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TiO2 films as electron collecting interlayers are important in determining the efficiency of organic photovoltaics (OPVs). Various methods of film deposition have been explored, and they revealed the tradeoff between pinhole free coverage (large shunt resistance) and small film thickness (small series resistance). It is hypothesized that atomic layer deposition (ALD) with its self-limiting nature and sub-nanometer level control would be able to circumvent this problem and provide TiO2 films of pinhole free coverage and small thickness. TiO2 films made by chemical vapor deposition (CVD) and ALD were investigated and compared. Conductive atomic force microscopy (CAFM) was used to characterize film morphology and conductivity. X-ray photoelectron spectroscopy (XPS) was utilized to analyze film composition and chemical state. Cyclic voltammetry (CV) was able to reveal the hole blocking capability of films. Finally, organic photovoltaic devices were made with different TiO2 films to reveal the relationship between device property and film characteristic. It is found that both CVD and ALD created TiO2 films with Ti4+ species containing oxygen from hydroxyl groups. They both showed conformal coverage of the electrode via CAFM and CV measurements, and clearly ALD method achieved this with a thinner film and smaller series resistance. This work provided the evidence of effective and surprising capabilities of electron harvesting and hole blocking of ultrathin ALD TiO2 films for OPVs.

The importance of platinum group metals for catalytic and microelectronic applications has prompted research into the development of novel molecular precursors for chemical vapor deposition of thin films of these metals. A variety of molecular architectures, ligand systems, as well as deposition conditions are investigated and related to the morphology and composition of the resultant films. For example, amorphous thin films of ruthenium and phosphorus alloys are deposited using single source metal hydride precursors, while use of the 3,5-di-substituted pyrazolate ligand in conjunction with various rhodium starting materials leads to a variety of different volatile monomeric and dimeric complexes. Synthesis of pyrazole and pyrazolate complexes of tungsten and palladium are also explored. In a related research area, progress towards the development of novel synthetic routes to mesostructured transition metal phosphides and borates for Li-ion battery electrode applications is summarized. Traditional routes to these materials involve high-temperature syntheses, allowing limited control over morphology. Identification of low-temperature reaction conditions necessary to afford a desired composition, morphology and electrochemical performance of the bulk material are the main goals of this project, and results are discussed with various early transition metals. / text

Chronic venous disease (CVD) of the lower limbs is a major problem in the western world with 1% of the adult population estimated to be affected at any one time. The clinical sequelae of CVD of the lower limbs range from oedema, haemosiderosis and pigmentation, to gross lipodermatosclerosis (LDS) and venous ulceration. The site most commonly affected is the gaiter area of the lower limb. The extent and severity of venous disease can be assessed by clinical and physiological methods which include duplex ultrasonography and plethysmography. Tissue oedema can be assessed by volumetric or circumferential measurements and venous ulcers may be quantified by area measurements and response to treatment in ulcer healing studies. In the vast majority of patients a spectrum of skin changes precedes venous ulceration. At present, there is no standardised objective method of assessing the degree of skin change in these patients, so that the response to treatment can be objectively monitored. I have developed a tissue tonometer and standardised the methodology for the objective assessment and quantification of the skin changes seen in patients. The tissue tonometer is a simple non-invasive instrument which uses a sensing device that detects the movements of a loaded plunger placed on the skin. The movement of the plunger is dependent on the mechanical properties of the skin and subcutaneous tissue. The instrument is positioned on the gaiter region of the leg with the subject in the supine position. The movement of the plunger into the tissues is recorded and analysed by a computer. The data obtained from the tonometer were analysed as distance and rate constant parameters. A simple mathematical model using spring and dashpot constants was also applied to see if it fitted the data. Skin compliance was investigated in normal control subjects and patients with varying severity of skin changes due to CVD, clinically classified according to the CEAP (Clinical, (A)Etiological, Anatomical and Pathophysiological) method. There was a significant reduction in skin compliance in patients with clinically severe LDS as compared to normal controls and patients with pigmentation alone or oedema without any clinical evidence of skin change. I further investigated the correlation between the recently introduced CEAP method of classification and scoring of chronic venous disease of the lower limbs with the tissue tonometry findings and parameters obtained with duplex ultrasonography, air plethysmography and photoplethysmography. Tissue tonometry provides a standardised objective means of assessing the severity of skin change in CVD which may prove to be useful in evaluating response to a particular treatment and comparing data from different centres. The deterioration of the venous physiology shown by blood flow measuring techniques correlates poorly with the clinical sequelae of venous disease, whether assessed by a trained observer or measured by the tonometer. Patients show a wide range of sensitivity to venous valvular incompetence, suggesting that factors related to the tissue response to venous hypertension are crucial in determining which patients develop venous ulceration.

The chemical vapour deposition (CVD) of graphene is the most promising route for production of large-area graphene films. However there are still major challenges faced by the field, including control of the graphene coverage, quality, and the number of layers. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. This thesis contributes to the growing body of work on graphene CVD by uniquely exploring the gas phase chemistry and fluid flow in the hot-wall graphene CVD reactor. Firstly the reported parameter space for the hot-wall CVD of graphene on copper was mapped, informing the subsequent work and providing a resource for the wider community. A CVD reactor was constructed to extend this parameter space to lower pressures using methane as a carbon source, and the films were categorised using scanning electron microscopy, Raman spectroscopy and optical dark field microscopy. The latter showed particular promise as a rapid and non-destructive characterization technique for identifying graphene films on the deposition substrate. The gas phase equilibrium compositions were calculated across the parameter space, and correlations between the stabilities of various chemical species and the types of deposition were drawn. This laid a foundation for the remainder of the experimental work, which explored the effect of diluent gases and different feedstocks on the growth to understand the importance of the identified correlations. Diluent gases (argon and nitrogen) were added to the experimental conditions and the thermodynamic model, and were found to reduce the degree of coverage of the graphene films. This result shows that the CVD of graphene is sensitive to factors other than the thermodynamic state parameters, such as the fluid flow profile in the reactor and inelastic collisions between the higher mass diluent gases and the methane/hydrogen/copper system. Using a nitrogen diluent raises the equilibrium carbon vapour pressure and seems to allow larger graphene grains to form. This suggests that thermodynamic factors can contribute to the nucleation of graphene films. Varying the hydrocarbon feedstock and the process conditions indicated that the structure of the deposited carbon is closely related to the nucleation kinetics. Three nucleation regimes are associated with different types of deposition: homogeneous nucleation with amorphous carbon or soot; uncatalysed nucleation with multilayer deposition; and nucleation processes controlled by the copper substrate withpredominantly monolayer deposition. Changing the feedstock from methane to acetylene resulted in poorer graphene coverage, showing that thermodynamic control does not apply in the portion of the parameter space at the high temperatures and lowpressures most successfully used for the deposition of continuous graphene monolayers.

No description available.

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.

No description available.

Unavailable / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-08-02 23:11:16.825

No description available.