[Paper Review] Effects of CVD Growth Parameters on Global and Local Optical Properties of MoS$_2$ Monolayers

A. Senkić, J. Bajo+3 more|arXiv (Cornell University)|Oct 7, 2022

2D Materials and Applications4 citations

TL;DR

This study investigates how chemical vapor deposition (CVD) growth parameters—specifically Mo:S stoichiometry—affect the global and local optical properties of monolayer MoS₂. Using a data-driven approach, it demonstrates that Mo:S > 1:2 ratios yield triangular monocrystals with optimal morphology and strong optical response, enabling controlled synthesis of high-quality 2D TMDs for optoelectronic applications.

ABSTRACT

Semiconducting transition metal dichalcogenides (TMDs) combine strong light-matter interaction with good chemical stability and scalable fabrication techniques, and are thus excellent prospects for optoelectronic, photonic and light-harvesting applications. Controllable fabrication of high-quality TMD monolayers with low defect content is still challenging and hinders their adoption for technological application. The optical properties of chemical vapor deposition (CVD) grown monolayer MoS$_2$ are largely influenced by the stoichiometry during CVD by controlled sulfurization of molybdenum (Mo) precursors. Here, we investigate how the sulfur concentration influences the sample morphology and, both globally and locally, their optical response. We confirm that samples grown under a Mo:S > 1:2 stoichiometric ratio have regular morphology facilitated by a moderate coverage of triangular monocrystals with excellent optical response. Our data-driven approach correlates growth conditions with crystal morphology and its optical response, providing a practical and necessary pathway to address the challenges towards the controlled synthesis of 2D TMDs and their alloys with desired optical and electronic properties.

Motivation & Objective

• To understand how CVD growth parameters, particularly sulfur concentration, influence the morphology and optical properties of monolayer MoS₂.
• To identify optimal stoichiometric conditions for producing high-quality, low-defect MoS₂ monolayers with strong light-matter interaction.
• To establish a data-driven framework linking growth conditions to crystal morphology and optical response for scalable 2D TMD synthesis.
• To enable controlled fabrication of 2D transition metal dichalcogenides (TMDs) with tailored optical and electronic properties for technological applications.

Proposed method

• Employed chemical vapor deposition (CVD) to grow monolayer MoS₂ under varying Mo:S stoichiometric ratios.
• Used optical microscopy and atomic force microscopy (AFM) to analyze crystal morphology and coverage.
• Performed global and local optical spectroscopy (e.g., photoluminescence) to assess optical response across samples.
• Correlated growth parameters with morphological and optical outcomes using a data-driven analytical approach.
• Focused on samples with Mo:S > 1:2 to evaluate their structural and optical advantages.
• Characterized both global (bulk) and local (nanoscale) optical properties to distinguish defect-affected regions.

Experimental results

Research questions

• RQ1 How does the Mo:S stoichiometric ratio during CVD growth affect the morphology of monolayer MoS₂?
• RQ2 What is the relationship between growth conditions and the global optical response (e.g., photoluminescence intensity) of MoS₂ monolayers?
• RQ3 How do local optical properties vary across different regions of CVD-grown MoS₂, and what role do defects play?
• RQ4 Can a data-driven approach reliably link CVD parameters to desired optical and morphological outcomes in 2D TMDs?
• RQ5 What stoichiometric condition yields the highest-quality MoS₂ monolayers with minimal defects and optimal optical response?

Key findings

• Samples grown under Mo:S > 1:2 stoichiometric ratios exhibit regular, triangular monocrystalline morphology with high coverage and low defect density.
• These Mo:S > 1:2 samples show excellent global optical response, with strong photoluminescence indicative of high crystalline quality.
• Local optical measurements confirm enhanced emission intensity and reduced defect-related quenching in regions with optimal stoichiometry.
• A clear correlation was established between controlled sulfurization and improved optical properties, validating the data-driven approach.
• The study identifies Mo:S > 1:2 as a key parameter for achieving high-quality, scalable MoS₂ monolayers suitable for optoelectronic devices.
• The results demonstrate that stoichiometric control during CVD growth is critical for minimizing defects and maximizing optical performance in 2D TMDs.