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Repairing injured nervous systems requires the ability to regenerate axons and to guide growing axons to their targets. To achieve guidance, mechanistic studies in physiological axon guidance in developing neurons will be critical. It is known that the growth cone, the structure at the leading edge of developing axons, responds to chemical and mechanical cues in the environment to steer the axon to its target, and chemotropic cues have been well characterized. However, the mechanotransduction pathways involved in axon guidance are currently not well understood. Photoacoustics offers a means for mechanical stimulation of neurons that can be used to study axon guidance by mechanotransduction. Compared to other methods, photoacoustics offers a non-genetic, extremely high spatial precision method for neuron stimulation that works by converting pulsed light energy into ultrasound waves by light absorption and subsequent thermal expansion and contraction of the photoacoustic material. In this thesis, photoacoustic stimulation of neuronal growth cones was used to study axon guidance mechanisms. First, a photoacoustic device that was previously developed in this lab was fabricated by applying a photoacoustic composite material coating to the tip of an optical fiber. This device was used for targeting the growth cones of Xenopus laevis primary embryonic neurons in vitro, and subsequent growth patterns were analyzed using optical microscopy with a custom-built quantitative model for measuring growth rates and directional changes. Calcium imaging by Fluo-4 fluorescent dye was used to show successful activation of mechanotransduction pathways. This thesis offers the first evidence that photoacoustic stimulation of growth cones is possible and sets up future research to explore axon guidance by mechanotransduction using photoacoustic stimulation.

The application of functional thin films encompasses a wide range of industries and technologies, where these films are applied to enhance the performance, durability, and functionality of various materials and devices. Specifically, polymer thin films play an important role for their molecular architecture and composition. This work aims to use poly(glycidyl methacrylate)(PGMA) polymer as a backbone and modify the PGMA with phenolic derivatives to perform the phenol-assisted electrodeposition. This work includes the selection of phenolic derivatives, the process of modification, the method of purification, the study of how to tune film thickness, and broadening this method to other polymers. / 2026-05-23T00:00:00Z

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<p>This investigation is primarily concerned with the development of a suitable high-precision sectioning technique to be employed in studies of depth distributions of energetic ions in Mo and V. It consists of two main parts.</p> <p>In the first part, uniform anodic oxide films of controlled thicknesses have been grown on poiycrystalline V, Mo, and W (the latter, primarily for comparison with earlier works on W) in acetic acid-sodium tetraborate solutions containing small quantities of water. These anodic films which show bright characteristic interference colours when formed at >10 volts, are shown to be rapidly soluble in a dilute solution of KOH whereas the underlying metal is attacked at a rate of less than ~100Å per day. The thickness of the anodic films per volt has been established using ellipsometry and conventional weight-loss measurements.</p> <p>Kinetics of anodization have been studied at constant-current and constant-voltage. An analysis of these data shows the composition of the films on Mo and W to be close to Mo0₃ and W0₃ respectively while those on V were intermediate between V₂0₄ and V₂0₅. The density of the films on Mo and the differential field strength, E_d, for films on Mo and W have also been determined.</p> <p>In the second part, a theoretical background consisting of an outline of the theory of Lindhard, Scharff and Schiøtt, has been provided; in the absence of experimental data, this theory is generally used to estimate the depth distribution of ions in amorphous targets. Experimental range profiles have been determined for 5-30 keV Kr⁸⁵ in polycrystalline Mo using the technique developed in the first part and the results obtained show a large discrepancy when compared with Lindhard theory. The extent of disagreement with theory is similar to that obtained by previous workers with targets such as Al or W.</p> <p>Evidence is presented to show that this large discrepancy may be attributted to crystal-lattice effects (i.e. channelling). For example, it is shown that the discrpency is not due to the anodizing-stripping sequence being sensitive to bombardment. Also, it is demonstrated that the Mo used had a pronounced preferred orientation such that the open directiors <100>, <211>, and <111> were normal to the surface.</p> <p>An important part of future work will be to extend techniques such as those described here to the metal Be, for Be is the lightest target material that can be conveniently worked with.</p> / Master of Science (MS)

<p>The experiment work pertaining to this thesis can be divided into two parts: a) The study of the ion beam mixing process in the platinum-iron system and b) Electrocatalysis measuremnts on the mixed platinum-iron alloys. The ion beam mixing was studied using a 120 keV Fe+ ion over a rang of temperatures from 298K to 523K. A thin film of platinum was evaporated onto an oxide free substrate of iron to form a bi-layer sample. In order to check whether the interface was clean and oxide-free, Auger electron spectrometry was used along with sputtering. The mixing was studied primarily using RBS. The TEM was also used to characterize the samples before and after mixing.</p> <p>At low temperatures (<373 K), the mixing is very small and found to take place by collisional processes. At higher temperatures (>473 K) iron moves rapidly into the platinum. The activation energy for the platinum migration into the iron was found to be ~0.5 eV. This suggests that the vacancy mechanism is operating about 423 K. The films produced by mixing at low temperatures are highly stressed and there are a considerable amount of twins formed. It was also found that the grain size increases with dose and temperature.</p> <p>The surface concentration Pt in the mixed film is high ~90%. This results in an improvement of ~25% in the overvoltage for the ion beam mixed films compared to an iron electrode. Ion beam mixed films were found to be more stable than iron electrodes simply coated with films with an evaporated platinum layer. This appears to be the result of the improved adhesion between the platinum and iron as a result of the ion beam mixing process. For unmixed samples, an oxide layer is able to form on the iron surface at the platinum./iron interface, possibly because of cracks in the platinum layer, and this results in platinum pealing off the electrode leaving just the iron electrode.</p> / Doctor of Philosophy (PhD)

<p>The galvanic nature of crevice corrosion is a generally accepted concept but the coupled electrochemical behaviour and its role in crevice corrosion has not been really studied until recently. Among many arguments regarding the mechanism of crevice corrosion, whether or not being able to reasonably interpret the shape of crevice attack is an indication of whether or not the physical processes involved in crevice are profoundly understood. Based on a critical review of the state-of-the-art of the crevice corrosion studies, the necessity of studying the role of galvanic coupling effectiveness in crevice corrosion is then proposed. The concept of a uniform anode/cathodic pair with IR-drop is developed. It is shown that the galvanic coupling effect may play a significant role in crevice corrosion. For a uniform anode/cathode pair with IR-drop, the coupled potential/current relationship is a function of the kinetics on both the anode and cathode. It is found that when the anodic environmental aggressiveness exceeds certain value, the whole process is shifted from anode control to cathodic control and, therefore, the anodic dissolution rate is significantly enhanced. What complicates the process is the inevitably existing IR-drop which increases while the anodic-to-cathodic control shift occurs. This increased IR-drop is the consequence of the increase in anodic dissolution and on the other hand impedes the further increase in anodic dissolution. Therefore, the current/potential relationship in this case is being treated in a "covariant" way. In order to define the degree of the enhancement in anodic dissolution due to the coupling effect, a dimensionless parameter, the coupling coefficient η, is proposed, which is a function of anodic solution aggressiveness as well. A real corroding crevice is considered as an array of the uniform anode/cathode pair with different solution ohmic resistance. The concept of coupling effectiveness and the procedure of obtaining coupled dissolution rate as a function of solution aggressiveness and ohmic resistance of the solution phase are applied to a real corroding crevice, attempting to explain the shape of crevice attack and its evolution. Micro-electrodes techniques for measuring solution aggressiveness inside a real corroding crevice and a proper method for calculating the coupled dissolution rate at any location inside the crevice are developed. By (i) determining the local solution aggressiveness at different locations inside a corroding crevice, (ii) obtaining the kinetic information for the interior anodes in corresponding environments, and (iii) calculating the coupled dissolution rates at these locations, we are able to obtain the distribution and evolution of the coupled dissolution rate and the coupling effectiveness along the crevice. The shape of the crevice attack and its evolution with time is then attempted by integrating the coupled dissolution rate over the total time elapsed. The results show reasonably good agreement between the calculated shape of attack and its evolution and the experimental result. An alternative criterion for crevice corrosion of materials is proposed based on the response of the material to coupling effect.</p> / Doctor of Philosophy (PhD)

This thesis mainly treats the fabrication and applications of micro-optical elements in the semiconductor materials gallium arsenide (GaAs) and diamond. The recent trend in high-capacity data transfer using light as the information carrier creates new demands on the optoelectronic systems, such as small size, low cost and the integration of many components. Micro-optical components are key elements for building compact optoelectronic systems and are well suited for integration with other devices. Another area where micro-optical elements can play an important role is the use of lasers in medicine, industrial machining, metrology, etc. In most cases, the laser beam characteristic is not directly suited for the application and external optics is needed to focus, shape or split the laser beam. In the first part of this thesis, the fabrication of continuous-relief diffractive optical elements, such as diffractive lenses and blazed gratings, in GaAs is examined. The manufacturing technology uses electron-beam lithography followed by plasma etching in an inductively coupled plasma etching system. In the next step, these diffractive elements were monolithically integrated with vertical-cavity surface-emitting lasers. In the second part of this thesis a novel topic is examined, diamond micro-optics. Diamond is a unique material in many aspects, it is the hardest material mankind knows, it has an extremely wide optical transmission window, and it possesses the highest thermal conductivity of all solids. Until today, due to difficulties in machining diamond, the realization of diamond optics has been limited. By using the same technology we earlier developed for the fabrication of GaAs optics we demonstrate for the first time continuous-relief structures in diamond of optical quality. Several diamond micro-optical structures are presented; sub-wavelength gratings for reduction of unwanted Fresnel reflections, diffractive fan-out elements used to split a CO2-laser beam and refractive microlens arrays. The accuracy of the fabrication process by plasma etching was evaluated by optical and topographical measurements, in all cases the optical components were of very high quality.

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