Spiral and pyramidal WS2 domains controllably synthesized through chemical vapour deposition technique exhibit interesting optical properties.

We present helicity resolved photoluminescence (PL) measurements of WS 2 spiral (SPI) nanostructures. We show that very high degree of circular polarization (DCP) (~94 ± 4%) is obtained from multilayer SPI samples at room temperature upon excitation with a circularly polarized laser at a wavelength near-resonant with the A-exciton (633 nm). TEM analysis showed that these SPI nanostructures have AB stacking in which the inversion symmetry is broken, and hence this leads to very high DCP. Comparison with PL from monolayer and bi-layer WS 2 samples, along with polarization resolved PL studies provide evidence for suppression of interlayer/intravalley scattering in the multilayer SPI samples.

The realization of optoelectronic devices using two-dimensional materials such as graphene and its intermediate product graphene oxide (GO) is extremely challenging owing to the zero band gap of the former. Here, a novel amplified spontaneous emission (ASE) system based on a GO-embedded all-dielectric one-dimensional photonic crystal (1DPhC) micro-resonator is presented. The mono- to few-layered GO sheet is inserted within a microcavity formed by two 5-bilayered SiO2/SnO2 Bragg reflectors. Significantly enhanced photoluminescence (PL) emission of GO embedded in 1DPhC is explicated by studying the electric field confined within the micro-resonator using the transfer matrix method. The inherent randomness, due to fabrication limitations, in the on-average periodic 1DPhC is exploited to further enhance the PL of the optically active micro-resonator. The 1DPhC and randomness assisted field confinement reduces the ASE threshold of the mono- to few-layered weak emitter making the realization of an ASE source feasible. Consequently, ASE at the microcavity resonance and at the low-frequency band-edge of photonic stop-band is demonstrated. Variation of the detection angle from 5° to 30°, with respect to the sample surface normal allows reallocation of the defect mode ASE peak over a spectral range of 558-542 nm, making the GO-incorporated 1DPhC a novel and attractive system for integrated optic applications.

We report circularly polarised emission, with helicity opposite to the optical excitation, from a van der Waals heterostructure (HS) consisting of a monolayer MoS2 and three-layer WS2. Selective excitation of...

Monolayer (ML) transition metal dichalcogenides (TMDCs) have been rigorously studied to comprehend their rich spin and valley physics, exceptional optical properties, and ability to open new avenues in fundamental research and technology. However, intricate analysis of twisted homobilayer (t-BL) systems is highly required due to the intriguing twist angle (t-angle)-dependent interlayer effects on optical and electrical properties. Here, we report the evolution of the interlayer effect on artificially stacked BL WSe 2 , grown using chemical vapor deposition (CVD), with t-angle in the range of 0 ≤ θ ≤ 60°. Systematic analyses based on Raman and photoluminescence (PL) spectroscopies suggest intriguing deviations in the interlayer interactions, higher-energy exciton transitions (in the range of ∼1.6−1.7 eV), and stacking. In contrast to previous observations, we demonstrate a red shift in the PL spectra with t-angle. Density functional theory (DFT) is employed to understand the band-gap variations with t-angle. Exciton radiative lifetime has been estimated theoretically using temperature-dependent PL measurements, which shows an increase with tangle that agrees with our experimental observations. This study presents the groundwork for further investigation of the evolution of various interlayer excitons and their dynamics with t-angle in homobilayer systems, critical for optoelectronic applications.