The cell membrane is a highly complex structure consisting of a large diversity of phospholipids and macromolecules. There exist a variety of diseases that compromise the integrity of this key component of the cell. This thesis considers the investigation of interactions between β-amyloid peptide (Aβ₄₂) and lipid bilayers. To facilitate understanding of this complex system, it is advantageous to employ a model sample; supported lipid bilayers (SLB) and giant multilamellar vesicles (MLVs) are used as proxy cell membranes. These nanostructures are widely used as models of cellular membranes in many areas of scientific research. Phospholipid molecules self-organise into bilayer structures containing phase-separated microdomains, which are believed to be important in many biological processes. This study aims to develop model systems and experimental tools to explore hypothetical mechanisms through which the β-amyloid interacts with the lipid membranes. A lack of mechanistic understanding is the major challenge to our efforts to elucidate not only the interactions of the Aβ42 with the lipid membranes, but also the behaviour of these systems towards the changes of the environmental conditions (pH, concentration, temperature). Our results suggest that there are various different methods, such as AFM, CARS microscopy and Raman spectroscopy as well as neutron scattering that are capable of fast imaging. Overall, all these techniques contributed in a complementary study of Aβ₄₂ aggregation states under extreme and physiological conditions as well as to image Aβ₄₂ interactions with lipid bilayers consisted of specific lipids.

Chemical Vapor Deposition (CVD) Diamond is a promising technology for the passive cooling of high power Gallium Nitride (GaN) semiconductor devices. The high thermal conductivity diamond can be placed near the junction of the GaN transistor either by direct growth on the backside of the GaN or by bonding it to the GaN. In both cases, the thermal resistance near the interface with the diamond and any semiconductor it is attached to has the potential for large thermal resistance that limits the effectiveness of the diamond layer. In this work, several techniques are developed to understand the thermal conductivity of thin diamond films and the thermal boundary resistance with Si and GaN substrates. Anisotropic thermal conductivity measurements are made using Raman spectroscopy temperature mapping along with electric resistance heating. For devices, the thermal boundary resistance is measured using transistors as the heat source and thermal mapping using Raman spectroscopy. Quick screening methods based on Raman, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) are also correlated with the thermal properties of the films. Based on this work, the properties of CVD diamond films near the interface of semiconductor substrates is revealed for layers less than 5 µm in thickness and their impact or limitations on thermal management shown through simulations.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Carbon nanotubes have been found to have extraordinary properties, such as ballistic electrical conductivity, extremely high thermal conductivity and they can be metallic or semiconducting with a wide range of band gaps. There are however several issues that have to be solved before these properties can be fully utilised. One of these issues is that the nanotube growth temperature must be lowered in order to make the synthesis compatible with the fabrication processes used in electronics. The whole environment is heated to temperatures typically higher than 500 °C in the standard growth techniques whereas only a very localised area is heated in the technique developed here. This technique thus provides a way around the temperature issue. In the method developed here, the catalyst is deposited on top of a small metal (molybdenum) wire on the substrate. The high temperature required for nanotube growth is then reached by Joule heating by sending a current through the metal wire. This process eliminates the furnace which is used in conventional chemical vapour deposition and localises the high temperature to a very small and controlled area of the sample. Consequently, this technique is compatible with the semiconductor technology used today. Another advantage of this technique is that, since no furnace is required, a small growth chamber, which fits under a microscope, can be used. This allows in situ studies of the growth by optical microscopy and by Raman spectroscopy. By changing the carbon precursor, single- or multiwalled nanotubes can be grown. This can be important when producing devices since single-walled nanotubes predominantly are semiconducting whereas multi-walled mainly are metallic. The multi-walled nanotubes grow in a rapid and concerted process. This growth was monitored through an optical microscope. It was found that the thickness of the support layer and especially the catalyst are even more crucial parameters for nanotube growth using this local heating technique than in conventional processes. The activation energy could be extracted and was found to be 1.1-1.3 eV. The carbon nanotube growth was investigated by in situ Raman spectroscopy. The growth evolution could be well described by a model using the initial growth rate and the catalyst lifetime as parameters. The process was found to be limited by the mass transport of the carbon precursor. It was found that the molybdenum wire creates an additional pathway for the carbon cycle from gas to nanotube formation. The Raman spectra were studied at elevated temperatures. A decrease in intensity and a shift towards lower wavenumbers with increasing temperature was observed for the Stokes signal. It was found that the laser used for the Raman measurements could heat the nanotubes to high temperatures without any other heat source. Vertically aligned arrays of nanotubes were grown by conventional CVD. These arrays were actuated by applying a DC voltage between them. An effective Young's modulus of the arrays was found to be similar to that of rubber, which is orders of magnitude lower than for individual nanotubes. The capacitance between the arrays was measured to be tens of fF with a tunability of over 20%.

Knowledge of the structural arrangement of the atoms in a solid is an important prerequisite to a detailed understanding of physical and chemical properties. In this work, structural investigations of phosphate (Ca-P-O) and aluminofluorophosphate (Na/Ba-Al-P-O-F) glasses with and without nitridation were performed. Nitrogen was introduced via metal nitrides (AlN, Ba₃N₂, or Ca₃N₂) or ammonia gas treatment of the melt. These glasses were characterized by chemical, thermal and optical techniques. Infrared, Raman, and MASS NMR spectroscopies were used to determine the local coordination and atomic structure of these glasses. The presence of peaks corresponding to P-O-P and PO₂ molecular vibrations in Ca-P-O glasses provided a basis for proposing a calcium metaphosphate glass structure comprised of long chains. As calcium oxide is added to calcium metaphosphate glasses, the long chains are broken up into shorter pyrophosphate units, as indicated by the presence of PO₃²⁻ terminal groups. MASS NMR of Ba-Al-P-O glasses showed that Al occurs as Al(4), Al(6), and either Al(5) or Al(6) linked through Al-O-Al bonds (such as in α-Al₂O₃). The addition of F in both the Ba-Al-P-O-F and Na-Al-P-O-F systems increases the relative abundance of Al(6). The ³¹P peak maxima in the MASS NMR spectra at about -5 to -10 ppm for Ba-Al-P-O-F-N glasses and -9 to -17 for Na-Al-P-O-F-N glass, indicate that pyrophosphate units dominate the structure of these glassy solids. Raman spectroscopy of a series of Al(PO₃)₃-NaF glasses showed that an increase in NaF content causes a shortening of the P-O-P chains and a more disrupted structural network. The presence of P-O-F units were observed only at the higher (>80 mole %) NaF contents. While the complexity of the Raman spectra make it difficult to confirm the presence of P-N bonding, glasses prepared in an ammonia atmosphere (nitrogen content of 1.6 wt%) suggest the possibility of P-N bonding on the basis of a vibrational peak at 826 cm⁻¹.