Polymers, by virtue of their chemical composition and molecular architecture, exhibit a diverse range of microstructural features and properties. As thin films, due primarily to effects associated with confinement and interfacial interactions, their properties may be film-thickness dependent. The significance of their thicknessdependent behavior is underscored by the fact that polymer films are of technological interest in areas that include, sensors, catalysts and organic electronics. One challenge associated with the use of thin film polymers is to understand the role of confinement and interfacial interactions on thermally induced transitions, such as vitrification and various morphological transitions. To this end, the work presented in this dissertation focuses on the behavior of thermally induced transitions in two thin film polymer-based systems: (1) an A-b-B diblock copolymer which can undergo a disorder-to-order transitions (ODT), wherein the ordered state exhibits varying geometrical symmetries, depending on the relative volume fractions of the A and B components; (2) an amorphous polymer filled with particles of nanoscale dimensions. The first of three problems examined is the influence of supercritical carbon dioxide (scCO₂) on the order-disorder transition of thin film symmetric A-b-B diblock copolymer systems. We show that the transition (xN)ODT, where x is the energetic A-B Flory-Huggins interaction parameter and N is the total degree of polymerization of the copolymer, of the thin film decreased ~ 20% compared to the bulk; the decrease was more significant in scCO₂ environments. The decrease of (xN)ODT in scCO₂ is contrary to observations in bulk copolymer-scCO₂ systems where the effective A-B interactions are weaker, hence the condition for the transition increases to higher (xN)ODT values. With regard to the second problem, we show for the first time experimentally that nanoparticles induced order into thin films of a symmetric A-b-B diblock copolymer at temperatures below the bulk ODT. Finally, we examine the influence of polystyrene (PS) grafted nanoparticles on the glass transition of PS films of varying molecular weight and thickness. We demonstrate that by controlling spatial distribution of nanoparticles, through driving forces of entropic origin, the glass transition temperature of the film can be changed drastically, as much as tens of degrees.

This dissertation explores magnetic-field- and electric-current-driven domain-wall motion in thin-film-based magnetic microstructures. Conventional thin-film growth and microstructure fabrication techniques including electron-beam lithography and focused ion beam milling are used to fabricate nanometer-scale one-dimensional and two-dimensional magnetic structures that support magnetic domains (regions of different magnetization orientation separated by domain walls). A high-spatial resolution, hightemporal resolution technique for measuring the field- or current- driven dynamics of the domain walls, based on the magneto-optic Kerr effect, is developed and used to study the wall dynamics. Field-driven domain-wall motion at slow magnetic field sweep rates is dominated by Barkhausen jumps, the discontinuous random movement of domain-wall displacements. The experiments described represent one of the first successful attempts to extend the study of Barkhausen effects into the two-dimensional region. The experiments successfully probe velocity distributions, jump amplitude distributions, and attempt to address issues that pertain to the universal exponents that describe the scaling behavior of Barkhausen jump distribution function including effects of dimensionality and sweep-rate effects on the exponents. A novel dual-beam magneto-optical experiment is performed on thin-film microstructure that probes negative Barkhausen jumps (jumps that oppose the direction favored by Zeeman energy driving the magnetic reversal). A new mechanism for negative Barkhausen jumps is proposed that accounts for the observed effects. Domain-wall motion driven by (spin-polarized) electric current is studied in nanoscale thin-film based wires. The experiments address issues pertaining to the basic mechanisms responsible for current-driven domain-wall motion, which are believed to be the adiabatic spin-torque mechanism and non-adiabatic mechanisms. The experiments described are the first true time-resolved measurements of current-driven displacements, and the results reveal new information about the stochastic properties of current-driven domain wall displacements. The results also provide information on domain-wall velocities and spin-flip efficiencies that address issues related to spin-torque mechanisms.

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Two-photon optical bistability in commercial thin-film interference filters with ZnS and ZnSe spacers is observed with switching times ≳ 200 μs. The accompanying drifting of the bistability loop in time and laser-induced "damage" indicate a thermal mechanism. The problem of water vapor absorption in such filters must be addressed before the inherent potential and advantages of these devices in two-dimensional image processing applications can be realized. Trans- verse effects in GaAs superlattice etalons are observed which cannot be explained on the basis of a plane-wave analysis. The optical nonlinearity in GaAs and diffraction combine to produce drastic effects on the measured beam profiles and bistable loops, due to an intensity-dependent virtual focus. Lastly, the first observation of optical bistability due to a biexcitonic nonlinearity in CuCl etalons is reported with detector-limited switching times of 600 ps. In addition, lasing action along the pump axis in a cavity defined by the end mirrors is observed in a very thin (2.0 μm) CuCl etalon. The lasing transition is unique in that it involves the creation of a virtual excitation of biexcitons which decay to the longitudinal exciton state.

Nearly all the deficiencies of conventional vacuum evaporated coatings trace to a single physical property of condensed films: low packing density. One way to increase packing density is to bombard the growing film with ions during deposition, called ion-assisted deposition (IAD). The beginning chapters of this dissertation analyze IAD as a perturbation of the conventional vacuum evaporation process. The experimental chapters begin with an examination of the effect on moisture penetration behavior of oxygen-ion bombarding completed optical filters. Moisture adsorption and desorption is retarded after bombardment in filters composed of titania and silica, but not in those of zirconia and silica. Bombardment evidently induces a crystalline-to-amorphous transition in titania, causing the surface to swell and occluding the pores. The transition in zirconia is the reverse, and no impediment to moisture appears. Argon-ion-assisted magnesium fluoride (MgF₂) can show ultraviolet (UV) absorption. The primary mechanism is probably the formation of F-centers (single fluorine-ion vacancies), although an unsaturated oxygen bond may also be responsible. Absorption can be removed by baking and often by irradiation with UV. After baking, fluorine is lost and replaced by oxygen. Absorption-free MgF₂ films can be deposited by minimizing the substrate temperature and bombardment flux. Ion-assisted films contain up to 2% argon and up to 170 parts-per-million of tungsten from the ion gun filaments. They show a slightly higher refractive index, are much less porous, and are much more resistant to damage by abrasion and exposure to fluorine gas. Ion-assisted aluminum oxide (alumina, Al₂O₃) films show a small increase in UV absorption after argon-ion bombardment; however, a mixture of argon and oxygen ions avoids the problem. Excess oxygen is often incorporated into alumina films, and depresses both the mass density and the refractive index. IAD increases refractive index and decreases porosity. Ion-assisted alumina films are somewhat more stable in humid environments. Ion-assisted deposition has been shown by this study to cause substantial improvements in many of the physical and some of the optical and chemical properties of evaporated magnesium fluoride and aluminum oxide films.

No description available.

This research effort investigated the influence of confinement on the physical aging behavior of thin and ultrathin glassy polymer membranes. Membrane permeability changes with time due to physical aging, and for reasons not completely understood, the rate of permeability change can become orders of magnitude faster in films thinner than one micron. Special experimental techniques were developed to enable the study of free standing, ultrathin glassy polymer films using gas permeability measurements. The gas transport properties and physical aging behavior of free-standing glassy polysulfone (PSF) and Matrimid® films from 18-550 nm thick are presented. Physical aging persists in glassy films approaching the length scale of individual polymer coils. The membranes exhibited significant reductions in gas permeability and increases in selectivity with aging time. Additionally, the influence of physical aging on the free volume profile in thin PSF films was investigated using variable energy positron annihilation lifetimespectroscopy (PALS). The films exhibited decreasing o-Ps lifetime during physical aging, while o-Ps intensity remained constant. The o-Ps lifetime was reduced at lower implantation energies, indicating smaller free volume elements near the film surface. Thin films aged dramatically faster than bulk PSF and the PALS results agree favorably to behavior tracked by gas permeability measurements. The physical aging behavior of ultrathin films with different previous histories was also studied. The state of these materials was modulated by various conditioning treatments. Regardless of the previous history, the nature of the aging response was consistent with the aging behavior of an untreated film that was freshly quenched from above Tg, i.e., permeability decreased and pure gas selectivity increased with aging time. However, the extent of aging-induced changes in transport properties of these materials depended strongly on previous history. The properties of these ultrathin films deviate dramatically from bulk behavior, and the nature of these deviations is consistent with enhanced mobility and reduced Tg in ultrathin films, which allows them to reach a lower free volume state more quickly than bulk material. The Struik physical aging model was extended to account for the influence of film thickness on aging, and was shown to accurately describe the experimental data. / text

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published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy