Tailored Synthesis of Heterogenous 2D TMDs and Their Spectroscopic Characterization

Two-dimensional (2D) vertical van der Waals heterostructures (vdWHs) show great potential across various applications. However, synthesizing large-scale structures poses challenges owing to the intricate growth parameters, forming unexpected hybrid film structures. Thus, precision in synthesis and thorough structural analysis are essential aspects. In this study, we successfully synthesized large-scale structured 2D transition metal dichalcogenides (TMDs) via chemical vapor deposition using metal oxide (WO₃ and MoO₃) thin films and a diluted H₂S precursor, individual MoS₂, WS₂ films and various MoS₂/WS₂ hybrid films (Type I: Mo_xW_1-xS₂ alloy; Type II: MoS₂/WS₂ vdWH; Type III: MoS₂ dots/WS₂). Structural analyses, including optical microscopy, Raman spectroscopy, transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy, and cross-sectional imaging revealed that the A_1g and E_2g modes of WS₂ and MoS₂ were sensitive to structural variations, enabling hybrid structure differentiation. Type II showed minimal changes in the MoS_2's A_1g mode, while Types I and III exhibited a ~2.8 cm^-1 blue shift. Furthermore, the A_1g mode of WS₂ in Type I displayed a 1.4 cm^-1 red shift. These variations agreed with the TEM-observed microstructural features, demonstrating strain effects on the MoS₂-WS₂ interfaces. Our study provides insights into the structural features of diverse hybrid TMD materials, facilitating their differentiation through Raman spectroscopy.