This document describes how to create a Boron Nitride mono-layer (Fig. 3b) and how to modify it replacing one or more atoms and adding atoms. BN has a layered structure that consists of rings of 3 B or 3 N atoms arranged in horizontal sheets (Fig. 1b).

To create a BN model one has to select a single layer of BN groups. This is done in 2 steps by Make orthogonal (Fig. 1c) and To slices (Fig. 2).

1. With the BN P 63mc crystal structure create an orthorhombic unit cell (Fig. 1d).

2. Duplicate the orthorhombic unit cell 19 and 11 times in the x and y directions respectively to obtain a orthorhombic of large, nearly equal, a and b cell parameters (Fig. 2).

3. The orthorhombic structure is described by BN_slices.txt file.

4. Slicing the BN_slices.txt file in 3 sub-slices and the second sub-slice BN_0001.txt is the .txt model file.

With the popup menu attached to the model (Fig. 3b) the projected potential, HAADF, WPOA and SAED images are readlily calculated with the current settings of the microscope, aberrations, coherence, etc. (Figures 4a, 4b, 4c, 4d).

ADF images of the BN layer are obtained using the ADF imager. The simulations parameters are:

• Accelerating voltage 20 kV.

• W₄₀ (C₃₀) 0 mm, W₀₀ (Cc) 1 mm.

• W₂₀ (C₁₀) -6.8 nm.

• Electron beam energy spread 0.1 eV.

• Lens current and voltage stability 0.1 ppm.

• Aperture diameter 24 nm^-1.

• Detector sensitiviy is uniform and by default it is centered on the optical axis (000).

Each simulation run produces 4 Bright Field images with BF detector radius 10, 30, 50, 70 nm^-1 (Figures 5a, 5b, 5c, 5d). With a negative W₄₀ (C₃₀) the first BF image is similar to the HRTEM image.

Each simulation run produces also 4 Dark Field images with detector inner and outer radii 60 to 150, 80 to 170, 100 to 190, 120 to 210 nm^-1 (Figures 6a, 6b, 6c, 6d). With a negative W₄₀ (C₃₀) the first BF image is similar to the HRTEM image.

4 sector detectors (1 to 4) are placed between the BF and DF detectors. By default the inner and outer radii of the sector detectors are set to the outer radius of the BF detector and the inner radius of the DF detector (Figures 7a, 7b, 7c, 7d).

Differential Phase Contrast imaging is an interesting feature of sector detectors. DPC images calculated using the sector images (Figures 7a, 7b, 7c, 7d) are shown below. Indeed these DPC images result of simulations, experimentally provided ones will most likely be somehow different due to non-uniformity of the detectors, etc. In spite of that simulated DPC images could provide valuable insights on the BN structure when it contains impurities like W.

As noted by K. Ishizuka, A practical approach for STEM image simulation based on the FFT multislice method, Ultramicroscopy 90 (2002) 71–83, it is not necessary for accurate calculations to scan the whole periodic model. Fig. 10a shows a HAADF image calculated with Ishizuka approach. The images shown in Figures 5, 6, 7, 8, 9 and 10a, were computed on a smaller part of the model of size 512 × 512 (Fig. 10a), with a probe shape shown in Fig. 10b. The projected potential was initialized on 1024 x 1024 grid with Weickenmeier-Kohl atomic form factors.

During the scanning one can observe the power spectrum, bright field, dark field and 4 sectors detectors (12a, 12b, 12c, 12d).

Finally the probe wave-function is shown in Fig. 13.

Adding or changing one atom can be done by modifying the BN layer using a text editor or the crystal Builder. When pointing to a B or N atom the builder will provide its fractional coordinates (Fig. 14).