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Effects of Fundamental Processing Parameters on the Structure and Composition of Two-Dimensional MoS2 Films

Waite, Adam Richard
http://orcid.org/0000-0003-2094-3666
http://rave.ohiolink.edu/etdc/view?acc_num=dayton149315978414366

Abstract Details

2017, Doctor of Philosophy (Ph.D.), University of Dayton, Materials Engineering.
The unique properties resulting from strongly anisotropic chemical bonds found in the whole family of transition metal dichalcogenide materials (TMDs) have been researched for over 50 years for various applications, with MoS2 being the most heavily researched. The pace of research has surged with the recent isolation and analysis of 2D materials exfoliated from Van der Waals solids, first reported by Novoselov and Geim. MoS2 was first identified to have interesting electrical properties in 2D form by Mak et al. in 2010, where it was discovered that at a monolayer, the band structure had shifted to a direct bandgap semiconductor and the band gap shifts from ~1.3 eV to ~1.9 eV. Coupled with mechanical flexibility, optical transparency, and many other unique properties, 2D MoS2 an ideal semiconductor candidate for nanoelectronic applications. The defect engineering that makes silicon-based technology so flexible has yet to be explored in 2D TMD materials. Grain boundaries are currently a structural defect that cannot be eliminated in wafer scale synthesis of these materials, therefore, a better understanding of how to control grain boundary density and understand the effects on properties is an urgent need. Each grain boundary acts as a scatter defect thought to adversely affect carrier mobility and density, negatively affecting device performance. This grain boundary problem is the driving force behind this study to discover the underlying basic principles and impact of sputter plasma deposition parameters, substrate processing conditions, and the nucleation and growth kinetics of 2D MoS2 films. This dissertation consists of three studies designed to tailor grain boundary density in 2D MoS2: 1) a study on the impact of intrinsic plasma parameters and characteristics of the pulsed DC magnetron sputtering discharge on the resulting 2D MoS2 films and their structure/properties, 2) a study on the impact of the partial pressure of the diatomic (S2) species in sulfur vapor, which dictates the high processing temperatures necessary for nucleation and growth kinetics of 2D MoS2 and correlation of processing conditions to the chemistry and structure of the deposited films, and 3) a study of the impact of the MoO3 precursor film grain size, thickness, structure, and morphology on the nucleation and growth kinetics of 2D MoS2 on composition and structure properties. Novel approaches to reduce grain boundary density and synthesis temperature without compromising stoichiometry in waferscale 2D films were developed based on fundamentals of thin film nucleation and growth. For the first time in 2D MoS2 literature, the identification of the S2 species in the sulfur vapor mixture has definitively been determined to be the only reactant to produce 2D MoS2. This revelation will allow for enhanced control of the 2D MoS2 reaction kinetics allowing for the growth of larger grain and higher crystallinity 2D films. Another first in 2D MoS2 literature, was the report of a new synthesis process where 1) room temperature sputtered MoO3 precursor films are sputtered onto sapphire substrates, 2) annealed to where they react to create a thin Al2(MoO4)3 interface layer, 3) the excess MoO3 was allowed to sublime away, and 4) then sulfidized at 850°C in a S/Ar environment where the Al2(MoO4)3 slowly decomposed releasing MoO3 precursor for subsequent reaction with the S2 vapor species. This process produced highly crystalline, large grain, approximately 1.5 layer thick 2D MoS2 films.
Christopher Muratore, PhD (Advisor)
Andrey Voevodin, PhD (Committee Member)
Paul T. Murray, PhD (Committee Member)
Antonio Crespo, PhD (Committee Member)
126 p.
Engineering; Materials Science; Nanoscience
2D MoS2; MoO3; aluminum molybdate; 2D nucleation and growth; sulfur vapor; S2; plasma diagnostics

Recommended Citations

Citations

  • Waite, A. R. (2017). Effects of Fundamental Processing Parameters on the Structure and Composition of Two-Dimensional MoS2 Films [Doctoral dissertation, University of Dayton]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=dayton149315978414366

    APA Style (7th edition)

  • Waite, Adam. Effects of Fundamental Processing Parameters on the Structure and Composition of Two-Dimensional MoS2 Films. 2017. University of Dayton, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=dayton149315978414366.

    MLA Style (8th edition)

  • Waite, Adam. "Effects of Fundamental Processing Parameters on the Structure and Composition of Two-Dimensional MoS2 Films." Doctoral dissertation, University of Dayton, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton149315978414366

    Chicago Manual of Style (17th edition)

dayton149315978414366
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This open access ETD is published by University of Dayton and OhioLINK.