Abstract
Atomically thin transition metal dichalcogenides (TMDCs) are promising candidates for implementation in next generation semiconducting devices, for which laterally homogeneous behavior is needed. Here, we study the electronic structure of atomically thin exfoliated WSe2, a prototypical TMDC with large spin–orbit coupling, by photoemission electron microscopy, electron energy-loss spectroscopy, and density functional theory. We resolve the inhomogeneities of the doping level by the varying energy positions of the valence band. There appear to be different types of inhomogeneities that respond differently to electron doping, introduced by potassium intercalation. In addition, we find that the doping process itself is more complex than previously anticipated and entails a distinct orbital and thickness dependence that needs to be considered for effective band engineering. In particular, the density of selenium vs tungsten states depends on the doping level, which leads to changes in the optical response beyond increased dielectric screening. Our work gives insight into the inhomogeneity of the electron structure of WSe2 and the effects of electron doping, provides microscopic understanding thereof, and improves the basis for property engineering of 2D materials.
Highlights
Semiconducting transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 have attracted enormous scientific attention in the last years.1 Their layered crystal structure allows downsizing them to single atomic layers without dangling bonds, which can be functionalized in electronic devices with promising performance parameters
X-ray photoemission spectroscopy of the Se 3d and W 4f core levels confirms the absence of oxides and other foreign phases
We measured the electronic structure of atomically thin WSe2 by photoemission electron microscopy (PEEM), energy-loss spectroscopy (EELS), and density functional theory (DFT)
Summary
Semiconducting transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 have attracted enormous scientific attention in the last years. Their layered crystal structure allows downsizing them to single atomic layers without dangling bonds, which can be functionalized in electronic devices with promising performance parameters. Semiconducting transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 have attracted enormous scientific attention in the last years.. Semiconducting transition metal dichalcogenides (TMDCs) such as MoS2 and WSe2 have attracted enormous scientific attention in the last years.1 Their layered crystal structure allows downsizing them to single atomic layers without dangling bonds, which can be functionalized in electronic devices with promising performance parameters. This meets the desire to find electronically active materials that may substitute silicon at the extreme miniaturization limit.. TMDCs exhibit various other intriguing physical properties holding strong potential for optoelectronic applications, such as thickness dependent bandgaps in the visible energy range and the locking of spin and momentum at the K/K′ valleys giving rise to the field of valleytronics.. It is easier to control the character of the charge carriers ranging from hole dominated, ambipolar to electron dominated. the spin–orbit coupling is larger than that in MoS2, making WSe2 especially suitable for studying spin and valley dependent properties
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