Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Scott Bunch

Second Advisor

Victor M. Bright

Third Advisor

Xiaobo Yin

Fourth Advisor

Jianliang Xiao

Fifth Advisor

Thomas R. Schibli

Abstract

The isolation of graphene, a single atomic layer of carbon atoms, leads to the exploration of a group of new materials - 2 dimensional (2D) crystals, which have unique properties in mechanical, electrical and optical fields. This thesis demonstrates our work on the development of nanomechanical systems from 2D materials (graphene and MoS2) and using them for the study of material properties.

At first, we developed large arrays of 3-terminal graphene NEMS switches with a novel design, which help the devices to achieve low actuation voltages (down to ~3V), improved reliability and mechanical integrity. These switches may find applications in mechanical computing, data storage, and RF communication, and the design can be used for other 2D materials based NEMS switches. We also studied the electromechanical properties of the devices. A study of the threshold switching voltages is carried out, and the switching voltage is simulated with a finite element model which includes nonlinear mechanics. From this we deduce a scaling relation between the switching voltage and device dimensions.

Next, we present a unique nanomechanical configuration that allows us to determine the interfacial forces between graphene and Au/SiO2. The nature of the interfacial forces at ~ 10 - 20 nm separations is consistent with an inverse fourth power distance dependence, implying that the interfacial forces are dominated by van der Waals interactions. Furthermore, the strength of the interactions is found to increase linearly with the number of graphene layers. The experimental approach can be used to measure the strength of the interfacial forces for other atomically thin two-dimensional materials, and help guide the development of nanomechanical devices such as switches, resonators, and sensors.

Finally, we show the modulation of electronic band structure in monolayer suspended MoS2 membranes with local biaxial strain at the center of a spherical blister. We observed a linear direct band gap (A peak) decrease rate of ~100 meV/% strain in monolayer MoS2. Future work includes biaxial strain engineering on bilayer and trilayer MoS2.

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