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.

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.

Hu, Jianliang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 88-105). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Orientador: Guillermo Gerardo Cabrera Oyarzun / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-09-24T19:11:22Z (GMT). No. of bitstreams: 1 Dartora_CesarAugusto_D.pdf: 2101604 bytes, checksum: 3eb6940416ec56ede441909468db04be (MD5) Previous issue date: 2005 / Resumo: O interesse atual e crescente nos sistemas mesoscópicos se deve à miniaturização cada vez maior dos dispositivos eletrônicos e à produção de materiais com possibilidade de armazenar informação em altas densidades (Gbits e Terabits/pol 2 ). A Física Mesoscópica descreve fenômenos que ocorrem em uma escala de tamanhos intermediária entre o macroscópico e o microscópico. Esta região cinzenta permite interpolar entre o regime atômico-molecular e o limite macroscópico, dominado este último pelas propriedades de volume (bulk ), que são objetos usuais de estudo em Física da Matéria Condensada. Na escala de nanometros e dezenas de nanometros, os elétrons podem propagar-se sem sofrer espalhamento inelástico (regime balístico) e a fase da função de onda pode manter sua coerência em escala da ordem do tamanho do sistema, dando lugar aos típicos fenômenos de interferência quântica. Neste trabalho fazemos um estudo detalhado das propriedades de transporte quântico em sistemas mesoscópicos, onde as barreiras de tunelamento fazem parte de diversos dispositivos eletrônicos. Estes sistemas incluem barreiras isolantes entre eletrodos metálicos, nanocontatos metálicos e junções tipo Josephson entre supercondutores. As principais estruturas aqui estudadas são as junções magnéticas de tunelamento e os nanofios e nanocontatos ferromagnéticos. Em ambos o fenômeno da magnetorresistência gigante (GMR) está presente, porém as origens do fenômeno são diferentes. Em junções de tunelamento a GMR tem origem na densidade de estados dos elétrons de condução nos eletrôdos ferromagnéticos, entre os quais uma barreira isolante é colocada, bem como no tunelamento inelástico assistido por mágnons que surgem nas interfaces entre eletrodos e região isolante. Em nanocontatos e nanofios o fenômeno deve-se principalmente ao forte espalhamento de elétrons com dependência de spin na presença de paredes de domínio magnéticas / Abstract: The interest in mesoscopic systems has grown significantly due to the increasing miniaturization of electronic devices and the production of materials which makes possible to store information in higher densities (Gbits and Terabits/in 2 ). The Mesoscopic Physics describes phenomena that happen in an intermediary scale of sizes between the macroscopic and the microscopic world. This gray region allows to interpolate between the atomic-molecular regime and the macroscopic limit, the last one dominated by bulk properties which are the usual subject of Condensed Matter Physics. In the nanometer and tens of nanometers scale electrons can pro-pagate without suffering inelastic scattering (ballistic regime) and the phase of the wavefunction maintain its coherence in the scale of system¿s size, giving place to the typical phenomena of quantum interference. In this work a detailed study of quantum transport properties in mesoscopic systems, where the tunnelling barriers make part of many electronic devices, is done. These systems include insulating barriers between metallic electrodes, metallic nanocontacts and nanowires, and Josephson junctions between superconductors. The main structures here studied are magnetic tunnelling junctions and ferromag-netic nanowires and nanocontacts. In both cases the giant magnetoresistance phe-nomenon (GMR) is present, however the origins of it are quite different. In tun-neling junctions, where an insulating barrier is placed between two ferromagnetic electrodes, the GMR is due to both, density of states effects at the ferromagnetic elec-trodes, and inelastic tunneling from magnons at the interface regions. In nanowires and nanocontacts the transport is strongly in uenced by spin-dependent scattering in the presence of magnetic domain walls / Doutorado / Física da Matéria Condensada / Doutor em Ciências

The recently developed Shear-Force Acoustic Near-Field Microscope (SANM) is used to investigate the viscoelastic properties of a mesoscopic fluid layer confined between two trapping boundaries, one being a stationary substrate and the other the apex of a laterally oscillating tapered probe. Hardware improvements and evaluation of the SANM-probe robustness will be a major focus of this thesis. The investigation first discusses characterization and recent developments made to the microscope, including: modifications to the sensor head, conditioning of the Nano positioners electrical drive signal, and the assessment of the probe against eventual plastic deformation or compliance against interactions with samples (the latter comprising a solid substrate and its adhered fluid layer which is typically a few monolayers thick). Furthermore, this study includes an analysis of the adsorbed mesoscopic fluid's viscoelastic properties. This inquiry aims to better understand probe-sample interactions with the mesoscopic fluid. This includes adhesion, wetting, and to inquire the nature of the hydrophobic interaction, which is relevant in many areas of study such a protein folding, and interfacial friction which has wide ranging applications including desalination. This analysis will be performed using a Sheer force microscopy (implemented with quartz tuning fork QTF), and another recently introduced technique Whispering Gallery Acoustic Sensor (WGAS). The latter allows more direct monitoring of the QTF's mechanical displacement. These measurements will be supplemented by simultaneously monitoring the acoustic emission from the mesoscopic fluid under confinement between the probe and the substrate, which will be monitored using the SANM sensor positioned beneath the substrate.

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