SUBSTRATE ENGINEERING FOR IMPROVED SYNTHESIS OF TWO DIMENSIONAL CHALCOGENIDES
Open Access
- Author:
- Kahn, Ethan Lewis
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 10, 2020
- Committee Members:
- Mauricio Terrones, Dissertation Advisor/Co-Advisor
Mauricio Terrones, Committee Chair/Co-Chair
Suzanne E Mohney, Committee Member
Joshua Alexander Robinson, Committee Member
Saptarshi Das, Outside Member
Susan B Sinnott, Program Head/Chair - Keywords:
- MoS2
WS2
Bi2Te3
2D
Chemical Vapor Deposition
Surfactant - Abstract:
- Since the discovery of a direct band gap in monolayer MoS2, the monolayers of transition metal dichalcogenides (TMDs) have been subject to intensive investigation. Numerous fascinating physical phenomena have been discovered, in addition to demonstrations of the applicability of TMD monolayers and their heterostructures for optoelectronic applications. To date, the most reliable source of high-quality monolayers has been mechanical exfoliation from bulk crystals. The research in this dissertation is aimed at understanding and improving the growth of monolayer TMDs and heterostructures. In Chapter 1, relevant families of two dimensional (2D) materials are introduced as well as the materials and methods of crystal growth and characterization. In Chapter 2, a salt-based growth promoting technique is developed. It is proposed that alkali ions are responsible for the growth enhancement for MoS2. Through extensive experimental and theoretic investigations, the Diffusion De-exchange Passivation (DDP) model of surfactant-mediated growth is identified as a possible growth mechanism. In Chapter 3, MoS2 is grown via powder vaporization at temperatures down to 500 oC on Gorilla Glass substrates. The suppression in growth temperature is attributed to the K+ content of the substrates, indicating the surfactant-based method can be extended to commercially relevant conditions. In Chapter 4, vertical heterostructures of Bi2Te3/WS2 and Bi2Te3/MoS2 are grown, and observed to have optoelectronic properties distinct from their constituent layers. Engineering defects in the TMD basal plane is also observed to be a viable technique for patterning the nucleation and growth of heterostructures. Finally, Chapter 5 suggests future works that could build on the studies here, to further advance the growth of 2D materials. The work summarized here constitutes a step forward in the understanding and engineering of the growth of chalcogenide monolayers and their heterostructures.