Spectroscopic ellipsometry is a nondestructive, ambient surface analysis technique for studying surfaces, interfaces and thin films. To take advantage of this method an automatic spectroscopic ellipsometer was designed and constructed for the microstructural characterization of thin films. This high precision instrument is capable of measuring in real-time the optical properties of bulk or thin film materials over the visible-UV region (1.5 - 6.0 eV). The microstructure of thin films can be determined from an effective medium theory analysis of the spectroellipsometric data to investigate how the film morphology evolves with varying preparation conditions and to determine the optimum deposition parameters. In this thesis the pseudodielectric function of palladium films prepared by dc planar magnetron sputtering was measured while the substrate temperature, argon partial pressure and rf-induced substrate bias were varied independently during deposition. The film data are in excellent agreement with the effective medium theory of Sen, Scala, and Cohen, relevant for a random coated-particle microstructure where the grains are optically isolated from each other. With increasing substrate temperature, the Pd volume fraction in the bulk was found to decrease slightly, while the rms microroughness of the film surface increased in magnitude. At 190° C, the rms microroughness was 80 ± 3 Awith the Pd volume fraction in the bulk region falling slightly to 97 ± 1% relative to the film deposited at 22° C. For argon partial pressures below a transition pressure, Pt≃15 mTorr, the films consisted of densely packed grains, corresponding to the zone T in Thornton's structure zone model. Above this transition pressure, the films developed into a more voided columnar structure, characteristic of the zone 1 region. A microstructural analysis indicated a general trend towards increased porosity and microroughness of the films with higher argon pressures. The zone 1 region was best described optically by a random coated-particle microstructure and the electron microscopy confirmed that for thin films prepared at argon pressures higher than Pt, the grains became isolated by void boundaries. The optical data could not distinguish whether or not the films were 2- or 3-dimensionally isotropic. With increasing rf-induced substrate biasing, the Pd film microstructure was modified in a manner similar to that obtained by varying the substrate temperature alone. Significant resputtering of the Pd films occurred, varying from 2 to 11 A/sec for bias voltages of -550 V to -1375 V, respectively. The measured deposition rate while bias sputtering was significantly higher than that expected upon the measured resputtering rate and several mechanisms were proposed to account for the enhancement in the deposition rate. The films were best characterized by a 2-dimensional isotropy which was supported by the columnar nature of the films observed by electron microscopy. Finally, the dielectric function of the "best" palladium film is compared to optical constants of Pd previously reported in the literature for bulk and thin film specimens. While all the authors quote essentially the same values for the real part of the dielectric function, regardless of the preparation or measurement technique, the imaginary part differs up to a factor of two. Surface microroughness, bulk porosity and oxide layers are unable to account for the difference. A possible grain boundary scattering mechanism is suggested. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is a study of the properties of thin GaAs films grown on molybdenum substrates by the close spaced vapour transport (CSVT) deposition technique with the intention that the GaAs/Mo structure would be used as the semiconductor and substrate for economic solar cells. The GaAs films were polycrystalline cubic crystals with no preferred orientation. The crystallite area increased with the temperature at which the substrate was held during growth and at 710°C grain sizes of 100 μm² were observed. The crystallites formed a columnar-like structure with crystal size comparable to the film thickness. No impurities of foreign instrus-ions existed in the films in quantities observable on the electron micro-probe. The resistivity of the GaAs films was 220 Ω cm, hence acceptable for thin film solar cells, however, the GaAs/Mo contact was mildly rectifying. Diodes were fabricated by the deposition of Au onto the GaAs films and the resulting barriers showed values of barrier height of approximately 0.8 eV, ideality factor n = 1.5 to 2, and depletion-layer majority carrier concentration of roughly 10¹⁶ cm⁻³ as measured by J-V and C-V methods. The GaAs films show promise for use in solar cells provided that the Mo/GaAs interface resistance can be reduced. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3∙Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH = 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V versus Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye, copper colored, and survived a crude test called "the Scotch tape test", which involves sticking the scotch tape on the sample, then peeling off the tape and observing if the copper film peels off or not. Characterization by scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) and X-ray photon spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicated that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics does not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH > 1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (~ 1 micron or larger) are observed upon deposition at less negative potentials. Osmium metal has been successfully electrodeposited directly onto p-Si (100) from both Os3+ and Os4+ in both sulfuric and perchloric baths. This electrochemical deposition of osmium metal can provide sufficient amount of osmium which overcome ion beam implantation limitations. The deposited metal can undergo further processing to form osmium silicides, such as Os2Si3, which can be used as optical active materials. The higher osmium concentration results in large deposition currents and more negative peak potential due to larger transfer coefficient. No matter which supporting electrolyte is used, no stripping peak exists in this study. The oxidation ability of anion plays an important role in osmium electrodeposition because it will change the silicon substrate conductivity. In our case, perchloric acid oxidized silicon surface severely. Os4+ seems more favorable for reduction but has a stronger oxidization ability to lower the conductivity. The microscopic images verified osmium is deposited on silicon and forms cluster sizes of < 1 µm to > 10 µm. The Rutherford backscattering spectroscopy (RBS) data indicate osmium can diffuse into the silicon as far as 500 nm and the Si crystal structure is unchanged by the process. This means that the Si does not disassociate and migrate into deposited Os. Osmium is distributed randomly throughout the lattice interstitially. It appears field assisted diffusion can significantly drive the Os into Si (100). This finding is very valuable but needs further study.

The thesis describes novel glass micropipette thermal sensor fabricated in cost-effective manner and thermal conductivity measurement of carbon nanotubes (CNT) thin film using the developed sensor. Various micrometer-sized sensors, which range from 2 µm to 30 µm, were produced and tested. The capability of the sensor in measuring thermal fluctuation at micro level with an estimated resolution of ±0.002oC is demonstrated. The sensitivity of sensors was recorded from 3.34 to 8.86 µV/oC, which is independent of tip size and dependent on the coating of Nickel. The detailed experimental setup for thermal conductivity measurement of CNT film is discussed and 73.418 W/moC was determined as the thermal conductivity of the CNT film at room temperature.

A guided-wave THz System-on-Chip (TSoC) is emerging as an attractive alternative to the routine free-space THz systems to reduce physical bulk, propagation loss, pulse dispersion and cost of free-space THz systems. Recently, our research group succeeded in demonstrating a novel waveguided TSoC based on the coplanar stripline (CPS) transmission lines on a 1 µm-thin Silicon Nitride membrane. The novelty of this membrane-based platform was bonding the transmitter and receiver directly on the transmission line to eliminate the radiation loss by the routine THz optics. Besides, the delicate thin-membrane dramatically reduces the dielectric loss of the platform which results in low-loss and low-dispersion THz-bandwidth pulses. This Ph.D. dissertation presents the first end-to-end TSoC components that were designed and fabricated using the CPS transmission lines on 1 µm-thin Si3N4 membranes. These components are integrated into a TSoC by bending or connecting different impedance CPS transmission-line sections. We demonstrate four passive TSoC components: THz low-pass filter (TLPF), THz power divider (TPD), THz apodized Bragg grating (TABG) and THz branch-line coupler (TBLC). One of the most significant gains from this work is the assurance that more complex TSoCs can be designed and fabricated using this membrane-platform based on the strong agreement between simulation and experimental results. / Graduate / 2021-12-01

This research was undertaken to improve the understanding of structure-property-performance relationships in crosslinked polyamide (PA) thin-film composite (TFC) membranes as characterized by liquid and gas permeation studies. The ultrathin PA selective layer formed by interfacial polymerization between meta-phenylene diamine and trimesoyl chloride was confirmed to contain dense polymer matrix regions and defective regions in both dry and hydrated states. The first part of this research studied the effect of non-selective convection through defective regions on water flux and solute flux in pressure-assisted forward osmosis (PAFO). Through systematic comparison with cellulose triacetate (CTA) and PEBAX-coated PA-TFC membranes, the existence of defects in pristine, hydrated PA-TFC membranes was verified, and their effects were quantified by experimental and modeling methods. In the membrane orientation of selective layer facing the draw solution, water flux increases of up to 10-fold were observed to result from application of low hydraulic pressure (1.25 bar). Convective water flux through the defects was low (< 1% of total water flux for PA-TFC membranes) and of little consequence in practical FO or reverse osmosis (RO) applications. However, it effectively mitigated the concentration polarization in PAFO and therefore greatly increased the diffusive flux through the dense regions. The second part of this research characterized the structures of the PA material and the PA selective layer by gas adsorption and gas permeation measurements. Gas adsorption isotherms (N2 at 77K, CO2 at 273K) confirmed the microporous nature of PA in comparison with dense CTA and polysulfone materials. Gas permeation through the commercial PA-TFC membranes tested occurred primarily in the defective regions, resulting in Knudsen gas selectivity for various gas pairs. Applying a Nafion coating layer effectively plugged the defects and allowed gas permeation through the dense PA regions, which significantly decreased gas permeance and increased gas selectivity. Specifically, high He and H2 selectivity against CO2 suggests the potential applications of this membrane in He recovery and CO2 capture in pre-combustion. Finally, the dense PA matrix was modified with two types of novel nanofiller to improve desalination performance in RO. A series of dense, nano-sized (1-3 nm) polyhedral oligomeric silsesquioxanes (POSS) with different functional groups were systematically incorporated into the PA matrix by physical blending or chemical fixation. The free volume of the PA matrix increased with addition of POSS, leading to water flux increases of up to 67 %, while maintaining high NaCl rejections. The effects of adding microporous, hydrophobic zeolitic imidazolate framework-8 (ZIF-8) nanoparticles into PA are presented in the last chapter. A 162 % water flux increase was achieved without decreasing NaCl rejection. This interesting result can be attributed to a less crosslinked PA structure and to the intrinsic desalination properties of ZIF-8.

Emerging transparent conducting and semiconducting oxide (TCO) and (TSO) materials have achieved success in display markets. Due to their excellent electrical performance, TSOs have been chosen to enhance the performance of traditional displays and to evaluate their application in future transparent and flexible displays. This dissertation is devoted to the study ZnO-based thin film transistors (TFTs) using multilayer dielectrics and channel layers. Using multilayers to engineer transistor parameters is a new approach. By changing the thickness, composition, and sequence of the layers, transistor performance can be optimized. In one example, Al2O3/Ta2O5 bilayer gate dielectrics, grown by atomic layer deposition at low temperature were developed. The approach combined high dielectric constant of Ta2O5 and the excellent interface quality of Al2O3/ZnO, resulting in enhanced device performance. Using zinc oxide (ZnO)/hafnium oxide (HfO2) multilayer stack as a TFT channel with tunable layer thicknesses resulted in significant improvement in TFT stability. Atomic layer deposited SnO2 was developed as a gate electrode to replace ITO in thin film transistors and circuits. The SnO2 films deposited at 200 °C show low electrical resistivity of ~3.1×10-3 Ohm-cm with the high transparency of ~93%. TFT fabricated with SnO2 gate show excellent transistor properties. Using results from the above experiments, we have developed a novel process in which thin film transistors (TFTs) are fabricated using one binary oxide for all transistor layers (gate, source/drain, semiconductor channel, and dielectric). In our new process, by simply changing the flow ratio of two chemical precursors, C8H24HfN4 and (C2H5)2Zn, in an ALD system, the electronic properties of the binary oxide HZO were controlled from conducting, to semiconducting, to insulating. A complete study of HZO thin films deposited by (ALD) was performed. The use of the multi-layer (HfO2/ZnO) channel layer plays a key role in improving the bias stability of the devices. The low processing temperature of all materials at 160 °C is an advantage for the fabrication of fully transparent and flexible devices. After precise device engineering, including growth temperature, gate dielectric, electrodes (S/D&G) and semiconductor thickness, TFT with excellent device performance are obtained.

Since the discovery of organic semiconductors (OSCs) over four decades ago, the field of organic electronics has broken our misconceptions regarding the possibilities of modern electronics. The synthetic toolkit of organic chemistry enables the creation of a limitless number of unique OSCs that can be specifically tailored and engineered with the specific and desired properties for unique applications. The rapid adoption of modern information systems, “Internet of Things,” in which smart devices and sensors ubiquitously collect and exchange data has resulted in a need for low-cost sensors to be deployed everywhere from the monitoring of food supply chains, environmental conditions, to human health. Organic thin-film transistors (OTFTs) are a necessary component to support these technologies. However, their mass adoption will require reduction in cost and improved compatibility with low voltage generating printed batteries or flexible and ultrathin photovoltaics. This thesis is focused on the development of high performing solid state polymer electrolytes to be employed as the gating medium in OTFTs. The choice of conventional gating materials often leads to a tradeoff between high capacitance, operating speed and material softness. For example liquid electrolyte gating materials have high capacitance but low operating speed and are liquid at room temperature which is unacceptable for many electronics application. Polymer gating materials often have lower capacitance but fast operating conditions and solid at room temperature. In this thesis we establish structure property relationships which aid in the design of novel block copolymer-based gating materials which simultaneously enable the increase in capacitance and switching speed while remaining solid at room temperature. In the first study I established a styrene-based ionic liquid monomer can be using as a controlling monomer in the nitroxide mediated copolymerization of methacrylates. The second study then focuses on the integration of these materials into OTFT devices; the morphology (block vs random copolymers) effect on device performance is assessed. The last study builds on the findings of the previous study and further explores the structural elements of block copolymers on device performance. The work presented here outlines the development of advanced poly(ionic liquid) based solid electrolyte materials that enables both reduced operating voltages and fast switching. Finally, we establish structure-property relationships that relate the molecular architecture to OTFT device performance paving the way for the adoption of a new generation of high performing, printable and flexible electronics.

This diploma thesis is devoted to a modern attitude of desktop computer usage, that uses operating system and applications virtualization. The paper describes theoretical principles of virtualization techniques and selection of the proper solution for the organization. Diploma thesis also describes the project implementation.

The never-ending quest to design and produce bespoke materials optimized for specific purposes has recently led to the discovery of a rapidly expanding subclass of porous materials known as Metal-Organic Frameworks (MOFs). The potential of MOFs appears to be immense due to the accessibility of a nearly-infinite number of both organic and inorganic components – building blocks that can be easily self-assembled in extended networks. Taking advantage of modular composition, high surface areas, adjustable pore sizes, and tunable surface properties, MOFs are emerging as one of the most promising materials for energy and environmental applications. \nThe main objective of this thesis is to explore different aspects concerning MOF materials, building on the knowledge from several subtypes of MOFs developed primarily in Prof. Eddaoudi’s group. In particular, this dissertation expands the diversity within and utility of the following MOF subtypes: MOFs comprised of sql supermolecular building layers (SBL), MOFs based on fluorometalates, and zeolite-like MOFs (ZMOFs). \nWhenever feasible, emphasis was placed on the synthesis and application of MOFs as supported thin films, particularly as the sensitive element of capacitive gas sensors or as a selective layer of composite membranes for gas separation. \nSome of the highlights from the results obtained in the course of this study include: \n \n- Introduction of MOFs to the field of reverse selective (CO2/H2) membranes for hydrogen purification. Notably, despite the challenges associated with the preparation of continuous “defect-free” MOF membranes, three different types of adsorption-driven MOF membranes have been synthesized and have shown a preferential permeation of CO2 over H2. In addition, the diffusion driven butane isomers separation was realized in ana-ZMOF membrane, being close to or even overperforming benchmark materials reported in the literature for the separation of both gas pairs. \n- Identification of an appropriate MOF compatible with the developed capacitive-based sensor system and capable of the detection of sulfur dioxide in ppb level. \n- Discovery of a ZMOF material with a new unprecedented zeolitic topology and its ability to separate propylene from propane upon the difference in diffusion of the adsorbates.