Surface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. A quantitative measurement of the relative contributions of surface and grain boundary scattering to resistivity is very challenging, requiring not only the preparation of suitably small conductors having independent variation of the two relevant length scales, namely, the sample critical dimension and the grain size, but also independent experimental quantification of these two length scales. In most work to date the sample grain size has been either assumed equal to conductor dimension or measured for only a small number of grains. Thus, the quantification of the classical size effect still suffers from an uncertainty in the relative contributions of surface and grain boundary scattering. In this work, a quantitative analysis of both surface and grain boundary scattering in Cu thin films with independent variation of film thickness (27 nm to 158 nm) and grain size (35 nm to 425 nm) in samples prepared by sub-ambient temperature film deposition followed by annealing is reported. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with several scattering models that include the effects of surface and grain boundary scattering. Grain boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is also observed for surface scattering. Several of the published models for grain boundary and surface scattering are explored and the Matthiessen's rule combination of the Mayadas and Shatzkes' model of grain boundary scattering and Fuchs and Sondheimer's model of surface scattering resistivity contributions is found to be most appropriate. It is found that the experimental data are best described by a grain boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works, which is in part due to the careful quantitative microstructural characterization of samples performed. The data does suggest that there is a roughness dependence to the surface scattering, but this was not conclusively demonstrated. Voids and impurities were found to have negligible impact on the measured resistivities of the carefully prepared films.

In this work, a body of knowledge is presented which pertains to the growth, characterization and exploitation of high quality, novel II-IV oxide epitaxial films and structures grown by plasma-assisted molecular beam epitaxy. The two compounds of primary interest within this research are the ternary films NixMg1-xO and ZnxMg1-xO and the investigation focuses predominantly on the realization, assessment and implementation of these two oxides as optoelectronic materials. The functioning hypothesis for this largely experimental effort has been that these cubic ternary oxides can be exploited - and possibly even juxtaposed - to realize novel wide band gap optoelectronic technologies. The results of the research conducted presented herein overwhelmingly support this hypothesis in that they confirm the possibility to grow these films with sufficient quality by this technique, as conjectured. NixMg1-xO films with varying Nickel concentrations ranging from x = 0 to x = 1 have been grown on lattice matched MgO substrates (lattice mismatch ε < 0.01) and characterized structurally, morphologically, optically and electrically. Similarly, cubic ZnxMg1-xO films with Zinc concentrations ranging from x = 0 to x ≈ 0.53, as limited by phase segregation, have also been grown and characterized. Photoconductive devices have been designed and fabricated from these films and characterized. Successfully engineered films in both categories exhibit the desired deep ultraviolet photoresponse and therefore verify the hypothesis. While the culminating work of interest here focuses on the two compounds discussed above, the investigation has also involved the characterization or exploitation of related films including hexagonal phase ZnxMg1-xO, ZnO, CdxZn1-xO and hybrid structures based on these compounds used in conjunction with GaN. These works were critical precursors to the growth of cubic oxides, however, and are closely relevant. Viewed in its entirety, this document can therefore be considered a multifaceted interrogation of several novel oxide compounds and structures, both cubic and wurtzite in structure. The conclusions of the research can be stated succinctly as a quantifiably successful effort to validate the use of these compounds and structures for wide bandgap optoelectronic technologies.

High entropy alloys (HEAs) are made of at least five principal elements in near-equimolar proportions. The vast number of possible alloys and unconventional combinations of properties are the main benefits of HEAs. Ti, Nb, Cr, Al and N were chosen in order to create a hard, corrosion resistant coating with good thermal stability. TiNbCrAl multicomponent nitride thin films with Ti content between 0 to 14.4 at.% were deposited using multi-magnetron reactive high power impulse magnetron sputtering (R-HiPIMS) to investigate the feasibility of this method and to study how the Ti content affects the properties of the film. The samples deposited using reactive direct current magnetron sputtering (R-DCMS) were used as benchmarks. The settings required for near-equimolar composition were fixed, with Ti magnetron power as the only variable. Substrate was grounded and not intentionally heated. The composition of HiPIMS samples was more stable while the DCMS samples had significant fluctuations in Al and N content when varying the Ti target power, and were understoichiometric in nitrogen, (T iCrN bAl)1N1−δ, due to low degree of ionization of N. All crystalline samples had NaCl-type fcc structure. Crystalline DCMS samples were (111) textured, while the higher ionization characteristic for HiPIMS resulted in samples with competitive growth between two growth directions. The energetic particle bombardment caused the columnar structure of the film to be denser and less jagged, while DCMS samples containing Ti were significantly more porous. Denser, harder and stiffer films with significantly higher compressive stress were produced with HiPIMS. The hardness and stiffness were almost linearly dependent on Ti content, with density slightly decreasing as the Ti content increased. Higher Ti content increased the rate of corrosion of the films.

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24746号 / 情博第834号 / 新制||情||140(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 佐藤 高史, 教授 橋本 昌宜, 教授 新津 葵一 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Increasing water reuse opportunities for communities has become increasingly important as access to clean water is becoming more scarce. Reverse Osmosis (RO) is an advanced treatment technology used in water recycling wastewater for potable reuse applications. RO is a promising technology; however, the membranes have limitations including their high energy demand and their susceptibility to membrane fouling. The main objective of this study was to develop a reproducible method for the fabrication of RO membranes with enhanced flux and reduced susceptibility to fouling. Literature contains numerous publications on fabrication of thin film composite (TFC) RO membranes with high performance. However, the reports lacked all the details needed to fabricate a TFC RO membrane, making it difficult to replicate those published fabrication protocols. Based on the efforts of this study, the membrane fabrication procedures utilized did not yield the same quality and performance as reported in these articles. In this study, five TFC RO control membranes were replicated and compared. The membranes produced an average water flux of 21.9 ± 3.6 L/m2h (LMH) and an average salt rejection of 97.6% ± 2.0%. Based on these results, it was concluded that a reproducible fabrication technique was developed for fabricating consistent and reliable TFC RO membranes. Furthermore, this study investigated the role of fouling on TFC RO membrane performance. Enhancing membrane resistance to fouling helps maintain membrane selectivity, lifespan, and permeability. There has been an increasing interest in the modification of the RO membranes for enhanced hydrophilicity, which leads to improvements in fouling resistance. In this study, a positive and high charge density polymer, polyethylenimine (PEI), was introduced into the membrane matrix in varying layers of the membrane structure. PEI-1 was fabricated in-situ by grafting the PEI onto the polysulfone (PSf) support, while PEI-2 was fabricated via grafting of the PEI onto the membrane PA surface. The resulting membranes were characterized using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), and Goniometry. PEI-2 produced a more hydrophilic membrane when compared to PEI-1, however, PEI-1 performed better in terms of flux and selectivity. Multiple model foulants were used for investigating the modified membrane fouling performance. These model foulants were tested at varying concentrations, pH values, and with and without the presence of Ca2+ ions. The model foulants used were bovine serum albumin (BSA), sodium alginate, and humic acid. None of the model foulants resulted in a decrease in performance for the membrane over the duration of the tests (up to 13 hours). Future research is needed to develop a robust protocol for testing the fouling of the produced RO membranes within a reasonable timeframe.

Yes / In the pharmaceutical industry, enhanced process understanding resulting in superior control of product attributes, has the potential to save up to 20% of process engineering and product development costs during drug development. With the aim of achieving enhanced process understating, a novel approach for granulation of fine powders is presented. First, a mould with the desired particle shape and size is created using 3D printing followed by casting using elastomeric material. The formulation is prepared through wet massing and tested as a thin film on flat elastomeric membranes. The thin film itself can be a product but it also gives a good indication of coating performance before coating the patterned elastic membrane with the formulation i.e., 3D printed elastic mould granulation. Results show that following granulation and drying, granules of controlled size and shape (e.g. cubic and 500 μm), strength, friability and flowability can be formed. The method presented may allow for more robust process development in particle engineering. / Research Development Fund Publication Prize Award winner, December 2018.

This work focuses on understanding the buckling deformation mechanisms of bending, wrinkling, and folding that occur on the surfaces and interfaces of polymer systems. We gained fundamental insight into the formation mechanism of these buckled structures for thin glassy films placed on an elastomeric substrate. By taking advantage of geometric confinement, we demonstrated new strategies in controlling wrinkling morphologies. We were able to achieve surfaces with controlled patterned structures which will have a broad impact in optical, adhesive, microelectronics, and microfluidics applications. Wrinkles and strain localized features, such as delaminations and folds, are observed in many natural systems and are useful for a wide range of patterning applications. However, the transition from sinusoidal wrinkles to more complex strain localized structures is not well understood. We investigated the onset of wrinkling and strain localizations under uniaxial strain. We show that careful measurement of feature amplitude allowed not only the determination of wrinkle, fold, or delamination onset, but also allowed clear distinction between each feature. The folds observed in this experiment have an outward morphology from the surface in contrast to folds that form into the plane, as observed in a film floating on a liquid substrate. A critical strain map was constructed, where the critical strain was measured experimentally for wrinkling, folding, and delamination with varying film thickness and modulus. Wrinkle morphologies, i.e. amplitude and wavelength of wrinkles, affect properties such as electron transport in stretchable electronics and adhesion properties of smart surfaces. To gain an understanding of how the wrinkle morphology can be controlled, we introduced a geometrical confinement in the form of rigid boundaries. Upon straining, we found that wrinkles started near the rigid boundaries where maximum local strain occurred and propagated towards the middle as more global strain was applied. In contrast to homogeneous wrinkling with constant amplitude that is observed for an unconfined system, the wrinkling observed here had varying amplitude as a function of distance from the rigid boundaries. We demonstrated that the number of wrinkles can be tuned by controlling the distance between the rigid boundaries. Location of wrinkles was also controlled by introducing local stress distributions via patterning the elastomeric substrate. Two distinct wrinkled regions were achieved on a surface where the film is free-standing over a circular hole pattern and where the film is supported by the substrate. The hoe diameter and applied strain affected the wavelength and amplitude of the free-standing membrane. Using discontinuous dewetting, a one-step fabrication method was developed to selectively deposit a small volume of liquid in patterned microwells and encapsulate it with a polymeric film. The pull-out velocity, a velocity at which the sample is removed from a bath of liquid, was controlled to observe how encapsulation process is affected. The polymeric film was observed to wrinkle at low pull-out velocity due to no encapsulation of liquid; whereas the film bent at medium pull-out velocity due to capillary effect as the liquid evaporated through the film. To quantify the amount of liquid encapsulated, we mixed salt in water and measured the size of the deposited salt crystals. The salt crystal size, and hence the amount of liquid encapsulated, was controlled by varying either the encapsulation velocity or the size of the patterned microwells. In addition, we showed that the deposited salt crystals are protected by the laminated film until the film is removed, providing advantageous control for delivery and release. Yeast cells were also captured in the microwells to show the versatility. This encapsulation method is useful for wide range of applications, such as trapping single cells for biological studies, growing microcrystals for optical and magnetic applications, and single-use sensor technologies.

Thesis advisor: Ilija Zeljkovic / The splendid world of quantum materials is being unveiled in modern condensed matter physics, thanks to the advanced material synthesis methods, refined experimental probing techniques and deeper theoretical understanding. Unconventional superconductivity and topological phenomena are two of the main themes in this realm. Many outstanding problems are waiting to be solved and there is also a great potential in future technological applications. Among many routes of studying the quantum materials, creating thin film structures provides a special opportunity to learn the physical properties in low dimensions, to explore the effect of substrate and strain and to make novel electronic devices.In this thesis, I will present successful molecular beam epitaxy thin film synthesis of: (1) unconventional superconductor FeSe, (2) topological insulator Bi2Se3 doped with magnetic Fe atoms and (3) kagome structure magnets FeSn and Fe3Sn2. For (1), I will describe the finding of a dislocation network, its impact on the spatially-modulated strain field and its interesting interplay with the spontaneous symmetry-broken nematic phase. This is a new finding in the FeSe/SrTiO3 heterostructure and also provides fresh insights in the understandings of nematicity. For (2), I will show how we cross-check the doping ratio using different characterization techniques. Our observation indicates the possible formation of Fe clusters or impurity phases and sets the foundation for future synthesis of similar structures. For (3), I will demonstrate the novel selective synthesis of FexSny thin films. A plethora of spectral features were found in Fe3Sn2, implying a link with the Weyl physics. The FexSny thin films can potentially be a platform for the exploration of correlated, topological quantum phases in low dimensions. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

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