# Addressing Individual Layers and Their Optical Properties in Artificial MoS2 Bilayers via Sulfur Isotope Labeling

## TL;DR

This paper introduces a method using sulfur isotope labeling to study individual layers in artificial MoS2 bilayers and their optical properties.

## Contribution

The novel use of sulfur isotope labeling enables the separate analysis of monolayers in transition metal disulfide heterostructures.

## Key findings

- Sulfur isotope labeling allows disentangling phonon and exciton spectral fingerprints in MoS2 bilayers.
- Raman spectra analysis reveals charge distribution on individual layers in the bilayer structure.
- The method provides new insights into the optical properties of transition metal chalcogenide heterostructures.

## Abstract

The physicochemical
properties of van der Waals (vdW)
heterostructures
are driven by the delicate interactions between the individual layers
in a multilayer stack. While addressing the monolayers of different
compositions in the multilayer is feasible, exploring the intrinsic
properties of the monolayers of the same composition within a multilayer
is extremely challenging. This becomes of utmost importance in energy
conversion and storage concepts based on layered vdW materials. For
example, the charge distribution on the individual layers can be determined,
and the behavior can be disentangled. We introduce sulfur isotope
labeling as a powerful tool for separately addressing monolayers in
vdW heterostructures composed of transition metal disulfides. Using
chemical vapor deposition (CVD), we prepared monolayers of MoS2 using natural sulfur (NatS) and 34sulfur
(34S) as precursors. Artificial bilayers were then prepared
by transferring Mo34S2 onto MoNatS2. Thanks to the different masses of NatS
and 34S, we were able to disentangle the spectral fingerprints
of phonons and excitons in the two layers using Raman and photoluminescence
microspectroscopy. Also, the charge distribution on the individual
layers was revealed through Raman spectra analysis. Our work thus
provides a different perspective for understanding the functionalities
and optical properties of smart architecture based on transition metal
chalcogenides.