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Nerowski, Alexander. "Electrochemical Metal Nanowire Growth From Solution." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-118937.
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The aim of this work is to make electrochemical metal nanowire growth a competitive method, being up to par with more standardized procedures, like e.g. lithography. This includes on the one hand the production of nanowires as reliable and reproducible parts, potentially suited for nanoelectronic circuit design. Therefore, this work presents a systematic investigation of the causes of nanowire branching, the necessary conditions to achieve straight growth and the parameters affecting the diameter of the wires. The growth of ultrathin (down to 15 nm), straight and unbranched platinum nanowires assembly is demonstrated. On the other hand, it is the objective to go beyond purely electronic applications. An examination of the crystallography of the wires reveals nanoclusters inside the wire with a common crystallographic orientation. The versatility of the wires is illustrated by implementing them into an impedimetric sensor capable of the detection of single nanoscaled objects, such as bacteria<br>Die Zielstellung der vorliegenden Arbeit ist es, die elektrochemische Herstellung von metallischen Nanodrähten zu einer wettbewerbsfähigen Methode zu machen, die sich mit standardisierten Prozessen, wie z. B. der Lithographie messen kann. Dies beinhält auf der einen Seite die Produktion der Nanodrähte als zuverlässige und reproduzierbare Bauteile, die im nanoelektrischen Schaltungsdesign Verwendung finden können. Daher befasst sich diese Arbeit mit einer systematischen Untersuchung der Ursachen für die Verzweigung von Nanodrähten, den notwendigen Bedingungen um gerades Wachstum zu erlangen und mit den Parametern, die Einfluss auf den Durchmesser der Drähte haben. Der Wuchs von sehr dünnen (bis zu 15 nm), geraden und unverzweigten Nanodrähten aus Platin wird gezeigt. Auf der anderen Seite ist es erklärtes Ziel, über rein elektronische Anwendungen hinaus zu gehen. Eine Untersuchung der Kristallographie der Nanodrähte zeigt, dass die Drähte aus Nanopartikeln bestehen, die eine gemeinsame kristallographische Orientierung aufweisen. Die Vielseitigkeit der Drähte wird anhand einer Sensoranwendung gezeigt, mit der es möglich ist, einzelne nanoskalige Objekte (wie z. B. Bakterien) zu detektieren
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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.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.<br>Vita.<br>Bibliography: leaves 117-119.<br>by Peter Frank Bordui.<br>Ph.D.
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Hodgen, Stephanie Lynne. "Investigation of crystal growth from solution using atomic force microscopy." Thesis, University of Strathclyde, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416199.
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Sullivan, Rachel. "Molecules, clusters and crystals : the crystallisation of p-aminobenzoic acid from solution." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/molecules-clusters-and-crystals-the-crystallisation-of-paminobenzoic-acid-from-solution(ec826e71-782f-4bb0-9dc2-48cf94a7c941).html.
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Nucleation is a key step in the crystallisation process, where a new crystalline solid phase is created from a supersaturated solution. The applications of crystallisation as a purification and separation technique span many industries, yet still no definitive molecular mechanism for nucleation exists. This PhD is part of a critical mass research project involving researchers from both the Universities of Manchester and Leeds. The aim is to reveal the relationship between structural components of the nucleation transition state, solution phase molecular self-assembly and nano cluster formation, through to critically sized crystalline nuclei which then grow to crystals. All work has been carried out on a small organic molecule, p-aminobenzoic acid (PABA). This PhD has delivered successful characterisation of PABA in the solid and solution state, along with a detailed understanding of its nucleation kinetics and growth rates from a range of solvents. PABA has two enantiotropically related polymorphs, α and β, with the former constructed of carboxylic acid dimers and the latter of a hydrogen bonded tetramer network linking alternate acid and amine functionalities. New determinations of the crystal structures of both forms were submitted to the CCDC with Ref codes of AMBNAC07 and 08 for α and β PABA respectively. A detailed morphological study on both forms of PABA employing modelling and experimental methods has revealed the effect of solvent on the growth habit. In all polar solvents, α PABA displays a more important or slower growing (002) face than the calculated morphology implies. In water, β PABA has a much smaller (101 ̅) face in comparison to β PABA grown from alcohols. Crystallisation experiments demonstrate a clear solvent effect on the appearance of the two polymorphs. From organic solvents only α PABA is obtained, from water both α and β PABA are crystallised. A database search (CCDC) suggests that water may play an important role in the stabilisation of the nucleation transition state for both α and β PABA. This is not possible in organic solvents. Detailed nucleation and crystal growth kinetics have been measured for α PABA at 20°C in water, acetonitrile, ethyl acetate and 2-propanol. A clear solvent trend was observed in both the derived rates of molecular attachment and crystal growth. These were fastest in water, followed by acetonitrile, then ethyl acetate and finally slowest, in 2-propanol. This can be explained by the solvation of the carboxylic acid functional group, where 2-propanol is deemed the most effective solvator of building units in solution and on a crystal surface. This conclusion is supported by the solution FTIR spectroscopy, which clearly confirms strong solvation.
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Ghani, Fatemeh. "Nucleation and growth of unsubstituted metal phthalocyanine films from solution on planar substrates." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2013/6469/.
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Organic solar cells (OSC) are interesting as low cost alternative to conventional solar cells. Unsubstituted Metal-phthalocyanines (Pc) are excellent electron donating molecules for heterojunction OSC. Usually organic solar cells with Pcs are produced by vapor deposition, although solution based deposition (like spin casting) is cheaper and offers more possibilities to control the structure of the film. With solution based deposition several parameters (like temperature, solvent and etc.) affect the self-organized structure formation via nucleation and growth. The reason why vapor deposition is typically used is the poor solubility of the metal-phthalocyanines in most common solvents. Furthermore the process of nucleation and growth of Pc aggregates from solution is not well understood. For preparation of Pc films from solution, it is necessary to find the appropriate solvents, assess the solution deposition techniques, such as dip coating, and spin casting. It is necessary to understand the nucleation and growth process for aggregation/precipitation and to use this knowledge to produce nanostructures appropriate for OSC. This is important because the nanostructure of the films determines their performance.
In this thesis, optical absorption and the stability of 8 different unsubstituted metal Pc’s were studied quantitatively in 28 different solvents. Among the several solution based deposited thin films produced based on this study, copper phthalocyanine (CuPc) dissolved in trifluoroacetic acid (TFA) is chosen as a model system for an in-depth study. CuPc has sufficient solubility and stability in TFA and upon solution processing forms appropriate structures for OSCs. CuPc molecules aggregate into layers of nanoribbons with a thickness of ~ 1 nm and an adjustable width and length. The morphology and the number of deposited layers in the thin films are controlled by different parameters, like temperature and solution concentration. Material properties of CuPc deposited from TFA are studied in detail via x-ray diffraction, UV-Vis and FT-IR spectroscopy. Atomic force microscopy was used to study the morphology of the dried film.
The mechanism of the formation of CuPc nanoribbons from spin casted CuPc/TFA solution in ambient temperature is investigated and explained. The parameters (e.g. solution concentration profile) governing nucleation and growth are calculated based on the spin casting theory of a binary mixture of a nonvolatile solute and evaporative solvent. Based on this and intermolecular interactions between CuPc and substrate a nucleation and growth model is developed explaining the aggregation of CuPc in a supersaturated TFA solution.
Finally, a solution processed thin film of CuPc is applied as a donor layer in a functioning bilayer heterojunction OSC and the influence of the structure on OSC performance is studied.<br>In den vergangenen Jahren wurden kosteneffiziente nasschemische Beschichtungsverfahren für die Herstellung organischer Dünnfilme für verschiedene opto-elektronische Anwendungen entdeckt und weiterentwickelt. Unter anderem wurden Phthalocyanin-Moleküle in photoaktiven Schichten für die Herstellung von Solarzellen intensiv erforscht. Aufgrund der kleinen bzw. unbekannten Löslichkeit wurden Phthalocyanin-Schichten durch Aufdampfverfahren im Vakuum hergestellt. Des Weiteren wurde die Löslichkeit durch chemische Synthese erhöht, was aber die Eigenschaften von Pc beeinträchtigte. In dieser Arbeit wurde die Löslichkeit, optische Absorption und Stabilität von 8 verschiedenen unsubstituierten Metall-Phthalocyaninen in 28 verschiedenen Lösungsmitteln quantitativ gemessen. Wegen ausreichender Löslichkeit, Stabilität und Anwendbarkeit in organischen Solarzellen wurde Kupferphthalocyanin (CuPc) in Trifluoressigsäure (TFA) für weitere Untersuchungen ausgewählt.
Durch die Rotationsbeschichtung von CuPc aus TFA Lösung wurde ein dünner Film aus der verdampfenden Lösung auf dem Substrat platziert. Nach dem Verdampfen des Lösungsmittels, die Nanobändern aus CuPc bedecken das Substrat. Die Nanobänder haben eine Dicke von etwa ~ 1 nm (typische Dimension eines CuPc-Molekül) und variierender Breite und Länge, je nach Menge des Materials. Solche Nanobändern können durch Rotationsbeschichtung oder auch durch andere Nassbeschichtungsverfahren, wie Tauchbeschichtung, erzeugt werden. Ähnliche Fibrillen-Strukturen entstehen durch Nassbeschichtung von anderen Metall-Phthalocyaninen, wie Eisen- und Magnesium-Phthalocyanin, aus TFA-Lösung sowie auf anderen Substraten, wie Glas oder Indium Zinnoxid.
Materialeigenschaften von aufgebrachten CuPc aus TFA Lösung und CuPc in der Lösung wurden ausführlich mit Röntgenbeugung, Spektroskopie- und Mikroskopie Methoden untersucht. Es wird gezeigt, dass die Nanobänder nicht in der Lösung, sondern durch Verdampfen des Lösungsmittels und der Übersättigung der Lösung entstehen. Die Rasterkraftmikroskopie wurde dazu verwendet, um die Morphologie des getrockneten Films bei unterschiedlicher Konzentration zu studieren.
Der Mechanismus der Entstehung der Nanobändern wurde im Detail studiert. Gemäß der Keimbildung und Wachstumstheorie wurde die Entstehung der CuPc Nanobänder aus einer übersättigt Lösung diskutiert. Die Form der Nanobändern wurde unter Berücksichtigung der Wechselwirkung zwischen den Molekülen und dem Substrat diskutiert.
Die nassverarbeitete CuPc-Dünnschicht wurde als Donorschicht in organischen Doppelschicht Solarzellen mit C60-Molekül, als Akzeptor eingesetzt. Die Effizienz der Energieumwandlung einer solchen Zelle wurde entsprechend den Schichtdicken der CuPc Schicht untersucht.
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Soler, Bru Laia. "Liquid-assisted ultrafast growth of superconducting films derived from chemical solutions." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667208.
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L'ús generalitzat de superconductors d'alta temperatura (HTS) en aplicacions a gran escala està, en part, encara limitat per l’elevat cost de fabricació de cintes recobertes (CCs). Amb la intenció d'aconseguir un avanç important per assolir un major rendiment, en aquesta tesi hem desenvolupat una tècnica innovadora que combina els beneficis de Deposició de Solucions Químiques (CSD) a baix cost amb les altes velocitats del creixement cristal·lí a partir de fases líquides. Es basa en la formació d'un líquid transitori derivat de solucions de carboxilats, aprofitant els obstacles cinètics per la cristal·lització de la fase d'equilibri.
En aquesta tesi doctoral, primer expliquem els fonaments del procés que condueix a la cristal·lització de YBa2Cu3O7-δ assistida per un líquid transitori; i després portem a terme una investigació detallada sobre aquesta tècnica. El "proof-of-principle" de la viabilitat d'aquesta nova aproximació es va aconseguir amb la disponibilitat dels forns tipus RTA que permeten rampes fins a 80ºC/s.
Les reaccions implicades en el procés s'observen amb mesures in situ i de microscòpia, entre altres. Primer, la piròlisi resultant de la barreja de propionats de Ba, Cu i Y a baixes temperatures (500ºC) és observada amb espectroscòpia in situ d’infraroig. A continuació, s’utilitza difracció de rajos-X amb llum de sincrotró per revelar les reaccions que tenen lloc per convertir el BaCO3, CuO i Y2O3 en la fase final, així com analitzar la nucleació i el creixement del YBa2Cu3O7-δ des del líquid transitori (TLAG).
Per dur a terme el procés, el pas de deposició es realitza amb mètodes d'impressió d'injecció de tinta o revestiment per rotació. Les característiques de les solucions s'han adaptat a la tècnica de deposició i es correlacionen amb la morfologia de la capa resultant.
A continuació s'han investigat diversos paràmetres per controlar la velocitat de la reacció limitant per l'eliminació del carbonat de bari amb l’objectiu d’evitar la retenció de carboni a les capes gruixudes epitaxials.
Posteriorment, s'estableixen els conceptes bàsics per a la comprensió dels mecanismes de nucleació i creixement del YBCO a partir de TLAG. Amb l'objectiu d'obtenir capes epitaxials de YBCO orientades en l’eix-c, es presenten diverses estratègies per controlar la força de cristal·lització. Els paràmetres rellevants són: la composició de la solució, la pressió d'oxigen, les rampes d’escalfament i les temperatures de creixement. Finalment, les condicions de cristal·lització es correlacionen amb les microestructures i propietats superconductores de les capes resultants.
Es presenten dos camins diferents per dur a terme el creixement mitjançant la formació de líquid. Un és a través d’un augment de temperatura a pressió d'oxígen constant (ruta-Temperatura). L’altre procés consisteix en dos passos (ruta-pO2). Per aquest últim, l'eliminació de BaCO3 es desvincula del creixement de YBCO mitjançant un salt en pO2.
Cal abordar diversos reptes en funció de la ruta. Alguns d’ells són: la reactivitat del líquid amb els substrats degut a la seva naturalesa altament corrosiva, o una mullabilitat inadequada.
Finalment, hem tingut èxit en obtenir pel·lícules fines de YBCO epitaxials d’entre 90-500 nm amb propietats superconductores molt elevades (Tc 90-92K, Jc fins a 5MA/cm2 a 77K), i velocitats de creixement fins a 100 nm/s, augmentat així en un factor 100 la velocitat de creixement de la metodologia de CSD convencional. Aquesta metodologia podria ser traslladada a altres materials.<br>The widespread use of High Temperature Superconductors (HTS) into large scale applications is, in part, still limited by the high costs of coated conductors manufacturing. Aiming for a breakthrough to achieve high throughput, in this thesis we have developed a novel technique that combines the low cost benefits of Chemical Solution Deposition (CSD) with the very high growth rates of crystallization from liquid phases. It relies on the formation of a transient liquid derived from carboxylate solutions, taking advantage of the kinetic hindrances on crystallization to reach the equilibrium phase.
In this dissertation, we first explain the basics of the process that leads to YBa2Cu3O7-δ crystallization assisted by a transient liquid and then we elaborate on the results of our investigation about this technique. The “proof-of-principle” of this new approximation viability has been achieved with the use of rapid thermal annealing furnaces, allowing heating rates up to 80ºC/s.
The reactions involved in the process are observed with in situ measurements and microscopic analyses, among others. First, the pyrolysis of the Ba, Cu and Y propionates mixture at low temperatures (500ºC) is observed with in situ infrared spectroscopy. Then, time resolved X-ray diffraction with synchrotron light is used to reveal the reaction paths to convert the resulting BaCO3, CuO and Y2O3 to the final phase, as well as nucleation and growth of the YBa2Cu3O7-δ film from the transient liquid.
To do so, the deposition step is performed with spin coating or Ink Jet printing methodologies. The solutions characteristics have been adapted to the deposition technique and correlated to the resulting film morphology.
Then, several parameters have been investigated to control the rate limiting BaCO3, elimination reaction in order to avoid carbon retention in the final thick epitaxial films.
Afterwards, the basic concepts for understanding the nucleation and growth mechanisms of YBCO with TLAG are set. With the aim of obtaining c-axis epitaxial YBa2Cu3O7-δ films, several strategies are presented to control the driving force for crystallization. The relevant parameters are solution composition, oxygen pressure, heating ramps and growth temperatures. Finally, the crystallization conditions are correlated to the resulting films microstructure and superconducting performances.
Two different paths are presented to reach TLAG. A direct temperature raise at constant oxygen pressure (Temperature-route), or a two step process (pO2-route). For the latter, BaCO3 elimination is disentangled from YBa2Cu3O7-δ growth by a jump on pO2.
Additionally, several challenges needed to be addressed depending on the route: liquid reactivity with the substrates due to its highly corrosive nature or improper wettability, are some of them.
Finally, we have succeeded in obtaining highly epitaxial YBCO thin films of 90-500nm with very high superconducting performances (Tc 90-92K, Jc up to 5MA/cm2 at self-field and 77K), at growth rates up to 100nm/s, increased by a factor 100 from those reported with conventional CSD. This methodology could be applied to other materials.
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Nerowski, Alexander [Verfasser], Gianaurelio [Akademischer Betreuer] Cuniberti, and Dominique [Akademischer Betreuer] Vuillaume. "Electrochemical Metal Nanowire Growth From Solution / Alexander Nerowski. Gutachter: Gianaurelio Cuniberti ; Dominique Vuillaume. Betreuer: Gianaurelio Cuniberti." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://d-nb.info/1068153377/34.
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Davey, Roger J. "The nucleation and growth of crystals from solution - molecular self assembly, materials science and process technology." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525976.
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Queraltó, López Albert. "Growth of functional oxide heterostructures from chemical solutions using advanced processing methodologies." Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/286006.
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En aquesta tesi doctoral, hem explorat innovadores tècniques de processat basades en el dipòsit de solucions químiques per tal de produir heteroestructures d’òxids, mitjançant processos d’autoassemblatge i autoorganització. Essencialment, s’ha dut a terme una profunda investigació dels mecanismes termodinàmics i cinètics involucrats en la nucleació i cristal·lització de diferents heteroestructures d’òxids (nanoilles i capes primes) amb materials com CeO2, LaNiO3, Ba0.8Sr0.2TiO3 i La0.7Sr0.3MnO3 sobre substrats monocristal·lins (Y2O3:ZrO2, LaAlO3, SrTiO3) i tecnològics com silici o cintes metàl·liques recoberts amb capes d’òxids.
Tractaments tèrmics usant rampes d’escalfament ràpides (∼20 ºC/s) han permès separar la nucleació del creixement. En primer lloc, hem reportat que es possible aconseguir cristal·litzar, fins i tot epitaxialment, a baixes temperatures (<500 ºC). També hem determinat el paper que juguen diferents paràmetres de processat (temperatura, rampa d’escalfament i atmosfera), i el tipus i orientació del substrat en les velocitats de nucleació i creixement, com també en la morfologia final del sistema. Anàlisis termodinàmics indiquen que la tensió creada entre capa i substrat té una contribució important en la nucleació i creixement. A més, s’ha pogut veure que la situació de tensió del sistema està altament influenciada per les diferències en l’expansió tèrmica soferta entre capa i substrat.
També hem demostrat que el creixement dels grans segueix un comportament auto-limitat està en gran mesura influenciat per un procés de difusió atòmica activat tèrmicament. Curiosament, la transformació des de material policristal·lí a epitaxial segueix el mateix comportament, i està impulsat per una reducció en les frontes de gra policristal·lines. Les velocitats de creixement del procés (0.01-0.1 nm/s) depenen en gran mesura de com ràpid el material epitaxial creix respecte el policristal·lí. En aquest sentit, hem pogut calcular que els coeficients de difusió atòmica epitaxials són un ordre de magnitud més grans que els policristal·lins, 10-19 i 10-20 m2/s respectivament. S’ha determinat que el gruix de la capa pot influenciar negativament en la velocitat de creixement epitaxial, dificultant la obtenció de capes epitaxials a gruixos grans.
En la mateixa línea, hem implementat i utilizat una metodologia innovadora com és la irradiació làser en condicions atmosfèriques per al creixement d’heteroestructures d’òxids, com a alternativa als tractaments tèrmics. La influència dels mecanismes tèrmics fotoinduïts s’ha avaluat mitjançant simulacions numèriques, usant els paràmetres òptics i termofísics dels diferents materials. Així doncs, hem demostrat la capacitat d’assolir la descomposició de capes metal·lorgàniques precursores, en particular propionats de Ce-Zr, amb temps de processat significativament inferiors i amb resultats equivalents als tractaments tèrmics convencionals. El disseny de patrons micromètrics ha estat possible gràcies al confinament espacial del feix làser. Altrament, també s’ha aconseguit la cristal·lització epitaxial de capes d’òxids sobre substrats monocristal·lins i tecnològics després d’una optimització en les condicions experimentals (fluència, nombre de polsos, temperatura del substrat, etc). S’ha observat que aquest creixement epitaxial és significativament més ràpid comparat amb els tractaments tèrmics (poques mil·lèsimes de segon comparat amb desenes de minuts). La raó d’aquest creixement tant ràpid s’ha atribuït principalment a les temperatures més elevades assolides amb els tractaments làser que tenen una influència rellevant en la difusió atòmica. Tanmateix, hem proposat que altres fenòmens com els grans gradients tèrmics dins les capes (1010 ºC/m), com també efectes fotoquímics derivats del trencament directe dels enllaços químics pels fotons làser poden tenir també una contribució important. Finalment, hem vist que les propietats funcionals de les capes crescudes amb làser són bastant similars a aquelles obtingudes amb tractaments tèrmics.
Les diferents metodologies de creixement combinades amb tècniques de caracterització avançades (microscòpies de força atòmica i electròniques, difracció de raig X, espectroscòpies infraroja-visible-ultravioleta, el·lipsometria) han permès aquest detallat estudi i una millor comprensió dels mecanismes de nucleació i creixement de heteroestructures d’òxids a partir del dipòsit de solucions químiques. Les metodologies i anàlisis desenvolupats han estat fonamentals per al desenvolupament d’aquesta tesi i el seu ús pot ésser traslladat a altres sistemes.<br>In this thesis, we have explored innovative processing methodologies based on the deposition of chemical solutions to produce oxide heterostructures through self-assembling and self-organization processes. Essentially, we performed an in-depth investigation of the thermodynamic and kinetic mechanisms involved in nucleation and crystallization of different oxide heterostructures (nanoislands and thin-films) involving doped-CeO2, LaNiO3, Ba0.8Sr0.2TiO3 and La0.7Sr0.3MnO3 on single crystals (Y2O3:ZrO2 (YSZ), LaAlO3, SrTiO3) and technical substrates like silicon wafers or oxide-buffered stainless steel metallic tapes.
Rapid Thermal Annealing (RTA) furnaces were successfully employed to separate nucleation and coarsening through the use of very fast heating ramps (∼20 ºC/s). First of all, we reported that crystallization and even epitaxial growth can be achieved at very low temperatures (<500 ºC). We also determined the role of the different processing parameters (temperature, heating ramp and atmosphere), substrate type and orientation on nucleation and growth rates of nanoislands and films, and the final morphology. Thermodynamic analyses indicated that strain has an important contribution in nucleation, as well as the final morphology of the system. The strain state of the different heterostructures was found to strongly depend on thermal expansion coefficients of film and substrate.
We also demonstrated that grain coarsening follows a self-limited behavior, and it is highly influenced by a thermally-activated atomic diffusion. Interestingly, we also determined that the transformation from random to epitaxially-oriented material follows the same growth behavior, and it is driven by the reduction of polycrystalline grain boundaries. The growth rate of the process (0.01-0.1 nm/s) highly depends on how fast the epitaxial material grows as compared to the coarsening of polycrystalline grains. We calculated that the epitaxial atomic diffusion coefficients are one order of magnitude larger than polycrystalline coefficients, 10-19 and 10-20 m2/s, respectively. Additionally, we determined that the epitaxial growth rate depends on precursor layer thickness, and this might be a drawback for reaching high epitaxial thick films.
A very new strategy such as Pulsed Laser Annealing at atmospheric conditions has been implemented and employed as an alternative to thermal treatments for the growth of oxide heterostructures. The influence of photo-induced thermal mechanisms has been evaluated through numerical simulations, employing optical and thermo-physical properties of different materials. We have demonstrated the capability to achieve decomposition of CSD precursor films with shorter processing times than in thermal treatments with equivalent results, particularly for the case of Ce-Zr propionates. The spatially-confined nature of the laser beam has also permitted to design micrometric patterned structures. Epitaxial crystallization of oxide films has also been achieved on single crystal and technical substrates after optimization of experimental conditions (fluence, number of pulses, substrate temperature, etc). A significantly faster epitaxial growth compared to thermal treatments has been achieved, i.e. few milliseconds vs tens of minutes. This rapid growth is mostly caused by the higher temperatures developed by laser annealing and influencing atomic diffusion. Additionally, we proposed that other mechanisms should be considered such as temperature gradients developed inside films (1010 ºC/m), as well as photochemical effects caused by direct bond dissociation by the laser photons. The functional properties of laser-grown films have been evaluated and compared with equivalent samples produced using thermal treatments, showing quite similar results.
The different growth methodologies employed combined with advanced characterization techniques (atomic force and scanning transmission electron microscopies, advanced x-ray diffraction measurements, infrared-visible-ultraviolet spectroscopies, ellipsometry) allowed me to perform the profound study undertaken and provided us with a better understanding of nucleation and growth mechanisms of oxide heterostructures from chemical solution deposition. The methodologies and analyses developed have been fundamental for the development of this thesis and their application can be made extensive to other systems.
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Ghani, Fatemeh [Verfasser], and HELMUTH [Akademischer Betreuer] MOEHWALD. "Nucleation and growth of unsubstituted metal phthalocyanine films from solution on planar substrates / Fatemeh Ghani. Betreuer: Helmuth Möhwald." Potsdam : Universitätsbibliothek der Universität Potsdam, 2013. http://d-nb.info/1033036617/34.
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Rossiter, Angelina Jane. "Solubility and crystal growth of sodium nitrate from mixed alcohol – water solvents." Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/505.
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Due to the ductile nature of the sodium nitrate crystal which deforms plastically under high levels of strain, most of the crystal growth studies in aqueous solution have focussed on the influence of tensile strain, supersaturation and dislocation, using x-ray surface topography to characterise the dislocation structure of the crystal. Most of the crystal growth studies have also focussed on growth from the melt since single crystals of sodium nitrate find application in optical pumping experiments, are a potential substitute for calcite in the preparation of polarising prisms and are interesting for the study of plastic properties because two types of plastic deformation, glide and twinning, take place in these crystals at room temperature. Its crystal habit is also difficult to modify and many researchers have used dyes to investigate its effect. Sodium nitrate is also a highly soluble substance with 96g of sodium nitrate dissolving in 100g of water at 30.0°C, making aqueous solutions of this salt and its supersaturation extremely unstable. Literature on its solubility in organic solvents, such as methanol, ethanol and isoproponal, are quite outdated and limited to specific conditions.This study involved the determination of the solubility of sodium nitrate in aqueous methanol, ethanol and isopropanol solutions at different temperatures and weight percents of the organic solvents. Splitting into two liquid phases was observed when using isopropanol, however this phase separation does not occur at low and high mass fractions of alcohol, as at lower concentrations of one solvent the two solvents are miscible. Whereas in the presence of methanol and ethanol the solubility of sodium nitrate in water was significantly reduced, with the solubility decreasing with increasing molecular weight of the alcohol. The experimental data for methanol and ethanol was used for the determination of the ion-specific Non random two liquid (NRTL) parameters by correlating with the modified extended NRTL model. It was observed for both methanol and ethanol that the model was found to satisfactorily correlate the data at low to moderate concentrations of alcohol. However, as the concentration of alcohol rises the model prediction was found to be less satisfactory, probably due to the interaction parameters of NRTL between alcohol and the ions not being able to represent the low solubility of electrolytes.The growth rates of individual faces of sodium nitrate crystals grown in situ in a batch cell and observed with an optical microscope were measured at different temperatures (20.0, 30.0 and 40.0°C) and relative supersaturations (0.02, 0.04, 0.06, 0.08 and 0.1) to determine the kinetics of growth for homogeneous nucleation. A combined growth order, of 1, and activation energy of 23,580 J/mol was obtained indicating that crystal growth in these sets of experiments was diffusion controlled. Crystal growth rates were also obtained for sodium nitrate crystal seeds grown at 20.0°C at a supersaturation of 0.02 and 0.04, in a modified growth cell where the saturated solution was circulated at a flow rate of 4mL/min. The crystal growth rates obtained were much lower in comparison to the growth rates obtained by homogeneous nucleation. In both sets of experiments size independent growth was observed.The surface morphology of the crystals was also observed by optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the crystals grown by homogeneous nucleation to elucidate the mechanism of growth. Liquid inclusions were observed by optical microscopy for crystals that were grown at high temperatures and for a long duration. SEM revealed the presence of pitting on the crystal surface due to the high solubility of sodium nitrate, while AFM images showed the presence of growth hillocks which suggests that crystal growth is surface integration controlled. However, the presence of growth hillocks could have been caused by the formation of some nuclei and surface artefacts when the crystal was taken out from solution. In seeded crystal growth experiments the solute was observed by optical microscopy to deposit onto the crystal surface.The effect of solvent composition on the growth rate and habit modification of sodium nitrate was also investigated with aqueous solutions of methanol and ethanol. Crystal growth rates of sodium nitrate crystals grown in situ in a batch cell by homogeneous nucleation in aqueous ethanol at 30.0°C at 20, 50 and 90 weight percent of ethanol and crystal seeds grown at 20.4°C at a supersaturation of 0.02 and 0.04 at 30, 50 and 90 weight percent of ethanol, in a modified growth cell was measured. It was found that growth rates decrease with increasing amounts of ethanol and the habit of the crystal remains unchanged. The growth rate was also observed to be much lower than the growth rates obtained from pure aqueous solution. For crystals grown by homogeneous nucleation it was observed that with increasing supersaturation, decreasing weight percent of ethanol and with increasing crystal size the number of liquid inclusions observed on the crystal surfaces increased, whereas for seeded crystal growth solute was observed to deposit on to the crystal surface mainly at low alcohol weight percents. Sodium nitrate crystals grown in aqueous methanol was also observed to behave similarly to crystals grown in ethanol, with lower growth rates obtained. For all cases size independent growth was observed.The influence of additives, DOWFAX 3B2 and amaranth was also investigated on the habit modification of sodium nitrate for crystals grown by homogeneous nucleation at 20.0°C at a supersaturation of 0.04. Both additives were observed to be effective in changing the crystal habit of sodium nitrate, with the appearance of triangular truncations or octahedral facets at the corners of the sodium nitrate crystal due to the additive being adsorbed onto the crystal surface. The influence of the additives on the crystal habit modification can be explained due to the presence of the anionic polar group, the sulphonate group. The growth ratio value for DOWFAX 3B2 was also found to decrease with increasing additive concentration.It is believed that the results of this thesis provides up to date data on the solubility of sodium nitrate in aqueous ethanol and for temperatures and weight percents that have not been reported before in literature for the aqueous methanol system. The work reported on crystal growth studies by homogeneous nucleation and using crystal seeds, the effect of solvent and DOWFAX 3B2 on crystal growth rates and habit modification is also new and has not been reported in literature before.
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Rosbottom, Ian. "The influence of the intermolecular synthons on the molecular aggregation, polymorphism, crystal growth and morphology of p-aminobenzoic acid crystals from solution." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12103/.
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Intermolecular pairwise interactions (synthons) have previously been used to predict physical properties of molecular crystals, such as polymorphism, morphology and mechanical properties. The overall goal of this research was to correlate the synthon strength and nature found in the crystal structures of the α- and β-forms of 4-aminobenzoic acid to experimentally observed data, assessing their applicability for predicting crystallisation conditions that would produce crystals of desirable physical properties. The strength and nature of the synthons found in the α-structure were found to significantly vary, while the strength and nature of the synthons in the β-structure were found to be much more similar. These synthons were also found to influence the conformation of the COOH and NH2 groups in both structures. Water was calculated to favourably bind to the COOH group than ethanol, along with the OH...O H-bonding dimers being calculated to be less stable in aqueous than ethanolic solutions. This suggests that water may hinder the formation of the α form more so than other solvents. The attachment energy morphological prediction of α-pABA was less needle-like than often observed, probably due to the growth rate of the capping faces growing by a rough interfacial growth mechanism along the long axis of the needle dominated by π-π stacking interactions, being underestimated. Nitromethane (NMe) was calculated to interact more strongly with the phenyl ring than other solvents and hence addition of NMe to ethanolic solutions shortens the long axis of the needle. The experimentally measured local surface molecular chemisty was found to vary between measurements of the bulk and surface at the (1 0 -1) surface, which is predicted to have unsaturated H-bonds at the surface. Complementing this, spatially resolved measurements across the (1 0 1) surface also showed changes in structure of a supposedly periodic surface. This study revealed how predicting the strength and nature of the synthons in the bulk structure and at the surface, along with their interaction with solvent molecules and stability in solution, can influence the morphology and polymorphism of the crystals produced from solution.
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Coquerel, Gérard. "Etude de dérives chiraux de la fenfluramine et de la norfenfluramine en vue de la séparation par cristallisation préférentielle." Rouen, 1986. http://www.theses.fr/1986ROUES045.
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Contrôle en solution aqueuse de la précipitation des variétés polymorphes du chlorhydrate de la S(+) fenfluramine. Le comportement d'antipodes est étudié au regard de la loi des phases et lors d'une cristallisation alternée polytherme par ensemencement de solutions. Les structures cristallines de trois espèces chirales précisent les conformations des amines et expliquent quelques problèmes liés à la croissance en solution racémique sursaturée
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Uwaha, Makio, and Katsunobu Koyama. "Transition from nucleation to ripening in the classical nucleation model." Elsevier, 2010. http://hdl.handle.net/2237/13867.
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Perrin, Daniel. "Élaboration de monocristaux de la solution solide Bi40Te54Se6 par les méthodes Bridgman et "travelling heater method" : influence de la méthode d'élaboration sur les propriétés thermoélectriques." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL130N.
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Ce travail porte sur la croissance cristalline et la caractérisation de la solution solide Bi40Te54Se6 de type n, dopée au brome ou avec excès de tellure, afin de connaitre les paramètres essentiels qui influent sur les propriétés thermoélectriques. L’étude de lingots cristallisés par la méthode Bridgman-Stockbarger a mis en évidence une inhomogénéité en composition, mais a permis de définir les coefficients de distribution du brome et du tellure en excès. Dans le but d'améliorer l'homogénéité et la qualité cristalline des lingots, nous avons effectué à partir d'un germe, la croissance par la méthode Travelling Heater Method (THM) de monocristaux non dopés. Pour cela, nous avons complété le diagramme de phase ternaire, du coté riche en tellure, en déterminant la courbe d'isoconcentration correspondant à la composition de la solution solide étudiée. Des échantillons T. H. M. Sont amenés à la composition du solidus par des recuits de saturation en tellure entre 565 et 588°C. La ligne solidus est exprimée en terme de concentration de porteurs en fonction de la température de recuit. La caractérisation de ces échantillons, par mesure du coefficient de Seebeck, de la résistivité électrique et de la conductivité thermique nous a permis de déterminer le facteur de mérite maximal: 2,7. 10-3 K-1. Des lingots T. H. M. Homogènes, dopés au brome et de très bonne qualité cristalline ont également été élaborés. Le facteur de mérite est égal à 2,9. 10-3 K-1 pour 10^19 atome de brome par cm3. Cette étude a montré l'intérêt de la méthode T. H. M. Pour effectuer la croissance de solutions solides ternaires dont la composition est bien définie du point de vue thermodynamique
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Stauder, Bruno. "Synthèse et caractérisation de films Al-O, Al-N et Zr-O prépares par pulvérisation cathodique magnétron en condition réactive." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL080N.
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Ce travail porte sur la synthèse et la caractérisation physico-chimique de films minces obtenus par pulvérisation cathodique magnétron en courant continu d'une cible métallique d'aluminium ou de zirconium dans des plasmas réactifs argon-oxygène ou argon-azote. Les solutions solides métastables sursaturées en oxygène ou en azote ainsi que les composes céramiques du type oxyde (Al₂O₃, Zro₂) ou du type nitrure (ALN) avec leurs différentes variétés cristallines ou amorphes sont étudiés par les principales techniques d'analyse structurale par diffraction et méthodes physiques d'analyse chimique. Une part importante de ce travail est consacrée à l'aspect procédé et particulièrement, aux mécanismes d'enrichissement en metalloïde des dépôts pulvérisés ainsi qu'au phénomène d'instabilité du régime de pulvérisation souvent rencontré en condition réactive. Une solution originale a ce problème est proposée: elle fait intervenir l'utilisation d'impulsions électriques de basse fréquence appliquées au courant de décharge qui permettent de contrôler la réaction chimique susceptible de se produire a la surface de la cible, de maintenir un régime stable de pulvérisation pendant une longue durée et de synthétiser sur le substrat un composé céramique stœchiométrique avec une grande vitesse de croissance
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Aouni, Abdessamad. "Aptitude à l'amorphisation par pulvérisation cathodique des systèmes Ni-C Co-C, Mn-C et étude structurale des produits de synthèse et de cristallisation." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL091N.
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Des alliages MT-C avec MT = Ni, Co ou Mn ont été élaborés par pulvérisation cathodique en mode radiofréquence. Leur stabilité thermique et l'évolution de leurs structures sont suivies par analyse enthalpique différentielle, diffraction des rayons X et microscopie électronique à transmission in-situ. Les principaux résultats sont les suivants: système Ni-C: des alliages essentiellement cristallins Ni1-xCx avec 0,10 x 0,67 ont été élaborés. Le carbure Ni3C à sites octaédriques est toujours présent. Le comportement thermique du dépôt Ni0, 33C0,67 laisse supposer la présence d'une phase amorphe métallique dont l'un des produits de cristallisation est Ni3C. Système Co-C: des alliages amorphes Co1-xCx avec 0,07 x 0,42 ont été élaborés. Leur cristallisation montre qu'il y a compétition entre le carbure à sites octaédriques Co2C et le carbure à sites prismatiques Co3C pour x < 0,34. Pour x > 0,34, le carbure à sites octaédriques devient majoritaire. Système Mn-C: des alliages amorphes Mn1-xCx avec 0,20 x 0,37 ont été, pour la première fois à notre connaissance, obtenus. Le suivi de leur cristallisation montre l'existence d'une concentration remarquable en carbone xr = 0,34, en dessous de laquelle les carbures obtenus sont à nappes prismatiques (CNP) et au dessus de laquelle se forme un nouveau carbure Mn2C à sites octaédriques, dont nous avons déterminé la structure et les paramètres de maille. Parmi les carbures CNP, nous identifions Mn5C2 et nous constatons des intercroissances entre ce carbure et Mn3C et/ou d'autres carbures CNP. Nous mettons en évidence des carbures métastables CNP de structures : périodiques correspondant à la formule Mn2n+1Cn. Ainsi deux nouveaux carbures Mn7C3 et Mn9C4 sont identifiés. Ce type de structure conduit à un carbure limite Mn2C à nappes prismatiques également observé ; apériodiques à une dimension de formule Mn1-x'Cx'. En ce qui concerne la cristallisation des alliages amorphes, la composition x = 0,33 semble remarquable quelque soit le système exploré et traduit vraisemblablement un changement de l'ordre local dans l'état amorphe
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Pötschke, Markus. "Simulation of electric field-assisted nanowire growth from aqueous solutions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-194735.
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The present work is aimed at investigating the mechanisms of nanowire growth from aqueous solutions through a physical and chemical modeling. Based on this modeling, deriving an optimized process control is intended. The work considers two methods of nanowire growth. The first is the dielectrophoretic nanowire assembly from neutral molecules or metal clusters. Secondly, in the directed electrochemical nanowire assembly metal-containing ions are reduced in an AC electric field in the vicinity of the nanowire tip and afterwards deposited at the nanowire surface. To describe the transport and growth processes, continuum models are employed. Furthermore, it has been necessary to consider electro-kinetic fluid flows to match the experimental observations. The occurring partial differential equations are solved numerically by means of finite element method (FEM). The effect of the process parameters on the nanowire growth are analyzed by comparing experimental results to a parameter study. The evaluation has yielded that an AC electro-osmotic fluid flow has a major influence on the dielectrophoretic nanowire assembly regarding the growth velocity and morphology. In the case of directed electrochemical nanowire assembly, the nanowire morphology can be controlled by the applied AC signal shape. Based on the nanowire growth model, an optimized AC signal has been designed, whose parametrization allows to adjust to the chemical precursor and the desired nanowire diameter<br>Ziel der vorliegenden Arbeit ist es, mittels physikalischer und chemischer Modelle die Mechanismen des Nanodrahtwachstums aus wässrigen Lösungen zu erforschen und daraus eine optimierte Prozesskontrolle abzuleiten. Dabei werden zwei Verfahren des Nanodrahtwachstums näher betrachtet: Dies sind die dielektrophoretische Assemblierung von neutralen Molekülen oder Metallclustern sowie die gerichtete elektrochemische Nanodrahtabscheidung (engl. directed electrochemical nanowire assembly), bei der metallhaltige Ionen im elektrischen Wechselfeld an der Nanodrahtspitze zunächst reduziert und anschließend als Metallatome abgeschieden werden. Zur Beschreibung der Transport- und Wachstumsprozesse werden Kontinuumsmodelle eingesetzt. Darüber hinaus hat es sich als notwendig erwiesen, elektrokinetische Fluidströmungen zu berücksichtigen, um die experimentellen Beobachtungen zu reproduzieren. Die auftretenden partiellen Differenzialgleichungen werden mittels der Finiten Elemente Methode (FEM) numerisch gelöst. Die Auswirkungen der Prozessparameter auf das Nanodrahtwachstum werden durch den Vergleich von experimentellen Ergebnissen mit Parameterstudien analysiert. Die Auswertung hat ergeben, dass für das dielektrophoretische Wachstum ein durch Wechselfeldelektroosmose (engl. AC electro-osmosis) angetriebener Fluidstrom die Drahtwachstumsgeschwindigkeit und -morphologie maßgeblich beeinflusst. Im Falle der gerichteten elektrochemischen Nanodrahtabscheidung lässt sich die Drahtmorphologie über das angelegte elektrische Wechselsignal steuern. Unter Verwendung des Wachstumsmodells ist ein optimiertes Signal generiert worden, dessen Parametrisierung eine gezielte Anpassung auf den chemischen Ausgangsstoff und den gewünschten Drahtdurchmesser erlaubt
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Lassalle, Francis. "Conception et mise en oeuvre d'un reacteur d'epitaxie gainas/inp par la methode aux hydrures, analyse des conditions de croissance." Clermont-Ferrand 2, 1987. http://www.theses.fr/1987CLF2D193.
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Reacteur permettant la croissance de couches epitaxiques dans le systeme (ga,in,as,p) par transport en phase vapeur et par la methode aux hydrures (ph::(3),ash::(3),h::(2),hcl,in,ga). Sa conception autorise la realisation d'heterostructures a interfaces abruptes en conservant une geometrie de reacteur monochambre. Analyse des conditions de croissance du ternaire gainas sur support inp (100). Mise en evidence de l'effet du non equilibre entre les especes as::(2) et as::(4) sur la presence d'un depot parasite en amont de l'echantillon et sur les caracteristiques du depot. Proposition d'un modele rendant compte de l'influence des cinetiques de reactions de surface sur la composition en gallium de gainas
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Porte, Agnès. "Determination des parametres qui regissent la cinetique et la composition d'un depot de gainas/inp par la methode aux hydrures." Clermont-Ferrand 2, 1988. http://www.theses.fr/1988CLF2D162.
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En s'appuyant sur les resultats experimentaux de la croissance de ga::(x)in::(1-x)as/inp en phase vpeur par la methode aux hydrures et sur une theorie cinetique de croisssance qui permet d'exprimer facilement le rapport des pressions partielles de chlorures en fonction de x, detection et analyse de differents phenomenes en jeu dans la croissance. Calcul des parametres necessaires a la prise en compte de ces phenomenes pour la determination des pressions partielles reelles de chacun des constituants de la phase vapeur dans chaque experience realisee. La maitrise de la cinetique du depot et de la composition de la couche de ga::(x)in::(1-x)as est de ce fait rendue possible dans l'epitaxie par la methode aux hydrures
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Petit, Samuel. "Structures de complexes dans le système (cuivre (II)-oxine-sulfoxine-eau), étude expérimentale et modélisation moléculaire de la cristallisation et de transitions de phases." Rouen, 1994. http://www.theses.fr/1994ROUES025.
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La résolution structurale d'une nouvelle variété anhydre d'oxinate de cuivre(II) (noté X) a été effectuée d'après le diagramme de diffraction X sur poudre. L'étude des filiations structurales et la prise en compte des données cinétiques, thermodynamiques et physico-chimiques ont mené à proposer un modèle pour les transitions solide-solide entre variétés dihydratées et anhydres d'oxinate de cuivre(II) (déshydratations et transitions polymorphiques). La résolution de structure sur monocristal et sur poudre de deux variétés hydratées de sulfoxinate de cuivre(II) a permis une étude par modélisation moléculaire de la nucléation homogène en solution aqueuse des variétés de structure connue. La croissance cristalline des sulfoxinates de cuivre(II) a été envisagée, conduisant à considérer la croissance d'une face associée à une tranche contenant deux molécules de conformations différentes. Le concept de sous-tranches non équivalentes par les opérations de symétrie du groupe d'espace est défini. Deux approches complémentaires ont été utilisées en vue d'expliquer l'influence de la sulfoxine sur l'évolution des oxinates de cuivre(II). D'une part, une étude des molécules d'oxine et de sulfoxine par les méthodes de chimie théorique a permis d'interpréter leur comportement en milieu aqueux. D'autre part, une étude expérimentale des complexes mixtes cuivre-oxine-sulfoxine a été entreprise
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Zaccaro, Julien. "Cristallogénèse et caractérisations de la solution solide dihydrogénophosphate-arseniate de 2-amino-5-nitropyridinium, cristaux organo-minéraux pour l'optique non linéaire." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10069.
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Les cristaux organo-mineraux sont un compromis avantageux entre l'efficacite optique non lineaire (onl) des molecules organiques et la stabilite des cristaux mineraux. La possibilite d'obtenir des solutions solides par substitution de la part minerale est un atout supplementaire que nous avons illustre dans le cas du systeme dihydrogenophosphate-arseniate de 2-amino-5-nitropyridinium (2a5npdp#(#1##x#)as#x (0 x 1)). Nous avons elabore des cristaux de grande taille (cm#3) pour l'ensemble de la solution solide. La realisation de cristaux homogenes en composition a necessite le developpement d'une technique originale de croissance par gradient vertical de temperature. Les premiers resultats obtenus par epitaxie en phase liquide prouvent qu'il est possible de realiser des couches guidantes en deposant une composition de la solution solide sur une autre. La croissance rapide de cristaux (environ 1 cm/jour) mise au point montre la possibilite d'appliquer cette technique a l'ensemble des cristaux hybrides ce qui pourrait etre un point decisif pour l'application eventuelle de ces materiaux. Les differentes techniques de caracterisation de la qualite cristalline (diffraction des rx topographie aux rx et spectroscopie d'absorption) ont permis de mettre clairement en evidence la relation existant entre la purete des cristaux, leur qualite cristalline et leur fenetre de transparence. Grace aux caracterisations optiques, nous avons pu preciser la contribution du chromophore organique aux proprietes optiques lineaires et non lineaires des cristaux de 2a5npdp#(#1#-#x#)as#x. La fenetre de transparence est limitee vers l'uv par la transition a transfert de charge du chromophore et les indices de refraction evoluent peu avec la substitution de la part minerale. L'efficacite onl et electro-optique a ete trouvee elevee et constante pour toute la solution solide ce qui montre que les proprietes onl quadratiques sont majoritairement conditionnees par la part organique de la structure hybride.
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Hilton, Anne Marie. "The formation and growth of COâ†2 gas bubbles from supersaturated aqueous solutions." Thesis, University of Nottingham, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334502.
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Lusson, Alain. "Preparation par epitaxie en phase liquide et etude physique des solutions solides cd : :(x)hg::(1-x)te 0,5 <- x <-1." Paris 6, 1987. http://www.theses.fr/1987PA066497.
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Dans le but d'etudier un materiau utilisable pour la fabrication de detecteurs pour les telecommunications par fibre optique a 1,3 et 1,55mu m, des echantillons de cd::(x) hg::(1-x) te(0,5 x 1) ont ete prepares par epitaxie en phase liquide en tube ouvert. Diverses methodes de caracterisation (microsonde electronique, topographie rx, effet hall, sonde ionique. . . ) ont montre la bonne qualite des couches. Le dopage effectue au cours de la croissance par in et cu a ete aborde. Etude des effets d'alliage dans cdhgte par photoluminescence
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Marage, Pierre. "Contribution à la mise au point du procédé aérosol-gel : application au dépôt de couches minces optiques dans le système SiO2-TiO2." Grenoble INPG, 1993. http://www.theses.fr/1993INPG0150.
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Le procédé aérosol-gel est une nouvelle technique de dépôt sol-gel. Son principe repose sur la pulvérisation d'un sol par voie ultrasonore. L'aérosol ainsi généré est transporte par un gaz vecteur vers le substrat et forme, en se déposant, un film liquide. Ce film conduit après évaporation du solvant et polymérisation du dépôt, a la formation d'une couche mince xérogel homogène et transparente. Des films SiO² ont pu être obtenus a partir d'un système chimique de type tetraethoxysilane/eau/acide chlorhydrique/alcool. Apres recuit à 500°C, ces films sont purs et présentent une densité proche de celle de la silice massive. Des films parfaitement denses ont été obtenus par recuit direct à 800°C, en plaçant l'échantillon dans un four préchauffé. Des films TiO² ont été élaborés a partir d'un système chimique de type tétrabutoxyde de titane/diéthanolamine/alcool. La diéthanolamine permet une bonne stabilisation du tetrabutoxyde de titane, et empêche la formation de précipités dans la solution source. Apres recuit à 500°C, les films TiO² sont purs et présentent une porosité de l'ordre de 25%. Cette porosité peut être abaissée à moins de 10% par recuit direct. Des films SiO²-TiO² mixtes ont été élaborés à partir du mélange des systèmes chimiques précédents. L'indice de réfraction de ces films a pu être module continument entre 1,43 (0% de titane) et 2,25 (100% de titane). Aucune déviation du rapport Ti/Si entre la solution source et les films recuits n'a été observée. Cette étude montre que le procédé aérosol-gel est adaptable à un grand nombre de systèmes chimiques. De plus, sa compatibilité avec une production massive (couplage possible avec un four a défile, ou four à carrousel) lui donne d'importantes potentialités, en vue d'une utilisation a échelle industrielle.
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Deodhar, Anirudh M. "Computational Study of Adiabatic Bubble Growth Dynamics from Submerged Orifices in Aqueous Solutions of Surfactants." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337100942.
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Roumiantseva, Babakina Marina. "Elaboration et caractérisation des couches minces SnO2(Cu,Ni) pour la détection gazeuse." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0178.
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Des couches minces de dioxyde d'etain (sno#2) pures et dopees (cu, ni) ont ete elaborees par le procede pyrosol sur des substrats de silicium oxyde en utilisant la pyrolyse d'un aerosol genere par ultrasons. Une etude systematique a permis de determiner l'influence des conditions d'elaboration sur la composition et la microstructure des couches. L'influence du cu et du ni sur les proprietes electriques de sno#2 a ete etudiee dans la gamme de temperature 77-773 k. Une concentration de cu de 1. 2-1. 5 at% et une concentration de ni de 0. 4-0. 6 at% conduisent a une augmentation de la resistance de h#2s d'un facteur 10#3. Les proprietes electriques des couches obtenues ont ete etudiees en regime stationnaire et en regime dynamique en fonction de la concentration des dopants et de la temperature en presence des melanges gazeux: 100-1200 ppm de h#2s dans l'azote, 300 ppm de co dans l'air et 80 ppm de c#2h#5oh dans l'air. Le dopage par le cu et par le ni augmente la sensibilite de sno#2 a h#2s d'un facteur 10#-#2-10#-#3. Contrairement au cas du cuivre, le nickel augmente la sensibilite de sno#2 en presence de co et de c#2h#5oh. Un modele d'interaction des couches sno#2(cu) et sno#2(ni) avec h#2s et l'oxygene de l'atmosphere est propose. Ce modele est base sur les reactions chimiques qui modifient l'etat des dopants dans sno#2 en fonction de la composition de la phase gazeuse
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Li, Ziliang. "Growth and Characterization of Nanocomposite YBa2Cu3O7-δ – BaMO3 (M = Zr, Hf) Thin Films from Colloidal Solutions". Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/663979.
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El YBa2Cu3O7-δ es el superconductor de alta temperatura con mayor potencial tecnológico para aplicaciones de potencia e imanes que trabajan bajo campos magnéticos elevados. Sin embargo, todavía es un reto mejorar sus prestaciones en forma de película delgada epitaxial con un coste bajo de fabricación. La deposición de soluciones químicas ha surgido como una técnica muy competitiva para obtener láminas delgadas epitaxiales y multicapas de alta calidad con nanoestructuras controladas.
Hemos desarrollado un proceso novedoso de crecimiento mediante Calentamiento Flash que muestra un excelente potencial para la producción industrial en continuo de conductores epitaxiales de YBa2Cu3O7-δ. En esta tesis hemos establecido, por primera vez, una imagen completa que describe las fases intermedias y la evolución de la microestructura durante el calentamiento. Hemos extendido la ventana de la temperatura de crecimiento sin ninguna degradación de las propiedades superconductoras, por lo que la deposición de conductores epitaxiales de YBa2Cu3O7-δ es compatible con el uso de sustratos de cinta metálica con capas tampón de CeO2. Además, también hemos encontrado que este proceso de crecimiento promueve la formación de una alta concentración de defectos de apilamiento y, por lo tanto, de tensiones a escala nanométrica.
Las láminas ultrafinas de YBa2Cu3O7-δ y nanocompuestos, en el rango de 5-50 nm, se prepararon después de una optimización de los parámetros de crecimiento. La reducción de la energía interfacial induce una alta densidad de defectos de apilamiento, lo que conduce a una matriz de YBa2Cu3O7-δ altamente distorsionada. Esta modificación microestructural se vuelve extremadamente grave cuando el grosor de la lámina delgada disminuye por debajo de 25 nm, degradando significativamente las propiedades superconductoras. También hemos estudiado la evolución de las características de las nanopartículas segregadas espontáneamente con el espesor de las láminas delgadas y su influencia en la eficiencia del anclaje de vórtices.
La preparación de nanocompuestos de YBa2Cu3O7-δ a partir de nanopartículas de óxido preformadas y no reactivas que forman soluciones coloidales ha demostrado ser una estrategia muy exitosa para lograr un estricto control de las características de las nanopartículas y la optimización de la nanoestructura de las láminas delgadas superconductoras. Las perovskitas BaMO3 (M = Zr, Hf) son las composiciones más prometedoras de nanopartículas preformadas que hasta ahora han conducido a láminas delgadas de nanocompuestos de alta calidad con altas concentraciones de nanopartículas (20-25% molar). La composición y el tamaño de las nanopartículas han demostrado ser factores cruciales para adaptar el rendimiento del anclaje de vórtices bajo campos magnéticos aplicados. La aplicación del proceso de crecimiento de calentamiento flash al crecimiento de láminas delgadas nanocompuestas permite la preservación del tamaño de las nanopartículas y la generación de una alta densidad de defectos de apilamiento de pequeña longitud, que desempeñan un efecto sinérgico para aumentar la eficiencia de los centros de anclaje de vórtices artificiales y mejorar así las propiedades de los conductores. La técnica de multideposición es efectiva para aumentar aún más el espesor de la lámina delgada, mientras que la eficacia del anclaje de vórtices se conserva y la capacidad de transporte de corriente eléctrica de las láminas delgadas nanocompuestas aumenta.<br>YBa2Cu3O7-δ (YBCO) is the best material choice to address the performances required in power applications and magnets working under high magnetic fields. However, it is still challenging to achieve low manufacturing costs and high superconducting performances of coated conductors (CCs) for large scale power applications. Chemical Solution Deposition has emerged as a very competitive technique to obtain epitaxial films and multi-layers of high quality with controlled nanostructures.
We have developed a novel Flash Heating growth process that shows high potential to be compatible with the industrial reel-to-reel production of YBCO CCs. Here we have set up, for the first time, a full image describing the intermediate phase and microstructure evolution during this heating process. We extend the growth temperature window down to 750 ºC without any degradation of superconducting properties, making it being compatible with the deposition of YBCO CCs on CeO2-caped metallic tape substrates. In addition, we have also found that this growth process promotes the formation of a high concentration of stacking faults and so of nanostrain.
YBCO and nanocomposite ultrathin films, in the range of 5-50 nm, have been prepared after a series optimization of growth parameters. The relief of the interfacial energy induces a high density of stacking faults, leading to a highly distorted YBCO matrix. Such microstructural disorder becomes extremely serious when the film thicknesses decrease below 25 nm, significantly degrading the superconductivity. We have also studied the evolution of the characteristics of spontaneous segregated nanoparticles with nanocomposite film thicknesses and their influence on the vortex pinning efficiency.
The preparation of YBCO nanocomposites from non-reactive preformed oxide nanoparticles forming colloidal solutions has demonstrated to be a very successful strategy to achieve a tight control of the nanoparticle characteristics and the optimized nanostructural landscape on the superconducting films. BaMO3 (M=Zr, Hf) perovskites are shown to be the most promising compositions of preformed nanoparticles up to now that led to high quality nanocomposite films at high nanoparticle concentrations (20-25 mol%). The composition and size of nanoparticles have demonstrated to be crucial factors for tailoring vortex pinning performance in applied magnetic field. The application of the Flash Heating growth process in the growth of nanocomposite films allows both the preservation of nanoparticle size and the generation of a high density of short stacking faults, which play a synergistic effect to increase the artificial pinning centers and enhance the strong pinning contribution. Multi-deposition technique is proved effective to further enhance the film thickness while vortex pinning efficiency is preserved and current-carrying capacity of the nanocomposite films is increased.
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Prouzet, Eric. "Ordre local dans de nouvelles formes de NiPS obtenues par chimie douce et par intercalation de lithium." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37617740f.
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Pötschke, Markus [Verfasser], Gianaurelio [Akademischer Betreuer] Cuniberti, and Robert Melville [Akademischer Betreuer] Metzger. "Simulation of electric field-assisted nanowire growth from aqueous solutions / Markus Pötschke. Betreuer: Gianaurelio Cuniberti. Gutachter: Robert Melville Metzger." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1088185630/34.
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Rouch, Hervé. "Modélisation du procédé de dépot chimique à partir d'une phase gazeuse (CVD) : application au cas du dépot de silicium-germanium." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0116.
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La simulation couplee des phenomenes de transport et de reactivite intervenant dans le procede de depot chimique a partir d'une phase gazeuse (cvd) est l'objectif de ce memoire. La description de la reactivite homogene (phase gazeuse) et heterogene (formation du depot) est souvent limitee par la rarete des donnees cinetiques concernant les mecanismes reactionnels mis en jeu. Par contre, un grand nombre de donnees thermodynamiques sur les systemes chimiques utilises en cvd sont disponibles. Un des buts de cette etude a donc ete le developpement d'une simulation couplee des phenomenes de transport et de l'equilibre thermodynamique local. Apres une breve presentation du procede cvd, les principes theoriques decrivant l'equilibre thermodynamique, la mecanique des fluides, les transferts de chaleur, et le transport de matiere sont presentes. Une attention toute particuliere est portee sur le couplage entre le transport de matiere reactive et l'equilibre thermodynamique local (etl). Ensuite, une etude theorique de l'equilibre thermodynamique du systeme chimique etudie (si-ge-h-cl-ar) permet de predire quelles sont les especes gazeuses intervenant dans la croissance du depot, puis de formuler des hypotheses sur les conditions aux limites qui seront utilisees au cours de la simulation des phenomenes de transport. L'analyse du transport montre que la thermodiffusion joue un role non negligeable lors de la croissance du depot de si#1#-#xge#x. Les resultats de ces deux types d'analyses sont compares aux resultats experimentaux obtenus prealablement. Le modele de transport bien que base sur un schema de reactivite simplifie reproduit les tendances experimentales. Des modifications geometriques du reacteur et des conditions experimentales optimales sont proposees. Enfin, afin d'obtenir des renseignements plus precis sur la reactivite chimique, le couplage du transport et du proche etl a ete mis en uvre. Cette approche est tres riche et permet de mettre en evidence le role des especes intermediaires et de leur transport au cours de la croissance du depot de siliciure de germanium
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Guillon, Nathalie. "Étude de composés Ti-B-N élaborés par dépot sous vide : relation entre microstructure, composition chimique et propriétés mécaniques." Grenoble INPG, 1997. http://www.theses.fr/1997INPG4207.
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Cette etude a pour objectif l'elaboration et la caracterisation des depots ti-b-n elabores par pulverisation cathodique magnetron dans le but d'une application industrielle telle que le revetement d'outils de coupe. Le diagramme de composition ternaire ti-b-n est explore par copulverisation reactive d'une cible de ti et de tib#2. Le domaine de composition chimique centre sur 55% at. De ti, 15% at. B et 30% at. N presente les proprietes mecaniques optimales. Afin d'etudier plus precisement l'evolution de la microstructure et des proprietes mecaniques de ce domaine, des depots sont ensuite elabores par pulverisation cathodique magnetron reactive d'une cible tibx en modifiant le debit d'azote. Le depot de composition chimique 55% at. Ti, 18. 2 % at. B et 26. 8 % at. N possede les meilleures caracteristiques mecaniques. Il correspond a une solution solide de b dans la maille tin. L'influence du bombardement ionique est etudiee ce debit d'azote. Les proprietes tribologiques ne sont pas alterees par le bombardement ionique. Une relation densite du revetement-puissance du bombardement ionique est mise en evidence. En augmentant la teneur en azote dans les depots, le bore est ejecte de la maille tin. Les revetements presentent une phase tin stoechiometrique et une phase bn observee par met. Les depots montrent alors une deterioration des proprietes tribologiques en presence de la phase bn (fragilisation des depots ou reaction physico-chimique). Tous les depots ti-b-n de structure type tin ont une durete elevee (4500 hv sous 50 g). L'hypothese d'un nanocomposite de nanocristaux tin dans une matrice amorphe tib#2 permet de conclure a un mecanisme de durcissement structural.
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Li, Xiang. "Study of pure-silica Zeolite Nucleation and Growth from Solution." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-08-9825.
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Zeolites are microporous crystalline materials, which are widely used in catalysis, adsorption, and ion-exchange processes. However, in most cases, the synthesis of novel zeolites as functional materials still relies on trial-and-error methods, which are time consuming and expensive. Therefore, the motivation for this thesis work is to understand the zeolite synthesis mechanismand further develop knowledge for manipulating zeolite properties and ultimately the rational design of porous materials. This work focused on formation of silicalite-1 (pure-silica ZSM-5) from basic aqueous solutions containing tetraorthosilicate (TEOS) as silica source, and tetrapropylammonium (TPA) cations as the organic structure-directing agent. The presence of silica precursor particles with size of 2-5 nm in these mixtures prior to and during hydrothermal treatments have been observed through dynamic light scattering (DLS), small-angle X-ray (SAXS) and transmission electron microscopy (TEM). However, to quantify composition and the molecular structure transformation of these silica precursor particles during zeolite synthesis is still a technical challenge. Another important yet unresolved question is how organocations interact with these nanoparticles and direct zeolite nuclei. Unlike many studies performed analyzing the inorganic phase (silica) present in synthesis mixtures, this study quantified the organocation-silica particle interaction and its ultimate effect on zeolite growth mainly through probing the behavior of the organocations. Pulsed-field gradient (PFG) NMR was used to capture the mobility change of organocations, and was complemented with scattering measurements (DLS, SAXS) on the silica nanoparticles. On the basis of the measurement results, the thermodynamic and kinetic properties of the organic-inorganic interaction were derived. Upon aging at room temperature, this interaction manifested as binding of TPA onto the silica particles due to electrostatic interactions, and such binding behavior can be well described by the Langmuir adsorption model. Upon hydrothermal treatment, a fraction of TPA adsorbed at room temperature dissociates from the growing silica nanoparticles and the corresponding desorption profiles were fitted well by the pseudo-second order kinetic model. The addition of tetramethylammonium (TMA) as "competitors" promoted TPA desorption kinetics and hindered silica nanoparticle growth due to stronger association of TMA with particles than that of TPA. Finally, the TPA adsorption strength increased via addition of monovalent salts with increasing ionic size whereas that of TMA shows an opposite trend. This suggests one potential route for tuning the organic-silica precursor particle interactions and thus possibly affecting some kinetics steps in the synthesis.
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Wang, Jyh-Ming, and 王志銘. "Liquid-Phase Epitaxy of GaInAsSb Growth from Sb-rich Solution and The Fabrication of Infrared Avalanche Photodiodes." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/54892038103213829531.
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Kidess, Anton. "Influence of static magnetic fields and solutal buoyancy on silicon dissolution into germanium melt." Thesis, 2009. http://hdl.handle.net/1828/1900.
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Elemental semiconductors like silicon and germanium have been used since the beginning of the electronics industry. Silicon has dominated research and production and thus silicon based devices can be produced at the lowest cost using the most mature technology. While dopants can be used to tailor the electric properties of the semiconductor within certain limits, more flexibility is gained using compound semiconductors such as silicon-germanium. The electric properties of a compound semiconductor are highly dependant on the composition, which in turn is influenced by the dissolution reaction and flow characteristics during the growth process.
Liquid phase diffusion (LPD) is a solution growth technique that has been proposed to grow silicon-germanium seed crystals for other growth techniques. The dissolution of silicon is a limiting factor for the growth rate in LPD and also Bridgman growth techniques. Investigation of the dissolution process is aimed at increasing the growth rate while still maintaining maximum uniformity of the crystal composition. To accomplish this, a static magnetic field was utilized in experiments done by Armour. The experimental results showed that a top seeded configuration without magnetic fields leads to a diffusion driven process and homogeneous dissolution, while the addition of a strong 0.8 Tesla magnetic field resulted in non-uniform and slightly increased dissolution. This work is complementary to the experimental investigation and aims to help understand the influence of magnetic fields on silicon dissolution.
For this work, an OpenFOAM magnetohydrodynamics application including heat and species transport and three different magnetic force models has been developed and validated. The simulations done show that an isothermal state is reached within 90 seconds if no temperature gradient is imposed. Additional simulations with a temperature gradient helped to rule out a possible thermal leak in the experimental system, confirming that it must have been close to isothermal. Since the solutal expansion coefficient of has not been measured properly to the Author's knowledge, two possible values for the expansion coefficient have been considered. It has been found that the exact value of the solutal expansion coefficient does not have a great influence on the results of this work.
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Lin, Zhen-Wen, and 林貞妏. "Seed-Mediated Growth of Silver Nanocubess in Aqueous Solution II. Formation of Au Nanocages from Ag nanocubes and Their Photothermal Effect." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/56760738137183129698.
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碩士<br>國立清華大學<br>化學系<br>103<br>CHAPTER 1
Seed-Mediated Growth of Silver Nanocubess in Aqueous Solution
In this work, we have developed a seed-mediated approach to synthesize Ag nanocubes with average edge lengths from 23 nm to 60 nm. Ag seed solution is added a growth solution containing CF3COOAg, cetyltrimethylammonium chloride (CTAC), and ascorbic acid. Ag nanocubes are synthesized by using ascorbic acid as reducing agent to reduce AgCl in the presence of CTAC. We have also used another method to synthesize Ag nanocubes. This approach involves adding the seed solution to a growth solution containing AgNO3, cetyltrimethylammonium bromide (CTAB), CuSO4 and ascorbic acid. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) patterns have been employed to characterize the Ag nanocubes. UV‒vis absorption spectra of the particles have been obtained.
CHAPTER 2
Formation of Au Nanocages from Ag Nanocubes and Their Photothermal Effect
In this study, we have used Ag nanocubes as templates to synthesize Au nanocages by adding HAuCl4 at 30 ºC for 10 minutes. This involves galvanic replacement reaction. Ag nanocubes are oxidized and AuCl4‒ is reduced to Au and deposited on the surface of Ag nanocubes. When different amounts of HAuCl4 were added to a growth solution including Ag nanocubes and CTAC, the morphology and Au/Ag ratio can vary. We used the cages to investigate photothermal effect. Using different cages, the solution temperature can rise to 90, 95 and 100ºC under the illumination of an 808 nm laser with 1.47 W. Use of a 1064 nm laser led to a lower heating efficiency. These cages may find applications including heat generation for as an energy source.
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Bartha, Attila. "Studium magnetismu vrstevnatých tetragonálních sloučenin na bázi vzácných zemin a uranu." Master's thesis, 2015. http://www.nusl.cz/ntk/nusl-335242.
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We have studied the interplay between the layered crystal structure and the 5f magnetism in uranium-based tetragonal compounds UnTIn3n+2. Sin- gle crystals of U2RhIn8, URhIn5 and UIn3 were prepared by In self-flux method. The novel U2RhIn8 compound adopts the Ho2CoGa8-type struc- ture with lattice parameters a = 4.6056(6) ˚A and c = 11.9911(15) ˚A. The behavior of U2RhIn8 strongly resembles that of related URhIn5 and UIn3 with respect to magnetization, specific heat and electrical resistivity except for magnetocrystalline anisotropy developing on stacking composition in the series UIn3 vs. U2RhIn8 and URhIn5. U2RhIn8 orders antiferromagnetically below TN = 117 K and exhibits slightly enhanced Sommerfeld coefficient γ = 47 mJ·mol−1 ·K−2 . TN increases with increasing c/a ratio in contrast to the behavior of their CenTIn3n+2 counterparts. Magnetic field leaves the value of the Néel temperature of URhIn5 and U2RhIn8 unaffected up to 9 T. On the other hand, TN increases with applied hydrostatic pressure up to 3.2 GPa with the ∂TN/∂p coefficient resembling URhIn5 and UIn3. Ther- mal expansion of U2RhIn8 reveals a hysteretic behavior of the antiferromag- netic transition pointing to its 1st -order character. The magnetic structure of URhIn5 obtained from neutron diffraction propagates with k = (1 /2, 1 /2, 1 /2) and the...
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Roszmann, Jordan Douglas. "Simulation and growth of cadmium zinc telluride from small seeds by the travelling heater method." Thesis, 2016. http://hdl.handle.net/1828/7347.
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The semiconducting compounds CdTe and CdZnTe have important applications in high-energy radiation detectors and as substrates for infrared devices. The materials offer large band gaps, high resistivity, and excellent charge transport properties; however all of these properties rely on very precise control of the material composition. Growing bulk crystals by the travelling heater method (THM) offers excellent compositional control and fewer defects compared to gradient freezing, but it is also much slower and more expensive. A particular challenge is the current need to grow new crystals onto existing seeds of similar size and quality.
Simulations and experiments are used in this work to investigate the feasibility of growing these materials by THM without the use of large seed crystals. A new fixed-grid, multiphase finite element model was developed based on the level set method and used to calculate the mass transport regime and interface shapes inside the growth ampoule. The diffusivity of CdTe in liquid tellurium was measured through dissolution experiments, which also served to validate the model. Simulations of tapered THM growth find conditions similar to untapered growth with interface shapes that are sensitive to strong thermosolutal convection. Favourable growth conditions are achievable only if convection can be controlled.
In preliminary experiments, tapered GaSb crystals were successfully grown by THM and large CdTe grains were produced by gradient freezing. Beginning with this seed material, 25 mm diameter CdTe and CdZnTe crystals were grown on 10 mm diameter seeds, and 65 mm diameter CdTe on 25 mm seeds. Unseeded THM growth was also investigated, as well as ampoule rotation and a range of thermal conditions and ampoule surface coatings. Outward growth beyond one or two centimeters was achieved only at small diameters and included secondary grains and twin defects; however, limited outward growth of larger seeds and agreement between experimental and numerical results suggest that tapered growth may be achievable in the future. This would require active temperature control at the base of the crystal and reduction of convection through thermal design or by rotation of the ampoule or applied magnetic fields.<br>Graduate<br>0346<br>0794<br>0548<br>jordan.roszmann@gmail.com
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Pötschke, Markus. "Simulation of electric field-assisted nanowire growth from aqueous solutions." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A29190.
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The present work is aimed at investigating the mechanisms of nanowire growth from aqueous solutions through a physical and chemical modeling. Based on this modeling, deriving an optimized process control is intended. The work considers two methods of nanowire growth. The first is the dielectrophoretic nanowire assembly from neutral molecules or metal clusters. Secondly, in the directed electrochemical nanowire assembly metal-containing ions are reduced in an AC electric field in the vicinity of the nanowire tip and afterwards deposited at the nanowire surface.
To describe the transport and growth processes, continuum models are employed. Furthermore, it has been necessary to consider electro-kinetic fluid flows to match the experimental observations. The occurring partial differential equations are solved numerically by means of finite element method (FEM).
The effect of the process parameters on the nanowire growth are analyzed by comparing experimental results to a parameter study. The evaluation has yielded that an AC electro-osmotic fluid flow has a major influence on the dielectrophoretic nanowire assembly regarding the growth velocity and morphology. In the case of directed electrochemical nanowire assembly, the nanowire morphology can be controlled by the applied AC signal shape. Based on the nanowire growth model, an optimized AC signal has been designed, whose parametrization allows to adjust to the chemical precursor and the desired nanowire diameter.<br>Ziel der vorliegenden Arbeit ist es, mittels physikalischer und chemischer Modelle die Mechanismen des Nanodrahtwachstums aus wässrigen Lösungen zu erforschen und daraus eine optimierte Prozesskontrolle abzuleiten. Dabei werden zwei Verfahren des Nanodrahtwachstums näher betrachtet: Dies sind die dielektrophoretische Assemblierung von neutralen Molekülen oder Metallclustern sowie die gerichtete elektrochemische Nanodrahtabscheidung (engl. directed electrochemical nanowire assembly), bei der metallhaltige Ionen im elektrischen Wechselfeld an der Nanodrahtspitze zunächst reduziert und anschließend als Metallatome abgeschieden werden.
Zur Beschreibung der Transport- und Wachstumsprozesse werden Kontinuumsmodelle eingesetzt. Darüber hinaus hat es sich als notwendig erwiesen, elektrokinetische Fluidströmungen zu berücksichtigen, um die experimentellen Beobachtungen zu reproduzieren. Die auftretenden partiellen Differenzialgleichungen werden mittels der Finiten Elemente Methode (FEM) numerisch gelöst.
Die Auswirkungen der Prozessparameter auf das Nanodrahtwachstum werden durch den Vergleich von experimentellen Ergebnissen mit Parameterstudien analysiert. Die Auswertung hat ergeben, dass für das dielektrophoretische Wachstum ein durch Wechselfeldelektroosmose (engl. AC electro-osmosis) angetriebener Fluidstrom die Drahtwachstumsgeschwindigkeit und -morphologie maßgeblich beeinflusst. Im Falle der gerichteten elektrochemischen Nanodrahtabscheidung lässt sich die Drahtmorphologie über das angelegte elektrische Wechselsignal steuern. Unter Verwendung des Wachstumsmodells ist ein optimiertes Signal generiert worden, dessen Parametrisierung eine gezielte Anpassung auf den chemischen Ausgangsstoff und den gewünschten Drahtdurchmesser erlaubt.
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Martins, Pedro Miguel da Silva. "Modelling crystal growth from pure and impure solutions : a case study on sucrose." Doctoral thesis, 2006. http://hdl.handle.net/10216/11639.
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Martins, Pedro Miguel da Silva. "Modelling crystal growth from pure and impure solutions : a case study on sucrose." Tese, 2006. http://hdl.handle.net/10216/11639.
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Davis, Kevin James. "Resolving the nanoscale mechanisms of calcite growth and dissolution from nonstoichiometric and microbial solutions." Thesis, 2008. http://hdl.handle.net/1911/22241.
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The relative rates of calcite (CaCO3) precipitation and dissolution largely determine the preservation and subsequent accumulation of carbonate in the geologic record and are fundamental parameters for predicting the fate of fossil fuel carbon dioxide as well as the sequestration of several co-precipitated trace elements. Here we use the surface techniques, atomic force microscopy (AFM) and vertical scanning interferometry (VSI) to elucidate the nanoscale mechanisms of calcite growth and dissolution from nonstoichiometric and microbial solutions. Our results clearly demonstrate that the Ca 2+/CO32- ratio of carbonate solutions, at constant saturation, determines both the kinetics and anisotropy of step advancement. Anisotropic step velocities, in turn, alter step generation rates at screw dislocations, thereby significantly affecting the overall growth and dissolution rates of calcite surfaces. These results reflect different mechanistic roles for the cation and anion during both growth and dissolution and suggest limitations on the application of concentration-based rate laws in solutions of varying ionic ratios. Further, this study offers clear demonstration that the crystal surface exerts a primary control on growth and dissolution rates through step-specific and defect-directed interactions, producing differences in rate that could not be predicted from considerations of bulk chemistry alone. Further insight into calcite dissolution in natural systems was achieved by investigating the effect of Shewanella oneidensis MR-1 surface colonization on the dissolution rates of calcite (CaCO3) and dolomite (CaMg(CO 3)2). By quantifying and comparing the significant processes occurring at the microbe---mineral interface, a mechanistic understanding of the way in which microbes alter the dissolution rates of carbonate minerals was achieved. MR-1 attachment under aerobic conditions was found to influence carbonate dissolution through two distinct mechanistic pathways: (1) inhibition through interference with etch pit development and (2) catalytic removal of carbonate material at the cell---mineral interface during irreversible attachment to the mineral surface. The relative importance of these two competing effects was found to vary with the solubility of the carbonate mineral studied. This study demonstrates the dynamic and competitive relationship between microbial surface colonization and mineral dissolution that may be expected to occur in natural environments.
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Blagden, Nicholas, M. Song, R. J. Davey, L. Seton, and Colin C. Seaton. "Ordered Aggregation of Benzamide Crystals Induced using a "Motif Capper" Additive." 2005. http://hdl.handle.net/10454/3554.
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No<br>This paper reports on the growth of benzamide crystals in the presence of 2'-aminoacetophenone. The resulting self-replicating intergrowth of benzamide crystals gives rise to ordered crystal aggregates in which individuals share a common c*. This behavior is interpreted using the concept of a motif capper additive which is able to halt the extension of structural motifs at the surface of a growing crystal. In this case the additive was selected to terminate the hydrogen-bonding ribbons, which extend along the b axis of the benzamide structure.