**4. HRTEM study of van der Waals structure of silicon nitride and aluminum nitride**

The atomic arrangement of (8 × 8) was also investigated here by the HRTEM method. For these studies, samples with the following sequence of layers were grown on the (111) Si substrate: 2–3 monolayers of silicon nitride with a structure (8 × 8) and thin epitaxial layer of AlN. The interplanar spacing in the Si substrate in the silicon nitride and AlN layers was determined, see **Figure 7**. It turned out that the interplanar spacing between the layers of silicon nitride and also between the last silicon layer and the silicon nitride layer is about 3.3 Å, which is noticeably larger than the interplanar distances in silicon (3.13 Å) and the known thickness of the β-Si3N4 monolayer (2.9 Å). In addition, the layers of silicon nitride differ sharply in contrast from the layers of Si and AlN.

The interplanar distances in silicon nitride of 3.3 Å are larger than the interplanar distances Si 3.13 Å and are larger than the thickness of the monolayer β-Si3N4 (2.9 Å). The interplanar distances in the еpitaxial AlN layer are also larger than normal interplanar distances in bulk wurtzite AlN (2.49 Å). Therefore, this epitaxial structure (SiN)2(AlN)4 turned out to be a van der Waals crystal.

**Figure 7.** *HRTEM image of layers of SiN and AlN on the Si (111) surface.*
