More that just magnificent views of atoms and molecules, Scanning Tunneling Microscopy, STM, images have the potential to answer some fundamental questions relating to surface molecular dynamics and bonding characteristics of localized species versus more common analytical tools that provide average of bulk sample information. A special feature of the STM is utilized in this study which is the ability to image organic monolayers at liquid-solid interface at ambient conditions. For STM analysis of organic fluids, the choice of a substrate is critical to the success of the images. The substrate must meet three criteria, the ability to sustain a tunneling current, retain an atomically flat surface over the area scanned, and immobilize a monolayer of the sample. The adsorption geometry created by the liquid crystalline materials analyzed in this study provided magnificent detailed features of the sample monolayer on a graphite substrate. These data provide information about the balance of intermolecular forces at the interface. It is illustrated that the quality or amount of information available from any fluid-solid interfacial image is dependent upon the existence of molecular symmetry within the monolayer of the substrate surface. / Graduation date: 1995

Soft x-ray microscopy is a powerful technique for natural-contrast, high-resolution imaging of organic materials. This Thesis describes new instrumentational and new image-processing methods to improve the image quality of the compact x-ray microscope at the Biomedical & X-Ray Physics division at KTH. The microscope is based on a laser-plasma source combined with different condenser optics, either multilayer mirrors or zone plates. Imaging is performed by micro zone plates. The microscope works in the water window (\lambda = 2.3-4.4 nm), where the attenuation lengths of oxygen and carbon differ strongly, providing high natural contrast for carbon-containing specimens in an aqueous environment. By optimizing the properties of the laser-plasma source and fabricating multilayer mirrors with high, uniform reflectivity, the performance of the microscope's illumination system could be improved and exposure times decreased significantly to about 2 min for imaging dry samples and 5 min for imaging wet samples. For imaging of wet samples, a wet-specimen chamber was developed, which is vacuum-compatible. Since it is horizontally mounted in the microscope, it offers advantages for investigations in polymer and soil science. To improve the quality of images taken by the compact x-ray microscope an image-restoration algorithm was developed. Denoising is performed by a filtering algorithm based on the discrete wavelet transform. This algorithm shows advantages compared to Fourier-based algorithms, since the filtering of spatial frequencies is done locally. An improvement in exposure time by a factor of about 2 could be realized without loss of image information. To stimulate experiments on functional imaging in x-ray microscopy an image-analysis algorithm for identifying colloidal-gold particles was developed. This algorithm is based on a combination of a threshold with respect to the local absorption and a shape discrimination, realized by fitting a Gaussian profile to the potential particles. The algorithm was evaluated and optimized on images taken by the transmission x-ray microscope at BESSY II. The size-selective identification and localization of single gold particles down to a diameter of 50 nm was demonstrated. / QC 20100920

Colloidal crystallization in sedimenting systems is an incompletely understood process, where the influence of interparticle forces on the three-dimensional (3-D) microstructure remains to be fully elucidated. This dissertation outlines work that is intended to improve our knowledge of this subject by studying sedimentation equilibrium and phase behavior for electrostatically repulsive systems, as well as the interfacial crystallization of attractive depletion systems. Towards this end, several analytical and experimental tools have been developed to explore the thermodynamic behavior of these systems. For example, the experimental challenges necessitated the development and implementation of the following in this work: (1) core/shell silica particles incorporating molecular fluorophores or semiconductor nanocrystals; (2) modification of silica particle surfaces; (3) the design of specialized sedimentation cells; and (4) the development of a novel fluorescent intensity-based approach to quantifying colloidal sediments. Analysis of the experimental data required the use of the following tools: (1) location of particle centers from images; (2) deconvolution of intensity profiles using a novel Monte Carlo-type algorithm; and (3) prediction of colloidal phase diagrams using perturbation theory. On the basis of this work’s experimental and simulation data, it is concluded that competing orientations of crystal grains may suppress crystallization at grain boundaries, resulting in a non-uniform depth of the fluid/solid transition. Also, it was demonstrated that the grain size in depletion crystals formed from quantum dot-coated silica particles can be increased by localized annealing with the confocal microscope’s laser. Additional findings include the ability of the intensity-based approach to measure interparticle forces in colloidal sediments, as well as the inability to use perturbation theory to predict two-dimensional colloidal fluid/solid transitions. While significant progress has been achieved, work on 3-D imaging of colloidal depletion crystals in a refractive index-match medium is ongoing. This work improves our understanding of 3-D colloidal crystallization at interfaces, as well as provides new tools for future research. Also, this work demonstrates a potential route for zone refining of colloidal crystals, a technique that may be important in the search for low-defect 3-D arrays that can be used as templates for photonic bandgap materials.

The purpose of this study was to characterize the micromechanical properties of various structural components in asphalt using Atomic Force Microscopy (AFM). The focus of the study was based on nano-indentation experiments performed within a micro-grid of asphalt phases in order to determine micromechanical properties such as stiffness, adhesion and elastic/plastic behavior. The change in microstructure and micromechanical behavior due to oxidative aging of the asphalt was also a primary focus of the study. The experiment was performed with careful consideration of AFM artifacts, which can occur due to factors such as geometry of the cantilever tip, hysteresis, filtering methods and acoustic vibrations. The materials used in this study included asphalts AAB, AAD and ABD from the Materials Reference Library (MRL) of the Strategic Highway Research Program (SHRP), chosen due to variations in crude source, chemical composition and elemental analysis for each asphalt type. The analysis of nano-indentation creep measurements corresponding to phase-separated regions ultimately revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging was found to induce substantial microstructural change within these domains, including variations in phase structure, phase properties and phase distribution. The form and extent of these changes, however, were different for each asphalt studied. Data analysis and information collected during this study were used for comparisons to existing models and asphalt data, which validated results and established correlations to earlier, related studies. From these comparisons, it was found that data parallels followed expected trends; furthermore, analogous interpretations and distinctions were made between results from this study and the micellar and microstructural models of asphalt. This study of micromechanical properties that govern asphalt behavior has yielded information essential to the advancement of hot mix asphalt (HMA) performance, including a new asphalt “weak zone” hypothesis and a foundation of data for implementation into new and existing asphalt models.

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Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 139-146)

Thesis (Ph. D.)--University of Chicago, Dept. of Molecular Genetics and Cell Biology, June 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Bacterial adhesion; ionic strength; polarity; lipopolysaccharides; heterogeneity; elasticity; FJC; steric interactions; AFM. Includes bibliographical references (p. 303-306).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.