In-plane and out-of-plane structural analysis of epitaxial 2D MoS2 thin films MOCVD-grown on distinct Al2O3(0001) surfaces

This proposal aims to investigate epitaxial, 2D thin films of MoS2, a prototypical transition-metal dichalcogenide (TMD) semiconductor with potential applications in nanoelectronics. Single-layers of MoS2 have been grown by metal-organic chemical vapor deposition (MOCVD) on sapphire (α-Al2O3) substrates with distinct O-terminated (1×1) and Al-terminated (√31×√31)R9° surface reconstructions. To better understand the distinct growth behaviour and epitaxial model, a detailed structural analysis of the surfaces and interfaces is proposed by in-plane GIXD and out-of-plane XRR studies. Moreover, an in situ study involving thermal annealing of MoS2/Al2O3 samples in H2S-atmosphere can simulate S-rich reaction conditions and monitor evolution of the topmost sapphire surface and MoS2/Al2O3 interface. These experiments will gain a fundamental understanding of the impact of sapphire surface reconstruction, which is expected to play a crucial role in the vdW epitaxy of TMDs.