Дисертації з теми "Glass Physics"
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1
Hulman, Andrea. "Breaking Glass: Exploring the Relationship Between Kinetic Energy and Radial Fracturing in Plate Glass." Scholarship @ Claremont, 2012. http://scholarship.claremont.edu/scripps_theses/95.
Повний текст джерелаАнотація:
When glass breaks from the impact of an object, it exhibits a distinctive shattering pattern comprised of two different regions. This pattern was investigated using experimental impacts and predicted using Young’s Modulus. Results were not as expected, and it is likely that there exists error in some measurements. Further investigation of this topic is recommended.
2
Pengpat, Kamonpan. "Ferroelectric glass-ceramics." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/66934/.
Повний текст джерелаАнотація:
Ferroelectric glass-ceramics have been investigated from the Bi203-Ge02, BiOl.s-Ge02-B0I.5, Bi0I.5-Ge02-Te02, 5PbO-3Ge02, PbO-Ge02-NbzOs, and PbsGe30u-PbNbz06-Si02+15%Ah03 systems. DTA, XRD and SEM analysis were used to obtain crystallographic and microstructural information. The dielectric properties and ferroelectric hysteresis loop behaviour of selected samples were determined. The stoichiometric Bjz03:Ge02 (BjzGeOs) composition devitrified on cooling, giving rise to the investigation of new systems BiO\.S-Ge02-B0I.5 and Bi0I.5-Ge02-Te0 2. It was found that the glass-forming region in Bi0I.5-Ge02-Te02 is narrow and good parent glasses for precipitating BjzGeOs crystals were not obtained. However, pure BizGeOs based glass-ceramic can be successfully formed from BiOl.s-Ge02-BOI.5. SEM backscatter imaging of these glass-ceramics showed surface crystallisation and XRD analysis confirmed that the preferred orientation is perpendicular to (311) planes. The dielectric behaviour and ferroelectric hysteresis loop study of the Bi2GeOs based glass-ceramic heat treated at 475°C for 12 hours, showed that this material can be ferroelectric at room temperature with Ps = 14 flC/cm2 and has Curie temperature at about 407°C. Glasses of compositions PG(PbSGe30I J)-xPN(PbNhz06) (x = 0.5, I, 2 3) were investigated from the PbO-Ge02-NbzOs system. Most of the samples devitrified on cooling and have poor mechanical strength except the sample PG-O.S PN sample which also contains interesting phases: ferroelectric PbSGe3011 and dielectric pyroniobate PhzNhz07. The surface crystallisation of PbSGe3011 with a-axis orientation and the bulk crystallisation of PhzNbz07 phase in this sample could be observed using SEM and XRD analysis. By applying heat treatment at 667°C for 48 hours to this sample, surface crystallisation along the a-axis can be enhanced. The Curie temperature of this heat treated sample is about 166 °C with Ps = 1 flC/cm2 from dielectric measurement and ferroelectric hysteresis loop behaviour. More samples were also investigated but it was difficult to form glass-ceramics containing both PbSGe3011 and PbNbz06 crystals from this PbO-Ge02-NbzOs system. In order to obtain the multiple ferroelectric PbSGe3011 and PbNbz06 based-glass ceramics, six glasses along the tie line from 62.5 mol%PbO: 25 mol%Ge02: 12.5 mol%Si02 to 40 mol%PbNbz06: 60 mol%Si02 were investigated from the PbSGe3011: PbNhz06: Si02+ 15%Ah03 system. Most of the glasses exhibited glass-in glass phase separation. From DT A analysis and subsequent crystallisation information, the most likely possible parameters, which control the glass-in glass phase separation, may be the NbzOslSi02 ratio for the glasses near the PbSGe3011 rich composition and Ah03 for the glasses near the PhzNhz06 rich composition. This system offered many interesting materials such as cubic pyrocWore PhzNbz07 based glass-ceramics and the orthorhombic PbNbz06 based glass-ceramics, and they are also mechanically robust.
3
Niyompan, Anuson. "Fast-ion conducting glass and glass-ceramics for the pH sensor." Thesis, University of Warwick, 2002. http://wrap.warwick.ac.uk/98497/.
Повний текст джерелаАнотація:
Fast-ion conducting glasses of the compositions Na1+xM2-x/3SixP3-xOI2-2x3 (0≤ x ≤3), where M = Zr, Ti, were studied to determine their structural arrangement, physical properties and ionic conductivity. Glass samples were prepared using the conventional melt-quench method in the melting temperature range, 1550 °C to 1650 °C. Glass products were characterised by XRD, DTA, dilatometry and density measurement. Solid state MAS NMR experiments of three accessible nuclei, 23Na, 29Si and 31P were used to determine short-range order arrangement in the glasses. XRD confirms the amorphicity of glasses for the compositions of x in range 0-3. Glass transition temperatures, Tg. TEC, and molar volume are controlled by glass composition. The MAS NMR results suggest that glass structure could be visualised as the silicate network modified by Na+ and Zr4+ or Ti4+ and [PO4] tetrahedra link up with the remaining of these modifiers with no Si-O-P observed. The glass structures were also controlled by the compositions. Using parameters determined by DTA, the corresponding glass-ceramics were produced by heat treatment for 4 hr. The composition containing ZrO2 provided the fast-ion conducting crystalline phase at a small concentration. The major crystalline phase is Na2ZrSi2O7. Glass-ceramics containing TiO2 produce very small concentration of the crystallised phase. Ionic conductivity measurement was used to determine the electrical properties of glass and glass-ceramics. Glasses having high Na2O content showed the higher ionic conductivity compared to the others.
4
Thesen, Michael. "Quantum statistical physics of a microscopic glass model." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968960014.
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5
Davatolhagh, Saeid. "Bond-ordering representation for the glass transition /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486397841222832.
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6
Grote, Christoph. "Dynamic theories of the glass transition." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318104.
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7
Yakinci, M. E. "Thick film glass-ceramic superconductor fabrication." Thesis, University of Warwick, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388377.
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8
Düring, Alexander. "Temporal aspects of spin-glass neural networks." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325892.
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9
Daniilidis, Nikolaos. "Experimental studies of the Bragg Glass transition in niobium." View abstract/electronic edition; access limited to Brown University users, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3318303.
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10
Cautun, Marius. "Photon production in the Color Glass Condensate formalism." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66993.
Повний текст джерелаАнотація:
In this thesis, the classical field model developed by Krasnitz et al. is used to compute quark and photon production in heavy ion collisions. The first part of the thesis serves as an independent verification of previous results for quark production. To do so, an iterative method is developed to solve the non-linear system of equations that gives the initial condition for the gluonic field. In the second part, the expression giving the photon production rate is simplified using the symmetries and properties of the Color Glass Condensate and McLerran-Venugopalan models. From the two Feynman diagrams that give the leading order contribution, one is much larger than the other. The dominant diagram is given by a continuum spectrum with a very prominent peak superimposed on it.Dans cette thèse, le modèle développé par Krasnitz et al. basé sur les champs classiques est utilisé pour calculer la production de quarks et de photons dans les collisions d'ions lourds. La première partie de la thèse consiste en une vérification indépendante de certains résultats sur la production de quarks. Pour se faire, une méthode itérative est développée afin de solutionner le système d'équations non-linéaires qui donnent les conditions initiales du champ de gluon. Dans la seconde partie, l'expression donnant le taux de production de photons est simplifié en utilisant les symétries et les propriétés du Color Glass Condensate et du modèle de McLerran-Venugopalan. Deux diagrammes de Feynman donnent la contribution à l'ordre dominant mais l'un d'eux est plus important que l'autre. Le diagramme dominant donne un spectre continu superposé d'un pic proéminant.
11
Peng, Xiang. "Erbium-doped tellurite glass microsphere amplifiers and lasers." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280529.
Повний текст джерелаАнотація:
Due to the properties of extremely high quality factor and small mode volume, microsphere resonators have attracted considerable attention for signal processing, fiber communication and photon computation applications. This research work studies the optical properties of microsphere amplifier and laser. The Er³⁺-doped tellurite glass was examined, including emission cross-section, absorption cross-section and lifetime analysis. McCumber and Judd-Ofelt theories were used for theoretical calculations. Whispering gallery modes in the microsphere were calculated by using the measured parameters. Signal enhancement was obtained in this Er³⁺-doped tellurite glass microsphere. The enhancement of this Er³⁺-doped tellurite glass microsphere exceeds 12dB. Besides, the mode in a single mode tapered fiber was analyzed. Theoretical analysis was also performed to optimize the coupling scheme. We also analyzed the lasing characteristics of microsphere laser, including threshold, lasing wavelength, output power optimization, and temperature dependence. Theoretical calculations for these properties were also presented. State-of-the-art L-band microsphere laser with maximum output power of 124.5 μW was demonstrated which has potential in various photonic applications.
12
Hole, David Edward. "Optical effects of ion implantation into glass." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386425.
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13
Ruan, Dihui. "Glass Formation Behavior of Model Ionomers." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430242844.
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14
Carroll, Donna L. "A multi-analytical investigation into glass dopant incorporation." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/2892/.
Повний текст джерелаАнотація:
The influence of various dopants on the properties and local structure of glass samples was explored and a quantitative determination of the structural changes in the network as the dopant concentration was varied was achieved using 27Al, 29Si, 33S MAS NMR. Findings showed that silver- and copper-doping of phosphate based glass gave rise to unexpected connectivity between the phosphate units most likely due to some phase separation creating a different composition to that intended in the majority glass. This emphasises the importance of a careful and systematic approach to sample manufacture in achieving high sample stabilities, leading to a good degree of predictability in both structure and properties. Lanthanum and yttrium ions, despite their huge difference in ionic size, showed very little difference in their effect upon the phosphate coordination in the glass samples as they remain outside the phosphate network, cross-linking between the terminal oxygen atoms. The aluminium ions however, showed evidence of behaving in both a cross-linking manner and in a network forming, tetrahedral role and it appears energetically favourable for them to avoid any Al-O-Al linkage, hence resulting in the formation of AlO4 rather than exceeding the AlO5 or AlO6 quantities that would lead to this. The sulphur NMR looks to be a very promising method for future use in understanding sulphur speciation in glasses.
15
Rappensberger, Csaba Ferenc. "Novel rare-earth aluminosilicate glasses and glass-ceramics." Thesis, University of Warwick, 1996. http://wrap.warwick.ac.uk/56937/.
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16
Yan, Yong-Xin. "Time-domain light scattering and study of liquid-glass transitions." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/96439.
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17
Brüning, Ralf. "Structural relaxation and the glass transition in metallic glasses." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74345.
Повний текст джерелаАнотація:
This thesis presents for the first time direct structural measurements of both reversible and irreversible structural relaxation and the glass transition in the metal-metalloid glass Pd$ sb{40}$Ni$ sb{40}$P$ sb{20}$. The techniques have been x-ray diffraction and Mossbauer spectroscopy, and a new analysis method for changes of amorphous diffraction patterns was developed.It is found that irreversible relaxation proceeds by many local shear-type motions involving the metal atoms, and that it is accompanied by a small densification. Reversible relaxation at high annealing temperatures entails the same microscopic processes, but it does not change the density of the glass. The type of atomic processes changes continuously as the annealing temperature is lowered, and at sufficiently low temperatures the distribution of metal atoms remains constant, so that reversible relaxation then proceeds via rearrangement of the metalloid atoms. This rearrangement leads to more ordered, but less isotropic atomic sites.
The second part of the thesis is concerned with the motion of the atoms in a metallic glass below and above the glass transition. Mossbauer spectroscopy allows the direct measurement of vibrational and diffusional motion. The increase of the amplitude of atomic vibration has the same temperature dependence as the increase in volume that marks the glass transition, thus the two processes are governed by the same mechanism. The directly measured diffusional motion is in agreement with macroscopic measurements of diffusion.
18
Morrison, Christopher Brian. "The Universe Under a Magnifying Glass| Measuring and Predicting Large-scale Structure Statistics." Thesis, University of California, Davis, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602168.
Повний текст джерелаАнотація:
In this dissertation, we describe observational and theoretical work related to the large-scale clustering of matter in the universe. Such work is crucial in constraining models of the Universe in future surveys and is one of the most powerful probes of the nature of dark energy. In Chapter \ref{magnification}, we present work performed using the Deep Lens Survey (DLS) to measure the growth of structure over cosmic time using weak lensing magnification. This is the first time such a measurement has been performed and represents a significant step forward for this relatively new probe of large-scale structure (LSS) which is known to be complementary to other weak lensing measurements. Later in Chapter \ref{conclusions}, we discuss steps needed for magnification become a competitive, precision probe of cosmology. Chapter \ref{covariance} presents a model for the emulation cosmology dependent error covariances in LSS probes. Estimating these covariances are necessary in order to compare models to the data and require a large amount of computational time to create the simulations required. Tools to reduce the number of simulations required and model the cosmology dependence are needed. We utilize a novel decomposition of LSS error covariances that allows for construction of a emulator that fulfills both of these criteria. In order for future surveys to reach their goals, methods to model measurement error and new probes of LSS complementary to those planned are required. The conclusions of this dissertation in Chapter \ref{conclusions} address the future outlook for this work and research that must be done between now and when the next set of survey data is available. Many systematic errors need to be addressed in magnification before it can be considered a precision cosmology tool. For the error covariances, additional methods to reduce the required number of simulations to estimate the matrices are required. In the Appendix, we present a high level description of an open sourced software package that we developed and implemented over the course of these two projects.
19
Elliott, Gregor Robert. "Optical micro-resonators in chalcogenide glass." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/70912/.
Повний текст джерелаАнотація:
This thesis focuses on the production of gallium lanthanum sulphide (GLS) microspheres and their potential uses. Microspheres, and micro-resonators in general, have attracted considerable attention because of their promise in all-optical-switching, micro-lasers, multiplexers and many other applications. In this thesis, several applications have been investigated, culminating in the demonstration of laser action in a neodymium doped GLS microsphere. The possibility of using microspheres as ball lenses has been investigated and shown to be possible. Laser action was observed in a neodymium doped GLS microsphere. The laser had a threshold of 83mW of incident pump power, with a peak at 1082nm and a line width of <0.05nm
20
Sanderson, Kevin David. "The atmospheric chemical vapour deposition of coatings on glass." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/11897.
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21
Mao, Ming. "Structural relaxation and the glass transition in metal-metal glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41708.
Повний текст джерелаАнотація:
This thesis presents the results of a systematic study on the structural relaxation and the glass transition of ternary metal-metal glasses Zr$ sb{67}$(Ni$ sb{1-x}$Cu$ sb{x}) sb{33}$. Differential scanning calorimetry provides macroscopic evidence of structural changes from the compositional and temperature dependence of enthalpy change. Results from high precision x-ray diffraction and Mossbauer spectroscopy, performed mainly on $ rm Zr sb{67}Ni sb{10}Cu sb{23}$ (x = 0.7), complete the picture of structural changes at the atomic level.Irreversible structural relaxation leads to densification and enthalpy release. Shear-like atomic motion enhances local atomic order, highlighting the atomic processes during the irreversible relaxation. Reversible structural relaxation involves two partly overlapping processes initiated at different temperatures, which are characterized by the solid and liquid atomic mobilities, respectively. Interatomic positional exchanges between Cu and Ni atoms change the local structure and are active during the reversible relaxation at low temperatures, which are also partly responsible for the irreversible relaxation. Above 500 K, shear-like atomic movements characterize the reversible relaxation, involving all three atomic species in a length scale of a few near-neighbor atomic shells. The overall density is unchanged during reversible relaxation.
The strong compositional dependence of the glass transition in the ternary glasses indicates an intimate association of the glass transition with interatomic bondings among different atomic species. The atomic motion from room temperature up to above the glass transition temperature, measured by the Mossbauer spectroscopy, is macroscopically tracked by the volume expansion and the enthalpy evolution. The glass transition occurs when the length scale of the atomic motion expands so rapidly that the interatomic potential can no longer maintain the on-site atomic vibration. The rapid development of translational atomic motion upon approaching the glass transition is reflected by the dramatic enhancement of the diffusive atomic motion.
22
Dikeakos, Maria. "Fe-TM-Zr alloys : from glass to big cube crystal." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38181.
Повний текст джерелаАнотація:
An extensive study of a-FexTM 1-xZr2 with TM = {V, Cr, Mn, Co, Ni, Cu} was undertaken in order to gain insight into the glassy structure, the metastable "big-cube" structure of the intermediate crystallisation product, and the evolution process involved therein. The stability of the glassy state was examined by differential scanning calorimetry (DSC). Generally higher temperatures and more negative enthalpies of crystallisation were observed for the glass system where Fe was substituted with {Co, Ni, Cu} than for the system where Fe was substituted with {V, Cr, Mn}. A proposed hypothetical crystallisation mechanism involved in the evolution of the metastable cF96 state (instead of the equilibrium tI12 state) was tested. Oxygen impurities present in the amorphous state were shown to be responsible for nucleating the cF96 big cube. Upon removal of the oxygen nucleation sites through hydrogenation of the glasses, the crystallisation proceeded directly to the equilibrium tetragonal structure bypassing the metastable phase. The validity of an assumed invariant structure in late transition-early transition metal (LT-ET) binary glasses was examined by means of Mossbauer spectroscopy. Variations in isomer shift (delta) and quadrupole splitting (Delta) upon TM substitution were consistent with variations in the density of states (DOS) at the Fermi level (EF). An assumed constant structure for (4d ET)-(3d LT) glasses is indeed justified. Variations in atomic packing were followed by measuring Delta. Delta increased as the atomic number of the TM increased. For the a-Fe xCu1-xZr 2 series, a break in the concentration dependence of Delta at x ≈ 0.3 is observed which mirrors the change in crystallisation from cF96 to tI6. Furthermore, comparisons of the glassy, metastable cubic and equilibrium tetragonal Mossbauer spectral data show obvious similarities between the glass and big cube which strongly suggest the existence of a common local (short-range) order between the two
23
Lo, Wei-Chang. "Ring polymers as topological glass, a new phase of matter?" Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/46819/.
Повний текст джерелаАнотація:
In this thesis the dynamic properties of unknotted ring polymers at high densities is investigated. We hypothesise an unusual type of glass transition which is purely attributed to the topological constraints between the penetrating rings. A mean-field model is developed to describe the strongly constrained ring polymers as ideal lattice trees. Equilibrium properties can be derived within the framework of statistical thermodynamics using an argument based on structural recurrence. Here each ring can be seen as a linear object|as a loop strand with branching protrusions. The ring polymers were simplified as loop strands without any branching. We focused on the constraints emerging from the circular topology, and the polymer dynamics was simulated using a Monte Carlo technique. The degree of inter-ring penetrations essentially controls the slowing of dynamics and represents a universal parameter for the glass transition. The penetrating rings form a percolating network involving reversible quasi-topological entanglements. As such, the stress relaxation of each ring is prolonged by the coupled penetrations which have limited pathways to release constraints from one another. The simulation data suggest the existence of a glassy material exclusively formed by the topological constraints associated with the circular structure. In order to test the picture of topological glass, the uorescence-labelled circular DNA was used to observe its self-diffusion in the entangled state. The experimental method has demonstrated its potential for the future investigation of the dynamics of entangled ring polymers despite the fact that it failed to provide evidence of the glassy state in our experiment.
24
Dobedoe, Richard Simon. "Glass-ceramics for ceramic/ceramic and ceramic/metal joining applications." Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/4217/.
Повний текст джерелаАнотація:
The use of sintered cordierite/enstatite glass-ceramics as interlayers for joining silicon nitride to itself and to metals has been investigated. The role of the additives B203 and P205, which control the dynamics of sintering and crystallisation, has been studied using SEM, XRD and non-isothermal DTA-based measurements of activation energy. The measured activation energies for the crystallisation of μ-cordierite, for compositions with no additives, with B203 only, and with P205 only, did not differ significantly and were in the range 415-460 kJ mol-1. When both B203 and P205 were present this was increased to 503-524 kJ mol-1. The activation energy for α-cordierite formation when no additives were present was 952 ± 57 kJ mol-1. This was substantially reduced by the presence of B203 (540 ± 27 kJ mol-1), P205 (668 ± 41 kJ mol-1) and when both were present (352 ± 26 kJ mol-1). Cordierite/enstatite glass-ceramics have been successfully used to join silicon nitride to itself. Joining at 1050-1100'C in N2 with an applied load of ~ 2.5 MPa, resulted in joint strengths, measured in 4-pt bending, of 110-170 MPa. This is comparable to the intrinsic strength of the glass-ceramic and sufficient for practical applications. These strengths were obtained using an interlayer with a TCE (5.7 MK-1) greater than that of the silicon nitride (3.0 MK-1). Suggestions for further improvements to the joint strength are discussed. The use of a glass-ceramic joint with graded thermal expansion to bridge a TCE mismatch is discussed, and the geometrical restrictions on the joint, which limit possible practical applications, are outlined. The concept of a ceramic/metal compression joint with a glass-ceramic interlayer has been demonstrated for joining silicon nitride to both Nimonic alloy 80A and Ti. The requirements for continuity of electronic structure at the Nimonic 80A/glass-ceramic and the Ti/glass-ceramic interfaces are satisfied by reaction between the glass/glass-ceramic and, the pre-oxidised surface of the Nimonic alloy to form a MgTi205-Al2TiO5 solid solution phase, and the Ti to form Ti5Si3. For the lower WE mismatch (Ti-silicon nitride) the residual joining stresses generated on cooling were marginally too high and need to be further reduced, either by a slight alteration to the joint geometry and/or a smaller WE mismatch.
25
Minani, Evariste. "Growth temperature and microstructural differences in hydrogenated amorphous silicon deposited on glass substrates." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/6995.
Повний текст джерелаАнотація:
Includes bibliography.Hydrogenated amorphous silicon (a-Si:H) is an important thin film semiconductor with a wide variety of applications in microelectronics and optoelectronics. However, it is metastable and photodegrades after a moderate light illumination (Staebler-Wronski effect). The most stable material has been suggested to be at the edge of crystallinity with microcrystalline inclusions. Using a combination of positron annihilation and X-ray diffraction techniques, the microstructure of hydrogenated amorphous silicon grown by hot wire chemical vapour deposition on glass substrates at different substrate temperatures ranging between 300°C and 500 °C is examined. In previous studies the crystallisation was accompanied by a relaxation of defect structure with an increase in free volume at positron annihilation site. In this work, both techniques show a relaxation of the network with increasing growth temperature, leading to a higher degree of ordering, shorter bond lengths, and a reduction in the average size of defects in the material.
26
Wallace, Matthew L. "The rigidity transition in a short-chain polymer glass." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26794.
Повний текст джерелаАнотація:
In this thesis, we present a thorough investigation into the rigidity of a polymer melt above and below its glass transition (GT) at a temperature TG = 0.465 (in reduced Lennard-Jones units). We use an isothermal-compression method to enter the glassy phase and NPT ensemble is realized through molecular dynamics simulations. We monitor such quantities as the mean-square displacement, the heat capacity CP, the volume and time-dependent shear modulus G(t). Whenever possible, these quantities are monitored below the GT as well. We also compute the shear modulus mu via external deformations and, in the zero-shear limit, find reasonably good agreement with G(t → infinity). The rigidity transition (RT) in the system is found to occur slightly below the GT at a temperature TR = 0.44. The results are explained in terms of sufficient free volume above TR allowing collective motion and local stress relaxation. This is seen through dynamics which are not only heterogeneous, but also spatially correlated. We appeal to notions such as "jamming" within the system and the presence of floppy modes (which allow for deformations without energy cost) to interpret the RT phenomenon. We also characterize the response to external deformation: small and large deformation regimes can be identified, the latter type causing a non-negligible reconfiguration, an over-stretching of the chains and a move to a more shallow potential energy "well." Furthermore, we analyze the "aging" phenomenon as a series of intermittent collective rearrangements and show that the two types of instantaneous shear deformations both induce "overaging," but in two completely different manners.
27
Owate, I. O. "The electrical properties of some alumina ceramics and glass ceramics." Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282951.
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28
West, Grant. "Microstructure and mechanical performance of SiC/BMAS glass-ceramic matrix composite." Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/66932/.
Повний текст джерелаАнотація:
A diverse range of microscopy techniques and mechanical testing methods have been used to characterize glass and glass-ceramic composites. The focus of the work has been a commercially available Barium Magnesium Aluminosilicate matrix reinforced by Tyranno SiC based yam type fibres. The mechanical behaviour has been related to the microstructure through use of models from the literature. The temperature range of study has been from room temperature to 1300°C in air. The microstructure of the BMAS(fyranno was a diphasic mixture of celsian and indialite/cordierite although the manufacturers intention was a monophasic bariumosumilite. The carbon rich interface was found to be thin (l0-15nm) but the composite displayed impressive strength when compared to similar glass-ceramic composites reported in the literature. The matrix could be converted to the equilibrium bariumosumilite phase by heating in an inert atmosphere at 1370°C (or possibly lower) but matrix elemental diffusion into the fibres is likely to impair fibre strength. Tensile failure was by conventional matrix microcracking with load transfer to the in line fibres. However the composite strength was found to be dependent upon the strain rate as was the microcracking threshold associated with cracking of the 0° plies. Failure of the UD BMAS(fyranno was by longitudinal splitting before the expected ultimate strength (from the 0,90° results) was reached. This was due to an apparent notch sensitivity in this fibre architecture, a trait not observed in the 2-D composite. Direct measurement methods were used to establish the interfacial shear strength and these were compared to various models. These were based on matrix cracking thresholds, matrix crack spacing and a relatively new method where an 'inelastic strain index' was found from loading and unloading curves or hysteresis loop widths. Greatest fidelity with the direct methods was found with the last of these models. As with all composites with carbon enriched interfaces oxidation of the interface and fibres was found to impair strength when tested in air at temperatures as low as 600°C and possibly below this when testing at lower strain rates. At high strain rates, near room-temperature-strengths were achieved, even at 1l00°C, as the degrading effects of the oxidizing environment had less time to act. Long term exposure at high temperatures (1200°C) was responsible for formation of an embrittled surface layer up to 70J.lm thick. Within this layer the fibres were severely degraded and strong bonding prevailed at the interface. At temperatures in excess of the expected fibre pyrolysis temperature, (l100°C), the composite was seen to shrink along the length of the fibre axis and dilate normal to it which was attributed to fibre instability. Stabilising the fibres by heat treatments at 1200°C for 24 hours was seen to improve the creep performance in terms of the total strain accumulated within the 100 hours of the creep tests. The creep was comparable to other commercial glass ceramics (CAS/Nicalon and BMAS/BN/SiC/Nicalon) indicating the dominance of fibre creep properties on those of the composite. Cycling of the creep load seemed to result in a greater embrittled depth from the surface but failure at 100MPa and 1200°C was not observed within 240 hours of testing. Other systems were investigated such as the CAS/Nicalon, MAS/Nicalon and AS/Nicalon. Of these the AS/Nicalon was used for modelling the creep behaviour since it represented a simple system where matrix creep was accompanied by elastic deformation of the fibres. A model from the literature was used to explain an apparent increase in the elastic modulus during load cycling at high temperature and also the lower strain accumulation seen during load cycling compared to conventional creep tests.
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Mwarania, Eustace Kaburu. "Planar ion-exchanged waveguide lasers in glass." Thesis, University of Southampton, 1992. https://eprints.soton.ac.uk/399434/.
Повний текст джерелаАнотація:
This thesis describes the realisation of integrated optical sources in rare-earth doped glass substrates using ion-exchange planar waveguide fabrication technology. The planar configuration offers the possibility of photolithographic definition of complex multiple-cavity devices, of monolithic integration of devices such as modulators for switching and tuning, and for mass production. A process to introduce rare-earth ions into ion-exchangeable glasses was developed, and used to fabricate neodymium-doped BK-7 glass substrates. Techniques for design, fabrication and characterisation of potassium ion-exchanged waveguides for laser applications in these substrates are described. The properties of waveguides in a substrate doped with 1.5wt.% neodymium oxide are presented. A method to form laser resonators incorporating ion-exchanged waveguides is described. Single- and multiple-cavity waveguide lasers operating in single transverse mode at both pump and lasing wavelengths have been demonstrated and their characteristics are presented. The factors affecting lasing thresholds of the single-cavity lasers were investigated, and devices with thresholds low enough to be pumped by a single-stripe laser diode were realised. A theoretical model for the analysis of optical multiple-cavity resonators is developed. These resonators are shown to exhibit frequency selecting properties that may be exploited to realise multifunctional sources. The potential of the planar configuration was demonstrated by integrating Y-junction multiple-cavity waveguide lasers and monolithic thermo-optic phase modulators. These lasers have been line-narrowed, tuned in wavelength, and Q-switched by applying modulation voltages to the thermo-optic modulators.
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Hong, Feng. "Interactions between glass-ceramic coatings and metals." Thesis, University of Warwick, 1991. http://wrap.warwick.ac.uk/108319/.
Повний текст джерелаАнотація:
A study of glass-ceramic coatings on metal substrates was carried out in order to understand how the coatings and substrates interact and how these interactions affect coating microstructures and properties. There are two systems involved. One is a lithium-silicate glass-ceramic coating on Ni/Cr/Co alloy and the other is a lithium-aluminosilicate glass-ceramic coatings (with some other optional compositions) on titanium metal. Simple techniques such as screen printing or the "droplet” method were used to coat the substrates with a layer of fine glass powder, and then a firing procedure followed to create a vitreous enamel layer on the metals. Heat treatment was usually applied to convert the vitreous coating into a highly crystallized, glass- ceramic coating since this generally results in superior properties. Because both the Ni/Cr/Co alloy and titanium metal are active metals, complicated interactions were observed at the coating/metal interface. In the Ni/Cr/Co case. Cr from the substrate tends to diffuse into the coating very rapidly at the firing temperature. The rapid diffusion of mainly Cr++ ions and subsequent change into Cr+++ ions results in saturation of Cr+++ ions in the glass coating. The second oxidation step proceeds more rapidly at the coating surface and LiCr(Si03)2 crystals start to precipitate on the surface of the coating. Mismatch of TEC, thermol expansion coefficient, between LiCr(Si03)2 and the coating causes severe disruption. In addition, some components in the coating, for instance, P2O5, react with Cr to form Cr^Pî. As a result, in the reaction zone, consumption of the intended nucleating agent P2O5 leads to a poorly crystallized structure affecting coating properties. In the titanium system, though long range diffusion across the interface was not observed, the major problem is the reactivity of titanium with coating components including Si( > 2. Direct reaction between titanium and silica gives TisSia as an interfacial layer and the gaseous O2 produced may disrupt the molten glass structure during firing. Other interactions such as Ti/P2Os can also proceed to give other damaging effects. In general, the coating on titanium after firing is usually very porous if these interactions are not prevented. Preoxidation of Ni/Cr/Co alloy created an adherent Cr203 layer on the alloy surface, and this layer is very stable in the coating glass due to its low diffusivity and solubility. The existence of this layer prevented direct contact of alloy and coating at the firing temperature, minimizing interfacial reactions and leading to the desired coating structure. From a chemical point of view, preoxidation of titanium metal can create a barrier of Ti02 between the coating and metal to hinder the formation of Ti5Si3. However, the poor bonding strength of this layer meant that it was ineffective in forming a transition layer between the metal and coating. Furthermore, the Ti02 can be readily dissolved by the coating glass during firing. Addition of an adherence oxide, CoO, was successful in 1) producing Ti02 in situ at the interfacial area and Co/Ti dendrites, both of which are necessary in maintaining chemical as well as mechanical bonding across the interface 2) diverting and hence minimizing the damaging direct reaction between Ti and SiC > 2 because the reaction between Ti and CoO always takes place prior to the reaction between Ti and Si02 thermodynamically. In the systems of glass-ceramic coatings for reactive metal substrates, various complications may occur. In this study, interactions of lithium-silicate/Ni/Cr/Co alloy and a wide range of glass-ceramic coatings/titanium have been studied. Detailed observation has been given together with explanation. Further work has also been suggested so that better understanding and application may generate from what has been observed in this project.
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Lapointe, Kyle. "Electrical Characterization of Silicon Cores from Glass-Cladded Fibres." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24825.
Повний текст джерелаАнотація:
Semiconductor core fibres represent an emerging technology with potential applications in many areas, including photovoltaics and optical transmission. Recent advances in fibre manufacturing techniques has allowed long, continuous silicon core fibres to be produced in commercial draw towers. The effect of the molten core fibre fabrication method on the electrical properties of silicon cores from glass-clad fibres have been studied. Fibres with core diameters ranging from 60 to 300 µm were produced using a CaO interface modifier between the core and cladding. Five silicon material types with increasing phosphorus doping levels were analysed before and after the drawing process using four point probe technique, supplemented with microscopy and compositional analysis. Novel techniques for preparing and measuring fibre samples were developed, which is suitable for a range of fibre diameters. Cores produced from lightly doped materials showed a large increase in conductivity, while cores produced from a relatively highly doped material showed a small decrease in conductivity. The results suggest that the manufacturing process has introduced significant amount of impurities to the silicon core, which corresponds to additional charge carriers.
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Kemp, Andrew Patrick. "The electrical and other physical properties of haloborate glasses and glass-ceramics." Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/109948/.
Повний текст джерелаАнотація:
The effect of a series of classical nucleating agents upon the nucleation and mechanical properties of anhydrous borax (AB,Na2B407) glasses and glass-ceramics have been investigated. These results have been compared to those obtained for NaCl-doped compounds and a commercial B”-Al2O3 ceramic to examine the applicability of haloborate glass-ceramics as a solid electrolyte in high temperature sodium-sulphur cell. The nucleation of these materials was found to be predominantly surface oriented. A new technique has been introduced to increase the number of surface nucleation sites. Direct and indirect structural comparisons of these materials have been carried out using X-ray diffraction and infra-red and Raman spectroscopy. Results from the NaCI-doped materials have tentatively indicated that the chlorine atom plays a direct structural role. Subtle modifications to the structure are thought to results in previously determined high ionic conductivities. A variety of techniques have been examined for the measurement of ionic conductivities based on time and frequency domain spectroscopy. A frequency domain measurement system has been designed and built and a computer program written to analyse the acquired data. Equipment exploring a complementary technique based on the multiple disc stacking arrangement postulated by Tubandt has been built. Results from these two techniques appear promising.
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Kirk, N. B. "Evaluation of glass polishing using sol-gel cerium oxide polishing compound." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388342.
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Rogers, Steven. "Examining the glass transition region of hard sphere colloids by simulations." Ohio University Honors Tutorial College / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1276749504.
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Baine, Paul Thomas. "Fabrication of thin single crystal silicon devices on glass using electrostatic bonding." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361353.
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Torchinsky, Darius H. "Optical study of shear and longitudinal acoustic waves and complex relaxation dynamics of glass forming liquids." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45440.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.Includes bibliographical references (p. 259-277).
The spectroscopic technique Impulsive Stimulated Scattering (ISS) was refined and used to study the complex structural relaxation dynamics of glass forming liquids, allowing both empirical modeling and testing of the predictions of the mode-coupling theory (MCT). Longitudinal and shear acoustic waves throughout much of the MHz frequency range, time-dependent thermal expansion on nanosecond and microsecond scales, and slower thermal diffusion were all monitored in real time. The data were used to construct complex longitudinal modulus spectra spanning from, 30 kHZ to 3 GHz, and complex shear modulus spectra from - 10 MHz to 1 GHz. In the liquid tetramethyl tetraphenyl trisiloxane, experiments which verified timetemperature superposition of its relaxation dynamics permitted construction of a master plot of scaled relaxation spectra in the entire temperature range studied. MCT predictions of power-law frequency dependencies of the high and low frequency wings of the loss modulus yielded a high-frequency exponent parameter in good agreement with the width of the non-exponential relaxation kinetics. The low-frequency exponent did not agree with the predicted value. In triphenyl phosphite, measurements of the measured shear relaxation spectrum over two decades in frequency revealed that it does not match the previously measured longitudinal spectrum, suggesting that different underlying degrees of freedom contribute to shear and compressional relaxation. Measurement of shear wave propagation as a function of temperature lent credence to the dominance of the temperature dependence of the transport by the instantaneous shear modulus. These measurements also call into question other relationships drawn between glass mechanical behavior and the supercooled liquid fragility. In work conducted collaboratively, the ISS technique was employed in singles hot measurements of liquid benzene under conditions of shock loading. The results indicate that benzene remains in a liquid state for at least 200 ns after the shock's arrival. ISS was also used to characterize both the thermal transport and mechanical properties of nanofluids.
(cont.) Finally, results of ISS acoustic measurements of thin films and their relationship with the study of glass forming liquids are briefly discussed.
by Darius H. Torchinsky.
Ph.D.
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Duki, Solomon Fekade. "Topics in Hard and Soft Condensed Matter Physics." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232737384.
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Ljungström, Ami. "Self-written waveguides in glass : experimental and numerical investigations." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/15467/.
Повний текст джерелаАнотація:
Self-writing is a technique of forming waveguide structures within a material. This thesis is an experimental and theoretical study of the self-writing process in glass, both in bulk materials and in planar layers. The first reported observations of self-writing effects in a bulk glass material are presented, with investigations into both Ce-doped Ga-La-S and Nd-doped BK7 samples. We observe increases in the refractive index of 2.5 x 10−5 in Ce-doped Ga-La-S due to illumination at 1047 nm, leading to the formation of a self-written taper. Corresponding numerical simulations show good agreement with observations, confirming the validity of the numerical model used to simulate these experiments. In the Nd-doped BK7 glass a decrease in index of 7 x 10−5 was observed when exposed at 488 nm, resulting in an increase in the diffraction of the propagating beam during the writing process, and subsequently an enhanced diffraction taper was induced. Here investigations with a Laguerre-Gaussian donut shaped writing beam show that a depressed-index pipe structure can be created by exploiting this negative index change. We have demonstrated both numerically and experimentally that the resulting complex waveguiding structure confines light and can be used as a channel waveguide. Self-written channel waveguides have also been formed in a K+ -ion exchanged Nd-doped BK7 planar glass layer by making use of an index increase of 5.2 x 10−5 induced at a wavelength of 457 nm. A threshold in power, below which photosensitivity does not occur, has been found. This threshold effect has been successfully incorporated in the numerical model, resulting in good agreement between observations and corresponding simulations. The experimental results obtained in the planar layer indicate that this material exhibits a high level of homogeneity and thus is an ideal host for self-writing. Investigations have also been carried out using a two-peaked writing beam to self-write an optical splitter, and both experimental and numerical results show that such a structure can be self-written using this type of writing beam. These results represent the first observations of a complex waveguiding structure being self-written using a single input beam in glass. In conclusion the self-writing fabrication method of waveguides shows great potential for future practical applications and integration with existing devices.
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Ohtsuki, Tomoko 1960. "Rare-earth-doped glass waveguides for amplifiers and lasers." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282169.
Повний текст джерелаАнотація:
Several different glass materials were investigated for waveguide amplifier and laser applications, and the potential to realize practical devices with these materials were examined using waveguides fabricated by ion exchange processes. Channel waveguides in an erbium doped phosphate laser glass were fabricated by a dry silver-film ion exchange technique, and the effects of high Er³⁺ concentration were investigated in terms of Er³⁺ ion interactions and energy transfer from Yb³⁺ to Er³⁺. Cooperative upconversion coefficients of the ⁴I₁₃/₂ level,7.7±0.7x 10⁻¹⁹ cm³/sec and 9.3±0.7x10⁻¹⁹ cm³/sec, were obtained experimentally for Er³⁺ concentration of 1x10²⁰ cm³ in the bulk and waveguide samples, respectively. These values are one order of magnitude smaller than the ones reported for silica glass. The increase in the cooperative upconversion coefficient with the increase in Er³⁺ concentration was found to be small. The effects of cooperative upconversion on the gain performance were analyzed for different Er³⁺ concentrations using a theoretical model which adopted experimentally obtained parameters. Given the small cooperative upconversion coefficients in this glass, Er³⁺ concentrations potentially as high as 3.7x10²⁰ cm⁻³ were shown to be feasible by the modeling. This would result in a 12 dB gain with a 4 cm long waveguide for 150 mW pump power at 1.48 μm. The transfer efficiency from Yb3+ to Er³⁺ was found to be 95% or higher for samples with Er³⁺ concentrations of 1.9x10²⁰ cm⁻³, and 24x10²⁰ cm⁻³, even when the ratio of the concentrations, Yb/Er, is only about 1.2 and 2. Planar channel waveguides of rare-earth doped fluoride glass were demonstrated with single mode excitation and propagation loss below 3 dB/cm. The waveguide core was fabricated by Ag⁺-Na⁺ molten salt ion exchange process in a borosilicate glass (BGG31), and a Nd³⁺-doped ZBLAN glass was used as a cladding. A 0.45 dB signal amplification at 1.064 μm was observed in the fabricated 1cm long waveguide, and a 0.9 dB amplification is expected at the emission peak (1.049 μm). Modeling results suggest that 2.5 dB/cm is possible by improving surface flatness of the ZBLAN glass.
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Roderick, Jonathan M. "A characterisation and radiation resistance study of a mixed-modifier borosilicate glass for HLW vitrification." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/63637/.
Повний текст джерелаАнотація:
The short-range structural order, in glasses from the technologically important Na20-LhO-B203-Si02 system, is investigated using NMR and thermophysical techniques. The change in the populations of tetrahedrally coordinated borate units and various trigonal borate units is deduced from llB NMR and compared with the most widely accepted, NMR based, structural model of Dell, Bray and Xiao 1. Differences from the model are discussed and substantiated with results obtained from 29Si NMR. Structure sensitive properties such as density, glass transition temperature and thermal expansion coefficient are reported across a wide range of modifier concentrations. This information is then related to and compared with the structural arrangements obtained from NMR studies of less complex systems. An empirical density modee·3 designed for the single-modifier borosilicate systems has been used to gain information regarding the structural arrangements in the current system. Investigation of specific, carefully controlled, compositional changes to the current HL W vitrification glass, MW, has been carried out. The effect of 8 20 3 concentration on the chemical durability of glasses from this system has been studied using dynamic leach tests. In addition, the role of La203, a waste simulant, has been investigated using similar analytical methods, and suggestions as to its primary function in the glass have been discussed. Finally, a preliminary study of the interaction of several compositions, related to MW, with high-energy a-particles and UV -radiation, has been pursued. The presence of radiation induced structural and physical changes has been probed using ESR and 'Y-ray spectroscopy, enabling suggestions for the types of defects produced and nuclear reactions taking place to be made.
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Meenakshisundaram, Venkatesh. "ELUCIDATING PHYSICS OF SEQUENCE-SPECIFIC POLYMERS AND THE GLASS TRANSITION VIA EVOLUTIONARY COMPUTATIONAL DESIGN." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1513717453745275.
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Turdean-Ionescu, Claudia Adriana. "Multinuclear solid state NMR of novel bioactive glass and nanocomposite tissue scaffolds." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/34621/.
Повний текст джерелаАнотація:
Sol-gel derived bioactive glasses are promising candidates for bone regeneration, where bone is a natural nanocomposite of collagen (organic polymer) and hydroxyapatite (inorganic mineral) with a complex hierarchical structure and excellent mechanical properties. Solid-state NMR is a sensitive probe and offers atomic-level information on the structure of sol-gel derived bioactive glasses. In this thesis, a multinuclear solid state NMR approach, as part of an extensive study, has been applied to a key range of sol-gel derived materials related to novel nanocomposites to act as tissue scaffolds. The nanostructure evolution of sol-gel derived bioactive glasses 70S30C (70 mol% SiO2 and 30 mol% CaO) was characterised by 29Si, 1H and 13C CP MAS NMR. Calcium was found to be incorporated into the silica network during the stabilisation stage and to increases its disorder. The inhomogeneity found within 70S30C bioactive glass monoliths showed that the calcium concentration was higher in the outer region of the monolith caused by the way calcium only enters into the structure after breakbown of the nitrate. Trimethylsilylation reaction mechanisms used to tailor the nanoporosity of sol-gel derived 70S30C bioactive glass was also studied. The 29Si NMR results showed that the modification processes affected the atomic scale structure of the glass, such as Qn structure and network connectivity. 1H and 13C NMR was used to follow the loss of hydroxyls and organic groups directly. The study was extended to 58S (60 mol% SiO2, 36 mol% CaO, 4 mol% P2O5) systems and compared for two synthesis routes: inorganic and alkoxide. Via the inorganic route high temperatures were needed for calcium incorporation, while via alkoxide route calcium was found to be incorporated at low temperatures. Reactive surface Ca ions were involved in the formation of different types of carbonates for the two routes. The addition of P2O5 to the silica-calcium oxide system results in a scavenging of calcium ions by phosphate groups to give orthophosphate and pyrophosphate units. Solid-state NMR of new organic-inorganic hybrid scaffolds, class II, in the silicagelatin and silica-calcium oxide-poly(γ-glutamic acid) (γ-PGA) systems indicates that 3- glycidoxypropyltrimethoxysilane (GPTMS) provides a covalent link between the organic and inorganic networks and increased the inorganic condensation. 1H-1H intra- and intermolecular proximities have been identified using 1H DQ (double-quantum) CRAMPS (combined rotation and multiple pulse spectroscopy) techniques. 13C NMR results indicate that an efficient promotion of epoxide ring opening of GPTMS was reached by either gelatin or γ-PGA. 43Ca NMR identified different calcium environments in the hybrid systems. The last part of this thesis is focused on the comparison studies in the mechanism of apatite growth on both melt-derived (Bioglass®) and sol-gel derived (TheraGlass®) bioactive glass surfaces. By using a combination of 1H, 13C, 31P, 29Si and 23Na, using one and two dimensional NMR spectroscopy, the inhibitive effects of serum proteins in the mechanism of the apatite growth was revealed. The solid-state NMR experimental data support the hydroxycarbonate apatite formation mechanism proposed by Hench. Apatite formation takes place from the largely amorphous phosphate ions initially deposited on the glass surface. Serum proteins adsorbed on the glass surface have been found to significantly inhibit the apatite formation. Multiple sodium sites have been identified in Bioglass® composition with the formation of a more ordered local structure on increasing immersion time.
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Asimakis, Symeon. "Nonlinear applications of step-index and microstructured soft-glass fibres." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65526/.
Повний текст джерелаАнотація:
This thesis focuses on the potential of compound-glass, highly nonlinear, small-core fibres for use in nonlinear applications. Both fibres with a conventional step-index design and small-core holey fibres are considered. While the former technology is more mature, the latter represents the ultimate candidate, since it offers the flexibility of combining novel dispersion properties with a very high nonlinearity. With regard to holey fibre designs, small-core, compound-glass holey fibres with different core diameters and designs are considered for two different background materials: a commercially available lead-silicate glass and a bismuth-oxide based glass. Firstly, characterization measurements are performed on the fabricated holey fibres. The measurements reveal the advantages of each glass type and each fibre design, the ultra-high nonlinearity that can be achieved in such fibres and the potential of achieving simultaneously a novel dispersion profile and high nonlinearity. Nonlinear applications are then demonstrated for some of the fibres presented. In particular, the use of a lead-silicate holey fibre, having a dispersion-shifted profile, with a zero-dispersion wavelength lying close to the C-band is demonstrated in cross-phase modulation based wavelength conversion and switching applications in the 1.55 μm window. Both a co-polarized pump and probe scheme and a Kerr-shutter configuration are considered. For the same fibre, the stimulated four-wave mixing process for amplification and wavelength conversion applications in the C-band is thoroughly studied. Numerical simulations and experimental findings are combined to study the fibre performance, demonstrate its applicability to nonlinear wavelength conversion applications and identify future improvement objectives. The suitability of compound-glass holey fibres is also examined for the generation of correlated photons, through spontaneous four-wave mixing, and the generation of a broad supercontinuum by pumping at the convenient in terms of high power laser availability wavelength regions of 1.0 μm and 1.5 μm. The experiments presented in this thesis constitute the first nonlinear applications ever reported for dispersion-tailored, compound-glass holey fibres, clearly revealing their potential in fibre-based nonlinear applications. Nonlinear applications are also demonstrated for a commercially available, fiberised, bismuth-oxide based fibre with a step-index design. Using this fibre, an all-optical regenerator of Return-to-Zero picosecond pulses is realized at repetition rates of 10 and 40 Gb/s. The same fibre is also employed in an all-fiberised pulse compression scheme, which relies on nonlinear pulse propagation in the normal dispersion regime and enables the compression of picosecond pulses down to the femtosecond scale. In both applications, the ultra high nonlinearity of the compound-glass, step-index fibre results in reduced fibre-length and peak power requirements. The thesis concludes by addressing the issues concerning the practicality of compound-glass fibres and proposing potential future directions.
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Mackechnie, Colin Jardine. "An investigation into thulium and ytterbium doped glass fibre lasers." Thesis, University of Southampton, 1994. https://eprints.soton.ac.uk/399144/.
Повний текст джерелаАнотація:
The work described in this thesis is the result of three years of study in thulium and ytterbium doped glass optical fibres with a view to investigating and characterising laser action in these media. In particular an investigation has been carried out into the effect that pump excited state absorption (ESA) has on the 1064nm-pumped Thulium-doped silica 2µm fibre laser, resulting in the first measurement, in terms of cross section, of the ESA from the 3H4 level in the 1-1.5µm region for Tm:silica. Laser oscillation has been observed at ~1.9µm in Tm-doped lead germanate fibre pumped at ~790nm. This new glass fibre was specially developed to have an appropriate phonon energy to enhance the lasing properties of this thulium transition over that in silica or fluoride hosts. It is the first glass fibre laser based on a germanate glass. The lowest ever recorded threshold for this transition in any glass has been recorded at 3.6mW of launched power. In order to investigate infra-red pumped visible upconversion lasers in Tm:ZBLAN fibre, ytterbium doped silica fibre lasers were first studied as a route to producing the required pump wavelengths. By using a novel pumping scheme in the wing of the absorption band at 1064nm or 1047nm, efficient laser action achieved in the long wavelength range of the emission, between 1096nm and 1180nm. The lowest recorded threshold was 17mW and the highest measured slope efficiency was 87% (both with respect to launched power). These investigations confirm the versatility of Yb:silica fibre lasers. With the successful development of the Yb:silica fibre laser operating at the required pump wavelength, an investigation was carried out into single-wavelength-pumped, room temperature upconversion in thulium-doped ZBLAN with the aim of producing a blue laser. Blue lasing was observed in the range 476nm - 486nm (the longest and shortest laser wavelengths recorded for this transition) with pump wavelengths between 1100nm and 1141nm (the longest and shortest pump wavelengths reported). The lowest threshold was measured as 11mW (launched power)and the maximum slope efficiency was 23% (with respect to launched power), results which indicate potential for an infra-red diode pumped blue laser.
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Gecevičius, Mindaugas. "Polarization sensitive optical elements by ultrafast laser nanostructuring of glass." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/374905/.
Повний текст джерелаАнотація:
In this theses I will concentrate on femtosecond laser induced modification in silica glass. One type of modification in fused silica is subwavelength nanogratings. This modification exhibits form birefringence and therefore optical elements can be fabricated based on nanogratings. The main goal of my work was development and fabrication of practical optical elements based on femtosecond laser induced nanogratings. In order to be able to fabricate optical elements, laser induced modification had to be uniform and exhibit strong birefringence. Also fabrication speed has to be high in order to write reasonable size optical element in short time. Optimal fabrication parameters were found by studying physical and optical properties of nanogratings. The first polarization sensitive optical element to be demonstrated was polarization converter, which transforms Gaussian beam with uniform polarization distribution into a cylindrical vector beam. Later on, polarization converters for different types of laser beams and spectral ranges were demonstrated. Properties of generated beams were measured and compared with theoretical modelling. Generated beams were also successfully exploited for material modification and results are compared with theoretical simulations. Same converters can be also used for optical vortices generation. Unique property of such converters is that they allow tuning orbital angular momentum of photons in the light beam and therefore adjusting the torque of the vortex beam. The important feature of this vortex generation technique is that optical angular momentum is changed without affecting intensity distribution of the laser beam. The benefits of tunable optical angular momentum were demonstrated in optical trapping experiment where silica micro spheres were trapped into a rotating ring is performed. The ability to tune the torque of the beam is proved by changing rotation speed change of the beads’ ring. Birefringence can be exploited not only for polarization control but also for phase. Half-wave retarder can induce phase delay to circularly polarized light depending on the azimuth of slow axis of the retarder. Based on that, converter for “diffraction-free” Airy and Bessel beams are fabricated. Properties of generated beams are measured and compared with theoretical simulations. Airy beam converter based on laser induced nanogratings has unique ability to generate dual Airy beam which is superposition two Airy beams accelerating in opposite direction. Generated Airy beam is also used in material modification. Self-detachment of fibre-like structure is observed from laser modified substrate which is speculated to be caused by properties of Airy beam. Finally, an array of micro waveplates is fabricated which together with a linear polarizer and a CCD camera allows real time polarization imaging. Full state of polarization can be measured. For the demonstration, polarization distribution of cylindrical vector beams was measured.
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Mairaj, Arshad Khawar. "Optical waveguides and lasers in improved gallium lanthanum sulphide glass." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/15476/.
Повний текст джерелаАнотація:
A number of developmental stages are still required to advance and mature optical waveguide technology in non-silica glasses. The primary stage includes raw material purification and improving quality and thermal stability of an optical glass for waveguide fabrication processes. Further stages can include design, application and integration of these waveguides with other photonic devices. Gallium lanthanum sulphide (Ga:La:S) chalcogenide glass (ChG), first discovered in 1976, is a material proposed as an optical waveguide for use in the infrared (IR). Interest in this glass system has been maintained, over the years, primarily due to its exceptional and unusual optical properties. The aim of this project is to advance the current state of art for Ga:La:S glass by demonstrating working solutions for fibre and planar waveguides. Chapter 1 of this thesis provides a general overview of current glass technology and the motivations of this project. The optical glass system under study has yet to attain acceptable stability for fibre production and as such investigation into fundamental manufacturing steps is still required. Raw material purity is an important aspect, of fabricating practical optical glasses, and directly affects performance. Chapter 2 of this thesis describes the purification and synthesis processes performed to produce raw materials with purity far superior to similar products available commercially. Each powdered precursor synthesised in our labs and used in fabrication of Ga:La:S based optical glasses has a transition metal impurity content of less than 1 parts-per-million (ppm wt%). The water content, OH-, of these fabricated glasses has been reduced to < 2 ppm. The primary concern when fabricating Ga:La:S based optical fibre is crystallisation. Optimising the composition to obtain a glass suitable for fibre fabrication is significant in providing thermal stability for fibre drawing. Chapter 3 describes some of the steps taken towards the fabrication and improvement of Ga:La:S based glasses for waveguide technology. The invention of a new variant in the Ga:La:S family of glasses provides key enhancements over existing Ga:La:S and Ga:La:S:O glasses. The hybrid oxy-chalcohalide glass, Ga:La:S:O:F, contains compounds of sulphide, oxide and fluoride as constituents. This new glass type provides significant thermal stability, in the context of fibre drawing. Fibre drawn from a single piece of polished Ga:La:S:O:F glass had attenuation at 1.5 and 4.0 µm of 3.3 and 2.1 dB m-1 respectively. The reduction of the OH- absorption at 2.9 µm to < 1 ppm in Ga:La:S:O:F glass, can potentially allow development of planar waveguide devices for the mid-IR. A range of extremely stable compositions for Ga:La:S, Ga:La:S:O and Ga:La:S:O:F glasses was also identified. These glasses were amorphous upon slow cooling in the furnace (8 oC min-1) indicating danced thermal stability against crystallisation. In Chapter 4 and 5, the fabrication and characterisation of channel waveguides is discussed. Photoinduced changes were introduced by directly writing waveguides into Ga:La:S glass through exposure to short wavelength light (l = 244 nm). Focused fluence of 1.5 - 150 J/cm2 from a continuous wave laser operating at 244 mn was applied, inducing photocompaction and photochemical changes. These passive channel waveguides were spatially single-mode and bad Dn ~ +10-3. The first chalcogenide channel waveguide laser in Nd3+-Ga:La:S glass was also demonstrated. Maximum laser output (l = 1075 nm) of 8.6 mW for an absorbed laser pump power of 89 mW and slope efficiency of 17% was achieved with measured device attenuation of < 0.5 dB cm-1. Discussed in Chapter 6 is the first demonstration of the hotdip spin coating process used to fabricate thin films of a ChG (Ga:La:S). This promising technique is presented as an enhancement to waveguide development. In addition, buried (50 µm) channel waveguides were directly written into the spun thin film using a pulsed laser source (l = 830 nm). These buried channel waveguides had a measured attenuation of < 1 dB cm-1.
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Panitchob, Yuwapat. "Integration of glass microspheres and planar waveguides for microsphere lasers." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/69881/.
Повний текст джерелаАнотація:
Microsphere resonators with sizes in the micrometer range are reported to support very high Q’s of more than 109 for a fused silica microsphere. This high Q value represents many promising characteristics such as low cavity loss, long cavity life time, and narrow band width. With their remarkable characteristics, microsphere resonators can be used in various applications such as the narrow band filter, add-drop multiplexer, microlasers, and etc. In this work, the integration of microspheres with planar waveguides is the main focus. High quality neodymium-doped BK7 microspheres are fabricated and characterised to observe laser oscillation at 1.06 μm from the 4F3/2 - 4I11/2 transition. Theoretical calculation of the microsphere mode and field and the characteristic equation which describes the relation of the sphere mode numbers l, m, n to the wavelength, are obtained. The theoretical expressions of the microsphere WGM can be described with the sphere mode numbers based on spherical Bessel and Hankel functions. Coupling and quality factors of the waveguide-coupled system are obtained by integrating the overlapped fields of the microsphere and waveguide, and the study of Q factors as a function of sphere/waveguide separation are elaborated. Theoretical models to calculate the total loss and gain of the microsphere lasers and the Q which is required for lasing action, are developed. The expressions for power threshold in the microsphere and in the input waveguide are derived, and the threshold pump power as a function of sphere/waveguide separation is obtained. Experimental work to observe the WGM propagation of a passive microsphere has been carried out, and results obtained at wavelengths in the 800 nm and 1550 nm regions, and modal assignment including the evaluation of Q for each system are carried out. The experiments to observe the fluorescence and the lasing oscillation of the neodymium-doped BK7 microspheres are demonstrated. The measurement of the fluorescence lifetime of a neodymium-doped BK7 microsphere, is obtained. A laser oscillation is demonstrated with the free-space pump excitation, with the threshold pump power of 8 mW at λ = 808nm.
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Harwood, Duncan William John. "Towards a 1.39 µm planar neodymium doped fluoride glass waveguide amplifier." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/15495/.
Повний текст джерелаАнотація:
This thesis describes the steps towards the fabrication of a planar neodymium doped fluoride glass waveguide amplifier operating in the 1.3µm band. Approximations of the amplifier performance, combined with more detailed models of an integrated neodymium doped fluoroaluminate glass amplifier based on spectroscopic measurements from the bulk glass (Nd:ALF70), show that channel waveguides with propagation losses below 0.5dB/cm at the pump wavelength are needed to produce a device with a pump requirement of 200mW or less. In the absence of any fabrication technique available for fluoride glasses with this level of performance, the novel process of hot dip spin coating was developed for the fabrication of single mode Nd:ALF70 planar waveguides. The process is based on the inverted spin coating of molten glass onto a solid glass substrate and currently holds the record for the minimum propagation losses of less than 0.1dB/cm @ 1048nm in a fluoride glass waveguide measured in a 5 micron thick film. In order to capitalise on such exceptional waveguide performance, a new method for fabricating channel waveguides in fluoride glass thin films was developed based on direct UV writing of a negative index change using photothermal expansion. The process is based on generating a negative index change, via exposure to laser radiation at a wavelength of 244nm. The negative index change forms the lower refractive index 'cladding' on either side of the desired guiding region and is induced by a thermal mechanism generated by the large absorption of UV radiation by cerium ions doped into the slab guiding region. A maximum index range of close to 0.01 was produced for a 40µm thick unclad waveguide doped with 0.5mol% Ce3+ and an index change of approximately 2x10-3 was estimated for a 2.5mol% Ce3+ doped, 6 micron thick buried waveguide. Propagation losses of 0.1±0.1dB/cm @ 1048nm were determined by the Findlay-Clay technique for a 90µm wide multimode channel waveguide laser whilst an average value of 0.3±0.1dB/cm @ 1048nm was obtained for less multimode guides with an average width of 20µm. The best device performance has been characterised in a 1mol% Nd3+ doped 90µm wide and 6µm thick waveguide. Laser action at 1048nm has been observed with a slope efficiency of 27% for a 56% output coupler and a threshold pump Power of just 4mW. The threshold for laser action at 1317nm was 32mW for a 0.3% output coupler giving a slope efficiency of 2%. A peak internal gain of 1dB at 1317nm was achieved in this waveguide for a pump power of 100mW and suggests that the performance of optimised single mode guides should be close to that predicted by theory.
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Duffy, Jonathan A. "Positron and positronium annihilation studies of the phase behaviour of carbon dioxide in mesoporous VYCOR glass." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294537.
Повний текст джерела
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Rivers, Paul Edmund. "Pulsed laser deposition of chalcogenide glass materials for potential waveguide laser applications." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/15493/.
Повний текст джерелаАнотація:
There are many applications for small scale, solid state lasers in the near infrared, where conversely there are very few such devices. A lasing device in a rare earth doped gallium-lanthanum-sulphide thin film is attractive due to emission at wavelengths in the 2 to 5 µm region where many gasses and liquids have fundamental vibrations and overtones and so are detectable. This region also covers the 3 to 5 µm atmospheric 'windows'. Some examples of such detection is presented in this thesis. Using Pulsed Laser Deposition, a relatively new deposition technique, we are able to grow thin films of the chalcogenide glass; gallium-lanthanum-sulphide, gallium-sodium-sulphide and variations of oxysulphides, on a variety of substrates. EXAFS measurements have shown that some of the elements in the glass structure change their bonding arrangement when grown at different energy density producing 'wrong bonds'. This points to the origin of the increased absorption and shift of the optical bandgap which is seen in the materials. It is this tail absorption which ultimately prevented the production of an actual solid state, rare earth laser device. These amorphous semiconductors have a transmission range from the visible through to the mid infrared part of the spectrum. Chalcogenides can be photomodified. i.e. they have an ability to change refractive index when illuminated with photons whose energies lie in the optical bandgap of the material. This process can be reversible or irreversible depending on post deposition treatment and so gives them potential applications such as optical memory, holographic recording media, lithographically written waveguide structures and potentially laser mediums. For such uses a detailed knowledge of the chalcogenide materials optical parameters is needed. A novel technique for the optical characterisation of the thin films has been developed which has is able to measure differences in refractive index to an accuracy of 8.5 x 105. We are able to map refractive index changes across an entire surface and more uniquely whilst they are occurring during, and after, photomodification or heating.