Thesis (Ph. D.)--University of Hong Kong, 1999. / Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 133-151).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 102-106). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2009. / Title from PDF title page (University of Texas Digital Repository, viewed on Sept. 9, 2009). Vita. Includes bibliographical references and index.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Orientador: Peter Alexander Bleinroth Schulz / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T10:20:11Z (GMT). No. of bitstreams: 1 CarrilloNunez_Hamilton_M.pdf: 5573082 bytes, checksum: 82c48bf8cb538a5a4c7444d18080814b (MD5) Previous issue date: 2008 / Resumo: Neste trabalho discutimos e comparamos diferentes definições de localização eletrônica em sistemas quase-1D: o caso estritamente 1D de cadeias de polianilinas e o DNA modelado como uma cadeia dupla. Em ambos os sistemas se estudou o comprimento de localização, obtido da condutância e do numero de participação, tentado estabelecer uma equivalência entre as duas quantidades. Para o sistema 1D a condutância foi obtida pelo método de matriz transferência. Entretanto, para o DNA a condutância se calcula usando o método recursivo das funções de Green, pois o método de matriz transferência para cadeias duplas apresenta instabilidades numéricas. O resultado obtido sugere um novo critério para analisar a extensão da função de onda em sistemas mesoscópicos dentro do regime difusivo de transporte como uma informação complementar para o comprimento de localização / Abstract: In this work we discuss and compare different definitions for localization of electronic states in quase-one-dimensional systems: the 1-D case of polianilines chains and DNA-like molecules. In order to establish ranges of equivalence, the localization length from both, the conductance and participation ratio, is computed. For the 1-D case the con-ductance is obtained by mean of the transfer matrix method, while the conductance for DNA-like double strands are calculated by mean of the recursive Green¿s function method since the transfer matrix method shows numerical instabilities. The final results suggest also criteria to infer the extension of wave function in mesoscopic systems with-in the diffusive transport regime as a complementary information to the localization length / Mestrado / Física da Matéria Condensada / Mestre em Física

Abstract The quantum-mechanical effects typical for single atoms or molecules can be reproduced in micrometer-scale electric devices. In these systems the essential component is a small Josephson junction (JJ) consisting of two superconductors separated by a thin insulator. The quantum phenomena can be controlled in real time by external signals and have a great potential for novel applications. However, their fragility on uncontrolled disturbance caused by typical nearby environments is a drawback for quantum information science, but a virtue for detector technology. Motivated by this we have theoretically studied transistor kind of devices based on single-charge tunneling through small JJs. A common factor of the research is the analysis of the interplay between the coherent Cooper-pair (charge carriers in the superconducting state) tunneling and incoherent environmental processes. In the first work we calculate the current due to incoherent Cooper-pair tunneling through a voltage-biased small JJ in series with large JJs and compare the results with recent experiments. We are able to reproduce the main experimental features and interpret these as traces of energy levels and energy bands of the mesoscopic device. In the second work we analyze a similar circuit (asymmetric single-Cooper-pair transistor) but under the assumption that the Cooper-pair tunneling is mainly coherent. This predicts new resonant transport voltages in the circuit due to higher-order processes. However, no clear traces of most of them are seen in the experiments, and similar discrepancy is present also in the case of the symmetric circuit. We continue to study this problem by modeling the interplay between the coherent and incoherent processes more accurately using a density-matrix approach. By this we are able to demonstrate that in typical conditions most of these resonances are indeed washed out by strong decoherence caused by the environment. We also analyze the contribution of three typical weakly interacting dissipative environments: electromagnetic environment, spurious charge fluctuators in the nearby insulating materials, and quasiparticles. In the last work we model the dynamics of a current-biased JJ perturbed by a smaller JJ using a similar density-matrix approach. We demonstrate that the small JJ can be used also as a detector of the energy-band dynamics in a current biased JJ. The method is also used for modeling the charge transport in the Bloch-oscillating transistor.

The shear force mechanism has been utilized as a distance regulation method in scanning probe microscopes. However, the origin of shear force is still unclear. One of the most important reasons for the shear-force damping is due to the presence of a water contamination layer at the sample surface in ambient conditions. Understanding the behavior of such mesoscopic fluid-like films is of significance for studies of not only scanning probe microscopy but also other complex surface phenomena, such as nanotribology, lubrication, adhesion, wetting, and the microfluidity of biological membranes. This thesis investigates, in particular, the dynamics of mesoscopic fluids confined between two sliding solid boundaries. When fluids are constrained to nanometer-sized regions, their physical properties can greatly differ from those displayed by bulk liquids. To gain an insight into the fundamental characteristics of the confined fluid films, we exploit the versatile capabilities of the novel shear-force/acoustic near-field microscope (SANM), which is able to concurrently and independently monitor the effects of the fluid-mediated interactions acting on both the microscope's probe and the sample to be analyzed. Two signals are monitored simultaneously during each experimental cycle: the tuning fork signal, which is the oscillation amplitude of the probe and gives access to the shear force; and acoustic signal, which is detected by an acoustic sensor placed under the sample. Systematic experiments are carried out to investigate the effects of probe geometry, environmental humidity, and chemical properties of probe and sample surface (water affinity: hydrophobicity or hydrophilicity) on the probe-sample interactions, expressing the influence of the fluid-like contamination films.

This dissertation focuses on characterization of the mesoscopic fluid film, testing its behavior in different application scenarios, including its role in near-field scanning probe microscopy imaging, contribution to the phononic mechanism in nanotribology phenomena, utilizing it as a natural environment in the study of carbohydrate-protein interactions, and harnessing it as bridge to transport ions in the fabrication of nanostructures on responsive polymer materials. Due to their high resolution and versatile applications in a variety of fields, the family of scanning probe microscopy (SPM) has found widespread acceptance as an analytical and fabrication tool. However, the working mechanism of SPM that allows maintaining the probe-sample distance constant is still controversial. At the heart the problem is a lack of precise knowledge about the nature of the probe-sample interaction. One key factor is the presence of a mesoscopic fluid-like layer that naturally forms at any surface at ambient condition in which most SPMs are operated. Its mesoscopic nature (~20 nm in thickness) results in extraordinary behavior compared to the properties of bulk liquid. For example, the effective shear viscosity of confined mesoscopic fluids is enhanced, and viscoelastic relaxation times are prolonged. Despite the wide use of SPM techniques in ambient air, the basis of their working mechanisms is still not well understood. The probe-sample interaction is monitored using a combination of tuning-fork based shear force microscopy and our recently developed near-field acoustic technique. To characterize the mesoscopic fluid film a series of experiments are performed under different conditions in order to explore the benefits of having extra probing (acoustic) technique in addition to the shear-force approach. The presence of mesoscopic fluid layers as a natural environment enables the detection of protein-carbohydrate interactions. We demonstrated the capability of our shear-force/acoustic technique to monitor the rupture of chemical bonds between carbohydrate and protein pairs. Finally, we present fabrication of nanostructures via electric-field assisted dip-pen nanolithography by exploiting the responsive feature of a particular class of polymers, where the mesoscopic fluid layer also plays an important role in pattern creation.

We have studied the electron quantum phase by fabricating low dimensional (d ≤ 2) mesoscopic interferometers in high-quality narrow-gap semiconductor (NGS) heterostructures. The low effective-mass electrons in NGS heterostructures enable observation of delicate quantum phases; and the strong spin-orbit interaction (SOI) in the systems gives us means by which we can manipulate the quantum-mechanical spin of these electrons through the orbital properties of the electrons. This enables the observation of spin-dependent phenomena otherwise inaccessible in non-magnetic systems. We have performed low temperature (0.4 K ≤ T ≤ 8 K), low noise (â V ~ 1μV ) transport measurements, and observed evidence of Aharonov-Bohm (AB) and Alâ tshuler-Aronov-Spivak (AAS) quantum oscillations in meso- scopic devices that we fabricated on these NGSs. Our measurements are unique in that we observe both AB and AAS in comparable magnitude in ballistic networks with strong SOI. We show that, with appropriate considerations, diffusive formalisms can be used to describe ballistic transport through rings, even in the presence of SOI. This work also contains an introduction to the physics of geometric phases in mesoscopic systems, and the experimental and analytic processes through which these phases are probed. A discussion of the results of our measurements presents the case that quantum interferometric measurements of geometric phases can be understood quite thoroughly, and that these measurements may have deeper utility in discovery than has yet been recognized. / Ph. D.