Dissertations / Theses on the topic 'Characterizations of the materials'

El desenvolupament de nanotermòmetres luminescents de no contacte basats en ions lantànids per ser utilitzats com a eines de diagnòstic precises, eficients i ràpides, propietats atribuïdes a la seva versatilitat, estabilitat i perfils de banda d'emissió estrets, ha portat cap a la substitució de les sondes tèrmiques de contacte convencionals. L'aplicació de nanopartícules dopades amb ions lantànids com nanosensors de temperatura, excitats amb llum ultraviolada, visible o infraroja propera, i la generació d'emissions en les regions espectrals de les finestres biològiques: I-BW (650 nm-950 nm), II-BW (1000 nm -1350 nm), III-BW (1400 nm-2000 nm) i IV-BW (centrada en 2200 nm), està creixent notablement a causa d’avantatges com la reducció de la fototoxicitat i el fotoblanqueig, un contrast d'imatge millor i una major profunditat de penetració en els teixits biològics. Entre aquestes finestres biològiques, la III-BW permet lectures tèrmiques més profundes dins de teixits biològics específics, atribuïdes a una major profunditat de penetració a causa de la reducció de l'absorbància i la dispersió en comparació amb les altres finestres biològiques. No obstant això, la termometria de luminescència en aquest règim espectral s'ha explorat poc. Aquí, hem sintetitzat i caracteritzat materials luminescents dopats amb Ho3+ i Tm3+ amb emissions ubicades a la III-BW per a la seva aplicació com a termòmetres luminescents i agents fototèrmics. Hem utilitzat partícules de KLu(WO4)2 i Y2O3 dopades amb Ho3+ i Tm3+ com a possibles agents fototèrmics automonitoritzats capaços d'alliberar calor i de determinar la temperatura simultàniament. Per a la seva síntesi, hem adaptat mètodes solvotermals (autoclau convencional i assistit per microones) i químics humits (descomposició tèrmica i maduració digestiva). Per acabar, hem aprofitat la peculiar configuració electrònica i les característiques morfològiques de les nanopartícules de Y2O3 per aplicar-les com a emissors de llum blanca i com a agents antioxidants ex vivo.
El desarrollo de nanotermómetros luminiscentes de no contacto basados en iones lantánidos para ser usados como herramientas de diagnóstico precisas, eficientes y rápidas, propiedades atribuidas a su versatilidad, estabilidad y perfiles de banda de emisión estrechos, ha llevado a la sustitución de las sondas térmicas de contacto convencionales. La aplicación de nanopartículas dopadas con lantánidos como nanosensores de temperatura, excitados con luz ultravioleta, visible o infrarroja cercana, y la generación de emisiones en las regiones espectrales de las ventanas biológicas: I-BW (650 nm-950 nm), II-BW (1000 nm -1350 nm), III-BW (1400 nm-2000 nm) y IV-BW (centrada en 2200 nm), está creciendo notablemente debido a ventajas como la reducción de la fototoxicidad y el fotoblanqueo, un mejor contraste de imagen y una mayor profundidad de penetración en tejidos biológicos. Entre estas ventanas biológicas, la III-BW permite lecturas térmicas más profundas dentro de tejidos biológicos específicos, atribuidas a una mayor profundidad de penetración debido a la reducción de la absorbancia y la dispersión en comparación con las otras ventanas biológicas. Sin embargo, la termometría de luminiscencia en este régimen espectral se ha explorado poco. Aquí, hemos sintetizado y caracterizado materiales luminiscentes dopados con Ho3+ y Tm3+ con emisiones ubicadas en la III-BW para su aplicación como termómetros luminiscentes y agentes fototérmicos. Hemos utilizado partículas de KLu(WO4)2 y Y2O3 dopadas con Ho3+ y Tm3+ como posibles agentes fototérmicos automonitorizados capaces de liberar calor y determinar la temperatura simultáneamente. Para su síntesis, hemos adaptado métodos solvotermales (autoclave convencional y asistido por microondas) y químicos húmedos (descomposición térmica y maduración digestiva). Para finalizar, hemos aprovechado la peculiar configuración electrónica y las características morfológicas de las nanopartículas de Y2O3 para aplicarlas como emisores de luz blanca y como agentes antioxidantes ex vivo.
The development of non-contact luminescent lanthanide nanothermometers as accurate, efficient and fast diagnostic tools, attributed to their versatility, stability and narrow emission band profiles, have led to the replacement of the conventional contact thermal probes. The application of lanthanide doped nanoparticles as temperature nanosensors, excited with ultraviolet, visible or near infrared light, and the generation of emissions lying in the biological windows spectral regions: I-BW (650 nm-950 nm), II-BW (1000 nm-1350 nm), III-BW (1400 nm-2000 nm) and IV-BW (centered at 2200 nm), is notably growing due to the advantages of reduced phototoxicity and photobleaching, better image contrast and deeper penetration depths into biological tissues. Among these biological windows, the III-BW allows for deeper thermal readings within specific biological tissues, attributed to a higher penetration depth due to the reduction of absorbance and scattering when compared to the other biological windows. Nevertheless, luminescence thermometry in this spectral regime is randomly explored. Here, we synthesized and characterized luminescent Ho3+ and Tm3+ doped materials with emissions located in the III-BW for their application as luminescent thermometers and photothermal agents. We explored Ho3+ and Tm3+ doped KLu(WO4)2 and Y2O3 particles as potential self-assessed photothermal agents able to release heat and determine temperature simultaneously. For their synthesis, we adapted solvothermal (microwave-assisted and conventional autoclave) and wet-chemical (thermal decomposition and digestive ripening) methods. To conclude, we took profit of the peculiar electronic configuration and morphological characteristics of the Y2O3 nanoparticles to apply them as white light emitters and as ex-vivo antioxidant agents.

Metal–organic frameworks are a rapidly expanding family of crystalline porous materials and have shown great promise to address various challenges such as gas storage and separation due to their well-defined pore size and unprecedented tunability in both composition and pore geometry. Here, we have synthesized and structurally characterized a number of new metal- organic framework materials and studied the effects of ligands and metal types on the construction and properties of metal–organic frameworks. To probe the effects of functional groups on ligands, two zinc-based three-dimensional frameworks have been synthesized. They consist of zinc-triazolate layers pillared by dicarboxylates with different functional groups. In addition, a very unusual magnesium metal-organic framework material has been made. It consists of novel magnesium acetate chains crosslinked by 1,4-benzenedicarboxylate into a three-dimensional framework with large channels. The phase purity and structures of these materials have been determined by powder and single-crystal X-ray diffraction. Their thermal stability and sorption a properties for gas molecules such as N ₂, H₂, and CO₂ have also been studied.

Thesis (M.Sc.)--City University of Hong Kong, 2006.
"Master of Science in Materials Engineering & Nanotechnology dissertation." Title from title screen (viewed on Nov. 21, 2006) Includes bibliographical references.

Förfrågan efter nya och mer avancerade applikationer är en pågående process vilket leder till en konstant utveckling av nya material. För att förstå relationen mellan en applikations egenskaper och dess sammansättning krävs full förståelse och kontroll över materialets uppbyggnad. En sådan kontroll över uppbyggnaden hos material hittas i en undergrupp till dendritiska polymerer som kallas dendrimerer. I den här doktorsavhandlingen belyses nya metoder för att framställa dendrimer med hjälp av selektiva kemiska reaktioner. Sådana selektiva reaktioner kan hittas inom konceptet klickkemi och har i detta arbete kombinerats med traditionell anhydrid- och karbodiimidmedierad kemi. Denna avhandling diskuterar en accelererad tillväxtmetod, dendrimerer med inre och yttre reaktiva grupper, simultana reaktioner och applikationer baserade på dessa dendritiska material. En accelererad tillväxtmetod har utvecklats baserad på AB2- och CD2-monomerer. Dessa monomerer tillåter tillväxt av dendrimerer utan att använda sig av skyddsgruppkemi eller aktivering av ändgrupper. Detta gjordes genom att kombinera kemoselektiviteten hos klickkemi tillsammans med traditionell syraklorid kopplingar. Dendrimerer med inre alkyn- eller azidfunktionalitet syntetiserades genom att använda AB2C-monomerer. Den dendritiska tillväxten skedde med hjälp av karbodiimidmedierad kemi. Monomererna som användes bär på en C-funktionalitet, alkyn eller azid, och på så sätt byggs får interiören i de syntetiserade dendrimeren en inneburen aktiv funktionell grupp. Ortogonaliteten hos klickkemi användes för att sammanfoga monomerer till en dendritisk struktur. Traditionell anhydridkemi- och klickemireaktioner utfördes samtidigt och på så sätt kunde dendritiska strukturer erhållas med färre antal uppreningssteg. En ljusemitterande dendrimer syntetiserades genom att koppla azidfunktionella dendroner till en alkynfunktionell cyclenkärna. Europiumjoner inkorporerades i kärnan varpå dendrimerens fotofysiska egenskaper analyserades. Mätningarna visade att den bildade triazolen hade en sensibiliserande effekt på europiumjonen. Termiska studier på några av de syntetiserade dendrimerer utfördes för att se om några av dem kunde fungera som templat vid framställning av isoporösa filmer.
The need for new improved materials in cutting edge applications is constantly inspiring researchers to developing novel advanced macromolecular structures. A research area within advanced and complex macromolecular structures is dendrimers and their synthesis. Dendrimers consist of highly dense and branched structures that have promising properties suitable for biomedical and electrical applications and as templating materials. Dendrimers provide full control over the structure and property relationship since they are synthesized with unprecedented control over each reaction step. In this doctoral thesis, new methodologies for dendrimer synthesis are based on the concept of click chemistry in combination with traditional chemical reactions for dendrimer synthesis. This thesis discusses an accelerated growth approach, dendrimers with internal functionality, concurrent reactions and their applications. An accelerated growth approach for dendrimers was developed based on AB2- and CD2-monomers. These allow dendritic growth without the use of activation or deprotection of the peripheral end-groups. This was achieved by combining the chemoselective nature of click chemistry and traditional acid chloride reactions. Dendrimers with internal azide/alkyne functionality were prepared by adding AB2C monomers to a multifunctional core. Dendritic growth was obtained by employing carbodiimide mediated chemistry. The monomers carry a pendant C-functionality (alkyne or azide) that remains available in the dendritic interior resulting in dendrimers with internal and peripheral functionalities. The orthogonal nature of click chemistry was utilized for the simultaneous assembly of monomers into dendritic structures. Traditional anhydride chemistry and click chemistry were carried out concurrently to obtain dendritic structures. This procedure allows synthesis of dendritic structures using fewer purification steps. Thermal analyses on selected dendrimers were carried out to verify their use as templates for the formation of honeycomb membranes. Additionally, a light emitting dendrimer was prepared by coupling of azide functional dendrons to an alkyne functional cyclen core. A Europium ion was incorporated into the dendrimer core, and photophysical measurements on the metal containing dendrimer revealed that the formed triazole linkage possesses a sensitizing effect.
QC 20100629

Thesis (Ph. D.)--Dept. of Chemistry and School of Pharmacy. University of Missouri--Kansas City, 2005.
"A dissertation in chemistry and pharmaceutical sciences." Advisor: Zhonghua Peng. Typescript. Vita. Description based on contents viewed June 26, 2006; title from "catalog record" of the print edition. Includes bibliographical references (leaves 173-190). Online version of the print edition.

Les oxydes de type pérovskites présentent différentes propriétés selon leur structure et leur composition chimique. Les principales pérovskites étudiées, BaTiO3 et YBa2Cu3O7, possèdent d’intéressantes propriétés ferroélectriques et supraconductrices. Une des limitations de ce type d’oxydes est la transition de phase à haute température qui peut modifier leurs propriétés. Le matériau CaCu3Ti4O12 (CCTO) est un oxyde connu comme double perovskite (ABO3) à structure cubique, qui a été étudié ces dernières années en tant que matériau diélectrique de permittivité élevée. De plus, CCTO subit une transition magnétique à antiferromagnétique au-dessous de la température de Néel (TN=25K). Les propriétés du matériau CCTO sont fortement dépendantes de sa structure et offrent des possibilités d’applications photoélectrochimiques. D'un autre côté, les nanofeuillets de nitrure de bore (h-BN) et d’oxyde de graphène (GO) sont des matériaux 2D présentant des propriétés très intéressantes.Dans le cadre de ce travail, des matériaux composites à base de CCTO et de nanofeuillets de nitrure de bore et d’oxyde de graphène ont été synthétisés et étudiés. Les céramiques composites CCTO/GO et CCTO/h-BN ont été synthétisées par réaction solide-solide. Les différentes propriétés photoélectrochimiques, diélectriques, et magnétiques ont été caractérisées. L’addition de 3% de h-BN aboutit à l’incorporation des atomes du bore et d’azote dans le réseau cristallin du CCTO et forme les liaisons Ti-B-O et Ti-N-O, et génère des lacunes d’oxygène à la surface, ce qui améliore la génération de porteurs de charges. La génération de porteurs de charges est augmentée en 50% par rapport au CCTO pur, après l’addition de 3% de GO, due à l’oxydation de GO à haute température qui réduit Ti4+ et Cu2+ en site actifs Ti3+ et Cu+ respectivement. Les propriétés magnétiques du CCTO avec 6% de nanofeuillets ont été étudiées, et ont montré que la température Néel n’était pas modifiée. Enfin, un polissage est effectué à la surface des céramiques pour étudier leurs propriétés diélectriques. Les résultats montrent des valeurs de permittivité plus basse que celles décrites dans la littérature. En conclusion, ces travaux ont démontré que l’incorporation des nanofeuillets 2D n’affecte pas les propriétés diélectriques et magnétiques, mais améliore considérablement les propriétés photoélectrochimiques du CCTO
Perovskite oxides exhibit a large variety of properties because of their structures and chemical compositions. Well known properties of the perovskite oxides are Ferroelectricity in BaTiO3-based oxides and superconductivity in YBa2Cu3O7. The major limit of these compounds is their phase transitions at high temperature, which lead to modify the perovskite properties. CaCu3Ti4O12 (CCTO) exhibit a cubic structure stable at high temperature, it is a double-perovskite (ABO3). CCTO was known as high dielectric material, and can play a key role in photoelectrochemical activity due to its structure. In addition, CCTO can occur a phase transition into the antiferromagnetically ordered phase below Neel temperature TN = 25 K. On the other hand, 2D nanomaterials including graphene oxide (GO) and hexagonal boron nitrides (h-BN) were widely used due their exceptional properties.The aim of this thesis is to investigate the photoelectrochemical, dielectric, and magnetic properties of CCTO based composites. Composites made of CCTO/GO and CCTO/h-BN ceramics were fabricated by solid-state reaction. With the addition of 2D nanosheets materials, the photoelectrochemical performance is enhanced by increasing the generation of photocurrent. CCTO with 3%wt of h-BN showed the insertion of bore (B) and nitrogen (N) into CCTO lattice, leading to Ti-B-O, Ti-N-O bonds and oxygen vacancies on the surface which reduce the bang gap energy and increase the density of generated photocurrent. With 3% of GO, Ti4+ and Cu2+ were reduced to active species Ti3+ and Cu+ respectively and oxygen vacancies were generated at the surface for charge neutralization, leading to generate photocurrent density 50% higher than pure phase of CCTO. In order to investigate 2D nanomaterials effects on magnetic properties of composites, CCTO with 6%wt of nanosheets was prepared and have shown no significant changes in Neel temperature. Finally in the last section, all composites were surface polished to investigate their dielectric properties, measurements showed a low permittivity in comparison to the literature. In conclusion, this work has shown that 2D nanosheets materials incorporation does not affect dielectric and magnetic properties, but enhance strongly the photoelectrochemical behavior of CCTO

Research in metal-organic frameworks (MOFs) has risen greatly in recent decades Owing to their unequaled potential tunability and structural diversity. MOFs may be described as crystalline structures composed of metal cations or clusters of cations, commonly referred to as secondary building units (SBUs), and custom-designed organic ligands. The variety of structural motifs, ligands, and SBUs that may be incorporated promote the attainment of essentially countless potential MOFs and application in numerous areas of interest, such as gas adsorption, catalysis, gas separation, and sensing. Further functionalization of MOF materials by means of post-synthetic modification(PSM)33–37 of metal clusters or organic ligands, constructing frameworks using functional ligands or metal clusters, and incorporating advantageous molecules including organometallic molecules,38–41 enzymes,42–45 metal nanoparticles (NPs),8,46–48 heteropolyacids49–51 within the pores advance the diverse number of species, including organic ligands, inorganic metal ions/clusters, and guests, used to construct MOFs materials lead to MOFs materials possessing phenomenal properties. Implementation of these materials in sensing arises from the frameworks’ characteristic ability to increase the concentration of a desired analyte to a greater degree than its overall presence within the system; imparting an inherent sensitivity to the aforementioned analyte. MOFs materials also possess the potential for selectivity for specific analytes or classes of analytes through mechanisms such as size exclusion (molecular sieving), chemically specific interactions between the adsorbate and framework, and the directed design of pore and aperture size through the selection of appropriate organic linkers or struts. Flexible azamacrocycle-based ligands are constructed through the use of pliable carboxylate pendant arms and azamacrocycles, e.g cyclen and tacn, and used in the pursuit of novel metal macrocycle frameworks (MMCF). Polyazamacrocycles represent a popular class of macrocyclic ligands for supramolecular chemistry and crystal engineering. This popularity may be due to their complexes’ high thermodynamic stability, relative kinetic inertness, basicity, transition metal-ion coordinating ability and rigid structure. Furthermore, their utilization promotes intriguing network topologies as coordination in complexes containing tetradentate azamacrocycles generally produces only two isomers differing via the coordination ligand’s conformation. The highly reported equatorial N4¬ ¬coordination of the macrocycle allows for interaction at the two vacant trans-axial positons, whilst the folded conformations permits interaction at two vacant cis positions. Azamacrocycle complexes differ from those of other classes of macrocycles due to the fact the macrocyclic cavity is commonly occupied by metal cations. Materials containing azamacrocycles have found use in applications such as bleaching and oxidative catalysis and molecular recognition. Cyclen units have reportedly been incorporated to construct pH-dependent selective receptors for copper (II), zinc(II), yttrium(III), and lanthanum(III) ions. Herein, we describe the synthesis and characterizations of a new lanthanide framework, La(C40H40N4O8)(NH2(CH2)2)NO3 or MMCF-3, which retains a vacancy in the macrocycle unit encourages the utilization of the framework as a cation receptor and precursor for heterometallic frameworks. The inclusion of azamacrocycles into MOF materials combine the characteristic high thermodynamic stability, basicity, and strong metal complexation of the macrocycles with the high porosity, surface area, and tunability of the frameworks. Full realization of the potential of Azamacrocyclic-based MOFs requires the preparation of new entrants to this class of materials that espouse various topological structures while incorporating diverse azamacrocycles. It has been shown that the hierarchical porosity associated with macrocyclic based frameworks can be obtained using this class of ligands.71,99 The development of more frameworks exhibiting this characteristic is needed to fully investigate the potential applications of MOFs retaining the vacant cavities of the azamacrocycles. Effectuation of hierarchical porosity of azamacrocyclic frameworks will broaden sensing applications, e.g. azamacrocycles have performed as receptors of anions, cations, amino acids and other analyte molecules, and provide an ideal slot to integrate open metal site into MOFs.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 123-132).
Metal-Organic Frameworks (MOFs) are a class of porous materials with a crystalline structure that can be designed based on extremely tunable building blocks of organic molecules and metal ions. They are typically insulators but making them [pi]-conjugated with two-dimensional structure results in high electrical conductivity. This makes the two-dimensional a-conjugated MOFs (2D [pi]MOFs) good candidates for applications that need porous conductors such as supercapacitors and batteries. More importantly, tunability of the crystal structure enables us to explore exotic physical properties, including topological protection. This great potential has inspired the synthesis of various 2D [pi]MOFs, but their crystal growth remains challenging, preventing the characterization of intrinsic electrical properties. In this thesis, I will explain the growth mechanisms of 2D [pi]MOFs and the limitations of conventional growth methods.
Based on the analysis, I developed a novel growth method that generates single-crystal plates of a 2D [pi]MOF, Ni₃(HHTP)₂ (HHTP= 2,3,6,7,10,11 hexahydroxytriphenylene), over 10 [mu]m in lateral dimension, two orders of magnitude larger than previous reports. The growth mechanism of the new method is also studied by varying multiple growth parameters. The properties of the single crystals are characterized by various spectroscopic techniques. Among assorted characteristics, the electrical properties are explored closely. The large single-crystal plates enable us to study in-plane properties of a 2D [pi]MOF for the first time. The in-plane conductivity of Ni₃(HHTP)₂ is up to 2 S/cm, two orders of magnitude higher than pressed pellet, and shows a clear temperature dependence. Hall measurements reveal that the origin of the high conductivity is a high charge carrier density rather than high charge carrier mobility.
We anticipate our demonstration will facilitate the discovery of fundamental properties of various 2D [pi]MOFs and further our realization of their potential as electronic materials.
Kwangjeong educational foundation for financial support
by Dong-Gwang Ha.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

The objective of this research was to develop highly efficient and yet effective MnO2 electrode materials for supercapacitors applications. Most attention had focussed on MnO2 as a candidate for pseudo-capacitor, due to the low cost of the raw material and the fact that manganese is more environmental friendly than any other transition metal oxide system. The surface area and pore distribution of MnO2 can be controlled by adjusting the reaction time. The MnO2 synthesised under optimum conditions display high capacitance, and exhibit good cycle profile. This work investigates the ways in which different morphological structures and pore sizes can affect the effective capacitance. Various -MnO2 were successfully synthesised under low temperature conditions of 70 oC and hydrothermal conditions at 120 oC. The reaction time was varied from 1 to 6 hours to optimise the conditions. KMnO4 was reduced by MnCl.H2O under low temperature, whereas MnSO4.4H2O, (NH4)2S2O8 and (NH4)2SO4 were co-precipitated under hydrothermal conditions in a taflon autoclave to synthesise various -MnO2 nano-structures.

Ce travail de thèse est axée sur la découverte de nouveaux matériaux d'électrodes utilisées dans les batteries Li ou Na ion et rechargeables. Notre approche pour générer et identifier de nouveaux matériaux d'électrode à fort potentiel est basé sur la synthèse directe par chimie douce (précipitations, hydrothermale), échange d'ions et réactions électrochimiques d'oxydation/réduction. Dans le système des oxydes de vanadium, une nouvelle classe de matériau a été synthétisé avec la formule générale AVO3 (avec A = Li, Na, Ag, Cu). Dans le cas du lithium, nous avons observé la formation d’une nouvelle phase Li2VO3 de structure NaCl désordonnée délivrant une capacité spécifique réversible de 250 mAh/g à un potentiel moyen de 2,5 V vs Li/Li+. Un autre nouveau matériau d'électrode à base de phosphate de vanadium Na2VO(HPO4)2 a été préparé par échange ionique à partir du phosphate acide de vanadium VO(H2PO4)2. Ce composé est un conducteur ionique ( = 10-3S/cm à 200°C) et livré une capacité spécifique de 70 mAh/g à tension plus élevée ~ 3,9 V vs Li/Li+ avec une excellente réversibilité. A la recherche de nouvelles compositions dans le système Li-M-O, nous avons synthétisé la nouvelle phase Li5W2O7 à partir de la phase en ruban Li2W2O7 par insertion électrochimique de lithium. Cette phase présente une structure de type NaCl ordonnée et un comportement électrochimique attrayant avec une capacité spécifique initiale de 162 mAh/g. Nous avons étudié également la phase Ag2W2O7 iso-structurale qui offre quant à elle une capacité de 193 mAh/g
This thesis work is focused on the discovery of new electrode materials used in rechargeable lithium and sodium ion batteries. Our approach to generate and identify new high potential electrode materials is based on direct soft chemistry synthesis (precipitation, hydrothermal), ion exchange and electrochemical oxidation/reduction reactions. In the A-V-O system (A=Li, Na, Ag, Cu), a new class of material has been synthesized by lithium/sodium insertion with the general formula A2VO3. We found that the fully reduced phase Li2VO3 is showing a disordered rock-salt-type structure and delivered a reversible specific capacity of 250 mAh/g at an average potential of 2. 5 V vs. Li+/Li. Another candidate Li5W2O7 has been explored as new electrode material for Li-ion batteries in the A-W-O system. Starting from the ribbon-type structure Li2W2O7, the fully reduced phase Li5W2O7 is showing an ordered rock-salt-type structure and the electrochemical behavior of these new phases is attractive with an initial specific capacity of 162 mAh/g. We studied also the iso-structural phase Ag2W2O7 and it delivers a capacity of 193 mAh/g. Another new electrode material based on vanadium phosphate Na2VO(HPO4)2 has been prepared by ion exchange method starting from the acidic vanadium phosphate VO(H2PO4)2. This compound is an ionic conductor (=10-3S/cm at 200°C) and delivered a specific capacity of 70 mAh/g at higher voltage ~3. 9 V vs. Li/Li+ with an excellent reversibility

Le travail présenté dans cette thèse porte sur la synthèse, la caractérisation des propriétés structurelles et électroniques du sulfure de cuivre Cu22Fe8Ge4S32, un matériau dérivé de la germanite ayants des propriétés thermoélectriques prometteuses. Les deux premiers chapitres sont consacrés à l'optimisation des propriétés thermoélectriques par différentes approches. Le dernier chapitre est une étude structurelle approfondie de la germanite Cu22Fe8Ge4S32. Premièrement, les conditions spécifiques de la synthèse permettant de produire un échantillon ‘‘pure’’ de germanite par tube scellé sont examinées par le biais de réactions in situ. Ensuite, deux approches différentes de synthèse sont comparées, à savoir l’alliage mécanique et la synthèse en tube scellé, combinées à deux méthodes de densification différentes: le frittage SPS et le pressage à chaud. Deuxièmement, les séries de composés Cu22-xZnxFe8Ge4S32 (0 ≤ x ≤ 2) et Cu22Fe8Ge4-xSnxS32 (0 ≤ x ≤ 4) ont été étudiées dans l’espoir d’améliorer les propriétés thermoélectriques en augmentant la diffusions des phonons. En plus de la diminution de la κ_Latt, l'augmentation de la concentration en Zn dans le réseau de cuivre entraîne une diminution de la concentration en trous. De plus, l’incorporation de Sn diminue la κ_Latt en augmentant la diffusion des phonons par des défauts ponctuels due à des disparités de masse, de taille et de force de liaison. Enfin, un nouvelle structure crystalline pour la germanite synthétique a été proposé en conservant le groupe d'espace et le paramètre de maille du matériau minéral (P4 ̅3n and a ≈ 10.595 Å). La détermination de la structure cristalline a été possible par la complémentarité des techniques de DRX sur poudre et monocristal, de spectroscopie Mössbauer 57Fe et de diffusion résonante. L’originalité de ce travail réside dans l’approche expérimentale développée pour surmonter la complexité inhérente à la distribution cationique de germanite
The work presented in this Ph.D. thesis deals with the synthesis, the structural and electronic properties characterization of the Cu22Fe8Ge4S32 copper sulfide, a material derived of the germanite mineral with promising thermoelectric properties. The first two chapters are dedicated to the optimization of the thermoelectric properties. The last chapter is an in-depth structural study of Cu22Fe8Ge4S32. First, the specific synthesis conditions to yield a ‘‘pure’’ germanite sample by sealed tube are investigated by the means of in situ reactions. Then, two different powder synthesis approaches are compared, namely mechanical alloying and conventional sealed tube synthesis, combined with two different densification methods: spark plasma sintering and hot pressing. This study drags attention to the process impact on the transport properties of complex Cu-based sulfides. Second, the series of compounds Cu22-xZnxFe8Ge4S32 (0 ≤ x ≤ 2) and Cu22Fe8Ge4-xSnxS32 (0 ≤ x ≤ 4) were investigated in the hope to enhance the TE properties through enhanced phonon scattering due to differences in atomic mass. In fact, in addition to lowering the κ_Latt, the Cu by Zn substitution in Cu22-xZnxFe8Ge4S32 leads to a decrease in the concentration of hole carriers. In addition, a reduction of κ_Lattis observed with the Sn-incorporation due to point defect scattering enhancement of the heat carrying phonons as a result of mass, size, and bonding strength disparities. Finally, a new structural model for synthetic germanite was proposed with respect to the space group and lattice parameter of the mineral material, P4 ̅3n and a ≈ 10.595 Å. The crystal structure is proposed based on the complementarity from powder and single crystal XRD, 57Fe Mössbauer spectroscopy and resonant scattering. The originality of this work lies in the experimental approach that was developed to overcome the inherent complexity of germanite cationic distribution

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2006.
"May, 2006." Title from electronic dissertation title page (viewed 10/11/2006) Advisor, Erol Sancaktar; Committee members, James L. White, Kyonsuku Min, Darrell H. Reneker, Wieslaw Binienda; Department Chair, Sadhan C. Jana; Dean of the College, Frank N. Kelley; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Alkali-ion batteries have revolutionized modern life through enabling the widespread application of portable electronic devices. The call for adapting renewable energy in many applications will also see an increase in the demand of alkali-ion batteries, specially to account for the intermittent nature of the renewable energy sources. However, the advancement of such technologies will require innovation on the forefront of materials development as well as fundamental understanding on the physical and chemical processes from atomic to device length scales. Herein, we focus on advancing energy storage devices such as alkali-ion batteries through cathode materials development and discovery as well as fundamental understanding through multiscale advanced synchrotron spectroscopic and microscopic characterizations. Multiscale electrochemical properties of cathode materials are unraveled through complementary characterizations and design principles are developed for stable cathode materials for alkali-ion batteries. In Chapter 1, we provide a comprehensive background on alkali-ion batteries and cathode materials. The future prospect of Li-ion and beyond Li-ion batteries are summarized. Surface to bulk chemistry of alkali-ion cathode materials is introduced. The prospect of combined cationic and anionic redox processes to enhance the energy density of cathode materials is discussed. Structural and chemical complexities in cathode materials during electrochemical cycling as well as due to anionic redox are summarized. In Chapter 2, we explain an inaugural effort on tuning the 3D nano/mesoscale elemental distribution of cathode materials to positively impact the electrochemical performance of cathode materials. We show that engineering the elemental distribution can take advantage of depth dependent redox reactions and curtail harmful side reactions at cathode-electrolyte interface which can stabilize the electrochemical performance. In Chapter 3, we show that the surface to bulk chemistry of cathode particles is distinct under applied electrochemical potential. We show that the severe surface degradation at the beginning stages of cycling can impact the long-term cycling performance of cathode materials in alkali-ion batteries. In Chapter 4, we utilize the structural and chemical complexities of sodium layered oxide materials to synthesize stable cathode materials for half cell and full cell sodium-ion batteries. Meanwhile, challenges with enabling long term cycling (more than 1000 cycles) are deciphered to be transition metal dissolution and local and global structural transformations. In Chapter 5, we utilize anionic redox in conjunction with conventional cationic redox of cathode materials for alkali-ion batteries to enhance the energy density. We show that the stability of anionic redox is closely related to the local transition metal environment. We also show that a reversible evolution of local transition metal environment during cycling can lead to stable anionic redox. In Chapter 6, we provide design principles for cathode materials for advanced alkali-ion batteries for application under extreme environments (e.g., outer space and nuclear power industries). For the first time, we systematically study the microstructural evolution of cathode materials under extreme irradiation and temperature to unravel the key factors affecting the stability of battery cathodes. Our experimental and computational studies show that a cathode material with smaller cationic antisite defect formation energy than another is more resilient under extreme environments.
Doctor of Philosophy
Alkali-ion batteries are finding many applications in our life, ranging from portable electronic devices, electric vehicles, grid energy storage, space exploration and so on. Cathode materials play a crucial role in the overall performance of alkali-ion batteries. Reliable application of alkali-ion batteries requires stable and high-energy cathode materials. Hence, design principles must be developed for high-performance cathode materials. Such design principles can be benefited from advanced characterizations that can reveal the surface-to-bulk properties of cathode materials. Herein, we focus on formulating design principles for cathode materials for alkali-ion batteries. Aided by advanced synchrotron characterizations, we reveal the surface-to-bulk properties of cathodes and their role on the long-term stability of alkali-ion batteries. We present tuning structural and chemical complexities as a method of designing advanced cathode materials. We show that energy density of cathode materials can be enhanced by taking advantage of a combined cationic and anionic redox. Lastly, we show design principles for stable cathode materials under extreme conditions in outer space and nuclear power industries (under extreme irradiation and temperature). Our study shows that structurally resilient cathode materials under extreme irradiation and temperature can be designed if the size of positively charged cations in cathode materials are almost similar. Our study provides valuable insights on the development of advanced cathode materials for alkali-ion batteries which can aid the future development of energy storage devices.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
Devido ao rÃpido progresso no desenvolvimento de sistemas de comunicaÃÃo em microondas, as cerÃmicas dielÃtricas e magnÃticas (ferritas) se tornaram atrativas para o uso em dispositivos. Embora as ferritas do tipo espinel terem sido os primeiros materiais utilizados para microondas, as granadas possuem menores perdas dielÃtricas e, portanto, sÃo preferidas em muitas aplicaÃÃes. As elevadas exigÃncias que as aplicaÃÃes elÃtricas modernas requerem dos materiais magnÃticos fazem com que novas tÃcnicas e produtos estejam permanentemente sendo pesquisados, com o conseqÃente aparecimento de novas soluÃÃes para uma ampla sÃrie de aplicaÃÃes. Nesse sentido, a pesquisa sobre compÃsitos à empregada para a busca de novos materiais. Este trabalho apresenta a obtenÃÃo do compÃsito ferrimagnÃtico, constituÃdo pelas fases Y3Fe5O12 (YIG) e Gd3Fe5O12 (GdIG), atravÃs da rota sintÃtica no estado sÃlido com a utilizaÃÃo de moagem mecÃnica de alta energia. A DifraÃÃo de Raios-X, a Espectroscopia Raman, Infravermelho e MÃssbauer foram essenciais para caracterizaÃÃo estrutural dos compÃsitos. As peculiaridades da morfologia das amostras foram elucidadas pela Microscopia EletrÃnica de Varredura e Microdureza de Vickers. Adicionalmente, foram realizados experimentos para se avaliar o comportamento elÃtrico e magnÃtico dos compÃsitos na faixa de radio freqÃÃncia e de microondas para depois sugerir uma aplicaÃÃo tecnolÃgica cabÃvel. Os compÃsitos comportaram-se adequadamente como antenas ressoadoras de ferritas (FRAs) e de microlinha (filmes espessos depositados sobre a superfÃcie metalizada de um substrato de alumina, pela tÃcnica âscreen printingâ), na faixa de operaÃÃo das microondas. Os experimentos com os FRAs se mostraram satisfatÃrios devido ao controle das caracterÃsticas de radiaÃÃo das antenas e a sua sintonizaÃÃo pela aplicaÃÃo de um campo magnÃtico externo. As mesmas tiveram a caracterÃstica de antenas de banda larga. Os ressoadores provenientes dos compÃsitos projetados neste trabalho podem ser importantes para desenvolver uma antena de banda larga de terceira geraÃÃo (3G) para telefones celulares e outros produtos para redes sem fio.
Devido ao rÃpido progresso no desenvolvimento de sistemas de comunicaÃÃo em microondas, as cerÃmicas dielÃtricas e magnÃticas (ferritas) se tornaram atrativas para o uso em dispositivos. Embora as ferritas do tipo espinel terem sido os primeiros materiais utilizados para microondas, as granadas possuem menores perdas dielÃtricas e, portanto, sÃo preferidas em muitas aplicaÃÃes. As elevadas exigÃncias que as aplicaÃÃes elÃtricas modernas requerem dos materiais magnÃticos fazem com que novas tÃcnicas e produtos estejam permanentemente sendo pesquisados, com o conseqÃente aparecimento de novas soluÃÃes para uma ampla sÃrie de aplicaÃÃes. Nesse sentido, a pesquisa sobre compÃsitos à empregada para a busca de novos materiais. Este trabalho apresenta a obtenÃÃo do compÃsito ferrimagnÃtico, constituÃdo pelas fases Y3Fe5O12 (YIG) e Gd3Fe5O12 (GdIG), atravÃs da rota sintÃtica no estado sÃlido com a utilizaÃÃo de moagem mecÃnica de alta energia. A DifraÃÃo de Raios-X, a Espectroscopia Raman, Infravermelho e MÃssbauer foram essenciais para caracterizaÃÃo estrutural dos compÃsitos. As peculiaridades da morfologia das amostras foram elucidadas pela Microscopia EletrÃnica de Varredura e Microdureza de Vickers. Adicionalmente, foram realizados experimentos para se avaliar o comportamento elÃtrico e magnÃtico dos compÃsitos na faixa de radio freqÃÃncia e de microondas para depois sugerir uma aplicaÃÃo tecnolÃgica cabÃvel. Os compÃsitos comportaram-se adequadamente como antenas ressoadoras de ferritas (FRAs) e de microlinha (filmes espessos depositados sobre a superfÃcie metalizada de um substrato de alumina, pela tÃcnica âscreen printingâ), na faixa de operaÃÃo das microondas. Os experimentos com os FRAs se mostraram satisfatÃrios devido ao controle das caracterÃsticas de radiaÃÃo das antenas e a sua sintonizaÃÃo pela aplicaÃÃo de um campo magnÃtico externo. As mesmas tiveram a caracterÃstica de antenas de banda larga. Os ressoadores provenientes dos compÃsitos projetados neste trabalho podem ser importantes para desenvolver uma antena de banda larga de terceira geraÃÃo (3G) para telefones celulares e outros produtos para redes sem fio.
Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. In this sense, the research in composites is employed to reach new materials. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. The X-Ray Diffraction and the Raman, Infrared and MÃssbauer Spectroscopy were essential for the structural characterization of the composites. The peculiarities in the morphology of the samples were elucidated by Scanning Electron Microscopy and Vickers Microhardness. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screen-printing technique), in the microwave frequency range. The experiments with FRAs showed satisfactory due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. They present a wideband antenna profile. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.
Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. In this sense, the research in composites is employed to reach new materials. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. The X-Ray Diffraction and the Raman, Infrared and MÃssbauer Spectroscopy were essential for the structural characterization of the composites. The peculiarities in the morphology of the samples were elucidated by Scanning Electron Microscopy and Vickers Microhardness. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screenprinting technique), in the microwave frequency range. The experiments with FRAs showed satisfactory due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. They present a wideband antenna profile. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.

This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.

To date, the search efforts have shifted from the toxic II-VI, III-V and IV-VI semiconductors to more environmentally friendly materials. Among Group II-V semiconductors, Zn3P2 has shown to be a more benign option, similar to Group IV (Ge, Si) materials, for future applications in photovoltaics and optoelectronics. This work is dedicated to the development of wet-chemical synthetic routes of (1) Zn3P2 and (2) Group IV (Ge, Si, Si1-xGex) nanocrystals with precise control over composition, crystal structure, size and dispersity by adjusting different reaction parameters such as temperature, time and solvent composition. Different characterizations will also be employed to probe the size- and composition-dependent physical and optical properties of resulting products. The first part of this work illustrates the synthesis of luminescent Zn3P2 nanocrystals, an earth-abundant and a direct-gap semiconductor possessing high absorption coefficient and long carrier diffusion length, which uphold promising potential in many optoelectronic applications. A hot injection method by using highly reactive P and Zn precursors (P[Si(CH3)3]3 and diethyl zinc) in hexadecylamine and octadecene was developed to prepare a series of alkyl-amine-passivated tetragonal Zn3P2 crystallites with varying size sizes. Substantial blue shifts in the absorption onsets (2.11−2.73 eV) in comparison to the bulk counterpart (1.4−1.5 eV) and a clear red shift with increasing particle size indicates the quantum confinement effects. This is also consistent with the photoluminescent studies with the size-tunable maxima in the visible region (469−545 nm) as a function of growth temperature and time. The phase purity and alkyl-amine passivation of the nanocrystals were determined by structural and surface analysis, confirming the presence of N–Zn and N–P bonds on the tetragonal Zn3P2 crystallites. The second part of this works focuses on the development of a colloidal synthetic strategy of alkyl-amine capped Si1-xGex nanocrystals with control over size- and composition-dependent optical properties. Despite their high miscibility at all compositions, developing a wet-chemical synthesis of Si1-xGex alloys in the nanoscale remains a challenging task, owing to the difference of their crystallization temperatures and the high surface oxidation of Si. Thus an adapted colloidal method is utilized to fabricate single-element Ge and Si nanocrystals. Powder X-ray diffraction indicates successful production of cubic crystalline Ge and amorphous Si nanoparticles individually in oleylamine/octadecene (surfactant/solvent) mixture at 300°C. Absorption onset values of 1.28 eV and 3.11 eV are obtained for resulting Ge and Si colloids, respectively. By alloying these two materials in their nano-regime, tunable optical properties can be achieved throughout the visible to the near IR region by simply varying their elemental compositions. The success of this bandgap engineering process offers more options for new material design by taking advantage of unique properties from each component material.

Un inconvenient de les energies renovables, a part del cost d’inversió inicial el qual està decreixent, és la necessitat de bateries tèrmiques. L’emmagatzematge d’energia tèrmica és fonamental per quadrar la producció i la demanda, i així proporcionar fred o calor (energia tèrmica) als consumidors quan així ho requereixin, independentment de quan ha estat obtinguda. Hi ha diverses maneres de fer-ho, la més comuna és un tanc d’aigua. No obstant, hi ha maneres més compactes i eficients, com ara els materials de canvi de fase (PCM) i els materials termoquímics (TCM). És per això, que l’objectiu de la present tesis és contribuir a la caracterització de PCM des d’un punt de vista de les tècniques d’anàlisi tèrmica, estabilitat fisicoquímica i morfològica, així com investigar experimentalment sobre la ciclabilitat tèrmica dels sucres-alcohols. Pel que fa als materials termoquímics l’objectiu és dur a terme un estat de l’art dels reactors utilitzats, així com aprofundir en els requeriments quan es procedeix a elegir un TCM. A més a més, també és presenten els resultats de tests de corrosió sota diferents atmosferes, simulant els reactors, i nous materials desenvolupats, basats en grafit, per millorar la transferència de calor.
Uno de los inconvenientes de las energías renovables, a parte de la inversión inicial la cual está disminuyendo, es la necesidad de baterías térmicas. El almacenamiento de energía térmica es fundamental para hacer coincidir la producción y la demanda, para así proporcionar energía térmica cuando sea requerida por los inquilinos, independientemente de cuándo ésta ha sido obtenida. Existen diferentes maneras de hacerlo, la más común el agua. No obstante, hay maneras más eficientes y compactas, como los materiales de cambio de fase (PCM) y los materiales termoquímicos (TCM). Es por eso, que el objectivo de la tesi es contribuir a la caracterización de los PCM desde un punto de vista de las técnicas de análisis térmico, estabilidad fisicoquímica y morfológica, así como investigar experimentalmente sobre la ciclabilidad térmica de los azúcares-alcoholes. En relación a los TCM, el objetivo es llevar a cabo un estado del arte de los reactores utilizados, así como profundizar sobre los requerimientos para la elección de un TCM. Asimismo, se presentan resultados de ensayos de corrosión bajo diferentes atmósferas y materiales desarrollados en base a grafito para la mejora de la transferencia de calor.
A resulting drawback of renewable energies use, besides the investment cost which is actually decreasing, is the need of thermal batteries. Thermal energy storage is essential to match production and demand, and therefore to provide heat or cold to the consumers when required independently of when it was obtained. Several ways exist to fulfil this requirement in buildings, the most common one is a water tank. But there are more compact and efficient ways, such as phase change materials (PCM) and thermochemical materials (TCM) storage. These materials need to be properly characterized and their thermophysical properties perfectly known in order to design the most appropriate and optimum system for heating, cooling and domestic hot water applications in dwellings.Therefore, the main objective of this thesis is to contribute on PCM characterization from a material thermal analysis, physicochemical stability and morphological point of view, and experimentally investigate on thermal cycling stability of sugar-alcohols. Then, on TCM side the aim is to provide an overview among TCM available reactors and requirements to choose the suitable storage material. Moreover, corrosion tests under different atmospheres and enhancement of heat transfer by developing graphite based composites are performed and shown in detail in this thesis.

Assessing hazards due to energetic or reactive chemicals is a challenging and complicated task and has received considerable attention from industry and regulatory bodies. Thermal analysis techniques, such as Differential Scanning Calorimeter (DSC), are commonly employed to evaluate reactivity hazards. A simple classification based on energy of reaction (-H), a thermodynamic parameter, and onset temperature (To), a kinetic parameter, is proposed with the aim of recognizing more hazardous compositions. The utility of other DSC parameters in predicting explosive properties is discussed. Calorimetric measurements to determine reactivity can be resource consuming, so computational methods to predict reactivity hazards present an attractive option. Molecular modeling techniques were employed to gain information at the molecular scale to predict calorimetric data. Molecular descriptors, calculated at density functional level of theory, were correlated with DSC data for mono nitro compounds applying Quantitative Structure Property Relationships (QSPR) and yielded reasonable predictions. Such correlations can be incorporated into a software program for apriori prediction of potential reactivity hazards. Estimations of potential hazards can greatly help to focus attention on more hazardous substances, such as hydroxylamine (HA), which was involved in two major industrial incidents in the past four years. A detailed discussion of HA investigation is presented.

 

Organic semiconductors are prime candidates for thermoelectric applications, because one can maximize the dimensionless figure of merit ZT (by maximizing the Seebeck coefficient and electrical conductivity) while simultaneously minimizing the thermal conductivity. In this work, we explore a few materials and try to find their thermoelectric characteristics. For the n-leg of the thermogenerator, we studied a modified fullerene (PCBM) which is doped with TDAE vapor. For the p-leg, we studied PEDOT and found the TDAE dedoping level at which the figure of merit is maximized.

The advancement of photonics technologies depends on synthesis of novel materials and processes for device fabrication. The characterization techniques of the optical, electrical and magnetic properties of the synthesized materials and devices, by non-contact, non-invasive and nondestructive methods plays a significant role in development of new photonics technologies. The research reported in this thesis focuses on two such aspects of photonic materials characterization: Magneto-Optic characterization and Spectroscopic Ellipsometry. The theoretical and experimental basis of these two techniques, and experimental data analysis are presented in two parts. In Part 1, the changes in magneto-optic parameters of FePT PS-P2VP block copolymer nanocomposites with increasing concentrations of FePt nanoparticles in the block copolymer are analyzed. We present the results of change in MO anisotropy factor with the wt% of FePt and try to analyze these changes with further experimentation. Part 2 presents the results of spectroscopic ellipsometry of group III-IV multilayered thin film materials to give their precise thicknesses and optical constants. Both these techniques are unique ways to understand novel material characteristics for future use in device development.

The development of a versatile system capable of providing rapid, portable, and inexpensive detection of explosives and energetic compounds is needed critically to offer an enhanced level of protection against current and future threats to homeland security, as well as to satisfy a wide range of applications in the fields of forensic analysis, emergency response, and industrial hazards analysis. The hand-held nanocalorimeter will serve as a first-of-its-kind screening tools for explosive and energetic compounds directly in the settings where they are needed with high efficiency, reduced cost, and simplicity with ease of use. Unlike current explosives detectors, this system is based on calorimetric techniques that are inherently capable of providing direct measurements of energy release potential and therefore do not depend on prior knowledge of familiar compounds. The microfabricated calorimetry instrument consists of (i) a thermal control module incorporating arrays of microfabricated heaters and temperature sensors, as well as any necessary electronic interconnections, and (ii) a sample encapsulation module incorporating etched enclosures designed to accommodate either solid or liquid samples. Initial work has led to successful fabrication of a chip capable of sampling nano-sized solid or liquid compounds. Control algorithms incorporating the DSC principle have also been written using LabVIEW. Device performance of the original and redesigned chips were tested by studying the thermal transitions associated with the boiling points of acetone and pentane. With the redesigned chip, the heat loss issue was reduced: the measured input heat was reduced from 32 times of the required energy to 5 times of the required energy. Future work will focus on modifying the chip design and control algorithm to improve accuracy and sensitivity, developing a trace analysis software to link it to a database of explosive information, and adapting different fabrication procedures for high temperature operation and large scale production.

Vibrational and thermal behavior of several important systems were studied. The first study was a measurement of the infrared vibrational spectra of glucose and two important glucose dimers (cellobiose and maltose) as a function of temperature. The purpose of his study was to measure shifts in vibrational band positions to gain insight into carbohydrate reactivity. The second study was on hydrothermally treated coffee waste biomass. Here, collaborators at University of Campinas (UNICAMP, Brazil) treated coffee waste biomass in a flow-through subcritical water hydrolysis reactor. The purpose of the M.S. study on coffee waste was to understand the chemical changes that occurred to the residual solids during hydrolysis treatment. Vibrational spectroscopy and thermal analysis techniques were used. The third and final study was to understand the chemical composition of the solid product resulting from co-solvent enhanced lignin fractionation (CELF) of several biomass feeds. Collaborators at University of California Riverside (UCR) recently developed the CELF process. The purpose of the M.S. study on the CELF solid product was to understand its composition to help guide the CELF reactor design and determine applications for the CELF solids. Taken together, the 3 studies are integrated into a cohesive whole that demonstrates the use of spectroscopic and thermal techniques for characterizing biomass and understanding its composition at the molecular level.

Nowadays, material, energy and information technologies are three pillar industries. The materials that have close relation with our life have also been the foundation for the development of energy and information technologies. As the new member of the material family, functional molecular materials have become increasingly important for many applications, for which the design and characterization by the theoretical modeling have played the vital role. In this thesis, three different categories of functional molecular materials, the endohedral fullerenes, the fullerene derivatives and the self-assembled monolayers (SAMs), have been studied by means of first principles methods. The non-metal endohedral fullerene N@C60 is a special endohedral fullerene that is believed to be relevant to the construction of future quantum computer. The energy landscape inside the N@C60 has been carefully explored by density functional theory (DFT) calculations. The most energy favorable potential energysurfaces (PESs) for the N atom to move within the cavity have been identified. The effect of the charging on the PESs has also been examined. It is found that the inclusion of dispersion force is essential in determining the equilibriumstructure of N@C60. Furthermore, the performance of several commonly useddensity functionals with or without dispersion correction has been verified for ten different endohedral fullerenes A@C60 with the atom A being either reactive nonmetal or nobel gases elements. It shows that the inclusion of the dispersion forcedoes provide better description for the binding energy (BE), however, none ofthem could correctly describe the energy landscape inside all the ten endohedral fullerenes exclusively. It thus calls for the further improvement of current density functionals for weak interacting systems. Soft X-ray spectroscopy is a powerful tool for studying the chemical and electronic structures of functional molecular materials. Theoretical calculations have been proven to be extremely useful for providing correct assignments for spectraof large systems. In this thesis, we have performed first principles simulations forthe near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectra (XPS) of fullerene derivatives and aminothiolates SAMs. Our calculatedspectra can accurately reproduce experimental results available for all the systemsunder investigations, and identify the species or structures that are responsible for those unexpected spectral features observed in experiments. We have suggested a modified building block (MBB) approach that allows to calculate NEXAFS spectraof a large number of fullerene derivatives with very small computational cost, and resolved the long standing puzzle around the experimental XPS and NEXAFS spectra of SAMs with aminothiolates.

QC 20120523

Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains vii, 62 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 61-62).

Thesis (M.S.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 30, 1981) Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xiv, 148 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 122-129).

Thesis (Ph. D.)--Missouri University of Science and Technology and University of Missouri--St. Louis, 2008.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 28, 2008) Thesis completed as part of a cooperative degree program with Missouri University of Science & Technology and the University of Missouri--St. Louis. Includes bibliographical references (p. 129-142).

This thesis describes a method for using stripline resonators to characterize the electrical properties of materials used in the construction of planar geometry transmission lines and circuits. The method characterizes both dielectric and conductor materials. It can be used to find the relative dielectric constant and to separate the conductor and dielectric losses. The separation of the loss terms is achieved by fitting measurements of stripline losses to a well known model. This model identifies the loss terms separately based on variation of the losses with stripline dimensions.

This thesis presents the complete stripline resonator model used. The model has been incorporated into a computer simulation which predicts the resonator response. This simulation is useful in many ways, including the design of various resonators needed in experiments. Also presented are the results of an experiment which demonstrates the feasibility of this method when applied to real samples. These results show that this method works well for low loss materials.

Further development may produce 6 model which will allow this method to be used on higher loss materials. A similar theoretical derivation may be used to develop a model for using this method with other transmission line structures such as coaxial lines. This method is advantageous because it does not assume that material properties are independent of frequency and can be designed to produce results at a specific frequency. Stripline resonators are easily manufactured and a network analyzer is the only test equipment required. For these reasons, this method can be used to provide accurate results at a low cost.

Master of Science

In this dissertation, the studies aim to characterize the electronic structure at the internal interface of hybrid materials. The characterization challenge is originating from the spectral superposition of hybrid constituents. A characterization protocol based on photoemission spectroscopy (PES) was developed and applied to investigate the orbital alignment at the internal interface of the oligothiophene-TiO2 and ArS-CdSe hybrid materials by characterizing the individual constituents and the assembly hybrids respectively. Electrospray deposition technique was used to deposit targeting materials which enabled preparation of thin films in vacuum minimizing ambient contaminations while transmission electron microscopy (TEM) was used to investigate the morphology and the particle size of the pure nanoparticles and the hybrids. Ultraviolet-visible (UV-vis) spectroscopy was also used in the estimation of the optical band gap of the pure nanoparticles and the HOMO-LUMO gap of the organic ligands. One of the hybrid materials studied in this dissertation is oligothiophene-TiO2 nanoparticle hybrids in which the oligothiophene ligands are bonded to the surface of TiO2 nanoparticles covalently. This hybrid system was used to develop and demonstrate a measurement protocol to characterize the orbital alignment at the internal interface. Low intensity X-ray photoemission spectroscopy (LIXPS) was used to determine the work function of the oligothiophene ligands and the TiO2 nanoparticles. In combination with the highest occupied molecular orbital (HOMO) cutoff and the valence band maximum (VBM) measured by ultraviolet photoemission spectroscopy (UPS), the ionization energies (IE) of these two constituents were determined. X-ray photoemission spectroscopy (XPS) was used to characterize the core level emissions of the constituents and the hybrid assembly, which were used to determine the charge injection barriers at the internal interface. The results showed that there was an interface dipole at the internal interface between organic and inorganic constituents of the hybrid. The dipole was determined to be 0.61 eV and the hole injection barrier at the internal interface amounted to 0.73 eV. The electron injection barrier was estimated by taking into account the gap between highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO). The procedure followed only suggested the presence of an insignificant barrier in the oligothiophene-TiO2 nanoparticle hybrids. Arylthiol functionalized Cadmium Selenide (ArS-CdSe) is a novel hybrid material which can be used in hetero-junction solar cells. The ArSH ligands are bonded on the surface of the CdSe nanoparticles covalently through sulfur atoms serving as anchors. The internal interface in the ArS-CdSe hybrids between the organic constituent and the inorganic constituent was studied by the same characterization protocol developed in this dissertation. Furthermore, a physisorbed interface between the ArSH ligands and the CdSe nanoparticles was created through multi-step in-vacuum deposition procedure. The electrospray deposition technique enabled the formation of a well-defined physisorbed interface which was characterized by LIXPS, UPS and XPS for each deposition step. Accordingly, the orbital alignment at the physisorbed interface was determined. Based on the results obtained, detailed orbital alignments at the ArSH/CdSe physisorbed interface and the internal interface in the ArS-CdSe hybrid materials were delineated and discussed. The hole injection and electron injection barrier at the physisorbed ArSH/CdSe interface are 0.7 eV and 1.0 eV respectively. An interface dipole of 0.4 eV was observed at the interface. In the ArS-CdSe hybrid materials, the electronic system of the ArSH component shifts down due to the charge transfer induced by the covalent hybridization. The hybridization also shifts the electronic system of the CdSe constituent to a lower energy level due to saturation of the unoccupied bonds of the Cd atoms on the surface. The hole injection barrier and electron injection barrier were determined to be 0.5 eV and 1.2 eV respectively. A small interface dipole (0.2 eV) was observed at the internal interface as a result of the presence of covalent bonds.

Multiferroic materials, in which two or more ferroic ordering take place in the same phase, have driven major interest in the last few years, not only due to the possibility of exploring novel physical properties in those materials, but also the implications that such properties show in novel technological applications. From those materials, the especially interesting are those in which the ferromagnetic (FM) and ferroelectric (FE) ordering take place, due to their direct application in magnetodielectric devices. In the field of multiferroic materials such materials could play an important role in a new generation of none volatile magnetic random access memories (M RAM), in which a sufficiently strong magnetodielectric coupling could allow for the modification of the magnetic state, not only with a magnetic field, but with an electric field. This fact would allow for a dramatic reduction in energy consumption and would promote the further technological integration (the major commercial drawback of MRAMs), due to the fact that an electric field, contrary to the magnetic field, can be applied locally. Additionally, such multiferroic materials could prove useful in magnetic tunnel junctions, in which the ferroelectric and ferromagnetic nature would allow them to codify four resistive states, instead of the traditional two states of ferroelectric or ferromagnetic junctions, allowing for the implementation of a generation of four state memories. The materials with perovskite structure, ABB"03 (A=Rare Earth, Bismuth, Lead and Yttrium), bring a broad spectrum of possibilities when it comes to design of multifunctional materials. This is due to the wide variety of A, B, B" cations that are compatible with such structure. However, in the case of R(NiMn)03, such oxides have been poorly studied and many detailed studies, both in bulk and thin films are needed. The cation selection of B and B' seems to transform the paramagnetic ordering (PM) into FM below room temperature. The multiferroicity of these materials is typically provided by the A cation of the perovskite formula, which can be Bi or Pd, in order to create a Type 1 multiferroic. In this type of materials, i.e: Bi2NiM n06, the ferroelectricity and ferromagnetism arose by separate mechanisms, the FE is provided by the A cation, with so called long pair electrons, which are free electrons in the valence band that do not participate in any chemical reaction in the compound, while the Ni2+(d8) and (M n4+) (d3) provides the FM. However, even though the materials are multiferroic, their magnetodielectric coupling, crucial for future industrial applications, is weak, due to the different mechanisms that provide their FM and FE ordering. On the other hand, the FE induction by geometrical distortion of the perovskite lattice, for example in YM n03, is an interesting case since rotations of the M nO6 octahedrons promote an important structural change, in which the oxygen atoms move closer to the Y and, due to a large dipole interaction, generate a stable FE state. Moreover, the deformation of the unit cell generates a weak spin canting on the Mn cations, that can be promoted by Li doping or lattice distortions. This behavior could prove useful in the R(NiM n)06 family, which shows strong FM . This thesis is devoted to the study of R(Ni0.5M n0.5)03 (Y,Sm, Nd and Pr) and Bi(Fe0.5M n0.5)06 grown in thin films by pulsed laser deposition technique. Firstly, this thesis focuses on the growth and characterization of thin films of Y(Ni0.5M n0.5)03 (YNM 0) on strontium titanate substrates SrTiO3(001) (STO). The influence of the deposition parameters, such as temperature, fluence and ablation frequency, on the morphology and crystalline quality of the films is investigated. The study reveals that the YNMO films grown on STO(001,011 and 111) substrates are epitaxial and that their crystalline quality and epitaxial relationship are similar to those of the YMO compound. In particular, it is observed that a single out of plane domain is the norm for all the substrate orientations, while there are various in-plane domains. Moreover, chemical composition studies reveal Ti diffusion from the substrate to the YNMO film when STO(111) substrates are used. Once the growth conditions of YNMO are optimized, the magnetic and dielectric properties are studied. All the films show a paramagnetic to ferromagnetic transition at a temperature around 95K, with a magnetic moment of YNMO(001) = 4.35µB/f.u, YNMO(100) = 4,4 µB/f.u and YNMO(101) = 3,7µB/f.u, confirming the ferromagnetic nature of the samples. The dielectric characterization reveal a FE ordering on the YNMO films, and what is more, the existence of a dielectric anisotropy on the films, that is characterized by the absence of ferroelectric response on YNMO samples deposited on STO(001), while YNMO samples on STO(111) show a strong FE response. This anisotropy could be explained, according to recent theoretical studies, in the improper origin of the observed ferroelectriciy. The coexistence of FM and FE response shows in a conclusive manner the multiferroic nature of the YNMO compound. Secondly, studies similar to those previously presented are performed for thin films of R(Ni0.5Mn0.5)O3 (Sm, Nd and Pr) compounds grown on STO(001). In this case the deposition temperature turns out to play a crucial role on the epitaxial growth of all the studied compounds. It is shown that the ratio between the b/a lattice parameters influences the epitaxial growth of the films, being the decisive factor between single or multi domain films. All the samples show a PM to FM transition at temperatures around 190K Finally, films of Bi(Fe0.5Mn0.5)O6 have been grown on STO(001) substrates. The films are epitaxial and grow under epitaxial strain. Samples show a FM behavior at room temperature with a weak signal of 7,42 emu/cm3 and 0,4 µB/f.u(Fe-Mn). The dielectrical characterization shows the influence of external magnetic fields on the dielectric properties of the film above room temperature.
Los materiales multiferroicos, en los que dos o más ordenes ferroicos tienen lugar en la misma fase, ha despertado gran interés en los últimos años debido, no solo al hecho de explorar nuevas propiedades físicas en los materiales, sino también a las implicaciones de las nuevas propiedades funcionales en las aplicaciones tecnológicas. De dichos materiales resultan especialmente interesantes aquellos que presentan un orden ferroeléctrico (FE) y ferromagnético (FM) debido a su aplicación directa en dispositivos magnetoelectrónicos. En este ámbito los materiales multiferroicos podrían tener una gran relevancia en una nueva generación de memorias magnéticas RAM (MRAM) de control eléctrico, no volátiles, en las que, si el acoplamiento magnetoeléctrico es suficientemente grande, se podría modificar el estado magnético no con un campo magnético sino con un campo eléctrico. Este hecho permitiría una reducción radical en el consumo de potencia y favorecería a su vez una mayor integración (la principal desventaja de las MRAMs para competir en el mercado), ya que el campo eléctrico, a diferencia del campo magnético, puede aplicarse de forma muy localizada. Por otro lado, dichos materiales multiferroicos podrían emplearse en una nueva generación de uniones túnel, en las que el carácter ferroeléctrico y ferromagnético permitiría codificar información en cuatro estados resistivos en lugar de en dos, como viene siendo hasta ahora en las convencionales uniones túnel magnéticas o ferroeléctricas, dando lugar a una nueva generación de memorias de cuatro estados. Los materiales con estructura perovskita, ABB '03, (A=Tierra Rara, Bismuto, Plomo e Ytrio) ofrecen una gran versatilidad a la hora de diseñar materiales funcionales debido a la gran variedad de cationes A, B y B' compatibles con tal estructura. Sin embargo en el caso de R(NiMn)03, estos óxidos han sido poco estudiados y muchos carecen de estudios detallados tanto en forma másica como en capa fina. Esta selección de cationes en la posición B y B' parece transformar la estructura perovskita la cual típicamente presenta un ordenamiento paramagnético (PM) en FM a temperaturas inferiores a la ambiente. El carácter multiferroico de estos materiales es típicamente aportado por el catión A en la formula perovskita, el cual puede ser un átomo de Bi, o Pb, para crear un multiferroico tipo 1. En los materiales de este tipo, por ejemplo el Bi2NiMnO6, la ferroelectricidad y el ferromagnetismo provienen de fuentes diferentes, el carácter FE es aportado por el catión A con -lone pairs electrons-, los cuales son electrones libres en la banda de valencia que no participan en las reacciones químicas del compuesto, mientras la combinación Ni2+ (d8) and Mn4+ (d3) aporta el FM. Pese al carácter multiferroico de estos materiales su acoplamiento magnetoelectrico, indispensable para sus aplicaciones industriales futuras, es débil, puesto que su FE y FM provienen de efectos independientes. Por otra parte la inducción de FE por distorsiones geométricas de la celda perovskitas, como es el caso de YMnO3 (YMO), es un caso interesante de considerar ya que la rotación de los octaedros Mn05 genera un cambio estructural importante, en el cual los oxígenos se desplazan a una posición más cercana al Y, esto sumado a una larga interacción de los dipolos conduce al material a un estado FE estable. Además la deformación de la celda genera un débil FM en este material, el cual proviene un pequeño giro en los espines del Mn ya sea debido a un dopaje con Li o por la deformación de la celda. Este comportamiento podría resultar interesante en la familia de perovskitas R(NiMn)03 las cuales presentan un fuerte FM. Esta tesis está dedicada al estudio de la perovskitas R(Ni0.5Mn0.5)O3 (Y, Sm, Nd y Pr) y Bi(Fe0.5Mn0.5)O6 crecidas en capa fina usando la técnica de depósito mediante ablación por láser pulsado. En primer lugar, esta tesis se centra en el crecimiento y caracterización de capas finas del compuesto Y(Ni0.5Mn0.5)O3 (YNMO) sobre substratos de titanato de estroncio, SrTiO3(001) (STO). Se estudia la influencia de los parámetros de depósito tales como temperatura, fluencia y frecuencia de ablación sobre la morfología y la calidad cristalina de las capas obtenidas. El estudio pone de manifiesto que las capas de YNMO crecidas sobre substratos de STO(001,011 y 111) son epitaxiales de YNMO y que la calidad cristalina y las relaciones epitaxiales entre la capa y el substrato son semejantes a las obtenidas en el compuesto YMO. En particular se observa un único dominio cristalino fuera del plano independientemente de la orientación del sustrato, mientras que dentro del plano se presentan varios dominios cristalinos. Por otra parte, los estudios de composición química revelan una difusión de Ti desde el sustrato hacía la capa de YMNO cuando se utilizan substratos STO(111).. Una vez optimizadas las condiciones de crecimiento del compuesto YNMO, se estudian sus propiedades magnéticas y dieléctricas. Todas las capas presentan una transición de fase paramagnetica a ferromagnética a una temperatura alrededor de 95K con un momento magnético de YNMO(001)= 4.35µB/f.u, YNMO(100) = 4,4 µB/f.u and YNMO(101) = 3,7µB/f.u, confirmando el carácter ferromagnético de las muestras. La caracterización dieléctrica revela el carácter FE de las capas de YNMO y lo que es más interesante, la existencia de anisotropía dieléctrica en las capas, ésta se pone de manifiesto en la ausencia de respuesta FE en capas YNMO sobre STO(001) que contrasta con la fuerte respuesta de las capas de YNMO sobre STO(111). Esta anisotropía puede tener su origen, a la luz de los recientes estudios teóricos, en el carácter impropio de la ferroelectricidad observada, a la luz de recientes estudios teóricos. La coexistencia de FM y FE muestra de manera conclusiva el carácter multiferroico del compuesto YNMO. En segundo lugar se han realizado estudios similares a los anteriores para el caso de capas finas de los compuestos del tipo R(Ni0.5Mn0.5)O3 (Sm, Nd y Pr) crecidas en STO(001). En este caso la influencia de la temperatura de depósito resulta ser un factor importante para la obtención, en todos los compuestos estudiados, de crecimiento epitaxial. Se observa que el cociente b/a entre las constantes red juega un factor importante en la epitaxia de las capas, siendo este cociente un factor determinante en el crecimiento mono-dominio o multi-dominio de las capas. Todas las muestras presentan transiciones PM a FM a temperaturas alrededor de 190K. Por último, se han crecido y estudiado capas finas del compuesto Bi(Fe0.5Mn0.5)O6 depositadas sobre STO(001). Las capas obtenidas son epitaxiales y crecen sometidas a estrés inducido por el substrato. Presentan comportamiento FM a temperatura ambiente pero con una débil señal de 7,42 emu/cm3 y 0,4 µB/f.u(Fe-Mn). La caracterización dieléctrica pone de manifiesto la influencia, a temperaturas superiores a la ambiente, de la presencia de campo magnético sobre las propiedades dieléctricas.

Planar optical waveguides fabricated by K$ sp+$-Na$ sp+$ ion-exchange in soda-lime glass substrates are investigated.
Experimental characterizations of planar waveguide with respect to a wide range of fabrication conditions have been carried out, including detailed measurements of the refractive index anisotropy resulting from the large induced surface stresses.
Parallel to this, the non-linear diffusion process of ion-exchange was simulated numerically to provide, along with the results of the characterizations, a complete description of the refractive index profile from any set of fabrication conditions.
The magnitude of the maximum surface index change observed was shown theoretically to be almost entirely due to the induced stress at the surface of the substrate, arising from the presence of the larger potassium ions.
Finally, a novel class of single-mode channel waveguides, made by a "two-step" ion-exchange was analyzed. A simple model for these waveguides was developed and used in the design of two directional coupler structures which were fabricated and measured.
The two-step process was conceived because it relaxes waveguides' dimensional control, yielding single-mode guides of larger size, better suited for low-loss connections to optical fibers. It also provides an additional degree of freedom to adjust device properties.

博士
國立交通大學
電子物理系
91
We have grown the hexagonal and cubic GaN by using our homemade atmospheric metalorganic vapor phase epitaxy system (AP-MOVPE). The characteristics of these samples were investigated by using X-ray measurements, Hall measurements, photoluminescence, and Raman scattering. The spatial correlation modal of Raman scattering was adopted to analyze the asymmetric broadening of Raman modes. At the beginning, we tried to optimize the growth parameters of undoped GaN on sapphire, such as, buffer layer thickness, growth temperature, V/III ratio, nitridation, N2/H2 carrier gas mixing ratio, etc. For the cubic GaN growth, we tried to grow GaN on GaAs (001) substrate at different temperature. We found co-existing of hexagonal and cubic phase in the samples. To investigate the As incorporation effect in GaN, we introduced the TBA (tertiarybutylarsnie) into the reactor when preparing GaN samples at different growth temperature or different flow rate. The lightly As-doped GaN grown at the temperature of 900oC~1000oC showed better quality than undoped GaN. At 700oC~800oC, we obtained GaAsxN1-x with As content of ~0.7%. For the study of As diffusion effect in GaN, we tried to anneal the GaN samples with thin GaAs interlayer. The intensity of characteristic green-line emission around 500 nm in the PL spectra increased with annealing temperature. However, the green emission disappeared because the annealing temperature of 1000 oC was too high.

碩士
國立臺北科技大學
材料科學與工程研究所
97
The thesis reports that a technology has been developed to coating Al2O3 powders with PMMA polymer to form ceramic-polymer composite for denture application γ-MPS was used as coupling agent to form and strengthen a chemical bond between PMMA polymer(organic) and Al2O3 powders(inorganic). To create an alkaline condition, ethyl alcohol was first added; then, γ-MPS reacted with Al2O3 to form a bond. after the condensation reaction, Free radical initiator and MMA were added into above material in sequence, so that the surface of Al2O3 powders was able to be successfully coated with uniform PMMA. A uniform film of PMMA polymer coated on Al2O3 powders was observed under the Transmission Electron Microscopy(TEM).The test specimens formed by the polymer coated Al2O3 powders had higher strength after being tested by three-point bending test. In addition, the lost quantity of polymers was almost the same as what we had added in (γ-MPS and PMMA) via the TGA.by the analysis of the FTIR.the C=O peak showed that the surface of coated Al2O3 had a chemical shift, and its surface potential was different from the uncoated one under the measurement of Zeta Potential meter. Based on the experimental results through a series of analyses,they show that the composite particles (coated Al2O3) would be a good material for future denture application.

碩士
大同大學
光電工程研究所
98
This thesis is mainly focused on carbon nano-materials. Two structures of carbon are discussed which are carbon nano-partitions (CNPs) and multi-walled carbon nanotubes (MWCNTs). In the first part of this thesis, we fabricated carbon flakes vertically standing on the substrate by radio frequency sputter. Then we measured the reflection and transmission in 250 to 850 nm of the wavelength on such CNPs array. We found that the CNP has good anti-reflection property. The average reflectance is 0.2% from one of our best sample in visible range. The lowest reflectance is 0.13% at 328 nm. This unique nano-material can be acted as a black body which is similar to the optical property with highly absorption of light by the sparse CNT. The detail optical characterization of anti-reflection verse different angles from such nano-material is also discussed. On the second part of this thesis, we measured the electrical property of the MWCNT. Our experiment show the rapid thermal annealed (RTA) multi-walled CNT can be imported. The post treated CNT exhibited higher conductance. As for control sample, the high density defects limited the carrier mobility which leads to the higher resistance. As experimental sample, the defects are nearly removed, so the carrier can achieve higher mobility. From the measurement of electrical conductance in different temperatures, the annealed CNT exhibited semiconductor characteristic. Higher temperature gives more excited carriers which leads to better conduction. Our results suggested that well-structured MWCNT can acts as a semiconductor which the carrier transport via outer shell of CNT and gives the electrical conductance via the 1D nano-channel.

The synthesis, structure and physical properties of a series of Mnx(Co, Mg)₁ˍxFe₂O₄, (Mg, Sr)₀.₂ Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ (where RE are rare earth elements) nanoferrites have been studied. These compounds were synthesized at low reaction temperature of about 200 ⁰C using the glycol-thermal method. The starting materials were high-purity metal chlorides or nitrates which were precipitated by NH₄OH and KOH respectively. In addition, MnxCo₁₋xFe₂O₄ (x = 0, 0.5 and 1) samples were produced directly from high-purity metal oxides by high-energy ball milling technique. Single-phase cubic spinel structure and nanoparticle structure of the synthesized samples were confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the produced powders of the asprepared samples have average grain sizes ranging from 7 to 16 nm. Filtering the precipitates by Whatman glass microfiber filters (GF/F) appears to be important in obtaining the small particle sizes. We suspect higher stability of the MnxCo₁₋xFe₂O₄ at x = 0 and 0.5 where complete symmetry in the proportion of the atoms on tetrahedral (A) and octahedral (B) sites would tend to favour larger nanoparticles. The evolutions of the magnetic properties as a function of composition, annealing temperature under air and argon atmospheres or measuring temperature have been investigated by ⁵⁷Fe Mössbauer spectroscopy, vibration sample magnetometer (VSM) and superconducting quantum interference device (SQUID). Significant changes in magnetic properties are observed across the composition ranges studied. The Mössbauer spectra indicate ferrimagnetic, superparamagnetic and paramagnetic behaviours of the compounds. The results show evidence of transformation from single-domain to multi-domain structure with thermal annealing in our samples. Temperature dependence of magnetization shows differences between field cooling (FC) and zero field cooling (ZFC) which we attribute to spin-freezing and thermal relaxation for typical nanoparticles. Significant increase in coercive field with reduction in measuring temperature is obtained in Co- based compounds. Mn₀.₅Co₀.₅Fe₂O₄, Sr₀.₂Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₂Mn₀.₁Co₀.₇Fe₂O₄ have large coercive fields of 1.45, 3.02 and 10.70 kOe at 4 K compared to 0.17, 0.05 and 0.05 kOe at room temperature respectively. Variation of coercive fields (Hc) with measuri ing temperature for MnxCo₁₋xFe₂O₄ (x = 0.1 and 0.05), (Mg, Sr)₀.₂Mn₀.₁Co₀.₇Fe₂O₄ nanoferrites follow the Kneller's law for uniaxial non-interacting single domain particles of the form Hc(T) = Hc(0)[1-( T/Tβ)α]. The observed temperature dependences are consistent with α = 1/2. We also find evidence of the departure from this law at lower temperature. The temperature dependence of the saturation magnetizations were observed to vary with temperature according to the modified Bloch's law Ms(T) = Ms(0)[1 - ( T/T₀)ᵝ] where β is at least 1.5. This is attributed to the confinement effects of the spin-wave spectrum for magnetic clusters. The equation appears to fit the saturation magnetization data over the entire temperature range with values of β from 2.1 to 2.4 for the samples studied. These results are consistent with the nanoparticle nature of the compounds. In Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ nanoferrites, the grain sizes, lattice parameters and saturation magnetizations increase with RE substitution which we attribute to larger RE ions substituting smaller Fe ions. The results show evidence of superparamagnetic behaviour of the nanoparticles. The highest grain size and magnetizations are obtained for the Gd substituted sample. We find strong correlation between the saturation magnetizations, grain sizes and microstrains with de Gennes factor G. The correlation with grain sizes and microstrains appear to be unique and characteristic of the nanoparticle nature of the compounds. Bulk samples in the form of pellets were also produced from the as-prepared samples of MnxCo₁₋xFe₂O₄ for resistivity measurements. The temperature dependence of the electrical resistivity for samples sintered from 600 - 1100 ⁰C under argon atmosphere were studied using the four-probe method from room temperature to about 110 ⁰C. Two possible mechanisms for resistivity involving Tˉ¹ and Tˉ¹/² dependences were investigated which we associated with semiconducting and inter-grain conductivity respectively. The Tˉ¹/² dependence is found to fit the data better and predicts higher activation energies. The resistivity was observed to be sensitive to the surface of the pellet being probed and the annealing temperature.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.

碩士
大同大學
光電工程研究所
88
We respectively study the current-voltage characteristics of AuGeNi contacts made on rapid-thermal annealed arsenic-ion-implanted S.I. GaAs (GaAs:As+) and Au contact made on S.I. GaN by using the measurements of TLM and I-V analysis. The key parameters such as leakage current, contact resistance, sheet resistance, specific contact resistivity, barrier height, breakdown voltage, saturation current, and photocurrent responsivity are primarily reported. For the GaAs:As+ materials, the mechanism responsible for the large dark current in the as-implanted GaAs:As+ is attributed to the hopping conduction of trapped carriers among the dense deep-level defects. After annealing, the defect density gradually reduces and the perfection of crystal lattice recovers. This results in the evanescence of the hopping conduction and the increasing resistance for GaAs:As+. The contact resistances are estimated to be ranged from 7.8x104 to 8x109 W as the annealing time increases from 0 to 300 seconds, respectively. The sheet resistances are increased from 2.4x104 to 2x1010 W/¨, and the specific contact resistances are increased from 13.8 to 1.6x105 W-cm2 as the annealing time increases. In comparison, the characteristic of the GaAs:As+ annealed for 5 minutes has the lower dark current. The current saturation and overshoot phenomenons in the conductivity of the GaAs:As+ diode are found. After annealing, the photocurrent tends to shift to lower applied voltage. The continuous-wave responsivity of the GaAs:As+ is measured to be 50 mA/W at bias of 30 volts. For the S.I GaN materials, the minumum leakage current of the diode with a 15-mm gap is about 55pA at bias of 1 volt, which is dramatically increased to 4 nA as the bias increases up to 10 volts. After alloying, the leakage current of the same device at bias of 10 volts further reduces to < 1 nA. The evaluated contact resistance, sheet resistance, and the specific contact resistances of the S.I. GaN diode biased at <10 volts are about 1.5´1010 W, 2.5x109 W/o, and 4.5x105 W-cm2 respectively, and are found to slightly increases after alloying. We find that the electrical characteristic of nearly S.I. GaN is similar to S.I. GaAs.

碩士
國立臺北科技大學
材料及資源工程系研究所
98
This study is based on the technology of Al2O3 powders coated with PMMA polymer to form ceramic-polymer composite. Al2O3 powders and MMA cannot form a chemical bonding, therefore, γ-MPS was used as coupling agent to form and strengthen a chemical bond between PMMA polymer(organic) and Al2O3 powders(inorganic). Organic-inorganic material is prepared in alkaline condition. First, Al2O3 powders and γ-MPS proceeded condensation reaction in the ethanol to form a chemical bonding. Then free radical initiator and MMA were added into above material in sequence, so that the surface of Al2O3 powders was able to be successfully coated with uniform PMMA. A uniform film was observed under the Transmission Electron Microscopy(TEM) to show that Al2O3 powders can be coated with a thin polymer film. By the analysis of the FTIR, the C=O peak showed that the surface of coated Al2O3 had a chemical shift. Its surface potential was different from the uncoated one under the measurement of Zeta Potential meter. The test specimens formed by the polymer coated Al2O3 powders had higher strength after being tested by three-point bending test. Based on the experimental results through a series of analyses, they show that the composite particles (coated Al2O3) would be a good material for future denture application.

碩士
輔仁大學
化學系
103
We have successfully synthesized the concentration-gradient cathode materials of LiNi0.95Co0.05O2 ((G)C5-LN), LiNi0.9Co0.1O2 ((G)C10-LN), LiNi0.8Co0.2O2 ((G)C20-LN) and LiNi0.81Co0.19O2 ((G)C10-LNC10) via a co-precipitation route. According to the analysis of physical, electrochemical, and thermal propeties, the concentration-gradient cathode material has a structure with different chemical compositions of primary particles from the surface toward core of each of the secondary particles. The primary particle with rich Co content on the surface and the primary particle with rich Ni content in the core of secondary particle of the concentration-gradient cathode materials have provided the advantages of high safety and high capacity. For the synthesis of (G)C10-LNC10, 10% mol. Co(OH)2 is uniformly coated on the surface of 90% mol. Ni0.9Co0.1(OH)2, and mixed with lithium hydroxide, then high temperature sintered. The mole ratio of Co in the core of (G)C10-LNC10 cathode material is at least 10% mol, and the mole ratio of Co on the surface of (G)C10-LNC10 cathode materia is higher than 25% mol.. The (G)C10-LNC10 has a better concentration-gradient structure, so it can provide the best electrochemical performences.