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Nano Lett. 2016 Feb 10;16(2):953-9. doi: 10.1021/acs.nanolett.5b03883. Epub 2016 Jan 20.

Direct Measurement of the Tunable Electronic Structure of Bilayer MoS2 by Interlayer Twist.

Author information

1
Department of Electrical Engineering, Columbia University , New York, New York 10027, United States.
2
Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.
3
Department of Chemistry, Columbia University , New York, New York 10027, United States.
4
Theoretical Chemistry, TU Dresden , 01062 Dresden, Germany.
5
Department of Mechanical Engineering, Columbia University , New York, New York 10027, United States.
6
Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
7
Department of Electrical and Computer Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68588, United States.

Abstract

Using angle-resolved photoemission on micrometer-scale sample areas, we directly measure the interlayer twist angle-dependent electronic band structure of bilayer molybdenum-disulfide (MoS2). Our measurements, performed on arbitrarily stacked bilayer MoS2 flakes prepared by chemical vapor deposition, provide direct evidence for a downshift of the quasiparticle energy of the valence band at the Brillouin zone center (Γ̅ point) with the interlayer twist angle, up to a maximum of 120 meV at a twist angle of ∼40°. Our direct measurements of the valence band structure enable the extraction of the hole effective mass as a function of the interlayer twist angle. While our results at Γ̅ agree with recently published photoluminescence data, our measurements of the quasiparticle spectrum over the full 2D Brillouin zone reveal a richer and more complicated change in the electronic structure than previously theoretically predicted. The electronic structure measurements reported here, including the evolution of the effective mass with twist-angle, provide new insight into the physics of twisted transition-metal dichalcogenide bilayers and serve as a guide for the practical design of MoS2 optoelectronic and spin-/valley-tronic devices.

KEYWORDS:

MoS2; Stacked van der Waals structures; low energy electron microscopy (LEEM); photoemission; spectromicroscopy; twisted van der Waals materials

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