Academic literature on the topic 'Hexagonal crystal structure'

In this thesis, geometry is used as a basis for conducting experiments aimed at growing and arranging inorganic minerals on curved interfaces. Mineralisation is directed using crystalline and liquid-crystalline metallic soaps and surfactant/water systems as templates.¶ A review of the history, syntheses, structure and liquid crystallinity of metallic soaps and other amphiphiles is presented as a foundation to understanding the interfacial architectures in mesostructured template systems in general.¶ In this study, a range of metallic soaps of varying chain length and cation type are synthesised and characterised to find potentially useful templates for mineral growth. These include alkaline-earth, transition metal, heavy metal and lanthanide soaps. These are systematically characterised using a variety of analytical techniques, including chemical analyses, x-ray diffraction (XRD) infrared spectroscopy (IR) and differential scanning calorimetry (DSC). Their molecular and crystal structures are studied using transmission electron microscopy (TEM), cryo-TEM, electron diffraction (ED), electron paramagnetic spin resonance (EPR), absorption spectroscopy (UV-VIS), high resolution laser spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), electron dispersive x-ray analysis (EDXA), thermal gravimetric analysis (TGA) and magnetic measurements. Models for the molecular and crystal structures of metallic soaps are proposed. The soaps are predominantly lamellar crystalline or liquid crystalline lamellar rotor phases with tilted and/or untilted molecular constituents. These display evidence of varying degrees of headgroup organisation, including superstructuring and polymerisation. A single crystal structure is presented for a complex of pyridine with cobalt soap. Simple models for their structure are discussed in terms of their swelling properties in water and oils. Experiments are also presented to demonstrate the sorbent properties of aluminium soaps on oil spills.¶ The thermotropic liquid crystallinity of alkaline earth, transition metal, heavy metal and lanthanide soaps is investigated in detail. This is done to assess their suitability as templates, and to document their novel thermotropic behaviour, particularly the relatively unknown lanthanide soaps. Liquid crystalline behaviours are studied using high-temperature XRD (HTXRD), hot-stage optical microscopy and DSC. Models for a liquid crystalline phase progression from crystals to anisotropic liquids are discussed in terms of theories of self-assembly and interfacial curvature. The terminology required for this is drawn from various nomenclature systems for amphiphilic crystals and liquid crystals. General agreement with previous studies is reported for known soaps, while liquid crystallinity is demonstrated in the lanthanide and some non-lanthanide soaps for the first time. A general phase progression of crystalline lamellar through liquid crystalline lamellar to non-lamellar liquid crystalline is discussed in terms of models concerned with the molecular and crystal structures of the soaps and their phase transitions via headgroup and chain re-arrangements.¶ Experiments aimed at guiding growth of metal sulfides using metallic soaps as templates are described, and a model for this growth is discussed. Metal sulfides have been successfully grown by reacting crystalline and liquid crystalline transition metal and heavy metal soaps with H2S gas at room temperature and at elevated temperature. These have been characterised using XRD, TEM, ED and IR. Sulfide growth is demonstrated to be restricted and guided by the reacting soap template architecture. Zinc, cadmium, indium and lead soaps formed confined nanoparticles within the matrix of their reacting soap template. In contrast, curved and flat sheet-like structures, some resembling sponges were found in the products of sulfided iron, cobalt, nickel, copper, tin and bismuth soaps. A model to explain this behaviour is developed in terms of the crystal and liquid crystal structures of the soaps and the crystal structures of the metal sulfide particles.¶ Liquid crystalline iron soaps have been subjected to controlled thermal degradation yielding magnetic iron oxide nanoparticles. Some XRD and TEM evidence has been found for formation of magnetic mesostructures in heat-treated iron soaps. Models for the molecular and liquid crystalline structure of iron soaps, their thermotropic phase progression and eventual conversion to these magnetic products are discussed. Systematic syntheses of mesoporous silicates from sheeted clays are discussed.¶The templates that have been used are cationic surfactants and small, organic molecular salts. Experiments are reported where a cooperative self-assembly of surfactant/water/kanemite plus or minus salt and oils yields 'folded sheet materials' (FSM'S). Templating of kanemite has also been achieved using cobalt cage surfactants. A theoretical prediction of the specific surface areas and specific volumes of homologous sets of FSM's gave excellent agreement with measured values. The geometry and topology of the mesostructures are discussed. A theoretical model is also discussed regarding the curvature found in the sheets of natural clays , and results of templating clays and silica using metallic soaps are presented. Experiments and a model for low temperature nucleation and growth of microporous silicalite-1 are described in terms of silica templating by water clathrates.¶ Finally, the problem of finding minimal surface descriptions of crystal networks is addressed. Combinatoric methods are used to disprove the existence of possible embeddings of type I and II clathrate networks in non-self intersecting periodic minimal surfaces. The crystal network of the clathrate silicate, melanophlogite is successfully embedded in the WI-10 self-intersecting surface. Details of a previously unreported, genus-25 periodic surface with symmetry Im3m are discussed.

Un des problemes majeurs des procedes cvd reside dans le controle precis de la pression de vapeur des precurseurs, lorsque ceux-ci sont liquides ou solides. Un nouveau procede, brevete dans notre laboratoire, permet de resoudre ce probleme : il s'agit du procede cvd a injection. Son principe est base sur l'injection controlee de micro-quantites d'une solution contenant les precurseurs. Le premier objectif de ce travail a ete la construction et la mise au point d'une nouvelle enceinte d'elaboration de couches minces par voie cvd basee sur ce principe. Dans l'effort d'augmentation de la densite de stockage sur milieu magnetique, l'enregistrement perpendiculaire suscite depuis de nombreuses annees un interet de tout premier plan. L'hexaferrite de baryum bafe#1#2o#1#9 presente des caracteristiques interessantes pour cette application : les films doivent etre textures et convenablement dopes pour reduire le champ d'anisotropie. Jusqu'alors seules des techniques physiques de depot ont ete utilisees pour la synthese de telles couches. Nous avons etudie la possibilite d'elaborer des films de bafe#1#2o#1#9 par voie chimique au moyen du procede cvd a injection. Concernant la lecture des informations stockees, l'accroissement de la densite de stockage necessite l'utilisation de nouvelles tetes de lecture : dans ce domaine, les tetes magnetoresistives sont les plus prometteuses. Les recherches se sont recemment intensifiees avec la decouverte de la magnetoresistance colossale des composes la#1#-#xa#xmno#3#-# (a=sr,ca,ba). Nous nous sommes interesses aux manganites de lanthane lacunaires la#1#-#xmno#3#-#, deposes sous forme de couches minces par cvd a injection, dont les proprietes ont ete peu etudiees jusqu'a ce jour. Nous montrons que la technique de depot mise au point peut etre tres performante pour l'elaboration de tels films. Les proprietes structurales et physiques des couches la#1#-#xmno#3#-# sont etudiees : une magnetoresistance de 20%/tesla est obtenue a temperature ambiante

Nanomaterials, typically less than 100 nm size in any direction have gained noteworthy interest from scientific community owing to their significantly different and often improved physical properties compared to their bulk counterparts. Semiconductor nanoparticles (NPs) are of great interest to study their tunable optical properties, primarily as a function of size and shape. Accordingly, there has been a lot of attention paid to synthesize discrete semiconducting nanoparticles, of where Group III-V and II-VI materials have been studied extensively. In contrast, Group IV and Group IV-V based nanocrystals as earth abundant and less-non-toxic semiconductors have not been studied thoroughly. From the class of Group IV, Ge1-xSnx alloys are prime candidates for the fabrication of Si-compatible applications in the field of electronic and photonic devices, transistors, and charge storage devices. In addition, Ge1-xSnx alloys are potentials candidates for bio-sensing applications as alternative to toxic materials. Tin phosphides, a class of Group IV-V materials with their promising applications in thermoelectric, photocatalytic, and charge storage devices. However, both aforementioned semiconductors have not been studied thoroughly for their full potential in visible (Vis) to near infrared (NIR) optoelectronic applications. In this dissertation research, we have successfully developed unique synthetic strategies to produce Ge1-xSnx alloy quantum dots (QDs) and tin phosphide (Sn3P4, SnP, and Sn4P3) nanoparticles with tunable physical properties and crystal structures for potential applications in IR technologies. Low-cost, less-non-toxic, and abundantly-produced Ge1-xSnx alloys are an interesting class of narrow energy-gap semiconductors that received noteworthy interest in optical technologies. Admixing of α-Sn into Ge results in an indirect-to-direct bandgap crossover significantly improving light absorption and emission relative to indirect-gap Ge. However, the narrow energy-gaps reported for bulk Ge1-xSnx alloys have become a major impediment for their widespread application in optoelectronics. Herein, we report the first colloidal synthesis of Ge1-xSnx alloy quantum dots (QDs) with narrow size dispersity (3.3±0.5 – 5.9±0.8 nm), wide range of Sn compositions (0–20.6%), and composition-tunable energy-gaps and near infrared (IR) photoluminescence (PL). The structural analysis of alloy QDs indicates linear expansion of cubic Ge lattice with increasing Sn, suggesting the formation of strain-free nanoalloys. The successful incorporation of α-Sn into crystalline Ge has been confirmed by electron microscopy, which suggests the homogeneous solid solution behavior of QDs. The quantum confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for Ge1-xSnx alloy QDs with composition-tunable absorption onsets (1.72–0.84 eV for x=1.5–20.6%) and PL peaks (1.62–1.31 eV for x=1.5–5.6%). Time-resolved PL (TRPL) spectroscopy revealed microsecond and nanosecond timescale decays at 15 K and 295 K, respectively owing to radiative recombination of dark and bright excitons as well as the interplay of surface traps and core electronic states. Realization of low-to-non-toxic and silicon-compatible Ge1-xSnx QDs with composition-tunable near IR PL allows the unprecedented expansion of direct-gap Group IV semiconductors to a wide range of biomedical and advanced technological studies. Tin phosphides are a class of materials that received noteworthy interest in photocatalysis, charge storage and thermoelectric devices. Dual stable oxidation states of tin (Sn2+ and Sn4+) enable tin phosphides to exhibit different stoichiometries and crystal phases. However, the synthesis of such nanostructures with control over morphology and crystal structure has proven a challenging task. Herein, we report the first colloidal synthesis of size, shape, and phase controlled, narrowly disperse rhombohedral Sn4P3, hexagonal SnP, and amorphous tin phosphide nanoparticles (NPs) displaying tunable morphologies and size dependent physical properties. The control over NP morphology and crystal phase was achieved by tuning the nucleation/growth temperature, molar ratio of Sn/P, and incorporation of additional coordinating solvents (alkylphosphines). The absorption spectra of smaller NPs exhibit size-dependent blue shifts in energy gaps (0.88–1.38 eV) compared to the theoretical value of bulk Sn3P4 (0.83 eV), consistent with quantum confinement effects. The amorphous NPs adopt rhombohedral Sn4P3 and hexagonal SnP crystal structures at 180 and 250 °C, respectively. Structural and surface analysis indicates consistent bond energies for phosphorus across different crystal phases, whereas the rhombohedral Sn4P3 NPs demonstrate Sn oxidation states distinctive from those of the hexagonal and amorphous NPs owing to complex chemical structure. All phases exhibit N(1s) and ʋ(N-H) energies suggestive of alkylamine surface functionalization and are devoid of tetragonal Sn impurities.

碩士<br>國防大學中正理工學院<br>應用物理研究所<br>94<br>In this paper, the photonic crystal with two-dimensional hexagonal pipes structures is investigated. This photonic crystal includes the special case that with the two-dimensional hexagonal cylinders structure. In this investigation, we know that the energy band of the hexagonal cylinders structure photonic crystal will shift to lower frequency when the filling rate and dielectric coefficient increasing. And the width of complete gap will increase then decreasing. The structure of the Complete Gap is not effected by the alteration of dielectric coefficient. It would effect the width of band gap and frequencies when the dielectric coefficient been changed. In the different materials of hexagonal cylinders structure photonic crystal, the energy band gaps shift to lower frequencies when the dielectric coefficient increasing. When the cylinders radii are equal, the conditions of maximum gap been found. And in the hexagonal pipe structure photonic crystals, when the fitting materials are changed from cylinders to pipes, the energy band shift to higher frequencies just as the filling rate is decreasing. In this condition, it would be Complete Gape that it should not be Complete Gape. The Complete Gap of the hexagonal pipes structure photonic crystals would be found by this way.

碩士<br>淡江大學<br>物理學系碩士班<br>95<br>Rubidium tungsten bronze RbxWOy (0.19< x< 0.33,2.9< y< 3.05) has been observed that the oxygen concentration dependent metal-nonmetal transition, and the rubidium and oxygen concentration dependent distribution for superconductivity critical temperature. In order to investigate the properties of RbxWOy more clearly, the preparation for single crystalline samples Rb0.23WOy (2.90≦y≦3.00) was carried out. The melting point of Rb0.23WOy increases as the oxygen concentration decreases. The melting point of Rb0.23WO3.00 is 1190oC and that of Rb0.23WO2.90 is 1210oC. And the size of single crystals affected by the cooling rate of calcination. The back-reflection Laue method presents p2mm symmetry along (1 0 0), and p6mm symmetry along (0 0 1) respectively for all single crystals with different oxygen concentration. The single crystalline Rb0.23WO3.00 was annealed in oxygen, and the superconductivity was observed above 3 K while the original material didn''t superconduct above 2 K, and the lattice parameter c decreased as the annealing times increased.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1990.<br>Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

碩士<br>國立中正大學<br>物理所<br>96<br>In this thesis, the electro-resist is firstly made with the pattern of hexagonal photonic crystal resonant cavity and circular photonic crystal on the SOI (silicon on insulator) using the E-beam lithography technique. The reactive ion etching (RIE) is then used to transfer the pattern of the electro-resist to the top layer of the SOI, and the SOI is soaked into the BOE (the mixed solvent of HF and NH4F) to remove the silica of the SOI to form the 3-D confinement. Once the sample is produced, the planer wave expansion (PWE) method and the finite difference time domain (FDTD) method are individually used to simulate the band structure, transmission spectra, resonance spectra, and Q factor in 2-D and 3-D structure. The result of simulation is further used to analyze the influence of the Q factor and resonance wavelength by varying the value of structure parameter. It is then expected to find the period or the filling ratio (radius/period) of the photonic crystal which corresponds to the communication wavelength. Finally, we compare the results of 2-D and 3-D simulation.

No<br>The present work explores inner structuration of in situ gelling system consisting of glyceryl monooleate (GMO) and oleic acid (OA). The system under study involves investigation of microstructural changes which are believed to govern the pharmaceutical performance of final formulation. The changes which are often termed mesophasic transformation were analysed by small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), rheology and plane polarised light (PPL) microscopy. The current work revealed transformation of blank system from W/O emulsion to reverse hexagonal structure upon addition of structural analogues of ibuprofen. Such transformations are believed to occur due to increased hydrophobic volume within system as probed by SAXS analysis. The findings of SAXS studies were well supported by DSC, rheology and PPL microscopy. The study established inverse relationship between log P value of structural analogues of ibuprofen and the degree of binding of water molecules to surfactant chains. Such relationship had pronounced effect on sol-gel transformation process. The prepared in situ gelling system showed sustained drug release which followed Higuchi model.