Most electrical, magnetic or optical devices are today based on several, usually extremely thin layers of different materials.  In this thesis chemical synthesis processes have been developed for growth of less stable and metastable layers, and even multilayers, of nickel containing compounds. A chemical vapor deposition (CVD) method for deposition of metastable Ni3N has been developed.  The deposition process employs ammonia as nitrogen precursor. An atomic layer deposition (ALD) process for deposition of both polycrystalline and epitaxial NiO and using low oxygen activity, has also been developed. Both deposition processes utilizes bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II) (Ni(thd)2) as the metal precursor. The Ni3N deposition proceeds via surface reactions. The growth rate is very sensitive to the partial pressure of ammonia, why adsorbed –NHx species are believed to be of importance for the film growth. Similar reactions can be expected between the metal precursor and H2O. For ALD of NiO a large excess of water was needed For the multilayered structures of Ni3N/NiO, growth processes, working at low activities of oxygen and hydrogen, are needed to avoid oxidation or reduction of the underlying layer. Chemical vapor growth methods such as CVD and ALD are often suffering from using high activities of hydrogen or oxygen to deposit metals and oxides. An alternative deposition pathway for metal deposition, without any hydrogen in the vapor, has been demonstrated. The metal has been formed by decomposition of the metastable nitride Ni3N in a post-annealing process.  Ni3N decomposes via different mechanisms, depending on environment in the annealing process. The different mechanisms result in different degrees of ordering in the resulting Ni films. From the knowledge gained about the chemical growth of NiO and Ni3N as well as the decomposition of Ni3N, well-defined multilayer structures have been produced in different combinations of NiO, Ni3N and Ni.

Eine ortsauflösende Spannungs- und Dehnungssensortechnik soll durch die Nutzung magnetostriktiver Materialien auf der Oberfläche von Kohlenstoffeinzelfasern (C-Fasern) und Mikrofeinstrukturierung dieser Schichten erzeugt und zur elektronischen Überwachung des Belastungszustandes von sicherheits- oder servicerelevanten Faserverbundbauteilen eingesetzt werden. Eine auf lokaler Gasphasenabscheidung und Mikrostrukturierung mittels der Focused Ion Beam (FIB)-Technik beruhende Sensorfabrikationsmethode wurde gemeinsam mit dem Institut für Mikrotechnologie Hannover (imt) entwickelt. Mehrschichtig mittels CVD und PVD bedampfte und zusätzlich galvanisch beschichtete C-Fasern weisen neuartige Eigenschaften auf, die im vorgestellten Vorhaben am Lehrstuhl für Verbundwerkstoffe (LVW) charakterisiert wurden. Insbesondere die Untersuchung der verschiedenen Schichten sowie deren Interfaces nehmen eine bedeutende Rolle ein.

Many materials exhibit interesting and novel properties when prepared as thin films. Thin film metal oxides have had an impact on the technological progress of the microelectronics mainly due to their electrical and optical properties. Since the future goes towards the nanometre scale there is an increasing demand for thin film deposition processes that can produce high quality metal oxide films in this scale with high accuracy. This thesis describes atomic layer deposition of Ta2O5, HfO2 and SnO2 thin films and chemical vapour deposition of SnO2 thin films. The films have been deposited by employing metal iodides and oxygen as precursors. All these processes have been characterised with regards to important processing parameters. The films themselves have been characterised by standard thin film analysing techniques such as x-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. The chemical and physical properties have been coupled to critical deposition parameters. Furthermore, additional data in the form of electrical and gas sensing properties important to future applications in the field of microelectronics have been examined. The results from the investigated processes have shown the power of the metal iodide based atomic layer deposition (ALD) and chemical vapour deposition (CVD) processes in producing high quality metal oxide thin films. Generally no precursor contaminations have been observed. In contrast to metal chloride based processes the metal iodide processes produces films with a higher degree of crystalline quality when it comes to phase purity, roughness and epitaxy. The use of oxygen as oxidising precursor allowed depositions at higher temperatures than normally employed in water based ALD processes and hence a higher growth rate for epitaxial growth was possible.

L'objectif de cette thèse porte sur la fabrication et la caractérisation de cellules solaires à jonction radiale à base d'assemblée de nanofils de silicium cristallin. Une étude sur la croissance des nanofils à partir de deux catalyseurs métalliques (cuivre et aluminium) dans une machine de dépôt chimique en phase vapeur (CVD) à pression réduite est présentée. L'inflžuence des conditions de croissance sur la morphologie, le dopage et la contamination des nanols par le catalyseur est analysée par des mesures électriques, chimiques (SIMS, Auger) et structurales (SEM, TEM, Raman). Le cuivre est utilisé pour la fabrication d'une cellule solaire avec des nanofils de type p et une jonction radiale créée avec du silicium amorphe de type n. Les performances photovoltaïques de la cellule solaire sont ensuite mesurées et interprétées. Un rendement de conversion de 5% est mesuré sur une cellule avec des nanofils de hauteur 1,5 µm.

The Virtual Chemical Vapor Deposition (CVD) Process Development Project provides the context for the two areas of the research presented in this dissertation. The first area, generally referred to as feedback in this dissertation, focuses on student learning and the interactions of students and instructors that take place in the project, specifically focused on characterizing feedback and determining the influence of feedback as student teams progress towards completing the project. The characteristics of feedback found in this project are presented within a situative perspective using the analytical framework of episodes. The characteristics include: a list and categorization of episode themes, the structure and flow of episodes during the coaching session, the sub-structure present within individual episodes, and the types of feedback present. This dissertation shows how these characteristics frame participation in a community of practice and can be used as tools to scaffold instructor feedback in project-based learning. Episodes analysis is also used to investigate how feedback on professional skills can help to enculturate students into a community of practice and influence their fluency with professional skills and engagement in more technical activities. The second area examines the spread of this innovative project from its home institution to other institutions. In this area an analysis of the spread of the Virtual CVD Process Development Project in the high school setting is presented. The project was found to provide versatility for instructors and afford student learning in the areas of motivation, cognition, and epistemological beliefs. These two areas inform each other. As the project is assessed at different institutions, it is continually improved and the sensitivity of different aspects of the project is explored, e.g., the aspects of the project that are crucial to maintain effectiveness are identified. One of these aspects is the feedback that takes place in the project. As the project is further examined at the home institution in depth, more can be learned about the best ways it can be delivered. This information informs scaffolding that then can be provided to faculty at other institutions such that they can attend to crucial aspects of the project in the most efficient, effective manner, improving not only the probability of successful adaptation, but also the likelihood that the project will further diffuse to other institutions. / Graduation date: 2013

This report details work toward the fabrication of a single-electron transistor created from a single-walled carbon nanotube (SWNT). Specifically discussed is a method for growing carbon nanotubes (CNTs) via carbon vapor deposition (CVD). The growth is catalyzed by a solution of 0.02g Fe(NO3)3·9H2O, 0.005g MoO2(acac)2, and 0.015g of alumina particles in 15mL methanol. SWNT diameter ranges from 0.6 to 3.0 nm. Also discussed is a method to control nanotube growth location by patterning samples with small islands of catalyst. A novel “maskless” photolithographic process is used to focus light from a lightweight commercial digital projector through a microscope. Catalyst islands created by this method are approximately 400 μm2 in area.

This report details work toward the fabrication of a single-electron transistor created from a single-walled carbon nanotube (SWNT). Specifically discussed is a method for growing carbon nanotubes (CNTs) via carbon vapor deposition (CVD). The growth is catalyzed by a solution of 0.02g Fe(NO3)3·9H2O, 0.005g MoO2(acac)2, and 0.015g of alumina particles in 15mL methanol. SWNT diameter ranges from 0.6 to 3.0 nm. Also discussed is a method to control nanotube growth location by patterning samples with small islands of catalyst. A novel “maskless” photolithographic process is used to focus light from a lightweight commercial digital projector through a microscope. Catalyst islands created by this method are approximately 400 μm2 in area.

Hot-wire chemical vapour deposition (HWCVD) is a promising technique that permits polycrystalline silicon films with grain size of nanometers to be obtained at high deposition rates and low substrate temperatures. This material is expected to have better electronic properties than the commonly used amorphous hydrogenated silicon (a-Si:H).In this work, thin-film transistors (TFTs) were fabricated using nanocrystalline hydrogenated silicon film (nc-Si:H), deposited by HWCVD over thermally oxidized silicon wafer. The employed substrate temperature during the deposition process permits inexpensive materials as glasses or plastics to be used for various applications in large-area electronics. The deposition rate was about one order of magnitude higher than in other conventionally employed techniques. The deposited nc-Si:H films show good uniformity and reproducibility. The films consist of vertically grown columnar grains surrounded by amorphous phase. The columnar grains are thinner at the bottom (near the oxide interface) and thicker at the top of the film. Chromium layer was evaporated over the nc-Si:H in order to form drain and source contacts. Using photolithography techniques, two types of samples were fabricated. The first type (simplified) was with the chromium contacts directly deposited over the intrinsic nc-Si:H layer. No dry etching was involved in the fabrication process of this sample. The transistors on the wafer were not electrically separated from each other. Doped n+ layer was incorporated at the drain and source contacts in the second type of samples (complete samples). Dry etching was employed to eliminate the nc-Si:H between the TFTs and to isolate them electrically from each other.The electrical characteristics of both types of nc-Si:H TFTs were similar to a-Si:H based TFTs. Nevertheless, some significant differences were observed in the characteristics of the two types of samples. The increasing of the off-current in the simplified structure was eliminated by the n+ layer in the second type of samples. This led to the improving of the on/off ratio. The n+ layer also eliminated current crowding of the output characteristics. On the other hand, the subthreshold slope, the threshold voltage and the density of states were slightly deteriorated in the samples with incorporated n+ layer. Surface states created by the dry etching could be a possible reason. Other cause could be a bad quality of the nc-Si:H/SiO2 interface. The TFTs with incorporated n+ contact layer and electrically separated on the wafer were used in the further studies of stability and device modelling.The nc-Si:H TFTs were submitted under prolonged positive and negative gate bias stress in order to study their stability. We studied the influence of the stressing time and voltage on the transfer characteristics, threshold voltage, activation energy and density of states. The threshold voltage increased under positive gate bias stress and decreased under negative gate bias stress. After both positive and negative stresses, the threshold voltage recovered its initial values without annealing. This behaviour indicated that temporary charge trapping in the channel/gate insulator interface is the responsible process for the device performance under stress. Measurements of space-charge limited current confirmed that bulk states were not affected by the positive nor by negative stress.Analysis of the activation energy and the density of states gave more detailed information about the physical processes taking place during the stress. Typical drawback of the nc-Si:H films grown by HWCVD with tungsten (W) filament is the bad quality of the bottom, initially grown, interfacial layer. It is normally amorphous and porous. We assume that this property of the nc-Si:H film is determining for charge trapping and the consecutive temporary changes of the TFT's characteristics. On the other hand, the absence of defect-state creation during the gate bias stress demonstrates that the nc-Si:H films did not suffer degradation under the applied stress conditions. The electrical characteristics and the operational regimes of the nc-Si:H TFTs were studied in details in order to obtain the best possible fit using the Spice models for a-Si:H and poly-Si TFTs existing until now. The analysis of the transconductance gm showed behaviour typical for a-Si:H TFTs at low gate voltages. In contrast, at high gate voltages unexpected increasing of gm was observed, as in poly-Si TFTs. Therefore, it was impossible to fit the transfer and output characteristics with the a-Si:H TFT model neither with poly-Si TFT model.We performed numerical simulations using the Silvaco's Atlas simulator of semiconductor devices in order to understand the physical parameters, responsible for the device behaviour. The simulations showed that the reason for this behaviour is the density of acceptor-like states, which situates the properties of nc-Si:H TFTs between the amorphous and the polycrystalline transistors. Taking into account this result, we performed analysis of the concentrations of the free and the trapped carriers in nc-Si:H layer. It was found that nc-Si:H operates in transitional regime between above-threshold and crystalline-like regimes. This transitional regime was predicted earlier, but not experimentally observed until now. Finally, we introduced new equations and three new parameters into the existing a-Si TFTs model in order to account for the transitional regime. The new proposed model permits the shapes of the transconductance, the transfer and the output characteristics to be modelled accurately.

<p>Leukotrienes are arachidonic acid derivatives long known for their inflammatory properties and their involvement with a number of human diseases, most notably asthma. Recently, leukotriene-based inflammation has also been implicated in atherosclerosis: ALOX5AP and LTA4H, two genes in the leukotriene biosynthesis pathway, have been associated with various cardiovascular disease (CVD) phenotypes. To assess the role of the leukotriene pathway in CVD pathogenesis, we performed genetic association studies of ALOX5AP and LTA4H in a non-familial data set of early onset coronary artery disease. Our results support a modest role for the leukotriene pathway in atherosclerosis pathogenesis, reveal important genomic interactions within the pathway, and suggest the importance of using pathway-based modeling for evaluating the genomics of atherosclerosis susceptibility. Motivated by this need, we investigated the statistical properties of a class of matrix-based statistics to assess epistasis. We simulated multiple two-variant disease models with haplotypes to gain an understanding of pathway interactions in terms of correlation patterns. Our goal was to detect an interaction between multiple disease-causing variants by means of their linkage disequlibrium (LD) patterns with other haplotype markers. The simulated models can be summarized into three categories: 1. No epistasis in the presence of marginal effects and LD; 2. Epistasis in the presence of LD and no marginal effects; and 3. Epistasis in the presence marginal effects and LD. We then assessed previously introduced single-gene methods that compare whole matrices of Single Nucleotide Polymorphism (SNP) LD between two samples. These methods include comparing two sets of principal components, a sum-of-squared-differences comparing pairwise LD, and a contrast test that controls for background LD. We also considered a partial least-square (PLS) approach for modeling gene-gene interactions. Our results indicate that these measures can be used to assess epistasis as well as marginal effects under certain disease models. Understanding and quantifying whole-gene variation and association to disease using multiple SNPs remains a difficult task. Providing a single statistical measure per gene will facilitate combining multiple types of genomic data at a gene-level and will serve as an alternative approach to assess epistasis in genome-wide association studies. The matrix-based measures can also be used in pathway ascertainment tools that require scores on a gene-level.</p> / Dissertation

Thin films and coatings of oxides are used in various fields of science and technology, such as semiconductor and optoelectronic devices, gas sensors, protective and wear resistant coatings etc. Of late, there has been a tremendous interest in pure and doped vanadium dioxide as thermoelectric switch material. VO2 has been doped with hetero-atoms such as W, Mo, Nb, Ti etc. and effects of doping have been correlated with feasibility of being used as a smart window material. The oxide Al2O3 has been studied as an alternative gate dielectric. Ga2O3 is also a contender for replacing SiO2 as a dielectric material. Atomic layer deposition (ALD) is a technique for the deposition of thin films of various materials and is found to be of considerable scientific and technological importance. In particular, using β-diketonate complexes as precursors is very useful in preparing thin films of oxides, as these precursors already contain a metal-oxygen bond. In this thesis, β-diketonate complexes have been used as precursors for deposition of thin films. The thesis has been divided into two parts: First part deals with deposition and characterization of thin films of VO2 on glass and fused quartz. The second part deals with synthesis and chemical and thermal characterization of bimetallic Al-Ga acetylacetonates along with thin film deposition using the same. Chapter 1 presents a brief introduction to application of thin films of oxides in various fields of science and technology. A brief introduction to the ALD reactor used for the current work is also presented. The importance of thermal analysis of precursors for CVD is briefly reviewed. Chapter 2 deals with the instruments and methods used for the work done for this thesis. In Chapters 3 and 4 of the thesis, a detailed study of deposition of VO2 films on glass and fused quartz has been presented. The films deposited have been analyzed using a host of techniques, for their texture, microstructure and electrical properties. In spite of chemical similarities, considerable differences in structure and properties have been observed between the films deposited on the two substrates. These differences have been explained on the basis of the small chemical differences between the two substrates. Chapters 5, 6 and 7 deal with synthesis, thermal characterization and use of bimetallic Al-Ga precursors, respectively. The bimetallic acetylacetonates have been synthesized using ‘homogenization in solution’ approach. Chemical characterization of the precursors revealed that nominal percentages of Al and Ga are retained in the solid precursors. Single crystal structure confirmed the observation. Thermal analysis of the precursors showed that the precursors, which are solid solutions of Al and Ga acetylacetonates, show negative deviation from the Raoult’s Law. Films were deposited using these precursors and were found to near completely retain the composition of the precursors. Chapter 8 of the thesis presents the conclusions of the current work and proposes future directions.