Stress in electrochemically deposited (ECD) magnetic films is an important parameter that can have a critical effect on the performance of MEMS devices such as microinductors. This is especially the case when thick layers of materials are required and where it is important to monitor and hence control stress to prevent cracking and delamination. The reliability of devices, therefore, deeply depends on process parameters and conditions used in depositing these materials on silicon wafers. A MEMS technique for measuring stress spatially around such a wafer has been developed and used to characterise the materials involved in the fabrication of a microinductor. This thesis discusses the design and fabrication of test structures, along with a custom built automatic measurement technique to wafer map the spatial variation of strain, on any sized wafers. The effect of agitation on the grain structure of NiFe has been observed to affect strain which were spatially mapped and correlated with the film composition and thickness. Film uniformity were also shown to improve in the absence of agitation in the bath. To further understand the fundamentals of ECD small scale beaker level galvano-static experiments have been employed to use the same test structures fabricated on small Si chips. The effects of hydrogen evolution on film stress and efficiency with the inclusion of boric acid and saccharin, have been discussed. It was concluded that the tensile stress developed in Ni and NiFe films have an inversely proportional relationship with the plating efficiency. The characterisation of electrodeposited copper films is also of importance as copper films are integrated with magnetic materials in the form of windings for microinductors. The variations in recrystallization and evolution of grains of ECD copper, is for the first time demonstrated spatially using the test structures. The effect of additives in bath on film uniformity was investigated and it was observed that with carrier and additive together the three phases of self annealing were more pronounced. Finally the use of these strain test structures have been demonstrated on thick polymer SU-8 films, which is employed as a structural material in microinductors. The effect of UV exposure dose on the cross linking properties of SU-8 has also been studied. It was observed that non-uniformity in the coated film thickness over the wafer can cause variations in the UV exposure during photolithography that effects the cross linking of the polymer hence, inducing different levels of tensile stress in the material. This unique methodology has therefore opened up many possibilities and can be used for characterising newer materials employed in MEMS, fine-tuning the manufacturing processes to achieve set goals in terms of material properties as well as uniformity and gaining a better understanding of the influence of processing conditions on the produced films.

Metallic glass is a class of materials which have a disordered structure of atoms, due to this, glasses lack grains and grain boundaries, which are present in their crystalline counterparts. Metallic glasses have many interesting properties worth investigating, such as high corrosion resistance or high mechanical strength. However, metallic glasses are metastable and will therefore crystallise if heated above the crystallisation temperature. MoSiZr alloys have been studied and to gain knowledge of how the composition affects the crystallisation temperature, which enables further improvement of thermal stability. Crystallisation temperatures of the MoSiZr alloys were investigated by heat treatments in vacuum and ex-situ X-ray diffraction and X-ray reflectivity analysis. The highest thermal stability of the alloys was exhibited by M48Si48Zr4, Mo43Si50Zr7, Mo50Si40Zr10 and Mo45Si43Zr12, they remained amorphous after heat treatment at 1073 K. The resulting crystalline phases are Mo3Si, Mo5Si3 and ZrO2. Oxidation of Zr in the alloys is present only when the Zr content is at least 10 at%, crystallisation is otherwise mainly driven by formation of Mo3Si. Further improvement of the thermal stability is possible by introducing new alloying elements at the cost of those that promote crystallisation. Keeping the content of Zr below 10 at% is of great importance to prevent oxidation.

A three-beam lateral shearing interferometer has been developed. The three-beam shearing interferograms consist of two sets of fringes, one of which acts as a carrier whose intensity is modulated by the second set. The depth of modulation is directly proportional to the phase difference between the middle beam and the outer beams. Phase errors on the order of π/2 cause every other fringe to go from complete dark to complete bright. Therefore, phase errors much smaller than π/2 can be detected. The three-beam interferometer is implemented in three ways: (1) thin film thickness measurement, (2) surface roughness measurement, and (3) surface figure measurement. The three-beam interferometer implemented to measure thin film thickness and surface roughness is accurate to 25 Å. Surfaces with different microstructure are characterized. We have found that each of those surfaces may have one or more of the following: (1) random roughness, (2) slow waviness, and/or (3) periodic structure. The three-beam interferometer is also implemented for testing optical surfaces. The three-beam interferometer is more capable in detecting small zonal errors than the two-beam interferometer. Three-beam interferograms of different surfaces are produced and analyzed. The three-beam interferometer has many advantages: (1) it is a stable, common path interferometer, (2) white light can be instead of coherent light to get rid of the effects of speckle and dust particles, and (3) it is a very low cost interferometer.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Bloodstain pattern analysis has been used in criminal investigations for more than 100 years. It provides valuable information about the events that took place prior to the formation of bloodstains at a crime scene. Forensic scientists use empirical laws to make a deduction from bloodstains, but the validity of these conclusions has been challenged in courts due to a lack of understanding of the underlying fluid mechanics. With this motivation, this thesis illustrates how mathematical modeling and numerical simulation can help gain insight into the spreading of blood droplets which eventually leads to the formation of a bloodstain. Understanding the fluid mechanics of droplet spreading and sliding has been accomplished with the help of the lubrication approximation which simplifies the Navier-Stokes equations to a more tractable form, i.e. a coupled set of non-linear partial differential equations. The resulting highly non-linear coupled set of equations is discretized using Finite-Difference. The resulting algebraic system is solved via an efficient Multigrid algorithm. These equations are modified to understand the effects of contact angle hysteresis, fluid rheology and absorptive properties of substrates on sliding dynamics. Variations in the inclination of the substrate cause the droplets to attain different advancing and receding contact angles as they slide down the incline under gravitational pull. This work explores a new way to introduce contact angle hysteresis in the numerical simulation to predict the different phases of a sliding droplet. Experiments of fluid droplet spreading/sliding on inclined surfaces have been performed to measure the terminal sliding velocity. A simplified hysteresis model has been proposed. This model automatically locates the section of the contact line which is advancing and the section which is receding which enables the application of the contact angles for the advancing and receding fronts and therefore takes into account contact angle hysteresis. A simplified analytical model is also suggested for droplets moving down the incline with near circular footprints. With the inclusion of the contact angle hysteresis, simulation results were brought in closer agreement with the experimental ones and the results from both were compared with the results from the analytical model. Blood is a shear-thinning fluid. One of the main objectives of this study is to investigate numerically the effect on the spreading and/or sliding of non-Newtonian fluid droplets on surfaces. To achieve this, the effect of rheology on the leveling of thin fluid films on horizontal solid substrates is first investigated as a preliminary investigation since this problem does not involve a contact line and is therefore more tractable. A mathematical model based on the lubrication approximation which defines non-Newtonian rheology using a power-law model is presented. Results for the leveling of sinusoidal perturbations of the fluid film highlight important differences between the leveling of shear-thinning and shear-thickening fluids. Namely, the onset of leveling occurs earlier for the shear-thinning fluid than for the shear-thickening one. However, the rate of leveling is higher for the shear-thickening fluid than the shear-thinning one. An important aspect of this part of the work is the verification of the numerical implementation using the Method of Manufactured Solutions (MMS). This leveling study also highlights differences between the leveling of two-dimensional and three-dimensional perturbations. This verified numerical formulation is then used to study the effects of rheology on the spreading/sliding of droplets. Results for the spreading of fully wetting droplets on a horizontal substrate show that, for all other quantities being equal, an increase of the flow index leads to a more rapid wetting. It also shows that, even for non-Newtonian fluids, the droplet velocity asymptotes to a constant value when sliding down an inclined substrate. This terminal velocity is strongly dependent on the rheological parameters and as it is reached, the droplets travel with a visibly constant profile. Finally, the numerical simulations revealed the formation of a tail at the rear of the droplet as it slides down the incline plane in the case of shear-thickening fluids. Finally, a more complex dynamics of fluid being absorbed in a porous substrate as it slides/spreads is considered. A mathematical model based on the lubrication approximation which defines the absorptive property of a substrate using a Darcy’s model is presented. This numerical model is verified with the help of comparison between the analytical and numerical solutions for the absorption of thin film on horizontal porous substrates. Results show that physical properties of the substrates, i.e. permeability, porosity, capillary pressure and equilibrium contact angle affect the rate of absorption of the fluid. Adding inclination to the problem, introduces the gravitational pull in the absorption dynamics. This directly shows its effects on the footprints formed inside the porous substrates. The following papers, based on sections of this thesis, have appeared or been accepted for publication: - Ahmed, G., Sellier, M., Lee, Y., Jermy, M., and Taylor, M. (2013). Modeling the spreading and sliding of power-law droplets. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 432:2–7. - Ahmed, G., Sellier, M., Lee, Y., Jermy, M., and Taylor, M. (2014). Rheological effects on the leveling dynamics of thin fluid films. Accepted for publication in the International Journal of Numerical Methods for Heat and Fluid Flow. - Ahmed, G., Sellier, M., Jermy, M., and Taylor, M. (2014). Modelling the effects of contact angle hysteresis on sliding of droplets on inclined surfaces. Submitted for peer review in The European Journal of Mechanics - B/Fluids.

Current technology has made possible the fabrication of multilayered optical elements for soft x-ray radiation. These structures find a variety of important applications. Difficulties in the design and fabrication of multilayers for soft x-rays are related to the lack of information about the properties of materials in the very thin layers (~5-100 Å) required. Imperfections cause the measured optical properties of the multilayers to deviate strongly from ideal behavior. Realistic calculations of reflectance must take these imperfections into account. We review the pertinent theory, with attention to the problem of including non-ideal properties. We also review characterization techniques suitable for the measurement of relevant structural and stoichiometric parameters of the multilayer. A detailed characterization procedure is presented. This procedure is capable of accurately determining the layer thicknesses, material densities, interfacial rms roughness or diffusion values, crystalline structure, concentration of contaminants, and extent of surface oxidation. The techniques used included low-angle x-ray θ-2θ diffraction with parallel-beam and Bragg-Brentano geometries, wide-film Debye-Scherrer ("Read") camera and Seemann-Bohlin diffractometer, Rutherford backscattering spectroscopy, and transmission electron microscopy. Si/W multilayer mirrors were designed for normal-incidence 210 Å radiation. Samples were fabricated using a magnetically-confined-plasma dc-triode sputtering technique. Our characterization procedure was applied to these samples. To our knowledge, this is the first time such a comprehensive set of characterization techniques has been applied to a multilayer x-ray optical element. The same samples were tested with synchrotron radiation over a wide spectral range, and for several incidence angles. The measured reflectance is in excellent agreement with curves calculated using the information obtained from the characterization results, with no adjustable parameters. The Si/W combination is shown to have good layering characteristics. The near-normal reflectance of the multilayers was 20 to 30 times better than the reflectivity of the best single-surface mirrors at the same wavelengths.

Optical filters and thin film optical devices play an important role in Science and Industry. Several significant applications have emerged in optics, microelectronics and computer technology. In this work, we study some aspects of their design and applications. One class of optical fibers, known as Christiansen filters, are based on scattering phenomena in suspensions of solid particles in a liquid medium. Some new scattering filters in the visible and the near UV regions and their performance characteristics are reported here. Feasibility to fabricate such optical filters in solid matrix form is established. Some applications of these scattering filters are discussed. After an introduction to the optics of homogeneous and isotropic thin films, I discuss the general design of anisotropic thin film media and a scheme implemented to calculate their performance. Optical anisotropy, produced by the growth-induced columnar microstructure in thin films and its effects on the performance of optical filters are studied. Large shifts in the peak wavelength of a typical narrow band filter are predicted. Magneto-optical (MO) thin film media of great importance to erasable optical data storage technology are studied. An approximate technique based on a 2 x 2 matrix formalism is developed to calculate the normal incidence performance of these media. To investigate anisotropic effects, to incorporate more than one magnetic film with arbitrary orientations of magnetization, and to study oblique incidence performance, a completely general 4 x 4 matrix technique is implemented in a computer program. Effects of substrate/superstrate birefringence in the read-out signal of MO media are investigated. Several optimizing design criteria, particularly, the effectiveness in employing appropriate metal or dielectric reflector layers are studied. The influence of the plasma edge of metals in enhancing the polar Kerr rotation of MO media is discussed with illustrations. A contour plot of the Kerr rotation and reflectance is developed to help in the design of these media. An explanation is given for the observation of Kerr rotation enhancement near the plasma reflection edge of the reflector layer adjacent to the active MO layer and in general, where the reflectance spectrum shows a steep gradient.

Thin films of alumina were deposited on ferrite (NiₓZn₍₁₋ₓ₎Fe₂O₄), glass, single crystal silicon and graphite substrates by RF sputtering. Though standard, amorphous Al₂O₃ films are readily soluble in hot phosphoric acid, these sputtered films exhibited only reluctant etchability by the acid. Experiments were initially performed to understand the parameters in the sputtering process which were influential in the formation of unetchable films. The results showed that a high concentration of water vapor or oxygen molecules in the sputtering chamber during deposition was the most significant variable controlling the growth of unetchable films. The films were categorized according to their degree of solubility in H₃PO₄ and were examined using various microanalytical characterization techniques. TEM analysis directly showed the existence of crystalline γ-Al₂O₃ in the film at the film-substrate interface. The γ-Al₂O₃ phase grew with a preferred orientation coincident with the substrate orientation--as in heteroepitaxial growth. The occurrence of this film phase was related to the oxygen partial pressure, the substrate material, and the substrate temperature and was believed to be the cause of the film's incomplete etching behavior.

Voltammetric and spectroelectrochemical results are presented for the one-electron reduction of n-heptyl viologen on clean and silane-modified tin oxide, and on ion-beam modified, indium-tin oxide metallized plastic optically transparent electrodes (ITO MPOTE) surfaces. The use of viologens (dialkyl and diaryl 4,4' bipyridium compounds) in redox chromic displays is well known with a number of papers and patents discussing their use. The ability to vary the coloration rates of the electrochromic reaction of these compounds can be strongly influenced by the state of the electrode surface. Potential-step experiments, where the electrode potential is controlled at low overpotentials, has shown that the viologen reduction occurs through a nucleation process. The work here indicates that an "instantaneous nucleation" model appears to be the favored pathway for the n-heptyl viologen reaction. Chronoabsorptometric analysis of the nucleation process is made possible by monitoring the strongly absorbing viologen cation radical. Chronoabsorptometric data can be used to calculate the nucleation site density on an electrode surface. On silane-modified and ion-beam modified electrode surfaces, a more preferred nucleation site is found for the deposition of the first monolayers of viologen. Through the attachment of a silane or the ion-beam modification of an ITO metallized plastic film (ITO MPOTE), a nonpolar layer is created adjacent to the electrode surface. Prior to electrochemical reduction the n-heptyl viologen dication is partioned and concentrated into this nonpolar layer. The effect is a preconcentration of the viologen next to the electrode surface resulting in a fixed number of nucleation sites and an enhancement of the nucleation rate.