The pyroelectric ceramic thin films and detectors based on PbTiO3[abbreviated to PT] that exhibit a low dielectric constant and a high pyroelectric coefficient, which were fabricated by a sol-gel method in this thesis. The (PVDF/PT) pyroelectric bilayer thin films with low leakage current were deposited on PbTiO3/Pt/SiO2/Si substrates by the spin coating. 1,3 propanediol was used as solvent to minimize the number of cycles of the spin coating and drying processes to obtain the desired thickness of PbTiO3 thin film. By changing the concentrations of PVDF solutions (0.6M~1.0M) and thickness of PVDF thin films (50nm~580nm), the effects of various processing parameters on the bilayer thin films growth and the response of pyroelectric infrared detector device are studied. Experimental results reveal that the thickness of PVDF thin films will influence strongly on dielectricity, ferroelectricity, leakage current and pyroelectricity of (PVDF/PT) bilayer thin films. With the increase of the thickness of PVDF thin films, the relative dielectric constant of (PVDF/PT) bilayer thin films decrease from 63 to 20. The tan£_ increases from 0.00152 to 0.0024, leakage current decreases from 1.54x10-6 A/cm2 to 3.86x10-7 A/cm2, Ec decreases from 70.7 KV/cm to 35 KV/cm, Pr decreases from 6.29 £gC/cm2 to 1.14 £gC/cm2, and £^ decreases from 22.5x10-9 C/cm2K to 6.8 x10-9 C/cm2K with an increase of the thickness of PVDF thin film. In addition, the results also show that the largest figure of merit Fv is 1.31x10-10 Ccm/J as the thickness of PVDF thin film is 80nm. With the increase of the thickness of PVDF thin film, the figure of merit Fm decreases from 2.26x10-8 Ccm/J to 1.07x10-8 Ccm/J. The voltage responsivities (Rv) measured at 20 Hz decrease from 1383 V/W to 804 V/W and the specific detectivities (D*) measured at 100Hz decrease from 2.72x107 cmHz1/2/W to 1.71x107 cmHz1/2/W. From the result of D*/J, the result shows the device possesses the best property as the thickness of the PVDF thin film is 165nm. Therefore, the (PVDF/PT) bilayer thin film with the thickness 165nm of PVDF thin film is the most suitable for the applications of pyroelectric thin film IR detectors.

This dissertation is focused on understanding heterogeneous metal catalysts supported on oxides using a model catalyst system of SiO2 thin film supported metal nano-clusters. The primary technique applied to this study is scanning tunneling microscopy (STM). The most important constituent of this model catalyst system is the SiO2 thin film, as it must be thin and homogeneous enough to apply electron or ion based surface science techniques as well as STM. Ultra-thin SiO2 films were successfully synthesized on a Mo(112) single crystal. The electronic and geometric structure of the SiO2 thin film was investigated by STM combined with LEED, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The relationship between defects on the SiO2 thin film and the nucleation and growth of metal nano-clusters was also investigated. By monitoring morphology changes during thermal annealing, it was found that the metal-support interaction is strongly dependent on the type of metal as well as on the defect density of the SiO2 thin film. Especially, it was found that oxygen vacancies and Si impurities play an important role in the formation of Pd-silicide. By substituting Ti atoms into the SiO2 thin film network, an atomically mixed TiO2-SiO2 thin film was synthesized. Furthermore, these Ti atoms play a role as heterogeneous defects, resulting in the creation of nucleation sites for Au nano-clusters. A marked increase in Au cluster density due to Ti defects was observed in STM. A TiO2-SiO2 thin film consisting of atomic Ti as well as TiOx islands was also synthesized by using higher amounts of Ti (17 %). More importantly, this oxide surface was found to have sinter resistant properties for Au nano-clusters, which are desirable in order to make highly active Au nano-clusters more stable under reaction conditions.

Recently, with the escalating demands for optical communication, the need to use broadband laser light sources in optical communication network system has increased. Henceforward, the broadband characteristes of Cr4+:YAG crystal fiber possess signifies its indispensability. Furthermore, Yb3+:YAG-silica also has its advantages in high power laser domain. In this thesis, the crystal fiber grown by the laser heated pedestal growth method is used as the laser gain medium with fused silica packaging technique. Cr4+:YAG double-clad crystal fiber with a core diameter as small as 11 £gm was achieved. Moreover, a Yb3+:YAG-silica layer was formed due to the strong inter-diffusion between silica capillary and Yb3+:YAG crystal. When the silica all diffused into the Yb3+:YAG, a Yb3+:YAG-silica fiber with 125-£gm core was obtained with waveguide structure. By directly coating the optical thin films onto the end faces of the two types of fibers, the laser configuration is compact and cost effective. Besides, heat dissipation is also improved. By Cu-Al alloy packaging, a record-low Cr4+:YAG double-clad crystal fiber laser was achieved with threshold of 0.75 mW and a record-high slope efficiency of 6.9% at room temperature. And we also successfully fabricate the Yb3+:YAG-silica fiber laser with low threshold (100 mW) and high efficiency (67.2%) at room temperature. In fiber laser development, we have successfully fabricated the coating of high-reflective thin films which match the faces of fiber heterostructure (single cladding and double cladding structures). It forms a cavity with anti-reflectivity for pumping wavelength and high-reflectivity for lasing wavelength. For these reasons, low threshold, high slope efficiency, and stable laser output have been achieved. Finally, through different thin-film designs, the strain effect between thin film and heterosubstrate is significantly reduced, which facilitates the realization of high performance fiber lasers.

Tunable nanostructures have many important uses in thin film applications. Tunability can be achieved by creating a film that has features that respond to external stimuli, such as temperature, humidity, or pH. However, the response can vary greatly between a confined and unconfined case. In the case of confined materials, this response can be greatly reduced, even completely suppressed, which indicates that separate studies must be conducted on confined states in order to better understand their use for real applications. Microgels have been previously shown to have exceptional responsive properties that depend on their chemical structure and synthesis. Unlike solid thin hydrogel films that respond on the order of hours, microgels arrange on a surface with no external force and create a highly porous layer which responds rapidly, on the order of minutes, to outside stimuli. These properties make microgels a promising candidate for use in tunable thin films. Although the responsive properties of microgels have been extensively studied in solution and unconfined films, this is not indicative of conditions that would most likely have the microgels placed between two stiffer layers of material. Microgels have been shown to respond to glucose concentration, temperature, pH, and light. One well-studied microgel is poly-N-isopropylacrylamide copolymerized with Acrylic Acid (pNIPAM-co-AAC). These microgels use the thermal response of pNIPAM combined with the pH sensitivity of pAAC to create a dually-responsive material. To study the effects of confinement on pNIPAM-co-AAC microgels, we encapsulated these particles within bi-layers of poly(allylamine hydrochloride)-poly(sodium 4-styrenesulfonate) (PAH-PSS) in order to simulate their response within a polyelectrolyte material. Our samples were prepared with a method called tilt-drying, which creates a microgel concentration gradient. This allowed us to study both the confinement caused by the multi-layered film as well as the effects of microgels on each other. Our results have shown that the change in particle height is unaffected by the concentration of the film, but the thermal response of pNIPAM-co-AAC microgels is significantly suppressed by the encapsulation of microgels into nanoscale layers.

Diffusion behavior of spin cast polymer thin films was studied in detail as a function of film thickness. Diffusion coefficients of water molecules in poly(methyl methacrylate) (PMMA) were found to decrease from 10-8 cm2/s in thick films to 10-13 cm2/s in ultra-thin films. In order to probe if there is a characteristic length scale set by the polymer chain size, the effect of PMMA molecular weights on this behavior was tested and deviation of diffusion coefficient from bulk was observed in all molecular weights of PMMA investigated. Diffusion coefficients in these films was also studied as a function of aging time at 25°C and was not found to change significantly over a time period of approximately four months. The impact of residual casting solvent in thick and thin films was studied and found to have no influence in the diffusion behavior. Positron Annihilation Lifetime Spectroscopy (PALs) was used to probe the free volume (FV) pocket size and its distribution within the film as a function of film thickness in PMMA. Decrease in FV pocket size was found to be one of the general underlying causes for such thickness dependent diffusion behavior observed in thin polymer films. In addition, Protracted Colored Noise Dynamics (PCND) that enables efficient sampling of phase space and faster relaxation of the systems compared to Molecular Dynamics (MD) was investigated for its extensibility to three dimensional systems and was found to be sensitive to initial conformation.

Contact mechanical study of layered structures is useful to various fields of engineering, such as - mechanical engineering, civil engineering, materials engineering and biomechanics. Thin hard film coating on a compliant substrate used in cutting tool industry is an example of a layered structure. The protective coating saves the substrate from fracture and wear. However, due to film material brittleness, fracture in the films is of concern. We have developed an analytical model for a film-substrate bilayer system under normal contact loading, which helps us to obtain the stress distribution in the film and fracture behaviour. Our contact model is based on Hankel’s Transform technique, where we assume a Hertzian pressure boundary condition. At each depth of penetration of the indenter in the film-substrate system, we estimate effective modulus of the system based on Gao’s approach. We have validated our analysis by surface strain measurements and photoelastic stress study in the film on a substrate. Experimental observations from literatures show the dependence of different fracture modes in a thin hard film with columnar structure on film thickness and substrate plasticity. We perform fracture analysis, a parametric study of the fracture modes in the film under contact loading. When the film thickness is small and the substrate is relatively hard (e.g. tool steel), the film and the substrate deform conformally under contact loading and the columns of TiN slide against each other into the substrate. On the other hand, when the film is thicker and the substrate is soft (e.g. mild steel or aluminium), the strain mismatch between the film and substrate acts as an added traction at the interface and drives cracks, such as radial tensile stress driven bending cracks that start from the interface at the center of indentation; maximum shear stress driven inclined shear crack that starts inside the film and propagate at an angle to the indentation axis and tensile stress driven edge crack that starts from the free surface outside the contact. We can draw a fracture map based on these calculations which provides a guide to select film thickness depending on the substrate hardness, so that the benign mode of damage, i.e., columnar shear occurs in the film. Apart from generating the fracture map, we can obtain rationale for different fracture phenomenon in the film by studying the indentation stress field. Principal tensile stresses, responsible for driving edge cracks from the free surface outside the contact, become compressive as one approaches the substrate if the substrate is compliant. The cracks therefore do not penetrate deep into the film rather curve away from the axis of indentation. At the transition zone from one mode of damage to other in the fracture map, different modes of fracture may co-exist. The whole column may not shear, rather the shear can start from somewhere in the middle of the film, where the shear stress is maximum and it can end without reaching the interface. The indentation energy is then dissipated in other forms of damage. The contact analysis is further applied to TiN /AlTiN multilayered films having similar elastic properties. Experimental observations suggest that with decreasing layer thickness the fracture resistance of the multilayers increase and some plastic yielding occurs at the top layers of the film. However no substantial change in strain capacity (Hardness/ Young’s Modulus) of the film is observed. Hence we attribute the increase of fracture resistance of multilayers to film plasticity and mimic it by reducing the modulus of the film. The analysis validates the propensity of edge cracking and transgranular cracking as they decrease with increasing number of layers in a multilayer. We next extend our bilayer analysis to a more general trilayer problem where the moduli of the layers vary by several orders. The test system here is a mica-glue-glass system which is used in surface force apparatus experiments. Gao’s trilayer analysis is used to fit the experimental data obtained from surface force apparatus experiments, where a glass sphere indents the trilayer. The parallel spring model used in Gao’s approximation is found to be inadequate to rationalize the experimental data. We have modified Gao’s formulations by reducing the problem to a bilayer problem where the layers are the first layer (in contact) and an equivalent layer which has properties determined by a rule of mixture of the properties of all the layers excluding the top layer set out as a set of springs in series. The modified formulations give a better fit to the experimental data and it is validated from nanoindentation experiments on the same system. The formulation is used to obtain the compression of the glue, which contributes significantly to the deformation of the trilayer system in the SFA experiments. Thus, the analysis can be used to deconvolute the influence of glue in the actual mechanical response of the system in an SFA experiment, which has so far been neglected.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 97-109). Also available on the World Wide Web.

Thesis (doctoral)--Helsinki University of Technology, 2009. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2004. / Abdel-Khalik, Said, Committee Chair. Vita. Includes bibliographical references (leaves 376-384).

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Materials Science and Engineering." Includes bibliographical references (p. 134-150).