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In addition, we have studied the growth conditions and the properties of ZnSSe alloy nano-tetrapods grown by chemical vapor deposition. Different from the ZnSSe nanowires synthesized by MOCVD, the ZnSSe nano-tetrapods are of hexagonal structure. We observed a wavelength-tunable near band gap luminescence in the UV-blue region from this nanostructurally-designed system. / Recently, semiconductor nanostructures have attracted much attention because they are potentially useful as fundamental building blocks in nanodevices. As an important member of group II-VI semiconductors, ZnS and its alloys with ZnSe are particularly important for optical applications in the UV-blue region . Thus, we concentrated on the synthesis of ZnS, ZnSe and ZnSSe nanostructures and studied their optical properties. / Vertically-aligned ZnSe nanowires were also synthesized by MOCVD using Ag and Ga nanoparticles as catalysts. In the photoluminescence spectra from Ag or Ga catalyzed ZnSe nanowires, we observed recombination of excitons bound to substitutional Ag or Ga impurities respectively, which indicates that Ag and Ga have been doped into ZnSe nanowires in our experiments. / We are among the first group to grow vertically well-aligned ZnSSe alloy nanowires of controllable composition. Most of ZnSSe nanowires were found to have a cubic structure. We also found a compositional relationship between the nanowires and precursors, which is useful for predicting the lattice constant and band-gap emission energy of ZnSSe nanowires. / ZnS nanowire arrays were fabricated on the GaAs (100), (110) (311)A and (111)B substrates by metal organic chemical vapor deposition (MOCVD) using Ag, Au and Ga particles as catalysts. Their orientation was adjusted by changing the crystallographic orientation of the substrate. Moreover, Ga was doped into ZnS nanowires, when Ga nanoparticles serve as catalysts. / Liang, Yao = ZnS和ZnSSe納米結構的生長和光學性質 / 梁瑤. / Adviser: Hank Suikong. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Liang, Yao = ZnS he ZnSSe na mi jie gou de sheng chang he guang xue xing zhi / Liang Yao.

by Tsai Yau Moon = 錳氧化物的金屬-絶緣體轉變 : 多層薄膜及異構結 / 蔡友滿. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Tsai Yau Moon = Meng yang hua wu de jin shu-jue yuan ti zhuan bian : duo ceng bo mo ji yi gou jie / Cai Youman. / Abstract / 論文摘要 / Acknowledgements / Table of Contents / List of Figures / List of Tables / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Perovskite-type structure / Chapter 1.2 --- Metal-insulator transition / Chapter 1.3 --- Magnetoresistance / Chapter 1.3.1 --- Giant magnetoresistance (GMR) / Chapter 1.3.2.1 --- Colossal magnetoresistance (CMR) in perovskite manganites / Chapter 1.3.2.2 --- Possible origin of CMR / Chapter 1.4 --- Brief review of p-n junction between perovskite manganites and STON (001) / Chapter 1.5 --- Our project / Chapter 1.6 --- Scope of this thesis work / References / Chapter Chapter 2 --- Preparation and characterization of manganite thin films / Chapter 2.1 --- Thin film deposition / Chapter 2.1.1 --- Facing-target sputtering (FTS) / Chapter 2.1.2 --- Vacuum system / Chapter 2.1.3 --- Deposition procedure / Chapter 2.1.4 --- Deposition conditions / Chapter 2.1.5 --- Oxygen annealing system / Chapter 2.1.6 --- Silver electrode coating system / Chapter 2.2 --- Characterization / Chapter 2.2.1 --- Alpha step profilometer / Chapter 2.2.2 --- X-ray diffraction (XRD) / Chapter 2.2.3 --- Transport property measurement / References / Chapter Chapter 3 --- [LCSMO/PCMO] multilayers / Chapter 3.1 --- [LCSMO (100 A)/PCMO (X A)] multilayers / Chapter 3.1.1 --- Sample preparation / Chapter 3.1.2 --- Results and discussion / Chapter 3.1.2.1 --- Structural analysis / Chapter 3.1.2.2 --- Transport properties / Chapter 3.2 --- [LCSMO (50 A)/PCMO (X A)] multilayers / Chapter 3.2.1 --- Sample preparation / Chapter 3.2.2 --- Results and discussion / Chapter 3.2.2.1 --- Structural analysis / Chapter 3.2.2.2 --- Transport properties / References / Chapter Chapter 4 --- [LSMO/PCMO] multilayers and LSMO/STON p-n junction / Chapter 4.1 --- [LSMO/PCMO] multilayers / Chapter 4.1.1 --- Sample preparation / Chapter 4.1.2 --- Results and discussion / Chapter 4.1.2.1 --- Structural analysis / Chapter 4.1.2.2 --- Magnetization / Chapter 4.2 --- LSMO/STON heterojunction / Chapter 4.2.1 --- Sample preparation / Chapter 4.2.2 --- Results and discussion / Chapter 4.2.2.1 --- Structural analysis / Chapter 4.2.2.2 --- Metal insulator transition of LSMO revealed by four point I-V measurement / Chapter 4.3 --- Conclusion / References / Chapter 5 Conclusion / Chapter 5.1 --- Conclusion / Chapter 5.2 --- Future outlook

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This work describes the synthesis pathways to the development of optically and thermally responsive nanovalves with fast response times in nanoporous membranes. As an approach, we developed synthesis pathways to couple a thermally responsive polymer with metallic nanoparticles and build a nanocomposite that synergizes the capability of metallic nanoparticles to convert light into heat, and the fast thermal response exhibited by the polymeric material. In addition, we developed a technique to immobilize the synthesized nanocomposite to the surface of nanoporous membranes, which allowed building valves with light and heat triggering responses. This dissertation describes two syntheses pathways developed to produce optically and thermally responsive nanocomposites by coupling metallic nanoparticles, gold and silver, with a thermally responsive polymer, p-N-isopropyl acrylamide (PNIPAM). The coupling is achieved by using PNIPAM as a capping and nucleating agent in the in situ redox reaction of a silver salt with sodium borohydride, and using PNIPAM as a capping and stabilizing agent in the redox reaction of a gold salt with ascorbic acid. The size and shape of the nanoparticles were controlled and the synthesized nanocomposites exhibit “cocoon-like” structures due to the PNIPAM surrounding the metal nanoparticles, giving the capability to aggregate and resolubilize, through many thermal (shown for gold and silver nanocomposites) and optical (shown by exposing to 532 nm wavelength low-power lasers) cycles. The steady state and dynamic heat conduction of the heat generated from the particles was modeled and the results agreed with the observed optical switching at our experimental conditions. Finally, a method to incorporate nanocomposites into nanoporous membranes (NPM) was developed. It involved prior immobilization of PNIPAM through plasma-induced grafting, followed by a reduction in situ of a metallic salt. The composite NPMs showed thermal responses and through simulation of heat conduction within the pores using the model developed in this work we were able to conclude that the synthesized composite membranes will exhibit optical switching when exposed to focused low power lasers. The nanovalves developed in this work have potential applications as optothermally responsive valves for the spatio-temporal delivery of bioactive agents, cell array, and advanced cell culture systems. / text

Fillers are often incorporated in polymer matrices in order to improve cost, mechanical, thermal, and transport properties. This work explores the hypothesis that pollen, a natural particle, has the potential to be an effective biorenewable reinforcing filler due to its unique surface architectures, high strength, chemical stability, and low density. Pollens from sources such as ragweed plants are ubiquitous natural materials that are based on sustainable, non-food resources. Pollen is a remarkable example of evolutionary-optimized microscale particle with structures and/or chemistries tailored for effective adhesion to a variety of surfaces and protection of genetic material under different dynamic and environmental conditions. The pollen shell is perhaps the most chemically resistant naturally occurring material. As many pollens achieve pollination simply by being carried by wind, they are very light-weight. These properties make pollen an attractive option as a natural filler for polymers. This research aims to characterize pollen interfacial properties and utilize pollen as an effective reinforcing filler in polymer materials. In this work, interfacial properties are characterized using Fourier transform infrared spectroscopy (FTIR), the BET method, and inverse liquid chromatography (ILC). These techniques were useful in determining the effect of surface treatments and further chemical modifications on pollen interfacial properties. Characterizing these properties allowed for improved understanding and utilization of pollen as a filler by revealing the enhanced surface interactions and surface properties of acid-base treated pollens when compared to as received untreated pollens. Epoxy and polyvinyl acetate (PVAc) matrices were used to demonstrate the effectiveness of pollen as a filler, as a function of pollen loading and surface treatments/chemical modifications. Scanning electron microscopy (SEM) was used to determine interfacial morphology, a high throughput mechanical characterization device (HTMECH) was used to determine mechanical properties, and differential scanning calorimetry (DSC) was used to determine glass transition behavior. In epoxy, pollen was an effective load bearing filler only after modifying its surface with acid-base hydrolysis. In PVAc, pollen was an effective load bearing filler only after an additional functionalization with a silane coupling agent. Finally, the species of pollen incorporated in PVAc matrices was varied in order determine the effect of the size of surface nano- and micro- structures on wetting, adhesion, and composite properties. Composites containing pollen displayed enhanced wetting and interfacial adhesion when compared to composites with smooth silica particles. Additionally, it was observed that pollen with smaller surface structures were wetted more effectively by the polymer matrix than pollen with larger structures. However, mechanical properties did not suggest significant changes in interfacial adherence with varied pollen microstructure size. The results of this work highlight the feasibility and potential of utilizing pollen as a natural filler for creating high strength, light-weight polymer composites with sustainable filler.

The in-plane properties of paperboard have always been of interest to paper scientists. Tensile properties are crucial when the board is fed through converting machines at high speeds. Compressive properties are essential in the later use. Inhomogeneities affect both the compressive and tensile properties. For the tensile properties, it is the inherent heterogeneity of the paperboard that might cause problems for the board-maker. Varying material properties, through the thickness of the paperboard, are on the other hand used to achieve high bending stiffness with low fiber usage. It is of interest to know how this practice affects the local compressive properties. Papers A and B aims to address this, while C, D and E focus on in-plane heterogeneities. Paper A investigates the mechanism that causes failure in the short span compression test (SCT). It was concluded that the main mechanism for failure in SCT is delamination due to shear damage. In paper B the effect of the through-thickness profiles on the local compression strength was examined. It was concluded that the local compression is governed by in-plane stiffness and through thickness delamination. The latter was in turn dependent on the local shear strength and in-plane stiffness gradients. In paper C the tensile test is investigated with focus on sample size and strain distributions. The strain behavior was dependent on the length to width ratio of the sample and was caused by activation of local zones with high strainability. Paper D focuses on the strain zones seen in C. The thermal response in paper was studied. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. It was concluded that the heat patterns observed coincided with the deformation patterns. It could be shown that the formation was the cause of the inhomogeneous deformation. In final paper, E, the virtual field method was applied on data from C. / Egenskaperna hos ett kartongark kan grovt delas upp i två kategorier: i-planet egenskaper och ut-ur-planet egenskaper. I-planet egenskaperna har länge varit ett område som pappersmekanister och andra pappersforskare visat intresse för. Anledningen till detta är att de är avgörande för hur väl det går att konvertera kartongen till färdiga förpackningar, samt hur väl de förpackningarna klarar sin uppgift. Dragegenskaperna prövas när kartongen dras genom tryck- och konverteringsmaskiner i hög hastighet. Tryckegenskaperna spelar stor roll för hur väl en förpackning klarar att staplas och hålla sitt innehåll intakt. Inhomogeniteter påverkar både drag och tryckegenskaper. Papprets naturliga variation påverkar dragegenskaperna hos kartongen och kan orsaka problem för kartongmakarna. Särskilt när utvecklingen går mot mer avancerade kartong utseenden. Å andra sidan så använder sig kartongmakare flitigt av egenskapsvariationer genom tjockleken på kartongen, när dom vill åstadkomma böjstyva kartonger utan att slösa med fibrer. I detta fall är det intressant att veta hur de lokala kompressionsegenskaperna påverkas av kartongens ut-ur-planet profil. Det första två uppsatserna i denna avhandling, A och B, handlar om just detta. Uppsatserna C, D och E avhandlar hur i-planet variationer påverkar kartongens egenskaper. I Artikel A undersöks vilka skademekanismer som aktiveras under ett kortspannskompressionstest (SCT). Tre flerskiktskartonger undersöktes. De hade valts så att de hade distinkt olika skjuvstyrkeprofiler. Kartongerna karakteriserades och datan användes som materialdata i en finit element modell av SCT-testet. Modellen bestod av skikt, betraktade som kontinuum, mellan vilka det fanns kohesiva ytor. Huvudmekanismen i SCT var att kartongen delaminerade på grund av skjuvskador. Den andra uppsatsen, Artikel B, var en fortsättning på den första. Denna gång undersöktes fem flerskiktskartonger framtagna så att de hade olika skjuvstyrka beroende på positionen i tjockleksled. Det konstaterades att kompressionsegenskaperna lokalt styrs av skjuvstyrkeprofilen och styvhetsgradienter. Vidare konstaterades det att mekanismerna innan kartongen delaminerar är, i huvudsak, elastiska. Den tredje artikeln, Artikel C, fokuserade på hur dragprov på kartong påverkas av provstorleken och töjningsvariationen. Tre olika flerskiktskartonger användes som provmaterial och provbitar med olika storlek analyserades. Förutom dragprov så användes digital image correlation (DIC) för analysen. Det visade sig att den globala töjbarheten varierade med storleken på provet beroende på kvoten mellan längd och bredd. DIC visade att detta i sin tur berodde på att zoner med hög töjbarhet aktiverades i provet. Dessa zoner hade samma storlek oberoende av provstorlek och påverkade därför den totala töjbarheten olika mycket. Artikel D undersöker töjningszonerna som sågs i Artikel C samt hur de påverkas av kreppning. Vidare undersöktes pappersproverna med hjälp av termografi. Termografin visade att varma zoner uppstod i proven när det töjdes. Zonerna blev synliga när provet töjdes plastiskt. Termografi kördes parallellt med DIC på några prover. Det visade sig att de varma zonerna överenstämde med zoner med hög lokal töjning. Vidare kunde det visas att dessa zoner övenstämde med papperets mikrostruktur, formationen. En finit element analys av hur papper med olika formation töjs gjordes. Delar av provningen gjordes på kreppade papper som har högre töjbarhet. Det visades sig att någon form av skada hade överlagrats på papprets mikrostruktur under kreppningen, och att den deformationen återtogs när pappret töjdes. I den sista artikeln, Artikel E, behandlas hur VFM (Virtual Field Method) kan användas på DIC-data från kartong. DIC-datan som användes hämtades från Artikel C. Detta gjordes för att visa på hur olika VFM-formuleringar kan användas för att karakterisera styvhetsvariationen hos kartong. Provet delades upp i tre subregioner baserat på den axiella töjningsgraden. VFM-analysen visade att dessa subregioners styvhet och tvärkontraktionstal sjönk monotont, men att skillnaden mellan regionerna ökade med ökande spänning. även om endast ett prov undersöktes, så indikerade resultaten att områden med hög styvhet endast förbättrar de mekaniska egenskaperna marginellt. Analysen visade också att även om subregionerna inte är sammanhängande, så har dom liknande mekaniska egenskaper. / <p>QC 20160429</p>

This dissertation reports on the study of black molybdenum, a new cermet consisting of small Mo particles embedded in MoO₂. As with most two-phase materials, the optical properties of black molybdenum are significantly different from those of either constituent, and can be adjusted within wide limits through modifications of composition and microstructure due to variations of the fabrication process parameters. The subject of this work is to understand the exact relationships, to allow reproducible production of films with chosen optical properties. Theoretical interpretation of the optical properties of two-phase materials has in the past been hampered by insufficient microstructural characterization. Recent theoretical work by others has lifted the requirements of detailed microstructural knowledge, leaving only two required parameters for characterization of cermet reflectance: the optical properties of the constituent phases and their volume fractions in the cermet. Better characterization is obtained when structural considerations, such as film topology, surface texture and the presence of a possible amorphous phase, are taken into account. We adopted this approach to the study of black molybdenum, and accomplished satisfactory agreement between theoretical and observed reflectances. Black molybdenum films were prepared using two separate chemical vapor deposition (CVD) techniques, involving deposition from either Mo(CO)₆ or MoO₂Cl₂. We found the influence of composition through a comparison of films with different Mo:MoO₂ ratios, while the influence of structure on film reflectance was determined by comparing films from these two deposition techniques. During this investigation we produced black molybdenum films which display a spectrally selective profile--low visible reflectance combined with high infrared reflectance, and which may be applied to photothermal solar energy conversion. The versatility of CVD in adjusting film composition and structure resulted in another film of interest in photothermal conversion--black tungsten, a tungsten-tungsten oxide composite material. The black molybdenum and black tungsten systems studied here establish the utility of CVD for the production of high temperature thin film optical devices.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy