Date of Award

Summer 7-17-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Martin L. Dunn

Second Advisor

Jianliang Xiao

Third Advisor

Carlos Felippa

Abstract

Graphene, being an atomically thin two dimensional crystalline material with a very low mass and high elastic strength, has great potential in next generation nano-mechanical devices. Additionally, it has attractive electronic, thermal and optical properties. In spite of possessing a high Young's modulus, graphene is highly bendable and ultra-floppy due to its atomic thickness. At the nano-scale the surface forces are very strong and being very flexible makes graphene membranes interact and adhere strongly to materials and structures in its vicinity. The effect of these interactions needs to be understood at different length scales - micro, nano and atomistic level to be able to design efficient and reliable graphene based nano-devices like electromechanical switches and resonators. Through this work, in the first step, we measure the strength of the adhesion of graphene membranes to a substrate using modified blister tests with the help of a detailed model accounting for the non-linear mechanics of graphene and the thermodynamics of the blister test. We also demonstrate, along the way, graphene nano-mechanical devices that can switch shapes depending on the applied pressure, adhesion strength, geometry etc. In the second step, an attempt is made to characterize the surface forces through a novel experimental setup involving pull-in of graphene membranes. The experimental observations are satisfactorily explained with the help of an analytical model. Finally, we investigate the atomistic mechanisms of adhesion and de-adhesion of graphene membranes. We used molecular mechanics simulations to investigate the effect of topography on graphene adhesion energy. The analytical model we developed captures the basic physics involved in these simulations quite well. We also study, using the same methodology, the peeling of graphene membranes on 1D sinusoidal corrugated substrates. The results reveal that the peel mechanics involves periodic instabilities due to the corrugated nature of the substrate and sliding of the graphene atoms on the substrate.

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