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Controlling the Electronic Structures and Properties of in-Plane Transition-Metal Dichalcogenides Quantum Wells.

Wei W, Dai Y, Niu C, Huang B - Sci Rep (2015)

Bottom Line: The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons.The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells.In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale.

View Article: PubMed Central - PubMed

Affiliation: School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.

ABSTRACT
In-plane transition-metal dichalcogenides (TMDs) quantum wells have been studied on the basis of first-principles density functional calculations to reveal how to control the electronic structures and the properties. In collection of quantum confinement, strain and intrinsic electric field, TMD quantum wells offer a diverse of exciting new physics. The band gap can be continuously reduced ascribed to the potential drop over the embedded TMD and the strain substantially affects the band gap nature. The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons. Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials. The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells. In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale.

No MeSH data available.


Related in: MedlinePlus

(a) Evolution of indirect (Γ-A) and direct (Γ) band gap of MoTe2/WS2/MoTe2 quantum wells as a function of the WS2 thickness n = 1–10. (b) DOS projected on WS2 and MoTe2 in the MoTe2/WS2/MoTe2 quantum well with WS2 thickness being n = 4; the Fermi level is set to zero. (c) VBM and (d) CBM at the A-point for the MoTe2/WS2/MoTe2 quantum well with the thickness of MoSe2 being n = 4. The small spheres are non-metal atoms (S and Te), while big spheres are metal atoms (Mo and W).
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f5: (a) Evolution of indirect (Γ-A) and direct (Γ) band gap of MoTe2/WS2/MoTe2 quantum wells as a function of the WS2 thickness n = 1–10. (b) DOS projected on WS2 and MoTe2 in the MoTe2/WS2/MoTe2 quantum well with WS2 thickness being n = 4; the Fermi level is set to zero. (c) VBM and (d) CBM at the A-point for the MoTe2/WS2/MoTe2 quantum well with the thickness of MoSe2 being n = 4. The small spheres are non-metal atoms (S and Te), while big spheres are metal atoms (Mo and W).

Mentions: In MoTe2/WS2/MoTe2 quantum well, relatively large tensile strain is imposed on WS2. As discussed above, direct-indirect band gap crossover is presented due to the upward shift of VBM at the Γ-point as WS2 thickness being n = 5, as shown in Figure S5. Figure 5(a) summarizes the direct and indirect band gap values, which are smaller than 1.0 eV. The indirect band gap linearly decreases as the WS2 thickness increases to n = 4 and then tend to be convergent; the convergence of direct band gap is faster than that of indirect one. In comparison to WS2/MoSe2/WS2 quantum well, the behavior of band edge states show similar trends; however, a difference lies in the obviously smaller band gap of the MoTe2/WS2/MoTe2 quantum wells. In the case of n = 4, for example, the band gap of WS2/MoSe2/WS2 quantum well is 1.56 eV, while MoTe2/WS2/MoTe2 quantum well corresponds to a band gap of 0.61 eV. In WS2/MoSe2/WS2 quantum well, direct-indirect band gap crossover occurs with significantly larger MoSe2 thickness than WS2 due to the faster rise of VBM at the Γ-point in MoTe2/WS2/MoTe2 quantum wells. When n = 4, the density of states (DOS) plots projected on MoTe2 and WS2 are shown in Fig. 5(b), which reveals a type-I alignment with both VBM and CBM located on MoTe2. In contrast to the WS2/MoSe2/WS2 quantum well, however, the VBM and CBM are spatially separated striding the embedded WS2, see Fig. 5(c,d). In the presence of intrinsic electric filed, electron and hole wave functions are localized at opposite sides and such a localization is conducive to reduce the band gap. As a result, MoTe2/WS2/MoTe2 quantum wells manifest themselves to be promising candidates used in solar energy absorption and conversion. It is of interest and importance, fairly small band gap and physical separation of electron-hole pairs demonstrate the new possibility in achieving solar cells and photocatalysts within infrared or near infrared light region.


Controlling the Electronic Structures and Properties of in-Plane Transition-Metal Dichalcogenides Quantum Wells.

Wei W, Dai Y, Niu C, Huang B - Sci Rep (2015)

(a) Evolution of indirect (Γ-A) and direct (Γ) band gap of MoTe2/WS2/MoTe2 quantum wells as a function of the WS2 thickness n = 1–10. (b) DOS projected on WS2 and MoTe2 in the MoTe2/WS2/MoTe2 quantum well with WS2 thickness being n = 4; the Fermi level is set to zero. (c) VBM and (d) CBM at the A-point for the MoTe2/WS2/MoTe2 quantum well with the thickness of MoSe2 being n = 4. The small spheres are non-metal atoms (S and Te), while big spheres are metal atoms (Mo and W).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663467&req=5

f5: (a) Evolution of indirect (Γ-A) and direct (Γ) band gap of MoTe2/WS2/MoTe2 quantum wells as a function of the WS2 thickness n = 1–10. (b) DOS projected on WS2 and MoTe2 in the MoTe2/WS2/MoTe2 quantum well with WS2 thickness being n = 4; the Fermi level is set to zero. (c) VBM and (d) CBM at the A-point for the MoTe2/WS2/MoTe2 quantum well with the thickness of MoSe2 being n = 4. The small spheres are non-metal atoms (S and Te), while big spheres are metal atoms (Mo and W).
Mentions: In MoTe2/WS2/MoTe2 quantum well, relatively large tensile strain is imposed on WS2. As discussed above, direct-indirect band gap crossover is presented due to the upward shift of VBM at the Γ-point as WS2 thickness being n = 5, as shown in Figure S5. Figure 5(a) summarizes the direct and indirect band gap values, which are smaller than 1.0 eV. The indirect band gap linearly decreases as the WS2 thickness increases to n = 4 and then tend to be convergent; the convergence of direct band gap is faster than that of indirect one. In comparison to WS2/MoSe2/WS2 quantum well, the behavior of band edge states show similar trends; however, a difference lies in the obviously smaller band gap of the MoTe2/WS2/MoTe2 quantum wells. In the case of n = 4, for example, the band gap of WS2/MoSe2/WS2 quantum well is 1.56 eV, while MoTe2/WS2/MoTe2 quantum well corresponds to a band gap of 0.61 eV. In WS2/MoSe2/WS2 quantum well, direct-indirect band gap crossover occurs with significantly larger MoSe2 thickness than WS2 due to the faster rise of VBM at the Γ-point in MoTe2/WS2/MoTe2 quantum wells. When n = 4, the density of states (DOS) plots projected on MoTe2 and WS2 are shown in Fig. 5(b), which reveals a type-I alignment with both VBM and CBM located on MoTe2. In contrast to the WS2/MoSe2/WS2 quantum well, however, the VBM and CBM are spatially separated striding the embedded WS2, see Fig. 5(c,d). In the presence of intrinsic electric filed, electron and hole wave functions are localized at opposite sides and such a localization is conducive to reduce the band gap. As a result, MoTe2/WS2/MoTe2 quantum wells manifest themselves to be promising candidates used in solar energy absorption and conversion. It is of interest and importance, fairly small band gap and physical separation of electron-hole pairs demonstrate the new possibility in achieving solar cells and photocatalysts within infrared or near infrared light region.

Bottom Line: The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons.The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells.In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale.

View Article: PubMed Central - PubMed

Affiliation: School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.

ABSTRACT
In-plane transition-metal dichalcogenides (TMDs) quantum wells have been studied on the basis of first-principles density functional calculations to reveal how to control the electronic structures and the properties. In collection of quantum confinement, strain and intrinsic electric field, TMD quantum wells offer a diverse of exciting new physics. The band gap can be continuously reduced ascribed to the potential drop over the embedded TMD and the strain substantially affects the band gap nature. The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons. Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials. The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells. In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale.

No MeSH data available.


Related in: MedlinePlus