Browsing by Subject "thin film"

Now showing 1 - 4 of 4
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    Data for Surface Relief Terraces in Double Gyroid-Forming Polystyrene-block-Polylactide Thin Films
    (2023-09-28) Yang, Szu-Ming; Oh, Jinwoo; Magruder, Benjamin R; Kim, HeeJoong; Dorfman, Kevin D; Mahanthappa, Mahesh K; Ellison, Christopher J; cellison@umn.edu; Ellison, Christopher J; University of Minnesota Department of Chemical Engineering and Materials Science
    This study describes the thin film self-assembly behavior of a polystyrene-block-polylactide (SL-G) diblock copolymer, which undergoes melt self-assembly in bulk into a double gyroid (DG) network phase with a cubic unit cell parameter a = 52.7 nm. Scanning electron microscopy (SEM) and grazing-incidence small-angle X-ray scattering (GISAXS) reveal that thermally annealing 140–198 nm thick copolymer films on SiO2 substrates below the morphological order-to-disorder transition temperature yields polydomain DG structures, in which the (422) planes are oriented parallel to the surface. Bright-field optical microscopy (OM) and atomic force microscopy (AFM) analyses further reveal the film thickness-dependent formation of topographical terraces, including islands, holes, and bicontinuous features. The occurrence of these features sensitively depends on the incommensurability of the as-prepared film thickness and the (211)-interplanar spacing (d211) of the DG unit cell. While the steps heights between adjacent terraces exhibiting characteristic “double wave” patterns of the DG (422) planes coincide with d211, previously unreported transition zones between adjacent terraces are observed wherein “boomerang” and “droplet” patterns are observed. These intermediate patterns follow the expected sequence of adjacent termination planes of the bulk DG unit cell along the [211] direction, as confirmed by comparisons with self-consistent mean-field theory calculations.
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    Magnetization Dynamics in Thin Film and Multilayer Structures
    (2022-06) Peria, William
    Spintronics is a field of research that seeks to exploit the spin rather than the charge ofthe electron for information-technology applications, with the promise of computational devices that use less energy while being faster and more powerful. A major challenge in this field has been the understanding and control of how the energy contained in a system of electron spins is transferred, and ultimately lost, to the rest of the material. This thesis presents experimental measurements of magnetization damping using ferromagnetic resonance in a variety of different thin films and multilayer structures, along with unique ways of understanding the physical mechanisms that cause damping. First, the effect of an extrinsic two-magnon scattering mechanism on the magnetization damping is demonstrated in a series of Heusler alloy thin films. A model of two-magnon scattering is developed to fit the data, and particular emphasis is placed on the mechanisms which cause the effect to be stronger in the Heusler films. It is then shown how two-magnon scattering can shift the resonance frequency, an effect that is almost always neglected, which is important due to the ubiquity of using ferromagnetic resonance measurements to extract magnetic anisotropy energies. The following portion of the thesis deals primarily with magnon-phonon coupling and its effect on damping. A mechanism of magnetization damping due to magnon-phonon coupling is shown to dominate the overall damping in a series of Fe0.7Ga0.3 alloy thin films. The mechanism causes a giant anisotropy of the damping, with the damping coefficient varying by as much as a factor of 10 depending on the orientation of the magnetization. This mechanism is extrinsic, and so it is important to account for when measuring the intrinsic damping of a material. Finally, a phonon pumping mechanism is demonstrated in a series of Co/Pd multilayers. Phonon pumping causes a resonant damping of the magnetization dynamics, at a frequency that is determined by the total thickness of the multilayer. The temperature dependence is much stronger than expected, which underscores the importance of magnetic boundary conditions in the problem. There is also a resonance frequency shift that accompanies the resonant damping, which can be predicted accurately using linear response theory.
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    Modeling of Multicomponent Coatings
    (2023-05) Larsson, Christopher
    Thin liquid films play a central role in coating processes and other industrial and natural applications. Efficient optimization of these processes requires an understanding of capillary leveling, Marangoni flow, evaporation, and related phenomena. Although mathematical models are useful for gaining such understanding, it can be difficult to extract physical insight as the number of phenomena considered increases, so simplifying assumptions such as the vertical-averaging (VA) approximation for solute concentration are often employed. In the first part of this work, we examine the performance of the VA approximation for three common evaporation models: constant, one-sided, and diffusion-limited. We find that the formal regime of validity of the VA approximation is inaccurate and strongly depends on the evaporation rate. Furthermore, applying the VA approximation outside of its regime of validity results in drastically different film-height and solute-distribution predictions depending on the evaporation model. Many applications often demand multilayer films where each layer has distinct properties, and this gives rise to additional challenges. It has been experimentally demonstrated that two-layer films in which the layers are miscible can undergo dewetting, but theoretical understanding of this phenomenon is lacking. The second part of this work addresses the mechanisms that may initiate dewetting in miscible two-layer two-component films. It is found that a disparity in initial solute concentration between the film layers drives flows that lead to significant film-height nonuniformities. The third part of this talk focuses on evaporating sessile droplets which are critical to many industrial applications and are also ubiquitous in nature. Two predominant evaporation models have emerged in the literature, one-sided and diffusion-limited, with differing assumptions on the evaporation process. While both models are widely used and their predictions can differ greatly from each other, the physical mechanisms underlying these differences are not yet well understood. For the one-sided model, we derive expressions for the droplet lifetime, show that the evaporation rate is proportional to the droplet surface area, and demonstrate that the contact line is always warmer than the bulk of the droplet. Furthermore, we show that differences in the structure of the evaporation models near the contact line lead to qualitatively different behavior of the apparent contact angles and interface temperature profiles.
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    Nonthermal Plasma Synthesis of Silicon-Based Materials
    (2023-02) Eslamisaray, Mohammad Ali
    Nonthermal plasmas are finding increasing attention for the bottom-up synthesis of thin films, nanostructures, and nanoparticles that are difficult or impossible to produce with other fabrication techniques. The unique nonequilibrium environment provided in plasmas bypasses the thermodynamic constraints seen in other bottom-up approaches. Using a plasma-enhanced chemical vapor deposition (PECVD) process we synthesize thin films of hydrogenated amorphous silicon and silicon-germanium. The amorphous films then undergo a solid phase crystallization process to transform into a polycrystalline phase. The structural and transport properties of the films in both the amorphous and polycrystalline forms are studied and optimized for thermoelectric applications. We also utilize a nonthermal flowing plasma to produce highly monodisperse crystalline silicon particles. We present experimental evidence that during their growth in the plasma, particles become temporarily confined in an electrostatic trap until they grow to a critical size. Using this trapping mechanism, particles with controlled mean diameters between 60 to 214 nm are obtained. The results of this study contribute to our understanding of the mechanisms involved in the synthesis of silicon-based materials using nonthermal plasmas and provide a framework for designing more complex material systems.