This thesis research focuses on the characterization of thinfilms made of poly(vinylidene fluoride) (PVDF) using an atomic force microscope. Thinfilms of PVDF were fabricated by a spin coating method with different conditions and characterized using the Atomic Force Microscopy (AFM) for morphological changes. Phase and conformational changes of PVDF were investigated using both wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). From this analysis, in-situ corona poling with annealing of spin-cast PVDF enabled a phase change from α to the mixture of β and γ phases. This process can decrease the complexity of the conventional method which requires mechanical stretching before poling PVDF in addition to thermal annealing for β phase transformation. This thesis describes some materials and surface properties of solution-cast PVDF thinfilms with various conditions such as topography and phase image, adhesion force, friction force, and roughness. Through the AFM topography and phase images, polymeric behavior and spherulites are discussed in the later part of the thesis.

Recent progress in the field of semiconductor nanocrystals or Quantum Dots (QDs) has seen them find wider acceptance as a tool in biomedical research labs. As produced, high quality QDs synthesized by high temperature organometallic synthesis, are coated with a hydrophobic ligand. Therefore, they must be further processed to be soluble in water and made biocompatible. A process to coat the QDs with silk fibroin, a fibrous protein derived from the Bombyx mori silk worm, is described. Following the coating process, the characterization of size, optical properties and biocompatibility profile of these particle systems is described. In addition, conjugation of the silk fibroin coated QDs to different labeling proteins such as phalloidin and streptavidin is described. Proteins on the surface of ovarian cancer cells (HeyA8) and of cytoskeletal components participating in the formation of focal adhesion complex (FAC), such as F-actin in endothelial cells (HUVECS) were labeled using the bio-conjugated QDs. Various imaging techniques such as epi-fluorescence, TIRF and AFM were used to study the QD labeled cells. Overall the project has produced luminescent nanoprobes that enable the study of FAC formation dynamics and potentially a better in vivo fluorescent marker tool.

The high magnetoresistance is one of the most important properties that led the colossal magnetoresistance (CMR) materials been kept attention, however, because of the low phase transition temperature (Tp) and Curie temperature (TC) limits the application of the materials. The Tp could be influenced by many factors, as for the R1-xAxMnO3(R=rare earth element, A=alkaline metal, 0¡Õx¡Õ1) CMR materials, the selections of elements on R, A, and the ratio of x would make the difference. Besides these factors, when the film was grown on a substrate, the strain effect initiated at the substrate/film interface plays an essential role on the change of Tp and other physic properties. In other hand, the Sr element, existed in the SrTiO3(100) substrate, may also diffuse into the thin films during growth and alter the composition of the film and change its physic properties. In this thesis, we mainly focused on the modifying of the surface of substrates to prevent the diffusion problems. A wet chemical method was applied to modify the top layer of substrates such that the surface layer of the substrate is consisted of Ti-O layer only. By varying the high temperature annealing and etching processes, an optima processing condition was established.

A fundamental yet unresolved issue in cell biology is how force regulates actin dynamics and how this biophysical regulation is modulated by biochemical signaling molecules. Here we show, by atomic force microscopy (AFM) force-clamp experiments, that tensile force regulates the kinetics of G-actin/G-actin and G-actin/F-actin interactions by decelerating dissociation at low forces (catch bonds) and accelerating dissociation at high forces (slip bonds). The catch bonds can be structurally explained by force-induced formation of new interactions between actin subunits (Steered molecular dynamics (SMD) simulations performed by Dr. Jizhong Lou, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China). K113S mutation on yeast actin suppressed the actin catch-slip bonds, supporting the structural mechanism proposed by SMD simulations. Moreover, formin controlled by a RhoA-mediated auto-inhibitory module can serve as a "molecular switch", converting the catch-slip bonds to slip-only. These results imply anisotropic stability of the actin network in cells subjected to directional forces, possibly explaining force-induced cell and actin fiber alignment controlled by RhoA and formin. Our study suggests a molecular level crosstalk mechanism bridging the actin-mediated mechanotransduction and biochemical signal transduction pathways.

The incorporation of rare earth-V (RE-V) semimetallic nanoparticles embedded in III-V compound semiconductors is of great interest for applications in solid-state devices including multijunction tandem solar cells, thermoelectric devices, and fast photoconductors for terahertz radiation sources and receivers. With regard to those nanoparticle roles in device applications and material itself, electrical and thermal properties of embedded RE-V nanoparticles, including nanoscale morphology, electronic structure, and electrical and thermal conductivity of such nanoparticles are essential to be understood to engineer their properties to optimize their influence on device performance. To understand embedded RE-V semimetallic nanostructures in III-V compound semiconductors, nanoscale characterization tools are essential for analysis their properties incorporated in compound semiconductors. In this dissertation, we used atomic force microscopy (AFM) with other secondary detection tools to investigate nanoscale material properties of semimetallic RE-V and GaAs heterostructures, grown by molecular beam epitaxy. We used scanning capacitance microscopy and conductive AFM techniques to understand electronic and electrical properties of ErAs/GaAs heterostructures. For the electrical properties, this thesis investigates details of statistical analysis of scanning capacitance and local conductivity images contrast to provide insights into (i) nanoparticle structure at length scales smaller than the nominal spatial resolution of the scanned probe measurement, and (ii) both lateral and vertical nanoparticle morphology at nanometer to atomic length scales, and their influence on electrical conductivity. To understand thermal properties of ErAs nanoparticles, in-plane and cross-sectional plane of ErAs/GaAs superlattice structure were investigated with a scanning probe microscopy technique implemented with 3[omega] method for thermal measurement. By performing detailed numerical modeling of thermal transport between thermal probe tip and employed samples, and estimation of additional phonon scattering induced by ErAs nanoparticles, we could understand influences of ErAs nanoparticles on the host GaAs thermal conductivity. Investigation of ErAs semimetallic nanostructure embedded in GaAs matrix with scanned probe microscopy provided detailed understanding of their electronic, electrical and thermal properties. In addition, this dissertation also demonstrates that an atomic force microscope with secondary detection techniques is promising apparatus to understand and investigate intrinsic properties of nanostructure materials, nanoscale charge transports, when the system is combined with detailed modeling and simulations. / text

The giant protein titin is the third myofilament in the cardiac sarcomere. It is responsible for generating passive forces in stretched myocardium and maintaining sarcomere structure. The force generation properties of titin are determined by titin's elastic springlike elements, and this dissertation focuses on the determination of the physical properties of these springlike elements using atomic force microscopy. The primary project of this dissertation investigates the link between a single point mutation in one of titin's subdomains and arrhythmogenic cardiomyopathy.

The aim of present work was to study corrosion properties of magnetron sputtered Mg–Al alloys and characterize semiconductor properties of the surface layers developed during corrosion. Atomic force microscopy (AFM) demonstrated that sputtered alloys had a smaller grain size and a smoother surface. Corrosion and electrochemical behaviour of the alloys was studied in 0,1M (NH4)3BO3 + 0,1M NaCl (pH = 8,4) solution. Sputtered films of Al-Mg and Al had a superior resistance to pitting corrosion when compared to cast counterparts. The corrosion resistance of sputtered samples increased with decrease in Mg content. The Mott – Schottky plots of Al-Mg and pure Al electrodes showed a linear relationship between modified capacitance (C-2) on applied potential. It was concluded n – type semiconductivity for the layers on Al and p – type for Al-Mg alloys.

Current research interest in multi-scale modeling of cement paste requires accurate characterization of the time-dependent mechanical properties of the material, particularly the C-S-H phase. Nanoindentation is evaluated as a tool for measuring both the instantaneous and the short-term viscoelastic properties of cement paste. Atomic force microscopy (AFM) based indentation is compared to conventional nanoindentaion in measuring mechanical properties of cement pastes. Time-dependent solutions are derived to characterize creep indentation tests performed on hardened cement paste and to extract the time-dependent properties. The effect of approximating C-S-H viscoelastic properties with a time-independent Poisson's ratio is discussed, and arguments for utilizing a time-independent Poisson's ratio for short-term response are presented. In evaluating AFM as a mechanical characterization tool, various analytical and numerical modeling approaches are compared. The disparities between the numerical self-consistent approach and analytical solutions are determined and reported. The measured elastic Young's modulus values acquired by AFM indentation tests are compared to Young's modulus values from nanoindentation measurements from cement paste. These results show that the calcium silicate hydrate (C-S-H) phase of hydrated portland cement has different properties on the nanometric scale than on the micron scale. Packing density of C-S-H particles is proposed as an explanation for the disparity in the measured results. The AFM measured uniaxial viscoelastic compliance values are compared to similar values obtained with traditional nanoindentation for the same material. The comparison of these results shows that the calcium silicate hydrate (C-S-H) phase of portland cement has similar but distinct properties on the sub micron scale than on the micron scale. Additionally, the effect of moisture is evaluated by controlling the relative humidity (RH) of the testing environment between 40% and 100% plus, or wet. The viscoelastic compliance appears to be highest at 40% RH and the material appears to be less compliant at higher relative humidity levels. Possible mechanisms controlling the viscoelastic deformation are presented and evaluated in conjunction with the moisture related poromechanical effect.

The overall objective of this PhD thesis research is to characterize, understand and ultimately control phase-separated structures in mixed films consisting of a perfluorinated fatty acid and a photopolymerizable surfactant. In these systems, film morphology, mechanical properties and spectroscopic properties are inter-related and this thesis explores these relationships. In this context the interaction between perfluorotetradecanoic acid (C13F27COOH, referred to as PF in this dissertation), and 10,12-pentacosadynoic acid (CH3(CH2)11−C≡C−C≡C−(CH2)8COOH, referred to as PCDA in this dissertation) has been studied in monolayers using a combination of surface and spectroscopic characterization techniques. To investigate the inter-relationship of the properties described above, film behavior under a variety of conditions, including behavior at different interfaces (solid-liquid, air-liquid), different film compositions and under different conditions of photoillumination and mechanical stress were explored. Thermodynamic and morphological studies of mixed monolayer surfactant films of PF and the photo-polymerizable diacetylene molecule, PCDA, were carried out. The films were prepared at the air-water interface and transferred onto solid supports such as a glass slides via Langmuir-Blodgett (LB) deposition technique. The presence of the perfluoroacid helped to stabilize the diacetylene surfactant monolayer in comparison with the diacetylene alone, allowing film transfer onto solid substrates without needing to add cations to the sub-phase or photo-polymerize the components prior to deposition. Addition of the perfluorocarbon to PCDA resulted in films with the photopolymer strands oriented perpendicular to the direction of the film compression in a Langmuir trough. This is in contrast with film structures formed from pure PCDA. Formation of these features could be explained by a two-step process that happened sequentially: first, the compression of monolayer with trough barriers while trying to maintain the surface pressure constant induces stress on the film surface; second, additional film buckling which was enhanced by the strong cohesion between PF and PCDA. Film compression data, supported by in situ fluorescence spectrophotometry, Brewster angle microscope imaging and atomic force microscope images of deposited films, supported this mechanism. Factors that controlled the orientation of the photopolymer fibers were also investigated. Fibers were found to consist of multiple strands, with each strand having a different orientation. Our investigation also revealed there was a preferred orientation for fibers in the film as a whole. The angle of approximately 60o to the direction of film compression during deposition from a Langmuir trough has been calculated with the help of dual-view, polarized fluorescence microscopy. This orientation was attributed to the mechanical stress exerted by the trough compression barriers coupled with rotation of the polymer fibers during film draining. The combination of Atomic Force Microscope (AFM) and fluorescence microscopy (FM) provided a thorough and comprehensive mapping of fundamental properties of mixed monolayer system, and enabled a quantitative determination of the degree of selectivity of the polymerization process.

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