Since the successful isolation of graphene in 2004, two-dimensional (2D) materials have become one of the hottest research fields in material science. My research is about two kinds of popular 2D materials--graphene and transition metal dichalcogenides (TMDCs). Making graphene into nanoribbons has been predicted and demonstrated to be an effective way to open a bandgap in this pristinely zero-bandgap 2D material. But the rough edge condition of etched graphene nanoribbons has always been a big issue adversely affecting electron transport performance. The electron mean free path of this kind of devices is usually way below the channel width. By using a dual-gate structure based on bilayer graphene/hexagonal boron nitride heterostructure, we found a way to form 300nm-wide conducting channels with high aspect ratio (>15) that can achieve ballistic transport, indicating perfect edge conditions. As the first star member of TMDCs family, monolayer MoS2 is predicted to be strongly piezoelectric, an effect that disappears in the bulk owing to the opposite orientations of adjacent atomic layers. We conduct the first experimental study of the piezoelectric properties of two-dimensional MoS2 and show that cyclic stretching and releasing of thin MoS2 flakes with an odd number of atomic layers produces oscillating piezoelectric voltage and current outputs, whereas no output is observed for flakes with an even number of layers. In agreement with theoretical predictions, the output increases with decreasing thickness and reverses sign when the strain direction is rotated by 90 degrees. Transport measurements show a strong piezotronic effect in single-layer MoS2, but not in bilayer and bulk MoS2. Monolayer WSe2, another popular TMDC, has also attracted much recent attention. In contrast to the initial understanding, the minima of the conduction band are predicted to be spin split. Because of this splitting and the spin-polarized character of the valence bands, the lowest-lying excitonic states in WSe2 are expected to be spin-forbidden and optically dark. We show how an in-plane magnetic field can brighten the dark excitonic states and allow their properties to be revealed experimentally in monolayer WSe2. In particular, precise energy levels for both the neutral and charged dark excitons were obtained. Greatly increased emission and valley lifetimes were observed for the brightened dark states as a result of their spin configuration.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Materials Science, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 173-182). Also available for download via the World Wide Web; free to University of Oregon users.

The speed of microelectronic devices is controlled by the size of the transistor gate. In order to create faster devices, the size of this transistor gate must shrink. Microlithography is the method used to define patterns in semiconductor devices, and it is optimized periodically to create smaller features. It is a subtractive process that relies on the selective removal of sections of a photosensitive polymeric film called photoresist. This photoresist is exposed to patterned ultraviolet radiation that changes the local solubility of the film and allows for the creation of relief patterns in the resist using a developing solvent. Decreasing the wavelength of the light used to expose the patterns is the primary method for decreasing the minimum feature size that can be printed by this process. There are a number of challenges associated with decreasing the exposure wavelength for conventional lithographic processes. First of all, the polymeric films must be transparent at the exposure wavelength in order to allow light to propagate through the entire thickness of the film. Secondly, there is a limit in the thickness of the photoresist films that can be used. This thickness limits the etch resistance of the film. In fact, the issues concerning etch resistance and transparency are generally in opposition. This makes designing photoresist platforms for future lithographic applications very difficult. Therefore, to overcome these limitations, we are developing an unconventional approach to microlithography. In our approach, entitled Surface Monolayer Initiated Polymerization, polymer structures are formed on a surface by polymerizing a monomer in a patterned fashion using a self-assembled monolayer that can be locally activated to initiate the reaction. This process has been demonstrated by creating patterned polystyrene films on native silicon dioxide surfaces. In these initial studies, it took more than one day to create features. This is unacceptable for a lithographic application. The kinetics of all the processes involved in making these patterned layers is described. Along with these rate constants, means of optimizing these rates are also presented. Additionally, the patterns grown in these initial studies exhibited poor uniformity. Methods of optimizing the patterns formed are also presented.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, June 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (M.Sc.), Memorial University of Newfoundland, 2000. / Bibliography: leaves 115-118.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, June 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept of Chemistry, August 2003. / Includes bibliographical references. Also available on the Internet.

In vitro cell culture is an essential part of many cell and tissue engineering approaches. In particular, monolayer culture of mammalian cells is a key tool for applications such as cell therapy. Novel bioreactors like the Cellerator(TM) allow for expansion of cell populations on mechanically stimulated surfaces coated with proteins. This thesis constitutes a preliminary study which focused on cell-matrix interactions in the absence of stretch. The aim was to establish standard protocols for protein coating on poly (dimethyl siloxane) (PDMS) and for measuring cell proliferation. Specifically, the proliferation of rat pulmonary artery vascular smooth muscle (PAC1) cells on type I collagen and soluble fibronectin was studied. Growth curves were obtained and the doubling time for subconfluent cultures was computed. Although cell-matrix interactions do not enhance proliferation of PAC1 cells, it was found that a preliminary sulphuric acid treatment is necessary to yield a well-behaved culture.

Polyelectrolytes coated on high surface curvature nanoparticles (NPs) have been prepared and characterized by a variety of solid-state nuclear magnetic resonance (NMR) experiments in order to examine surface interactions, polymer-water association and polymer dynamic properties of layer components. Gold nanoparticles of four nanometers in diameter pre-stabilized by 4-dimethylaminopyridine (DMAP), and silica and neodymium NPs were chosen as substrates for these studies. The high surface to volume ratio provided by such nanoparticles is advantageous for NMR analysis, which requires a high material content for adequate sensitivity. Firstly, poly(styrene sulfonate) was deposited on gold NPs by electrostatic self-assembly where charged polyelectrolytes adsorb onto an oppositely charged substrate. Surface charges on gold NPs were provided by the ligand DMAP that induces a positive charge at the NP surface that is otherwise neutral. Nanoparticle encapsulation by PSS was monitored by the gold surface plasmon absorption band (SPB) which revealed a good stability under assembly conditions where the pH was maintained above the DMAPsoln pKa and for a polymer radius of gyration comparable to the particle radius. An electrostatic association between DMAPbound and PSS, rather than a ligand substitution, was detected by solid state 13C NMR. When a subsequent layer composed of a weak or a strong polycation was added, the stability of the bilayer was found to be dictated by the nature of the multiple, weak interactions of the polymer functional groups (SO3, NH2, N(CH 3)2+Cl-, NH3 +) with the gold surface relative to that of DMAPbound which in turn is influenced by the assembly pH. / A detailed study of the interactions between the polyelectrolytes, stabilizers and substrates was also extended to polyelectrolyte multilayers coated on gold NPs of different dimensions. Limitations in the application of the layer-by-layer self-assembly technique to very small NPs were investigated and strategies to optimize the method were proposed. 1H NMR analysis in the solid state and 2H NMR analysis in solution revealed that water association and film dynamics were closely related to the identity of the capping layer and independent of even/odd layer effects. These results were compared to those obtained for larger NP substrates which revealed many similarities between the two systems. / A study of the parameters that affect the fabrication of Poly(L-lysine) and DNA polyelectrolyte multilayer films was also conducted for both flat and highly curved surfaces. Such polyelectrolyte films coated on nanopartic1es can be considered as potential vectors for gene therapy. Control over DNA loading into films was performed by varying the ionic strength and pH of polyelectrolyte assembly solutions. DNA density, film degradability and transfection efficiency were examined to determine optimal conditions for vector preparation in gene therapy. Finally, the acid-base properties of lanthanide-based nanoparticles of 10 nm of diameter were explored under a wide range of pH conditions. The interactions of the neodymium oxide nanoparticles with the cationic poly(allylamine hydrochloride) and the anionic poly(styrene sulfonate) polymers were investigated by following spectroscopically optical changes in suspension absorbance and visual changes in NP dimensions. Transparancy and efficiency of stabilization were the evaluated criteria for polymers to be considered as potential stabilizing agents for neodymium oxide NPs used in neutrino detection experiments.