Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2

Abstract

Geometrical confinement effect in exfoliated sheets of layered materials leads to significant evolution of energy dispersion with decreasing layer thickness. Molybdenum disulphide (MoS2) was recently found to exhibit indirect to direct gap transition when the thickness is reduced to a single monolayer. This leads to remarkable enhancement in the photoluminescence efficiency, which opens up new opportunities for the optoelectronic applications of the material. Here we report differential reflectance and photoluminescence (PL) spectra of mono- to few-layer WS2 and WSe2 that indicate that the band structure of these materials undergoes similar indirect to direct transition when thinned to a single monolayer. Strong enhancement in PL quantum yield is observed for monoayer WS2 and WSe2 due to exciton recombination at the direct band edge. In contrast to natural MoS2 crystals extensively used in recent studies, few-layer WS2 and WSe2 show comparatively strong indirect gap emission along with distinct direct gap hot electron emission, suggesting high quality of synthetic crystals prepared by chemical vapor transport method. Fine absorption and emission features and their thickness dependence suggest strong effect of Se p-orbitals on the d electron band structure as well as interlayer coupling in WSe2.

to be published in ACS Nano

References in corpus (16)

• Atomically thin MoS2: A new direct-gap semiconductor
• Two Dimensional Atomic Crystals
• Control of valley polarization in monolayer MoS2 by optical helicity
• Valley polarization in MoS2 monolayers by optical pumping
• Single-Layer MoS2 Phototransistors
• Observation of tightly bound trions in monolayer MoS2
• MoS_2 as an ideal material for valleytronics: valley-selective circular dichroism and valley Hall effect
• High Performance Single Layered WSe2 p-FETs with Chemically Doped Contacts
• How does quantum confinement influence the electronic structure of transition metal sulfides TmS2
• Integrated Circuits Based on Bilayer MoS2 Transistors
• Extraordinary room-temperature photoluminescence in WS2 monolayers
• Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
• Channel Length Scaling of MoS2 MOSFETs
• Electrical Tuning of Valley Magnetic Moment via Symmetry Control
• Quantitative Determination of the Band-Gap of WS2 with Ambipolar Ionic Liquid-Gated Transistors
• Electrical Control of Optical Properties of Monolayer MoS${}_2$

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