Structural and electronic properties of MoS2, WS2, and WS2/MoS2 heterostructures encapsulated with hexagonal boron nitride monolayers

In this study, we investigate the structural and electronic properties of MoS2, WS2, and WS2/MoS2 structures encapsulated within hexagonal boron nitride (h-BN) monolayers with first-principles calculations based on density functional theory by using the recently developed non-local van der Waals density functional (rvv10). We find that the heterostructures are thermodynamically stable with the interlayer distance ranging from 3.425 Å to 3.625 Å implying van der Waals type interaction between the layers. Except for the WS2/h-BN heterostructure which exhibits direct band gap character with the value of 1.920 eV at the K point, all proposed heterostructures show indirect band gap behavior from the valence band maximum at the Γ point to the conduction band minimum at the K point with values varying from 0.907 eV to 1.710 eV. More importantly, it is found that h-BN is an excellent candidate for the protection of intrinsic properties of MoS2, WS2, and WS2/MoS2 structures. © 2017 Author(s)

Stacking domains and dislocation networks in marginally twisted bilayers of transition metal dichalcogenides

We apply a multiscale modeling approach to study lattice reconstruction in marginally twisted bilayers of transition metal dichalcogenides (TMD). For this, we develop DFT-parametrized interpolation formulae for interlayer adhesion energies of MoSe$_2$, WSe$_2$, MoS$_2$, and WS$_2$, combine those with elasticity theory, and analyze the bilayer lattice relaxation into mesoscale domain structures. Paying particular attention to the inversion asymmetry of TMD monolayers, we show that 3R and 2H stacking domains, separated by a network of dislocations develop for twist angles $\theta^{\circ}<\theta^{\circ}_P\sim 2.5^{\circ}$ and $\theta^{\circ}<\theta^{\circ}_{AP}\sim 1^{\circ}$ for, respectively, bilayers with parallel (P) and antiparallel (AP) orientation of the monolayer unit cells and suggest how the domain structures would manifest itself in local probe scanning of marginally twisted P- and AP-bilayers

Structural and electronic properties of MoS2, WS2, and WS2/MoS2 heterostructures encapsulated with hexagonal boron nitride monolayers

Yelgel, Celal/0000-0003-4164-477X; Gulseren, Oguz/0000-0002-7632-0954WOS: 000407742400034In this study, we investigate the structural and electronic properties of MoS2, WS2, and WS2/MoS2 structures encapsulated within hexagonal boron nitride (h-BN) monolayers with first-principles calculations based on density functional theory by using the recently developed non-local van der Waals density functional (rvv10). We find that the heterostructures are thermodynamically stable with the interlayer distance ranging from 3.425 angstrom to 3.625 angstrom implying van der Waals type interaction between the layers. Except for the WS2/h-BN heterostructure which exhibits direct band gap character with the value of 1.920 eV at the K point, all proposed heterostructures show indirect band gap behavior from the valence band maximum at the Gamma point to the conduction band minimum at the K point with values varying from 0.907 eV to 1.710 eV. More importantly, it is found that h-BN is an excellent candidate for the protection of intrinsic properties of MoS2, WS2, and WS2/MoS2 structures. Published by AIP Publishing.Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [115F024]OG acknowledges the support from the Scientific and Technological Research Council of Turkey (TUBITAK) under Project No. 115F024. the numerical calculations reported in this paper were fully performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA resources)

The role of intrinsic atomic defects in a Janus MoSSe/XN (X = Al, Ga) heterostructure: a first principles study

The interactions between different layers in van der Waals heterostructures have a significant impact on the electronic and optical characteristics. By utilizing the intrinsic dipole moment of Janus transition metal dichalcogenides (TMDs), it is possible to tune these interlayer interactions. We systematically investigate structural and electronic properties of Janus MoSSe monolayer/graphene-like Aluminum Nitrides (MoSSe/g-AlN) heterostructures with point defects by employing density functional theory calculations with the inclusion of the nonlocal van der Waals correction. The findings indicate that the examined heterostructures are energetically and thermodynamically stable, and their electronic structures can be readily modified by creating a heterostructure with the defects in g-AlN monolayer. This heterostructure exhibits an indirect semiconductor with the band gap of 1.627 eV which is in the visible infrared region. It can be of interest for photovoltaic applications. When a single N atom or Al atom is removed from a monolayer of g-AlN in the heterostructure, creating vacancy defects, the material exhibits similar electronic band structures with localized states within the band gap which can be used for deliberately tailoring the electronic properties of the MoSSe/g-AlN heterostructure. These tunable results can offer exciting opportunities for designing nanoelectronics devices based on MoSSe/g-AlN heterojunctions

Raman spectroscopy of GaSe and InSe post-transition metal chalcogenides layers

III-VI post-transition metal chalcogenides (InSe and GaSe) are a new class of layered semiconductors, which feature a strong variation of size and type of their band gaps as a function of number of layers (N). Here, we investigate exfoliated layers of InSe and GaSe ranging from bulk crystals down to monolayer, encapsulated in hexagonal boron nitride, using Raman spectroscopy. We present the N-dependence of both intralayer vibrations within each atomic layer, as well as of the interlayer shear and layer breathing modes. A linear chain model can be used to describe the evolution of the peak positions as a function of N, consistent with first principles calculations