A sequence of 40 slices is saved on disk (anyName_0000, anyName_0001,..., anyName_0039).

To perform multislice calculations, load the first (top) slice (Fig. 13), start the Multislicer and load all the slices (Fig. 14).

Figure13

Figure 13 First slice of Si-Ge model.

Figure14

Figure 14 Mulislicer with stack of Si-Ge model slices.

Figure15

Figure 15 Si-Ge core-shell on amorphous carbon film.

The wave-function at the exit plane of the core-shell model is opened with the HRTEM Imager and further simulations including aberration, change of defocus or missalignments performed (Fig. a).

Figure16

Figure 16 HRTEM Imager started with the exit wave-function of Si-Ge core-shell model.