Philosophiae Doctor - PhD / This project is aimed at fabricating a smart material. Zinc oxide and vanadium dioxide have received a great deal of attention in recent years because they are used in various applications. ZnO semiconductor in particular has a potential application in optoelectronic devices such as light emitting diodes (LED), sensors and in photovoltaic cell industry as a transparent electrode. VO2 also has found application in smart windows, solar technology and infrared smart devices. Hence the need to synthesis or fabricate a new smart material using VO2 and an active ZnO based nano-composites family in which ZnO matrix will be hosting thermally active VO2 nano-crystals is the basis of this study. Since VO2 behave as an MIT Mott’s type oxides and exhibits a thermally driven semiconductor-metal phase transition at about 68 oC and as a direct result ZnO:VO2 nano-composites would exhibit a reversible and modulated optical transmission in the infra-red (IR) while maintaining a constant optical transmission in the UV-Vis range. The synthesis is possible by pulsed laser deposition and ion implantation. Synthesis by pulsed laser deposition will involve thin films multilayer fabrication. ZnO buffer layer thin film will be deposited on the glass and ZnO single crystals and subsequent layer of VO2 and ZnO will be deposited on the substrate. X-ray diffraction (XRD) reveals that the series of ZnO thin films deposited by Pulsed Laser Deposition (PLD) on glass substrates has the hexagonal wurtzite structure with a c-axis preferential orientation. In addition the XRD results registered for VO2 samples indicate that all thin films exhibits a monoclinic VO2 (M) phase. UV-Vis NIR measurements of multilayered structures showed the optical tunability at the near-IR region and an enhanced transparency (>30 %) at the visible range.

Although it is known that gold (Au) is diamagnetic in bulk form, it has been reported that Au displays magnetic properties when reduced to the nano-scale. Researchers found magnetism in Au nanoparticles (NPs) in a size range from 2 to 10 nanometers. Moreover, the Au nanoparticles are usually coated by thiol-containing organic caps, which are believed to be responsible for the magnetism. However, others suggest that organic capping is not necessary to observe magnetism in Au NPs, and magnetism may be an intrinsic property for nano-structured gold. For this investigation, we used pulsed laser deposition to prepare nano-structured gold of different sizes and concentrations to investigate the magnetic properties. Our experiment results confirmed that for the samples in which Au is in the metallic state as nanoparticles with ~5 nm diameter, as well as inthe alloy form, bonded with indium, the samples show ferromagnetism when embedded in an Al2O3 matrix without any thiol-containing organic capping. Our results suggest that ferromagnetism is an intrinsic property of Au nano-structures, which means that it is not necessary to incorporate Au-S bonds with organic coatings in order to observe this phenomenon. We believe due to the significant broken symmetry at the surface of the nanoparticles, holes are generated in d bands of the surface Au atoms. These holes are most possibly responsible for ferromagnetism in Au nanoparticles. The realization of magnetism in Au coupled with the lack of clear understanding of its origin makes the investigation of magnetism of diamagnetic metals ripe for further inquiry. / Ph. D.

The thesis focuses on synthesis and characterization of nanocatalysts for applications in wastewater treatment and hydrogen production through electrochemical water splitting. Different photocatalysts and electrocatalysts are synthesized using wet chemistry techniques as well as Pulsed Laser Deposition (PLD). The synthesized catalysts pave demonstrate excellent catalytic activity thereby paving way for their use on an industrial scale.

Pulsed laser deposition (PLD) was used to deposit hydroxyapatite (HA) thin films on various substrates, including silicon (100) and titanium (Ti-6Al-4V) alloy. Thin films of amorphous HA were deposited at room temperature and then annealed over a range of temperatures. The microstructure and composition of the films were determined using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD). The HA films were found to achieve total crystallinity at 350㮠The mechanical properties of the films were studied by means of nanoindentation and scratch adhesion testing. Crystalline and adherent HA thin films prepared using PLD and post deposition annealing have many potential medical and dental applications.

ZnO thin films and nanostructures were grown by eclipse pulsed laser deposition (EPLD) for the first time. On bare sapphire held at 600 °C, a complex nanostructured surface was formed when ablating a metallic Zn target in an oxygen ambient. Nanorods grown by a vapor-solid mechanism clumped together in well separated, micron-sized regions. Nanoscale pyramids with 6 fold symmetry formed between the nanorod clumps by vapor-liquid-solid growth. Strong photoluminescence (PL) was observed from the EPLD grown samples, an order of magnitude stronger than PLD grown nanorods formed under similar growth conditions. Low temperature PL was dominated by the I₇ exciton, which still has an unknown origin. Excitation intensity dependence of I₇ was drastically different than the rest of the nearby excitonic features, behavior which has not been previously reported for bound excitons in ZnO. I₇ also showed large, seemingly random variations in intensity across the surface of each sample compared to the other nearby recombinations, suggesting a structural connection. Introduction of a buffer layer had a profound effect on the morphology and PL from EPLD grown ZnO from a metallic Zn target. Pt has a high melting temperature, which helped suppress the vapor-liquid-solid nanostructure growth resulting in thin-film formation. For standard PLD, the ZnO film showed large grains separated by cracks on the surface. Due to the reduced growth rate in the EPLD geometry, the ZnO layer had a high density of nanoscale pores, reminiscent of the porous Pt buffer layer. Strong PL emission, which was dominated by I₇, was observed from the ZnO/Pt/Al₂O₃ which showed unusual blue/violet emission when the EPLD geometry was used for growth. Thin ZnO buffer layers deposited at reduced temperature also had a profound effect on EPLD grown ZnO, resulting in a random array of nanorods with alignment which was dependent on the growth temperature of the buffer layer. Buffer layers offer another dimension in the control over epitaxial structures and show large potential for EPLD growth of ZnO. Pb was the dominant impurity in the Zn targets used for EPLD growth, hinting at a Pb-related origin for the I7 peak. To explore this idea, hydrothermally grown bulk ZnO was ion-implanted with Pb and then annealed in oxygen at 600 °C to repair damage to the crystal. PL emission intensity was substantially reduced in the Pb-implanted ZnO but the line widths were preserved. No evidence of an I₇ feature was seen for Pb concentrations of up to 0.10%, three orders of magnitude higher than the expected level in the EPLD grown ZnO. However, this does not rule out a Pb-related complex as the origin of I₇ since Pb has complicated interactions with the impurities and native defects in ZnO. Instead of I₇, other sharp excitonic features were observed near the band edge. A bound exciton with a localization energy of 12.4 ± 0.2 meV was observed in the Pb-implanted samples and was attributed to neutral interstitial Pb donors. Pb-implantation produced a clear PL signature which is unique enough to unambiguously detect its presence in ZnO. EPLD also proved successful at depositing oxides of the noble metals. Ir, Pt, Pd, and Ru targets were ablated in oxygen and argon ambients and films were collected on room temperature substrates. Growth in argon resulted in pure metal while oxidized layers were obtained in oxygen. This was clearly evident by the semiconductor-like transmission spectra observed for the oxidized samples. The high fluence used for these growths promoted the oxidation of these resilient metals while the shadow mask blocked most of the molten particulates generated by the high fluence. EPLD is an excellent way to produce oxides from metallic targets, a technique which should be explored in more detail for many material systems.

ZnO thin films and nanostructures were grown by eclipse pulsed laser deposition (EPLD) for the first time. On bare sapphire held at 600 °C, a complex nanostructured surface was formed when ablating a metallic Zn target in an oxygen ambient. Nanorods grown by a vapor-solid mechanism clumped together in well separated, micron-sized regions. Nanoscale pyramids with 6 fold symmetry formed between the nanorod clumps by vapor-liquid-solid growth. Strong photoluminescence (PL) was observed from the EPLD grown samples, an order of magnitude stronger than PLD grown nanorods formed under similar growth conditions. Low temperature PL was dominated by the I₇ exciton, which still has an unknown origin. Excitation intensity dependence of I₇ was drastically different than the rest of the nearby excitonic features, behavior which has not been previously reported for bound excitons in ZnO. I₇ also showed large, seemingly random variations in intensity across the surface of each sample compared to the other nearby recombinations, suggesting a structural connection. Introduction of a buffer layer had a profound effect on the morphology and PL from EPLD grown ZnO from a metallic Zn target. Pt has a high melting temperature, which helped suppress the vapor-liquid-solid nanostructure growth resulting in thin-film formation. For standard PLD, the ZnO film showed large grains separated by cracks on the surface. Due to the reduced growth rate in the EPLD geometry, the ZnO layer had a high density of nanoscale pores, reminiscent of the porous Pt buffer layer. Strong PL emission, which was dominated by I₇, was observed from the ZnO/Pt/Al₂O₃ which showed unusual blue/violet emission when the EPLD geometry was used for growth. Thin ZnO buffer layers deposited at reduced temperature also had a profound effect on EPLD grown ZnO, resulting in a random array of nanorods with alignment which was dependent on the growth temperature of the buffer layer. Buffer layers offer another dimension in the control over epitaxial structures and show large potential for EPLD growth of ZnO. Pb was the dominant impurity in the Zn targets used for EPLD growth, hinting at a Pb-related origin for the I7 peak. To explore this idea, hydrothermally grown bulk ZnO was ion-implanted with Pb and then annealed in oxygen at 600 °C to repair damage to the crystal. PL emission intensity was substantially reduced in the Pb-implanted ZnO but the line widths were preserved. No evidence of an I₇ feature was seen for Pb concentrations of up to 0.10%, three orders of magnitude higher than the expected level in the EPLD grown ZnO. However, this does not rule out a Pb-related complex as the origin of I₇ since Pb has complicated interactions with the impurities and native defects in ZnO. Instead of I₇, other sharp excitonic features were observed near the band edge. A bound exciton with a localization energy of 12.4 ± 0.2 meV was observed in the Pb-implanted samples and was attributed to neutral interstitial Pb donors. Pb-implantation produced a clear PL signature which is unique enough to unambiguously detect its presence in ZnO. EPLD also proved successful at depositing oxides of the noble metals. Ir, Pt, Pd, and Ru targets were ablated in oxygen and argon ambients and films were collected on room temperature substrates. Growth in argon resulted in pure metal while oxidized layers were obtained in oxygen. This was clearly evident by the semiconductor-like transmission spectra observed for the oxidized samples. The high fluence used for these growths promoted the oxidation of these resilient metals while the shadow mask blocked most of the molten particulates generated by the high fluence. EPLD is an excellent way to produce oxides from metallic targets, a technique which should be explored in more detail for many material systems.

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

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)

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.