Includes bibliographical references (p. 62-64).

Thesis (Ph.D.)--City University of Hong Kong, 2005. / "Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.

Includes bibliographical references (p. 154-160).

Thesis (Ph. D.)--Virginia Commonwealth University, 2006. / Prepared for: Dept. of Electrical Engineering. Bibliography: leaves 193-205.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 61-63). Also available in electronic version.

Thesis (M.S. in materials science and engineering)--Washington State University. / Includes bibliographical references.

The objective of this work is to develop methods to investigate the thermoelectric (TE) transport in semiconducting nanowires (NWs). The thermal conductivity of degenerately doped electrochemically-etched (EE) silicon NWs was measured to be lower than silicon NWs synthesized by a vapor-liquid-solid (VLS) method without showing a clear dependence on the NW diameter. The thermoelectric figure of merit (ZT) at near room temperature obtained from the three measured TE properties on the same EE Si NW was found to be between 0.01 of a very rough NW and 0.08 of a relatively smooth NW, the latter of which is about four times higher than that reported for bulk p-type Si at the optimum doping concentration. In addition, the NW samples could be contaminated or oxidized during the device processing. Based on the TEM characterization, they have relatively thick oxide layer and small surface roughness, and are apparently different from the EE Si NWs that a Berkeley team reported. Typical rough NWs reported by the Berkeley team have thin oxide layer and are free of major structural defects. Hence, given the significant structural differences in the samples, it would be scientifically inappropriate to compare the transport properties obtained from the two studies. In addition, a five to ten fold reduction in thermal conductivity was observed in wurtzite InAs NWs compared to bulk InAs of zinc blend phase, and is mainly attributed to diffuse surface scattering of phonons. Moreover, InSb NWs have been synthesized at three different base pressures. The NWs were found to be zinc-blende structure with <110> growth direction. The ZT of the two NWs is about 10 times lower than the bulk values mainly because of the much higher doping levels in NWs than the bulk as well as mobility suppression in the NWs. The ZT of one NW grown at a high vacuum base pressure is higher than another NW grown at low vacuum. These results show that it is necessary to better control the impurity doping in order to increase the ZT of the InSb NWs. / text

Post-operative osteomyelitis attributing to the biofilm formation on implant surface and medical grade 316L stainless steel have been reported to gain a higher rate of infection among other clinically applied metals. It is believed suppressing bacterial adhesion on implant surface at early stages can help prevent biofilm formation. The major challenges of current antibacterial surface treatments include limited biocompatibility, potential development of antibiotic resistant bacteria, short life cycle and high fabrication cost. In this study, it is aimed to explore the feasibility of an inexpensive and simple surface modification technique to achieve a long-term antibacterial effect on medical grade 316L stainless steel while maintaining its biocompatibility. Thus, a novel 1D nanostructured ZnO nanowire coating that can provide different special topographies and can be easily fabricated by simple hydrothermal method is suggested to coat on stainless steel surfaces. Two kinds of ZnO nanowire coatings, ZnO_5hrs and ZnO_17hrs, are fabricated for further investigation. Relatively well-aligned ZnO nanowires with diameters of ~50 nm were found on ZnO_5hrs samples, while randomly-oriented ZnO nanowires with diameters of ~150 nm were found on ZnO_17hrs samples. In the antibacterial tests, both ZnO_5hrs and ZnO_17hrs samples exhibited excellent antibacterial effects, which represent over 90% of bacterial reduction among all of the tested bacterial strains including S. aureus, P. aeruginosa and E. coli, with exception to the case of ZnO_17hrs sample with S. aureus. It is confirmed that antibacterial Zn2+ ions are released from the coatings during the test and help against bacterial adhesion. On the other hand, it is suspected that the increase in hydrophilicity and special physical topography are also antibacterial factors of the ZnO nanowire coatings. The cytocompatibilities in both ZnO_5hrs and ZnO_17hrs samples were not satisfactory. In the cell adhesion test, the GFP-OB cells did not habitually spread and attach on the treated sample surfaces after 6 hours incubation. Cytotoxicity test results further confirm no viable MC3T3 cells were found on the treated sample surfaces. The cytocompatibility of the coating remains to be improved. In the in-vivo study, the group of rats with ZnO_5hrs rod samples displayed a reduced number of bacterial cells in the implantation site at day 0, as well as a shorter duration (within 8 days) for bacterial termination as compared to that with untreated stainless steel rod samples. The presence of ZnO nanowire coating on medical grade 316L stainless steel rod samples demonstrates the in vivo antibacterial effect. In short, the novel 1D antibacterial ZnO nanowire coating is successfully fabricated and coated on medical grade 316L stainless steel surfaces by a simple and inexpensive hydrothermal method. However, the biocompatibility of the ZnO nanowire coating remains to be improved. One of the critical issues is to engineer the coating in order to precisely control the Zn2+ ions release rate. For future study, the key is to find out how to manipulate the characteristics of special surface topography, together with a controllable release of Zn2+ ions on the ZnO nanowire coating to maximize the antibacterial effect while maintaining the original biocompatibility of medical grade 316L stainless steel. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

Nanoscale wires and molecules have remarkable electrical properties that make them well suited for new electronic devices. The projected device densities result in very small separation distances and therefore the possibility of device-device interactions. However, we do not know what impacts wire-wire interactions might have on the properties of closely spaced devices. If two quantum wires interact, what types of effects will there be on transport properties such as conductance? How would the coupling strength, length of wire, position of contact, or the energy of the electrons affect conductance? Understanding the effects of the interactions will assist the construction of efficient nanoscale devices.This thesis examined the effects of interaction on the low-field conductance using a simple classical model and two quantum models of coupled quantum wires fabricated electrostatically in the two-dimensional electron gas at the interface of the heterostructure A1GaAs/GaAs. We considered the effect of position and length of an interaction between two parallel quantum wires formed by hard wall boundaries and connected to electron reservoirs. Our second model consisted of two artificial molecular wires, i.e., parallel chains of quantum dots. We used a one-electron Schrodinger equation in the envelope approximation, a tight-binding Hamiltonian, and a recursive Green's function method to study the electron transport properties. Multi-parameter computations using a fortran-95 computer model provided data for an analysis of the relationships among conductance, the interaction strength, interaction location, and electron energy.In contrast to the monotonic changes predicted by the classical model, the lowfield conductance of interacting hard wall quantum wires varies in an oscillatory manner with the perturbing interaction strength and position. For electron energies below the first conductance plateau, Breit-Wigner resonances appear as a consequence of coupling. These conductance properties are explained with reference to quasi-bound states created by reflections at the end boundaries of the wires and the separating wall.At low electron energies, the conductance signature of a symmetric artificial molecule composed of serial quantum dots is a band of resonances. Coupled artificial molecular wires display a split-off molecular band with an energy separation that grows with the coupling strength and a bandwidth that narrows. The position of the Fermi energy relative to the molecular band states plays a dominant role in determining the lowfield conductance of interacting artificial molecules. The conductance variation with coupling ranges from oscillatory to monotonic, depending on the Fermi energy. Varying the atom-atom coupling position in the molecular wires causes a relatively small shift in the resonance band energies. / Department of Physics and Astronomy

L’objectif de cette thèse est de moduler le transport électrique dans des nanofils de GaAs par effet piézoélectrique ou ferroélectrique. Pour cela, une étude préliminaire des propriétés électriques et mécaniques des nanofils est nécessaire. C’est donc le premier pas vers la fabrication de nouveaux dispositifs, tels que le transistor ferroélectrique à nanofil unique ou le nanogénérateur piézotronique. Le premier chapitre de ce travail est consacré à l’élaboration par épitaxie par jets moléculaires de nanofils autocatalysés de GaAs sur Si (111). L’optimisation des paramètres de croissance a permis la première fabrication de nanofils ultra-longs de GaAs de 80 μm, jamais mis en évidence par cette méthode de croissance à notre connaissance par le passé. Une étude de leur cinétique de croissance ainsi que de leurs propriétés structurales et optiques est présentée. Les deux chapitres suivants s’intéressent aux caractérisations électriques et mécaniques de ces nanofils de GaAs. Il a été montré que ces derniers présentent des propriétés de conduction tout à fait intéressantes et les caractéristiques mécaniques attendues pour de tels nanofils. Le dernier chapitre présente une étude préliminaire des couplages avec la piézoélectricité et la ferroélectricité. La piézoélectricité des nanofils de GaAs est tout d’abord examinée. On présente ensuite le couplage avec une matrice piézoélectrique de P(VDF-TrFE). Il a enfin été mis en évidence une modulation du transport dans un nanofil grâce à l’orientation de la polarisation de la couche ferroélectrique de PZT. / The aim of this thesis is to modulate the electrical transport in GaAs nanowires by piezoelectric or ferroelectric effect. To perform this, a preliminary study of electrical and mechanical properties of these nanowires is required. It is the first step towards the elaboration of new devices as nanowire ferroelectric transistor or piezotronic nanogenerator. First chapter is dedicated to elaboration by molecular beam epitaxy of self-catalyzed GaAs nanowires on Si (111). By optimization of growth parameter, we managed the first growth ultra-long nanowires, with length up to 80 μm by this elaboration technic. Growth kinetic and crystallographic and optical properties of these nanowires has been highligth. The two following chapters are focused on electrical and mechanical characterizations of theses nanowires. It has been shown that theses nanowires have interesting conduction properties and expected mechanical behaviour. The last chapter presents a preliminary study of coupling with piezoelectricity and ferroelectricity. First of all, piezoelectricity in GaAs nanowires is observed. Then, we present coupling with a piezoelectric matrix of P(VDF-TrFE). Finally, we proved a modulation of the transport by polarization orientation of a ferroelectric PZT thin film.