Electronic properties and optical spectra ofMoS2andWS2nanotubes

Influence of curvature strain and Van der Waals force on the inter-layer vibration mode of WS2 nanotubes: A confocal micro-Raman spectroscopic study

“…For layered structures of TMDs, there have been fast developments in both understanding of fundamental properties and applications of electronic/optoelectronic devices, for example, energy band structure transition from indirect to direct bandgap when thinned to monolayers and remarkable layer-number dependent electronic and optical properties7891011. For TMD nanotubes, like carbon nanotubes, their electronic structures as well as physical and chemical properties also exhibit an interesting dependence on the structural properties such as chirality and diameter1213. In particular, a recent theoretical study shows that Raman signals of the in-plane and out-of-plane (or inter-layer used in the present article) lattice vibration modes depend significantly and linearly on the strain in TMD nanotubes, and concludes that Raman spectroscopy is an excellent tool to determine the strain of the TMD nanotubes and hence monitor the progress of nanoelectromechanical experiments14.…”

MoS2 nanotube field effect transistors

“…[15][16][17] The difference in behavior of nanotubes from that of layered crystals does not seem to be due to the differences of nanotube diameter. The intra-layer strain from curvature should start to play an important role at diameters 19,20 several times smaller than the size of the present nanotubes. Since MoS 2 is a van der Waals solid, the inter-layer strain should be too small to reduce the energy gap, 27 so the device variations are not thought to be arise from inter-nanotube strain.…”

“…3,5 The demonstration of effective field effect transistors (FET) based on single layer MoS 2 6 has drawn attention to a different class of inorganic materials -transition metal dichalcogenides (TMDs) 7 18 According to theoretical calculations, MoS 2 nanotubes should inherit the properties of layered structures down to very small radii. 19,20 In particular, the NTs should remain semiconducting even for the smallest experimentally achievable diameters. The chirality of the tubes does not have a perceivable effect on their properties, distinguishing them from CNTs, so successive layers in multilayer nanotubes are expected to have similar properties, thus avoiding one of the most important issues limiting the use of CNTs for nano-electronics devices, where different layers may be either metallic or semiconducting preventing straightforward implementation of multiwall tubes in FETs.…”

Routes to identification of intrinsic twist in helical MoS2nanotubes by electron diffraction and annular dark-field scanning transmission electron microscopy imaging

“…Although not widely used, quantum treatments that make use of helical instead of the translational symmetry are also available 16,17 . Using objective molecular dynamics 16 (MD) coupled with symmetry-adapted nonorthogonal tight-binding 17 implemented in Trocadero 18 and a density functionalbased tight binding (DFTB) model 19,20 , we have previously confirmed 21 that the rolled-up predictions are also valid in large diameter chiral MoS 2 NTs. However, under ∼ 7 nm in diameter, the rolled-up construction was increasingly inaccurate especially for near 15 degrees chiral NTs.…”