Directing the Morphology of Chemical Vapor Deposition-Grown MoS2 on Sapphire by Crystal Plane Selection

Crystalline substrates are known to function as a template for the growth of Van der Waals materials. Van der Waals materials, specifically transition metal dichalcogenides, have gained attention in the past decade due to their interesting chemical and physical properties, as well as the potential they hold for applications, particularly in the field of (opto-)electronics. The crystalline quality of these materials can be improved by epitaxial growth. Herein, the influence substrate selection has on ordering the growth of MoS2 is examined. Specifically, the impact sapphire crystal orientation has on the morphology and alignment of MoS2 grown by chemical vapor deposition is investigated. C-plane (0001), R-plane (11 over bar 02), A-plane (112 over bar 0), and M-plane (101 over bar 0) Al2O3 substrates, annealed at high temperature in air, are used as templates for MoS2 growth. Comparative analysis, including photoluminescence spectroscopy, Raman spectroscopy, and atomic force microscopy, reveals distinct characteristics and growth modes depending on the growth substrate used. It is found that aligned growth of MoS2 is influenced by the terrace size, atomic steps, and substrate interaction with the MoS2. Aligned growth occurs on both R- and M-plane sapphire. For A-plane sapphire, the MoS2 flakes are variable in size and thickness. The weakest substrate interaction is observed for growth on C-plane sapphire, which consists of randomly oriented flakes.