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Title: Isotope Effect in Bilayer WSe 2

Abstract

Isotopes of an element have the same electron number but differ in neutron number and atomic mass. However, due to the thickness-dependent properties in MX 2 (M = Mo, W; X = S, Se, Te) transition metal dichalcogenides (TMDs), the isotopic effect in atomically thin TMDs still remains unclear especially for phonon-assisted indirect excitonic transitions. Here, we report the first observation of the isotope effect on the electronic and vibrational properties of a TMD material, using naturally abundant NAW NASe 2 and isotopically pure 186W 80Se 2 bilayer single crystals over a temperature range of 4.4–300 K. We demonstrate a higher optical band gap energy in 186W 80Se 2 than in NAW NASe 2 (3.9 ± 0.7 meV from 4.41 to 300 K), which is surprising as isotopes are neutral impurities. Phonon energies decrease in the isotopically pure crystal due to the atomic mass dependence of harmonic oscillations, with correspondingly longer E 2g and A 2 1g phonon lifetimes than in the naturally abundant sample. Finally, the change in electronic band gap renormalization energy is postulated as being the dominant mechanism responsible for the change in optical emission spectra.

Authors:
 [1];  [2];  [3]; ORCiD logo [4]
  1. Univ. of Connecticut, Storrs, CT (United States). Dept. of Mechanical Engineering, and Inst. of Materials Science
  2. Univ. of Connecticut, Storrs, CT (United States).Inst. of Materials Science
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Univ. of Connecticut, Storrs, CT (United States). Dept. of Mechanical Engineering, and Inst. of Materials Science; Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF)
OSTI Identifier:
1499358
Report Number(s):
LA-UR-18-29405
Journal ID: ISSN 1530-6984
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 19; Journal Issue: 3; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Material Science; Isotope engineering; band gap engineering; tungsten diselenide; transition metal dichalcogenide; photoluminescence; Raman

Citation Formats

Wu, Wei, Morales-Acosta, Mayra Daniela, Wang, Yongqiang, and Pettes, Michael Thompson. Isotope Effect in Bilayer WSe2. United States: N. p., 2019. Web. doi:10.1021/acs.nanolett.8b04269.
Wu, Wei, Morales-Acosta, Mayra Daniela, Wang, Yongqiang, & Pettes, Michael Thompson. Isotope Effect in Bilayer WSe2. United States. doi:10.1021/acs.nanolett.8b04269.
Wu, Wei, Morales-Acosta, Mayra Daniela, Wang, Yongqiang, and Pettes, Michael Thompson. Tue . "Isotope Effect in Bilayer WSe2". United States. doi:10.1021/acs.nanolett.8b04269.
@article{osti_1499358,
title = {Isotope Effect in Bilayer WSe2},
author = {Wu, Wei and Morales-Acosta, Mayra Daniela and Wang, Yongqiang and Pettes, Michael Thompson},
abstractNote = {Isotopes of an element have the same electron number but differ in neutron number and atomic mass. However, due to the thickness-dependent properties in MX2 (M = Mo, W; X = S, Se, Te) transition metal dichalcogenides (TMDs), the isotopic effect in atomically thin TMDs still remains unclear especially for phonon-assisted indirect excitonic transitions. Here, we report the first observation of the isotope effect on the electronic and vibrational properties of a TMD material, using naturally abundant NAWNASe2 and isotopically pure 186W80Se2 bilayer single crystals over a temperature range of 4.4–300 K. We demonstrate a higher optical band gap energy in 186W80Se2 than in NAWNASe2 (3.9 ± 0.7 meV from 4.41 to 300 K), which is surprising as isotopes are neutral impurities. Phonon energies decrease in the isotopically pure crystal due to the atomic mass dependence of harmonic oscillations, with correspondingly longer E2g and A21g phonon lifetimes than in the naturally abundant sample. Finally, the change in electronic band gap renormalization energy is postulated as being the dominant mechanism responsible for the change in optical emission spectra.},
doi = {10.1021/acs.nanolett.8b04269},
journal = {Nano Letters},
number = 3,
volume = 19,
place = {United States},
year = {2019},
month = {2}
}

Journal Article:
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This content will become publicly available on February 12, 2020
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