10.1021/acs.nanolett.8b04269.s001
Wei Wu
Wei
Wu
Mayra Daniela Morales-Acosta
Mayra Daniela
Morales-Acosta
Yongqiang Wang
Yongqiang
Wang
Michael Thompson Pettes
Michael Thompson
Pettes
Isotope Effect in Bilayer WSe<sub>2</sub>
American Chemical Society
2019
thickness-dependent properties
transition metal dichalcogenides
mass dependence
Bilayer WSe 2 Isotopes
electron number
emission spectra
E 2 g
band gap renormalization energy
2 1 g phonon lifetimes
TMD material
temperature range
neutron number
186 W 80 Se 2
MX 2
vibrational properties
186 W 80 Se 2 bilayer single crystals
NA W NA Se 2
isotopically
Isotope Effect
band gap energy
excitonic transitions
Phonon energies decrease
isotope effect
2019-02-12 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Isotope_Effect_in_Bilayer_WSe_sub_2_sub_/7767017
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<sub>2</sub> (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 <sup>NA</sup>W<sup>NA</sup>Se<sub>2</sub> and isotopically pure <sup>186</sup>W<sup>80</sup>Se<sub>2</sub> bilayer single crystals over a temperature range of
4.4–300 K. We demonstrate a higher optical band gap energy
in <sup>186</sup>W<sup>80</sup>Se<sub>2</sub> than in <sup>NA</sup>W<sup>NA</sup>Se<sub>2</sub> (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<sub>2g</sub> and A<sup>2</sup><sub>1g</sub> phonon lifetimes than
in the naturally abundant sample. The change in electronic band gap
renormalization energy is postulated as being the dominant mechanism
responsible for the change in optical emission spectra.