In dieser Dissertation wird beschrieben, wie es durch systematische Anwendung unterschiedlicher Methoden zur Herstellung und Modifizierung von Diamant gezielt und verlässlich möglich ist, die Eigenschaften von Diamanten zu beeinflussen. Es wird gezeigt, wie durch Variation der Parameter bei dem Wachstum von Diamant Einfluss auf dessen Morphologie und Eigenschaften genommen werden kann. Des Weiteren wird ein Verfahren vorgestellt, mit dem die Oberfläche des Diamanten durch Ozon effizient oxidiert beziehungsweise reduziert werden kann. Um diese veränderte Oberflächenbelegung möglichst genau zu analysieren, wird im letzten Teil der Dissertation eine Methode zur qualitativen und quantitativen Analytik der Oberflächen von Kohlenstoffnanomaterialien beschrieben. / This dissertation describes how it is possible to alter the properties of diamond utilizing varying methods for diamond growth and surface modification. It is shown, how by varying the parameters during the growth of diamond, influence can be exerted on its morphology and properties. Furthermore, a procedure is described to efficiently oxidize or reduce the surface of diamond using ozone. In order to analyze this modified surface as precisely as possible, a method for qualitative and quantitative analysis suitable for carbon nanomaterials is presented.

No description available.

Thermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. [1] In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because they are not capable of supporting larger structures. [2] The limitations of polymer reinforced composites have limited their entry into these applications, except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These materials have been successfully demonstrated their utility in extreme environments, such as spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited their use to similarly high performance applications where the costs are justifiable. Previous work by others with “fuzzy fiber” composites have shown that aligned carbon nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To this end vertically aligned CNTs were studied for their potential use, but found to be difficult to process with current conventional techniques. A composite material comprised of basalt, a relatively new reinforcing fiber, and phenolic, which has been used in high-temperature applications with great success was made to attempt to create a new material for these applications. To further improve upon the favorable properties of the resulting composite, the composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel iv technique was also developed to promote in-situ carbon nanotube growth of the resulting basaltcarbon composite without using a monolithic piece of cured phenolic resin in place of the standard aromatic hydrocarbon-catalyst precursor. [3, 4] The in-situ growth of carbon nanotubes (CNTs) was explored as their thermal stability [5] and effectiveness in improving performance has been previously demonstrated when used as a resin additive [6]. The specimens were examined with SEM, EDS, and TGA to determine the effects of both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the parameters of CVD processing. Additional testing would also show that the growth behavior of the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is a threshold temperature necessary to facilitate the availability of catalysts from within the basalt fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the newly formed composite with a high degree of thermal stability, making the new materials potentially usable in applications such as turbines, in addition to large-scale thermal protection systems.

Functionalized poly(para-xylylene) (PPX) coatings can be useful for biomaterials applications due to their biocompatibility and useful chemistry for the immobilization of biomolecules. However, their application is not widespread due to the difficulty in synthesizing the corresponding precursors. Here, a two-step method for amine functionalization of [2.2]paracyclophane (PCP) via direct nitration and reduction is developed. Nitration at super acidic conditions and temperatures as low as -78 °C, improved the stability of PCP toward strong acids and successfully minimized side reactions such as oxidation and polymerization. This procedure resulted in quantitative yields of 4-nitro-PCP, which was successively reduced by Raney nickel catalysis with sodium borohydride. Compared to the many other reduction systems, this method is simple, inexpensive and applicable in large scales. Additionally, carboxylation of PCP using the Freidel-Crafts acylation was attempted and so far, we have been able to show the synthesis of intermediate acylated products. Then, through the chemical vapour deposition polymerization of amino-PCP amine-functionalized poly(para-xylylene) (PPX-A) thin films were coated on Si wafer substrates. The substrates coated with PPX-A showed a higher surface energy compared with those of coated with un-substituted or chlorine substituted PPX films. Furthermore, results of the surface characterization demonstrated that the CVD process was able to transfer the functionalities of the precursors to deposited polymer films without alteration. However, the stability of primary amine groups in air and aqueous solutions is a matter of concern. Aging of amino-PCP and corresponding PPX-A films showed a decrease in the amount of primary amines which was accompanied by the appearance and increase of oxygen, indicating that the decrease of available amine groups is associated with oxidation. Nevertheless, both aminated precursor and polymer films remained intact under argon. The method presented here has great potential for widespread application of PPX-A as a convenient biomaterial for microarrays and cell culture. / Thesis / Master of Science (MSc)

Functionalized reactive polymer coatings can be used in various biomaterials applications such as immunoassays and biomolecule immobilization. Poly(para-xylelene) is a relatively new biomaterial that has attracted attention over the past few decades in these areas due to its unique properties and biocompatibility. The introduction of functionalized, particularly aminated, poly(para-xylylene) will extend the application of these polymer coatings to a wide variety of biological studies. However, their application is not widespread due to the difficulty in synthesizing the corresponding precursors. Here, a two-step method for amine functionalization of [2.2]paracyclophane via direct nitration and reduction is developed. Nitration at super acidic conditions and temperatures as low as -78 °C, improved the stability of [2.2]paracyclophane toward strong acids and successfully minimized side reactions such as oxidation and polymerization. This procedure resulted in quantitative yields of 4-nitro[2.2]para-cyclophane, which was successively reduced by Raney nickel catalysis with sodium borohydride. Compared to the many other reduction systems, this method is simple, inexpensive and applicable in large scales. It does not require harsh reaction conditions and within short reaction times, delivers quantitative amounts of the reduced product. At the end, 4-amino[2.2]paracyclophane was collected in 77% overall yield. Additionally, carboxylation of [2.2]paracyclophane using the Freidel-Crafts acylation was attempted and so far, we have been able to show the synthesis of intermediate acylated products. The successful syntheses of products were verified by FT-IR, NMR and MS, and comparison of their solubility and physical properties showed significant changes upon substitution of the pristine [2.2]paracyclophane. Then, through the chemical vapour deposition polymerization of 4-amino[2.2]paracyclophane amine-functionalized thin films were coated on Si wafer substrates and their properties were compared with Parylene N and C, two well-known poly(para-xylylene) films. The substrates coated with amino-poly(para-xylylene) showed a higher surface energy compared with those of coated with un-substituted or chlorine substituted poly(para-xylylene) films. Furthermore, results of the surface characterization conducted by grazing angle reflectance IR spectroscopy and XPS, demonstrated that the CVD process was able to transfer the functionalities of the precursors to deposited polymer films without alteration. However, with the applied process parameters we obtained a higher functional density of amine groups on the surface. These polymer films can be deposited on a variety of substrates and be used as functional surfaces for a variety of applications. However, the stability of primary amine groups in air and aqueous solutions is a matter of concern. Aging of 4-amino-[2.2]paracyclophane and corresponding poly(para-xylylene) films in air and mili-Q water was studied via XPS and NMR spectroscopies. The results showed a decrease in the amount of primary amines with storage time in air or water for both aminated precursor and polymer. The kinetics for these changes, however, were not equal for the precursors and polymer films. The decay of amine groups was accompanied by the appearance and increase of oxygen, indicating that the decrease of available amine groups is associated with oxidation which can transform them to more stable amide and nitro compounds. In total, practical challenges involved in manufacture, durability and applications of amine-functionalized Parylene coatings are discussed and a reliable scheme for fabricating such films with high tunabiliy of the surface functional density is demonstrated. The highly practical method presented here provides great potential for widespread application of amine-functionalized poly(para-xylylene) as an outstanding biomaterial for microarrays, tissue engineering and cell culture studies. / Thesis / Master of Science (MSc)

This thesis documents research done for a transient hot wire system that will be used in future thermal conductivity measurements of molten salts. Research done with molten salts have been limited because of erroneous measurement capabilities, but the current research strives to introduce a new technique to accurately record thermal conductivity over a wide range of temperatures. This work follows up on past transient hot wire researchers whose designs and tests produced an instrument that can measure the thermal conductivity of molten metals up to 750 K. The transient hot wire (THW) technique has been selected to be used in molten salt to derive thermal conductivity values. While running a THW test in molten salts is outside the scope of this thesis, a modular system has been created for the use of running transient hot wire test that allows for a robust and repeatable testing. A PEGDA/galinstan sensor is used for the validation of the system. A robust GUI has been created to automate the experimental procedure in a glovebox environment. The inverse finite element method has been paired with a non linear fit script to optimize calculations and reduce run times. Test have been done to determine the thermal conductivity of PEGDA. The overall uncertainty of the thermal conductivity measured with the PEGDA sensor is estimated to be ±5% at a 95% confidence level. With a THW system implemented and validated a sensor has been designed to work in molten salts. A model has been created in two separate FEA programs to validate design changes and material properties. The sensor is made up of a chemical vapor deposition (CVD) diamond substrate and tungsten wires to overcome corrosion and heat challenges introduced when measuring molten salts. New manufacturing processes have been designed to allow the technique to use these materials in the THW sensor design. The selected material properties of the sensor and extensive finite element work have laid down the ground work for future experimentation and understanding of the thermal properties of molten salts. It is predicted that the CVD diamond (carbide) apparatus design will use the THW techniques to operate with an estimated accuracy of ±3% over a wide range of temperatures, from ambient up to 1200 K. Manufacturing of the diamond-tungsten sensor have proven the viability of depositing tungsten wire onto CVD diamond and growing a secondary layer of CVD diamond over the tungsten wire.

Significant progress in reducing the growth temperature of the SiC epitaxial growth became possible in the previous work by using new chloro-carbon epitaxial growth method. However, it was established that even in the new process, homogenous nucleation of Si in the gas phase limited the growth rate. In the present work, new chlorinated silicon precursor SiCl4 was investigated as a replacement for the traditional silicon precursor SiH4 during the low-temperature chlorocarbon epitaxial growth. The new process completely eliminated the homogenous nucleation in the gas phase. Growth rate of 5-6 μm/h was achieved at 1300°C compared to less than 3 μm/h in the SiH4-based growth. The growth dependence on the C/Si ratio revealed that the transition from the C-supply-limited to the Si-supply-limited growth mode takes place at the value of the C/Si ratio much higher than unity, suggesting that certain carbon-containing species are favorably excluded from the surface reactions in the new process. Morphology degradation mechanisms, which are unique for the lowtemperature growth, were observed outside the established process window. Prior to this work, it remained unclear if CH3Cl simply served as a source of Cl to suppress homogeneous nucleation in the gas phase, or if it brought some other unknown improvements. In this work true benefits of CH3Cl in providing unique improvement mechanisms have been revealed. It was established that CH3Cl provided a much wider process window compared to C3H8. In contrast, even a very significant supply of extra Cl from a chlorinated silicon precursor or from HCl during the C3H8-based growth could not provide a similar benefit. The combination of the chloro-carbon and the chloro-silane precursors was also investigated at conventional growth temperature. High-quality thick epitaxial layers, with the growth rate up to 100μm/h were obtained, and the factors influencing the growth rate and morphology were investigated. Extensive optical and electrical characterization of the low-temperature and the regular-temperature epitaxial layers was conducted. The device-quality of the lowtemperature chloro-carbon epilayers was validated for the first time since the development of the chloro-carbon epitaxial process in the year 2005 by fabricating simple Schottky diodes and investigating their electrical characteristics.

No description available.

No description available.

No description available.