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This content will become publicly available on March 14, 2017

Title: Electronic structure, surface doping, and optical response in epitaxial WSe2 thin films

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. Lastly, 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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [3] ;  [5] ;  [6] ;  [3] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [12] ;  [8] ;  [13] ;  [8]
  1. Nanjing Univ., Nanjing (China); SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); CIC nanoGUNE, Donostia-San Sebastian (Spain); Ikerbasque, Basque Foundation for Science, Bilbao (Spain)
  3. Univ. of California, Berkeley, CA (United States)
  4. Univ. of California, Berkeley, CA (United States); Rensselaer Polytechnic Inst., Troy, NY (United States)
  5. Univ. of California, Berkeley, CA (United States); Univ. Autonoma de Madrid, Madrid (Spain)
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Pohang Univ. of Science and Technology, Pohang (Korea)
  7. Stanford Univ., Stanford, CA (United States); Chinese Academy of Sciences, Shanghai (China)
  8. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  9. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Stanford Univ., Stanford, CA (United States); Univ. of Oxford, Oxford (United Kingdom)
  10. Pohang Univ. of Science and Technology, Pohang (Korea); Pusan National Univ., Busan (Korea)
  11. Univ. of Oxford, Oxford (United Kingdom)
  12. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  13. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States)
Publication Date:
OSTI Identifier:
1257732
Report Number(s):
SLAC-PUB--16566
Journal ID: ISSN 1530-6984
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 16; Journal Issue: 4; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE ARPES; exciton binding energy; MBE; STM/STS; Transition metal dichalcogenides; WSe2