Crystalline domain orientation of a two-dimensional WS2 film deposited on a (0001) sapphire substrate

A two-dimensional (2D) tungsten disulfide (WS2) film deposited by chemical vapor deposition on (0001) sapphire substrate is investigated by optical and transmission electron microscopy (TEM), Raman and photoluminescence (PL) spectroscopy, and in-plane X-ray diffraction (IP-XRD). The Raman and PL spectra confirm the 2D characteristics of WS2 film. The layered structure of 2D WS2 film is revealed in the TEM observation. According to the results of IP-XRD, 2D WS2 film is composed of two oriented domains on (0001) sapphire substrate. Two WS2 domains rotate 30֯ from each other. The crystal orientation relationships of a WS2 domain are (0001)WS2//(0001)sapphire and (101¯0)WS2//(112¯0)sapphire, whereas the crystal orientation relationships of another one are (0001)WS2//(0001)sapphire and (112¯0)WS2//(112¯0)sapphire. In 2D WS2 film, two-third portion belongs to the domain with the relationship of (101¯0)WS2//(112¯0)sapphire. Based on the theoretical calculation, the relationship of (101¯0)WS2//(112¯0)sapphire has smaller lattice mismatch than the relationship of (112¯0)WS2//(112¯0)sapphire.