scholarly journals Chalcogen···Chalcogen Bonding in Molybdenum Disulfide, Molybdenum Diselenide and Molybdenum Ditelluride Dimers as Prototypes for a Basic Understanding of the Local Interfacial Chemical Bonding Environment in 2D Layered Transition Metal Dichalcogenides

Inorganics ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 11
Author(s):  
Pradeep R. Varadwaj ◽  
Helder M. Marques ◽  
Arpita Varadwaj ◽  
Koichi Yamashita

An attempt was made, using computational methods, to understand whether the intermolecular interactions in the dimers of molybdenum dichalcogenides MoCh2 (Ch = chalcogen, element of group 16, especially S, Se and Te) and similar mixed-chalcogenide derivatives resemble the room temperature experimentally observed interactions in the interfacial regions of molybdenites and their other mixed-chalcogen derivatives. To this end, MP2(Full)/def2-TVZPPD level electronic structure calculations on nine dimer systems, including (MoCh2)2 and (MoChCh′2)2 (Ch, Ch′ = S, Se and Te), were carried out not only to demonstrate the energetic stability of these systems in the gas phase, but also to reproduce the intermolecular geometrical properties that resemble the interfacial geometries of 2D layered MoCh2 systems reported in the crystalline phase. Among the six DFT functionals (single and double hybrids) benchmarked against MP2(full), it was found that the double hybrid functional B2PLYPD3 has some ability to reproduce the intermolecular geometries and binding energies. The intermolecular geometries and binding energies of all nine dimers are discussed, together with the charge density topological aspects of the chemical bonding interactions that emerge from the application of the quantum theory of atoms in molecules (QTAIM), the isosurface topology of the reduced density gradient noncovalent index, interaction region indicator and independent gradient model (IGM) approaches. While the electrostatic surface potential model fails to explain the origin of the S···S interaction in the (MoS2)2 dimer, we show that the intermolecular bonding interactions in all nine dimers examined are a result of hyperconjugative charge transfer delocalizations between the lone-pair on (Ch/Ch′) and/or the π-orbitals of a Mo–Ch/Ch′ bond of one monomer and the dπ* anti-bonding orbitals of the same Mo–Ch/Ch′ bond in the second monomer during dimer formation, and vice versa. The HOMO–LUMO gaps calculated with the MN12-L functional were 0.9, 1.0, and 1.1 eV for MoTe2, MoSe2 and MoS2, respectively, which match very well with the solid-state theoretical (SCAN-rVV10)/experimental band gaps of 0.75/0.88, 0.90/1.09 and 0.93/1.23 eV of the corresponding systems, respectively. We observed that the gas phase dimers examined are perhaps prototypical for a basic understanding of the interfacial/inter-layer interactions in molybdenum-based dichalcogenides and their derivatives.

NANO ◽  
2021 ◽  
Author(s):  
Arslan Usman ◽  
Abdul Sattar ◽  
Hamid Latif ◽  
Muhammad Imran

The impact of phonon and their surrounding environment on exciton and its complexes were investigated in monolayer WSe2 semiconductor. Phonon up-conversion has been studied in past for conventional III–V semiconductors, but its role in two-dimensional layered transition metal dichalcogenides has rarely been explored. We investigated the photoluminescence up-conversion mechanism in WSe2 monolayer and found that a lower energy photon gain energy upto 64[Formula: see text]meV to be up-converted to emission photon at room temperature. Moreover, the phonon-exciton coupling mechanism has also been investigated and the role of dielectric screening has been explored to get complete insight of coulomb’s interaction in these electron-hole pairs. Investigations of charge carrier’s lifetime reveal that boron nitride encapsulated monolayer has shorter recombination time as low as 41 ps as compared to a bare monolayer on SiO2 substrate. These results are very promising for realizing spintronics-based application from two-dimensional layered semiconductors.


2D Materials ◽  
2021 ◽  
Author(s):  
Kun Ye ◽  
Lixuan Liu ◽  
Liying Chen ◽  
Wenlong Li ◽  
Bochong Wang ◽  
...  

Abstract The layered transition metal dichalcogenides (TMDs) exhibit the intriguing physical properties and potential application in novel electronic devices. However, controllable growth of multilayer TMDs remains challenging. Herein, large-scale and high-quality multilayer prototype TMDs of W(Mo)Se2 were synthesized via chemical vapor deposition. For Raman and PL measurements, 2H and 3R multilayer WSe2 crystals displayed significant layer-dependent peak position and intensity feature. Besides, different from the oscillatory relationship of SHG intensity for odd-even layer numbers in 2H-stacked multilayer WSe2, the second harmonic generation intensity of 3R-stacked ones parabolically increased with the thickness due to the absence of inversion symmetry. For device application, photodetectors based on WSe2 with increasing thickness exhibited p-type (bilayer), ambipolar (trilayer), and n-type (4 layers) semiconductor behaviors, respectively. Furthermore, photodetectors based on the as-synthesized 3R-stacked WSe2 flakes displayed an excellent responsivity (R) of 7.8×103 mA/W, high specific detectivity (Da*) of 1.7×1014 Jones, outstanding external quantum efficiency (EQE) of 8.6×102 %, and fast response time (τRise=57 ms and τFall=53 ms) under 532 nm illumination with bias voltage of Vds=5 V. Similar results have also been achieved in multilayer MoSe2 crystals. All these findings indicate great potential of 3R-stacked TMDs in two-dimensional optoelectronic applications.


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