Dissertations / Theses on the topic 'Crystal growth and design'
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Masaoka, Shigeyuki. "Studies on Crystal Design and Crystal Growth Control of Multinuclear Metal Complexes." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147663.
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Berry, David J. "Pharmaceutical Co-crystals. Combining thermal microscopy and phase space considerations to facilitate the growth of novel phases." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/4932.
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The crystalline solid state is invaluable to both the pharmaceutical and fine chemical sectors. The advantages primarily relate to reducibility criteria required during processing of stable solid state materials and delivering purification, which is inherently performed by the crystal growth process. A major challenge is achieving control through crystallising solids with the desired physico-chemical properties. If this can be achieved the crystalline solid is of great financial and practical benefit. One emerging methodology for manipulating the solid crystalline form is the application of co-crystals. This work relates to key steps in the understanding of rational design of co-crystals utilizing crystal engineering concepts to determine systems before then applying screening criteria to the selected sub-set. Co-crystal screening is routinely undertaken using high-throughput solution growth. We report a low- to medium-throughput approach, encompassing both a melt and solution crystallization step as a route to the identification of co-crystals. Prior to solution studies, a melt growth step was included utilizing the Kofler mixed fusion method. This method allowed elucidation of the thermodynamic landscape within the binary phase diagram and was found to increase overall screening efficiency. This led to the discovery of a number of co-crystal systems with the co-former nicotinamide, with the single crystal structures determined for the following systems; R/S ibuprofen: nicotinamide, S ibuprofen: nicotinamide, R/S flurbiprofen: nicotinamide and salicylic acid: nicotinamide. To assess the crystallization and phase behaviours of determined co-crystals the R/S ibuprofennicotinamide system was selected and successful studies were undertaken determining the aqueous ternary phase behavior and the pre-nucleation speciation in methanol. There have, as yet, been a limited number of published examples which are concerned with pharmaceutical property enhancement by co-crystals, as vast proportion of the literature concerns the growth and isolation of these novel phases. To elucidate further the pharmaceutical relevance of co-crystals the properties of the R/S ibuprofen- nicotinamide system were then assessed showing a positive profile for this material.
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Patel, Dhaval D. "KINETICS AND MECHANISMS OF CRYSTAL GROWTH INHIBITION OF INDOMETHACIN BY MODEL PRECIPITATION INHIBITORS." UKnowledge, 2015. http://uknowledge.uky.edu/pharmacy_etds/47.
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Supersaturating Drug Delivery Systems (SDDS) could enhance oral bioavailability of poorly water soluble drugs (PWSD). Precipitation inhibitors (PIs) in SDDS could maintain supersaturation by inhibiting nucleation, crystal growth, or both. The mechanisms by which these effects are realized are generally unknown. The goal of this dissertation was to explore the mechanisms underpinning the effects of model PIs including hydroxypropyl β-cyclodextrins (HP-β-CD), hydroxypropyl methylcellulose (HPMC), and polyvinylpyrrolidone (PVP) on the crystal growth of indomethacin, a model PWSD. At high degrees of supersaturation (S), the crystal growth kinetics of indomethacin was bulk diffusion-controlled, which was attributed to a high energy form deposited on the seed crystals. At lower S, indomethacin growth kinetics was surface integration-controlled. The effect of HP-β-CD at high S was successfully modeled using the reactive diffusion layer theory. The superior effects of PVP and HPMC as compared to HP-β-CD at high S were attributed to a change in the rate limiting step from bulk diffusion to surface integration largely due to prevention of the high energy form formation. The effects of PIs at low S were attributed to significant retardation of the surface integration rate, a phenomenon that may reflect the adsorption of PIs onto the growing surface. PVP was selected to further understand the relationship between adsorption and crystal growth inhibition. The Langmuir adsorption isotherm model fit the adsorption isotherms of PVP and N-vinylpyrrolidone well. The affinity and extent of adsorption of PVP were significantly higher than those of N-vinylpyrrolidone, which was attributed to cooperative interactions between PVP and indomethacin. The extent of PVP adsorption on a weight-basis was greater for higher molecular weight PVP but less on a molar-basis indicating an increased percentage of loops and tails for higher molecular weight PVPs. PVP significantly inhibited indomethacin crystal growth at high S as compared to N-vinylpyrrolidone, which was attributed to a change in the growth mechanism resulting in a change in the rate limiting step from bulk diffusion to surface integration. Higher molecular weight PVPs were better inhibitors than lower molecular weight PVPs, which was attributed to a greater crystal growth barrier provided by a thicker adsorption layer.
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Ramesh, Dinesh. "The Role of Interface in Crystal Growth, Energy Harvesting and Storage Applications." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1752367/.
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A flexible nanofibrous PVDF-BaTiO3 composite material is prepared for impact sensing and biomechanical energy harvesting applications. Dielectric polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3)-PVDF nanofibrous composites were made using the electrospinning process based on a design of experiments approach. The ultrasonication process was optimized using a 2k factorial DoE approach to disperse BaTiO3 particles in PVDF solution in DMF. Scanning electron microscopy was used to characterize the microstructure of the fabricated mesh. The FT-IR and Raman analysis were carried out to investigate the crystal structure of the prepared mesh. Surface morphology contribution to the adhesive property of the composite was explained through contact angle measurements. The capacitance of the prepared PVDF- BaTiO3 nanofibrous mesh was a more than 40% increase over the pure PVDF nanofibers. A comparative study of dielectric relaxation, thermodynamics properties and impact analysis of electrospun polyvinylidene fluoride (PVDF) and 3% BaTiO3-PVDF nanofibrous composite are presented. The frequency dependent dielectric properties revealed micro structural features of the composite material. The dielectric relaxation behavior is further supported by complex impedance analysis and Nyquist plots. The temperature dependence of electric modulus shows Arrhenius type behavior. The observed non-Debye dielectric relaxation in electric loss modulus follows a thermally activated process which can be attributed to a small polaron hopping effect. The particle induced crystallization is supported with thermodynamic properties from differential scanning calorimetric (DSC) measurements. The observed increase in piezoelectric response by impact analysis was attributed to the interfacial interaction between PVDF and BaTiO3. The interfacial polarization between PVDF and BaTiO3 was studied using density functional theory calculations and atomic charge density analysis. The results obtained indicates that electrospinning offers a potential way to produce nanofibers with desired crystalline nature which was not observed in molded samples. In addition, BaTiO3 can be used to increase the capacitance, desired surface characteristics of the PVDF nanofibers which can find potential application as flexible piezoelectric sensor mimicking biological skin for use in impact sensing and energy harvesting applications.
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Frewin, Christopher L. "Design and Implementation of a 200mm 3C-SiC CVD Reactor." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001855.
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Despréaux, Stéphane. "Optimisation de forme en cristallogenèse." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10220.
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L'origine de ce travail est l'étude d'un problème industriel sur la mise en forme de cristaux par l'intermédiaire des forces capillaires. Le modèle mathématique utilisé consiste à résoudre un problème surdimensionné basé sur l'équation à courbure principale. Nous avons résolu le problème en lui associant un problème d'optimisation de forme. Le travail présenté dans cette thèse comprend deux principales parties : - l'étude mathématique de l'équation à courbure principale avec conditions aux limites mixtes - l'étude mathématique et numérique du problème d'optimisation de forme. Nous avons prouvé l'existence et l'unicité d'une solution à l'équation à courbure principale moyennant une hypothèse liant la courbure et l'épaisseur du domaine. Cette condition est bien moins restrictive que celle usuellement utilisée qui suppose le domaine convexe. Dans cette classe de domaines, nous avons ensuite prouvé l'existence d'un domaine optimal et mis au point une méthode numérique pour le calculer, par la technique de variation de domaine. Cependant, numériquement, cette méthode nécessite la donnée d'un bon domaine initial. Si ce dernier est mal choisi, l'algorithme diverge vers une forme souvent fantaisiste. Pour obtenir automatiquement un bon domaine initial, nous avons utilisé une technique d'optimisation de forme par domaine fictif. Nous avons ensuite présenté les résultats numériques ainsi obtenus
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Smith, Matthew T. "Design And Development Of A Silicon Carbide Chemical Vapor Deposition Reactor." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000145.
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Kananagh, A. "The crystal growth and crystal growth inhibition of calcium carbonate." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383820.
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Peltier, Raoul. "Biomimetic modification of crystal growth." Thesis, University of Auckland, 2011. http://hdl.handle.net/2292/7150.
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Lee, William Thomas. "Surface relaxations and crystal growth." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621106.
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Gao, Wei. "Crystal growth of alpha-rhombohedral boron." Thesis, Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/4171.
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Dutt, Yougesh Chander. "Crystal growth of monosodium urate monohydrate." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24633.
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Hyperuricemia and local temperature changes in the joints of the extremities are known to be responsible, in part, for the development of gouty arthritis. No satisfactory explanation is yet available for (1) the selective deposition of monosodium urate monohydrate (MSUM) crystals in connective tissues (2) the increased incidence of gout in the later years of life and (3) the increased incidence of MSUM crystal deposition in connective tissues after trauma and in joints with preexisting disease. It is possible that the alterations in composition of the non-fibrillar matrix of cartilage and synovial fluid which are thought to occur with ageing, trauma or preexisting disease, may predispose these tissues to crystal deposition. The objectives of this study were to determine the effect of the cartilage and synovial fluid components, chondroitin sulfate, hyaluronic acid, proteoglycan monomer, proteoglycan aggregate, phospholipids and albumin on the growth of MSUM.
The degradation of MSUM solutions was studied under sterile and non-sterile conditions to determine the possible causes of degradation and to define the time span of crystal growth experiments. The rate of degradation of MSUM solutions increased with an increase in temperature. The concentration of MSUM in solution fell sharply after autoclaving and solutions stored in containers with rubber closures showed greater degradation of MSUM than autoclaved solutions stored in all-glass containers. Rubber stoppers apparently absorbed MSUM from solution. The degradation of MSUM solutions was thought to be due to both bacterial consumption and chemical decomposition in non-sterile solutions but was due only to chemical decomposition in sterile solutions.
The aqueous solubility of MSUM was determined at different temperatures and in the presence of varying concentrations of sodium chloride. Sodium chloride suppressed MSUM solubility.
The aqueous solubility of MSUM was also determined in the presence of several connective tissue components at 37°. Chondroitin sulfate (CS) decreased the saturation solubility of MSUM probably due to the sodium present in the CS samples. Proteoglycan aggregate, proteoglycan monomer, hyaluronic acid an albumin resulted in very slight increases in the solubility of MSUM.
The growth kinetics of MSUM was studied using the seeded growth technique. An equation of the general form: [formula omitted] was used to determine the overall growth rate constant, [formula omitted]. Linear plots of the integrated form of the second order growth equation gave the best fit between the points and gave reasonably constant values for [formula omitted] determined at a given initial supersaturation concentration and varying seed amounts.
An induction period or a period of slow growth was observed at both the initial supersaturation concentrations studied. The length of the induction period was inversely proportional to the added seed amount.
Differing concentrations of additives were included in the growth medium and K' determined.
Chondroitin sulfate (CS) significantly increased the growth rate constant for MSUM growth. However, the proportion of CS decreases in aged and osteoarthritic cartilage and thus a decreasing proportion of a growth accelerator is unlikely to be a factor in the deposition of MSUM in cartilage. CS has been found in the synovial fluid of arthritic joints and may act as an MSUM growth accelerator in this medium.
Hyaluronic acid (HA) and albumin caused significant inhibition of the growth of MSUM crystals. This effect may be due to the adsorption of these molecules onto the MSUM seed crystals resulting in the poisoning of the active growth sites on the crystal surface. Cartilage HA and synovial fluid albumin levels are increased in aged and/or diseased joints. Increased proportions of growth inhibitors do not offer likely explanations of crystal deposition in joint tissues. At concentrations of 0.1-1.0 mg mL⁻¹ proteoglycan monomer (PGM) and proteoglycan aggregate (PGA) slightly increased the MSUM growth rate constant but this increase was statistically insignificant.
The two phospholipids, phosphatidylcholine and phospha-tidylserine increased the growth rate constant of MSUM. Phosphatidylserine, however, did not significantly increase the growth rate constant at the concentrations studied. It is possible that the raised levels of phospholipids in aged or diseased cartilage and synovial fluid could accelerate the growth of MSUM crystals resulting in MSUM deposition in these tissues.Pharmaceutical Sciences, Faculty of
Graduate
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Umemura, Ayako. "Modelling Crystal Growth in Zeolite A." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506601.
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Day, Robert Watson. "Crystal Growth on One-Dimensional Substrates: Plateau-Rayleigh Crystal Growth and Other Opportunities for Core/Shell Nanowire Synthesis." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17464133.
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Nanowires hold significant promise for both fundamental studies and technological applications ranging from energy conversion to electronics to biological sensing. The detailed understanding of nanowire synthesis and the realization of new synthetic approaches have enabled precise control over their size, morphology, and composition, and, consequently, their material properties. While much of the work on synthesis in the literature relates to axial nanowire growth, where growth proceeds in the direction of its long axis, this thesis has focused on probing the unique opportunities of shell growth, where material deposits radially around a nanowire core. To this end, I will show, first, that faceted Si core/shell nanowires can be synthesized with embedded pn junctions and that these structures can function as efficient photovoltaic devices with enhanced light absorption properties distinct from bulk Si devices. Second, through choice of reactants and reaction conditions used for shell growth, we demonstrate fine control over the size and morphology of these nanowires, which, in turn, drastically enhances their light absorption at particular wavelengths. Finally, we report for the first time a growth phenomenon that is unique to one-dimensional materials and which combines the underlying physics of the Plateau-Rayleigh instability with crystal growth. By exploiting this phenomenon, which we term Plateau-Rayleigh crystal growth, we demonstrate the growth of periodic shells on one-dimensional substrates. Specifically, we show that for conditions near the Plateau-Rayleigh instability the deposition of Si onto uniform-diameter Si cores, Ge onto Ge cores, and Ge onto Si cores can generate diameter-modulated core/shell nanowires. Rational control of deposition conditions enabled tuning of distinct morphological features, including diameter-modulation periodicity, amplitude and cross-sectional anisotropy. More generally, Plateau-Rayleigh crystal growth highlights the opportunities in understanding the thermodynamics and kinetics unique to crystal growth on nanowires and other low dimensional systems.Chemistry and Chemical Biology
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Elliott, Mary Alice. "Crystal aging of terephthalic acid." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/10935.
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Do-Quang, Minh. "Melt convection in welding and crystal growth." Doctoral thesis, Stockholm : Department of Mechanics, Royal Institute of Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-83.
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Henderson, M. B. "Fatigue crack growth in single crystal superalloys." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314993.
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Hicks, T. W. "Hydrodynamics of liquid encapsulation Czochralski crystal growth." Thesis, University of Bristol, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233905.
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McComber, Kevin A. "Single-crystal germanium growth on amorphous silicon." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69792.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 130-136).
The integration of photonics with electronics has emerged as a leading platform for microprocessor technology and the continuation of Moore's Law. As electronic device dimensions shrink, electronic signals encounter crippling delays and heating issues such that signal transduction across large on-chip distances becomes increasingly more difficult. However, these issues may be mitigated by the use of photonic interconnects combined with electronic devices in electronic-photonic integrated circuits (EPICs). The electronics in proposed EPIC designs perform the logic operations and short-distance signal transmission, while photonic devices serve to transmit signals over longer lengths. However, the photonic devices are large compared to electronic devices, and thus the two types of devices would ideally exist on separate levels of the microprocessor stack in order to maximize the amount of silicon substrate available for electronic device fabrication. A CMOS-compatible back-end process for the fabrication of photonic devices is necessary to realize such a three-dimensional EPIC. Back-end processing is limited in thermal budget and does not present a single-crystal substrate for epitaxial growth, however, so high-quality crystal fabrication methods currently used for photonic device fabrication are not possible in back-end processing. This thesis presents a method for the fabrication of high-quality germanium single crystals using CMOS-compatible back-end processing. Initial work on the ultra-high vacuum chemical vapor deposition of polycrystalline germanium on amorphous silicon is presented. The deposition can be successfully performed by using a pre-growth hydrofluoric acid dip and by limiting the thickness of the amorphous silicon layer to less than 120 nm. Films deposited at temperatures of 350° C, 450° C, and 550° C show (110) texture, though the texture is most prevalent in growths at 450° C. Poly-Ge grown at 4500 C is successfully doped n-type in situ, and the grain size of as-grown material is enhanced by lateral growth over a barrier. Structures are fabricated for the growth of Ge confined in one dimension. The growths show faceting across large areas, in contrast to as-deposited poly-Ge, corresponding to enhanced grain sizes. Growth confinement is shown to reduce the defect density as the poly-Ge grows. When coalesced into a continuous film, the material grown from 1 D confinement exhibits a lower carrier density and lower trap density than as-deposited poly-Ge, indicating improved material quality. We measure an increased grain size from as-deposited poly-Ge to Ge grown from ID confinement. Single-crystal germanium is grown at 450° C from confinement in two dimensions. Such growths exhibit faceting across the entire crystal as well as the presence of E3 boundaries ({111} twins), with many growths showing no other boundaries. These twins mediate the growth of the crystal, as they serve as the points for heterogeneous surface nucleation of adatom clusters. The twins can form after the crystal nucleates and are strongly preferred in order to obtain appreciable crystal growth rates. We model the growths from the confining channels in order to find the optimum channel geometry for large, uniform, single-crystal growths that consistently emerge from the channel. The growths from 2D confinement show lower trap density than those from 1 D confinement, indicating a further enhancement of the crystal quality due to the increased confinement. This method of single-crystal growth from an amorphous substrate is extensible to any materials system in which selective non-epitaxial deposition is possible.
by Kevin A. McComber.
Ph.D.
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Masheder, Benjamin. "Zirconium molybdate crystal growth and morphological control." Thesis, University of Bristol, 2011. http://hdl.handle.net/1983/e8beeb71-04f4-4a53-8ec8-aa4c1bbdd90b.
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This thesis investigated the formation of zirconium molybdate (ZM) (ZrMo207(OHh)2H20) crystals in conditions designed to reflect those found during the processing of spent nuclear fuel, in which these crystals are seen to form. Greater understanding of the formation of ZM was sought by studying the effect of many chemical species, including many known to be present in the mixture and a number of others specifically selected. The final goal was to provide means to control the creation of ZM crystals which exhibited advantageous physical characteristics. The ZM crystal morphology was found to be highly influenced by a few species which gave rise to several newly characterized novel crystal forms of ZM that exhibited interesting rheological and packing properties.
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Batchelor, E. "Acid:base Co-crystal formation in crystal engineering and supramolecular design." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596460.
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The chemical and physical properties of organic molecular crystals depend on both the molecular and crystal structure. The systematic approach to understanding and controlling crystal structure lies in the field of "crystal engineering". One strategy to emerge within crystal engineering has been the utilisation of specific interactions or couplings / synthons to predictably build supramolecular arrays such as tapes, ribbons or sheets. These arrays form a subset of the crystal structure. While many couplings take the form of cyclic motifs in which component interactions are of comparable strength, a cyclic coupling consisting of an O-- H...N and a C-H...O interaction was noted as having a potential use in designing supramolecular arrays. This type of strong / weak coupling is possible upon the interaction of an N-heterocycle with a carboxyl group. The following research describes the co-crystallisation of various N-heterocyclic bases with a number of olefinic and aliphatic dicarboxylic acids. The crystal structures of various complexes of phenazine, 1,10-phenanthroline and quinoxaline were solved from single-crystal X-ray diffraction data and are discussed. Two distinct strong / weak couplings were identified within the three sets of co-crystals. A comparison of the relative stabilities of the two couplings was made using the quinoxaline system. Supramolecular tapes were observed in all of the phenazine co-crystals and in three of the four quinoxaline co-crystals. (The stoichiometry of the phenazine co-crystals may be related to the position of the carboxyl groups on the participating acid.) The packing of the tapes is discussed with particular reference to tape topography and inter-tape C-H...O interactions. Proton transfer occurred in four of the five co-crystals of 1,10-phenanthroline. Co-crystals were prepared via two methods: by growth from a solution and by grinding of a physical mixture of the starting components. Solid-state grinding was found to be a viable method for the preparation of co-crystals. Complexes of 1,10-phenanthroline prepared via the two routes were analysed using solid-state 13C MAS NMR and the effects of protonation on certain carbon resonances is discussed.
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Aswartham, Saicharan. "Crystal growth and physical properties of Ferro-pnictides." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-99601.
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The thesis work presented here emphasizes important aspects of crystal growth and the influence of chemical substitution in Fe-As superconductors. High temperature solution growth technique is one of most powerful and widely used technique to grow single crystals of various materials. The biggest advantage of high temperature solution growth technique is the, possibility of growing single crystals from both congruently and incongruently melting materials. Solution growth technique has the potential to control high vapour pressures, given the fact that, in Fe-based superconductors elements with high vapour pressure like As, K, Li and Na have to be handled during the crystal growth procedure. In this scenario high temperature solution growth is the best suitable growth technique to synthesize sizable homogeneous single crystals.
Using self-flux high temperature solution growth technique, large centimeter-sized high quality single crystals of BaFe2As2 were grown. This pristine compound BaFe2As2 undergoes structural and magnetic transition at TS/N=137 K. By suppressing this magnetic transition and stabilizing tetragonal phase with chemical substitution, like Co-doping and Na-doping, bulk superconductivity is achieved. Superconducting transitions of as high as Tc = 34 K with Na substitution and Tc = 25 K with Co-doping were obtained. A combined electronic phase diagram has been achieved for both electron doping with Co and hole doping with Na in BaFe2As2.
Single crystals of LiFe1−xCoxAs with x = 0, 0.025, 0.05 and 0.075 were grown by a self-flux high temperature solution growth technique. The charge doping in LiFeAs is achieved with the Co-doping in Fe atoms. The superconducting properties investigated by means of temperature dependent magnetization and resistivity revealed that superconductivity is shifted to lower temperatures and with higher amount of charge carriers superconductivity is killed.
Single crystals of KFe2As2 were grown with two different fluxes, namely, FeAs-flux and KAs-flux. The superconducting transition is found to be at 3.8K in both the crystals. The influence of doping with selected elements like Na, Rh, Co and Cr has been investigated systematically in KFe2As2 single crystals. With Na-doping at the K-site, yield (K1−xNax)Fe2As2; superconductivity is suppressed to lower temperatures.
Substitution of Co and Cr at Fe site, yield K(Fe0.95Co0.05)2As2, K(Fe0.95Cr0.05)2As2 superconductivity is rapidly killed. Single crystals of (Ba0.6Eu0.4)(Fe1−xCox)2As2 with x = 0, 0.05, 0.1, 0.15 and 0.2 were grown with solution growth technique using Fe-As flux and investigated with several physical measurements.
The growth conditions are highly optimized to grow flux free large single crystals especially in case of BaFe2As2 family. The high quality of the crystals were revealed by several physical properties, for e.g. single crystals of Ba(Fe1−xCox)2As2 are of the highest quality which was confirmed by the magnetic ac susceptibility which showed a very sharp superconducting transition.
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Mcmillen, Colin David. "Hydrothermal crystal growth of oxides for optical applications." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1181251539/.
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Haire, Lesley Findlay. "Strategies for protein crystal growth-screening and optimization." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243778.
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Stevens, Sam. "Understanding Porous Crystal Growth By Scanning Electron Microscopy." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532223.
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Webster, Gareth. "Sucrose crystal growth kinetics using a rotating disc." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277687.
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Braybrook, Alison Louise. "Parallel computational and experimental studies of crystal growth." Thesis, Keele University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251513.
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Lin, Chenting. "Single crystal growth and characterization of BSO (Bi12SiO20)." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11647.
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Bordui, Peter Frank. "Crystal growth of KTiOPO₄ from high-temperature solution." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14962.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Vita.
Bibliography: leaves 117-119.
by Peter Frank Bordui.
Ph.D.
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Brakel, Thomas W. "Mathematical modelling of the Czochralski crystal growth process." Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4868.
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Includes bibliographical references (leaves 142-149).In this document a mathematical model for the Czochralski crystal growth process is developed. The trend in current research involves developing cumbersome numerical simulations that provide little or no understanding of the underlying physics. We attempt to review previous research methods, mainly devoted to silicon, and develop a novel analytical tool for indium antimonide (lnSb) crystal growth. This process can be subdivided into two categories: solidification and fluid mechanics. Thus far, crystal solidification of the Czochralski process has been described in the literature mainly qualitatively. There has been little work in calculating actual solidification dynamics. Czochralski crystal growth is a very sensitive process, particularly for lnSb, so it is crucial to describe the system as accurately as possible. A novel ID quasi-steady method is proposed for the shape and temperature field of an lnSb crystal, incorporating the effects of the melt. The fluid mechanics of the Czochralski melt have been modelled by numerous researchers,with calculations performed using commercial software. However, a descriptionof the buoyancy and rotation interaction in the melt has not been adequatelyperformed. Many authors have presented flow patterns but none have indicated either: melt conditions preferential for crystal growth or at least a description of a typical melt structure. In this work, a scale analysis is performed that implies an idealized flow structure. An asymptotic model is then derived based on this order of magnitude analysis, resulting in a fast and efficient fluid flow calculation. The asymptotic model is validated against a numerical solution to ensure that the macroscopic features of the flow structure are present. The asymptotic model does not show exact agreement, but does provide an estimate of the melt heat flux that is necessary for the solidification calculation. The asymptotic model is also used to predict macroscopic changes in the melt due to rotation.
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Zhang, Hao. "Gravity-dependent transport phenomena in zeolite crystal growth." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1060021149.
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Vompe, Dmitry A. "Numerical modeling of crystal growth in bridgman device /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487947501136706.
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Smith, Rachel. "Probing crystal growth in methanol-to-olefins catalysts." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/probing-crystal-growth-in-methanoltoolefins-catalysts(83b999a1-775e-4e55-8e94-47403d2a86c6).html.
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The methanol-to-olefins reaction is an important industrial process for the production of light olefins (C2-C4). Silicoaluminophosphates are the most common catalysts for this process with SAPO-34 (CHA), SAPO-18 (AEI) and their intergrowths being considered the most catalytically active and selective. Understanding the crystal growth of such materials is important for control of the structure and defect incorporation, which can have a large effect on the catalytic behaviour. In this thesis, the synthesis, characterisation, catalysis and crystal growth of such materials are investigated. A series of CHA/AEI intergrowth materials were synthesised by sequential increases in silicon content, where low silicon content led to formation of AEI and higher silicon content led to CHA and intergrowth formation. X-ray diffraction and MAS-NMR were used to quantify the amount of intergrowth and there was a strong correlation between both techniques. Atomic Force Microscopy (AFM) revealed the mechanism by which these intergrowth structures grow. There is competition at the surface between the spiral-growth and layer-growth mechanisms, which has a significant effect on the resulting intergrowth, as intergrowth formation is only permitted with a layer-growth mechanism. Intergrowth on screw dislocations is not allowed, and thus discrete blocks of pure-phase AEI or CHA form. These intergrowth materials were tested for their performance in the methanol-to-olefins reaction. With a higher level of silicon, the catalysts had a larger acid site density but equivalent acid strength. The conversion of methanol over the catalysts correlated with the acid site density, where a greater acid site density led to higher conversion and faster deactivation. The selectivity over time was similar for all catalysts, with a high selectivity to ethylene and propylene. However, at the same percentage conversion, the C2/C3 ratio showed a strong correlation to the cage shape. Catalysts with a higher ratio of AEI cages had a higher selectivity to C3 and C4 products than the other catalysts, owing to the larger size of the internal AEI cage compared to the CHA cage. The crystal growth mechanism on SAPO-18 was investigated in detail to interrogate the complex spiral pattern that forms on the surface. Spirals form in a triangular type pattern due to differences in growth rates in different crystallographic directions. Interlaced terraces were also present. The unit cell and the relative orientation of the AEI cages define the different growth rates. In-situ AFM was used to investigate the dissolution behaviour of SAPO-18 and SAPO-34. In both cases, dissolution occurred via classical step retreat. The similarity in the layer stacking in both materials led to equivalent structure dissolution in both cases. The 0.9 nm layers dissolved first to 0.7 nm (closed cages) then to 0.4 nm (unstable intermediates). Dissolution of SAPO-18 revealed unusual spiral dissolution pits near the core of the dislocations. CHA/AEI intergrowth materials were also prepared using a dual-template method, where two templates, morpholine for CHA and N,N-diisopropylethylamine for AEI, were combined during synthesis. The phase transition from CHA to AEI occurred at different molar ratios with different synthesis procedures. XRD modelling confirmed the synthesis of an intergrowth phase at a molar ratio of 70% morpholine and 30% DPEA. Changes in chemical shift in the 13C MAS-NMR were used to observe the different template interactions with the framework as the ratio of CHA and AEI cages changed.
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Dahal, Yuba Raj. "Equilibrium and kinetic factors in protein crystal growth." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/36220.
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Doctor of PhilosophyDepartment of Physics
Jeremy D. Schmit
Diseases such as Alzheimer’s, Parkinson’s, eye lens cataracts, and Type 2 diabetes are the results of protein aggregation. Protein aggregation is also a problem in pharmaceutical industry for designing protein based drugs for long term stability. Disordered states such as precipitates and gels and ordered states such as crystals, micro tubules and capsids are both possible outcomes of protein–protein interaction. To understand the outcomes of protein–protein interaction and to find the ways to control forces, it is required to study both kinetic and equilibrium factors in protein–protein interactions. Salting in/salting out and Hofmeister effects are familiar terminologies used in protein science field from more than a century to represent the effects of salt on protein solubility, but they are yet to be understood theoretically. Here, we build a theory accounting both attractive and repulsive electrostatic interactions via the Poisson Boltzmann equation, ion–protein binding via grand cannonical partition function and implicit ion–water interaction using hydrated ion size, for describing salting in/salting out phenomena and Hofmeister and/or salt specific effect. Our model free energy includes Coulomb energy, salt entropy and ion–protein binding free energy. We find that the salting in behavior seen at low salt concentration near the isoelectric point of the protein is the output of Coulomb energy such that the addition of salt not only screens dipole attraction but also it enhances the monopole repulsion due to anion binding. The salting out behavior appearing after salting in at high salt concentration is due to a salt mediated depletion interaction. We also find that the salting out seen far from the isoelectric point of the protein is dominated by the salt entropy term. At low salt, the dominant effect comes from the entropic cost of confining ions within the aggregates and at high salt, the dominant effect comes from the entropy gain by ions in solution by enhancing the depletion attraction. The ion size has significant effects on the entropic term which leads to the salt specificity in the protein solubility. Crystal growth of anisotropic and fragile molecules such as proteins is a challenging task because kinetics search for a molecule having the correct binding state from a large ensemble of molecules. In the search process, crystal growth might suffer from a kinetic trap called self–poisoning. Here, we use Monte Carlo simulation to show why protein crystallization is vulnerable to the poisoning and how one can avoid such trap or recover crystal growth from such trap during crystallization. We show that self–poisoning requires only three minimal ingredients and these are related to the binding affinity of a protein molecule and its probability of occurrence. If a molecule attaches to the crystal in the crystallographic state then its binding energy will be high but in protein system this happens with very low probability (≈ 10−5). On the other hand, non–crystallographic binding is energetically weak, but it is highly probable to happen. If these things are realized, then it will not be surprising to encounter with self–poisoning during protein crystallization. The only way to recover or avoid poisoning is to alter the solution condition slightly such as by changing temperature or salt concentration or protein concentration etc.
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Woo, Robyn Lai-wun. "Crystal growth and properties of indium phosphide nanowires." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1692370461&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Succaw, Gary Lee. "Dynamics of crystal growth of self-assembling systems /." view abstract or download file of text, 2004. http://wwwlib.umi.com/cr/uoregon/fullcit?p3136448.
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Thesis (Ph. D.)--University of Oregon, 2004.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 209-215). Also available for download via the World Wide Web; free to University of Oregon users.
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Rocco, Luisa. "Crystal growth and physical properties of helimagnetic oxides." Doctoral thesis, Universita degli studi di Salerno, 2017. http://hdl.handle.net/10556/2572.
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2015 - 2016This work is focused on two helimagnetic materials: Ba2CuGe2O7 and Cu3Nb2O8. Recent studies report a number of interesting anisotropic proper- ties [1, 2, 3]. Ba2CuGe2O7 melilite oxide shows a complex magnetic behaviour, indeed it is known that at low temperature the system undergoes a transition from a paramagnetic phase to an incommensurate antiferromagnetic cycloid spin structure. Applying a magnetic field, additional magnetic transitions take place, as for example a spin-cone phase [3]. Moreover, Ba2CuGe2O7 shows also multiferroic properties [1]. Several works report that the physical properties of melilite oxides mainly depend on the nature of the transition metal ion, thus interesting proper- ties could emerge in mixed melilite oxides. In this work Ba2MGe2O7 with M=Cu,Ni and Mn have been studied. Cu3Nb2O8 is an unusual helimagnetic compound that undergoes a series of magnetic ordering at low temperature. Development of electric polarization P has been reported at TN=25K corresponding to emergence of a non-collinear helicoidal ordering. P is oriented perpendicularly to the common plane of rotation of the spins. This observation cannot be reconciled with the conven- tional theory developed for cycloidal multiferroics [2]. The study of all these complex anisotropic phenomena requires the availability of good single crystals. In this thesis, an investigation on crystal growth conditions of Ba2MGe2O7 and of Cu3Nb2O8 will be presented [4, 5]. Single crystal samples are vital to study the physical properties exhibited by compounds which have high magnetic/ferroelectric anisotropy where significantly different behaviour is seen along different crystallographic directions. Preliminarily, high quality polycrystalline powders have been prepared for all compounds, indeed this is a critical point to grow pure crystalline samples. 1 Abstract 2 In this work the procedure to synthesize polycrystalline powders with high purity is reported. Moreover, by using powder X-ray diffraction and energy dispersive spectroscopy (EDS), the composition of the starting polycrystalline powder is checked. Successfully, the growth conditions to realize large and pure single crystals suitable for low temperature magnetometry and lattice dynamic studies are described. The chemical composition and the morphology of the crystals are investigated by X-ray diffraction and by scanning electron microscopy (SEM), with wave- length dispersive spectrometry (WDS). Furthermore, the excellent quality of the crystals is confirmed by rocking curve measurements. The X-ray Laue back reflection and electron backscattered diffraction (EBSD) techniques are used to orient single crystals specifically for selected experi- ments. To study the magnetic phase diagrams of grown crystals, magnetization measurement vs temperature is performed in the range 1.5 K
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SIBILIA, MIRTA. "Organic semiconducting single crystal growth on naostructured matrices." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908140.
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In recent years, the development of the organic electronics has led to the employment of organic materials as the basis for many electronic devices, such as organic light emitting diodes, organic field effect transistors, organic solar cells and radiation sensors. As regards radiation sensors, the studies reported in literature mainly refer to devices based on thin film organic semiconductors, which, however, present problems due to instability, degradation and low reproducibility. Organic single crystals overcame most of the major limitations inherent to thin film-based detectors.
In this experimental work, a starting plethora of commercially available compounds has been crystallized and evaluated in terms of both overall crystallizability and applicability as direct X-ray detectors. This first step of work allow to select only those structures capable to provide single-crystals with good morphological properties and electronic properties suitable for X-ray detections.
A careful screening of some thermodynamic variables affecting the growth has been carried out and the obtained results suggest applicability of the present approach to achieve the control of size, quality and crystal habit. Indeed, single crystals with dimensional and morphological properties suitable to the application as X-ray detector have been prepared.
Single-crystals have been physically attached to Au electrodes deposited on a thin film of polyethylennaphthalate – via the functionalization of the electrode with different self-assembled monolayers (SAMs), chemically and structurally similar to the molecule constituting the selected crystal. In particular, two of the explored SAMs showed very promising results in the first qualitative adhesion tests.
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Al-Tamimi, Mohammed A. "Growth of gallium nitride on silicon substrate using the interlayer growth technique." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1173462509.
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Perryman, L. J. "Cavity growth mechanism maps." Thesis, University of Surrey, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381676.
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Lloyd, Gareth Owen. "Crystal engineering of porosity." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/1087.
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Rätsch, Christian. "Effects of strain on heteroepitaxial growth dynamics." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30647.
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Tong, Wusheng. "Chemical beam epitaxial growth of ZnS : growth kinetics and novel electroluminescent strutures." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/31012.
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Srivastava, Ankit. "Void Growth and Collapse in a Creeping Single Crystal." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc84281/.
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Aircraft engine components can be subjected to a large number of thermo-mechanical loading cycles and to long dwell times at high temperatures. In particular, the understanding of creep in single crystal superalloy turbine blades is of importance for designing more reliable and fuel efficient aircraft engines. Creep tests on single crystal superalloy specimens have shown greater creep strain rates for thinner specimens than predicted by current theories. Therefore, it is necessary to develop a more predictive description of creep processes in these materials for them to be used effectively. Experimental observations have shown that the crystals have an initial porosity and that the progressive growth of these voids plays a major role in limiting creep life. In order to understand void growth under creep in single crystals, we have analyzed the creep response of three dimensional unit cells with a single spherical void under different types of isothermal creep loading. The growth behavior of the void is simulated using a three dimensional rate dependent crystal plasticity constitutive relation in a quasi-static finite element analysis. The aim of the present work is to analyze the effect of stress traixiality and Lode parameter on void growth under both constant true stress and constant engineering stress isothermal creep loading.
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Moh, Pak Yan. "Crystal growth of the metal-organic framework ZIF-8." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/crystal-growth-of-the-metalorganic-framework-zif8(03e7bf63-dc66-48f7-9786-86b98caaf6eb).html.
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The crystal growth of nanoporous materials is different from most other classes of material in that their framework architectures contain periodic arrangement of pores or voids in which there is no direct bonding between adjacent units of the framework. This poses a variety of questions as to how such parts of framework develop during the crystallization process, atomistically and energetically. Here we use the nanoporous metal-organic framework, ZIF-8 as a prototypical material to obtain a basic understanding of the growth of a nanoporous material. The crystals of ZIF-8 produced in the N,N-dimethylformamide solvent [ZIF-8(DMF)] and methanol-co-N,N-dimethylformamide solvent [ZIF-8(MeOH)] are both rhombic dodecahedron in shape with a much smaller crystal size in the latter. In the study of the kinetics of ZIF-8(DMF) crystallization, we get a good agreement in the values of activation energies using both Avrami-Erofe’ev-Hancock-Sharp and Gualtieri’s models, i.e. about 120 kJ mol-1 for nucleation, and 95 kJ mol-1 for crystal growth process. The study of kinetics of ZIF-8 surface growth, by in situ AFM, with ZIF-8(DMF) as seed crystal that are grown in the methanolic growth solution we see faster rate in the <100> directions than the <110> directions, with the most probable activation energy of about 80 kJ mol-1 in both directions. This is the first example of in situ AFM being used to obtain activation energy for a surface growth in MOF. We also reveal here that growth process of ZIF-8 occurs through the nucleation and spreading of successive metastable unenclosed sub-steps to eventually form stable terrace steps of the enclosed framework structure in which this process is reliant on the presence of nonframework species to connect the framework species that have voids between them. The experiments also enable identification of some of the fundamental units in the growth process and the stable crystal surface plane. Further, the spreading of terraces at high supersaturation condition (early state) is fairly isotropic as is seen through the formation of almost-rounded terraces on the surface of ZIF-8. The growth direction becomes clear as the supersaturation condition nears to equilibrium (later stage) by the formation of rhombohedral terraces with pointy ends growing along the <100>, and <110> directions and straight edges growing perpendicular to the <111> direction. Formation of this rhombohedral morphology is explained by a coarse grain approach similar to that used in the Kossel model by making assumptions that the sodalite cage is the growth unit and attachment of one sodalite cage in each growth direction is the rate determining step for the formation of a new row of sodalite cages in each direction. Finally, based on the profiles of growth spirals formed from screw dislocations on the ZIF-8 surface obtained from the ex situ AFM images and ICE theory, plausible screw dislocations with Burgers’ vector of 1/2 <111> and <100>, but not <110>, are deduced. Some of the findings in this work will be applicable to numerous nanoporous materials, and the work in general will support efforts to synthesize and design new framework materials and to control the crystal properties of these materials.
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Brendel, Lothar. "Lebensdauer lagenweisen Kristallwachstums Lifetime of layer wise crystal growth /." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=965481476.
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Brendel, Lothar. "Lebensdauer lagenweisen Kristallwachstums - Lifetime of Layer-Wise Crystal Growth." Gerhard-Mercator-Universitaet Duisburg, 2002. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-09272002-010843/.
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The lifetime of layer-by-layer growth of crystal surfaces, mainly in the context of growth conditions found in molecular beam epitaxy (MBE), is the central issue of this thesis. These conditions imply a driven system far from equilibrium which relaxes due to surface diffusion. At first, the ceasing of layer-by-layer growth due to fluctuations in the particle supply is considered. A theory for the according lifetime is presented and confirmed for the one-dimensional surface. Special care is taken for the two-dimensional case where deviations from previous results are found, explained, and used to revise the assumptions on which the theory is based. In particular the applicability of the -- commonly accepted -- conserved KPZ continuum equation and the premise of a single morphologically relevant length scale are affected. The practically more relevant scenario of layer-by-layer growth's breakdown caused by barriers to interlayer transport (which give rise to the Villain instability) is studied. Data obtained fr om computer simulations is compared to the predictions of a linear stability analysis and is used to foretell the effect of counteracting variations of energy barriers. The latter enables to decide in which cases a strained surface is either hindering or advantageous for layer-by-layer growth. A mean field model describing surface growth, which lacked up to now a systematic treatment, is investigated. For the basic version, the asymptotic behavior is derived exactly and -- tuning the sole control parameter -- a transition from Poisson-like growth to persistent layer-by-layer growth is found together with a non-trivial powerlaw behavior right at the transition point. Finally the extensibility of the model to include a finite lifetime of layer-wise growth is examined. The damping of oscillations of certain surface-sensitive quantities is the manifestation of the surface's roughening which terminates the layer-by-layer growth. A scenario alternative to the roughening is suggested. It leads as well to damping of oscillations and consists of a step bunch which dissolves during growth and 'floods' an adjacent terrace. Growth simulations of this process are compared to a deterministic model and to experimental results. Finally several toy models for surface growth, subjected to noise reduction are considered. The latter technique makes possible layer-by-layer growth also in these models and the dependence of its lifetime on the degree of the noise reduction is studied. The main focus is on the behavior's relation to continuum equations and the corresponding universality classes, which are commonly used to classify the different models.
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Zhumekenov, Ayan A. "Halide Perovskite Single Crystals: Design, Growth, and Characterization." Diss., 2020. http://hdl.handle.net/10754/664934.
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Halide perovskites have recently emerged as the state-of-the-art semiconductors with the unique combination of outstanding optoelectronic properties and facile solution synthesis. Within only a decade of research, they have witnessed a remarkable success in photovoltaics and shown great potential for applications in light-emitting devices, photodetectors, and high-energy sensors. Yet, the majority of current perovskite-based devices still rely on polycrystalline thin films which, as will be discussed in Chapter 2, exhibit inferior charge transport characteristics and increased tendency to chemical degradation compared to their single-crystalline analogues. In this regard, unburdened from the effects of grain boundaries, single crystals demonstrate the upper limits of semiconductor performance. Their study is, thus, important from both fundamental and practical aspects, which present the major objectives of this dissertation.
In Chapter 3, we study the intrinsic charge transport and recombination characteristics of single crystals of formamidinium lead halide perovskites. While, in Chapter 4, we investigate the mechanistic origins of rapid synthesis of halide perovskite single crystals by inverse temperature crystallization. Understanding the nucleation and growth mechanisms of halide perovskites enables us to design strategies toward integrating their single crystals into device applications. Namely, in Chapters 5 and 6, we demonstrate crystal engineering approaches for tailoring
the thicknesses and facets of halide perovskite single crystals to make them suitable for, respectively, vertical and planar architecture optoelectronic devices. The findings of this dissertation are expected to benefit future studies on fundamental characterization of halide perovskites, as well as motivate researchers
to develop perovskite-based optoelectronic devices with better crystallinity, performance and stability.
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Hsia, Ying-Ting, and 夏英庭. "Zone-Leveling Czochralski Growth of Lithium Niobate Crystals-Crystal Diameter Control and Hot-Zone Design." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/30544748039818108456.
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碩士國立臺灣大學
化學工程學研究所
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In industry, lithium niobate (LN) single crystals are usually grown by the Czochralski (Cz) method. Because the Cz growth is a batch process, the distribution of dopant concentration in not uniform in the growth direction direction due to segregation. With a continuous solid feeding, this problem can be improved greatly by the zone-leveling Czochralski (ZLCz) method. Nevertheless, the ZLCz LN growth still has problems in diameter control and cracking of the crystal. In principle, the ZLCz method is a self-stabilized system, and the crystal diameter could be controlled by the temperature gradient above the melt level. Unfortunately, due to the end effect of the thermal environment, a constant diameter growth is hard to achieve. In this study, an upper weighting system was designed, and applied successfully to the diameter control of LN growth. The diameter variation of a 4-cm-diameter crystal over 9 cm in length was below 3%. On the other hand, the crystal cracking was found to be the cause of a large thermal gradient of over 20oC/cm for a 2-in-diameter crystal having the growth rate of 3mm/h. By using a heat pipe and a cover made of platinum, the region having smaller thermal gradients was extended to more than 9cm. As a result, a cracking-free single crystal could be easily grown.
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Winkenwerder, Wyatt August 1981. "Surface chemistry of FeHx with dielectric surfaces : towards directed nanocrystal growth." 2008. http://hdl.handle.net/2152/17825.
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The surface chemistry of GeH[subscript x] with dielectric surfaces is relevant to the application of germanium (Ge) nanocrystals for nanocrystal flash memory devices. GeH[subscript x] surface chemistry was first explored for thermally-grown SiO₂ revealing that GeH[subscript x] undergoes two temperature dependent reactions that remove Ge from the SiO₂ surface as GeH₄ and Ge, respectively. Ge only accumulates due to reactions between GeH[subscript x] species that form stable Ge clusters on the SiO₂ surface. Next, a Si-etched SiO₂ surface is probed by GeH[subscript x] revealing that the Si-etching defect activates the surface toward Ge deposition. The activation involves two separate reactions involving, first, the capture of GeH[subscript x] by the defect and second, a reaction between the captured Ge and remaining GeH[subscript x] species leading to the formation of Ge clusters. Reacting the defect with diborane, deactivates it toward GeH[subscript x] and also deactivates intrinsic hydroxyl groups toward GeH[subscript x] adsorption. A structure is proposed for the Si-etching defect. The surface chemistry of GeHx with HfO₂ is studied showing that the hafnium germinate that forms beneath the Ge nanocrystals exists as islands and not a continuous film. Annealing the hafnium germinate under a silane atmosphere will reduce it to Ge while leading to the deposition of hafnium silicate (HfSiO[subscript x]) and silicon (Si). Treating the HfO₂ with silane prior to Ge nanocrystal growth yields a surface with hafnium silicate islands on which Si also deposits. Ge deposition on this surface leads to the suppression of hafnium germinate formation. Electrical testing of capacitors made from Ge nanocrystals and HfO₂ shows that Ge nanocrystals encapsulated in Si/HfSiO[subscript x] layers have greatly improved retention characteristics.text