Diffraction studies of WS2 crystallographic ordering during laser MBE growth on Al2O3(0001)

For optimal integration of 2D materials into fab-compatible processes, it is essential to grow them directly onto suitable insulating substrates, thereby avoiding error-prone transfer procedures. In the present paper, ultrathin films of WS2 were grown on Al2O3 using laser molecular beam epitaxy (LMBE). By applying our advanced 3D reciprocal space mapping technique, the presence of long-range order in the growing layers during the growth process could be identified. We observed a strong influence of pre-growth annealing of the substrate on the lateral crystallographic lattice ordering of ultrathin WS2 films. In particular, it was found that high-temperature annealing of the substrate before film growth changed the preferential lattice orientation of WS2 crystallites from 30° to 0° with respect to Al2O3. These observations contribute to a better understanding of epitaxial growth processes and crystallographic relationships between WS2 and Al2O3. We demonstrate growth of the WS2 film on the Al2O3 substrate by using the LMBE method at significantly lower substrate temperatures (500 °C) than that used by other techniques. The feasibility of achieving better structural order in WS2 films through optimized substrate treatments using LMBE presents significant implications for the future integration of 2D materials in electronic devices.