Electronic Theses and Dissertations

Identifier

4927

Li Li

Date

2017

Document Type

Thesis

Degree Name

Master of Science

Major

Physics

Concentration

Materials Science

Committee Chair

Jingbiao Cui

Committee Member

Xiao Shen

Committee Member

Sanjay Mishra

Committee Member

Mohamed Laradji

Abstract

Recently, monolayer molybdenum disulfide (MoS2), a direct bandgap 2-D semiconductor, has shown its great potential for applications in electrical and optoelectronic devices such as Field-effect Transistors (FETs), memory devices, solar cells, photodetectors and lithium ion batteries. Depending on the arrangement of S atoms, MoS2 appears in two distinct crystal structures: thermodynamically stable hexagonal 2H phase (semiconductor), and metastable Octahedral 1T phase (metal). Theoretical considerations of the interlayer S/S and intra-layer Mo/S glide within MoS2 crystals clearly showed the preference of the 2H-MoS2 allotrope over the 1T-MoS2 structure. However, the 1T phase was reported to transform from 2H-MoS2 by Li and K intercalation. In this study, the phase transition of 1T MoS2 nanosheets grown by a hydrothermal process was investigated by annealing the samples in air or in vacuum up to 350 °C. SEM, Raman microscope, Hall effect measurement, and UV-Vis absorption were used to characterize the morphology, electrical, surface, and electrical properties of the annealed samples. The phase transition from 1T to 2H-MoS2 along with property change has been observed around 150 °C in air but slower in vacuum. This study provides the first hand data on the phase transition of MoS2 nanosheets, which helps better understand the fundamentals of this material for potential applications in electronic devices such as batteries and capacitors.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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