Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Honsberg, Christiana; Committee Co-Chair: Citrin, David; Committee Member: Doolittle, Alan; Committee Member: First, Phillip; Committee Member: Ralph, Stephen; Committee Member: Rohatgi, Ajeet

Thesis (Ph.D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on August 13, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Medical Sciences - Biomedical Engineering, University of Alberta." Includes bibliographical references.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Dr. Andrei G. Fedorov; Committee Member: Dr. Azad Naeemi; Committee Member: Dr. Suresh Sitaraman; Committee Member: Dr. Vladimir V. Tsukruk; Committee Member: Dr. Yogendra Joshi. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Novel technology which can provide new solutions and enable augmented capabilities to CMOS based technology is highly desired. Piezotronic nanodevices and integrated systems exhibit potential in achieving these application goals. By combining laser interference lithography and low temperature hydrothermal method, an effective approach for ordered growth of vertically aligned ZnO NWs array with high-throughput and low-cost at wafer-scale has been developed, without using catalyst and with a superior control over orientation, location/density and morphology of as-synthesized ZnO NWs. Beyond the materials synthesis, by utilizing the gating effect produced by the piezopotential in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) and universal logic operations such as NAND, NOR, XOR gates have been demonstrated for performing piezotronic logic operations for the first time. In addition, the first piezoelectrically-modulated resistive switching device based on piezotronic ZnO NWs has also been presented, through which the write/read access of the memory cell is programmed via electromechanical modulation and the logic levels of the strain applied on the memory cell can be recorded and read out for the first time. Furthermore, the first and by far the largest 3D array integration of vertical NW piezotronic transistors circuitry as active pixel-addressable pressure-sensor matrix for tactile imaging has been demonstrated, paving innovative routes towards industrial-scale integration of NW piezotronic devices for sensing, micro/nano-systems and human-electronics interfacing. The presented concepts and results in this thesis exhibit the potential for implementing novel nanoelectromechanical devices and integrating with MEMS/NEMS technology to achieve augmented functionalities to state-of-the-art CMOS technology such as active interfacing between machines and human/ambient as well as micro/nano-systems capable of intelligent and self-sufficient multi-dimensional operations.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / Nanoelectromechanical systems (NEMS) are the integration of nanotechnology and microelectromechanical systems (MEMS). The idea of this thesis is to give a basic preparation to approach NEMS, a subcategory of nanotechnology. This is performed by gaining knowledge of the two separate fields NEMS consist of, namely MEMS and nanotechnology. This document will discuss the basic theory and fabrication tools for microelectromechanical systems, as well as its limits as MEMS feature sizes decrease, reaching toward nanotechnology. It starts with an introduction that includes the history, giving a basic background. The essence is captured with theory of the equipment, the main material, some concepts of design and the creation of structures. To stimulate further interest, this thesis also illustrates practical design and fabrication methods. With the knowledge and skills that were discussed, one should be ready to get started with NEMS.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This report intends to show how able the Stellenbosch Electrical and Electronic Engineering Department’s micro fabrication laboratory is to manufacture nanomechanical switches and similar structures. Following the investigation, an attempt will be made to produce these devices. In attaining this goal, a literature study was performed focusing on mechanical switching and nanotechnology. Their origins, development and current application are investigated, as well as the requirements for developing these devices. Having completed the literature study, a series of current nanomechanical switches where investigated, selecting those most likely to be manufactured at the available facilities and having the required attributes for taking the place of silicon transistors in low speed, hostile environments. The most common method of manufacturing nanoswitches is simulated using several methods of predicting device failure. This will aid in the selection of manufacturing process guidelines, such as dimensions in the photoresist templates and layer thickness before etching, allowing for the repeated production of functional switches. The two manufacturable nanomechanical switches are investigated, using techniques and materials available at the micro fabrication laboratory to manufacture them. Subsequently, their electrical properties will be determined and used in simulating their failure characteristics. In conclusion, the result are discussed along with advice and improvements for the continued investigation and production of nanodevices at Stellenbosch University / AFRIKAANSE OPSOMMING: Die doel met hierdie tesis is om die vermoë van die Departement Elektriese en Elektroniese Ingenieurswese se mikro-elektronika laboratorium te ondersoek ten opsigte van die vervaardiging van nanomeganiese skakelaars en aanverwante komponente. Na afloop van die ondersoek sal ’n poging aangewend word om hierdie toestelle te vervaardig. In nastrewing van hierdie doel is ’n literatuurstudie uitgevoer wat fokus op meganiese skakeling en nanotegnologie. Die oorsprong, ontwikkeling en huidige aanwending van hierdie skakelaars word ondersoek, sowel as die vereistes vir die ontwikkeling daarvan. Na voltooiing van die literatuurstudie word ’n reeks van bestaande nanomeganiese skakelaars ondersoek. Skakelaars word dan geïdentifiseer op grond van hul waarskynlike vervaardigbaarheid met die beskikbare fasiliteite. Die vereiste eienskappe vir lae spoed toepassings in omgewings waar silikon-skakelaars nie kan werk nie, word ook in ag geneem. Die mees algemene metode vir die vervaardiging van nanoskakelaars word gesimuleer met behulp van verskeie tegnieke wat toestelfaling voorspel. Die simulasies sal help in die keuse van vervaardigingsriglyne van die proses, soos die dimensies van die fotolak template en die laagdiktes voor etsing, sodat goeie resultate verkry kan word wanneer die skakelaars vervaardig word, met goeie herhaalbaarheid. Die twee gekose vervaardigbare nanomeganiese skakelaars word dan ondersoek ten opsigte van die tegnieke en materiale wat in die mikro-elektronika laboratorium beskikbaar is. Daarna sal die elektriese eienskappe van die skakelaars bepaal word. Ter afsluiting word die resultate bespreek, saam met aanbevelings vir die voortsetting van die navorsing om nanomeganiese skakelaars by die Universiteit van Stellenbosch te vervaardig.

The focus of this work is to present in detail the implementation of a three dimensional direct simulation Monte Carlo methodology on unstructured Delaunay meshes (U-DSMC). The validation and verification of the implementation are shown using a series of fundamental flow cases. The numerical error associated with the implementation is also studied using a fundamental flow configuration. Gas expansion from microtubes is studied using the U-DSMC code for tube diameters ranging from 100Æ’ÃÂ�m down to 100nm. Simulations are carried out for a range of inlet Knudsen numbers and the effect of aspect ratio and inlet Reynolds number on the plume structure is investigated. The effect of scaling the geometry is also examined. Gas expansion from a conical nozzle is studied using the U-DSMC code for throat diameters ranging from 250 Æ’ÃÂ�m down to 250 nm. Simulations are carried out for a range of inlet Knudsen numbers and the effect of inlet speed ratio and inlet Reynolds number on the plume structure is investigated. The effect of scaling the geometry is examined. Results of a numerical study using the U-DSMC code are employed to guide the design of a micropitot probe intended for use in analyzing rarefied gaseous microjet flow. The flow conditions considered correspond to anticipated experimental test cases for a probe that is currently under development. The expansion of nitrogen from an orifice with a diameter of 100Æ’ÃÂ�m is modeled using U-DSMC. From these results, local ¡¥free stream¡¦ conditions are obtained for use in U-DSMC simulations of the flow in the vicinity of the micropitot probe. Predictions of the pressure within the probe are made for a number of locations in the orifice plume. The predictions from the U-DSMC simulations are used for evaluating the geometrical design of the probe as well as aiding in pressure sensor selection. The effect of scale on the statistical fluctuation of the U-DSMC data is studied using Poiseuille flow. The error in the predicted velocity profile is calculated with respect to both first and second-order slip formulations. Simulations are carried out for a range of channel heights and the error between the U-DSMC predictions and theory are calculated for each case. From this error, a functional dependence is shown between the scale-induced statistical fluctuations and the decreasing channel height.

This thesis describes studies of a two-dimensional (2D), hexagonal arrangement of carbon atoms, graphene. Because of graphene’s reduced dimensionality, the 2D material possesses many desirable mechanical and electrical properties compared to its three-dimensional (3D) counterpart, graphite. In fact, its mechanical strength and electrical mobility are one of the strongest and fastest in the world, prompting much excitements from science and engineering communities alike ever since its first experimental demonstration in 2004. The first part of this thesis deals with graphene in material level. Chapter 1 provides an introduction to graphene. Chapter 2 describes chemical vapor deposition (CVD) synthesis of graphene and various transfer techniques. Chapter 3 describes characterization of graphene using optical inspection, oxidation test, Raman spectroscopy, and electrical transport. The second part of this thesis concerns graphene in device level, electro-mechanical implementation in particular. Chapter 4 gives an introduction to graphene nano-electro- mechanical systems (GNEMS), where the material’s mechanical and electrical prowess can best be combined, and describes fabrication process as well as transduction mechanism. Chapter 5 shows how GNEMS can be used to build a pressure sensor or an accelerometer. Chapter 6 is a study of the graphene resonators for signal processing such as in RF filters or oscillators. Chapter 7 describes the graphene - silicon nitride heterostructure resonators. The third part of this thesis considers the integration of GNEMS at a system level. Chapter 8 depicts integration of graphene resonators onto a taped-out CMOS die using post-processing. This work, in conjunction with numerous other work done by fellow researchers in the field, tries to provide an overview - from the material synthesis to device fabrication and characterization, and further to system level integration - in utilizing graphene, and graphene NEMS in particular, for sensing and signal processing applications.

For decades, epitaxy is used in nanotechnologies and semiconductor fabrications. So far, it's the only affordable method of high quality crystal growth for many semiconductor materials. Heterostructures developed from these make it possible to solve the considerably more general problem of controlling the fundamental parameters inside the semiconductor crystals and devices. Moreover, as one newly arising study and application branch of epitaxy, selective area growth (SAG) is widely used to fabricate materials of different thicknesses and composition on different regions of a single wafer. All of these new and promising fields have caught the interests and attentions of all the researchers around the world. In this work, we will study the stress and strain analysis of epitaxy in nano-scale materials, in which we seek a methodology to bridge the gap between continuum mechanical models and incorporate surface excess energy effects, which can be obtained by molecular dynamical simulations. We will make a brief description of the elastic behavior of the bulk material, covering the concepts of stress, strain, elastic energy and especially, the elastic constants. After that, we explained in details about the definitions of surface/interface excess energy and their characteristic property tensors. For both elastic constants and surface excess energy, we will use molecular dynamic simulations to calculate them out, which is mainly about curve-fitting the parabola function between the total strain energy density and the strain. After this, we analyzed the stress and strain state in nanoisland during the selective area growth of epitaxy. When the nanoisland is relaxed, the lattice structure becomes equilibrated, which means the total strain energy of system need to be minimized. Compared to other researcher's work, our model is based on continuum mechanics but also adopts the outcome from MD simulations. By combining these microscopic informations and those macroscopic observable properties, such as bulk elastic constants, we can provide a novel way of analyzing the stress and strain profile in epitaxy. The most important idea behind this approach is that, whenever we can obtain the elastic constants and surface property tensors from MD simulations, we can follow the same methodology to analyse the stress and strain in any epitaxy process. This is the power of combining atomistic simulations and continuum method, which can take considerations of both the microscopic and macroscopic factors.