Growth Mechanism of Transition Metal Dichalcogenide Monolayers: The Role of Self-Seeding Fullerene Nuclei

Abstract

Due to their unique optoelectronic properties and potential for next generation devices, monolayer transition metal dichalcogenides (TMDs) have attracted a great deal of interest since the first observation of monolayer MoS2 a few years ago. While initially isolated in monolayer form by mechanical exfoliation, the field has evolved to more sophisticated methods capable of direct growth of large-area monolayer TMDs. Chemical vapor deposition (CVD) is the technique used most prominently throughout the literature and is based on the sulfurization of transition metal oxide precursors. CVD-grown monolayers exhibit excellent quality, and this process is widely used in studies ranging from the fundamental to the applied. However, little is known about the specifics of the nucleation and growth mechanisms occurring during the CVD process. In this study, we have investigated the nucleation centers or "seeds" from which monolayer TMDs typically grow. This was accomplished using aberration-corrected scanning transmission electron microscopy to analyze the structure and composition of the nuclei present in CVD-grown MoS2-MoSe2 alloys. We find that monolayer growth proceeds from nominally oxi-chalcogenide nanoparticles which act as heterogeneous nucleation sites for monolayer growth. The oxi-chalcogenide nanoparticles are typically encased in a fullerene-like shell made of the TMD. Using this information, we propose a step-by-step nucleation and growth mechanism for monolayer TMDs. Understanding this mechanism may pave the way for precise control over the synthesis of 2D materials, heterostructures, and related complexes.

Local characterization of mobile charge carriers by two electrical AFM modes: multi-harmonic EFM versus sMIM

“…Expect the mechanical exfoliation samples, the CVD grown MoS 2 flakes [44][45][46] has been studied by sMIM and MH-EFM. The MoS 2 flakes were grown on SiO 2 (300 nm)/Si substrate, via traditional CVD method.…”

Phosphorous doped p-type MoS2 polycrystalline thin films via direct sulfurization of Mo film

“…Therefore considerable efforts are required for scalable synthesis of p-type MoS 2 film to realize practical applications. To date, a direct growth method of MoS 2 thin films by chemical vapor deposition (CVD) via vapor-phase reaction of MoO 3 and sulfur (S) powders, [18][19][20][21] MoCl 5 and S powders, 22,23 and metal Mo films [24][25][26][27][28] in a CVD furnace have been demonstrated to overcome a large area film synthesis. Among them, the direct grown method of TMDs (e.g.…”

Transport properties of the top and bottom surfaces in monolayer MoS2grown by chemical vapor deposition

“…Moreover, it is reported that the nucleation of MoS2 on SiO2 is difficult and that MoS2 starts to grow from nominally oxi-chalcogenide nanoparticles as heterogeneous nucleation sites. 53 Based on this discussion, the MoS2/SiO2 interaction could be physisorption, which suggests positive prospects for further improvement of the crystallinity of MoS2 on oxide substrates by reconsidering the growth conditions.…”