Abstract
The transition from single-layer to bilayer growth of molybdenum disulfide on the Au(111) surface is investigated by in situ low-energy electron and photoemission microscopy. By mapping the film morphology with nanometer resolution, we show that a MoS2 bilayer forms at the boundaries of single-layer single-domain MoS2 islands and next to merging islands whereas bilayer nucleation at the island centers is found to be suppressed, which may be related to the usage of dimethyl disulfide as sulfur precursor in the growth process. This approach, which may open up the possibility of growing continuous films over large areas while delaying bilayer formation, is likely transferable to other transition metal dichalcogenide model systems.
Highlights
The interest in two-dimensional (2D) materials has been strongly increasing since the seminal discovery of the peculiar electronic properties of graphene in 2004 [1], including Dirac-like dispersion of the electronic bandstructure near the Fermi level [2, 3]
The growth and characterization experiments presented here were performed under ultra-high vacuum (UHV) conditions with a base pressure of 1×10−10 torr in an ELMITEC lowenergy electron microscopy (LEEM) III at the University of Bremen, Germany, and an ELMITEC SPE-LEEM installed at the Nanospectroscopy beamline at the Elettra Sincrotrone laboratory, Trieste, Italy
The epitaxial growth of MoS2 by reactive molecular beam epitaxy was studied on the Au(111) single crystal surface using in situ and ex situ experimental methods including low-energy electron and spectroscopic photoemission microscopy
Summary
The interest in two-dimensional (2D) materials has been strongly increasing since the seminal discovery of the peculiar electronic properties of graphene in 2004 [1], including Dirac-like dispersion of the electronic bandstructure near the Fermi level [2, 3]. In view of applications, as a semi-metal, graphene is not a suitable candidate for electronic devices, such as transistors or optoelectronics [1], because for these applications a sizeable, direct bandgap is necessary. A direct bandgap was demonstrated for single-layer MoS2 in first photoluminescence studies [5, 6]. Exhibiting an indirect bandgap, bilayer MoS2 showed promising electronic applications, e.g., as active channel material in field-effect transistors [9] as well as in novel electronic devices featuring a dynamically tuneable bandgap [10]. Even 2D heterostructures combining graphene and MoS2 could be synthesized, with demonstrated superior performance in optoelectronic devices, such as phototransistors [11], clearly underlining the potential of TMDs for applications
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