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Title: Experimental Determination of the Ionization Energies of MoSe 2, WS 2, and MoS 2 on SiO 2 Using Photoemission Electron Microscopy

Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe 2, WS 2, and MoS 2) on SiO 2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS 2, to WS 2, to MoSe 2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, we deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [3] ;  [2] ;  [2] ;  [1] ; ORCiD logo [3] ; ORCiD logo [2]
  1. Rice Univ., Houston, TX (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
SAND-2017-8462J
Journal ID: ISSN 1936-0851; 656074
Grant/Contract Number:
AC04-94AL85000
Type:
Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 11; Journal Issue: 8; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; band alignment; ionization energy; molybdenum disulfide; molybdenum selenide; photoemission electron microscopy; transition metal dichalcogenide; tungsten disulfide
OSTI Identifier:
1399563

Keyshar, Kunttal, Berg, Morgann, Zhang, Xiang, Vajtai, Robert, Gupta, Gautam, Chan, Calvin K., Beechem, Thomas E., Ajayan, Pulickel M., Mohite, Aditya D., and Ohta, Taisuke. Experimental Determination of the Ionization Energies of MoSe2, WS2, and MoS2 on SiO2 Using Photoemission Electron Microscopy. United States: N. p., Web. doi:10.1021/acsnano.7b03242.
Keyshar, Kunttal, Berg, Morgann, Zhang, Xiang, Vajtai, Robert, Gupta, Gautam, Chan, Calvin K., Beechem, Thomas E., Ajayan, Pulickel M., Mohite, Aditya D., & Ohta, Taisuke. Experimental Determination of the Ionization Energies of MoSe2, WS2, and MoS2 on SiO2 Using Photoemission Electron Microscopy. United States. doi:10.1021/acsnano.7b03242.
Keyshar, Kunttal, Berg, Morgann, Zhang, Xiang, Vajtai, Robert, Gupta, Gautam, Chan, Calvin K., Beechem, Thomas E., Ajayan, Pulickel M., Mohite, Aditya D., and Ohta, Taisuke. 2017. "Experimental Determination of the Ionization Energies of MoSe2, WS2, and MoS2 on SiO2 Using Photoemission Electron Microscopy". United States. doi:10.1021/acsnano.7b03242. https://www.osti.gov/servlets/purl/1399563.
@article{osti_1399563,
title = {Experimental Determination of the Ionization Energies of MoSe2, WS2, and MoS2 on SiO2 Using Photoemission Electron Microscopy},
author = {Keyshar, Kunttal and Berg, Morgann and Zhang, Xiang and Vajtai, Robert and Gupta, Gautam and Chan, Calvin K. and Beechem, Thomas E. and Ajayan, Pulickel M. and Mohite, Aditya D. and Ohta, Taisuke},
abstractNote = {Here, the values of the ionization energies of transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on the systematic determination of ionization energies for three prototypical TMD monolayers (MoSe2, WS2, and MoS2) on SiO2 using photoemission electron microscopy with deep ultraviolet illumination. The ionization energy displays a progressive decrease from MoS2, to WS2, to MoSe2, in agreement with predictions of density functional theory calculations. Combined with the measured energy positions of the valence band edge at the Brillouin zone center, we deduce that, in the absence of interlayer coupling, a vertical heterojunction comprising any of the three TMD monolayers would form a staggered (type-II) band alignment. This band alignment could give rise to long-lived interlayer excitons that are potentially useful for valleytronics or efficient electron–hole separation in photovoltaics.},
doi = {10.1021/acsnano.7b03242},
journal = {ACS Nano},
number = 8,
volume = 11,
place = {United States},
year = {2017},
month = {7}
}