Dielectric Function of 2D Tungsten Disulfide in Homo‐ and Heterobilayer Stacking

Abstract

The opto‐electronic properties of semiconducting 2D materials can be flexibly manipulated by engineering the atomic‐scale environment. This can be done by including 2D materials in tailored van der Waals (vdW) stacks, whose optical response is a function of the number and the type of adjacent 2D layers. This work reports a systematic investigation of the dielectric function of 2D semiconducting WS2 in various stacking configurations: monolayer, 3R/2H homobilayer, and WS2/MoS2 heterobilayer. Reliable, Kramers–Kronig‐consistent dielectric functions are obtained for WS2 in each configuration by means of spectroscopic ellipsometry (SE) and related parametric optical modeling in a wide spectral range (1.55–3.10 eV). The results of SE are combined with photoluminescence and absorbance spectra to identify the spectral position of the main excitonic features in WS2, which manifest sizable redshifts depending on the stacking configuration. These results represent a consistent reference set for the dielectric function of WS2 in vdW stacking configurations of particular interest for the scientific and technological field, and can be fruitfully exploited for reliable predictions of the optical response of WS2‐containing systems.

Local dielectric function of hBN-encapsulated WS2 flakes grown by chemical vapor deposition

“…The investigated system is shown in the optical micrograph of figure 1(a). The CVD-grown WS 2 flake is characterized by a typical triangular shape and a monolayer thickness extending for hundreds of microns across [43,44,52]. At the center of the flake, a bilayer region with a 0 • twist angle is present (3R stacking).…”

“…In the present study, the local properties of WS 2 flakes encapsulated by hBN were analyzed. The flakes were grown on Si/SiO 2 substrate via liquid precursor chemical vapor deposition (LqP-CVD) in a two-zone horizontal furnace (Lenton) [43,44,[50][51][52]. The growth mechanism of the LqP-CVD process was reported in detail in [50], and here the main steps are summarized.…”

“…Recent works showed that the combination of optical techniques with a micrometric lateral resolution, such as imaging spectroscopic ellipsometry (ISE) and photoluminescence (PL) spectroscopy, is effective to study the light absorption and emission-related properties of ML-TMDCs by probing, respectively, their dielectric function and the PL [43][44][45][46][47][48][49].…”

Fast Twist Angle Mapping of Bilayer Graphene Using Spectroscopic Ellipsometric Contrast Microscopy

“…The presence of optical resonances is confirmed with ARPES by analyzing the band structure at regions with different resonant wavelengths. This technique could be applicable to other material systems, including transition metal dichalcogneides and twisted heterostuctures . With the advent of spectroscopic microellipsometry extensions for conventional optical microscopes, SECM has become even more affordable and accessible .…”

“…This technique could be applicable to other material systems, 42 including transition metal dichalcogneides 64 and twisted heterostuctures. 65 With the advent of spectroscopic microellipsometry extensions for conventional optical microscopes, SECM has become even more affordable and accessible. 66 This work confirms that SECM is a powerful, fast, and nondestructive tool for material characterization, which unlocks the potential of material properties for a variety of research applications.…”