Optical Constants and Structural Properties of Epitaxial MoS2 Monolayers

Abstract

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS2 synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS2 with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS2 layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS2, thus making it an attractive candidate for photonic applications.

Optical Anisotropy and Excitons in MoS2 Interfaces for Sensitive Surface Plasmon Resonance Biosensors

“…The study of sensitivity enhancement with vdW materials has become a hot topic in the last decade, since they are promising both as immobilization layers [ 13 , 14 , 15 , 16 , 17 ] and as optical sensitivity enhancing layers [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Furthermore, additional layers of graphene or other materials can protect the metal from the environment, thereby improving the stability of the sensor structure [ 29 ].…”

Broadband Optical Constants and Nonlinear Properties of SnS2 and SnSe2

“…We employed a two-layer optical model for ellipsometry data analysis: quartz substrate with SnS 2 or SnSe 2 film with the thickness determined from AFM ( Figure 3 e,i). Similar to other TMDCs [ 52 , 53 ], we describe SnS 2 and SnSe 2 dielectric function by the Tauc–Lorentz oscillator model (see Methods) [ 54 , 55 ]. Figure 3 a,b shows the resulting optical constants n and k for SnS 2 and SnSe 2 films.…”

van der Waals epitaxy of transition metal dichalcogenides via molecular beam epitaxy: looking back and moving forward

“…However, it was noticed that MBE provides greater control on the epitaxial registry in both cases. Recently, Ermolaev et al 106 have presented a detailed study on the structural and optical properties of a monolayer of MoS 2 thin films grown by MBE on sapphire. The analysis has shown that the MBE-grown MoS 2 film exhibits a two-fold greater quantum yield of PL and lower photobleaching when compared with the CVD-synthesized MoS 2 films (Fig.…”