Geometrical Engineering of Giant Optical Dichroism in Rippled MoS₂ Nanosheets

Abstract

A cost effective method to tailor the optical response of large‐area nanosheets of 2D materials is described. A reduced effective metalayer model is introduced to capture the key‐role of the out‐of‐plane component of the dielectric tensor. Such a model indicates that the optical extinction of 2D materials can be strongly altered by controlling the geometry at the local (i.e., subwavelength) scale. In particular, a giant linear optical dichroism at normal incidence is demonstrated, with major features around the excitonic peaks, that can be tailored by acting on the average curvature and slope of the nanosheets. The approach is experimentally demonstrated in few‐layer MoS2 grown by chemical vapor deposition on cm‐scale anisotropic nanopatterned substrates prepared by a self‐assembling technique, based on defocused ion beam sputtering. Major variations in the photoluminescence spectrum as a function of the average curvature and slope are also revealed. A full‐vectorial numerical study beyond the effective metalayer model and comprising strain effects induced by the geometry turns out to be consistent with such a complex scenario. The results demonstrate that the extrinsic geometrical engineering definitely opens viable way to tailor the optical properties and modulate bandgap of low dimensional materials.

Magnetic Field Alignment and Optical Anisotropy of MoS2 Nanosheets Dispersed in a Liquid Crystal Polymer

“…Optical anisotropy in MoS 2 nanosheets can be significant, as was recently indicated in a report by Volkov and co-workers on the giant optical anisotropy in MoS 2 nanosheets, showcasing a large birefringence of Δ n = 3 and Δ n = 1.5 for visible and infrared (IR) light, respectively . In addition, anisotropic optical effects in MoS 2 may be substrate-induced due to morphological effects − or crystallographically dictated symmetry breaking and defectivity. , Excitonic emission by MoS 2 nanosheets is of particular interest for optoelectronic devices. MoS 2 photoluminescence (PL) can be manipulated through defect engineering and plasmonic coupling.…”

“…Optical anisotropy in MoS 2 has been experimentally explored by near-field measurements that have resolved differences in the Raman response , and dielectric constants of nanosheet basal planes and edges. , The anisotropy stems from the inherent 2D morphology of the MoS 2 nanosheets, which has been previously observed by aligning the nanosheets in a parallel or transverse configuration with respect to the probing beam. − …”

“…Despite the impetus to elucidate the anisotropic optical properties in few-layer MoS 2 , current methods to do so are lacking in their ability to robustly control few-layer MoS 2 nanosheet orientation, inhibiting the opportunities to devise technologies that harness the difference in optical properties parallel and transverse to the nanosheets surface normal or to further explore and study the anisotropy in detail. As highlighted above, studies of anisotropic effects in MoS 2 rely on orientation control of grown or patterned bulk MoS 2 films or particles, which are then studied by using traditional spectroscopic characterization techniques, ,− ,, but disregard few-layer nanosheets, whose anisotropic characteristics may vary considerably from the bulk material. Conversely, the study of individually exfoliated MoS 2 nanosheets has relied on near-field techniques that are challenging to leverage, particularly in statistically relevant scenarios. ,, Hence, the ability to suspend individual nanosheets and control their orientation in a suitable dielectric medium would enable important studies of PL and other optical anisotropies in MoS 2 with a versatility that has thus far been lacking.…”

The Rise of the Xenes: From the Synthesis to the Integration Processes for Electronics and Photonics

“…In this respect, a promising strategy is the realization of vertical and lateral Xene heterostructures [24]. Lastly, similar to TMDs [75][76][77][78], Xenes represent ideal materials where to test the fine-tuning control of the optoelectronic properties by applying external strain or controlled morphological modifications. In this scenario, both experimental and theoretical studies may have dramatic implications in the development of new technological platforms for flexible photonics and quantum communication technologies [74].…”

Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS$_{2}$

“…Two-dimensional (2D) semiconducting transition metal dichalcogenides (S-TMDs) have attracted significant attention in the last decade due to the thickness dependent electronic band structure that allows for at-will manipulation of optical and opto-electronic properties. [1][2][3][4][5] Novel configurations employing monolayers and van der Waals (vdW) heterostructures [6][7][8] have emerged as promising platforms for the development of cutting-edge technology spanning across a broad spectrum that include but is not limited to quantum information processing, 9,10 spintronics, 11,12 nanophotonics [13][14][15] and twistronics. 16,17 From the perspective to study lattice dynamics, non-invasive Raman scattering (RS) spectroscopy has emerged as a pivotal tool to uncover the physics of vibrational and electronic properties of 2D S-TMDs.…”