Browsing by Subject "multilayer"

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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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    Transport in Superconducting/Ferromagnetic Heterostructures
    (2019-07) Moen, Evan
    In this thesis I present my research on spin and charge transport in ferromagnet, superconductor (F=S) heterostructures using a self-consistent, clean limit theory. The goal is to characterize realistic samples. The primary focus is on the F1=N=F2=S superconducting spin valve. I also consider the S1=F1=N=F2=S2 ferromagnetic Josephson structures. We solve the Bogoliubov deGennes equations (BdG) using a self-consistent, numerical approach and determine the thermodynamic quantities such as the pair potential. For the charge transport, we use the Blonder-Tinhkam-Kapwijk (BTK) method to determine the conductance G. We study the conductance features and their dependence on the physical parameters such as the layer thicknesses and interfacial quality of the sample. The main results are the dependence of G on the misalignment angle of the magnetizations in F2 relative to F1, which constitutes a 'valve eect'. The valve eect in F=S structures is due to the proximity eect, which is angularly dependent. The critical bias (CB), equal to the gap energy, is non-monotonic with due to this proximity eect. The conductance features are split for incoming spin-up and spin-down electrons, which leads to a subgap (below CB) peak in the total conductance. This subgap peak is dependent on the intermediate F2 layer thickness and ferromagnetic exchange eld h in which the peak position oscillates between zero bias and the CB with a periodicity of =h. These subgap peaks are resistant to high interfacial barriers and lead to a monotonic angular dependence on in the peak maxima. In the S1=F1=N=F2=S2 quasiparticle conductance, there are multiple subgap peaks with similar oscillations in the peak positions. In addition, the conductance peak position oscillates with by a quarter phase between the parallel and antiparallel conguration. We also study the spin transport in the F1=N=F2=S system for realistic parameters. The spin transport quantities are not conserved due to the spin transfer torque (STT) within the ferromagnetic layers, and are spatially dependent. There exists a critical bias feature in which no spin current penetrates the S layer for biases below the CB, and the STT becomes quasilinear for biases above the critical bias.