Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films

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High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.
Publisher
AMER CHEMICAL SOC
Issue Date
2016-04
Language
English
Article Type
Article
Keywords

TRANSITION-METAL DICHALCOGENIDES; P-N-JUNCTIONS; 2-DIMENSIONAL MATERIALS; MONOLAYER MOS2; MOLYBDENUM-DISULFIDE; VALLEY POLARIZATION; DIRECT BANDGAP; SINGLE-LAYER; SPIN; STRAIN

Citation

NANO LETTERS, v.16, no.4, pp.2485 - 2491

ISSN
1530-6984
DOI
10.1021/acs.nanolett.6b00059
URI
http://hdl.handle.net/10203/213910
Appears in Collection
NT-Journal Papers(저널논문)
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