Journal
NANO LETTERS
Volume 16, Issue 2, Pages 953-959Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.5b03883
Keywords
Stacked van der Waals structures; photoemission; twisted van der Waals materials; spectromicroscopy; low energy electron microscopy (LEEM); MoS2
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Funding
- Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-FG 02-04-ER-46157]
- U.S. DOE Office of Science User Facilities at Brookhaven National Laboratory [DE-SC0012704]
- Center for Redefining Photovoltaic Efficiency through Molecular Scale Control, an Energy Frontier Research Center (EFRC) - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences [DE-SC0001085]
- Empire State Development's Division of Science, Technology and Innovation (NYSTAR) [C090147]
- New York State Energy Research Development Authority (NYSERDA) [17353]
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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 ((Gamma) over bar point) with the interlayer twist angle, up to a maximum of 120 meV at a twist angle of similar to 40 degrees. 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 (Gamma) over bar 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.
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