Wang Lei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / List of Figures --- p.vi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Scaling issues of Metal-Oxide-Semiconductor field effect transistor --- p.1 / Chapter 1.2 --- Alternative high-k gate dielectrics --- p.4 / Chapter 1.3 --- Overview of this thesis --- p.9 / References --- p.10 / Chapter Chapter 2 --- Deposition and characterization techniques for ultrathin HfO2 films --- p.11 / Chapter 2.1 --- Introduction --- p.11 / Chapter 2.2 --- Ultrathin Hf02 Films Growth and Post Deposition Modification --- p.11 / Chapter 2.2.1 --- Ultrahigh Vacuum Electron-beam Evaporation --- p.11 / Chapter 2.2.2 --- High Concentration Ozone Annealing --- p.12 / Chapter 2.2.3 --- Plasma Immersion Ion Implantation --- p.14 / Chapter 2.2.4 --- Rapid Thermal Annealing --- p.16 / Chapter 2.3 --- Compositional Characterization Techniques --- p.17 / Chapter 2.3.1 --- X-ray Photoelectron Spectroscopy --- p.17 / Chapter 2.3.2 --- Rutherford Backscattering Spectrometry --- p.18 / Chapter 2.4 --- Structural and Surface Morphological Characterization Techniques --- p.19 / Chapter 2.4.1 --- High-Resolution Transmission Electron Microscopy --- p.19 / Chapter 2.4.2 --- Ultrahigh Vacuum Scanning Tunneling Microscopy --- p.20 / Chapter 2.4.3 --- Ultrahigh Vacuum Atomic Force Microscopy --- p.22 / Chapter 2.5 --- Electrical Characterization --- p.24 / Chapter 2.5.1 --- Capacitance-voltage (C-V) Measurement --- p.24 / Chapter 2.5.2 --- Current-voltage (I-V) Measurement --- p.25 / References --- p.26 / Chapter Chapter 3 --- Control of interfacial silicate between Hf and SiO2 by high concentration ozone --- p.27 / Chapter 3.1 --- Introduction --- p.27 / Chapter 3.2 --- Experimental procedure --- p.28 / Chapter 3.3 --- Results and discussion --- p.29 / Chapter 3.4 --- Conclusion --- p.35 / References --- p.36 / Chapter Chapter 4 --- Electrical characteristics of postdepositon annealed ultrathin Hf02 films --- p.37 / Chapter 4.1 --- Introduction --- p.37 / Chapter 4.2 --- Capacitance of gate stack in metal-insulator-semiconductor structure --- p.38 / Chapter 4.3 --- Electrical characteristics of ultrathin HfO2 films by high temperature Ozone oxidation --- p.39 / Chapter 4.4 --- Electrical and structural properties of ultrathin HfO2 films by high temperature rapid thermal annealing --- p.46 / Chapter 4.5 --- Conclusion --- p.48 / References --- p.50 / Chapter Chapter 5 --- Effect of nitrogen incorporation on thermal stability of ultrathin Hf02 films --- p.51 / Chapter 5.1 --- Introduction --- p.51 / Chapter 5.2 --- Experimental procedure --- p.52 / Chapter 5.3 --- Results and discussion --- p.52 / Chapter 5.4 --- Conclusion --- p.58 / References --- p.59 / Chapter Chapter 6 --- Local characterization of ultrathin HfO2 films by in-situ Ultrahigh Vacuum Scanning Probe Microscopy --- p.61 / Chapter 6.1 --- Introduction --- p.61 / Chapter 6.2 --- Experimental procedure --- p.62 / Chapter 6.3 --- Morphology and structure of initial growth of HfO2 --- p.63 / Chapter 6.4 --- Local characterization of ultrathin HfO2 films by in-situ UHV-STM --- p.66 / Chapter 6.5 --- UHV c-AFM study of leakage path evolution in ultrathin Hf02 films --- p.71 / Chapter 6.6 --- Conclusion --- p.72 / References --- p.73 / Chapter Chapter 7 --- Conclusion --- p.74 / Publications --- p.76

Self-assembly and the induced orientation of microscopic biological systems is of great scientific interest, because it holds the promise of many pharmaceutical applications. This dissertation presents experimental studies done on proteins, short DNA fragments, and cholesterol structures self-assembled in an aqueous environment. The goal is to probe the thermo-physical properties of these systems, their phases and phase transitions, in order to better under-stand the principles behind their unique assemblies and function. It is accepted that in all these systems the solvent water plays an important role on the assembly folding, orientation, and activity of biopolymers. However, the abundance of water in typical samples presents many experimental challenges. It is indeed the case that changes in the properties of hydration in watery environments are responsible for the dynamics of protein and DNA biomolecules. We have explored in more detail the thermodynamics, the structural properties, and the dynamics near structural transitions of biomolecules in their native aqueous environment.

Energy storage is currently gaining considerable attention due to the current energy crisis and severe air pollution. The development of new and clean forms of energy and related storing devices is in high demanded. Dielectric capacitors, exhibiting high power density, long life and cycling life, are potential candidates for portable devices, transport vehicles and stationary energy resources applications. However, the energy density of dielectric capacitors is relatively low compared to that of traditional batteries, which inhibits their future development. In the current work, three types of dielectrics, namely antiferroelectric samarium-doped BiFeO3 (Bi1-xSmxFeO3), linear dielectric (potential antiferroelectric) BiNbO4 and incipient ferroelectric TiO2, have been investigated to develop their potential as energy storage capacitors. For the samarium-doped BiFeO3 (Bi1-xSmxFeO3) system, the effect of samarium content in the A-site (x=0.15, 0.16, 0.165 and 0.18) on the structural phase transitions and electrical properties across the Morphotropic Phase Boundary (MPB) were studied. A complex coexistence of rhombohedral R3c, orthorhombic Pbam and orthorhombic Pnma was found in the selected compositions. The R3c phase is the structure of pure BiFeO3, the Pbam phase has a PbZrO3-like antiferroelectric structure and the Pnma phase has a SmFeO3-like paraelectric structure. The presence of the PbZrO3-like antiferroelectric structure was confirmed by the observation of the 14{110}, 14{001}, 12{011} and 12{111} superlattice reflections in the transmission electron microscopy diffraction patterns. The weight fractions of the three phases varied with different calcination conditions and Sm substitution level. By increasing the calcination temperature, the weight fractions of the Pbam increased, while that of the R3c decreased. The fraction of the Pnma phase is mainly derived by the Sm concentration and is barely affected by the calcination temperature. The increase of Sm concentration, determined an increase of the weight fraction of the Pnma phase and a decrease of the Pbam and the R3c phases. Temperature dependent dielectric measurements and high temperature XRD of Bi0.85Sm0.15FeO3 revealed several phase transitions. The drastic weight fraction change between the Pbam and the Pnma phase around 200 °C is assumed as the Curie transition of the antiferroelectric Pbam phase. The transition at 575 °C is related to the diminishing of the R3c phase and is suggested as the Curie transition of the ferroelectric R3c phase. The Curie point of the antiferroelectric Pbam phase and the ferroelectric R3c phase in the Bi1-xSmxFeO3 ceramics shifted towards lower temperature with an increase of the Sm concentration. Current peaks were obtained in current-electric field loops in Bi0.85Sm0.15FeO3, which are correlated to domain switching in the R3c phase. The ferroelectric behavior was suppressed in Bi1-xSmxFeO3 (x=0.16, 0.165, 0.18), which is due to the gradually diminished contribution from the R3c phase. The system Bi0.82Sm0.18FeO3 showed the highest energy density of 0.64 J cm-3 (error bar ±0.02). For the BiNbO4 system, single phase α-BiNbO4 (space group Pnna) and β-BiNbO4 (space group P-1) powder and ceramics were produced. The longstanding issue related to the sequence of the temperature-induced phase transitions has been clarified. It is demonstrated that the β phase powder could be converted back to the  phase when annealed in the temperature range 800 °C -1000 °C with certain incubation time. The β to  phase transition is a slow kinetic process because sufficient temperature and time are required for the transition. In bulk ceramics with β phase, this transformation is impeded by inner stress, while it is favored by graphite-induced reducing atmosphere. A high temperature  phase has been revealed and the structure has been resolved. The structure of the  phase is monoclinic with a space group of P21/c. The lattice parameters are: a = 7.7951(1) Å, b = 5.64993(9) Å, c = 7.9048(1) Å,  = 104.691(2) Z=4. The volume is 336.76 (2) Å3. The calculated density is 7.217 g cm-3. The phase relationships among ,  and  phases have been clarified. It was found that the  phase (for both powder and ceramic) transforms into the  phase at 1040 °C on heating, and that the  phase always transforms into the  phase at 1000 °C on cooling. Meanwhile, a reversible first-order  to  phase transition is observed at ca. 1000 °C for both powder and ceramic if no incubation is processed on heating. The electric properties of both α- and - BiNbO4 have been investigated. The breakdown field of both ceramics were too low to observe any possible field-induced transition. As a result, linear P-E loops were obtained in each phase. The energy densities of α- and - BiNbO4 ceramics are 0.03 and 0.04 J cm-3 (error bar ±0.001), respectively. For the TiO2 system, ceramics were produced by conventional sintering and spark plasma sintering (SPS). Compared to conventional sintering, SPS technique produced dense ceramics without using sintering aids and avoided abnormal grain growth. Relaxation behavior related to the oxygen hopping among vacant sites is observed in the temperature range of 200 to 600 °C. TiO2 exhibits ultra-low loss at terahertz frequencies due to the reduced contribution of oxygen vacancies relaxation. TiO2 has a high breakdown field, but still has low polarization. The highest energy density obtained inTiO2 ceramics is 0.3 J cm-3 (error bar ±0.01).

Dielectric elastomers are electroactive polymers, which change size and shape in response to an electrical field. Dielectric elastomer actuators (DEAs) are highly promising new technologies in optical applications such as tuneable optical lenses, diffraction gratings and active camouflage. This thesis aims to develop a new approach to create a strain actuated compliant colour changing device that is controlled using DEAs as they offer stretchability, low weight, high efficiency, low cost and the possibility for miniaturisation. Conventional DEAs use transparent elastomeric materials with no significant colour change with strain. Conversely, liquid crystal materials are known to display dynamic colour changing behaviour, thereby making them good candidate materials. The thesis examines both the potential for colour changing soft actuators and the upcoming challenges in this field as well as the key concepts around liquid crystals that exhibit colour change. An initial approach was aimed at creating colour changes using dielectric elastomer actuators that drove a masked positioner. This method showed colour change since the mask changes the colour visualisation. The second approach used polymer dispersed liquid crystals, such as a nematic liquid crystal within a reactive silicone resin. The immiscibility of these compounds resulted in a dispersion of the liquid crystal droplets in the silicone matrix. However, the optical properties could not be controlled through mechanical deformation alone and the alignment of resulting LC droplets in the PDLC films was sensitive to the substrate used to perform the actuation. The next approach used reactive cholesteric liquid crystals (CLC) instead. A thin film coating process was preferred to carefully control the film's thickness by stretching. In free standing films a planar cholesteric alignment was obtained with mesogens aligned parallel to the substrate and colour was achieved based on the selective reflection of light. A transfer print technique was introduced to combine CLC coatings with elastomeric substrates that can be stretched. However, no colour change was achieved in response to mechanical deformation primarily due to the modulus and strength mismatch between the thin film and the elastomeric susbstrate material. Finally, lightly crosslinked liquid crystal elastomers using a combination of reactive and non-reactive liquid crystals were produced that were compatible with elastomer substrate materials. In free standing films planar cholesteric alignment was obtained with mesogens aligned parallel to the substrate. Successfully a reversible colour change based on selective reflection of light was achieved in response to a mechanical deformation.

In this thesis, I report on the investigation of the low frequency vibrational modes in a number of different systems using ultrafast spectroscopic techniques. These consist of biological systems, including the enzyme, morphinone reductase (MR) and the related biomolecules, riboflavin (Rb) and flavin mononucleotide (FMN), as well as non-biological systems, including the semiconductor gallium nitride (GaN) and gold nanoparticles (Au NPs). The term low frequency refers to terahertz (THz) frequencies, where vibrational modes exist at the molecular level, with molecular rotations, lattice vibrations and inter- and intra-molecular vibrations occurring in the THz spectral range. These vibrational modes occur on sub-picosecond timescales and therefore ultrafast techniques utilising femtosecond laser pulses provide a means of studying these modes, and are employed throughout this thesis. The two ultrafast techniques of transient absorption (TA) spectroscopy and terahertz time-domain spectroscopy (THz-TDS) were used. Firstly, a high-repetition rate transient absorption (HRRTA) spectrometer was commissioned to perform pump-probe measurements with an ultraviolet pump and broadband visible probe. The performance of the HRRTA spectrometer was benchmarked using Au NPs and used to investigate the existence of a promoting vibration in MR contributing to the catalysis process, predicted to occur at THz frequencies. Weak oscillations were detected in the charge-transfer absorption band of MR bound to the non-reactive cofactor 1,4,5,6-tetra-hydro-nicotinamide adenine dinucleotide (NADH4), with a frequency of approximately 1.5 THz and provide evidence of the first direct observation of a promoting vibration in an enzyme. To complement the TA measurements, THz-TDS was also used to obtain direct measurements of the absorption at THz frequencies. Due to the challenge of studying water-based biological samples, an initial investigation was performed on a wurtzite GaN wafer, which exhibited optical phonon modes in the THz frequency range that were found to determine the dielectric response of the semi-insulating semiconductor wafer. Use of a non-polar m-plane wafer allowed the anisotropic nature to be observed and values of 9.22 ± 0.02 and 10.32 ± 0.03 for the static dielectric constants were obtained for the THz electric field polarised both perpendicular and parallel to the c-axis of the wurtzite GaN wafer, respectively. Finally, biological studies using THz-TDS were performed with measurements on Rb pellets and films revealing vibrational modes in the THz region. The sharp absorption features were not observed in FMN, despite a small difference in molecular content from Rb, and dehydration was required to reveal small amplitude absorption features. Final measurements on MR and MR-NADH4 films were carried out and evidence of absorption features in the THz frequency range were observed, however further work is required to determine the precise origin of these features.

Cheng Kwok Kei = 高分子電解質-膠體複合體系的相互作用和極化率 / 鄭國基. / Thesis submitted in: November 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 68-73). / Text in English; abstracts in English and Chinese. / Cheng Kwok Kei = Gao fen zi dian jie zhi-jiao ti fu he ti xi de xiang hu zuo yong he ji hua lü / Zheng Guoji. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Polyelectrolyte Colloid Complex --- p.1 / Chapter 1.2 --- Image charges --- p.3 / Chapter 1.3 --- Objective of the thesis --- p.3 / Chapter 2 --- Equations for induced image charges (Review) --- p.5 / Chapter 2.1 --- Introduction --- p.5 / Chapter 2.2 --- Image effect --- p.6 / Chapter 2.2.1 --- The potential --- p.6 / Chapter 2.2.2 --- Surface charge density --- p.8 / Chapter 2.2.3 --- Potential energy --- p.9 / Chapter 3 --- Polarizability of a polyelectrolyte colloid complex --- p.11 / Chapter 3.1 --- Introduction --- p.11 / Chapter 3.2 --- The Simulation Model --- p.12 / Chapter 3.2.1 --- Energy of the Complex --- p.13 / Chapter 3.2.2 --- Dipole of the Complex --- p.15 / Chapter 3.2.3 --- Thermal Energy --- p.18 / Chapter 3.3 --- Calculating Method --- p.18 / Chapter 3.3.1 --- Monte Carlo Simulation --- p.19 / Chapter 3.3.2 --- Partition Function Calculation --- p.20 / Chapter 3.4 --- Polarizability --- p.22 / Chapter 3.4.1 --- Compare polarizability of the complex with a permanent dipole --- p.22 / Chapter 3.4.2 --- Results and Discussion --- p.23 / Chapter 3.5 --- Effect of image charges for the complex --- p.33 / Chapter 3.6 --- Conclusion --- p.37 / Chapter 4 --- Correlation and Interaction of complexes - without induced charges --- p.38 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- The Simulation Model --- p.39 / Chapter 4.2.1 --- Energy of the system --- p.40 / Chapter 4.2.2 --- Dipole Moment --- p.42 / Chapter 4.3 --- Results and Discussion --- p.43 / Chapter 4.3.1 --- Polarizability of complex --- p.43 / Chapter 4.3.2 --- Correlations between two complexes --- p.46 / Chapter 4.3.3 --- Potential of mean force --- p.50 / Chapter 4.4 --- Conclusion --- p.52 / Chapter 5 --- Correlation between Two Complexes - with induced charges --- p.53 / Chapter 5.1 --- Introduction --- p.53 / Chapter 5.2 --- Induced Surface Charges --- p.54 / Chapter 5.2.1 --- Surface charges --- p.54 / Chapter 5.2.2 --- Energy of system --- p.55 / Chapter 5.2.3 --- Dipole Moment --- p.57 / Chapter 5.3 --- Results and Discussion --- p.58 / Chapter 5.3.1 --- Polarizability of complexes --- p.59 / Chapter 5.3.2 --- Correlation between two complexes --- p.61 / Chapter 5.3.3 --- Potential of mean force --- p.63 / Chapter 5.4 --- Conclusion --- p.64 / Chapter 6 --- Summary --- p.66 / Bibliography --- p.68 / Chapter A --- Mathematical calculation of the dipole moment of a complex --- p.74 / Chapter A.1 --- Equation of mean squared dipole --- p.74 / Chapter A.2 --- z-component of dipole and squared dipole --- p.76

No description available.

Electrical insulation under high voltage can eventually fail, causing critical damage to electronics. Such electrostatic discharge (ESD) is the primary source of anomalies or failures on spacecraft due to charged particles from the Sun or planetary radiation belts accumulating in spacecraft insulators. Highvoltage direct current power distribution is another example of a growing industry that needs to estimate the operational lifetime of electrical insulation. My research compares laboratory tests of ESD events in common insulating materials to a physics-based model of breakdown. This model of breakdown is based on the approximation that there are two primary types of defects in structurally amorphous insulators. One of the two defect modes can switch on and off depending on the material temperature. This dual-defect model can be used to explain both ESD and less-destructive transient partial discharges. I show that the results of ESD tests agree reasonably well with the dual defect model. I also show that transient partial discharges, which are usually ignored during ESD tests, are closely related to the probability of catastrophic ESD occurring. Since many partial discharges are typically seen during one ESD test, this relationship suggests that the measurements of partial discharges could accelerate the testing needed to characterize the likelihood of ESD in insulating materials.

Abstract not available

With the rapid of growth of wireless connectivity more demand is placed on the need for innovative technologies capable of satisfying increasing user demand and network capacity. Adaptive antennas systems or most commonly known as Smart Antennas are expected to be implemented in the next generation of wireless systems. Their implementation avails in dynamic adaptation to spatial and temporal conditions affecting the quality of communication, while offering tremendous flexibility to wireless providers. However one of the major challenges facing Smart Antenna technology is the inherent complexity of the antenna structure, associated control algorithm and implemented RF components possibly contributing to the delay of commercial interest. This thesis will present various adaptive antenna configurations that utilize an embedded dielectric in order to achieve significant size reduction and mechanical rigidity while maintaining favorable electromagnetic performance. In order to constrict the lateral ground plane dimension, a cylindrical shaped hollow ground skirt was attached to the antenna structures effectively compromising between effective beam forming in the azimuth plane and physical size. The complexity of these antenna structures requires a more contemporary design approach which involved computer modeling using a commercial available Finite Element software package and optimization using a developed generic Genetic Algorithm based optimization program. A dielectric embedded 7-element monopole array antenna featuring switched parasitic elements is presented and optimized for maximum vertically polarized gain in the horizontal plane, producing an antenna structure with a radial length of less then 0.25λ and total height of 0.4&alamba which was shown to radiate a main lobe beamwidth of 80 degrees with an absolute gain of 4.8dBi at 2.45GHz. Further on a dielectric embedded 7-element monopole array antenna featuring parasitic elements terminated with finite set of terminating reactive loads is presented with a radial length of less then 0.25&alambda and total height of 0.4&alambda. The antenna structure and reactive load combination were optimized for maximum horizontal gain producing a principal main lobe with a measured gain of 5.1dBi and beamwidth of 110 degrees at 2.48GHz. Finally it was shown single and dual radiation lobes maybe produced when active monopoles elements are placed eccentric in a circular shaped dielectric material. A circular array of elements embedded in a dielectric material was realized with measured gains of single and dual beam radiation at 2.45GHz was shown to be 5.18dBi and 3.65Bi respectively with corresponding beamwidths of 78.5 degrees and 53 degrees.