Publication Date

2014-07-31

Availability

Embargoed

Embargo Period

2016-01-22

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Mechanical Engineering (Engineering)

Date of Defense

2014-07-02

First Committee Member

Qingda Yang

Second Committee Member

Jizhou Song

Third Committee Member

Weiyong Gu

Fourth Committee Member

Chun-Yuh Huang

Abstract

The focus of the doctoral research presented in this dissertation consists of two kinds of graphitic materials, graphene and single walled carbon nanotubes (SWNTs). Owing to its fascinating electrical, thermal, and mechanical properties, graphene and SWNTs have shown great promise for a multitude of applications, ranging from flexible and invisible displays, nanoelectronic components, nanosensors, to energy conversion and storage devices. The use of graphene/h-BN heterostructure for graphene electronics has attracted much interest from science and engineering communities because graphene/h-BN heterostructures exhibit much higher electron mobility, less intrinsic doping and improved on/off ration than conventional graphene devices on SiO2 substrate. Understanding the mechanical properties of graphene/h-BN, where the interface plays a key role, is crucial in enabling future high-quality graphene applications. A continuum framework is established for the cohesive law due to the van der Waals force for the interface between graphene and h-BN in terms of the area density of carbon atoms on the graphene and those of boron and nitrogen atoms on the h-BN layer, number of h-BN layer and the parameters in van der Waals interaction. Also, the buckling of graphene on h-BN substrate under equi-biaxial compression with five buckling patterns is studied. Total energy consisting of cohesive energy, graphene membrane energy and graphene bending energy is obtained analytically for each buckling mode. It is found that the total energies are quite same for all buckling modes at a compression slightly larger than the critical strain while the herringbone mode has the lowest total energy at a compression much larger than the critical compression. SWNTs remain of significant interest in the electronic materials research community due to their excellent electrical properties. However, the heterogeneity of synthesized SWNTs significantly hampers device performance. Recent efforts to remove metallic SWNTs using thermocapillary flow of thin film due to Joule heating yielded purified semiconducting SWNTs. An analytical model, as well as a fully coupled thermo-mechanical-fluid finite element model, is developed to understand the underlying physics associated with the thermocapillary flow. The predicted results agree well with experimental measurements such that the models are reliable for further optimization. It is shown that thermocapillary force due to the high temperature gradient makes the trench. A simple scaling law for the film thickness profile is established in terms of the geometrical (e.g., film thickness), material (e.g., thermal conductivity and viscosity) and loading parameters (e.g., power density). It shows that the normalized thickness profile only depends on three non-dimensional parameters in addition to the normalized position and normalized time. In particular, for the system of MG2OH/Quartz under a low power density, the thickness profile only depends on one non-dimensional parameter. These may serve as design guidelines for system optimization.

Keywords

Graphene; Hexagonal boron nitride; Single walled carbon nanotubes; Cohesive law; Buckling; Thermocapillary

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