Processing of two-dimensional molybdenum disulfdie: oxidation, etching, and deposition on the basal plane for novel nanofabrication processes
Open Access
- Author:
- Walter, Timothy Noah
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 09, 2019
- Committee Members:
- Suzanne E Mohney, Dissertation Advisor/Co-Advisor
Suzanne E Mohney, Committee Chair/Co-Chair
Adrianus C Van Duin, Committee Member
Saptarshi Das, Outside Member
Thomas Nelson Jackson, Committee Member
John C Mauro, Program Head/Chair - Keywords:
- MoS2
contact engineering
oxidation
ALD
nanofabrication - Abstract:
- Research on two-dimensional (2D) materials has resulted from their combinations of structural and electronic properties and potential for nanoscale customization. A promising 2D material is molybdenum disulfide (MoS2), which offers promise for nanoelectronics, particularly field-effect transistors (FETs). This dissertation aims to understand oxidation and etching of MoS2, to understand the growth of thin films on MoS2, and design fabrication processes utilizing this knowledge for the benefit of FET engineering. The first focus of this dissertation was on the oxidation of MoS2 flakes. Oxidizing atmospheres were modeled with thermodynamic calculations, and oxidized flakes of MoS2 were studied with microscopy and spectroscopy techniques to evaluate their chemical and morphological changes. Conditions that resulted in useful oxidation and etching of MoS2 were discovered and correlated to the thermodynamic predictions, and useful treatment in Ar gas and plasma was explored as well. The second study in this dissertation explored atomic layer deposition (ALD) of ZnO on MoS2 and WSe2. Both MoS2 and WSe2 surfaces resisted nucleation of ZnO by thermal ALD. Plasma-enhanced (PE)ALD deposited uniform and smooth films onto both MoS2 and WSe2 flakes; however, single-layer MoS2 and WSe2 both oxidized during PEALD. UV-O3 functionalization of the TMD surfaces resulted in growth of ZnO on the surface of MoS2 by thermal ALD, yet oxidized parts of the WSe2 that then allowed for growth. The final effort of this dissertation developed fabrication processes to etch a desired proportion of edge and top contacts to MoS2 for optimized contact resistance. In the first process, bilayers of Al2O3/ZnO were grown on MoS2 and SiO2 by PEALD; controllable, selective wet etches compatible with MoS2 were found for Al2O3 and ZnO, and lift off was achieved for SiO2. In the second process, Au nanoparticles on MoS2 were engineered during their deposition and by Cl2 plasma treatment. Fabricated FETs showed promising contact resistance and on current values. The work in this dissertation augments the understanding of oxidation and etching of MoS2 and growth of metal oxide and metal films on the MoS2 basal plane. From there, it also carves out novel, customizable fabrication processes for engineering of MoS2-based FETs.