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This work focuses on the investigation of platinum-based catalytic micro/nanomotors, including working mechanism, design, fabrication and related characterization. Three different categorized micro/nanomotors have been investigated, and key observations can be summarized as follows: i.A novel disk-like gold-nickel-platinum nanomotor is proposed. A bubble propulsion mechanism is employed to characterize the locomotion of the proposed nanomotor. The propulsion activities of the nanomotor are investigated at different hydrogen peroxide concentrations and different temperatures. Moreover, the magnetic effect on the propulsion of the nanomotor is also characterized. In addition, for the first time the three-dimensional propulsion of the nanomotor is characterized by using digital holographic microscope. ii. Two different types of gold-nickel-platinum nanojets are designed. One is with singular off-center nanoengine, the other one is with dual off-center nanoengines. The self-steerable propulsion activities of these two different nanojets are characterized at different hydrogen peroxide concentrations. The results show that the nanojet with singular off-center nanoengine is able to propel forward circularly; while the nanojet with dual off-center nanoengines can move forward linearly. iii.Another novel micro/nanomotor (platinum-nickel-SU-8 microrocket) is proposed. The microrocket has an eccentric nanoengine. A circularly self-steerable propulsion mechanism is proposed for characterizing the autonomous locomotion of the microrocket. The circularly steerable propulsion of the microrocket is characterized at different hydrogen peroxide concentrations. The results reveal that the speed of the microrocket increases with the increment of hydrogen peroxide concentrations. These observations prove the fabrication feasibility of newly designed micro/nanomotors. The wide applications of these micro/nanomotors can be expected. Doctor of Philosophy (MAE)

In the past several decades, membrane technology is widely used in separation process in various fields. In particular, membrane bioreactors (MBRs) as an application of membrane technology has attracted increasing attention from the researchers worldwide. However, there still exists many obstacles in membrane widespread application and the major challenge is membrane fouling. Recently, antifouling membrane fabrication by functional polymers is regarded as a promising and effective strategy to inhibit membrane fouling. Thus, this research work mainly focuses on poly(vinylidene fluoride) (PVDF) membrane modification by thermosensitive polymer PNIPAAm [poly(N-isopropylacrylamide)] and its copolymer with other functional polymers. Meanwhile, the objective of this thesis is to investigate the application potential of antifouling membrane prepared and to provide a feasible and effective strategy to achieve better antifouling performance for wide application, thereby providing a meaningful reference for future study. Firstly, functional polymer PNIPAAm was successfully bonded onto PVDF membrane via surface-initiated atom transfer radical polymerization (ATRP). The hydrophilicity of PVDF membrane was dramatically enhanced due to the incorporation of PNIPAAm chains. The microfiltration experiments indicated that PNIPAAm modified membrane exhibited a flux recovery ratio (FRR) as high as 91.59%. In addition, bacteria adhesion test revealed that the attachment of Escherichia coli on the modified membrane was reduced by 75% compared to the original membrane. Hence, the fouling tests demonstrated that PNIPAAm modified membrane exhibited obvious thermosensitive property and good antifouling ability compared with pure PVDF membrane. In order to further improve not only fouling resistance but also fouling release property of membrane, three types of modified membrane were well designed by grafting PNIPAAm, PHEMA [poly(hydroxyethyl methacrylate)] and P(HEMA-co-NIPAAm) respectively. Minimum protein adsorption and bacterial adhesion were both obtained on PVDF-g-P(HEMA-co-NIPAAm) membrane, with reduction by 44% and 71% respectively compared to the pristine membrane. The filtration testing indicated that the copolymer modified membrane exhibited high resistance to protein fouling and the foulant on the surface was removed easily by washing, suggesting easy-cleaning capacity. The biofouling on the membrane surface was analyzed using Gram-negative E. coli and Gram-positive Staphylococcus epidermidis. According to biofilm study using E. coli and S. epidermidis, it is inferred that microorganism species played an essential role in the formation and structure of biofilm as the species influenced the bacterial adhesion each other owing to their characteristics. Besides, the modified membrane exhibited higher fouling resistance during filtration and higher flux recovery after hydraulic cleaning compared with the original membrane for long-term use. Furthermore, for thermosensitive PVDF-g-P(HEMA-co-NIPAAm) membrane prepared in this thesis, water cleaning with temperature control provide an auxiliary and feasible strategy to promote the fouling release and to enhance the efficiency of fouling removal except for classical cleaning methods for wastewater treatment. This thesis was one of the limited studies to achieve higher antifouling property focusing on not only fouling resistance but also fouling release for PVDF membrane via grafting functional polymers P(HEMA-co-NIPAAm). This research study provided a feasible and effective strategy of antifouling membrane preparation which can be also used for other types of the membrane in wide range of applications. Doctor of Philosophy (IGS)

The sporoderms of pollen and plant spores provide an ideal source of robust monodisperse capsules for microencapsulation applications. Plant-based sporoderms are nature’s solution to protecting sensitive genetic material from harsh environmental conditions and offer a promising natural solution to the large-scale manufacture of microcapsules. The outer sporoderm layer (exine) of pollen and spores typically comprises a biopolymer, sporopollenin, with remarkable physicochemical stability, and the inner sporoderm layer (intine) typically comprises a combination of common cellulosic materials. It is important to note that the sporopollenin and cellulosic layers comprising the sporoderm are free from allergenic compounds commonly associated with pollen. Through standard wet chemistry processing methods, allergenic proteins and other contaminants may be completely removed. There currently exist a wide range of chemical processing protocols for extracting sporopollenin sporoderm microcapsules (S-SMCs), as well as various techniques for the loading of compounds within S-SMCs. However, there is still a need for a systematic analysis of the efficacy of S-SMC extraction steps, and key factors influencing the loading and release of compounds within S-SMCs. Therefore, in this thesis, detailed studies were undertaken of the most commonly utilized S-SMC extraction protocol, the applicability of this protocol to genetically distant sources of S-SMCs was explored, and the dynamics of compound loading and release from S-SMCs were elucidated. Standard S-SMC extraction steps involve, defatting of surface lipidic compounds, base-hydrolysis of proteinaceous cytoplasmic contents, acid-hydrolysis of cellulosic materials, and washing for removal of processing residues, under varying experimental conditions. Through these studies, it was shown that base-hydrolysis is redundant and may actually damage the integrity of the sporoderm from some plant species. It is now clear that defatting and acid-hydrolysis alone are adequate to isolate S-SMCs. Acid-hydrolysis temperatures can be reduced from 170°C to 70°C, and processing times can be reduced from 7 days to 5 - 30 hours. Additionally, it was observed that excessive duration acidolysis, based on existing standard protocols, destabilizes the S-SMC microstructure and causes capsule fragmentation. With regards to mechanisms of S-SMC loading and release, it was identified that air bubble collapse drives S-SMC loading, and that methods of assisted loading are important to ensure the full loading of all S-SMC cavities. Through optimization of macromolecule loading it was possible to elucidate practical loading efficiencies and distributions, as well as to estimate theoretical maximum loading efficiencies. In vitro release studies resulted in both qualitative and quantitative analysis of release dynamics. Further studies with enteric coencapsulation allowed for the development of an S-SMC system for targeted intestinal delivery with tunable controlled release. Overall, these studies provide important insights into the ongoing exploration of these promising natural microcapsules and their potential for utilization in a wide range of industrial applications. Doctor of Philosophy (MSE)

Using In2O3 as a host matrix, extensive density functional theory (DFT) calculations have been performed to study the mechanism of ferromagnetism in In2O3-based system. As a conventional approach to introduce local magnetic moment by transition metal doping, Fe-doped In2O3 (IFO) is the suitable prototype due to its high solubility of Fe in In2O3. Our DFT studies show that the ground state of pure IFO is antiferromagnetic. The coexistence of O vacancy (VO) and Cu co-doping (IFCO-VO) can greatly enhance the stability of the ferromagnetism. The role of Cu ions is to act as super-exchange mediators causing an indirect ferromagnetic (FM) coupling between Fe ions. In favor of the FM state, Cu ions prefer to locate adjacent to the Fe ions to facilitate Fe1-O1-Cu-O2-Fe2 coupling chains. Alternative approaches to introduce local magnetic moment are 2p elements or alkali metal doping. Our calculations show that, in case of the 2p element N doping, the FM coupling between N dopants is activated through holes induced by N doping via a N1:p-Inbr:d/p-N2:p coupling chain in short N-N separations. The FM coupling in alkali cation doped In2O3 is activated by intra- and inter-correlation of the XIn-6ONN complexes (X = alkali metal). DOCTOR OF PHILOSOPHY (SPMS)

The issue of skin friction related injuries has been one of the problems challenging the artificial sports turf industry. It has been identified by users as a major factor impeding acceptance of artificial turf at the professional level. However, information explaining the mechanisms for skin-turf abrasion is limited and little progress has been made, it appears, to derive an appropriate testing method for product approval or in evidence of improvement of the skin-friendliness of these products in sport surface surfaces. This research project focused on exploring the potential for improving the skin-friendliness of artificial turfs through a multi-faceted approach: identifying the contribution of the abrasive-components in modern artificial turf surfaces through mechanical testing; while critically evaluating currently available skin friction standards , evaluating strategies for polymer material modifications to reduce the skin-surface friction; and the designing of an appropriate bench-top set-up for the lab-based assessment of material skin-friendliness. The lack of understanding of skin-turf interaction was addressed by identifying the turf-component that has the greatest influence on the skin-turf friction – with the mechanical device used in the current industry standard. The ‘skin’-turf frictional profiles of a series of third generation (3G) turf surfaces were examined, in combination with independent measurements of the silicone ‘skin’ surface roughness pre- and post-friction testing. Results indicated that turf carpets without any infill material exhibited the highest frictional values while surfaces completely filled with either sand or rubber displayed similarly low frictional values, independent of infill type. Morphological measurements also showed the largest decrease in surface roughness for ‘skin’ samples tested on carpet-only surfaces, indicating a smoothening effect via abrasion. This abrading effect is alleviated with the addition of infill to the surface, with fully-filled surfaces having the least damage to the ‘skin’s. This unprecedented study suggests that the carpet may have the largest influence on the overall frictional behaviour of an artificial turf surface – narrowing down the turf component to be targeted when applying product improvements to address skin-friendly properties. The strategy of material surface modification was then employed, to study the effect of polyzwitterionic brushes on improving the skin-friendliness of the identified polypropylene substrate. To address the intended application for artificial turfs, a bench-top test was developed to investigate the frictional properties of the hydrated samples outside of commonly used aqueous environments, where an excess of lubricating water molecules is absent. Photo-grafted poly(sulfobetaine methacrylate) (pSBMA) brushes of various irradiation durations were prepared and the improvement in frictional properties was studied. Frictional measurements using silicone ‘skin’ tips, under both dry and hydrated surface conditions, showed that the applied modification was capable of forming a stable lubrication layer in the absence of excess water, significantly reducing the coefficient of friction by up to 78.8 %. The pSBMA brushes also provided the additional advantage of antifouling – exhibiting resistance towards pathogenic Staphylococcus aureus with almost zero surface colonization for well-grafted samples. The low ‘skin’-sample friction under ambient conditions and desirable fouling-resistance highlights the potential of pSBMA brushes as a modification strategy for achieving skin-friendly surfaces targeted at reducing the risk of skin abrasions. The tribological implications of counter-surface selection were investigated. Frictional assessments of the pSBMA-modified samples were carried out using standard steel tribo-tips, in addition to the ‘skin’ tips used. Measurements with the ‘skin’ tips showed that the hydrated pSBMA brushes were successful in reducing initial ‘skin’-sample friction though the effect diminishes with extended testing, attributed to the drying of the interfacial water. The standard steel tribo-tips were unable to reciprocate these results, returning consistently low frictional values regardless of extent of surface modification or hydration. These observations draw attention to the importance of counter-surface selection in frictional assessments, highlighting how appropriate test materials can identify characteristic surface properties while providing an interaction that simulates that of the intended application. The simple experimental set-up used may potentially be enhanced as an intermediate product qualification method in the manufacturing of skin-friendly artificial turf yarns. DOCTOR OF PHILOSOPHY (MSE)

Fabrication of new surapmolecular gel-phase materials based on selfassembly of low molecular weight gelator is motivated by potential applications of supramolecular gels in diverse fields. These types of materials have found application in field of biomaterial, electronic, sensing, and template for inorganic synthesis. However, most of low molecular gelator reported required complexes design and multi steps covalent practices. Hence, simple design and synthesis but at the same time posses advance functions are needed for fabrication supramolecular gel. In this thesis, firstly we reported a low molecular weight organogelators (LMWOGs) based on Fmoc-amino acid for multi purposed application. The gelator, Fmoc-lys(boc)-C16 was synthesized by one step coupling between amino acid bearing chromophore, Fmoc-lys(boc)-OH, and hexadecylamine. The gelator form stable transparent gel in cyclohexane and hexane with ultralow minimum gelation concentration (MGC) due to the cooperative formation of hydrogen bond and of π-π stacking of Fmoc moiety as indicated by fourier transform infrared spectroscopy (FTIR), fluorescence and circular dichroism (CD) study. Field emission scanning electron microscopy (FESEM) image revealed that gels consist of 1D self-assembly fibrous network. We demonstrated that Fmoc-lys(boc)-C16 selectively gelate organic solvent from their mixture in water. We also reported an efficient energy transfer between fluorenyl and dansyl moeities within self-assembled organogel. Energy transfer study indicate that the addition of acceptor group (octyl dansyl) decrease the emission of Fmoc group within the gel phase. Concentration dependent study revealed that high efficiency energy transfer (~89%) between Fmoc and Dansyl was achieved in gel phase. Moreover our study also shown that inclusion of 3% acceptor causes 50% quenching of donor that make Fmoc-Dansyl system as an ideal light harvesting system. As a multi purpose organogel, we also demonstrated that Fmoc-lys(boc)-C16 gel was able to remove organic dye from solution with high efficienty (~94%). In the second works, the formation of supramolecular hydrogel via ultra simple and facile approach using Fmoc-amino acid as building block was described. Fmoc-phenylalanine (F) was the smallest Fmoc-amino acid as building block for self-assembly into hydrogel. Our systematic studies revealed that molecular arrangement of F in self-assembly structure was driven by π-π stacking of Fmoc group and H-bond. In addition, the intermolecular interactionwas stabilized by the presence of phenyl group stacking. Furthermore, to fabricate straight forward strategy for antimicrobial supramolecular hydrogel, we described a facile route for antimicrobial hydrogel without involving expensive and time consuming covalent practices. The incorporation of Fmoc-leucine (L) into F hydrogel results in antimicrobial supramolecular hydrogel that able to kill bacteria pathogen S. aureus with fast killing rate. DOCTOR OF PHILOSOPHY (MSE)

This thesis reports successful synthesis of NKN solid solution powder series with compositions around the morphotropic phase boundary (MPB) hydrothermally at 200°C using a simple KOH and NaOH mixture with Nb2O5 as a precursor powder. Hydrothermal synthesis route adds the green-synthesis advantage to the already less toxic NKN by enabling growth at low temperatures (≤200°C, way below NKN Curie temperature), in water using simple chemicals and recyclable process. More significantly, this thesis demonstrates that the NKN solid solutions can be grown epitaxially over a conductive substrate using the same procedure. Thorough structural studies of hydrothermally grown NKN films and powders described in this thesis have shed light on the significant role of lattice trapped –OH related defects to the films’ electrical properties, crucial in devising strategies to remove the defects effectively and improve the ferro/piezoelectric performance. This thesis envisions to make widespread usage of I-V perovskite based lead-free ferro/piezoelectric materials a step closer to reality and shift the heavy reliance towards the high temperature, energy and labor intensive solid-state based materials synthesis. DOCTOR OF PHILOSOPHY (MSE)

This research project discovers several novel solvothermal systems that lead to the facile and controllable syntheses of various TiO2-based nanostructures. The potential applications of these nanostructures, including quasi one-dimensional rod-like bipyramidal nanocrystals, one-dimensional nanowires, two-dimensional nanosheets and their derived nanocomposites, as promising candidates of anode materials for high-performance lithium-ion batteries have been well demonstrated. It is shown that enhanced physicochemical properties of TiO2-based anodes can be achieved by properly designed and fabricated nanostructures, which paves the way towards low-cost, large-scale and environmentally friendly synthesis of advanced electrode materials with high power/energy density and long life for next-generation lithium-ion batteries. DOCTOR OF PHILOSOPHY (MSE)

The synthesis of novel materials drives forward the engine that is material science. The discovery of new materials is important not just from the standpoint of new applications, but is also important for the study of the fundamental forces that guide the reaction mechanism. Ever since Flanigen et. al. first reported the synthesis of zeolite like open framework in 1982, this field has grown exponentially. Nearly 25 elements of the periodic table have open framework structures attributed to them. Metal – chalcogenides have been a very important part of this Solid State chemistry. They have a wide range of applications like ion conductivity, magnetism and non – linear optical response. The larger size of chalcogen atoms allows them to have larger coordination numbers, thus increasing the number of ways they can form open frameworks. This offers a very good opportunity to study the area of open frameworks from different reactions. Solvent thermal synthesis has garnered much attention lately for its ability to produce diverse open framework topologies. By varying the reaction media and the structure directing agent, the desired properties expected of the final product can be finely tuned. Recently, using Ionic Liquids as reaction media, a number of new chalcogenide open frameworks have been reported. The high cost and limited commercial availability of Ionic Liquids has been a great obstacle to the exploitation of their properties as reaction media. Surfactants have long been used to influence the structure of open frameworks. In this investigation, surfactants are used as reaction media, in place of Ionic Liquids. The advantages of this approach is the cheaper costs of the surfactants and their vast varieties available, like acidic, basic, neutral, ionic, etc. This offers great scope for many different interactions between the reagents and the surfactants to form novel open frameworks. In this report, a series of chalcogenidoarsenates is used to demonstrate the excellent qualities of using Surfactants as reaction media. A homologous series of chalcogenidoarsenates is synthesised with dimensionalities varying from 0D clusters to 3D framework. The crystals exhibit semi conductor behaviour, with band gaps of 1.91eV to 2.46eV, which corresponds to the colour of the crystals. The crystals also exhibit magnetic properties, which are tested. Thus, this method offers new possibilities in the field of open framework syntheses of crystalline materials with diverse range of structures and properties. MASTER OF ENGINEERING (MSE)

Supramolecular assemblies have a key component with regards to supramolecular electronics, the study of its self-assembly behavior as well as functional properties will bring great impact in the sense of understanding and improving the performance of such devices from a fundamental point of view. We study supramolecular assemblies of hexa-peri-hexabenzocoronene (HBC) derivatives bearing different substituents, adsorbed on highly oriented pyrolytic graphite (HOPG) by using scanning tunneling microscopy at the solid-liquid interface. Two effects of intermolecular interaction were found to play a significant role in controlling the interfacial supramolecular assembly of these C3-symmetric HBC derivatives at the solid-liquid interface. One is hydrogen bonding interactions; the other is intermolecular dipole-dipole interactions. This work demonstrates how intermolecular interactions could enable fine control over the self-assembly of disk-like π-conjugated molecules. Furthermore, a host-guest system is established by utilizing the hydrogen bonding assisted honeycomb network established from HBC derivatives, and by incorporating coronene inside the porous structure, it offers potential applications such as use as molecular rectifiers in the future. Besides the bottom up approach of self-assembly of rigid molecules like HBC derivatives to establish a 2D π-conjugated structure, graphene has been viewed as the alternative material from the top-down point of view to possess 2D large π-conjugated area for promoting electron transport. By chemically modulating the monolayer graphene devices, positive photoreponse has been achieved, and with the help of conductive atomic force microscopy (C-AFM), the photoreponse performance could be correlated to the degree of functionalization at spatial distribution with nanoscale resolution. The mechanism was found to be desorption and adsorption of gas molecules in light and dark conditions; the positive photoresponse is due to the n-type doping behavior after functionalization. From the spatially distributed correlation between photocurrent and functionalization, it makes us realize that every functionalized pixel (~ nm2) offers a positive photoreponse, and the overall device performance is equivalent to the photoresponse of each individual pixel. This demonstrates that it is reliable to use the chemical method to generate a photoreponse from a 2D material like graphene. In order to explore further the relationship between the assembly structure behavior and its functional properties, π-conjugation interrupted frameworks (CIFs) have been studied and it was found that they are not only offering great three dimensionality, but are also sensitive to dopants and post-modification of their nanostructure based thin film with diazonium salt, which rendered their electrical properties highly tunable by up to two degrees of magnitude. Hence, it has been demonstrated that the π-conjugation-interrupted frameworks and their doped counterparts broaden the options for organic electronics. As a result of the H-shaped conformation and photosensitive properties of CIFs, we envisage their potential role as active components of memory devices and photodetectors in the future. In conclusion, this study offers valuable platforms by rational designing the self-assembly building blocks for the development and advancement in the field of supramolecular assemblies. It demonstrates the correlation between their structural behavior and resulted functional properties by means of scanning probe microscopes. HBC derivatives are designed for the bottom up approach of generating 2D π-conjugated area for molecular electronics; while graphene has been referred as the top-down alternative of producing such extended 2D structures and with chemical modulation, photoreponse of such devices are achieved with great repeatability. From 2D to 3D, a class of π-conjugation interrupted dendrimers exhibits tunable electrical properties by decorating small molecules. Finally, the perspectives on future directions and unsolved challenges are also addressed. DOCTOR OF PHILOSOPHY (MSE)

Polymer assisted solution synthesis is a common and versatile strategy for preparation of colloidal inorganic nano-materials with novel morphological and functional properties. Although block copolymers are usually employed, homopolymers are attractive substitutes for them, considering cost and scalability. This however requires further understanding and more stringent control of the interaction between homopolymer and precursor species. The objective of this work is to utilize functional homopolymers to control the structural properties and chemical compositions of synthesized nano-materials. This objective is approached through detailed studies on two hybrid material systems useful for energy-related applications: (i) aqueous-based poly(acrylic acid) (PAA) templated synthesis of copper oxide (CuOx); and (ii) organic solvent-based poly(3-hexyl thiophene) (P3HT) assisted synthesis of CuInSe2 (CISe) nano-particles. The chosen homopolymers are good representatives of its own category: PAA has an aliphatic, flexible, and ion conducting backbone; while P3HT is an aromatic, rigid, and semiconducting polymer. The bridging of the theoretical studies of PAA-Cu2+ interaction and PAA templated synthesis is attempted. In the CuOx project, investigation on the PAA-Cu2+ interaction was carried out. Important factors including [Cu2+]:[COOH]0, chain conformation, and non-uniform equilibrium charge distribution were identified to have contributed to counterion induced copolymer-like assembly of the PAA-Cu2+ complexes, eventually producing nano-tubular CuOx. The challenging control of stoichiometry and its uniformity is known to be an issue in tailoring the functional properties of CISe nano-particles. In the CISe project, CISe nano-particles having novel stoichiometric gradient (i.e. increasing In:Cu ratio from core to shell) and coordinated with P3HT were prepared. Synthesis systems without P3HT were carefully studied and a mechanism leading to novel core-shell-like stoichiometry is proposed. With employment of P3HT as functional ligands, the stoichiometric gradient could be moderated. This work investigates fundamental molecular-level phenomena associated with the starting precursor conversion, stabilized intermediate state, and eventual crystal growth. The concept and methodology developed can be extended to relevant material systems. This work highlights the vast opportunities remained to be explored in utilizing functional homopolymers for controlled synthesis of nano-materials. It can contribute to the fields of fundamental polymer science, inorganic nano-materials formation chemistry, as well as technological applications for printed electronics. DOCTOR OF PHILOSOPHY (MSE)

In the last decade, lanthanide-doped upconversion(UC) materials have become a shining star and been focused by a growing number of researchers all over the world, due to its unique and fascinating NIR-to-visible light conversion. Effective upconversion materials (e.g. NaYF4:Yb3+,Er3+ and NaYF4:Yb3+,Tm3+) have been demonstrated to be promising in a wide range of bio-medical and luminescent applications. However, such lanthanide-doped fluorides are found structurally unstable in ambient conditions and sensitive to aqueous solutions, leaving shadows in the further development and promotion of upconversion luminescence. Compared with fluorides, their oxide counterparts possess higher binding energies, more stable structures, and better tolerance to aqueous solutions, while being limited by difficulties in synthesizing nanocrystals and achieving effect upconversion luminescence. Hence, it’s of great promising to synthesize oxides-based upconversion materials in nanoscale and with high upconversion efficiency. In the first part, a systematic study in both controlled synthesis and enhanced luminescence of lanthanide-doped gadolinium oxides was performed. To start with, uniform and size-tunable gadolinium hydroxide rods were prepared through surfactant-free hydrothermal synthesis and could further transform into corresponding oxides through calcination treatment. The upconversion luminescence of as-prepared lanthanide-doped gadolinium oxide (Gd2O3:Ln3+) was substantially enhanced through a thermal treatment, being accompanied with the improvement of crystallinity. As a sequence, Gd2O3:Yb3+,Er3+ (10/1 mol%) nanorods with an upconversion efficiency comparable to fluoride counterparts were successfully obtained. To achieve a better understanding of energy transfer and upconversion luminescence, an investigation of host matrix-sensitized upconversion material (erbium-doped ytterbium oxide, denoted as Yb2O3:Er3+) was performed. By using ytterbium oxide powder and erbium chloride solution as precursors, Yb2O3:Er3+ with three-dimensional porous structure were prepared through hydrothermal synthesis followed by calcination treatment. The retention of the three-dimensional porous structure was demonstrated critical to overcoming the quenching effect. Such work proved a potential platform to study the short-term energy transfer between sensitizers and activators. Subsequently, oxide perovskite crystals with tunable cavities, in which doped cations were immobilized, were synthesized and used as host matrices for upconversion luminescence. To make it specific, Na1/2Y1/2TiO3 nanocubes were found promising for flexible lanthanide-doping and tunable upconversion luminescence. Markedly, through a further structural improvement and compositional optimization, effective upconversion luminescence with an ultrahigh power efficiency of 40.7 % was achieved on Na1/2Y1/2TiO3:Yb3+,Er3+ (20/2 mol%) nanocubes. Admittedly, effective upconversion nanoparticles could be potentially utilized in plenty of applications. As a proof of concept, a Gd2O3:Ln3+-based phosphor chip was fabricated to generate a combinational RGB-emission, achieving bright white-light emission consequently. Similarly, Na1/2Y1/2TiO3:Yb3+,Er3+ nanocubes were demonstrated eligible for light emitting and security pattern drawing. Furthermore, the dispersibility, stability, and biocompatibility of rare-earth oxide and titanate (e.g. Gd2O3 and Na1/2Y1/2TiO3) were assessed and demonstrated by cellular imaging. Taken together, rare-earth oxide/titanate nanocrystals were versatile and promising candidates for upconversion applications. Doctor of Philosophy

Organic-inorganic hybrid perovskites have emerged in recent years as one of the most promising materials for solution-processed electronics and optoelectronics including solar cells, light-emitting diodes (LED) and field-effect transistors (FET). Combining the rigid inorganic framework with soft organic materials, these hybrid perovskites provide the opportunity for investigating organic-inorganic interactions at the molecular scale. Using a molecular approach, this Ph.D. work explored a series of novel organic-inorganic hybrid perovskites targeting luminescence-related applications including LEDs and color-conversion phosphors. The structure-property relation was investigated and the underlying photophysical mechanism for the versatile luminescence was studied. The applications of these perovskites as light emitters in multicolored LED, white LED and long-lifetime phosphors were demonstrated... Doctor of Philosophy

Smart windows are promised with a significant contribution to the economization of building energy consumption. Such windows can dynamically modulate the indoor solar irradiation, leading to energy-saving for architectural heating and cooling systems. Development of smart windows can mainly be categorized as electro-, thermo-, and photo-stimulated optical response changes. Among them, thermochromic smart windows that change the optical properties in responsive to the temperature are highly competitive due to the low cost, passivity, and rational stimulus-response. Vanadium dioxide (VO2) is a promising candidate for thermochromic smart window application due to its reversible phase transition near the room temperature, accompanied with huge optical properties change. It can be transparent to the near-infrared solar irradiation at low temperature, while shield it at high temperature. However, challenges remain in VO2-based thermochromic smart windows, including the intrinsic yellow-brown color, the relatively low solar energy modulation (ΔTsol) and visible transmittance (Tlum). This thesis is dedicated to improve these shortages and promote the performance of VO2-based thermochromic smart windows, resulting in three effective methods. The photonic crystals were introduced to improve the undesirable yellow-brown color. The Silica/VO2 (SiO2/VO2) core/shell two-dimensional (2D) photonic crystal is prepared and demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR)modulation. Three-dimensional finite difference time domain simulations predict that the transmittance can be tuned across the visible spectrum while maintaining good ΔTsol of 11.0% and a Tlum of 49.6%. Though the experimental result is not as prominent, it proves that the color changes of VO2 films are accompanied by NIR modulation, which is aligned with the simulation result. In produced samples, colors beyond the yellow-brown are observed, such as green, blue, and red, demonstrating the effectiveness of photonic crystals for tuning the color of VO2-based smart windows. The localized surface plasmon resonance (LSPR) was introduced to promote the performance of the ΔTsol and the Tlum. The phenomenon is demonstrated in tuning the absorption peak position of VO2 to the region with dense solar energy, which was demonstrated on 2D patterned VO2 nanoparticles. Colloidal lithography method was applied to prepare the 2D patterned VO2-based nanocrystals, resulting in nanonet, nanodome, to nanoparticle arrays. LSPR and their application in thermochromic smart windows. The nanoparticle arrays exhibit tunable LSPR at different temperatures and the LSPR red-shift is observed with the increase of the particle size and the media reflective index. A competitive solar regulation efficiency (ΔTsol = 13.2%) and a transmittance contrast at 2000 nm (ΔTNIR = 44%) can be achieved. Pairing reconfigurable metamaterials with the active LSPR was demonstrated to provide performance. A kirigami-inspired elastomer containing plasmonic vanadium dioxide was developed, exhibiting adaptive, broadband, and high-efficient optical modulation. The geometrical transition and the active LSPR function synergistically by manipulating ultraviolet-visible and near-infrared regions, respectively. A new mechanical-thermal energy-saving smart window was developed adopting such materials exhibits an unprecedented solar energy modulation (ΔTsol = 37.7%). Fully thermal responsiveness is also achieved in such a system. Smart window based on such materials are promised better energy-saving ability than commercialized low-emissivity glasses in cities, such as Hong Kong and Houston. Doctor of Philosophy

Metal phthalocyanine (MPc), a class of organometallic materials, allows not just substituents on its phthalocyanine macrocycle, but also metal center variation. Such flexibility in molecular structure, as well as its semiconducting properties have thus promoted the use of MPc for numerous applications. One of these applications is on the sensing of gas analytes. Despite hundreds of publication on MPc as gas sensors, there is a lack of understanding on how the different substitutions will affect the gas sensitivity or to leverage on MPc properties to improve the selectivity or e-nose capabilities. On top of that, there is a general insufficiency on systematic studies done to investigate the properties of conductivity-based gas sensors based on organic materials. To elaborate, several properties that may be crucial, such as the thickness effect or sensing layer/electrode interface, have not been examined. This thesis attempts to bridge the knowledge gap by addressing three main topics; the thickness effect and the electrode/sensing layer interface effect on gas sensing, as well as giving a first insight on the gas sensing mechanism. In addition, this thesis will mainly focus on the gas sensitivity of MPc to nitrogen dioxide (NO2). By using CuPc chemiresistors, the thickness of the CuPc sensing layer demonstrated an inverse relationship to NO2 sensitivity. The reaction rate of the chemiresistors was found to follow the first order kinetics but that was inadequate to describe the difference in sensitivity. The device response to gas and the sensing layer thickness was then found to correlate to Knudsen diffusion, which aptly describe the inverse relationship of sensitivity and sensing layer thickness due to a decrease in the proportion of gas diffused into thicker sensing layers. The experiment was repeated with some variation in the chemiresistor structure and the same relationship between gas sensitivity and sensing layer thickness was observed. The electrode/sensing layer interface was also investigated in this thesis. CuPc sensing layers on Au or Pt electrodes were found to display ohmic properties while blocking contacts were formed with Al electrodes, in agreement with literature. NO2 sensitivity enhancement was demonstrated in CuPc chemiresistors with Al electrodes as compared to chemiresistors with Au or Pt electrodes due to the modulation in Schottky barrier upon exposure to NO2. As such, it is shown that similar phenomenon in metal oxide can also be expected in MPc sensing layers. Further on, preliminary study on the effect of substituent group or metal center change on NO2 sensitivity was conducted based on 5 different MPc materials. Results showed that the oxidation potential of the materials may be used as an indicator of the NO2 sensitivity. In particular, ZnPc with tertbutyl substituent group (electron donating group) demonstrated the highest sensitivity and may be correlated to the highest electron density in the Pc macrocycle, which is involved in the electron transfer process to NO2. Multiple measurements with new samples were utilized to affirm the results obtained. The interaction site was also examined in this thesis. In comparison to reported methods used to examine the interaction, such as Raman spectroscopy, x-ray absorption spectroscopy (XAS) was used with in-situ gas exposure for the first time on gas interaction characterization. Analysis of the XAS spectra suggests a lack of axial interaction of CuPc with NH3 or NO2 and revealed a compression of the Cu-N bond between the metal center and macrocycle upon exposure to NO2. The absence of a lengthening of this Cu-N also implies that the gas interaction does not occur at the metal center. Repeated measurements were found to display comparable results. Doctor of Philosophy

The conventional, linear, take-make-waste economy which was a by-product of the industrial revolution is not a viable option anymore. Environmental concerns are driving the development of a new circular model in which reduce, reuse, and recycle are key. Since this circular model would keep materials in commerce for longer, safer product designs that would reduce the amount of hazardous materials are vital. In this work, the aim is to implement this design philosophy in producing polymer/graphene nanocomposites as a rapidly emerging class of materials. The design philosophy is based on two strategies: first, to substitute conventional, synthetic components by their naturally-occurring counterparts and, second, by eliminating chemicals by assigning their roles to other multifunctional components. Graphene and, by extension, polymer/graphene nanocomposites have seen huge interest in academia and industry. Among different methods to produce graphene, liquid-phase exfoliation (LPE) is one of the most commonly used. LPE is a low cost, industrially-friendly, high-yield process in which graphite flakes are exfoliated into their 2D constituents, i.e., graphene, and stabilized in a liquid medium. Water is the most desirable medium for LPE but graphene needs stabilization with surfactants or stabilizers because of the huge mismatch between the surface energies of water and graphene. There have been a myriad of synthetic surfactants and stabilizers studied for this purpose, but natural surfactants have seen less attention. Here, lignin, an abundant, undervalued, byproduct of paper industry, will be used as a naturally-occurring stabilizer for graphene. Lignin-modified graphene (LMG) is non-covalently modified meaning its sp2 structure, which is the reason for its amazing properties, is unperturbed. Different polymer/graphene systems based on this sustainable design philosophy are produced. In the first work, LMG is added to waterborne polyurethane (WPU) to produce conductive films for antistatic coating applications. Since durability against environmental damage is an important factor for these coatings, functional properties such as self-healing and UV-resistance are required. However, instead of using self-healing agents and synthetic UV blockers, LMG is tasked with enabling self-healability and improving UV stability. Thanks to its multifunctional properties, LMG can act as a photothermal converter creating heat after being illuminated by near-infrared (IR). This increases the rate of polymer diffusion at the site of damage which results in fast self-healing of the damage. Due to the anti-UV properties of LMG and lignin, these nanocomposite coatings show remarkable UV resistance as well. The combination of self-healing and UV-stability renders these films highly durable. In the second work, graphene was used to produce multi-functional sensors. Commercially-available polyurethane (PU) sponges can become conductive by dip-coating in aqueous LMG suspensions. These sponges show electrical sensitivity to compression, and thanks to their high mechanical stability, they are able to accurately sense pressure with high accuracy over 5000 compression-release cycles. Since LMG acts as a negative temperature coefficient thermistor, these sensors can measure temperature with high sensitivity as well without the need for any temperature-sensitive component. Finally, this design philosophy is taken to the next level by completely removing lignin in the third work. Here, WPU can be used as a stabilizer to produce WPU-modified graphene (PMG). In contrast to the WPU/LMG system, WPU/PMG nanocomposites have no external stabilizer. These highly conductive nanocomposites are electromechanically sensitive and show huge electromechanical responses to deformation. In addition to being the polymer matrix and stabilizer, WPU endowed the sensors with shape conformality too, which significantly increased the real-life sensitivity of the sensors in monitoring biomechanical deformations and reproducing blood-pressure waveforms. This innate shape-conformality obviated the need for an additional skin-conformal layer. By adopting these strategies, organic liquid media and synthetic surfactants/stabilizers can be substituted by water and naturally-occurring lignin, or in case of the last study, lignin can be eliminated. Other functional additives such as self-healing agents, synthetic UV-stabilizers, or active materials are not required thanks to the multifunctional and multi-stimuli responsive nature of graphene. Doctor of Philosophy

Nickel titanium (NiTi) shape memory alloy is one smart material that has the capability to directly convert thermal energy into mechanical work. This unique property gives rises to shape memory effect and superelasticity. In order to fully utilise these two behaviours, NiTi needs to be processed into the different geometries for various applications. Nonetheless, the conventional manufacturing processes have several complications. Moreover, NiTi is not an easy material to process as well due to its compositional sensitivity and poor machinability. Thus, the full potential applicability of NiTi has not been achieved. To address these issues, one proposed solution would be to adopt Selective Laser Melting (SLM) to fabricate the NiTi parts. This new method of producing NiTi components is also known as 4D printing. The fabrication of NiTi via the SLM process not only contributes to solving the current problems encountered, it also allows complex NiTi smart structures to be produced directly for new applications. However, it is essential to first have the knowledge in fabricating functional SLM NiTi parts before manufacturing for actual applications. Furthermore, as compared to producing conventional metals through the SLM process, the fabrication of NiTi is much more challenging. Not only do the produced parts require a high density that leads to good mechanical properties, strict compositional control is needed as well for the SLM NiTi to possess suitable phase transformation characteristics. Therefore, in this thesis, the different SLM process parameters were first optimised, followed by the characterisation of the samples. Subsequently, the properties of the samples were enhanced through the implementation of repetitive scanning and post-process heat treatment. The SLM process parameters that were studied included the laser power, laser scanning speed, hatch distance and scanning strategy. These parameters were optimised and the produced SLM NiTi parts had low internal porosity, good geometrical accuracy, minimal oxidation and similar phase transformation characteristics as the NiTi powder. The small deviations in the internal porosity and transformation temperatures of the optimised single scanned samples have indicated the high repeatability of the SLM process. However, these samples demonstrated poor mechanical properties when subjected to tensile deformation. Multiple fractures were observed before the samples failed at a highest tensile strain of about 6%. Hence, repetitive scanning was implemented to enhance the properties of SLM NiTi. The results obtained from the repetitively scanned samples suggested that the laser absorptivity and heat conductivity of the materials before and after the first scan would significantly influence the final properties of the SLM NiTi. With carefully controlled repetitive scanning process, the fabricated samples demonstrated excellent properties. First, the samples exhibited comparable phase transformation characteristics as the raw NiTi powder used with high repeatability. Second, they displayed the capability to deform to 8% strain under the tensile mode without failure. Additionally, the samples have also demonstrated the highest magnitude of 5.11% transformation strain, with an average value of 4.61%. This scale of shape recovery was comparable to the conventionally-produced NiTi parts with a maximum transformation strain of about 6%. Nevertheless, the gap between the transformation strains of repetitively scanned samples and conventionally-made NiTi components indicated the possibility of further enhancing the shape memory properties of SLM NiTi. Therefore, post-process heat treatment was introduced to meet this objective. The results showed that the implementation of heat treatment had both positive and negative influences. A balance between these effects was needed to obtain an improvement in the shape memory responses of the repetitively scanned samples. It was observed that the samples subjected to heat treatment at 400 ˚C for a period of 5 minutes had higher transformation strain and percentage of shape recovery than the non-heat treated samples. The improvement in the shape memory properties was primarily due to the formation of a high density of fine Ni4Ti3 metastable precipitates. Nonetheless, increasing the heat treatment temperature to above 400 ˚C has resulted in overaging and further enlargement of the grain size. Consequently, degradations in the shape memory responses of the SLM NiTi samples were observed. Doctor of Philosophy

Undesired ice accumulation on outdoor sports facilities leads to severe economic issues and even loss of lives. Great efforts have been made to fabricate ice prevention surfaces or facilities since 1800s. The utilized methods can be categorized into four types: mechanical methods, chemical methods, thermal methods and combined methods (combing two or three former referred methods). Considering the economic impact and additional labour burdens, chemical methods are commonly adopted and widely studied. To avoid numerous environmental effect of drain-off chemicals, icephobic coatings, as effective passive anti-icing methods, have attracted much attention in recent decades. However, less attention has been paid on development of the anti-icing coatings for sports facilities and other related applications that requires additional properties including mechanical durability, transparency, easy processability and so on. With expectation to repel incoming water before ice formation, superhydrophobic coatings that exhibit superior water repellency and bouncy effect, have been widely studied since 1997. However, not all superhydrophobic coatings present anti-icing behaviours due to water condensation. This study begins with the investigation of the effect of water condensation on superhydrophobic coatings with different microstructures. To design superhydrophobic coatings with different microstructures, a sol-gel method was employed with adjustment of the weight ratio of nanoparticles with different surface energies. One of the prepared coatings demonstrated robust icephobicity with low ice-adhesion strength of ~ 60 kPa under water condensation conditions; at the same time, it also displayed a low ice-nucleation temperature of ~-26 degree celsius and low icing probability. With a strong demand for aesthetics appearance, transparent anti-icing coatings are needed for various applications. However, the well-studied superhydrophobic coatings are usually translucent or opaque because of the micro-nanostructures which greatly affect light transmittance. The state-of-the-art slippery liquid infused porous surface (SLIPS), which presented extremely low ice adhesion, can achieve a high transparency by choosing the substrate and lubricant liquid with matching refractive indices. However, the mechanical property of both kinds of coatings is weak due to the presence of porous microstructures. To obtain high transmittance and good mechanical properties, a new strategy is designed to fabricate a mechanical durable transparent anti-icing coating by a low cost sol-gel method. The prepared coatings presented a transmittance as high as 99 %, low ice adhesion, good condensation resistance, anti-frost and durable mechanical properties. Besides, this coating demonstrated self-cleaning properties and repellency to various liquids with surface energy ranging from 72.8~22.1 mJ/m2. With the demonstrated excellent properties, this coating is promising for anti-icing applications for sports applications and other applications that require good transparency and mechanical durability. Room-temperature processed anti-icing coatings are highly desirable for large outdoor structures besides the low-cost consideration. In this work, a room-temperature processable, fluorine-free anti-icing coating was designed and investigated. With the design of dual-size nanoparticle fillers, coatings presented denser micro-nanostructure than the ones with singe-size fillers. This denser structure of the dual-size coatings enabled better water repellency and anti-icing performance in terms of low ice adhesion and less ice accumulation than the single-size coatings and a commercially obtained polyurethane (PU) coating. To ensure the robustness and durability of the developed coatings, comprehensive mechanical and durability studies including tape adhesion, pencil hardness, dolly-pull tests, nano-indentation, ultraviolet (UV) irradiation, water condensation and sand erosion were carried out according to available ISO or ASTM standard methods. The dual-size coating presented better mechanical properties and UV resistance than the single-size and the PU coatings. Comparable sand erosion resistance were obtained on the dual-size particle coatings. To sum up, robust and durable anti-icing coatings which can satisfy different application requirements have been designed and developed successfully. The preparation method of these coatings follows some general principles of being simple, scalable, and low cost. Specially, the design of robust transparent coatings is a relatively new territory for passive anti-icing applications. Comprehensive mechanical and durability tests in these studies are novel, and can serve as a foundation for future evaluation of the practically applicable anti-icing coatings. The use of different surface energy nanoparticles, duals-size nanoparticles and mechanical-force induced deagglomeration are very enlightening methods for future design of functional coatings. Doctor of Philosophy

The employ of natural biomaterials as the basic building blocks of electronic devices is of growing interest for biocompatible and green electronics. Here, resistive switching (RS) devices based on naturally silk protein with configurable functionality are demonstrated. The RS type of the devices can be effectively and exactly controlled by controlling the compliance current in the set process. Memory RS can be triggered by a higher compliance current, while threshold RS can be triggered by a lower compliance current. Furthermore, two types of memory devices, working in random access and WORM modes, can be achieved with the RS effect. The results suggest that silk protein possesses the potential for sustainable electronics and data storage. In addition, this finding would provide important guidelines for the performance optimization of biomaterials based memory devices and the study of the underlying mechanism behind the RS effect arising from biomaterials.

Development of nonnoble metal catalysts for hydrogen evolution reaction (HER) is critical to enable an efficient production of hydrogen at low cost and large scale. In this work, a novel bimetallic carbide nanostructure consisting of Mo2C and WC is synthesized. Based on a highly conductive WC backbone, nanosized Mo2C particles are integrated onto WC, forming a well-defined and highly robust nanowire structure. More importantly, it is found that electrochemical activation can partially remove surface carbon and activate the catalyst by changing its surface hydrophilicity. As a result, the residual carbon contributes positively to the activity, besides its role of protecting carbide from oxidation. Benefiting from the structure, the catalyst achieves high activity, stable electrolysis towards HER.

The utilization of Ni(OH)2 as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)2 deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)2 is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g−1 at 5 mV s−1 and excellent rate capability (71.9% capacitance retention at 100 mV s−1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)2 nanomaterials. Using the ternary Ni(OH)2 hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg−1 at the power density of 780 W kg−1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)2 can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.

Layer-by-Layer (LbL) self-assembly has been proven to be a very facile and versatile method for thin film fabrication with precise control of the film components and structures. This technique possesses great advantage on integrating materials with different functionalities into a film with designed structures. These features enable LbL self-assembly technique to be a suitable platform for electrochemical applications, which usually require integration of multiple functional components and regulation of interface properties. Conventional polymer LbL films adopt individual polymers as building blocks. However, these films suffer from slow deposition process with only limited amount of materials could be deposited onto the substrate within a deposition cycle. Moreover, LbL films fabricated from individual polymers usually demonstrate compact structure, which also hinders their application in fabricating thin films of which non-compact configuration is preferred. Due to the basic requirements of LbL technique that the adjacent layer should directly interact with each other, this method possesses inherent drawbacks where multi-interfaces are not favourable. Further exploration and modification of LbL technique is desired for better utilization of this prospected technique on electrochemical applications. In this thesis, we focus on developing polymeric complexes as building blocks for LbL self-assembly, in order to surmount the drawbacks and broaden the application field of LbL technique. Polymeric complexes (PCs) are supramolecular assemblies built up by nonstoichiometric combination of two components. Compared with free polymers, PCs have several advantages including rich varieties of compositions, relatively large dimensions and diverse structures. Thus introducing PCs into LbL enriches the diversity of LbL films, especially for fast deposition of LbL films with special structures and functionalities. However, there are limited reports on using PCs as building blocks for LbL deposition for electrochemical device applications. Aiming at exploiting the potential and merits of adopting PCs in LbL for electrochemical related studies and applications, this thesis is devoted to develop suitable PCs as building blocks to fabricate LbL films for three typical components in an electrochromic device: the electrochromic active layer, the solid polymer electrolyte (SPE) layer as well as the transparent conducting film (TCF). Based on the basic mechanism and requirements of these three functional layers, different types of PCs were developed to achieve superior performance. Polyelectrolyte-polyelectrolyte complexes (PECs) were chosen as building blocks for electrochromic active layer, contributing to a fast growth LbL film with porous structure due to the relative large dimensions and charge accumulation of PECs. The resultant electrochromic active films presented larger colouration modulation as well as fast kinetics compared to conventional LbL films. Polymer-alphaCD inclusion complexes via host-guest interaction were designed and adopted as building blocks for LbL SPE layer fabrication. Taking merits of the steric effect of polymer-alphaCD complexes, the resultant LbL films possessed lower glass transition temperature and higher ionic conductivity compared to LbL films made from uncomplexed polymers. Conductive PCs were selected to form capping layer on conducting Ag nanowire network. The LbL overcoated films lowered surface roughness of the metallic network without sacrificing the conductivity of the whole layer. The existence of LbL coating was demonstrated to protect Ag nanowire network from oxidation corrosion during the redox reaction. In conclusion, adopting PCs as building blocks was demonstrated to be a feasible and effective method to fabricate LbL films for electrochemical device applications, surmounting the drawbacks of conventional LbL technique and delivering superior performance. Doctor of Philosophy (MSE)

Corneal disease is a major leading cause of blindness worldwide. The majority of the reversible causes could benefit from corneal transplantation. However, transplantation-grade donor corneas are often difficult to procure. In addition, organ transplantation is frequently plagued by clinical, ethical and logistical issues. Prognosis of corneal transplantation is also poor in most advanced corneal diseases. In these cases, implantation of an artificial cornea becomes the next viable option. Core-skirt keratoprosthesis (KPro) is a type of artificial cornea and the most widely used ocular prosthetic device. This KPro construct consists of a transparent optical core which is usually made of a polymer, such as poly(methyl methacrylate) (PMMA), surrounded by a skirt material which is usually a biological material that promotes biointegration, such as the donor corneal tissue. Various studies in the literature have highlighted a common problem associated with core-skirt KPros, which is the poor interfacial bonding and biointegration between the two materials (PMMA and biological material). Surface modification is an attractive technique that can be employed to improve the interactions and bonding strength between the two dissimilar materials without significantly altering the design of the KPro. The main objective of this thesis, therefore, was to apply surface modification on PMMA to enhance its interactions and adhesion to the skirt material. Collagen type I hydrogel was selected as the substitute skirt material to eliminate the use of human donor corneas. A novel dip coating method, which was simple and inexpensive to execute for immobilizing HAp nanoparticles on PMMA was introduced in this thesis to address problems associated with conventional HAp coating method. One time dip in 20% (w/v) HAp nanoparticles in 5% (w/v) PMMA/chloroform for 60 seconds, followed by surface plasma irradiation (referred to as HAp-coated PMMA) resulted in a homogenous coating on PMMA sheets, offering high hydrophilicity, resistance to delamination and preservation of Ca/P ratio of pure HAp. These advantages resulted in 2.5 times improvement in adhesion strength (over 28 days in artificial tear fluid) between collagen hydrogel and HAp-coated PMMA than between hydrogel and d-CaP (apatite coating via simulated body fluid incubation), and an order of magnitude improvement compared to untreated PMMA. Corneal stromal fibroblasts were able to form good adhesion and proliferate on the HAp-coated PMMA. The dip coating technique could be extended to immobilize HAp nanoparticles on PMMA cylinders, bringing the studies closer to the clinical application of the coating for KPro optical cylinders. However, minor modification in the dip coating method (12 times 5-second-dips instead of 1 time 60-second-dip) was necessary to immobilize the nanoparticles on PMMA cylinders of 3 mm in diameter due to the curved surface and smaller surface area compared to PMMA sheets. An advantage of substituting donor cornea with collagen hydrogel as the skirt material was also presented in this thesis, whereby an antibiotic (vancomycin) was loaded in the hydrogel (referred to as VH) and was shown to be bactericidal effective in vitro for up to 7 days. When implanted in the rabbit corneas, which were infected with Staphylococcus aureus, the VH-implanted corneas were clear and non-edematous and showed a reduction of log 2.5 in bacteria compared to the blank hydrogel-implanted corneas. Doctor of Philosophy (MSE)

During service, anticorrosion coatings in seawater are susceptible to wear and scratched damages resulting in the re-exposure of steel substrates. Smart coatings are prepared by formulating microcapsules in polymeric coatings, where healing agents can be released to seal scratches or as lubricant to mitigate wear damages after the microcapsules are broken. Among these microcapsules, isocyanates-loaded microcapsules attracted increasing attentions due to easy operation. However, short service life in moist environments, poor stability in organic solvents and weak mechanical strength of microcapsules restrict their further applications. Therefore, further development of robust microcapsules is of great importance. 4,4’-methylenebis (cyclohexyl isocyanate) (HMDI) was encapsulated successfully in water resistant microcapsules by combining interfacial polymerization and modified in situ polymerization in an oil-in-water emulsion system. The water resistant microcapsules were characterized through various analytical methods, and the influence of agitation rate on diameters, shell thickness and core fraction of microcapsules were investigated systematically. The relative residue of core fraction was higher than 80% after 20 days in moist environments including ambient water, open air, warm water, acidic and alkaline aqueous solutions. However, water resistant microcapsules resist poorly to organic solvents. In addition, HMDI was also encapsulated successfully in double resistant microcapsules possessing superior stability in both aqueous solutions and organic solvents. Besides outstanding stability in aqueous solutions, double resistant microcapsules also possess outstanding stability in organic solvents. The relative residue of core fractions was beyond 90% after 30 days in ambient hexane, xylene and ethyl acetate, respectively. The influences of parameters including microcapsule size, concentration and immersion duration on the stability of double resistant microcapsules in organic solvents were investigated systematically. However, double resistant microcapsules possess poor stability in acetone and weak mechanical strength. In order to improve shell strength and acetone resistance of resultant microcapsules, another layer of metal shell was covered on double resistant microcapsules as trifunctional microcapsules. The trifunctional microcapsules were characterized systematically, presenting superior stability in acetone, and higher mechanical strength than that of double resistant microcapsules. In order to investigate the influence of metal shell on microcapsules, systematic comparison was conducted between double resistant microcapsules and trifunctional microcapsules. The trifunctional microcapsules possess shell strength several times higher than that of double resistant microcapsules. Even in polymeric matrix, the multifunctional composite coatings containing trifunctional microcapsules also possess higher compressive strength and compressive modulus than those containing double resistant microcapsules. Self-healing samples and self-lubricating samples were fabricated successfully by dispersing two types of microcapsules in epoxy resin. Both double resistant microcapsules and trifunctional microcapsules showed superior self-healing anticorrosion performance towards steel panels. However, trifunctional microcapsules possess marginal self-lubricating performances in epoxy resin due to the existence of metals shell, comparing with outstanding self-lubricating performance of double resistant microcapsules. Robust microcapsules were fabricated successfully through various encapsulation techniques. However, further investigations are still needed to improve the shortages of current microcapsules. Doctor of Philosophy (MAE)

Microfluidics is a branch of fluid dynamics which deals with investigations of fluid behavior at the micron scale, characterized by low Reynolds number, which results in laminar flow. The field of microfluidics is of high significance due to its broad spectrum of applications, including as a Lab-on-a-Chip (LoC) platform. For example, droplet microfluidics offers a large increase in the multiplex capability desired for most LoC; applications the droplets act as individual pl to nl volume range containers. Integration of magnetofluidics with microfluidics can provide control of droplets in the flow to develop a practical LoC device. The resulting domain of droplet micro-magnetofluidics (MMF) offers the excellent capability for the wireless and remote control of droplets, leading to versatile droplet micro-magnetofluidics (DMMF) applications. Magnetic fluids in the ferrohydrodynamic regime (termed as ferrofluids), exhibit liquid magnet like behavior. Ferrofluids exhibit a significant response to both uniform and hybrid magnetic fields. Hence, the behavior of ferrofluid droplets (FD) and magnetic Janus droplets (MJD) exposed to uniform and hybrid magnetic fields have been investigated in a microfluidic environment. A MMF setup by integrating microfluidics and magnetofluidics have been developed. Various designs of microfluidic chips were employed for LoC droplet generation at different length scales for DMMF investigations. A droplet MMF numerical model was developed to elucidate the dynamic behavior of ferrofluid droplets in uniform as well as hybrid magnetic fields. This model simulated droplet generation, droplet deformation, and merging of droplets in uniform magnetic fields. Experimental and numerical investigations for continuous flow MMF and investigations of MMF spreading of a ferrofluid core stream clad by diamagnetic streams have been performed. A water-based ferrofluid was utilized as the magnetic phase and aqueous glycerol as the diamagnetic phase. The effect of applied uniform magnetic field was investigated for a range of flow rates, flow rate ratio, viscosity, magnetic particle concentration and ferrofluid susceptibility. The role of diffusion of particles, drift velocity of magnetic particles, and convective diffusion was studied. We found that difference in magnetic susceptibility between the core and diamagnetic streams led to a distortion of the magnetic field, resulting in a magnetic force acting on the ferrofluid. Spreading was observed mainly near the channel walls due to the lower flow velocity near the walls. Convective diffusion is the main factor for MMF spreading, which was favored at low flow rates, low flow rate ratio and high magnetic field. After investigating continuous flow behavior, the studies were extended to DMMF and demonstrated LoC droplet merging and fabrication of magnetic Janus particles. The combination of FD and uniform magnetic field offers wireless, programmable remote control, which is useful for LoC applications. LoC experiments and numerical studies were performed to investigate FD behavior in uniform magnetic fields. The dynamic behavior of FD was evaluated by investigating droplet size, aspect ratio, droplet velocity and droplet spacing. The size, shape, velocity and inter-droplet spacing of these droplets could be controlled by tuning magnetic field strength, ferrofluid susceptibility, viscosity and flow rates. The droplet micro-magnetofluidic numerical model found to be in good agreement with experimental results. Controlled LoC merging of droplets is a challenge. This challenge was addressed by numerical modeling and experimental studies of uniform magnetic field induced merging of ferrofluid based droplets; control of droplet velocity and merging was achieved. Merging and mixing of composite droplets, such as color dye+ magnetite, was demonstrated. Our numerical results were found to be in good agreement with experiments. These studies are useful for wireless and programmable droplet merging as well as mixing relevant to biosensing, bioassays, microfluidic-based synthesis, reaction kinetics, and magnetochemistry. These experimental and simulation findings were utilized to develop a DMMF platform for magnetic Janus particle (MJP) fabrication. This system is capable of magnetically controlled, selective LoC polymerization, resulting in the synthesis of MJP. Since the method is wash-less and does not use oils or surfactants, MJP are “ready to use”. The effect of flow rate and magnetic field on the particle size, magnetization, and polymeric properties of the MJP was investigated. Particle synthesis at high flow rates of 4 ml/h was demonstrated. The properties of synthesized MJP were assessed and the application of the particles for protein detection was demonstrated. The development of MMF and droplet MMF techniques relevant to LoC applications have been demonstrated. These studies are useful for the development of next-generation technology with multiplexing, wireless, programmable, and remote control capabilities. The DMMF investigations demonstrate control of magnetic droplets on a LoC platform using uniform magnetic fields, which overcomes the limitations of nonuniform magnetic field based systems. DMMF was utilized to develop magnetically controlled LoC Janus particle synthesis. Such particles are useful for bioassays, tagging of particles or cells and protein detection. Doctor of Philosophy (MSE)

Complex hollow structures of metal sulfides could be promising materials for energy storage devices such as supercapacitors and lithium-ion batteries. However, it is still a great challenge to fabricate well-defined metal sulfides hollow structures with multi-shells, hierarchical architectures, and non-spherical shape. In this work, a template-engaged strategy is developed to synthesize hierarchical NiS box-in-box hollow structures with double-shells. The NiS box-in-box hollow structures constructed by ultrathin nanosheets are evaluated as electrode materials for supercapacitors. As expected, the NiS box-in-box hollow structures exhibit excellent rate performance and impressive cycling stability due to their unique nano-architecture. More importantly, the synthetic method can be easily extended to synthesize other transition metal sulfides box-in-box hollow structures. For example, we have also successfully synthesized similar CuS and MnS box-in-box hollow structures. The present work makes a significant contribution to the design and synthesis of transition metal sulfides hollow structures with non-spherical shape and complex architecture, as well as their potential applications in electrochemical energy storage.

Although Li-oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end-opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT-encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li2O2 nanocrystals on CNT surfaces instead of localized distribution of Li2O2 aggregation, thus providing efficient charge transfer for the decomposition of Li2O2.

In a ferroelectric random access memory (FeRAM), the two logic states, “1” and “0”, are represented by the spontaneous polarization directions in the ferroelectric material, which can be altered by an external electric field. FeRAM has many advantages, such as high speed and excellent data retention, over magnetic hard disk drive and flash memory. However, one drawback of the conventional FeRAM is that the reading process may erase the stored information and a re-write step is needed. This is because the read-out in a conventional FeRAM is achieved by sending a voltage pulse larger than the coercive field to the memory cell and detecting the current. For the past decade, researchers have been exploring various concepts for non-destructive read-out of FeRAM. In 2013, we have demonstrated the feasibility to use the ferroelectric photovoltaic response as the read-out signal of FeRAM, as both the signs of open-circuit voltage (Voc) and short-circuit photocurrent (Isc) depend on the polarization direction in the ferroelectric layer. Such a photovoltaic effect-based FeRAM features a non-destructive reading process, giving rise to low energy consumption and increased lifetime of the memory. In this study, we further investigate the fundamentals of fatigue in ferroelectric materials and clarify the origin of switchable photovoltaic effect, aiming to improve the performance of the proposed novel FeRAM. Polarization fatigue, i.e. the reduction of switchable polarization after repetitive electrical cycling, poses a serious problem for the performance and the lifetime of ferroelectric-based devices. The first part of this work is to study the mechanism of the polarization fatigue in a typical ferroelectric material, BiFeO3. By using planar BiFeO3-based capacitors, we have carried out in-situ study on the domain evolution and space charge redistribution in the ferroelectric layer during fatigue measurements. It is found out that charge injection/accumulation at the electrode/film interface is responsible for domain pinning and the macroscopic polarization fatigue in BiFeO3 films. Furthermore, the Schottky barrier at the electrode/BiFeO3 interface is likely to play a crucial role in the charge injection/accumulation process by deep-trapping the injected electrons under the localized high electric field. Lowering the barrier height, with either oxides or low work function metals as the electrodes, effectively suppresses or even eliminates the electron accumulation due to the high detrapping rate, and thus improves the fatigue performances of the device. The systematic study on vertical BiFeO3-based capacitors using different top electrodes further supports the Schottky barrier-controlled charge accumulation model for polarization fatigue. With the mechanism of polarization fatigue clarified, we move on to improving the ferroelectric photovoltaic response in BFO systems. Through controlling the interface conditions, we have studied the origin of the switchable ferroelectric photovoltaic effects in BFO heterostructures and both effects from bulk depolarization field and interface have been explored. In vertical Pt/BiFeO3/La0.7Sr0.3MnO3 capacitors, the polarization modulated built-in field at the Pt/BiFeO3 interface plays the dominating role in separating the photo-excited carries and producing photovoltages, whereas the contribution from bulk depolarization field proves to be relatively small. After clarifying the origin, we have also investigated the photovoltaic property of domain engineered epitaxial BiFeO3 films. Consistent with the photovoltaic effects being driven by the built-in field at the Pt/BiFeO3 interface, the domain structures in BiFeO3 films do not affect the Voc values in the vertical heterostructures. However, the improvements of Isc can be achieved by increasing the domain wall density, which is attributed to the larger photoconductivity of the domain walls. In addition, preliminary results on the enhancements of the photovoltaic responses by chemical substitution have also been obtained, though the mechanism is still unclear. DOCTOR OF PHILOSOPHY (MSE)

Alternative energy-efficient desalination technology is an exciting research field. Forward osmosis (FO) as a novel desalination technology has attracted much attention in that it is driven by chemical potential with low fouling potential and high fouling reversibility. In FO, the draw agent interacts with water forming a draw solution to reduce the water chemical potential, and thus water would automatically permeate through a selective membrane from brackish water to dilute the draw solution. The draw agent should also separate from water in the regeneration process to leave fresh water behind as the final product. In this thesis, I synthesized a series of responsive materials as draw agents, including hydrogels, polymers and (poly) ionic liquids, and studied the importance of balanced FO and regeneration performances. The merit of responsive draw agent is that the regeneration process can be realized with external stimulus, e.g., temperature, instead of solely relying on traditional reverse osmosis that consumes highgrade electrical energy and faces membrane fouling. The purpose of this thesis is to reveal the potential of responsive draw agents to enable FO to desalinate seawater or even brine with energy cost competent to other technologies. Thermally responsive hydrogels, including semi-interpenetrating network hydrogels and polyionic liquid hydrogels, are studied as responsive draw agents in FO desalination. All these hydrogels are designed with both hydrophilicity and hydrophobicity in structures to assume thermosensitivity. The hydrogels can automatically swell and absorb fresh water from brackish water through an FO membrane at temperatures below their lower critical solution temperature (LCST); at temperatures above the LCST, the hydrogels deswell to release the readily available fresh water. This is quite interesting since I realize a desalination process driven by temperature modulation between room temperature and, for example, 40℃. The thermal energy requirement is lower than that of thermal distillation methods since the enthalpy and temperature of responsive draw agent phase separation with water are much lower than those of water vaporization. Although hydrogels are unfortunately found incapable to desalinate seawater, the aim of this thesis is quite clear, which is to utilize low grade thermal energy from industrial waste heat or solar source to completely or at least largely replace the high grade electrical energy consumption in seawater or even brine desalination. A dual responsive polymer is synthesized and studied in order to fulfill this target. The dual responsive polymer can be reversibly switched by introducing and removal of CO2 between a polyelectrolyte state that can generate water flux from seawater, and a thermally responsive state that facilitates regeneration at temperatures above the LCST. Again, a temperature of 50℃ is sufficient to precipitate the majority of polymers, and a nanofiltration process is then employed to polish the water quality with a low hydraulic pressure of only 1.5 bar. Our aim is partially fulfilled since the majority amount of energy input is low grade thermal energy, if regeneration of CO2 is not considered. A group of thermally responsive ionic liquids are found to be able to generate a water flux from 1.6 M NaCl solution, which is almost 3 times the salinity of seawater. Meanwhile, their diluted draw solutions can undergo a liquid-liquid phase separation at 50℃ to generate a sedimentation phase that can be directly reused as draw solution without regeneration, and a supernatant phase with an osmotic pressure of less than 6 bar. The theoretical energy calculation reveals that FO requires only about one fifth of RO‘s electrical energy consumption for seawater desalination (theoretically 1.1 kWh/m3), and the energy cost of FO is much lower than (less than half of) RO owing to the utilization of much cheaper low grade thermal energy. Finally, a proprietary draw agent is studied to be able to concentrate feed solution into a 17 wt% NaCl solution that facilitates ensuing crystallization process for zero-liquid discharge. Combining with a typical seawater RO plant, the energy consumption for brine treatment would be only the electrical energy equal to that of seawater RO, and additional low grade thermal energy associated with temperature modulation between 20 and 50℃. Therefore, FO enabled by responsive draw agents would be a competent desalination technology to challenge RO and thermal distillation methods in seawater and brine treatment. DOCTOR OF PHILOSOPHY (MSE)

Zinc oxide (ZnO) is a wide bandgap semiconducting oxide with many potential applications in optoelectronic devices such as light emitting diodes (LEDs) and field effect transistors (FETs). Controlling the conductivity of ZnO is a foremost concern in the optoelectronic industry. Understanding the nature of ZnO native defects is vital for the application of ZnO in the semiconductor industry. Many electronic properties depend significantly on the intrinsic defect concentration as it affects the doping efficiency and the growth of the material. These properties also depend on the type and amount of impurities and degree of crystallinity. There is a need to understand the function of native point defects and the incorporation of impurities, with the intention for a better control of the conductivity of ZnO. However, one major issue in determining whether it is zinc or oxygen deficiency that provides ZnO its unique properties remains. In this thesis, ZnO films and powders were synthesized via a low temperature aqueous solution chemical bath deposition route and its short to medium range structure order characterized. In addition, Ga-doped ZnO films and powders were also synthesized as Ga has been found to be an excellent donor, increasing the conductivity of ZnO films. All samples were post-growth thermally annealed in air in order to improve the electrical and optical properties, and correlate the annealing temperature with the defect structure. The epitaxial nature of the ZnO films (undoped and Ga-doped) were determined via high resolution X-ray diffraction (HRXRD). The morphology of the films was studied via field emission gun scanning electron microscopy (FEGSEM) showed that the films were smooth and continuous on the plane-view. Cross-sectional images showed that the films were about 2 µm thick after a growth time of 4 hours at 90°C. Visible pores were also observed in the films after post-growth thermal annealing at temperatures of above 200°C. Electrical properties were obtained via Hall measurements showed characteristic n-type conductivity and a carrier concentration of the order of 1020 cm-3 after post-growth thermal annealing at 400°C in air for 1 h for the Ga-doped ZnO films. For the ZnO powders, phase identification was determined by conventional powder XRD methods. The morphologies were obtained via FEGSEM and showed different nanorods morphologies for the different precursors used for the syntheses. Internal pores were observed in the ZnO nanorods upon thermal annealing at >300 °C and were examined using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Three-dimensional electron tomography reconstruction shows that pores exist within the nanorods. These pores coalesce and also increase in size as the ZnO nanorods were annealed at higher temperatures or for extended periods of time, as observed by an in situ TEM study. As such, this pore formation phenomenon will significantly affect the utilisation of solution-synthesized ZnO for optoelectronic devices, but new application fronts such as gas sensors and photo/electro catalysis will benefit due to its high light absorption properties and high surface areas. Further defect characterization was performed for the all the ZnO samples, largely using synchrotron-based characterization techniques, namely X-ray absorption spectroscopy (XAS) and X-ray pair distribution function (PDF) techniques. XAS is an ideal, atom specific characterization technique that is able to probe defect structure in many materials, including ZnO. Comparative studies of commercially available ZnO and aqueous solution grown (≤ 90°C) ZnO powders using XAS and PDF has allowed for the study of short to medium range structure order. The ZnO films were studied via ex situ XAS and the ZnO powder samples were studied via ex situ and in situ XAS and in situ PDF experiments. The local structure order of the ZnO films and powders were determined. From XAS of the Ga-doped ZnO samples, it was evidently shown that Ga3+ resides tetrahedrally in the Zn2+ site within the ZnO lattice. The understanding of the role of defects and the short to medium range order and structure within the ZnO system has provided useful insight for further exploitation of the material and is invaluable for the exploitation of ZnO for further development of optoelectronic device applications. DOCTOR OF PHILOSOPHY (MSE)

Ferroelectric ceramics are important electronic materials that have a wide range of industrial and commercial applications, such as high-dielectric constant capacitors, piezoelectric sonar or ultrasonic transducers, pyroelectric security sensors, medical diagnostic transducers, electro-optical light valves, and ultrasonic motors, to name a few. The performances of ferroelectrics are closely related to the ways they are processed. The conventional solid state reaction method requires high calcination and sintering temperatures, resulting in the loss of lead, bismuth or lithium components due to their high volatilities, thus worsening the microstructural and subsequently the electrical properties of the ferroelectric materials. Various wet chemistry based routes have been developed to synthesize ultra-fine and even nano-sized ferroelectric powders. However, most of the chemistry based routes still involve calcinations, although at relatively lower temperatures. High energy mechanochemical milling process has been shown that some ferroelectric materials can be synthesized directly from their oxide precursors in the form of nano-sized powders, without the need for the calcination at intermediate temperatures, thus making the process very simple and cost-effective. A large number of ferroelectric materials, including lead-containing ferroelectrics, antiferroelectrics and relaxors, and bismuth-containing Aurivillius families, have been synthesized by the high-energy milling process. Some ferroelectrics, such as barium titanate (BaTiO 3 or BT), lead iron tungstate [Pb(Fe 2/3 W 1/3 )O 3 or PFW], and several bismuth-containing materials, that cannot be directly produced from their oxide mixtures, have been formed at relatively low temperature after their precursors are activated by an high-energy milling. Ferroelectric ceramics derived from the activated precursors demonstrated better microstructure and electrical properties than those without mechanochemical treatment. This review presents an overview of the recent progress in the synthesis of ferroelectric ceramic powders using various high-energy milling techniques. The progress includes several aspects: (i) direct synthesis of nano-sized powders with better sinterability, (ii) promoted reactive sintering due to the modification of the precursors, (iii) amorphization of the precursors, and (iv) refinement of the precursors with high homogeneity. The underlying mechanisms of mechanochemical synthesis of ferroelectric materials are discussed. Further research emphasizes on issues related to the synthesis of ferroelectric ceramic powders are suggested.

The advent of implantable biomaterials has revolutionized medical treatment, allowing the development of the fields of tissue engineering and medical bionic devices (e.g., cochlea implants to restore hearing, vagus nerve stimulators to control Parkinson's disease, and cardiac pace makers). Similarly, future materials developments are likely to continue to drive development in treatment of disease and disability, or even enhancing human potential. The material requirements for implantable devices are stringent. In all cases they must be nontoxic and provide appropriate mechanical integrity for the application at hand. In the case of scaffolds for tissue regeneration, biodegradability in an appropriate time frame may be required, and for medical bionics electronic conductivity is essential. The emergence of graphene and graphene-family composites has resulted in materials and structures highly relevant to the expansion of the biomaterials inventory available for implantable medical devices. The rich chemistries available are able to ensure properties uncovered in the nanodomain are conveyed into the world of macroscopic devices. Here, the inherent properties of graphene, along with how graphene or structures containing it interface with living cells and the effect of electrical stimulation on nerves and cells, are reviewed.

One-stop center for functional polycyclic aromatic hydrocarbons — a dichlorodiazaperylene intermediate has been synthesized and employed for the synthesis of highly functionalized coronene derivatives., Combining core annulation and peripheral group modification, we have demonstrated a divergent synthesis of a family of highly functionalized coronene derivatives from a readily accessible dichlorodiazaperylene intermediate. Various reactions, such as aromatic nucleophilic substitution, Kumada coupling and Suzuki coupling proceed effectively on α-positions of the pyridine sites, giving rise to alkoxy, thioalkyl, alkyl or aryl substituted polycyclic aromatic hydrocarbons. In addition to peripheral group modulation, the aromatic core structures can be altered by annulation with thiophene or benzene ring systems. Corresponding single crystal X-ray diffraction and optical studies indicate that the heteroatom linkages not only impact the solid state packing, but also significantly influence the optoelectronic properties. Moreover, these azacoronene derivatives display significant acid-induced spectroscopic changes, suggesting their great potential as colorimetric and fluorescence proton sensors.

International audience; We use arrays of liquid crystal defects, linear smectic dislocations, to trap semi-conductor CdSe/CdS dot-in-rods which behave as single photon emitters. We combine measurements of the emission diagram together with measurements of the emitted polarization of the single emitters. We show that the dot-in-rods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. We demonstrate that the electric dipoles associated with the dot-in-rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and being perpendicular to the substrate, most likely due to the dipole/dipole interactions between the dipoles of the liquid crystal molecules and the dot-in-rods ones. Using smectic dislocations, we can consequently orient nanorods along a unique direction for a given substrate, independently of the ligands’ nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the associated dot-in-rods’ dipoles. These results open the way for a fine control of nanoparticle anisotropic optical properties, in particular a fine control of single photon emission polarization.

Morphotropic phase boundary (MPB), a highly sought-after concept in piezoelectric materials, is the key factor for large electromechanical response. Unfortunately, mainstream piezoelectric materials all contain lead, a toxic element that is incompatible to the ever-growing demands for global environmental and ecological conservation. In the new wave of searching for lead-free replacements, BiFeO3 (BFO) rises as a promising candidate due to the existence of both chemical- and strain-driven MPBs. In the chemical-driven MPB, the role of “chemical pressure” remains debated. To gain more insight into this issue, La-doped BFO films were systematically investigated in terms of structural, ferroelectric, dielectric and piezoelectric properties. It is found that under the weak chemical pressure induced by La, BFO still undergoes the ferroelectric – paraelectric phase transition with an intermediate metastable antipolar state that produces double hysteresis behavior. However, there is no enhancement in the piezoelectric measurement close to the MPB region, probably because the increase of the relative permittivity is small compared to those of BFO doped with rare-earth elements with smaller ionic radii. Furthermore, the chemical substitution is introduced into the highly-strained BFO films to combine the chemical- and strain-driven MPBs in this unique system, aiming to create multiple phase boundaries with ultrahigh piezoelectric response. Universal polarization rotation behavior is observed in rare-earth-element doped tetragonal-like BFO, analogous to those found in rhombohedral-like phase. However, a global polar instability is absent at high doping concentration before the tetragonal-like BFO lattice collapses due to epitaxial breakdown. The preliminary results of La-doped tetragonal-like BFO films show some degree of enhancement in the piezoelectric response, which requires further experimental validation. DOCTOR OF PHILOSOPHY (MSE)

We demonstrate here that for a given mixed multi-qubit state if there are at least two observers for whom mutual Einstein-Podolsky-Rosen steering is possible, i.e. each observer is able to steer the other qubits into two different pure states by spontaneous collapses due to von Neumann type measurements on his/her qubit, then nonexistence of local realistic models is fully equivalent to quantum entanglement (this is not so without this condition). This result leads to an enhanced version of Gisin's theorem (originally: all pure entangled states violate local realism). Local realism is violated by all mixed states with the above steering property. The new class of states allows one e.g. to perform three party secret sharing with just pairs of entangled qubits, instead of three qubit entanglements (which are currently available with low fidelity). This significantly increases the feasibility of having high performance versions of such protocols. Finally, we discuss some possible applications., Comment: 9 pages, 1 figure

Vanadium (IV) oxide (VO2) is the most widely researched thermochromic (TC) material. Owing to its fully reversible metal-insulator transition (MIT) at the critical temperature (τc) of 68 ˚C, which is the closest to the room temperature and adjustable through doping, it has the potential application as the energy-saving coating for smart windows. Recent researches revealed that introducing porosity and fabrication of nanoparticles (NPs)/matrix composite foils could produce VO2 coatings at the best TC performance. This research employs lyophilisation (freeze drying) technique to fabricate nanoporous VO2 thin films and agglomeration-free NPs. The best combination of TC properties for the former achieved Tlum ≈ 50% and ΔTsol = 14.7%, while that for the latter achieved average Tlum = 35%, ΔTsol = 6.8%, τc = 64.5 ˚C and Δτc = 4.5 ˚C, with small particle size and narrow distribution (37-53 nm) as well as high crystallinity (LC = 36.76 J/g, close to the commercial VO2 powder). Master of Engineering

Liposome and polymersome are hollow bilayer vesicles nanostructures formed by self-assembly of phospholipids and synthetic amphiphilic block copolymers, respectively. Liposomes have been widely studied and developed for wide range of applications. On the other hand, polymersomes have several features which make them better suited than liposomes for certain technological applications, amongst which are their superior stability and excellent chemical versatility. Nevertheless, the self-assembly as well as the interaction of phospholipids and block copolymers, during or after assembly process, have not been well understood. Mixing phospholipids and block copolymers forming hybrid vesicle has been proposed to tune the membrane properties to combine the robustness and chemical tunability of polymersomes with the softness, fluidity and biocompatibility of liposomes. The self-assembly, phase behaviour, membrane properties, and parameters controlling these hybrid vesicles are not yet fully understood. In chapter 3, nanoscale hybrid phospholipid/block copolymer vesicles of various compositions were prepared by film-hydration-extrusion and the mixing behaviours, stability, and membrane properties of these nanostructures have been explored. It was found that the size, encapsulation efficiency and content-release behaviour of nanoscale polybutadiene-b-poly(ethylene oxide) (PB-PEO)/1-palmitoyl-2-oleoyl-sn-glycero-3-hosphatidylcholine (POPC) hybrid phospholipid/block copolymer vesicles can be tuned by the mixing ratio of the amphiphiles. It was generally believed that in binary mixtures of phospholipids and block copolymers, each forms spherical vesicles when present alone, and form spherical hybrid vesicles in aqueous solution. Detailed characterizations by Cryo-TEM reveal that, surprisingly, mixing POPC and PB-PEO results in spontaneous formation of tubular vesicles. This tendency for tubular vesicle formation is most pronounced when the amphiphile composition reaches equimolar proportion of the lipid and the polymer. The spontaneous stabilization of tubular vesicles, which requires a significant spontaneous bilayer curvature or energy, was proposed to arise from the unusually asymmetric lipid/polymer membrane composition. Membrane active polypeptides are of large interest for development of novel therapeutics including peptide-mediated drug delivery and release systems, transfection agents and antibiotics. Finding routes to tune specificity and activity of membrane active polypeptides is hence of large importance to improve their efficacy and minimize harmful side effects. Chapter 5 describes a de novo designed antimicrobial-like helix-loop-helix polypeptide (JR2KC) that partition into zwitterionic lipid membranes when specifically and covalently anchored to the membrane. Anchoring and subsequent membrane partitioning triggers a structural transition of the polypeptide from random coil to α-helical conformation and induces pore formation. The extent of pore formation can be dynamically tuned by varying the number of anchoring moieties or by introducing a complementary polypeptide (JR2E) that is designed to heterodimerize with JR2KC and fold into four-helix bundles. Dimerization competes with membrane partitioning of the polypeptides and reduces the pore forming capacity of JR2KC. This system thus enables a precise and very specific route for tuning the permeability of lipid membranes and demonstrates a novel strategy for development of recognition based membrane active polypeptides. In Chapter 6, a tetramethylrhodamine-labeled peptides binder was assembled on graphene oxide in solution to develop as a fluorescence turn-on sensor for Lipopolysaccharide (LPS)/endotoxin detection. The fluorescence of the dye-labeled peptide is quenched upon interaction with GO. Specific binding to LPS triggers release of the peptide-LPS complex from GO, resulting in fluorescence recovery. This fluorescent turn-on sensor offers a limit of detection of 130 pM, which is the lowest ever achieved among all synthetic LPS sensors to-date. Importantly, this sensor is applicable for detection of LPS in commonly used clinical injectable fluids, and it enables selective detection of LPS from different bacterial strains as well as LPS on the membrane of living E. coli. Finally, the applications of self-assembled membranes, liposomes, polymersomes, and polypeptides for biosensing will be also demonstrated in the latter part of the thesis. Doctor of Philosophy (MSE)

Here, a new, fast, and versatile method for the incorporation of colloidal quantum dots (QDs) into ionic matrices enabled by liquid-liquid diffusion is demonstrated. QDs bear a huge potential for numerous applications thanks to their unique chemical and physical properties. However, stability and processability are essential for their successful use in these applications. Incorporating QDs into a tight and chemically robust ionic matrix is one possible approach to increase both their stability and processability. With the proposed liquid-liquid diffusion-assisted crystallization (LLDC), substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process allows to incorporate even the less stable colloids including initially oil-based ligand-exchanged QDs into salt matrices. Furthermore, in a modified two-step approach, the seed-mediated LLDC provides the ability to incorporate oil-based QDs directly into ionic matrices without a prior phase transfer. Finally, making use of their processability, a proof-of-concept white light emitting diode with LLDC-based mixed QD-salt films as an excellent color-conversion layer is demonstrated. These findings suggest that the LLDC offers a robust, adaptable, and rapid technique for obtaining high quality QD-salts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The synthesis and unique tunable optical properties of core/crown nanoplatelets having an inverted Type-I heterostructure are presented. Here, colloidal 2D CdS/CdSe heteronanoplatelets are grown with thickness of four monolayers using seed-mediated method. In this work, it is shown that the emission peak of the resulting CdS/CdSe heteronanoplatelets can be continuously spectrally tuned between the peak emission wavelengths of the core only CdS nanoplatelets (421 nm) and CdSe nanoplatelets (515 nm) having the same vertical thickness. In these inverted Type-I nanoplatelets, the unique continuous tunable emission is enabled by adjusting the lateral width of the CdSe crown, having a narrower bandgap, around the core CdS nanoplatelet, having a wider bandgap, as a result of the controlled lateral quantum confinement in the crown region additional to the pure vertical confinement. As a proof-of-concept demonstration, a white light generation is shown by using color conversion with these CdS/CdSe heteronanoplatelets having finely tuned thin crowns, resulting in a color rendering index of 80. The robust control of the electronic structure in such inverted Type-I heteronanoplatelets achieved by tailoring the lateral extent of the crown coating around the core template presents a new enabling pathway for bandgap engineering in solution-processed quantum wells. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Presently, environmetal disruption and economic recession of burning non-renewable fossil fuels have gained enormous awareness of renewable energy storage systems. By contrast with other energy storage devices, lithium-ion batteries (LIBs) are smaller and lighter, as well as capable of providing higher energy density and longer cycle life, making it one of the most promising choices. Currently, LIBs are used to power portable electronics e.g. laptops and mobile phones. With greater demand and widespread use of large applications such as electrified vehicles (EVs), LIBs with enhanced electrochemical performances i.e. high energy and power densities, reduced cost, lower toxicity and safety features are necessary. In this thesis, a collection of single and mixed metal oxalates by two synthesis routes namely facile chemical precipitation and solvothermal are evaluated as LIBs anodes. Based on our results, the electrochemical performances of chemical precipitated single and mixed metal oxalate are better than synthesis by solvothermal. Moreover, both synthesized metal oxalates yield superior properties compared to other oxalates reported. Highlighting the investigations, Li/FeC2O4 cells delivered an initial discharge capacity > 1288 mAh g-1 at 1C-rate and anhydrous FeC2O4 cocoons exhibited stable cycling (438 mAh g-1; greater than graphite) even at high C-rate (11C). In addition, the synthesis mechanisms i.e. factors influencing materials’ properties/morphologies are examined. Systematic studies on mixed metal oxalates i.e. Fe- and Mn- doped cobalt oxalates are also carried out, indicating improved electrochemical performances. It can be concluded that positive synergistic effects existed in these mixed metal oxalates, whereby the presence of Co is crucial for high capacity while Fe is needed in the structure for cyclability and stability of the cell. Finally, the effects of morphologies, compositional differences and synthesis methodologies on Li storage mechanisms for these metal oxalates are elucidated in detail. In general, properties of the metal oxalate anodes were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermogravimetric analyses (TGA), among other characterization methods. Furthermore, electrochemical properties of these metal oxalates were studied using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Additionally, the practical applications of metal oxalate anodes employing ILs (i.e. in mixed electrolytes) and in elevated temperature was presented. Lastly, the fundamental study of complex Li storage mechanism (i.e. involves conversion reactions together with double layer charge storage and reversible reactions with electrolyte) in these metal oxalates by employing CV sweep test and ex-situ techniques such as XPS, AFM, FE-SEM, XRD and FT-IR are investigated in this thesis. Along with, variation of salts and solvents (i.e. electrolytes) to offer new insights of interfacial phenomenon on metal oxalate electrodes are explored as well. Doctor of Philosophy (MSE)

The selective oxidation of sulfides into sulfoxides receives much attention due to industrial and biological applications. However, the realization of this reaction with molecular oxygen at room temperature, which is of importance towards green and sustainable chemistry, remains challenging. Herein, we develop a strategy to achieve the aerobic oxidation of sulfides into sulfoxides by exploring the synergy between a tertiary amine and titanium dioxide via visible-light photoredox catalysis. Specifically, titanium dioxide can interact with triethylamine (TEA) to form a visible-light harvesting surface complex, preluding the ensuing selective redox reaction. Moreover, TEA, whose stability was demonstrated by a turnover number of 32, plays a critical role as a redox mediator by shuttling electrons during the oxidation of sulfide. This work suggests that the addition of a redox mediator is highly functional in establishing visible-light-induced reactions via heterogeneous photoredox catalysis. Published version

Systems with strong interactions such as complex oxides show many emergent properties that are, still to this day, not fully understood. Of particular interest is the metal-insulator transition in complex oxides which arises from the competition between the tendencies of carrier localization and delocalization. To understand and ultimately control metal-insulator transitions in complex oxides, we need to explore the rules governing the interactions in charge, spin and lattice in these systems. To this end, the use of novel techniques in material fabrication, spectroscopy and lithography are invaluable for investigating the metal-insulator transition (MIT). Studies of electronic phases with advanced characterization techniques have revealed new insights into the correlated properties of these oxides. The focus of this dissertation is on understanding and tuning electronic phase transitions in complex oxide thin films and can be broadly divided into two parts. The first part of this thesis highlights the use of electrostatic modulation using electrolyte gating as a method to tune the electronic functionalities in a strongly phase-separated manganite Pr0.65(Ca0.75Sr0.25)0.35MnO3 and potentially control the emergence of colossal magneto-resistance. The device configuration of this powerful technique, known as the electric double layer technique, provides clean, quasi-continuous and high-density charge accumulation of carrier modulation in the manganite channel. A diverse behavior of transport modulation was observed and the modulation was remarkably enhanced by the application of a magnetic field. The experiments are also supported by the small polaron model, effective medium model and finite element simulation of inhomogeneous local electric field. The first part of the dissertation also discusses high quality thin film synthesis of manganites using Pulse Laser Deposition. Pr0.65(Ca0.75Sr0.25)0.35MnO3 manganite thin films under biaxial strain displayed presence of magnetic glassy state at low temperatures is accompanied by reemergence of insulating behavior. We discovered that the transport modulation in the channel increased multiple folds in the magnetic glassy state. The second part of this dissertation probes optical responses in the thin films of vanadium dioxide polymorphs using the techniques of terahertz and time-resolved femtosecond spectroscopy. Vanadium dioxide (VO2), just like manganites, is a prototypical MIT system. Although, VO2 exhibits a number of polymorphic forms, a major portion of research on this material has been devoted towards VO2(M1) polymorph because of its speedy and abrupt MIT (5−10 K) just above room temperature. VO2(B) polymorph, on the other hand, undergoes a broad MIT as wide as 150 K and remained mostly unexplored due to challenges in thin film fabrication. We studied for the first time optical conductivities of VO2(B) and construct the electronic phase diagram by indicating the critical temperatures deciding the width and the onset of the MIT in VO2(B). We also demonstrate ultrafast optical switching to a metallic state in this system using optical pump-probe technique. Compared to VO2(M1) the threshold value of laser fluence is about four times lower, and showed strong temperature dependence. The phase diagram of photoinduced transition in VO2(B), remarkably consists of two regions of photoinduced metallicity— one induced by weak pump excitation, and another by strong pump excitation. DOCTOR OF PHILOSOPHY (SPMS)

Stem cell–based therapies hold great promise in providing desirable solutions for diseases that cannot be effectively cured by conventional therapies. To maximize the therapeutic potentials, advanced cell tracking probes are essential to understand the fate of transplanted stem cells without impairing their properties. Herein, conjugated polymer (CP) nanodots are introduced as noninvasive fluorescent trackers with high brightness and low cytotoxicity for tracking of mesenchymal stem cells (MSCs) to reveal their in vivo behaviors. As compared to the most widely used commercial quantum dot tracker, CP nanodots show significantly better long-term tracking ability without compromising the features of MSCs in terms of proliferation, migration, differentiation, and secretome. Fluorescence imaging of tissue sections from full-thickness skin wound–bearing mice transplanted with CP nanodot-labeled MSCs suggests that paracrine signaling of the MSCs residing in the regenerated dermis is the predominant contribution to promote skin regeneration, accompanied with a small fraction of endothelial differentiation. The promising results indicate that CP nanodots could be used as next generation of fluorescent trackers to reveal the currently ambiguous mechanisms in stem cell therapies through a facile and effective approach. ASTAR (Agency for Sci., Tech. and Research, S’pore)

An all-solution processed and all-colloidal laser is demonstrated using tailored CdSe/CdS core/shell quantum dots, which exhibit highly stable and low-threshold optical gain owing to substantially suppressed non-radiative Auger recombination. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Besides the shape memory effect (SME), in which the permanent shape can be recovered at the presence of the right stimulus, the temperature memory effect (TME) is another feature of shape memory materials. The TME refers to a phenomenon that a particular temperature can be memorized in a certain manner. A systematical investigation of the mechanism from energy point of view for the TME in NiTi shape memory alloys (SMAs) is presented based on the results of a series of differential scanning calorimeter (DSC) tests. The traditional approach for the TME is expanded, and a modified one is identified, which can be utilized to monitor over-heating temperature with high accuracy. The triple-shape memory effect (triple-SME), which is easily achievable in shape memory polymers (SMPs) but not in SMAs, is achieved in a few types of NiTi SMAs. Two approaches, namely small strain program and larger strain program are proposed. The conditions on both material and programming parameters, as well as the mechanisms for the triple-SME, are identified and the influence of programming parameters is investigated. Both heating-induced and water-induced SMEs in human nail and silkworm silk, in which keratin is their main component, are systematically investigated. The influence of water content is studied. The triple-SME utilizing multiple-stimuli is realized in nail. The fundamentals behind the difference in heating and water based SMEs are studied. MECHANICAL ENGINEERING

In this work, a facile method to deposit fast growing electrochromic multilayer films with enhanced electrochemical properties using layer-by-layer (LbL) self-assembly of complex polyelectrolyte is demonstrated. Two linear polymers, poly(acrylic acid) (PAA) and polyethylenimine (PEI), are used to formulate stable complexes under specific pH to prepare polyaniline (PANI)/PAA-PEI multilayer films via LbL deposition. By introducing polymeric complexes as building blocks, [PANI/PAA-PEI]n films grow much faster compared with [PANI/PAA]n films, which are deposited under the same condition. Unlike the compact [PANI/PAA]n films, [PANI/PAA-PEI]n films exhibit porous structure that is beneficial to the electrochemical process and leads to improved electrochromic properties. An enhanced optical modulation of 30% is achieved with [PANI/PAA-PEI]30 films at 630 nm compared with the lower optical modulation of 11% measured from [PANI/PAA]30 films. The switching time of [PANI/PAA-PEI]30 films is only half of that of [PANI/PAA]30 films, which indicates a faster redox process. Utilizing polyelectrolyte complexes as building blocks is a promising approach to prepare fast growing LbL films for high performance electrochemical device applications.

This thesis presents ordered hybrid nanoneedle arrays for gas sensing application. The ion milling process on the metal/silicon material system is investigated in depth, in order to fabricate iron/silicon and platinum nanocrystallites/silicon hybrid nanoneedle array. The field ionization gas sensors using those unique highly ordered nanoarrays are prototyped and studied, which achieve the high gas sensitivity under an ultralow operation voltage. A hybrid nanostructure is a material system consisting of two or more components, which brings about the significant improvement of the property of the individuals. More recently, the capability of hybrid nanostructures has drawn the growing attention worldwide. However, the control during their assembly is rather challenging, especially for the one-dimensional metal/semiconductor hybrid nanomaterials. In the present thesis, a novel ordered metal/silicon hybrid nanoneedle array is fabricated using an ion beam that patterns the metal/silicon substrate producing a pillar array followed by the self-organization of hybrid nanoneedles. Each nanoneedle consists of a nanoneedle with a nanodot sitting on its top. The nanodot is an alloy of Ga and initially deposited metal. However, such ordered hybrid nanoneedles are not formed on the pure silicon substrate. Nor are the hybrid nanoneedles produced on the silicon surface coated with a thin metal that has a very high sputtering rate, such as Au and Ag. A mechanism of nanoneedle formation is proposed considering the alloying process during incident gallium ion irradiation to the silicon substrate coated with a thin layer of a sufficient low sputter rate. Iron, is a metal which has a pretty low sputtering rate and allows the formation of a perfectly ordered hybrid nanoneedle array on the surface of Fe/Si substrate. This unique nanostructure has been demonstrated to be highly sensitive to various types of gases, including air, nitrogen, hydrogen and carbon monoxide. And it also has ability to differentiate the same gas with various concentrations. Moreover, the sensitivity can be significantly enhanced when Fe metal is replaced by Pt nanocrystallites. In this case, a lateral electric field is applied across the nanoneedle array rather than a vertical electric field that is engaged during the evaluation of the Fe/Si gas sensing device. The breakdown voltage of nitrogen for Pt/Si comes up with only ~7 V in contrast to ~ 30V, which is required to N2 discharge for Fe/Si hybrid nanoneedle array. It is also found that the homogeneous silicon nanoneedles failed to generate any gas sensing signal. Based on the insightful analysis of gas ionization currents, such anomalous high field ionization efficiency has been attributed to the superimposed effects to the one-dimensional nanoneedles. For example, iron/silicon nanoarray provides abundant surface states for efficient gaseous electron tunneling, and polarized platinum nanocrystallites enhance the local electric field sufficient to direct ionization, respectively. Added by these experimental results and theoretic analysis, the previous physical scenarios of field ionization in a gaseous electronics system have been extended at nanoscale. DOCTOR OF PHILOSOPHY (MSE)

Hybrid crystals containing encapsulated functional species exhibit promising novel physical and chemical properties. The realization of many properties critically depends on the selection of suitable functional species for incorporation, the rational control of the crystallinity of the host materials, and the manipulation of the distribution of the encapsulated species; only a few hybrid crystals achieve this. Here, a novel synthetic method enables the encapsulation of functional species within crystalline metal-organic frameworks (MOFs). Various kinds of single-crystalline MOFs with incorporated particles are presented. The encapsulated particles can be distributed in a controllable manner, and the hybrid crystals are applied to the heterogeneous catalysis of the reduction of nitroarenes. These findings suggest a general approach for the construction of MOF materials with potential applications; by combining species and MOFs with suitable functionalities, new properties--not possible by other means--may arise.

In this thesis, the author describes the research work done during the four years Ph.D. study, focusing on the fabrication, motion study and possible applications of small motors, ranging from millimeter scale polymer motors to microscale and nanoscale catalytic motors. The millimeter scale capsule motors were made from polysulfone, and a series of studies were carried out on such motors, including the factors influencing the motion, motion manipulation with magnet, cooperative behaviors, and induced motion of oil droplets. Moreover, running of such motors in water/oil interface and the maze channel was studied. Additionally, the enhanced diffusion of pollutants in the natural environment was also investigated. The studies on the microscale and nanoscale catalytic motors were also carried out. Fabrication and characterizations of the tubular motors were realized, and magnetization was achieved for both nanomotors and micromotors. Upon magnetization, such microtubes can pick up the paramagnetic cargoes for possible delivery. Moreover, the effects of the running medium on the motion of the micromotors were also investigated. DOCTOR OF PHILOSOPHY (SPMS)