Journal
NANO LETTERS
Volume 14, Issue 3, Pages 1312-1316Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl4042824
Keywords
Molybdenum disulfide (MoS2); transition metal dichalcogenides (TMD); layered semiconductor; electronic structure; angle-resolved photoemission; van der Waals expansion
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Funding
- Thailand Research Fund, Suranaree University of Technology (TRF) [RSA5680052]
- Office of Higher Education Commissions under NRU project
- U.K. EPSRC [EP/I031014/1]
- ERC [207901]
- DPST
- Royal Society through a University Research Fellowship
- Office of Naval Research [N00014-12-1-0791]
- NANOTEC, NSTDA, Thailand through its program of Center of Excellence Network
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Engineering and Physical Sciences Research Council [EP/I031014/1] Funding Source: researchfish
- European Research Council (ERC) [207901] Funding Source: European Research Council (ERC)
- EPSRC [EP/I031014/1] Funding Source: UKRI
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Several transition-metal dichalcogenides exhibit a striking crossover from indirect to direct band gap semiconductors as they are thinned down to a single monolayer. Here, we demonstrate how an electronic structure characteristic of the isolated monolayer can be created at the surface of a bulk MoS2 crystal. This is achieved by intercalating potassium in the interlayer van der Waals gap, expanding its size while simultaneously doping electrons into the conduction band. Our angle-resolved photoemission measurements reveal resulting electron pockets centered at the (K) over bar and (K') over bar points of the Brillouin zone, providing the first momentum-resolved measurements of how the conduction band dispersions evolve to yield an approximately direct band gap of similar to 1.8 eV in quasi-freestanding monolayer MoS2. As well as validating previous theoretical proposals, this establishes a novel methodology for manipulating electronic structure in transition-metal dichalcogenides, opening a new route for the generation of large-area quasi-freestanding monolayers for future fundamental study and use in practical applications.
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