Optimization of MoS2 Chemical Vapor Deposition by Powder Precursors

Open Access
Author:
Bolotsky, Adam Joseph
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Mauricio Terrones Maldonado, Thesis Supervisor
  • Lucas Jay Passmore, Honors Advisor
  • Judith Todd Copley, Faculty Reader
Keywords:
  • MoS2
  • CVD
  • Optimization
  • Powder
  • Seedless
  • MoO3
Abstract:
Monolayer transition metal dichalcogenides (TMDs) are promising additions to the growing number of 2D materials. Numerous potential applications have been identified, especially in the fields of electronics and optoelectronics. Among the TMDs, MoS2 is the most well studied. A common synthesis technique is chemical vapor deposition (CVD), whereby layers are built from gas phase reactants. Here, we pursued an optimized atmospheric pressure CVD process for MoS2 using an MoO3 precursor powder. The optimization criteria were: (1) deposition of monolayer MoS2 (2) the presence of single crystal domains with edge lengths ≥20 µm (3) high photoluminescence (PL) intensity (4) widespread monolayer coverage on the substrate (5) reproducibility and consistency of results. The work was split into three phases; in phase one, only MoO3 and sulfur precursors were used. Consistent growth of monolayers only occurred adjacent to the MoO3 powder grains and despite a high PL intensity, the size and quality of the crystals were poor. In phase 2, a heterogeneous combination of MoO3 and MoS2 powders was used. The monolayer coverage and reproducibility increased dramatically, but the domain sizes were mostly below 20 µm and significant variations in PL were observed. In phase 3, NaBr was added to the MoO3 precursor. Monolayer domain sizes above 200 µm were achieved alongside large-area coverage and satisfactory PL intensity. A humidity spike in the laboratory greatly reduced the sample quality, demonstrating that the method is unreliable without proper parameter controls. Overall, the NaBr-MoO3 precursor provided the best results and optimization was close to complete, but further work needs to be done to improve the reproducibility and consistency of results.