Atomic Force Microscopy and Image Analysis of Epitaxial 2D WS₂ Crystals Grown via Metal-Organic Chemical Vapor Deposition

Abstract

The controlled synthesis of monolayer tungsten disulfide (WS₂) is essential for its application in next-generation electronic and optoelectronic devices. Metal-organic chemical vapor deposition (MOCVD) has emerged as a scalable and reliable method for growing high-quality WS₂ monolayers. However, optimizing the growth parameters remains challenging for achieving uniform coverage and well-defined domain structures. This study focuses on characterizing WS₂ monolayers grown on c-plane sapphire substrates under varying annealing and growth temperatures and times. Atomic force microscopy (AFM) and ImageJ analysis have been employed to quantify monolayer coverage, nucleation density, and domain size.

Our findings reveal that WS₂ monolayer coverage increases proportionally with the nucleation growth time, indicating a direct correlation between deposition duration and surface coverage. Additionally, we observe that the nucleation density decreases as the nucleation temperature increases, while the domain size grows larger at higher temperatures. Notably, the step edges on sapphire wafers strongly influence the WS₂ growth process, facilitating domain alignment along these steps and suggesting a potential method for improving film uniformity.

These results contribute to a deeper understanding of the WS₂ monolayer growth mechanisms and provide insights into optimizing the synthesis conditions. Future research will focus on refining growth parameters to achieve continuous monolayer coverage, investigating the role of step-edge depth in influencing nucleation density and domain size, and analyzing domain orientation at different nucleation temperatures. These findings could guide the development of scalable WS₂ synthesis techniques and other transition metal dichalcogenides (TMDs) for electronic and optoelectronic applications.