by Tang Yeung Shun. / On t.p., "2", u "3", "7-x", and O"3" are subscripts following "growth of" in the title. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 87-89). / Chapter Chapter 1 ： --- Introduction --- p.1 / Chapter Chapter 2 : --- Preparation of Thin Films --- p.10 / Chapter Chapter 3 : --- Structural Analysis / Chapter 3.1 --- Setup of XRD --- p.14 / Chapter 3.2 --- θ-2θ Scan --- p.17 / Chapter 3.3 --- Rocking Curve --- p.27 / Chapter 3.4 --- Pole Figure --- p.29 / Chapter 3.5 --- Off-axis Scan --- p.33 / Chapter 3.6 --- Grazing Incidence X-ray Diffraction --- p.53 / Chapter 3.7 --- Percentage of (110) Phase --- p.59 / Chapter 3.8 --- Lattice Parameters --- p.63 / Chapter Chapter 4 : --- Transport Properties / Chapter 4.1 --- Experimental --- p.66 / Chapter 4.2 --- Results --- p.68 / Chapter Chapter 5 : --- Surface Morphology --- p.75 / Chapter Chapter 6 : --- Discussion --- p.80 / Chapter Chapter 7 : --- Conclusions --- p.85 / References --- p.87 / Appendix A : Powder Diffraction Patterns of YBCO System

A pulsed fuel injector system was used to study flame structure, flame length, and emissions of ethylene jet diffusion flames over a range of injection times and duty-cycles with a variable air co-flow. In all cases the jet was completely shut off between pulses (fully-modulated) for varying intervals, giving both widely-spaced, non-interacting puffs and interacting puffs. Imaging of the luminosity from the flame revealed distinct types of flame structure and length, depending on the duration of the fuel injection interval. Flame lengths for isolated puffs (small injection times) were up to 83% less than steady state flames with the same injection velocities. With the addition of co-flow flame lengths grew to a maximum of 30% longer than flames without any co-flow. A scaling argument is also developed to predict the amount of co-flow that gives a 15% increase in mean flame length. Interacting flames with a small co-flow and small injection times (injection time = 5.475 ms) experienced flame length increases of up to 212% for a change in injection duty-cycle from 0.1 to 0.5. For interacting flames with long injection times (on time = 119 ms), essentially no change in flame length was noticeable over the same range of duty-cycles. Emission measurements suggest partial quenching of the reaction in isolated puffs with low duty-cycles and injection times (injection times less than 5.475 ms) resulting in high CO and UHC concentrations and low NO and NOx concentrations. With an increase in duty-cycle, the puffs began to interact and CO and UHC concentrations decreased while NO and NOx concentrations increased. For flames with injection times greater than 5.475 ms emission concentrations seem to be reasonably constant, with a slight increase in NO and NOx concentrations as the duty-cycle increased. Also the duty-cycle experienced in the vicinity of the probe is estimated and used as a scaling factor for the emission measurements.

In this thesis, I present my research into the development and use of a magneto-spectrometer operating at terahertz frequencies. Molecular samples with unpaired electrons were studied using electron paramagnetic resonance (EPR) spectroscopy and the properties of semiconducting samples were measured by cyclotron resonance. A terahertz time-domain spectrometer was constructed, fine-tuned and benchmarked. The use of a large area photoconductive antenna (PCA), with a bias voltage modulated at 1 MHz, allowed for a signal-to-noise ratio of 13800:1 to be achieved, which was equal or superior to comparable systems in use. The thermal behaviour of the PCA was studied and modelled to find that a 28% increase in emission occurred when the PCA was cooled to 100 K and a 22% increase in the maximum usable bias voltage was possible when the emitter substrate was cooled in a liquid nitrogen cryostat. The spectrometer was used to study a mixed type I/type II GaAs quantum well heterostructure as a test sample, in the process extending the existing research performed on this controllable terahertz filter. Together with a Gunn diode, bolometer and a Schottky diode, a pulsed magnet was developed into a 135 GHz, continuous-wave EPR spectrometer. EPR was detected in DPPH allowing for the spectrometer magnetic field accuracy to be determined and in ruby, which provided the crystal orientation of the sample and the base temperature of the spectrometer. Following this, three novel mixed-metal fluoride-centred triangles were studied on a multiple frequency EPR spectrometer allowing for the exchange interactions to be calculated along with the g-factors for two energy states. Two dimetallic cobalt complexes were studied to find that small changes to the molecules resulted in significant changes in the measured EPR spectra and so these molecules could be a useful part of the study of exchange coupled systems. The terahertz time-domain spectrometer was then combined with the pulsed magnet and an asynchronous optical sampling (ASOPS) system. Use of ASOPS allowed the number of waveforms measurable during a magnetic field pulse to be increased by at least a factor of 20 compared to contemporary alternatives. The spectrometer was used study cyclotron resonance in a two-dimensional electron gas (2DEG) formed at a GaAs/AlGaAs interface. Cyclotron resonance was successfully measured in the 2DEG at frequencies up to 1.6 THz, finding an electron effective mass of 0.071 m e , a sheet electron density of 3.3 × 10 11 cm -2 and a mobility of 1.5 × 10 5 cm 2 V -1 s -1 . Furthermore, using this system, the detection of EPR in a ruby sample was achieved, providing the first demonstration of ASOPS being used to study EPR at terahertz frequencies.

This thesis presents the application of ash thermography techniques to the analysis of documents. The motivation for this research is to develop the ability to non-destructively reveal covered writings in archaeological artifacts such as the Codex Selden or Egyptian car- tonnage. Current common signal processing techniques are evaluated for their effectiveness in enhancing subsurface writings found within a set of test documents. These processing techniques include: false colorization, contrast stretching, histogram equalization, median altering, Gaussian low-pass altering, layered signal reconstruction and thermal signal reconstruction (TSR), several contrast image definitions, differential absolute contrast (DAC), correlated contrast, derivative images, principal component thermography (PCT), dynamic thermal tomography (DTT), pulse phase thermography (PPT), tying-correlation analysis (FCA), Hough transform thermography (PTHTa), and transmission line matrix tying algorithm (TLMFa). New processing techniques are developed and evaluated against the existing techniques. The ability of ash thermography coupled with processing techniques to reveal subsurface writings and document strikeouts is evaluated. Flash thermography parameters are evaluated to determine most eeffective value for the document. In summary, this thesis reports the following contributions to the existing scientific knowledge: 1. A comprehensive analysis of existing pulsed thermography processing techniques. 2. New pulsed thermography processing techniques that improve upon the results of the existing techniques were developed. 3. A proof-of-concept for detecting subsurface ink writings in documents. 4. Varies the capability of pulsed thermography techniques to detect document strike- outs. 5. Demonstrates the ability to enhance surface writings based on differences in thermal characteristics when optical characteristics do not vary significantly. 6. Demonstrates that pulsed thermography significantly improves upon multi-spectral imaging for subsurface and surface writing enhancement. 7. Provides an evaluation of ash thermography parameters for the most effective document imaging.

Solid state thin film lithium microbatteries fabricated by pulsed-laser deposition (PLD) are suggested. During deposition the following process parameters must be considered, which are laser energy and fluence, laser pulse duration, laser pulse frequency, target composition, background gasses, substrate temperature, target-substrate distance and orientation. The effects of the variations of the process parameters can be obtained by measuring stoichiometry, thickness, phases and structure (grain size and texture), and stress of the deposited films. Electrochemical measurements will be conducted to test the microbattery properties through open-circuit voltage, charge-discharge cycling, cyclic voltammetry, and impedance analysis. / Singapore-MIT Alliance (SMA)

LiCoO₂thin films have been grown by pulsed laser deposition on stainless steel and SiO₂/Si substrates. The film deposited at 600°C in an oxygen partial pressure of 100mTorr shows an excellent crystallinity, stoichiometry and no impurity phase present. Microstructure and surface morphology of thin films were examined using a scanning electron microscope. The electrochemical properties of the thin films were studied with cyclic voltammetry and galvanostatic charge-discharge techniques in the potential range 3.0-4.2 V. The initial discharge capacity of the LiCoO2 thin films deposited on the stainless steel and SiO₂/Si substrates reached 23 and 27 µAh/cm², respectively. / Singapore-MIT Alliance (SMA)

Invented in the 1950s, gel electrophoresis has now become a routine analytical method to verify the size of nucleic acids and proteins in molecular biology labs. Conventional gel electrophoresis can successfully separate DNA fragments from several base pairs to a few tens of kilo base pairs, beyond which a point is reached that DNA molecules cannot be resolved due to the size independent mobility. In this case, pulsed field gel electrophoresis (PFGE) was introduced to extend the range of DNA fragment sizes that can be effectively separated. But despite the incredible success of PFGE techniques, some important drawbacks remain. First, separation time is extremely long, ranging from several hours to a few days. Second, detection methods still rely on staining the gel after the run. Real time observation and study of band migration behavior is impossible due to the large size of the PFGE device. Finally, many commercial PFGE instruments are relatively expensive, a factor that can limit their accessibility both for routine analytical and preparative use as well as for performing fundamental studies. In this research, a miniaturized PFGE device was constructed with dimension 2cm x 2.6cm, capable of separating DNA fragments ranging from 2.5kb to 32kb within three hours using low voltage. The separation process can be observed in real time under a fluorescence microscope mounted with a cooled CCD camera. Resolution and mobility of the sample were measured to test the efficiency of the device. We also explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization was performed during gel electrophoresis and the extension length, entanglement probability and reorientation time of different conjugates were measured to study their effect on DNA migration through the gel. Finally, electrophoresis of DNA conjugates was performed in the miniaturized PFGE device, and shaper bands were observed compared with the non end-labeled sample. Furthermore, by end-labeling DNA with quantum dots, the migration distance of shorter fragments is reduced, providing the possibility of separating a wider range of DNA fragment sizes on the same gel to achieve further device miniaturization.

The thesis explores preparation and properties of bismuthiron garnet (BIG) films and the incorporation of BIG films intoone-dimensional magneto-optical photonic crystals (MOPCs). Films were prepared by pulsed laser deposition. Weinvestigated or measured crystallinity, morphology,film-substrate interface, cracks, roughness, composition,magnetic coercivity, refractive index and extinctioncoefficient, and magneto-optical Faraday rotation (FR) andellipticity. The investigations were partly performed onselected samples, and partly on two series of films ondifferent substrates and of different thicknesses. BIG filmswere successfully tested for the application of magneto-opticalvisualization. The effect of annealing in oxygen atmosphere wasalso investigated - very careful annealing can increase FR byup to 20%. A smaller number of the above mentionedinvestigations were carried out on yttrium iron garnet (YIG)films as well. Periodical BIG-YIG multilayers with up to 25 single layerswere designed and prepared with the purpose to enhance FR at aselected wavelength. A central BIG layer was introduced asdefect layer into the MOPC structure and generated resonancesin optical transmittance and FR at a chosen design wavelength.In a 17- layer structure, at the wavelength of 748 nm, FR wasincreased from -2.6 deg/µm to -6.3 deg/µmat a smallreduction in transmittance from 69% to 58% as compared to asingle-layer BIG film of equivalent thickness. In contrast tothick BIG films, the MOPCs did not crack. We were first toreport preparation of all-garnet MOPCs and second toexperimentally demonstrate the MOPC principle inmagneto-optical garnets.

This thesis on multicarrier effects in the magnetotransport and optical properties of Mercury Cadmium Telluride (MCT or HgCdTe) covers mainly: design, construction and calibration of a 12T 4K and 19T 77K pulsed high magnetic field systems; temperature dependent magnetotransport measurements upto 15T performed on the home-built pulsed magnet systems; computational techniques developed to extract densities and mobilities of various carriers, especially low mobility heavy holes, participating in conduction; theoretical analysis of heavy hole mobility based on Boltzmann transport equation; temperature dependent optical absorption experiments in the Mid and Far-IR on bulk and thin film samples; and theoretical modelling of optical absorption below bandgap. The work essentially probes the low and high frequency conductivity of the semiconductor alloy Hg1?xCdxTe by performing microscopic calculations of scattering related phenomena of its free carriers at higher temperatures (200 K–300 K) and comparing with experimental data. Special attention is given to properties of heavy holes as the effects due to these carriers appear only at higher magnetic fields. It is demonstrated that in this temperature range and at high magnetic fields, taking both measured resistivity and derived conductivity in the multicarrier analysis gives better results which are then applied to explain both heavy hole mobility as well as free carrier absorption without further fitting parameters and using a minimal set of necessary intrinsic properties. The agreement thus obtained with experimental data is shown to be excellent. The bulk and epilayer samples used in this thesis were grown by the MCT group headed by R. K. Sharma (SSPL, Delhi). The organization of the thesis is as follows: Chapter 1 The importance of Mercury Cadmium Telluride as a narrow gap semiconductor for infrared detection is introduced. The relevant physical and material properties of HgCdTe are reviewed. Chapter 2 A low cost 12T pulsed magnet system has been integrated with a closed-cycle Helium refrigerator (CCR) for performing magnetotransport measurements. Minimal delay between pulses and AC current excitation with software lock-in to reduce noise enable quick but accurate measurements to be performed at temperatures 4K-300K upto 12T. An additional pulsed magnet operating with a liquid nitrogen cryostat extends the range upto 19T. The instrument has been calibrated against a commercial superconducting magnet by comparing quantum Hall effect data in a p-channel SiGe/Si heterostructure and common issues arising out of pulsed magnet usage have been addressed. The versatility of the system is demonstrated through magnetotransport measurements in a variety of samples such as heterostructures, narrow gap semiconductors and those exhibiting giant magnetoresistance. Chapter 3 The necessity of employing multicarrier methods in magnetotransport of narrow gap semiconductors is brought out. In these materials, mixed conduction is seen to exist at nearly all temperatures of interest. Methods of extracting two of the most important transport parameters of device interest, density and mobility, from the variable magnetic field Hall and magnetoresistance measurements are elaborated. Improvements have been made to the conventional non-linear least squares fitting procedure and are demonstrated. Chapter 4 Magnetotransport measurements in pulsed fields upto 15 Tesla have been performed on Mercury Cadmium Telluride (Hg1?xCdxTe, x?0.2) bulk as well as liquid phase epitaxially grown samples to obtain the resistivity and conductivity tensors in the temperature range 220K to 300 K. Mobilities and densities of various carriers participating in conduction have been extracted using both conventional multicarrier fitting (MCF) and Mobility Spectrum Analysis(MSA). The fits to experimental data, particularly at the highest magnetic fields, were substantially improved when MCF is applied to minimize errors simultaneously on both resistivity and conductivity tensors. The semiclassical Boltzmann Transport Equation (BTE) has been solved without using adjustable parameters by incorporating the following scattering mechanisms to fit the mobility: ionized impurity, polar and nonpolar optical phonon, acoustic deformation potential and alloy disorder. Compared to previous estimates based on the relaxation time approximation with out-scattering only, polar optical scattering and ionized impurity scattering limited mobilities are shown to be larger due to the correct incorporation of the in-scattering term taking into account the overlap integrals in the valence band. Chapter 5 Optical absorption measurements have been performed on bulk Mercury Cadmium Telluride (Hg1?xCdxTe, x?0.2) samples between 4K and 300 K. After fitting the Urbach part of the spectrum in the mid-infrared, below bandgap absorption is modeled using only basic processes and mechanisms, i.e. intervalence transitions and free carrier absorption (FCA). The additive FCA coefficients for individual carriers have been calculated using known quantum mechanically derived expressions for scattering due to polar and nonpolar optical phonons, ionized impurities and acoustic deformation potential mechanisms found to be relevant for electrical transport in this temperature range. The densities of carriers used in the calculations are derived from a modified multicarrier fitting (MCF) procedure on both resistivity and conductivity tensors from magnetotransport measurements in pulsed fields upto 15 Tesla from 220K to 300 K, thus making hole density more reliable. It is found that such a treatment is sufficient to model the absorption spectra below bandgap quite accurately without introducing any additional mechanical or compositional defect related phenomena. Chapter 6 A summary of the work carried out in this thesis is presented. Some future directions including preliminary work to measure carrier mobilities at high electric fields and effect of hydrogen passivation in MCT are briefly discussed.

Air sparging is a technique used to remediate gasoline contamination. In sparging, air is injected below the target zone and removes contamination via two separate mechanisms; volatilization and biodegradation. In volatilization, the air contacts the contamination as it moves upward. The contaminant will partition to the vapor phase based on its volatility and will be removed as the air reaches the atmosphere. For biodegradation, the oxygen in the airstream is used for microbial activity. Pulsed air sparging, otherwise known as pulsed biosparging, has been found to be more effective than continuous air sparging. Pulsed biosparging enhances treatment because it induces groundwater movement and mixing. The general mechanisms for treatment of gasoline sources using air sparging are relatively well characterized. However, air flow through the subsurface and the total hydrocarbon mass lost are difficult to predict and quantify. This project was intended to quantify the mass lost through volatilization and through biodegradation at the E10 gasoline source using pulsed biosparging, and to determine the effect of the source zone removal on downgradient dissolved BTEX concentrations. The remedial system consisted of two major components: the air sparging system, with three injection points; and a soil gas collection system. The soil gas collection system was comprised of an airtight box that covered the source area and the monitoring wells upgradient and downgradient of the source. Off-gas from the soil gas collection system was monitored continuously using a PID. The off-gas was also sampled frequently for BTEX, pentane, and hexane to determine the hydrocarbon mass removed; and for O2 and CO2 to determine biodegradation rates. The remedial system ran for approximately 280 hours over 33 days. Of the estimated 22.3 kg of gasoline residual in the source zone, 4.6 kg or 21% of the residual was removed via volatilization and 4.9 kg or 22% of the residual was removed via biodegradation. Leakage outside the system was estimated at less than 0.1% of the total mass. Groundwater samples were collected when the last sparged air was calculated to arrive at the row 2 downgradient fence. The average BTEX groundwater concentration after sparging was 40% of the pre-sparging concentration. The benzene mass discharge decreased 27%, the ethylbenzene mass discharge decreased 65%, the p/m-xylene mass discharge decreased 6%, and the o-xylene mass discharge decreased 5%. The mass discharge for naphthalene and TMB isomers increased 19%. However, these values fit in with long-term groundwater concentration trends. Additional sampling is recommended to determine if the sparging made a significant impact on mass discharge leaving the source.