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

Yi Zhang; Miguel M Ugeda; Chenhao Jin; Su-Fei Shi; Aaron J Bradley; Ana Martín-Recio; Hyejin Ryu; Jonghwan Kim; Shujie Tang; Yeongkwan Kim; Bo Zhou; Choongyu Hwang; Yulin Chen; Feng Wang; Michael F Crommie; Zahid Hussain; Zhi-Xun Shen; Sung-Kwan Mo

doi:10.1021/acs.nanolett.6b00059

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

Nano Lett. 2016 Apr 13;16(4):2485-91. doi: 10.1021/acs.nanolett.6b00059. Epub 2016 Mar 17.

Authors

Yi Zhang^{1

2

3}, Miguel M Ugeda^{4

5

6}, Chenhao Jin⁴, Su-Fei Shi^{4

7}, Aaron J Bradley⁴, Ana Martín-Recio^{4

8}, Hyejin Ryu^{3

9}, Jonghwan Kim⁴, Shujie Tang^{10

11}, Yeongkwan Kim³, Bo Zhou^{3

10

12}, Choongyu Hwang^{9

13}, Yulin Chen¹², Feng Wang^{4

14

15}, Michael F Crommie^{4

14

15}, Zahid Hussain³, Zhi-Xun Shen^{2

10}, Sung-Kwan Mo³

Affiliations

¹ National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China.
² Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
³ Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
⁴ Department of Physics, University of California at Berkeley , Berkeley, California 94720, United States.
⁵ CIC nanoGUNE , 20018 Donostia-San Sebastian, Spain.
⁶ Ikerbasque, Basque Foundation for Science , 48011 Bilbao, Spain.
⁷ Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
⁸ Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid , E-28049 Madrid, Spain.
⁹ Max Plank POSTECH Center for Complex Phase Materials, Pohang University of Science and Technology , Pohang 790-784, Korea.
¹⁰ Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University , Stanford, California 94305, United States.
¹¹ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences , Shanghai 200050, China.
¹² Department of Physics and Clarendon Laboratory, University of Oxford , Parks Road, Oxford, OX1 3PU, United Kingdom.
¹³ Department of Physics, Pusan National University , Busan 609-735, Korea.
¹⁴ Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
¹⁵ Kavli Energy NanoScience Institute at the University of California Berkeley and the Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.

PMID: 26974978
DOI: 10.1021/acs.nanolett.6b00059

Abstract

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.

Keywords: ARPES; MBE; STM/STS; Transition metal dichalcogenides; WSe2; exciton binding energy.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.