Abstract
Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS2) is a major n-doping source. The surface electron concentration of MoS2 is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS2 nanoflakes was observed. The transfer length method suggested the current transport in MoS2 following a two-dimensional behavior rather than the conventional three-dimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation.
Highlights
Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors
This study demonstrated the presence of surface electron accumulation (SEA) in transition metal dichalcogenide (TMD) and layered material systems
The micrographs show that the stripped flakes have a random shape and that some of them retained clear sharp edges
Summary
Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. The metallic nature of graphene[1,2] differs from that of twodimensional (2D) nanostructures based on transition metal dichalcogenide (TMD) layer materials, such as MoS2, WS2, and ReS2. These 2D nanostructures exhibit semiconducting characteristics and have attracted considerable attention[3,4,5,6]. The unusually high electron concentration in the unintentional doped layer semiconductor increases the difficulty of fabricating intrinsic and p-type MoS2 nanostructures. Van der Waals crystals without dangling bonds, such as MoS2, are expected to have an inert surface and fewer surface states
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