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<p dir="ltr">Thin film materials are used in many areas of our daily lives. From memory storage chips to optical coatings, these thin films are essential to the technologies on which we rely. Multiferroic thin films, a group of materials that simultaneously exhibit ferromagnetism and ferroelectricity, are of particular interest because of the new opportunities that they enable in memory storage and sensors. Bismuth-based oxide materials have proven to be excellent candidates for these applications, with multiferroic properties and anisotropic structures. This novel self-assembled structure found in layered supercell systems has applications in optical devices, such as isolators and beamsplitters. Throughout this study, thin film strain and epitaxy must be tended to as the fundamentals of film growth, adding to the complexity of these challenges.</p><p dir="ltr">In this dissertation, bismuth-based oxides, and more specifically the Bi₃Fe₂Mn₂O_x (BFMO) layered supercell phase, are studied from three perspectives. First, BFMO is integrated onto silicon substrates for commercialization using a complex buffer layer stack to mediate the differences in the crystal lattice. This allows for a demonstration of device fabrication with this film. Second, the growth and impact of strain are examined through geometric phase analysis, discovering that strain is essential for the growth of the supercell phase in BFMO. This strain can be tuned through buffer layer addition to optimize the growth of this phase. Third, two methods are demonstrated to free the BFMO material from the typical film-substrate lattice matching requirements. The process of transferring the film from the original substrate onto a different substrate removes these restrictions, allowing virtually unlimited access to applications that were previously not possible. The two methods demonstrate different solutions to the specific challenges of transferring the highly strained BFMO thin film. These findings pave a practical way to integrate multiferroic layered oxide thin films onto chips for the next generation of devices.</p>

Master of Science / Department of Chemistry / Daniel A. Higgins / Single molecule tracking (SMT) measurements have been applied to the study of molecular mobility in sol-gel-derived silica gradient films in this thesis. Such gradient films have broad potential applications in controlled adhesion and transport of cells, vesicles and polymers; separation of complex chemical mixtures and in the development of new catalysts. Silica films were prepared by “infusion-withdrawal dip-coating”. In this method, a suitable substrate is slowly withdrawn from a silica sol of time varying composition. The deposition reservoir is initially filled with a sol derived from one silica precursor (tetramethoxysilane). A second sol, prepared from a different precursor (methyltrimethoxysilane), is then infused into the deposition reservoir, as the mixed sol is withdrawn. Films thus prepared were initially characterized by bulk fluorescence spectroscopy, infrared (IR) microscopy, contact angle goniometry, spectroscopic ellipsometry and surface profilometry. The fluorescence, IR and contact angle data all demonstrate the presence of a gradient in the methyl content of the silica film. The primary objective of the work performed under this thesis was to investigate the diffusion of Nile Red molecules in and on these films, as a function of position along the gradient, by SMT methods. Histograms of the mean-square displacement of the molecules depict the presence of at least two distinct populations: one incorporating fixed (entrapped or adsorbed) molecules and the other clearly reflecting the presence of mobile molecules. The latter population was observed to vary along the gradient dimension and also changed as the films aged over the course of five days. Molecular mobility is attributed to the presence of liquid-like silica oligomers in the films. Spatial variations in the observed mobility are tentatively assigned to variations in oligomer viscosity along the gradient. Film viscosity also changes as the polymerization of the oligomers continues during film aging.

With technology scaling, the amount of transistors on a single chip doubles itself every 18 months giving rise to increased power density levels. This has directly lead to a rapid increase of thermal induced issues on a chip and effective methodologies of removing the heat from the system has become the order of the day. Thermoelectric (TE) devices have shown promise for on-demand cooling of ICs. However, the additional energy required for cooling remains a challenge for the successful deployment of these devices. This thesis presents a closed loop control system that dynamically switches a TE module between Peltier and Seebeck modes depending on chip temperature. The autonomous system harvests energy during regular operation and uses the harvested energy to cool during high power operation. The system is demonstrated using a commercial thin-film TE device, an integrated boost regulator and few off chip components. The feasibility of the integration of the TEM and the automated mode switching within the microprocessor package is also evaluated. With continuous usage of thermoelectric modules, it starts to degrade over time due to thermal and mechanical induced stress which in turn reduces the cooling performance over time. Impact of thermal cycling on thermoelectric cooling performance over time is evaluated using the developed full chip package model.

The bio-enabled syntheses of functional nano-structured metal oxide thin films is of importance for a range of applications, in photonics, electronics, sensing, cell engineering, and biochemical devices. This type of novel syntheses method can overcome problems common in conventional oxide processing. In general, conventional oxide processes often require thermal treatment, caustic chemicals, and mechanical processing when producing shape-controlled inorganic materials. In contrast, biological processes are usually carried out under mild conditions (low temperature, neutral pH, and atmospheric pressure) and are therefore promising for the development of benign processes. Functional materials synthesized at room temperature using biomolecules are promising due to their expediency. During recent years, significant discoveries and progress have been made in discovering, and finding new applications for such biomimetic oxide-based minerals. However, much of the research has focused on SiO- and TiO-bearing organic-inorganic hybrid materials, of which a significant limitation is that, there are relatively few water-soluble inorganic oxide precursors commercially available for such biological syntheses. Two common compounds that are used in the biomimetic syntheses of SiO₂ and TiO₂ are tetramethoxisilane (TMOS) and Ti(IV) -bis(ammonium lactato) dihydroxide ( TiBALDH ). As a result, approaches to synthesize new water-soluble transitional metal complexes for use as precursors in the biomineralization of the corresponding functional metal oxide thin films were explored in this work, in order to expand the range of functional oxide chemistries formed via bio-enabled methods. A Ti-containing compound was synthesized to compare the behavior of commercially-available and as-synthesized TiBALDH. Another titanium-containing complex with citrate ligands, instead of lactate, was also synthesized to investigate the influence of the ligand type on the deposition behavior of the precursors. Zirconium- and hafnium-containing complexes were also synthesized to demonstrate the feasibility and versatility of the idea of applying bio-enabled syntheses to the fabrication of functional mineral oxides other than the reported SiO₂ and TiO₂. The second part of this thesis focuses on developing a novel way to fabricate porous functional mineral oxide thin films with controlled pore size, which can be used in a variety of applications, such as dye loading for optical, photochemical, or electrochemical purposes. Commercially-available, carboxyl-group-terminated polystyrene spheres of different sizes were utilized as pore-size controllers in the bio-enabled syntheses of TiO₂ by protamine. This approach has been found to be an effective means of creating uniform pores in inorganic mineral oxide coatings. The accomplishments of this work have the potential to be integrated so as to expand the boundaries of biomineralization in materials science and engineering fields.

The huge environmental awareness emerging last years by reason of global warming and greenhouse effect, on one hand, and the need of finding other sources of energy production and conversion due to the declining of fossil resources and the increasing cost of this kind of energy resource, on the other hand, both have led position renewable energies as a powerful alternative on the energy production and conversion. PV-systems have emerged at an exponential rate in recent year as the main candidate and a satisfactory possibility with respect to environmental and economic sustainability. Nowadays, the large volume on photovoltaic market is currently dominated by four types of solar cells, divided by the semiconductor material used to absorb light and convert the energy into electricity: (1) crystalline silicon (monocrystalline and polycrystalline), (2) amorphous silicon, (3) CIGS and (4) cadmium telluride; and among them, monocrystalline silicon and CIGS technologies are installed on the building 45 of the University of Gävle, at the south face of the laboratory. In this context and with the motivation to contribute knowledge on PV field, a comparison between single crystal solar technology and thin film CIGS technology has carried out through f ratio and performance ratio procedures in order to perform an assessment of the energy conversion of each one under field conditions. A logger monitors the power conversion from the PV modules since June 2014 while two pyranometers monitor global and diffuse solar radiation since March 2016. It must take into account that only clear sunny days have been considered during a period from 8:00 to 14:00 in order to avoid shadows effect on the PV systems. The results come to conclude that single crystal silicon modules present a better behavior with respect to energy conversion under no shadows effect conditions by two reason: (1) f ratio, relationship of PV conversion per kW (PV yield) between CIGS and single crystal silicon, is about 87.25% with some variations along a day due to ambient temperature, cell temperature and incidence angle; (2) PV module's performance ratio of monocrystalline silicon modules is higher than thin film CIGS ones during a sunny day about 87.56% and 76.38%, respectively; and they are consistent with usual performance ratio values between 80% and 90% since 2010 onwards. In light of the outcome and in order to confirm these conclusions, it intends to launch a project with the objective of evaluating the data collected and compare the performance of the module after a year of measurements outdoors by the PV module's performance ratio procedure. Along the same lines, the next step of the University of Gävle will be to launch a project with the objective of evaluating the potential to be self-sufficient.

This thesis investigates lead oxides as photovoltaic materials. Vacuum deposition methods and ex-situ annealing are used to produce different stoichiometries of lead oxide. The relationship between structure and the optoelectronic properties is then investigated. Following this, a number of photovoltaic devices are prototyped and a Kelvin probe used to determine and understand the band structure of devices. Thin films of PbO produced via air annealing of thermally evaporated lead consist of a mixture of two phases, orthorhombic and tetragonal, that determine the materials properties and effectiveness as absorber layer in a Schottky device. Films of higher tetragonal content are more photoactive, showing lower series resistance. Kelvin probe reveals that with an increasing work function of the PbO with increasing duration of the annealing, the Schottky barrier between PbO and Al increases, which results in a higher VOC. This trend is inverted when the Fermi level of PbO drops below that of ITO, creating an opposing junction. Reactively sputtered PbO2 films are highly conductive degenerate semiconductors. Increasing oxygen flow rate during deposition leads to increased resistivity and decreased mobility, resulting from a decrease in grain size. Alongside this an increase in carrier concentration is observed as the material gets less ordered at higher oxygen flow rates, which results in an increase in Fermi level. Due to its high conductivity the material is not photoactive, and the high work function between -5.6 and -5.8 eV does not allow the formation of a Schottky junction or a p-n junction with the evaporated p- type PbO. Post deposition annealing of the sputtered films leads to the formation of the more resistive Pb3O4 phase. This material shows lower carrier concentration and mobility, however, work functions are similarly high. The changes induced by the heat treatment are not substantial enough to be able to create a junction between the as-deposited and the annealed material, as is revealed by Kelvin probe and Hall Effect measurements. Heterojunctions between P3HT and Pb3O4 were made to test predictions made by KP measurements. A heat treatment on P3HT improved its electronic properties and raised the Fermi level, resulting in the transformation of a diode in to a photovoltaic device and a decrease in dark current.

Properties of polymers in thin films are distinct from those in the bulk due to the significant effects of free or substrate surfaces. The presence of a free surface allows an increased mobility of polymer chains in the near surface region, therefore, a lower glass transition temperature (T_g). With this lower surface T_g, a surface-specific crystallization phenomenon occurring at temperatures much lower than the bulk crystallization temperature (T_c) in polymers including PET, PEN and PVOH has previously been observed. However, whether or not this surface-specific crystallization is a phenomenon observable in all crystallizable polymers is still a question. Similarly, due to this greater mobility, phase separation may also be able to take place in the near-surface region of a polymer blend at a temperature much lower than the bulk phase separation temperature. Yet, no such investigation on polymer blends has been carried out. In addition, it is interesting to study the thin-film behaviours of a block copolymer that undergoes both phase separation and crystallization and compare these with corresponding bulk behaviour. In this thesis, the thin-film crystallization behaviour of polyamide 12 (PA12) in spin-cast films is presented together with some investigation of crystallization of polyamide 6 (PA6) and polystyrene. Polystyrene and poly(methyl methacrylate) (PS/PMMA) systems are used to illustrate the phase behaviours specific to the near-surface region. Finally, the microstructural evolution in high hard block content thermoplastic polyurethane (TPU) thin films on annealing has also been investigated. These TPUs have hard segments (HS) extended by 2 methyl 1,3 propanediol (2M13PD) or 1,5 pentanediol (15PD). With its flexible chains, PA12 crystallizes during spin coating forming as-spin-cast crystals with morphology that varies with solvent evaporation rate and film thickness. Despite the as spin-cast crystals, the free surface allows secondary surface crystallization of PA12 at an annealing temperature (T_a) roughly 20&deg;C below the bulk T_c. The secondary surface crystals were indicated to exist in the most stable crystalline phase of PA12. Similar secondary surface crystallization has also been observed in the PA6 films but at a higher T_a due to the higher T_g of PA6. In addition, surface-specific crystals have been observed in PS (semicrystalline, likely due to some stereoregularity of composition), a polymer with bulky side groups. The PS surface crystals are, however, flat-on oriented showing the important effect of side groups on the morphology or growth shape of surface crystals. The discovery of these surface crystals supports the universality of surface specific crystallization. Using fast solvent quenching, it is possible to "freeze in" a structure containing both PS and PMMA in the near surface region. On annealing, surface-specific phase behaviours (observable as pits, undulations and aggregations) confined to the near-surface region take place first at temperatures around or just below the bulk polymer T_g, while bulk vertical phase separation and dewetting of PS to PMMA, forming holes, network structures and islands, occur at temperatures well above T_g. This surface specific phenomenon, being a result of the free surface, should be applicable to other phase separation systems with a free surface as well. An increase in the crystallinity of PS was found to promote the phase separation process, but the free surface effect is independent of the interplay between the crystallization and phase separation. Rather than having a two-phase morphology, as was previously observed in melt-quenched bulk samples, 2M13PD extended TPU spin-cast films showed a single-phase morphology as-spin-cast. However, the HS ordering, the formation of mesophase, the melting of HS ordered regions, and microphase mixing observed in thin films are consistent with the bulk results but with slightly different transition temperatures due to spatial confinement. With a more flexible chain extender, e.g. 15PD, the hard and soft phase separation is more limited. The thin film investigations have allowed a better understanding of the microstructural evolution in these high hard block content TPUs on annealing by imaging the morphology directly. A thin-film specific phenomenon: formation of large multilayer flat-on crystals, was also observed in these TPU thin films. These crystals are initially developed from preformed aggregations and are believed to be induced by the significant substrate effect in thin films and the free surface effect.

Hybridizing, in general, is the approach of combining multiple technologies, materials, or designs such to mitigate the drawbacks and enhance the benefits. The result of this combination can be referred to as a hybrid. The projects described in this work concern a number of these hybrids. The collection of projects are limited to optical applications, but are otherwise enormously different. There is perhaps no better way to illustrate this breadth than their characteristic length-scale. That is, the general size of the elements being hybridized. Ten orders of magnitude lie between the smallest system described and largest systems. At the several-nanometer scale, a single component of a composite optical material. Diamond possesses a unique combination of refractive and dispersive optical properties, making it an attractive optical material. Unfortunately, the lowest cost diamond available possesses large amounts of impurities and color. In an attempt to remove the visible color from commercially available detonation-origin nanodiamond powders we developed a facile three-step cleaning process. This process and the resulting qualities of the nanodiamond are discussed. At tens to hundreds of nanometers scale, we have worked to optimize a complete composite material system; a combination of Polystyrene-b-poly (2-vinyl pyridine) (PS-b-P2VP), a block co-polymer with self-assembly properties, and controlled size iron platinum (FePt) nanoparticles. The applications in mind are magnetic field sensors, used in medical testing and physical experiments, and fiber optic isolators, used extensively in telecommunications networks. These composites exhibited commercially significant Verdet constants in room temperature Faraday rotation measurements, and possess processing benefits over the current state-of-the-art magneto-optically active materials. Several behaviors with respect to wavelength, particle loading, and primary particle size are discussed. At the micron to centimeter scale, we have designed and characterized a high-speed fiber-optic switch for telecommunications networks capable of reconfiguring 100 times faster than currently available technologies with comparable port counts. The switch is an unconventional hybrid of the micron-scale optics of single-mode fiber modes, and the centimeter scale of free-space holography. Built primarily using off-the-shelf components and a commercially available digital micro-mirror device (DMD), the switch is protocol and bit-rate agnostic, robust against random mirror failure, and provides the basic building block for a fully reconfigurable optical add drop multiplexer (ROADM).Finally, at the scale of several meters, we address a system that hybridizes two established methods for harvesting solar energy. Sunlight can be captured as electricity using photovoltaics (PV), as well as heat, often called concentrated solar power (CSP). Each approach has benefits and drawbacks which will be discussed. A system possessing the peak efficiency of PV, with the deployable storage of CSP, would most effectively meet demand around the clock. In order to combine these technologies, we have developed an approach for designing a dichroic coating to optimize performance of such a system utilizing multi-junction photovoltaic cells while diverting unused light to heat collection. Through careful design substantial improvement to system efficiencies are shown to be possible.