nn6b01705_si_001.pdf (4.94 MB)
Growth Mechanism of Transition Metal Dichalcogenide Monolayers: The Role of Self-Seeding Fullerene Nuclei
journal contribution
posted on 2016-05-03, 00:00 authored by Jeffrey
D. Cain, Fengyuan Shi, Jinsong Wu, Vinayak P. DravidDue 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.