<p>This study focuses on developing a new online recursive numerical algorithm for a coupled nonlinear inverse heat conduction-microstructure problem. This algorithm is essential in identifying, designing and controlling many industrial applications such as the quenching process for heat treating of materials, chemical vapor deposition and industrial baking. In order to develop the above algorithm, a systematic four stage research plan has been conducted. </P> <p> The first and second stages were devoted to thoroughly reviewing the existing inverse heat conduction techniques. Unlike most inverse heat conduction solution methods that are batch form techniques, the online input estimation algorithm can be used for controlling the process in real time. Therefore, in the first stage, the effect of different parameters of the online input estimation algorithm on the estimate bias has been investigated. These parameters are the stabilizing parameter, the measurement errors standard deviation, the temporal step size, the spatial step size, the location of the thermocouple as well as the initial assumption of the state error covariance and error covariance of the input estimate. Furthermore, three different discretization schemes; namely: explicit, implicit and Crank-Nicholson have been employed in the input estimation algorithm to evaluate their effect on the algorithm performance. </p> <p> The effect of changing the stabilizing parameter has been investigated using three different forms of boundary conditions covering most practical boundary heat flux conditions. These cases are: square, triangular and mixed function heat fluxes. The most important finding of this investigation is that a robust range of the stabilizing parameter has been found which achieves the desired trade-off between the filter tracking ability and its sensitivity to measurement errors. For the three considered cases, it has been found that there is a common optimal value of the stabilizing parameter at which the estimate bias is minimal. This finding is important for practical applications since this parameter is usually unknown. Therefore, this study provides a needed guidance for assuming this parameter. </p> <p> In stage three of this study, a new, more efficient direct numerical algorithm has been developed to predict the thermal and microstructure fields during quenching of steel rods. The present algorithm solves the full nonlinear heat conduction equation using a central finite-difference scheme coupled with a fourth-order Runge-Kutta nonlinear solver. Numerical results obtained using the present algorithm have been validated using experimental data and numerical results available in the literature. In addition to its accurate predictions, the present algorithm does not require iterations; hence, it is computationally more efficient than previous numerical algorithms. </p> <p> The work performed in stage four of this research focused on developing and applying an inverse algorithm to estimate the surface temperatures and surface heat flux of a steel cylinder during the quenching process. The conventional online input estimation algorithm has been modified and used for the first time to handle this coupled nonlinear problem. The nonlinearity of the problem has been treated explicitly which resulted in a non-iterative algorithm suitable for real-time control of the quenching process. The obtained results have been validated using experimental data and numerical results obtained by solving the direct problem using the direct solver developed in stage three of this work. These results showed that the algorithm is efficiently reconstructing the shape of the convective surface heat flux. </P> / Thesis / Doctor of Philosophy (PhD)

Over the past 20 years’ researchers have tried to utilize the remarkable properties of single-walled carbon nanotubes (SWCNTs) to create new high-tech materials and devices, such as strong light-weight composites, efficient electrical wires and super-fast transistors. But the mass production of these materials and devices are still hampered by the poor uniformity of the produced SWCNTs. These are hollow cylindrical tubes of carbon where the atomic structure of the tube wall consists of just a single atomic layer of carbon atoms arranged in a hexagonal grid. For a SWCNT the orientation of the hexagonal grid making up the tube wall is what determines its properties, this orientation is known as the chirality of a SWCNT. As an example, tubes with certain chiralities will be electrically conductive while others having different chiralities will be semiconducting. Today’s large scale methods for producing SWCNTs, commonly known as growth of SWCNTs, gives products with a large spread of different chiralities. A mixture of chiralities will give products with a mixture of different properties. This is one of the major problems holding back the use of SWCNTs in future materials and devices. The ultimate goal is to achieve growth where the resulting product is uniform, meaning that all of the SWCNTs have the same chirality, a process termed chirality-specific growth. To achieve chirality-specific growth of SWCNTs requires us to obtain a better fundamental understanding about how they grow, both from an experimental and a theoretical point of view. This work focuses on theoretical studies of SWCNT properties and how they relate to the growth process, thereby giving us vital new information about how SWCNTs grow and taking us ever closer to achieving the ultimate goal of chirality-specific growth. In this thesis, an introduction to the field is given and the current state of the art experiments focusing on chirality-specific growth of SWCNTs are presented. A brief review of the current theoretical works and computer simulations related to growth of SWCNTs is also presented. The results presented in this thesis are obtained using first principle density functional theory. The first study shows a correlation between the stability of SWCNT-fragments and the observed products from experiments. Calculations confirm that in 84% of the investigated cases the chirality of experimental products matches the chirality of the most stable SWCNT-fragments (within 0.2 eV). Further theoretical calculations also reveal a previously unknown link between the stability of SWCNT-fragments and their length. The calculations show that at specific SWCNT-fragment lengths the most stable chirality changes. Thus, introducing the concept of a switching length for SWCNT stability. How these new results link to the existing understanding of SWCNT growth is discussed at the end of the thesis.

No description available.

No description available.

Here, silicon oxide was formed in a U-shaped trench of a power metal-oxide semiconductor field-effect transistor device by various processes. One SiO₂ formation process was performed in multiple steps to create a low-defect Si-SiO₂ interface, where first a thin initial oxide was grown by thermal oxidation followed by the deposition of a much thicker oxide layer by chemical vapor deposition (CVD). In a second novel approach, silicon nitride CVD was combined with radical oxidation to form silicon oxide in a stepwise sequence. The resulting stack of silicon oxide films was then annealed at temperatures between 1000 and 1100 °C. All processes were executed in an industrial environment using 200 mm-diameter (100)-oriented silicon wafers. The goal was to optimize the trade-off between wafer uniformity and conformality of the trenches. The thickness of the resulting silicon oxide films was determined by ellipsometry of the wafer surface and by scanning electron microscopy of the trench cross sections. The insulation properties such as gate leakage and electrical breakdown were characterized by current–voltage profiling. The electrical breakdown was found to be highest for films treated with rapid thermal processing. The films fabricated via the introduced sequential process exhibited a breakdown behavior comparable to films deposited by the common low-pressure CVD technique, while the leakage current at electric fields higher than 5 MV/cm was significantly lower.

<p>A new electron cyclotron plasma enhanced chemical vapour deposition (ECR-PECVD) reactor has been installed and tested at McMaster University. The focus of this project was the installation of the reactor and the growth of silicon oxide, silicon oxynitride, cerium doped silicon oxynitride and aluminium doped silicon oxide films to test the capabilities of the reactor. Silicon oxide films were prepared with near-stoichiometric compositions and silicon rich compositions. Good repeatability of the growths was seen. An increase in deposition temperature showed stable refractive index and a decrease in the growth rates. Silicon oxynitride films of varying compositions were prepared, and showed a non-uniformity of ~1% and growth rates of ~3.5 nm/min. Films prepared with a low oxygen flow were seen to be nitrogen rich. Although the depositions using Ce(TMHD)4 showed significant cerium incorporation, there was also high carbon contamination. One likely cause of this is the high sublimator temperature used during depositions or a thermal shock to the precursor during initial system calibration. A definitive cause of the carbon contamination has not been established. The cerium films showed strong blue luminescence after post-deposition annealing in N2 above 900° C. A drop in the luminescence was observed at 1100° C and a return of the luminescence at 1200° C. Generally, high cerium incorporation was associated with higher total luminescence. Al(THMD)3 was evaluated as an aluminium precursor for Al-doped silicon oxide films. The films showed aluminium content up to 6% demonstrating the viability of using Al(THMD)3 as a Al doping precursor.</p> / Master of Applied Science (MASc)

The contribution describes the construction of a CVD system, the deposition of thin molybdenum disulphide layers using this system and the analysis of the samples produced. The deposition of thin molybdenum disulphide layers and an intercalation of the silicon carbide substrate used were demonstrated and the measurement results obtained by atomic force microscopy and photoelectron spectroscopy were further discussed.

<p dir="ltr">Thin films of ceramic materials are of significant importance in various industries due to their unique properties, versatility, and abundance. These materials are applied as thin layers on different types of substrates, providing a wide range of benefits and applications in industries such as automotive, aerospace, electronics, energy, and environmental monitoring. Historically, ceramic thin films have been used to enhance the properties and performance of metallic substrates by providing corrosion resistance, wear resistance, and thermal stability in harsh environmental and extreme conditions. Among various ceramic materials, thin films of silicon oxide (SiO_x) and silicon nitride (SiN_x) are the most widely used in the semiconductor and biomedical industries due to their excellent barrier properties, biocompatibility, and environmental stability. Traditionally, thin ceramic films or coatings of SiO_x and SiN_x are deposited using various methods including sol-gel, physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and thermal spraying. Despite the widespread use of traditional vapor deposition methods, their limitations such as the requirement of vacuum systems, high processing temperatures, slow deposition rates, and limited substrate capabilities render them unfitting for large scale manufacturing. To address the challenges associated with these traditional methods, this dissertation focuses on exploring the potential use of the cold atmospheric plasma (CAP) technology as an effective, scalable, and low-temperature approach for depositing SiO_x and SiN_x thin films under atmospheric conditions and demonstrating its applicability in sensing and packaging applications. In the first part of this dissertation, the CAP deposited silica coating is used as a key sensing element in flexible sensors. For the first time in literature, the demonstration of a low-cost and flexible glass-based pH sensor (sensitivity ~ 48mV/pH) consisting of CAP deposited silica coating as a sensing membrane is reported. In the second part, to realize the reliability and durability of these flexible electronic devices, robust encapsulation is achieved through a systematic study optimizing the conditions of plasma deposition while utilizing the CAP-deposited silica coating as an adhesion promoter to enhance the barrier properties of traditional polymeric encapsulants on flexible electronics devices. The third part aims to provide corrosion protection to electronic devices by applying ultrathin films of silica coatings with various thicknesses ranging from 75 nm to 1110 nm and varying degree of crosslink density and barrier properties. The final part demonstrates the effectiveness of CAP-deposited silica coating with enhanced antibacterial properties by integrating quaternary ammonium functionality to the coating for biomedical applications. In summary, these contributions in the CAP deposition technology can open up a new platform with tremendous opportunities toward scalable manufacturing of cost-effective and reliable devices for a broad range of applications.</p>

In this work, we explored one material from the broad family of 2D semiconductors, namely WSe2 to serve as an enabler for advanced, low-power, high-performance nanoelectronics and optoelectronic devices. A 2D WSe2 based field-effect-transistor (FET) was designed and fabricated using electron-beam lithography, that revealed an ultra-high mobility of ~ 625 cm2/V-s, with tunable charge transport behavior in the WSe2 channel, making it a promising candidate for high speed Si-based complimentary-metal-oxide-semiconductor (CMOS) technology. Furthermore, optoelectronic properties in 2D WSe2 based photodetectors and 2D WSe2/2D MoS2 based p-n junction diodes were also analyzed, where the photoresponsivity R and external quantum efficiency were exceptional. The monolayer WSe2 based photodetector, fabricated with Al metal contacts, showed a high R ~502 AW-1 under white light illumination. The EQE was also found to vary from 2.74×101 % - 4.02×103 % within the 400 nm -1100 nm spectral range of the tunable laser source. The interfacial metal-2D WSe2 junction characteristics, which promotes the use of such devices for end-use optoelectronics and quantum scale systems, were also studied and the interfacial stated density Dit in Al/2D WSe2 junction was computed to be the lowest reported to date ~ 3.45×1012 cm-2 eV-1. We also examined the large exciton binding energy present in WSe2 through temperature-dependent Raman and photoluminescence spectroscopy, where localized exciton states perpetuated at 78 K that are gaining increasing attention for single photon emitters for quantum information processing. The exciton and phonon dynamics in 2D WSe2 were further analyzed to unveil other multi-body states besides localized excitons, such as trions whose population densities also evolved with temperature. The phonon lifetime, which is another interesting aspect of phonon dynamics, is calculated in 2D layered WSe2 using Raman spectroscopy for the first time and the influence of external stimuli such as temperature and laser power on the phonon behavior was also studied. Furthermore, we investigated the thermal properties in 2D WSe2 in a suspended architecture platform, and the thermal conductivity in suspended WSe2 was found to be ~ 1940 W/mK which was enhanced by ~ 4X when compared with substrate supported regions. We also studied the use of halide-assisted low-pressure chemical vapor deposition (CVD) with NaCl to help to reduce the growth temperature to ∼750 °C, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. The synthesis of monolayer WSe2 with high crystalline and optical quality using a halide assisted CVD method was successfully demonstrated where the role of substrate was deemed to play an important role to control the optical quality of the as-grown 2D WSe2. For example, the crystalline, optical and optoelectronics quality in CVD-grown monolayer WSe2 found to improve when sapphire was used as the substrate. Our work provides fundamental insights into the electronic, optoelectronic and quantum properties of WSe2 to pave the way for high-performance electronic, optoelectronic, and quantum-optoelectronic devices using scalable synthesis routes.

Die vorliegende Dissertation befasst sich mit dem Wachstum und der Charakterisierung von Silizium- und Germanium-Nanodrähten. Diese Strukturen gelten als aussichtsreiche Komponenten für zukünftige Bauelemente. Für die Anwendung ist die genaue Kenntnis der Größe, der kristallographischen Orientierung und der Position der Nanodrähte erforderlich. Ziel dieser Arbeit war daher die Untersuchung von Si- und Ge-Nanodrähten im Hinblick auf ihre Größe, Orientierung und Position. Die Herstellung erfolgte durch Physikalische Gasphasenabscheidung (PVD) im Ultrahochvakuum nach dem Vapor-Liquid-Solid (VLS)-Verfahren, das auf dem Wachstum aus Lösungsmitteltröpfchen basiert. Die Größe der Nanodrähte konnte im Falle von Silizium auf Si(111) mit Gold als Lösungsmittel durch die Parameter des Experiments reproduzierbar bestimmt werden. Höhere Goldbedeckung und höhere Substrattemperaturen führten zu Tröpfchen mit größerem Duchmesser und somit zu dickeren Drähten. Längere Si-Verdampfungszeiten und höhere Si-Verdampfungsraten führten zu längeren Drähten. Dünnere Drähte wuchsen schneller als dickere. Als zweites Lösungsmittel wurde Indium untersucht, da es sich im Vergleich zu Gold nicht nachteilig auf die elektronischen Eigenschaften von Silizium auswirkt. Basierend auf den Ergebnissen zur Tröpfchenbildung konnten die besseren Wachstumsresultate mit Gold erklärt werden. Germanium-Nanodrähte, die aus Goldtröpfchen auf Ge(111) gezüchtet wurden, zeigten im Gegensatz zu den Si-Nanodrähten nicht die kristallographische [111]-Orientierung des Substrates, sondern eine -Orientierung, was durch Berechnungen von Keimbildungsenergien auf verschiedenen Kristallflächen erklärt werden konnte. Zur Anordnung von Metalltröpfchen und damit von Nanodrähten wurden Substrate mithilfe von fokussierten Ionenstrahlen (FIB) vorstrukturiert, um die Tröpfchenbildung an bestimmten Stellen zu begünstigen. Es gelang, aus angeordneten Goldtröpfchen epitaktisch gewachsene Si- und Ge-Nanodrähte zu züchten. / This dissertation deals with the growth and the characterization of silicon and germanium nanowhiskers, also called nanorods or nanowires. The investigation of these structures is of great interest as they represent promising building blocks for future electronic devices. With regard to a possible application, the knowledge of size, crystallographic orientation and position of the nanowhiskers is essential. The purpose of this work was, therefore, to investigate the growth of Si and Ge nanowhiskers with regard to their size, orientation and position. The nanowhiskers were grown via physical vapor deposition (PVD) in ultra-high vacuum using the vapor-liquid-solid (VLS) mechanism which is based on growth from solution droplets. The size of the nanowhiskers could be reproducibly determined by the experimental parameters in the case of Si nanowhiskers on Si(111) with gold as the solvent. A higher gold coverage as well as a higher substrate temperature led to larger droplet diameters and thus to thicker whiskers. A longer silicon evaporation time and a higher silicon rate led to longer whiskers. Thinner whiskers grew faster than thicker ones. A second material used as the solvent was indium as it is more suitable for electronic application compared to gold. Based on results of droplet formation of the two solvents on silicon, the better results of whisker growth using gold could be explained. Ge nanowhiskers grown from gold droplets on Ge(111) did not show the [111] orientation of the substrate as in the case of Si nanowhiskers on Si(111) but a orientation. By calculating nucleation energies on different crystal facets, the experimental findings could be explained. To position nanodroplets of the solvent material and thus to obtain a regular arrangement of nanowhiskers, substrates were pre-structured with nanopores by focused ion beams (FIB). Silicon and germanium nanowhiskers could be epitaxially grown from ordered arrays of gold droplets.