Sinan Muftu, Andrew Gouldstone
Date of Award
Doctor of Philosophy
Department or Academic Unit
College of Engineering, Department of Mechanical and Industrial Engineering
mechanical engineering, adhesion, graphene, morphology
Adhesion is the interaction between dissimilar particles or surfaces, which has significant impacts in nanotechnology and life sciences, such as stability of microstructures, cell adhesion, and bacterial aggregation. In order to quantify adhesion, several theoretical models have been built from the pioneered work of Hertz contact theory to the Johnson-Kendall-Roberts (JKR), Derjaguin-Muller-Toporov (DMT), and Dugdale-Barenblatt-Maugis models. These celebrated contact mechanics models have been shown to be successful in a wide spectrum of metallic, ceramic and polymeric solid materials, and continue to make invaluable contributions in many branches of science and technology. However, these models inevitably break down in thin membranes, shells and microcapsules that exercise plate-bending and membrane-stretching and conform to the contact surface geometry.
Based on a thermodynamic energy balance method, this thesis constructs a framework to model the mechanical behavior of thin films under intersurface adhesion. Depending on the intersurface force magnitude and range, JKR limit and DMT limit are discussed. To account for the transition between these two limits, a new Tabor's parameter in the context of thin films is derived to relate the membrane thickness and stiffness and the intersurface force magnitude and range. The models are demonstrated for several thin film delamination configurations including standard pressurized blister test, constrained blister test, and punch test for a membrane clamped at the periphery. The adhesion hysteresis of loading and unloading a rigid punch to a clamped membrane is discussed as well. The trends and graphs are useful in experimentally gauging the adhesion strength of thin film material and the associated intersurface force magnitude and range, and are also helpful in formulating design criteria for micro- and nano- electromechanical systems (MEMS/NEMS) devices comprising voltage activated bridges such as RF-switches.
Graphene, being a monolayer of carbon atoms, possesses extreme mechanical and electrical properties and proves to be an indispensible conducting medium for next generation of micro electronics. The adhesion properties of graphene on electronic substrates hold the keys to high performance and long term reliability of electronics systems. Molecular mechanics simulation is implemented to explore the adhesion mechanics between two identical or misoriented graphene. Mechanical properties including elastic modulus, effective thickness and adhesion energy of two graphene layers are obtained. The simulation result is comparable with the continuum model. Experiments to study the adhesion properties between graphene and electronic substrates are conducted. The morphology of graphene on the substrates is found to be strongly related to the interfacial adhesion energy and geometrical properties of the undulated substrate surface. The results and trends obtained here set design guidelines for graphene based devices.
Li, Guangxu, "Thin film adhesion and morphology of graphene on undulated electronic substrates" (2012). Mechanical Engineering Dissertations. Paper 27. http://hdl.handle.net/2047/d20002650
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