Due to the fast expansion and development in the optical communication industry, the demand for the broad-band laser light source as used to the optical transmission network system has correspondingly increased. Cr4+ doped YAG crystal fibers, with its broad-band spectral property, is thus becoming more and more indispensable to the growth of the industry. However, the Cr4+:YAG crystal fiber in its own repetitive growth process brings with itself one problem: after each re-growth, the concentration of Cr2O3 and Cr4+ ions would reduce appreciatively. Hence, finding sound solutions for effectively raising the concentration of Cr4+ is now becoming an essential issue in the field. The thesis mainly focuses on the development of using Cr4+:YAG as the laser gain medium. Thin layers of CaO, MgO, and Cr2O3 was coated on the circumference of the Cr:YAG crystal fiber. The LHPG method was then employed to re-grow the coated samples, during which the doped concentration of CaO, MgO and Cr2O3 can in-diffuse. And the effect of charge compensation would go further to simultaneously raise the concentration of Cr4+ ions. Now we have successfully enhance the concentration of Cr4+ ions to 4.86x10-3 wt.%. This study, with the use of the E-Gun coating machine and the IAD (ion-beam assisted deposition) system, also probes the technical side of how to better improve the quality of the crystal fiber laser. Both end faces of the Cr4+:YAG crystal fiber were coated with optical thin films by TiO2 and SiO2 targets. In addition to raise the quality of the thin films, the IAD system also functions to create a laser cavity in which both the anti-reflectance (AR) effect (for pumping the light source) and the high reflectance (HR) effect (for stimulating the light source) are achieved. The accompanied benefits would be the reduction of transmission loss, the increased laser efficiency, and thus a more successful and more stable crystal fiber laser.

High dielectric constant barium doped titanium silicon oxide films with equivalent oxide thickness below 1 nm can be prepared by liquid phase deposition. We learn from this research that the deposition rate of titanium silicon oxide films can be much enhanced by nitric acid incorporation, and the dielectric constant of materials can be increased by the dipole polarization from barium. The key parameter for the deposition rate, refractive index, and the dielectric constant of barium doped titanium silicon oxide is the molarity of barium nitrate. The electrical properties can be improved effectively by thermal annealing treatments. The optimum equivalent oxide thickness of barium doped titanium silicon oxide thin film is 0.9 nm with the optical thickness of 7.4 nm. The high dielectric constant can reach 31.9 and the leakage current density is 5 ¡Ñ 10-6 A/cm2 at the electrical field intensity of 5 MV/cm, which has high potential application for the next generation MOSFET.

In this thesis, we study a series of Si doped InN films. These samples are grown on sapphire (0001) by molecular beam epitaxy (MBE). We have doped Si in InN films successfully. In this experiment, we control Si cell temperature to change carrier concentration of samples during InN film growth. The carrier concentration and mobility are explored by van der Pauw Hall measurement. As carrier concentration increases, mobility decreases. Carrier concentration changes with Si cell temperature from 6.16x1018 cm-3 to 1.19x1020 cm-3. Photoluminescence (PL) emission peak energy shows blue shift when carrier concentration increases, but the intensity decreases and full width at half maximum (FWHM) broadens. The PL peak of InN film with 1.19x1020 cm-3 split into two peaks 0.74 eV and 0.89 eV. In Raman spectra, Raman modes position and FWHM do not change with carrier concentration. In temperature dependence PL, the dependence of PL spectra shows decrease when carrier concentration increases. In power dependence PL, the PL emission peak energy of InN films with 6.16x1018 cm-3 and 8.50x1018 cm-3 show blue shift, while the PL peaks of InN films with 1.43x1019 cm-3 and 2.27x1019 cm-3 show no significant move. The fitting of power density vs. intensity is linear for all samples, but all slope of them are less than 1 expect for InN film with 1.43x1019 cm-3.

The synchronously pumped femtosecond optical parametric oscillator (OPO) based on was periodically poled 5-mol.% MgO-doped lithuium niobate was demonstrated by means of non-critical quasi phase matching. The femtosecond OPO is cable of operating at room temperature and shows no photorefractive damage. The spectrum can be tuned by varying the cavity length up to 70 £gm, the temperature of the nonlinear crystal from room temperature to 150¢J, and the grating periods. The cavity was designed to resonate at 1.33 £gm with bandwidth of 100 nm. The maximum output intensity of the signal is 43 mW with TEM00 mode. The signal slope efficiency is 11%. The spectrum range of the idler is tunable from 1.8 to 2.8 £gm.

Acid Doped Polybenzimidazole Membranes for High Temperature Proton Exchange Membrane Fuel Cells Author: Ahmet &Ouml / zg&uuml / r Yurdakul One of the most popular candidates for high temperature PEMFC&rsquo / s is phosphoric acid doped polybenzimidazole (PBI) membrane due to its thermal and mechanical stability. In this study, high molecular weight PBI was synthesized by using PPA polymerization. The stirring rate of reaction solution was optimized to obtain high molecular weight. The inherent viscosity of polymer was measured at four points in 96 percent sulphuric acid solution at 30 degree centigrade by using an Ubbelohde viscometer. The highest average molecular weight was found as approximately 120,000 using the Mark-Houwink equation. The polymer was dissolved in N,N-dimethylacetamide at 70 degree centigrade with an ultrasonic stirrer. The membranes cast from this solution were doped with phosphoric acid solutions at different concentrations. The doping levels of the membranes were 6, 8, 10 and 11 moles phosphoric acid/PBI repeat unit. The mechanical strength of the acid doped membranes measured by tensile tests were found as 23, 16, 12 and 11 MPa, respectively. Conductivity measurements were made using the four probe technique. The membranes were placed in a conductivity cell and measurements were taken in humidity chamber with temperature and pressure control. The conductivity of membranes was measured at 110, 130 and 150 degree centigrade in both dry air and water vapor. The highest conductivity was 0.12 S/cm at 150 degree centigrade and 33 percent relative humidity for the membrane doped with 11 moles of H3PO4. The measurements showed that conductivity increased with increasing doping and humidity. Moreover, membranes had acceptable conductivity levels in dry air.

The photoreflectance(PR) and Electroreflectance(ER) of surface-intrinsic-n+ type doped GaAs exhibit many Franz-Keldysh oscillations (FKOs), which enable the electric field (F) to be determined from the technique of the fast Fourier transform (FFT). It is known that F's determined from PR are subjected to photovoltaic effect, but it is difficult to estimate the strength of modulating field (dF) of the pump beam in the PR measurements . Alperovich et. al. have used imaginary part of FFT to determine the strengths of dF's in the ER measurements [V. L. Alperovich, et. al. Appl. Phys . Lett. 71, 2788 (1997)]. Here, we will apply this method to the PR measurements. The dF's thus obtained will be compared with those deduced from photo-voltage measurements. The result shows that the method of Alperovich's can be used to determine the strength of dF in the PR measurements.

Abstract During the last decade, the fast-growing communication need has promoted the development of the wavelength of 1.3 mm~1.6 mm laser light source. The Cr4+ doped YAG solid-state laser has potential to meet this super wideband demand. In addition, solid state laser has the merits of high laser beam quality, long lifetime, compact, and simple structure. In this thesis, crystal fiber was used as the laser gain medium, and coated with optical thin film at its end facets as the laser cavity. Using this configuration, the volume and cost of the laser can be appreciatively reduced, and the heat dissipation can be improved. The laser-heated-pedestal-growth method was used to grow crystal fiber, which can obtain small diameter at very fast rate and accurate control. High quality Cr4+:YAG crystal fiber with the smallest diameter of 50 mm was grown. A glass-packaged technique clothes the crystal fiber with a core diameter as small as 11 mm. Outside the glass clad Cr4+:YAG crystal fiber, Al-Cu alloy was employed as the heat sink to improve heat dissipation. After grinding, polishing, and coating of this device, the Cr4+:YAG crystal fiber laser was fabricated. Some characteristics of Cr4+:YAG crystal fiber, such as the distribution of Cr2O3 and CaO doping concentration, fluorescence intensity, refraction index, propagation loss, and absorption coefficient were measured and analyzed. In the meanwhile, some simulations of the laser output power depending on the absorption coefficient, propagation loss, output coupling, crystal fiber diameter, and crystal boundary temperature were discussed.

In this thesis, a 6-beam combiner using multiplexed holograms in dye-doped polymer is investigated. It is realized by recording six superimposed holographic gratings, which show uniform diffraction efficiency. The coupled wave theory for N superimposed gratings is more generalized and is used to analyze the amplitudes of diffracted waves in three different boundary conditions. Multiple-ring diffracted beam analysis is proposed to determine the dynamic range of a holographic material. The M/# is evaluated by recording a single hologram and counting the number of ring patterns in the diffracted beam. This analysis is extended to assess the equalized grating strength of N superimposed holograms. Six holograms with the equalized grating strength which can be assigned within the dynamic range of our material and show maximum diffraction efficiency are recorded. The phase locking of five beams to one reference beam is performed using PZT controller. The designs of lock-in amplifier, ramp generator and servo using commercial chips are demonstrated. The readout set-up used to split one single beam into six coherent copies is presented. The function of each part of the PZT controller in the readout set-up is discussed in detail. The intensity profile of an N-beam combiner is investigated by varying the phase angle between adjacent input waves. The entire solution which describes the amplitude of a combined beam is derived from generalized coupled wave theory. A simplified experimental set-up without a complicated PZT controller is demonstrated using a planoconvex lens. In order to provide six coherent light sources in future work, the injection locking of a single laser diode to the master laser diode is performed. An expected read-out setup is proposed to carry out both the achievement of six coherent sources and a 6 beam combination.

A novel high-k gate dielectric material, i.e., hafnium-doped tantalum oxide (Hf-doped TaOx), has been studied for the application of the future generation metal-oxidesemiconductor field effect transistor (MOSFET). The film's electrical, chemical, and structural properties were investigated experimentally. The incorporation of Hf into TaOx impacted the electrical properties. The doping process improved the effective dielectric constant, reduced the fixed charge density, and increased the dielectric strength. The leakage current density also decreased with the Hf doping concentration. MOS capacitors with sub-2.0 nm equivalent oxide thickness (EOT) have been achieved with the lightly Hf-doped TaOx. The low leakage currents and high dielectric constants of the doped films were explained by their compositions and bond structures. The Hf-doped TaOx film is a potential high-k gate dielectric for future MOS transistors. A 5 àtantalum nitride (TaNx) interface layer has been inserted between the Hf-doped TaOx films and the Si substrate to engineer the high-k/Si interface layer formation and properties. The electrical characterization result shows that the insertion of a 5 àTaNx between the doped TaOx films and the Si substrate decreased the film's leakage current density and improved the effective dielectric constant (keffective) value. The improvement of these dielectric properties can be attributed to the formation of the TaOxNy interfacial layer after high temperature O2 annealing. The main drawback of the TaNx interface layer is the high interface density of states and hysteresis, which needs to be decreased. Advanced metal nitride gate electrodes, e.g., tantalum nitride, molybdenum nitride, and tungsten nitride, were investigated as the gate electrodes for atomic layer deposition (ALD) HfO2 high-k dielectric material. Their physical and electrical properties were affected by the post metallization annealing (PMA) treatment conditions. Work functions of these three gate electrodes are suitable for NMOS applications after 800°C PMA. Metal nitrides can be used as the gate electrode materials for the HfO2 high-k film. The novel high-k gate stack structures studied in this study are promising candidates to replace the traditional poly-Si-SiO2 gate stack structure for the future CMOS technology node.

The interest in conjugated polymers has been two-fold. A rich variety of intriguing physical phenomena, combined with its immense technological implications in the area of molecular electronics, sensors etc. has inspired the researchers all over the globe. The work presented in this thesis is focussed on one of the most widely studied conjugated polymers, namely polyaniline (PANI), which is well known for its high conductivity and remarkable stability in the proton-doped form. The thesis is divided into two chapters and each chapter is further divided into several parts. In the first chapter, we take a look at some novel systems based on PANI that exhibit interesting electrical and optical properties. To begin with, we report the synthesis and characterization (Part I, Chapter 3) a new class of highly conducting polyaniline doped with electron deficient Lewis acids, namely the boron trihalides (BX3, X = F, Cl, and Br). We discuss the various attributes of this interesting class of materials that set it apart from the conventional proton-doped PANI systems. It is known that the conductivity in doped PANI is greatly influenced by the presence of structural disorder. Previous studies have associated the conductivity in doped PANI with the partial crystallinity that is achieved upon proton doping. At the same time, the amorphous regions that have a high degree of disorder were believed to suppress the metallic nature in these doped systems. In view of this "higher-crystallinity-higher-conductivity" picture, it is interesting to note that the BX3 doped PANI remain absolutely amorphous despite being more conducting than previously known samples. Through our investigation, we have been able to address some of the most important and long-standing questions pertaining to the nature of the charge carriers and the role of disorder in doped PANI. A detailed study of the transport properties in Part II, Chapter 3 helps us to understand the mechanism of charge transfer in these novel systems. With the help of our results, we establish that the present systems do not belong to the family of quasi one-dimensional conductors, in stark contrast to the conventional proton-doped samples. Instead, our systems are best described as granular metals, where the conduction mechanism is controlled by the size of the conducting grains and the nature of the grain boundaries. Through a comprehensive study of the magnetic properties based on d. c. magnetic susceptibility and EPR spectroscopy, we further establish that the intrinsic conductivity of these samples are much higher than the previously known systems. By studying the interaction of the mobile charge carriers and the localized spins in the systems, we have established that our samples are far less disordered, and therefore qualify as superior systems when compared to the more conventional proton-doped PANI. One of the serious disadvantages of the conventional protonated PANI lies in its thermal instability. On heating above 75 ±C in air, the polymer backbone undergoes an irreversible aerial oxidation that disrupts the extended conjugated structure. This is marked by a rapid drop in conductivity by a few orders of magnitude. BF3-doped PANI, which has the highest conductivity sample among the present series of samples, exhibits a remarkable thermal stability in air (Part III, Chapter 3). Upon heating, the conductivity initially increases and then reaches a saturation value. The polymer can be heated at temperatures as high as 225 ±C, without any signs of degradation. With the help of temperature dependent conductivity, XPS and FTIR spectroscopy we have tried to understand this unexpected phenomenon. In Part IV, Chapter 3, we report the synthesis and characterization of a novel class of functionalized PANI that exhibit an intense deep-blue photoluminescence. A de- tailed characterization based on absorption, photoluminescence, XPS, NMR and FTIR spectroscopy has been carried out to study the chemical state of this new class of light- emitting polymers. Further, we note that the synthetic procedure followed in this work can provide a very general route to the synthesis of diversely useful derivatives of PANI. In Chapter 4, we have investigated the microscopic origin of conductivity in doped PANI. Among the several factors that can influence the conductivity of doped polymers, one is the microstructural order. To understand this better, we carried out a detailed investigation, based on scanning tunneling microscopy (STM) and spectroscopy (STS) of undoped and doped PANI films (Part I, Chapter 4). We have shown for the ¯rst time that solution processed thin films of undoped PANI has an abundance of PANI anorods self organized over very large areas. Further, we observe that this ordered orphology is Preface vii very sensitive to the choice of dopants and the doping procedure. We have shown that the morphological order can greatly influence the electronic structure and therefore the properties of these systems. To understand the role of dopant-polymer interaction in controlling the conductivity of doped PANI, we carried out x-ray photoelectron spectroscopy (XPS) studies on a large number of partially and fully doped samples (Part II, Chapter 4). We find an interesting trend in the higher binding energy feature and the asymmetry of the N and C 1s spectra, which correlates directly with the respective conductivities of different samples. The analysis of these spectra brings out interesting facts about the chemical state and the electronic structure of these samples. In summary, we have reported new PANI based systems with improved electrical and interesting optical properties, and have studied various factors that influence the properties of these as well as some of conventional doped PANI systems.