Local Optical Properties in CVD-Grown Monolayer WS₂ Flakes

Abstract

Excitons dominate the light absorption and re-emission spectra of monolayer transition-metal dichalcogenides (TMD). Microscopic investigations of the excitonic response in TMD almost invariably extract information from the radiative recombination step, which only constitutes one part of the picture. Here, by exploiting imaging spectroscopic ellipsometry (ISE), we investigate the spatial dependence of the dielectric function of chemical vapor deposition (CVD)-grown WS2 flakes with a microscopic lateral resolution, thus providing information about the spatially varying, exciton-induced light absorption in the monolayer WS2. Comparing the ISE results with imaging photoluminescence spectroscopy data, the presence of several correlated features was observed, along with the unexpected existence of a few uncorrelated characteristics. The latter demonstrates that the exciton-induced absorption and emission features are not always proportional at the microscopic scale. Microstructural modulations across the flakes, having a different influence on the absorption and re-emission of light, are deemed responsible for the effect.

Excitonic absorption and defect-related emission in three-dimensional MoS2 pyramids

“…(2) ISE spatial resolution is still limited to the micrometric range. 51 QNAM's main limitation, instead, is that the substrate should have CL emissions in the optical spectral range of interest.…”

Seeded Growth of Mesoscale Quantum-Confined Semiconductor Nanoplatelets

“…These results draw comparison to 2D semiconductors-lateral heterogeneity of PL in 2D semiconductors can be demonstrated from many effects including defects, strain, chemical heterogeneity, and manipulation by 0D-2D heterostructures. [57][58][59][60][61][62][63][64] These vdW materials exhibit localized electronic structure changes that do not quench the entire nanostructure and can be spatially resolved through PL mapping. The heterogeneity of PL in our large NPLs contrasts them with smaller NPLs which have not demonstrated this behavior.…”

Optical Response of CVD-Grown ML-WS2 Flakes on an Ultra-Dense Au NP Plasmonic Array

“…A thickness-graded LiF layer, with the thickness increasing from zero to about 10 nm over several millimeters, was then evaporated on top of the Au NPs at normal incidence. WS 2 flakes were grown on SiO 2 /Si via liquid-precursor CVD (LqP-CVD) in a twozone horizontal furnace (Lenton), following a procedure already detailed in previous studies [49][50][51]. Briefly, an aqueous solution containing a tungsten precursor (ammonium metatungstate hydrate, AMT, Sigma-Aldrich Inc, St. Luis, MO, USA, 463922) was mixed with an aqueous solution with the growth promoter (NaOH) and iodixanol, used as a density gradient (Sigma-Aldrich Inc., Opti Prep, D1556) and deionized water, in a ratio 1.5:2:1:2.…”