Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Douglas Spearot

Committee Member

Ajay Malshe

Second Committee Member

Paul Millett

Keywords

Atomistic Simulations, Molybdenum Disulphide, Phase Transformation

Abstract

In addition to its use as a solid lubricant, molybdenum disulphide (MoS2) has gained recent attention as a possible substitute for silicon as it is increasingly difficult to keep shrinking down electronic devices made of silicon, the conventional electronic material. When thinned down to atomic thickness, monolayer MoS2 possesses very unique and promising electronic and electrical properties. Unlike electronic and electrical properties, knowledge of the mechanical properties and role of structural defects on these properties of monolayer MoS2 is unexplored. For this thesis, the two main objectives are (1) to gain insight about the failure mechanism of monolayer MoS2 by modeling nanoindentation performed on suspended free standing membrane with comparison to experiment and (2) to explore the influence of structural defects on the mechanical properties of monolayer MoS2 by modelling monolayer MoS2 membranes with defects and simulating the same nanoindentation process as in part (1). It is shown that the force required for fracture of the MoS2 monolayer increases with increasing indenter diameter. This relationship and the magnitudes of the breaking forces computed in this work are consistent with experiments presented in the literature. A phase transformation, caused by an abrupt drop in the S-S intralayer Z dimension, is observed prior to failure during both defect-free and defect-containing membrane simulations. This phase transformation is also observed in uniaxial tension simulations. Analysis suggests that structural defects alter the failure mechanisms of monolayer MoS2 and thus reduce its mechanical performance. For point defects, the phase transformation initiates from accumulated vacancies away from the center of the membrane and accelerates the new phase propagation process. For grain boundary structures, it was found that their fracture strength is independent of the grain boundary energy.

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