Free-standing ultra-thin films and micro to nanoscale fibers offer a unique geometry in which to study the dynamics of thin film stability and polymer chain dynamics. By melting these films and investigating the subsequent processes of hole formation and growth, and fiber thinning and breakup, many interesting phenomena can be explored, including the nucleation of holes, shear-thinning during hole formation, finite-extensibility of capillary thinning viscoelastic fibers, and confinement effects on entanglement of polymer chains. Free-standing films in the melt are unstable and rupture due to instabilities. The mechanism of membrane failure and hole nucleation is modeled using an energy barrier approach which is shown to capture the dependence of hole nucleation on thickness. The formed holes grow exponentially and are found to grow under a shear thinning, nonlinear viscoelastic, high shear strain regime. These holes impinge upon each other to form suspended fibers. The fibers thin according to a model for the elasto-capillary thinning of the suspended viscoelastic fluid filaments. Monitoring fiber thinning allows for the acquisition of rheological properties as well as the transient, apparent extensional viscosity giving insight into strain hardening and eventual steady-state extensional viscosity. The decay and breakup of these fibers and their interconnected branched structure indicates the effects of confinement on chain entanglement in ultra-thin films. A transition below a critical film thickness, comparable to the dimensions of a polymer chain, shows drastically reduced interchain entanglements and a remarkably faster breakup of suspended fibers. The processes of fiber formation from the melting of ultra-thin films are explored in high detail and produce a new technique for the investigation of rheological and material properties, confinement effects, and the dynamics of thin films and polymer chains.

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<p> Part One deals with thin films of SnO₂ which were prepared by ion-beam sputtering, reactive sputtering and anodic oxidation. The films were found to be either amorphous or crystalline in their prepared state. </p> <p> The structure of the as-deposited amorphous films, as revealed by transmission electron microscopy, presented interesting features: there was a continuous structure in the case of high-temperature deposition, whereas an "island structure" was revealed in the case of low-temperature deposition. Furthermore, heat treatment of films having an "island structure" showed this structure to be maintained provided the heating was done with unsupported films, while the structure became continuous when heat treatment was performed on supported specimens. </p> <p> The crystalline form of the films has been worked out, and found to generally be cassiterite; nevertheless a phase different from cassiterite has been occasionally noticed during this work. In some cases it could be tentatively identified as SnO, while other cases it remains unidentified. Crystallization temperatures found here are somewhat different from those indicated in the literature, namely: 500, 300, 225ºC according to substrate temperature and nature and type of heat treatment. Anodic oxidation of tin has been performed(apparently for the first time) in a non-solvent electrolyte, the films being consistently crystalline. </p> <p> The results obtained in the case of films deposited on water-cooled substrates, have revealed a dependence of film structure on film thickness and this effect has been confirmed in supplementary experiments. Thus thick films appear to crystallize spontaneously at room temperature. </p> <p> Part Two deals with radiation damage studies. Our experiments on krypton-ion bombarded SnO₂ films show that amorphous specimens remain amorphous following ion bombardment. The electron-microscope evidence of whether crystalline SnO₂ is amorphized by ion bombardment was tentatively negative, while the gas-release evidence was strongly negative. </p> Part Three deals with diffusion in inert-gas implanted SnO₂. In the first section we give the theoretical background that enabled us to deduce from our experiments rough estimates of the melting temperature, self-diffusion temperature. and activation-energy for self-diffusion of the less mobile ion in SnO₂. In particular, we obtain the following results: </p> <p> T_melting = 2600 - 3000ºK </p> <p> T_self-diffusion = 1480 - 1870ºK for a 2 min. time scale and 134±44Å distance scale. </p> <p> ∆H_self-diffusion = 87,200 - 131,00 cal/mole </p> <p> Note that the melting point for tine oxide is variously reported in different handbooks to lie between 1400 and 2200ºK. From a comparison with other work we have concluded that our value for ∆H is very likely that for oxygen-ion diffusion. </p> / Thesis / Master of Science (MSc)

<p>Carbon nanotubes (CNTs) are arguably the most widely studied material within the field of nanotechnology. The impressive physical and electronic properties of these materials have led to their investigation in a diverse range of applications. In recent years, the deposition of inorganic nanoparticles upon the surface of CNTs has received much attention. Research within this field has been driven by the desire to develop new composite materials exhibiting novel electronic, optical, and catalytic properties. In addition to the decoration of individual nanotubes, several groups have also investigated the use of CNT thin films as scaffolds for the assembly of inorganic nanostructures as well as other secondary components, including polymers and biomaterials. Nanotube films exhibit a number of physical properties that make them suitable for such applications, displaying impressive electrical conductivity, flexibility, and thermal stability while also possessing a high surface area upon which chemical modification can be conducted.</p><p>This thesis presents work that demonstrates the potential of CNT thin films as flexible conductive scaffolds for the support of a variety of inorganic nanostructures. Procedures are described for the preparation of SWNT -Au nanoparticle composite films that, as subsequently demonstrated, are suitable substrates for the growth of III-V semiconductor nanowires using gas-source molecular beam epitaxy. At the time of writing, the majority of published research within this field focused upon the preparation of SWNT composite films containing spherical metallic or semiconductor nanoparticles. In contrast, the growth of semiconductor nanowires upon nanotube thin films had not been explored. The work described in this thesis therefore represents the development of a novel composite material that combines the flexibility of CNT films with the unique optoeletronic properties exhibited by semiconductor nanowires. The development of functional electronic devices incorporating these materials is also discussed, as is the extension of the methods developed to investigate novel composite materials that combine other inorganic nanostructures with carbon based substrates.</p> / Thesis / Doctor of Philosophy (PhD)

<p> The analysis, construction and performance of a new type of evaporated thin-film filter is described. It has the capability of frequency tuning by means of a single bias voltage.</p> <p> The device is basically a uniformly distributed resistance-capacitance network (URC) with a thin semiconductor film incorporated in the structure. The resistive film, insulator and semiconductor films constitute a metal-insulator-semiconductor system (MIS) whose capacitance is bias dependent. The device differs from other proposed tunable thin-film filters in the fact that the capacitance can be altered independently of the distributed resistance.</p> <p> A theory is developed to account for the effects of MIS-losses and parasitic inductance on the performance of URC-null networks. These parasitic effects manifest themselves in four different ways: (i) A shift of the null from the position predicted by the ideal theory. (ii) A change in the notch parameter α for an optimum null. (iii) A detuning effect in the case of tunable notch filters. (iv) A reduction in the available tuning range; the so-called "tuning range compression".</p> <p> Experimental units were made by vacuum evaporation of Nichrome, Y2O3, CdS and Al onto alumina substrates. An attempt is made to relate the device characteristics to the material properties. In this respect, the relative dielectric permittivity and thickness of the insulator, the doping density of the semiconductor, the semiconductor-insulator interface states and the bulk states in the semiconductor are found to be the most important parameters.</p> <p> Filters were built which operated in the frequency range 600 kHz to 6 MHz. The best notch filter has a tuning capability of 30% with a ±15V bias voltage. The notch depth is over 60 dB in most cases. A tunable bandpass amplifier which was constructed, has a centre frequency which can be shifted between 6 MHz and 7 MHz with a ±3.5V bias voltage. The Q of this particular device was measured to be 742.</p> / Thesis / Doctor of Philosophy (PhD)

<p> This work presents theoretical calculations of some of the most important electrical characteristics of thin film, insulator-dominated semiconductor devices. Solutions of prespecified accuracy for an a.c. transmission line model of the semiconductor in such configurations as the MIS (Metal-Insulator-Semiconductor) structure and the SIS (Semiconductor-Insulator-Semiconductor) structure are given. Together with an accurate solution of the d.c. bias problem, exact C-V (Capacitance-Voltage) and G-V (Conductance-Voltage) characteristics can be found at any frequency. SRH (Shockley-Reed-Hall) impurity centres and surface states have been included in both the d.c. and a.c. solutions. In addition, accurate studies of the low temperature dopant impurity response can be made since the d.c. solution uses full Fermi integrals over arbitrary densities of states with the impurity dopant band treated like an SRH centre for the a.c. solution.</p> <p> In non-equilibrium situations, such as those which occur with the application of light or carrier injection by tunnelling, the a.c. solution requires active elements in the transmission line model but the transmission line can still be solved to a prespecified accuracy provided an accurate solution of the d.c. bias problem can be found. In this thesis the d.c. solution for the case of light-induced pair production is considered under the assumption of bulk controlled d.c. quasi Fermi level shifts. Thus the accuracy of the related a.c. conductance and capacitance solutions is dependent on the reliability of this assumption.</p> <p> The detailed treatment of the a.c. admittance of the MIS structure is justified by its technological importance and fundamental insight gained on impurity centre and surface state effects.</p> <p> The other work presented in this thesis is devoted to a study of a new thin film device structure, the SIS diode. First, the a.c. admittance characteristics for the thick insulator case are predicted to a prespecified accuracy. Then a simple treatment for part of the SIS d.c. tunnelling problem is done to qualitatively predict the effects of such parameters as doping density, temperature and insulator thickness on current-voltage characteristics. Finally, a simple generalization of the a.c. transmission line to include the effects of tunnelling is given which allows accurate solution for the a.c. admittance of tunnelling SIS diodes if the complete d.c. non-equilibrium problem can be accurately solved.</p> <p> Practical application of the thick-insulator SIS diode will undoubtedly stem from its wide range of interesting low and high frequency response characteristics. Among the most interesting of these characteristics is a bell-shaped high frequency C-V response previously unobserved in other two terminal devices.</p> <p> An interesting negative resistance feature, which partly resembles the negative resistance region of the p-n junction tunnel diode, is analyzed for the degenerate SIS p-i-n thin insulator structure. While the thick insulator SIS device has recently been fabricated and the bell-shaped high frequency response experimentally observed, experimental verification of the tunneling characteristics of the SIS diode has as yet not been fully realized.</p> / Thesis / Doctor of Philosophy (PhD)

<p> The objective of this investigation was to examine the potential of the point heat-flux meter in studying the dynamic heat transfer process in a scraped-surface heat exchanger.</p> <p> The heat-flux meters were an integral part of the copper heat exchanger which was steam-heated. Water was passed through the equipment as a thin film. The steam condensate was collected for measurement.</p> <p> Mathematical analysis related the transient differential temperature of the detector with the transient applied heat flux. A mathematical model was found that would estimate the instantaneous heat flux from the heat-flux-meter experimental temperature difference.</p> <p> Instantaneous and time-average local heat fluxes were measured by the heat-flux meter and the condensate respectively. The meter accuracy was -7000 Btu/hr sq ft.</p> <p> The heat-flux meter can be used in studying dynamic heat transfer processes.</p> / Thesis / Master of Engineering (MEngr)

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