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Cruz, Daniel Alejandro. "Hierarchical Self-Assembly and Substitution Rules." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7770.
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A set of elementary building blocks undergoes self-assembly if local interactions govern how this set forms intricate structures. Self-assembly has been widely observed in nature, ranging from the field of crystallography to the study of viruses and multicellular organisms. A natural question is whether a model of self-assembly can capture the hierarchical growth seen in nature or in other fields of mathematics. In this work, we consider hierarchical growth in substitution rules; informally, a substitution rule describes the iterated process by which the polygons of a given set are individually enlarged and dissected. We develop the Polygonal Two-Handed Assembly Model (p-2HAM) where building blocks, or tiles, are polygons and growth occurs when tiles bind to one another via matching, complementary bonds on adjacent sides; the resulting assemblies can then be used to construct new, larger structures. The p-2HAM is based on a handful of well-studied models, notably the Two-Handed Assembly Model and the polygonal free-body Tile Assembly Model.
The primary focus of our work is to provide conditions which are either necessary or sufficient for the ``bordered simulation'' substitution rules. By this, we mean that a border made up of tiles is allowed to form around an assembly which then coordinates how the assembly interacts with other assemblies. In our main result, we provide a construction which gives a sufficient condition for bordered simulation. This condition is presented in graph theoretic terms and considers the adjacency of the polygons in the tilings associated to a given substitution rule. Alongside our results, we consider a collection of over one hundred substitution rules from various sources. We show that only the substitution rules in this collection which satisfy our sufficient condition admit bordered simulation. We conclude by considering open questions related to simulating substitution rules and to hierarchical growth in general.
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Molnar, G., L. Dozsa, Z. Vertesy, and Z. J. Horvath. "Thickness Dependent Growth of Epitaxial Iron Silicide Nanoobjects on Si (001)." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35180.
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Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrate by conventional
Fe evaporation and subsequent annealing. The initial Fe thickness was in the 0.1-6.0 nm range and
the annealing temperature was 850 °C. The formed phases and structures were characterized by reflection
high energy electron diffraction, and scanning electron microscopy. The electrical characteristics were investigated
by I-V and C-V measurements, and by DLTS. The samples show silicide nanostructure formation
in the whole thickness range. The shape of the nanostructures varied from rod like to triangular
and quadratic depending on the initial Fe thickness. The size distribution of the formed iron silicide nanoobjects
was not homogeneous, but they were oriented in square directions on Si(001). Higher thickness
resulted in increased particles size.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35180
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Jiang, Feng. "Ligand Controlled Growth of Aqueous II-VI Semiconductor Nanoparticles and Their Self-Assembly." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311311.
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Colloidal semiconductor nanoparticles (NPs) contain hundreds to thousands of atoms in a roughly spherical shape with diameters in the range of 1-10 nm. The extremely small particle size confines electron transitions and creates size tunable bandgaps, giving rise to the name quantum dots (QDs). The unique optoelectronic properties of QDs enable a broad range of applications in optical and biological sensors, solar cells, and light emitting diodes. The most common compound semiconductor combination is chalcogenide II-VI materials, such as ZnSe, CdSe, and CdTe. But III-V and group IV as well as more complicated ternary materials have been demonstrated. Coordinating organic ligands are used to cap the NP surface during the synthesis, as a mean of protecting, confining, and separating individual particles. This study investigated the impact of the ligand on particle growth and self-assembly into hierarchical structures. ZnSe QDs were synthesized using an aqueous route with four different thiol ligands, including 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA), methyl thioglycolate (MTG), and thiolactic acid (TLA). The particle growth was monitored as a function of reaction time by converting the band gaps measured using UV-vis spectroscopy into particle sizes. A kinetic model based on a diffusion-reaction mechanism was developed to simulate the growth process. The growth data were fit to this model, yielding the binding strength in the order TLA < MTG ≈ TGA < MPA. This result showed the relationship between the QD growth rates and the chemical structures of the ligands. Ligands containing electron-withdrawing groups closer to the anchoring S atom and branching promoted growth, whereas longer, possibly bidendate, ligands retarded it. Removing TGA ligands from the surface of CdTe QDs in a controlled manner yielded new superstructures that were composed of either intact or fused particles. Purifying as-synthesized QDs by precipitating them using an anti-solvent removed most of the free ligand in solution. Aging this purified QD suspension for a week caused self-assembly of QDs into nanoribbons. The long time needed for self-assembly was due to the slow equilibrium between the ligands on QD surface and in solution. Accelerating the approach to equilibrium by diluting purifed CdTe QDs with organic solvents triggered rapid self-assembly of superstructures within a day, forming various nanostructures from nanoribbons to nanoflowers. The type of nanostructures that formed was determined by the solvation of TGA in the trigger solvent. Extracting the smallest portion of TGA in methanol promoted vectorial growth into ribbons consistent with dipole-dipole attractive and charge-charge repulsive interactions. Removing more of the TGA layer in IPA caused the dots to fuse into webs containing clustered ribbons and branches, and the directional nature of the superstructure was lost. Completely deprotecting the surface in acetone promoted photochemical etching and dissolved the QDs, yielding
ower-like structures composed of CdS. Nanocrystal (NC) growth mediated by a ligand was also studied in the organic synthesis of FeS₂ nanocubes. Oleylamine was used not only as the ligand but also the solvent and reductant during the reaction. A one hour reaction between iron (II) chloride and elemental sulfur in oleylamine at 200 ℃ and a S to Fe ratio of 6 yielded phase pure pyrite cubes with dimensions of 87.9±14.1 nm. X-ray diffraction (XRD) spectra and Raman peaks for pyrite at 340, 375, and 426 cm⁻¹ confirmed phase purity. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that the oleylamine remained on the FeS₂ surface as a ligand. The reaction mechanism includes the production of pyrrhotite Fe₁₋ᵪS (0≤x<0.5) via reduction of S⁰ to S²⁻ by oleylamine and the oxidation of pyrrhotite to pyrite with remaining S⁰.
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Bouville, Florian. "Self-assembly of anisotropic particles driven by ice growth : Mechanisms, applications and bioinspiration." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0155/document.
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Les phénomènes d'auto-assemblage sont au premier plan de la recherche en sciences des matériaux car ils comblent le vide laissé entre les procédés d'assemblage à l'échelle macroscopique et nanoscopique. L'auto-assemblage est basé sur l'organisation spontanée de composants individuels en motifs et structures. Contrôler l’agencement de la matière peut accroître les propriétés de matériaux en introduisant une certaine anisotropie. Cet agencement, comme de nombreux matériaux naturels le prouvent, peut même sous certaines conditions faire émerger de nouvelles caractéristiques. Au cours de ces trois années, nous avons utilisé l’ « ice templating » (texturation à la glace) pour déclencher l’alignement de plaquettes de dimensions microniques, le but final étant de répliquer la microstructure de la nacre. Cette technique induit la ségrégation des constituants d’une suspension à l’échelle du micron tout en obtenant des échantillons de quelques centimètres cubes. Ce procédé a permis la création de matériaux inorganique avec une microstructure semblable à la nacre, en additionnant trois niveaux de contrôles successifs : l’alignement local des plaquettes, l’alignement à longue distance des cristaux de glaces et enfin le contrôle de l’interface entre ces-mêmes plaquettes. L’utilisation d’une modélisation par éléments discrets nous a permis d’étudier la dynamique de l’auto-assemblage des particules anisotropes. Ce modèle, parce qu’il tient compte de la dynamique du procédé, nous a révélé comment l’organisation de ces particules se produit. La tomographie par rayon X a permis de visualiser les structures finales des échantillons et d’attester de la pertinence du modèle. L’alignement local des plaquettes dans les parois générées par la solidification de la glace peuvent accroître les propriétés fonctionnelles et structurales de composites. Dans ce cadres deux applications ont été étudiées : la conduction thermique dans des composites nitrure de bore hexagonal / silicone et les propriétés mécaniques d’alumine macroporeuses. Une adaptation du procédé a permis d’obtenir l’alignement à longue distance (quelques centimètres) des cristaux de glaces. Différents outils ont été développés pour caractériser la réponse fonctionnelle de ce type de composite en fonction de leurs architectures aux deux échelles considérées (celles des macropores et parois). Enfin, après la mise en place de ces deux niveaux de contrôle sur la structure, l’addition d’une phase vitreuse inorganique et de nanoparticules aux joints de grains des plaquettes a introduit, de façon similaire à la nacre, des interfaces pouvant dévier et arrêter la propagation de fissuresSelf-assembly phenomena are of prime interest in materials science, because they fill the gap between assembly of macrostructure and processing of nanomaterials. Self-assembly is based on the spontaneous organization of individual small constituents into patterns and structures. Controlling the spatial arrangement can possibly improve materials properties by maximizing its response in a given direction. Furthermore, particular types of spatial arrangement, such as found in natural structures, can even induce new properties. During the past three years, we have used ice templating process to trigger the assembly of platelet-shaped particles to replicate the hierarchical structure of nacre. Control over this technique allowed structural customization at different length-scales: local orientation of the platelets, ice crystal long range order, and the control if the interfaces between the platelets. This hierarchical process has set the ground for the creation of a new fully mineral nacre-like alumina. The local platelet self-assembly triggered by ice growth was investigated by Discrete Element Modelling which provided new insight into the dynamic phenomenon responsible for the particles alignment. Synchrotron X-ray tomography was used to validated the model results. The different architecture observed in the final samples are not the result of a percolation threshold, as one could expect, but is instead a consequence of the delicate balance between pushing and engulfment at the solidification front. The local alignment of platelets can be beneficial for the functional and structural characteristics of composites and relevant aspects for two potential applications were investigated: the thermal properties of the hexagonal boron nitride/silicon rubber composites and the mechanical properties of macroporous alumina. Further adaptation of the process allowed for long range ordering of the ice crystals (up to the centimeter scale). Different tools have also been developed in order to characterize the response of composites as a function of the architecture at the level of the macropores and particle organisation. Once those two levels of alignment were achieved, the addition of a glassy phase and nanoparticles to the grain boundaries of the platelets introduces, just like in nacre, interfaces capable of deflect and even stopping crack propagation
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Hille, Pascal [Verfasser]. "Advanced group III-nitride nanowire heterostructures - self-assembly and position-controlled growth / Pascal Hille." Gießen : Universitätsbibliothek, 2017. http://d-nb.info/1132510511/34.
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Nardi, Elena. "Growth of organic nanostructures through on-surface reactions : from phthalocyanines self-assembly to polymeric phthalocyanines." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4351/document.
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Le couplage covalent de précurseurs moléculaires spécialement conçus, assisté par une surface métallique, a récemment émergé comme nouvelle voie pour la création de nouvelles architectures moléculaires prometteuses pour l’électronique moléculaire. Les phtalocyanines et leurs dérivés ont attiré beaucoup d’intérêt à cause de leurs propriétés chimiques et optoélectroniques. Dans cette thèse la synthèse de composés de phtalocyanine est présentée. Les composés sont obtenus par une réaction en surface entre précurseurs fonctionnalisés avec quatre groupements carbonitriles et des atomes métalliques. L’étude expérimentale est faite par microscopie à effet tunnel et spectroscopie de photoémission X. Les précurseurs moléculaires de TCN-DBTTF et de PPCN ont été étudiés. Les TCN-DBTTF ont été déposés avec les atomes de Mn, Fe ou Cu sur Ag(111) et Au(111). La réaction de cyclotetramerization a été activée par recuits. Dans le cas le plus favorable (TCN-DBTTF avec Fe sur Ag(111)), la réaction peut être activée à 200°C et permet la synthèse de phtalocyanines individuelles. Un recuit à plus haute température permet de continuer la réaction en 1D (250°C) et en 2D (275°C). Des résultats similaires ont été obtenus pour le dépôt de PPCN avec Mn ou Cu sur Au(111). L’évolution des spectres des niveaux de coeur permet d’obtenir une preuve de la réaction. Les différents facteurs qui influencent la cyclotetramerisation ont été étudiés.L'étude démontre la versatilité de la méthode: la synthèse en surface permet la création de polymères 2D originaux connectés par des macrocycles de phtalocyanine susceptibles d’être étendus à un grand nombre de précurseurs et d’atomes métalliquesSurface-assisted covalent coupling of suitably designed molecular precursors on metal surfaces has recently emerged as a new route towards the design of novel molecular architectures promising for future applications. Phthalocyanines and their derivatives have been widely studied for their chemical and optoelectronic properties. In this thesis the synthesis of phthalocyanine compounds is presented. The compounds are obtained through an on-surface reaction between tetracarbonitrile-functionalized precursors and metals. The experimental investigation is carried out by means of scanning tunnelling microscopy and X-Ray photoemission spectroscopy. Two molecular precursors, TCN-DBTTF and PPCN, are studied. TCN-DBTTF molecules are deposited with metal atoms (Mn, Fe, or Cu) on Ag(111) and Au(111). Annealing is used to activate the reaction of cyclotetramerization between precursors and metals. In the most favourable case (TCN-DBTTF with Fe on Ag(111)) the reaction can be activated at 200°C and leads to the synthesis of individual phthalocyanines. Increasing the temperature allows the synthesis of polymeric lines, at 250°C, and small 2D domains, at 275°C. Similar results are obtained for PPCN deposition with Mn or Cu on Au(111). In this latter case, the evolution of core level spectra allows a chemical proof of the on-surface reaction. The factors affecting on-surface cyclotetramerization have also been studied. This study demonstrates the versatility of the method: on-surface cyclotetramerization allows creating original 2D polymers connected by phthalocyanine macrocycles, and may work with a wide range of tetracarbonitrile-functionalized precursors and metallic atoms
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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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Dahal, Yuba Raj. "Equilibrium and kinetic factors in protein crystal growth." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/36220.
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Doctor of PhilosophyDepartment of Physics
Jeremy D. Schmit
Diseases such as Alzheimer’s, Parkinson’s, eye lens cataracts, and Type 2 diabetes are the results of protein aggregation. Protein aggregation is also a problem in pharmaceutical industry for designing protein based drugs for long term stability. Disordered states such as precipitates and gels and ordered states such as crystals, micro tubules and capsids are both possible outcomes of protein–protein interaction. To understand the outcomes of protein–protein interaction and to find the ways to control forces, it is required to study both kinetic and equilibrium factors in protein–protein interactions. Salting in/salting out and Hofmeister effects are familiar terminologies used in protein science field from more than a century to represent the effects of salt on protein solubility, but they are yet to be understood theoretically. Here, we build a theory accounting both attractive and repulsive electrostatic interactions via the Poisson Boltzmann equation, ion–protein binding via grand cannonical partition function and implicit ion–water interaction using hydrated ion size, for describing salting in/salting out phenomena and Hofmeister and/or salt specific effect. Our model free energy includes Coulomb energy, salt entropy and ion–protein binding free energy. We find that the salting in behavior seen at low salt concentration near the isoelectric point of the protein is the output of Coulomb energy such that the addition of salt not only screens dipole attraction but also it enhances the monopole repulsion due to anion binding. The salting out behavior appearing after salting in at high salt concentration is due to a salt mediated depletion interaction. We also find that the salting out seen far from the isoelectric point of the protein is dominated by the salt entropy term. At low salt, the dominant effect comes from the entropic cost of confining ions within the aggregates and at high salt, the dominant effect comes from the entropy gain by ions in solution by enhancing the depletion attraction. The ion size has significant effects on the entropic term which leads to the salt specificity in the protein solubility. Crystal growth of anisotropic and fragile molecules such as proteins is a challenging task because kinetics search for a molecule having the correct binding state from a large ensemble of molecules. In the search process, crystal growth might suffer from a kinetic trap called self–poisoning. Here, we use Monte Carlo simulation to show why protein crystallization is vulnerable to the poisoning and how one can avoid such trap or recover crystal growth from such trap during crystallization. We show that self–poisoning requires only three minimal ingredients and these are related to the binding affinity of a protein molecule and its probability of occurrence. If a molecule attaches to the crystal in the crystallographic state then its binding energy will be high but in protein system this happens with very low probability (≈ 10−5). On the other hand, non–crystallographic binding is energetically weak, but it is highly probable to happen. If these things are realized, then it will not be surprising to encounter with self–poisoning during protein crystallization. The only way to recover or avoid poisoning is to alter the solution condition slightly such as by changing temperature or salt concentration or protein concentration etc.
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Farrer, I. "Growth and applications of self-assembled quantum dots." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598945.
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This thesis describes studies of the growth and subsequent characterisation of wafers containing layers of Self-Assembled Quantum Dots grown by Molecular Beam Epitaxy (MBE). Insertion of such layers into transport structures is of particular interest for the creation of the new generation of optoelectronic devices. The growth of calibration structures containing InAs/GaAs Self-Assembled Quantum Dots is then outlined and certain growth parameters varied with the aim of tuning the emission energy and achieving narrow linewidths in the photoluminescence spectrum. Utilising the inherent non-uniformity of the Indium cell, which originates from the crucible design, we are able to achieve radial variations in the deposited thickness. Consequently, it has been possible to study the early stages of dot formation in some detail via the growth of uncapped samples for subsequent study using an Atomic Force Microscope (AFM). The properties of electrical devices containing a layer of InAs dots are discussed. In particular the mobility of an adjacent two-dimensional electron gas (2DEG) is strongly affected by the charge state of the dots themselves. In this structure it is possible to alter the charge state by either illumination, which removes charge from the dots, or by application of a positive gate voltage, which recharges the dots. After illumination the channel resistance drops significantly and persists for long timescales. This effect enables the creation of new types of optical memory or photon detector structures.
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Yoshikawa, Taro [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "Toward ultra-thin nanocrystalline diamond film growth: electrostatic self-assembly of non-aggregated diamond nanoparticles onto substrate surfaces." Freiburg : Universität, 2017. http://d-nb.info/115294469X/34.
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Bartels, Martin. "Self-assembled epitaxial growth of CdSe quantum dot structures." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=971575142.
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Mohaddes, Ardabili Ladan. "Growth and characterization of self-assembled ferromagnetic iron nanowires." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3432.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Material Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Riel, Bruno J. "Mechanisms governing the growth of self-assembled quantum dots." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6448.
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We produced self-assembled quantum dot (QD) samples of InAs on GaAs by molecular beam epitaxy (MBE). With these, we explored growth effects as a function of InAs coverage for three arsenic pressures, and as a function of arsenic pressure at a specific InAs coverage. During growth, the samples were studied using reflection high energy electron diffraction (RHEED). These RHEED measurements were compared to low energy electron diffraction (LEED) measurements. To perform this ex-situ LEED characterisation, some samples were covered with an amorphous arsenic cap. This cap was thermally evaporated producing a clean, non-oxidised surface that was studied using LEED. We obtained non-ambiguous identification of the GaAs (001) surface reconstructions as well as timing information for the 2D to 3D transition during the growth of InAs on GaAs. Post growth characterisation of two sets of self-assembled QD samples, twelve samples in all, revealed the following: As a function of increasing the arsenic pressure used in QD growth, the photoluminescence (PL) of capped QDs is first redshifted at low arsenic pressures, and then blueshifted at high arsenic pressures. Scanning electron microscopy and atomic force microscopy of uncapped QDs show that as the arsenic pressure increases, the QD density increases while the average QD width and height decrease monotonically; these trends are consistent with the shift in PL for the high arsenic pressure samples, but are inconsistent with the shift in PL for the low pressure samples. This leads us to proposing a mechanism by which QDs may be modified as they are overgrown with capping material. We discuss the effects of adjusting the arsenic pressure on the formation of QDs and the mechanism by which QDs may be modified during capping.
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Joyce, Peter Brian. "Controlled growth of InAS/GaAs self-assembled quantum dots." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405028.
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Mukherjee, Sanjoy. "Synthesis, Characterization, and Growth Mechanism of Single-Walled Metal Oxide Nanotubes." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16176.
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Nanotubes have numerous potential applications in areas such as biotechnology, electronics, photonics, catalysis and separations. There are several challenges to be overcome in order to realize their potential, such as: (1) Synthesis of monodisperse (in diameter and in length) single-walled nanotubes; (2) Quantitative understanding of the mechanism of formation and growth of nanotubes; (3) Capability to engineer the nanotube size; (4) Low temperature synthesis process; and (5) Synthesis of impurity free nanotubes. Our investigation focuses on a class of metal oxide (aluminosilicate/germanate) nanotubes, which are; single walled nanotubes with monodisperse inner and outer diameters, can be synthesized in the laboratory by a low temperature (95ºC) process in mildly acidic aqueous solutions, and their formation timescales is hours, which makes it convenient as a model system to study the mechanisms of nanotube formation.
This work is focused on obtaining a qualitative and quantitative understanding of the mechanism of formation of aluminosilicate and aluminogermanate nanotubes. In order to achieve this overall objective, this thesis consists of the following aspects: (1) A systematic phenomenological study of the growth and structural properties of aluminosilicate and aluminogermanate nanotubes. The constant size and increasing nanotube concentration over the synthesis time strongly suggest that these nanotubular are assembled through self-assembly process. (II) Investigation of the mechanism of formation of single-walled aluminogermanate nanotubes provided the central phenomena underlying the formation of these nanostructures: (1) the generation (via pH control) of a precursor solution containing chemically bonded precursors, (2) the formation of amorphous nanoscale (~ 6 nm) condensates via temperature control, and (3) the self-assembly of short nanotubes from the amorphous nanoscale condensates. (III) Synthesis of mixed metal oxide (aluminosilicogermanate) nanotubes with precise control of elemental composition, diameter and length of the product nanotubes. (IV) Preliminary work towards generalization of the kinetic model developed for aluminogermanate nanotubes to a larger class of metal oxide nanotubes. It was found that the size of nanotubes is dependent on the amount of precursors that can be packed in a single ANP and in turn depends on the size of the ANP.
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Chen, Jing. "Novel H-bond donor polymers for layer-by-layer self-assembly multilayered films." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0087/document.
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Ce travail est consacré à la synthèse de nouveaux polymères donneurs de liaison Hydrogène et à leur utilisation comme partenaire dans la construction de nouveaux films multicouches préparés par le procédé d’élaboration en couche-par-couche (LbL). Plus particulièrement, une nouvelle réaction impliquant des mercaptoalcools non protégés et le poly(2,3,4,5,6-pentafluorostyrène) (PPFS) a été développé et appliquée à la synthèse de nouveaux polymères donneurs de liaisons H. Ce couplage régiosélectif et chimiosélectif de type « click » avec un thiol hétérofonctionnel peut être utilisée pour préparer une bibliothèque de polymères qui diffèrent de par leur degré de substitution (DS) et/ou leur fonctionnalité en groupements associatifs. Le contrôle de ces paramètres structuraux permet de moduler leur force d’interactions avec des partenaires accepteurs de liaison H variés, comme la poly(4-vinyl pyridine) (P4VP), le poly(acrylate de n-butyle) (PBA) et le poly(oxyde d'éthylène) (PEO), de telle façon que tous les types de mélanges binaires (mélange non miscible, partiellement ou totalement miscible, ou complexe interpolymère) peuvent être obtenus. Ensuite, les dérivés de PPFS donneurs de liaisons H ont été utilisés en partenariat avec le P4VP pour élaborer avec succès de nouveaux films multicouche dont la force motrice est l’établissement de liaisons H. L'influence de nombreux paramètres relatifs à la structure des polymères donneurs (DS, structure chimique du groupement associatif), au type de modification chimique subie par le substrat sur lequel est élaboré le film multicouche (monocouche auto-assemblée vs. polymère greffée en conformation de type brosse) ou encore des paramètres expérimentaux liés aux conditions de dépôt (concentration des solutions de dépôt, nature du partenaire adsorbé en premier) a été étudiée. Plus particulièrement, le mécanisme de croissance ainsi que les caractéristiques de surface du film ont été évaluésThis work deals with the design of novel hydrogen-bond donor polymers and their use as partner in new tailor-made multilayered films prepared by the layer-by-layer (LbL) process. In this context, a novel regioselective and chemoselective “click-type” reaction of unprotected mercaptoalcohols onto poly(2,3,4,5,6-pentafluoro-styrene) (PPFS) has been developed, and applied to the synthesis of new hydroxylated H-bond donor polymers. This coupling with heterofunctional thiol is used to prepare a library of polymers differing in the degree of substitution (DS) and/or functionality. The fine control of these parameters makes it possible to tune their interaction ability with various acceptor polymers such as poly(4-vinyl pyridine) (P4VP), poly(n-butyl acrylate) (PBA) and poly(ethylene oxide) (PEO), such that all possible scenarios (immiscible blend, partially or totally miscible blend or interpolymer complex) can be achieved. Subsequently, the resulting H-bond donor polymers (PPFS derivatives) were used to successfully build-up multilayered films with using P4VP as partner via layer-by-layer (LbL) through the dip deposition process. The influence of various parameters related to structure of the partners (DS, nature of the PPFS derivatives), the chemical structure of the surface onto which the film is built-up (self-assembled monolayer vs. polymer brush) and the deposition process (concentration of deposition solutions, nature of the first deposited partner) was in-depth evaluated, on both the growth mechanism and on the surface features of the multilayered films
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Jones, Aleksy K. "Kinetically determined surface morphology in epitaxial growth." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2499.
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Molecular beam epitaxy has recently been applied to the growth and self assembly of nanostructures on crystal substrates. This highlights the importance of understanding how microscopic rules of atomic motion and assembly lead to macroscopic surface shapes. In this thesis, we present results from two computational studies of these mechanisms.
We identify a kinetic mechanism responsible for the emergence of low-angle facets in recent epitaxial regrowth experiments on patterned surfaces. Kinetic Monte Carlo simulations of vicinal surfaces show that the preferred slope of the facets matches the threshold slope for the transition between step flow and growth by island nucleation. At this crossover slope, the surface step density is minimized and the adatom density is maximized, respectively. A model is developed that predicts the temperature dependence of the crossover slope and hence the facet slope.
We also examine the "step bunching" instability thought to be present in step flow growth on surfaces with a downhill diffusion bias. One mechanism thought to produce the necessary bias is the inverse Ehrlich Schwoebel (ES) barrier. Using continuum, stochastic, and hybrid models of one dimensional step flow, we show that an inverse ES barrier to adatom migration is an insufficient condition to destabilize a surface against step bunching.
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Kleppmann, Nicola [Verfasser], Sabine [Akademischer Betreuer] Klapp, and Andreas [Akademischer Betreuer] Heuer. "Simulation of growth and self-assembly of complex molecules on surfaces / Nicola Kleppmann. Gutachter: Andreas Heuer ; Sabine Klapp. Betreuer: Sabine Klapp." Berlin : Technische Universität Berlin, 2015. http://d-nb.info/1077040156/34.
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Pham, Son Tung. "Epitaxial growth and magnetic properties of self-assembled GeMn quantum dots." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0504.
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Dans le cadre de ce travail de thèse, nous avons étudié la croissance de boîtes quantiques auto-assemblés de GeMn sur Si par épitaxie par jets moléculaires. La concentration de Mn varie de 2 à 8%. Nous avons montré que la température la plus basse est d'environ 400 °C.Nous avons ainsi étudié la croissance de GeMn à 410 et 430 °C. En combinant de nombreuses techniques de caractérisation pour étudier les propriétés des boîtes quantiques GeMn, telles que les propriétés structurales (TEM), la morphologie de surface (RHEED, AFM), les propriétés magnétiques (SQUID, XMCD) et la composition (EDX), nous avons montré qu'il est possible de contrôler les propriétés magnétiques des boîtes quantiques GeMn. En particulier, nous avons démontré qu'en maîtrisant les paramètres de croissance, il est possible d'obtenir une température de Curie jusqu'à 380K.La deuxième partie de ce travail de thèse porte sur la croissance de boîtes quantiques GeMn dans des structures multicouches. Nous avons démontré que les boîtes dans les couches supérieures peuvent croître au-dessus des boîtes enterrées, conduisant ainsi à un ordre vertical selon la direction de croissance. Nous avons également montré que la diminution de l'épaisseur critique de la couche de mouillage dans les couches supérieures est le paramètre clé, qui conduit à l'augmentation de la dimension des boîtes. Ce phénomène peut être expliqué par une accumulation de la contrainte élastique dans les couches de barrière de Si et ceci est induit par des couches inférieures. Ce résultat ouvre la voie à la réalisation d'une structure multicouche dans laquelle les boîtes quantiques puissent avoir la même taille dans toutes les couchesIn the frame of this thesis work, we have investigated the growth of self-assembled GeMn quantum dots on Si substrates by means of Molecular Beam Epitaxy. The doping Mn concentration ranges from 2 up to 8%. We have found that the lowest temperature at which the formation of self-assembled quantum dots is still preserved is about 400 °C.We have thus performed the growth of GeMn quantum dots at 410 and 430 °C. By combining numerous characterization techniques to investigate the quantum-dot properties, including structural properties (TEM), surface morphology (RHEED, AFM), magnetic properties (SQUID, XMCD) and composition (EDX), we have determined the key parameters allowing to control the magnetic properties of GeMn quantum dots. Of particular interest, we have demonstrated that well-controlled GeMn quantum dots can exhibit a Curie temperature up to 380K.The second part of this thesis work deals with the growth of GeMn quantum dots in multilayered structures. Interestingly, we have observed that the dots in upper lays can grow on the top of the buried dots, leading to a vertical ordering of dots along the growth direction. We also shown that the decrease of the wetting layer thickness in the upper layers of a multilayered structure is the main parameter that leads to the increase of the dot size and height. Such an evolution of the wetting layer thickness can be explained by an accumulation of elastic strain in the Si spacer layers induced by the lower Ge wetting layers. This finding opens the route to the realization of a multilayer structure in which the islands have equal size in all layers
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Kamarudin, Mazliana Ahmad. "Growth and optical properties of self-assembled GaSb/GaAs quantum dots." Thesis, Lancaster University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.547945.
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Bierwagen, Oliver. "Growth and anisotropic transport properties of self assembled InAs nanostructures in InP." Doctoral thesis, [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985352930.
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Capacci-Daniel, Christina Anne. "Crystal growth of polymorphic bis-diphenyl ureas on self-assembled monolayer templates." Connect to Electronic Thesis (CONTENTdm), 2009. http://worldcat.org/oclc/463440944/viewonline.
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Johnson, Tamina L. "Elastin-Like Polypeptide Fusion Tag as a Protein-Dependent Solubility Enhancer of Cysteine-Knot Growth Factors." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7629.
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Elastin-like peptide (ELP) fusions promote therapeutic delivery and efficacy. Recombinant proteins, like neurotrophins, lack bioavailability, have short in vivo half-lives, and require high manufacturing costs. Fusing recombinant proteins with genetically encodable ELPs will increase bioavailability, enhance in vivo solubilization, as well as provide a cost-effective method for purification without the need for chromatography. During expression of neurotrophin-ELP (N-ELP) fusions, dense water-insoluble aggregates known as inclusion bodies (IBs) are formed. Inclusion bodies are partially and misfolded proteins that usually require denaturants like Urea for solubilization. Strong denaturants arrest ELPs stimuli-responsive property and increase unwanted aggregation, making purification difficult, yet possible. The current field of study exhibit issues with protein recovery due to solubility issues and aggregation. This study examines the solubility challenges of inclusion body proteins and the role ELP fusion tags play on IBs solubility. Elastin-like peptides are a class of stimuli-responsive biopolymers whose biocompatibility and limited toxicity are attractive for biological applications. ELPs are tunable polymers, which consist of peptide repeat units (VPGXG), where X is any amino acid except Proline while the guest residue or length of the sequence can be chosen. ELPs have uniquely tunable phase transitioning properties that allow the protein to undergo molecular self-assemblies into different nanostructures in response to the changes in their environment (e.g. pH or temperature). Optimizing the purification process via suppressing aggregation during the refolding process has increased protein recovery slightly however, more work is needed to attain 90 percent recovery. Usage of ELPs has increased the solubility of N-ELP fusions, specifically for brain-derived neurotrophic factor ELP fusions.
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Summerfield, Alex. "Studies of self-assembled metal-organic nanostructures and the MBE growth of graphene." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33067/.
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This thesis discusses the formation of metal-organic and organic structures grown on surfaces using bottom-up self-assembly techniques. Three systems are investigated primarily using scanning probe microscopy techniques. The growth of metal-organic frameworks (MOFs) on functionalised surfaces is investigated using high resolution atomic force microscopy (AFM). The earliest stages of MOF crystal nucleation are imaged using a layer-by-layer (LBL) growth technique and the ability to track the growth of individual nanocrystallites throughout the LBL process is demonstrated. This LBL method has been suggested as a route to fabricating epitaxially grown, oriented thin-films of MOFs. However, results from these studies indicate that, rather than a uniform crystalline layer, the morphology is that of a preferentially oriented but laterally polycrystalline film and the growth rates of the individual nanocrystallites exceed those expected for a LBL growth mode. This has significant implications for the fabrication of novel devices that incorporate MOFs due to the presence of domain boundaries and defects. Self-assembled monolayers of light-harvesting porphyrin nanorings are investigated with scanning tunnelling microscopy (STM) and AFM. The nanorings are found to form large supramolecular networks in ambient conditions on graphite and boron nitride surfaces. The size and order of these networks is found to be dependent on the number of porphyrin macrocycles that make up each ring. In addition, simulations of isolated nanorings are also performed using Monte Carlo methods to model the distortion previously been observed for isolated nanorings on gold surfaces. These are discussed in the context of spectroscopic measurements which suggest that both size dependent and thermally induced distortion affects the lifetime and delocalisation of excited states in these molecules. Graphene is grown on hexagonal boron nitride surfaces using high-temperature molecular beam epitaxy. Large domains of monolayer graphene are successfully grown and are investigated using AFM and Raman spectroscopy. These domains are found to exhibit hexagonal moiré patterns on the graphene surface which is suggestive of orientational alignment with the underlying boron nitride substrate. Regions with high period and distorted moiré patterns are also observed which suggest that the graphene is under tensile strain which is attributed to the high growth temperatures used. The strain is found to significantly affect the Raman spectrum of graphene and a relationship between the strain and the shifting of Raman spectral peaks is determined. Successful attempts are also made to modify the strain in the graphene monolayer using an AFM tip which is observed to relax when defects are introduced in a controlled manner to the graphene monolayer. These results represent new approaches to the introduction and control of strain in graphene which may be useful for the fabrication of high-performance graphene devices.
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Daher, Mansour Michel. "Transition metal nanolines on a nanopatterned silver substrate : self-organized growth and magnetic properties." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0287.
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L'intérêt pour les propriétés magnétiques des nanostructures de métaux de transition et de lanthanides de faible dimensionnalité n’a cessé de croitre au cours des deux dernières décennies, tant pour leur intérêt en recherche fondamentale que pour la perspective d’applications technologiques. De manière remarquable, les propriétés magnétiques des nanostructures peuvent être ajustées en contrôlant leur géométrie, leur structure atomique et leur environnement chimique. Dans cette thèse, un gabarit 1D composé de nanorubans de Si auto-organisés est utilisé pour guider la croissance de nanolignes de métaux de transition dans le but d’étudier leurs propriétés magnétiques. La géométrie et la structure atomique des nanorubans de Si et des nanolignes de métaux ont été étudiées in situ par microscopie par effet tunnel. Concernant le silicium, notre étude montre qu’une température de 490 K est nécessaire pour obtenir un gabarit 1D hautement ordonné. Les résultats obtenus sur les métaux de transition ont permis de déterminer la géométrie et la structure des nanolignes. Pour accéder aux propriétés magnétiques des nanolignes de Co, des mesures par XMCD ont été effectuées en température, en utilisant différentes orientations du champ magnétique. Les résultats montrent que les deux premières couches de Co adsorbées sur les nanorubans présentent une réponse magnétique faible, tandis que les couches supérieures présentent une aimantation exaltée. Deux axes d’anisotropie dans le plan ont été mis en évidence. Les moments magnétiques et l'énergie d’anisotropie magnétique ont été déterminés quantitativement. Les études en température suggèrent un comportement superparamagnétiqueInterest in the magnetic properties of low dimensional transition metal and lanthanide nanostructures has seen an unprecedented rise in the last two decades due to both their fundamental interest and perspectives of technological applications. Remarkably, the magnetic properties of nanostructures can be tuned by controlling their geometry, atomic structure and chemical environments. In this thesis, a one-dimensional template composed of self-organized Si nanoribbons is used to grow transition metal nanolines, prior to the characterization of their magnetic properties. The geometries and the atomic structure of both the Si nanoribbons and the metal nanolines were investigated in situ by scanning tunneling microscopy. The growth mechanisms were investigated by exploring a large set of growth conditions. Regarding the Si growth, our study shows that a temperature of 490 K is necessary to obtain a long-range ordered one-dimensional template. Concerning the transition metal study, the results resolved the nanoline geometries and atomic structures.To access the magnetic properties of the Co nanolines on Si, XMCD measurements were performed using different magnetic field orientations and temperatures.The results show that the first two Co layers directly adsorbed onto the Si nanoribbons present a weak magnetic response while the upper Co layers exhibit an enhanced magnetization. Remarkably, two in-plane easy axes of magnetization were evidenced.The magnetic moments and the magnetic anisotropic energy are determined quantitatively.Temperature-dependent investigations strongly suggest a superparamagnetic behavior
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Carnevale, Santino D. "Catalyst-free III-nitride Nanowires by Plasma-assisted Molecular Beam Epitaxy: Growth, Characterization, and Applications." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374066626.
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Haubold, Danny, Annett Reichhelm, Alexander Weiz, Lars Borchardt, Christoph Ziegler, Lydia Bahrig, Stefan Kaskel, Michael Ruck, and Alexander Eychmüller. "The Formation and Morphology of Nanoparticle Supracrystals." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-209752.
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Supracrystals are highly symmetrical ordered superstructures built up from nanoparticles via self-assembly. While the NP assembly has been intensively investigated, the formation mechanism is still not understood. To shed some light onto the formation mechanism, we are using one of the most common supracrystal morphologies, the trigonal structures, as a model system to investigate the formation process in solution. To explain the formation of the trigonal structures and determining the size of the supracrystal seeds formed in solution, we introduce the concept of substrate-affected growth. Furthermore, we show the influence of the NP concentration on the seed size and extend our investigations from Ag towards Au.
1.
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Baltazar, Jose A. "Polycyclic aromatic hydrocarbons: exploring new processes and materials for electronics." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51787.
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Graphene is a two-dimensional sp2 hybridized carbon lattice that is also the fundamental building block of graphite. Graphene has attracted significant interest recently due to its distinctive electrical, optical and mechanical properties. These properties have spurred research directed at modifying graphene for use in a variety of electronic, optoelectronic, and sensor technologies. However, before graphene can be used in products, it is necessary to find methods to tune, modify, grow and integrate graphene features while substantially boosting device performance and maintaining current processing compatibility and ease of integration with existing manufacturing infrastructure.
This dissertation focuses on developing techniques for controllably doping the graphene layer through scalable, industry friendly and simple chemical doping; using self-assembled monolayer compounds, photo-acid and photo-base generators, polymers and metal-organic species. We have, in fact, demonstrated simple p-n junctions fabricated in this manner. Characteristic I-V curves indicate the superposition of two separate Dirac points from the p and n regions, confirming an energy separation of neutrality points within the complementary regions; Raman studies of these methods have shown that these processes result in extremely low defect levels in the graphene. Our simple methods for producing patterned doping profiles in graphene films and devices open up a variety of new possibilities for forming complex doping profiles in a simple manner in graphene. This work can enable rapid testing, such as controlled work function tuning, complex doping profiles and simple post-fabrication tuning, of concepts for graphene that may be useful in both interconnect and transparent conductor applications.
In addition to graphene doping, we also investigated approaches to the synthesis of few-layer graphene flakes, since current techniques still produce inferior materials. Exfoliation of Graphene Sheets by an Electron Donor Surfactant was demonstrated to generate few-layers graphene flakes that rival the electrical quality of reduce graphene-oxide (rGO) flakes. Last but not least, Diels-Alder adducts on silica were explored as a controllable carbon precursor for pristine graphene; these allow for a rational direct-growth-of-graphene-on-surface reaction mediated by copper catalyst, without the use of flammable precursors, such as methane, that are used in current methods of chemical vapor deposition synthesis of graphene.
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Zhang, Kai. "Molecular beam epitaxy growth and structural property of self-assembled InAs quantum dots on GaAs." [S.l. : s.n.], 2000. http://www.sub.uni-hamburg.de/disse/240/Disskai.pdf.
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Mukai, Kohki. "Growth and Characterization of Self-Assembled InGaAs/GaAs Quantum Dots and Their Application to Lasers." Kyoto University, 2000. http://hdl.handle.net/2433/151537.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・論文博士
博士(工学)
乙第10504号
論工博第3541号
新制||工||1192(附属図書館)
UT51-2000-P671
(主査)教授 藤田 茂夫, 教授 北野 正雄, 教授 野田 進
学位規則第4条第2項該当
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Niu, Xiaobin. "Level-set simulations of self-assembled nano patterns and stacked quantum dots during heteroepitaxial growth." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1610041041&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Bejarano, Villafuerte Ángela. "Self-assembled monolayers and patterned surfaces derived from them as templates for the growth of chiral crystals." Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/123572.
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El proyecto de investigación presentado en esta Tesis tiene como principal objetivo establecer el efecto de las monocapas auto-ensambladas (SAMs) quirales en la nucleación y crecimiento cristalino de compuestos orgánicos, y encontrar las condiciones ideales para favorecer la nucleación heterogénea y su consecuente crecimiento cristalino.
La investigación realizada detalla el estudio realizado para conseguir la cristalización controlada sobre superficies funcionalizadas de determinados compuestos quirales y sales diastereoméricas. Para ello se realizaron estudios de cristalización de mencionados compuestos sobre diferentes superficies funcionalizadas.
El estudio de la cristalización controlada sobre superficies funcionalizadas comienza por la funcionalización de dicha superficie con phencyphos 4-metilentiol, la cual proporcionara resultados muy prometedores debido a su influencia, demostrada en esta tesis, sobre el proceso de cristalización. La cristalización de phencyphos sobre SAMs de este compuesto, no es controlada y presenta diferentes orientaciones. El disolvente es crucial ya que tiene una enorme influencia en el proceso, según el disolvente empleado en la cristalización de phencyphos sobre superficies funcionalizadas, en el caso de usar isopropanol se obtienen los cristales ramificados, un crecimiento muy peculiar.
El método conocido como impresión por microcontacto (microcontact printing en inglés) ofrece un sistema en la superficie que permite favorecer el transporte de masa hacia la zona deseada de la superficie. Las cristalizaciones sobre superficies micropaternadas, tanto de phencyphos como de la sal diastereomérica (p-metilphencyphos y feniletilamina) se han conseguido controlar tras un estudio detallado del efecto del disolvente, el tiempo de la superficie en la disolución, la forma del patrón en superficie, los tioles combinados en superficie y la velocidad de evaporación.The research presented in this Thesis has as the main objective of the establish the effect of chiral self-assembled monolayers (SAMs) on the nucleation and the crystal growth of organic compound, and find conditions which favour heterogeneous nucleation and subsequent growth. The possibility to control crystallization processes using self-assembled monolayers is an extremely interesting and promising approach in organic materials. This control has achieved by the use of inorganic crystalline substrates where nucleation is induced via epitaxy, although organic single crystals and SAMs have been used to control the polymorphic selectivity of the compound to crystallize, which is based on the lattice match between the molecular cluster and crystalline substrate terraces. According to this concept, SAMs have been used as controlled nucleation centres. This research describes the study in order to achieve the controlled crystallization of the compound phencyphos and diastereomeric salts on functionalized surfaces, and shows the differences between homogenous SAMs and combined SAMs (Microcontact printing method). The controlled crystallisation study starts with the formation of SAMs on gold with a novel chiral thiol, which has potential for nucleating crystal growth, (phencyphos 4-methylenthiol, PMT), and the crystallisation of phencyphos on them. The functionalisation of gold with monolayers of this compound has provided significant results due to its demonstrated influence in the crystallisation process. Thus, the successful functionalisation of the gold substrate by this resolving agent type molecule provided the chiral property to the self-assembled monolayer on gold. Phencyphos crystallises on PMT monolayer following different orientations and grow off the surface; depending on the solvent used these crystals grow as branched crystals (in isopropanol) on the functionalised surface. The microcontact printing method favours the mass transport to the desired thiol, minimizing evaporation effect at small scale. The surface combined of PMT and dodecanethiol has been the key for the development of surfaces which can induce the nucleation process on surface. On micropatterned surfaces, phencyphos crystallizes following a preferential orientation. Crystal growth is highly depending on the solvent used to crystalize phencyphos. The same enantiomer of phencyphos crystallized in different solvent (Chloroform and Isopropanol), yield different crystal growth, because the heterogeneous nucleation is effective when the solvent is allowed to evaporate slowly from the surface, allowing good mass transport to the desired regions. The diastereomeric salt most studied and presented here is the one formed by a phencyphos derivate, p-methyl phencyphos which provides a pair of crystalline salts with chiral amines. X-ray crystal structure of this diastereomeric salt reveal 10-membered rings constructed through hydrogen bonds, in which two ammonium groups formally replace phencyphos molecules seen in the phencyphos hydrate structure. The hydrogen bonds are strong and provide several polar faces to the crystalline structure, thus diastereomeric salts should have their crystals templated easily on polar SAM. There are several parameters that also have a dramatic influence on the crystallisation process such as the pattern shape and size which are critical. Thus the motif size which presents better results of favour the nucleation is for dots of 5 μm diameter spaced by 10 μm, for both crystallisation systems. The Dutch resolution has been also studied on micropatterned surfaces. The complexity of the family type crystallisation will require the development of specific additives to favour heterogeneous nucleation.
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Bollani, Monica. "Self-assembled monolayer (SAM) sensors realisation on Si (001) : surface modification, film growth, SAM and sensor characterisation." Aix-Marseille 3, 2000. http://www.theses.fr/2000AIX30072.
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The aim of this thesis is to report the results of an investigation aimed at exploiting synthetic methods to graft organic molecules onto (001) Si as well as at evaluating the applicability of SAM docking in the development of nanodevices. The target of this dissertation is to study a new nucleophylic reaction to bond directly the organic molecules at the surface. In the first part of this work we have focused onto silicon surface preparation. We have pointed out how the RCA cleaning method results in a modification of the structure of the first atomic layers of Si. We have demonstrated by HRTEM and EELS studies that the change of the lattice spacing is related to the subsequent Si oxidation that is known to occur by inward diffusion and insertion of oxygen in bond-centred positions in crystalline silicon. Such a process is favoured by the strain field due to the surface roughening which is characteristic of alkaline etches. To activate the surface toward chemical grafting reactions we have developed a method leading to bromine termination of the surface. This allowed to form an array of aromatic rings bonded through a covalent Si-C bond (i. E. Not implying oxygen bridges) by nucleophilic addition onto the Si-Br surface bond. We have evaluated the bromine termination and the surface reconstruction by Auger, FTIR and LEED analyses. .Ce travail porte sur l'investigation et la recherche des methodes du syntesis pour lier à la surface du Si (001) des monocouches organiques. Nous avons évalué l'applicabilité de ces systèmes pour le développement du nano-dispositif dans le domaine du détecteurs. La première partie de cette thèse regarde la préparation de la surface : on a évalué comment la methode du nettoyage (RCA) utilisée pour éliminer la contamination à la surface détermine une modification sur la structure des premières couches du silicone. Par HRTEM et EELS on a demostré que la variation de la distance des paramètres réticulaires des première couches, c'est dû au passage d'oxidation nommé APM qui permit la diffusion et l'insertion du 0 dans le volume du Si. .
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Al-Brasi, Enteisar. "The growth and characterization of films of noble metal nanocrystals and inorganic semiconductors at the interface of two immiscible liquids." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-growth-and-characterization-of-films-of-noble-metal-nanocrystals-and-inorganic-semiconductors-at-the-interface-of-two-immiscible-liquids(5652496a-6e6d-4e91-a21b-6ae1b3f36a87).html.
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Deposition of noble metal and semiconductor nanocrystalline thin films has received much attention. CdS and CdSe are important semiconductors used in optical devices. A wet chemical route which uses the interface of two immiscible liquids to control the growth and deposition of nanocrystalline thin films forms the basis of the current study. In this method, a metal precursor dissolved in toluene or decane is held in contact with a water layer containing a reducing or sulphiding agent. The reaction proceeds at the interface of the liquids and results in deposits adhering to the interfacial region. The products of such reactions typically consist of nanocrystals forming a thin film. Stable sols of Au, Ag were found to metathesize on contact with alkylamine in oil to form monolayer films that spread across large areas at the water/oil interface. The nature and properties of interfacial thin films depend on the alkylamine. Nanocrystalline thin films consisting of CdS adhering to the interface starting with a polydispersed aqueous sol of crystallites and alkylamine were obtained. The optical band gaps of the films formed are dependent on the alkylamine chain length, with the shortest chain yielding the largest gap. A systematic increase in particle diameters following adsorption is responsible for changes in the electronic structure of films. The formation of nanocrystalline films of CdS adhering at the interface using a toluene solution of cadmium diethyldithiocarbamate and aqueous Na2S solution, in the presence of tetraoctylammonium bromide (TOAB) in the aqueous phase, was investigated under various reaction parameters, while CdSe was obtained using Na2SeSO3 solution and the influences of deposition temperature and solution concentration were studied. A ternary water/decane/2-butoxyethanol /salt system was used to grow deposits of CdSe and CdS. Nanostructured thin films were obtained at the upper interface of the ternary system, between the emulsive middle layer and oil rich top phase. The influence of deposition conditions such as precursor concentrations and temperature, as well as the nature of the medium on the properties of the deposits was studied. Deposits grown using the ternary system were compared with those obtained using water/decane and water/toluene systems. Reaction parameters such as temperature, solution concentration and the size of CdS and CdSe were controlled. A thin film of CdS and CdSe nanocrystals was formed at the interface. The grain size was found to be dependent on reaction temperature and solution concentration, with higher temperatures and solution concentration resulting in larger grains. The nature of thin films obtained at the interface of two immiscible liquids and of a water/decane/2-butoxyethanol/salt ternary system were studied using Scanning and Transmission electron microscopy, X-ray diffraction and UV-visible spectroscopy.
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Teng, Die. "Computational studies of transition metal nanoclusters on metal-supported graphene moiré." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51830.
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The graphene moiré superstructure formed on Ru(0001) (g/Ru(0001)) has shown the potential as a template to self-assemble super-lattices of metal nanoparticles as model catalysts. To explore the possibility of rational catalyst design on g/Ru(0001), detailed density functional theory (DFT) calculations have been performed to investigate the adsorption and diffusion of Rh and Au adatoms on g/Ru(0001). The consequences of different hopping rates for cluster nucleation have been explored by performing Monte Carlo-based statistical analysis, which suggests that diffusing species other than adatoms need to be taken into account to develop an accurate description of cluster nucleation and growth on this surface. DFT calculations have also been carried out to investigate the adsorption and diffusion of 18 4d (Y-Ag) and 5d (La-Au) transition metal adatoms on g/Ru(0001). Given the necessity to study larger diffusing species than adatoms, DFT calculations have been performed to study the adsorption and diffusion of Rh and Au dimers and trimers on g/Ru(0001). It was shown that the mobility of Rh clusters decreases with the increase of cluster size, while for Au, dimers diffuse faster than monomers and trimers on the moiré surface. We then used a genetic algorithm combined with DFT calculations to predict the lowest energy structure of a Au8 cluster on g/Ru(0001). Our prediction leads us to propose that Au clusters aggregates through Oswald ripening with Au dimer being the major diffusing species. Finally, we examined the morphology of a Cu19 cluster on g/Cu(111) using MD simulations with COMB3 potential. We also studied the mobility of Cu clusters on g/Cu(111) at elevated temperatures. The analysis suggests that g/Cu(111) may not be a suitable substrate for the formation and growth of isolated Cu clusters. All these calculation results have provided us a better understanding and useful insights into the nucleation and growth mechanism of metal clusters on graphene moiré.
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Kirtland, David Rand. "Preparation of Heparin Surface for Quantification of Fibroblast Growth Factor-2 (FGF-2) Binding Using Surface Plasmon Resonance (SPR)." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33265.
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A mixed self assembling monolayer (mSAM) chip with attached heparin was developed to analyze heparin-protein interactions using a Reichert Inc, SR7000, surface plasmon resonance (SPR) instrument. The heparin was attached via streptavidin-biotin linkage where the streptavidin was covalently coupled to the mSAM and biotinylated heparin bound to it. These chips were then used to quantify the interactions of fibroblast growth factor-2 (FGF-2) with the surface bound heparin. Kinetic rate constants of association and disassociation were calculated. The association data of FGF-2 with heparin was fit to a single compartment, well-mixed model as the data did not exhibit mass transfer limitations. The results suggested that rebinding was prevalent and observed disassociation rates differed significantly in the presence of competing soluble heparin during disassociation. Our results indicate that the Reichert instrument and mSAM chips can be used to analyze heparin-protein interactions but that a careful protocol, outlined in this thesis, should be followed to obtain optimal data.Master of Science
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Pithan, Linus. "On the role of external stimuli to tailor growth of organic thin films." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17749.
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In dieser Arbeit werden neue Strategien zur Wachstumskontrolle funktionaler organischer Dünnschichtmaterialien aufgezeigt, mit denen sich die Eigenschaften molekularer Schichtsysteme gezielt beeinflussen lassen. Ein Fokus liegt dabei auf der Untersuchung des Einflusses von optischen Feldern auf das Wachstumsverhalten. Ein weiterer Schwerpunkt wird auf das Grundlagenverständnis von thermisch aktivierten, kinetischen Prozessen, die die Morphologie während und nach dem Schichtwachstum beeinflussen, gelegt. Zuerst wird am Beispiel des molekularen Halbleiters Sexithiophen (6T) gezeigt, wie sich Kontrolle über das Kristallphasengleichgewicht während des Wachstums auf Kaliumchlorid (KCl) erzielen lässt. Im zweiten Teil der Arbeit wird eine neue Herangehensweise zur direkten Ausrichtung von Molekülkristallen im optischen Feld während ihrer Entstehung studiert. Am Beispiel von Tetracene wird gezeigt wie sich so optische anisotrope Absorptionseigenschaften von Molekülen dazu nutzen lassen den Brechungsindex eines polykristallinen Films lokal durch ein photolitographisches Verfahren zu beeinflussen. Im dritten Teil wird der Einfluss von dynamisch variierenden Wachstumsbedingungen während des Schichtwachstums von PTCDI-C8 studiert. Es wird gezeigt, dass sich die Oberflächenrauigkeit stark reduzieren lässt, indem zu Beginn des Wachstums jeder individuellen molekularen Monolage die Nukleationsdichte stark erhöht und in den darauf folgenden Wachstumsphasen die Diffusivität gezielt gesteigert wird. Im vierten Teil wird das Diffusionsverhalten von n-Alkan Schichten unter thermischen Einflüssen betrachtet. Es wird gezeigt, dass die inhärente molekulare Anisotropie von C44H90 Molekülen (TTC) sowie die sehr geringe, stark anisotrope, Oberflächenenergie dieses Materials ein ungewöhnliches Diffusionsverhalten auslöst.The research performed in the framework of this thesis focuses on new strategies to effectively control the growth of crystalline thin films of functional organic molecules and attributes the quest for additional growth control parameters in organic molecular beam deposition (OMBD). First the influence of light on the growth process of the sexithiophene (6T) is studied. We find that 6T thin films deposited as conventional in dark environments on KCl exhibit a bimodal growth with phase coexistence of two crystal polymorphs. In contrast, films grown under illumination with 532 nm light show increased phase purity. Further, we establish light-directed molecular self-assembly (LDSA) to generate permanently aligned thin films of tetracene (C18H12) and demonstrate direct patterning with light. Polarized light illumination leads to azimuthally photoaligned films on isotropic, amorphous substrates. Thus, LDSA can be regarded as a new degree of freedom in the quest for control-parameters in organic thin film growth. Next the impact of dynamic temperature oscillations on the time scales of molecular monolayer growth during organic molecular beam deposition is discussed. We strongly increase the island density during nucleation and selectively increase interlayer diffusion at later stages of monolayer growth. We analyse the interplay between molecular interlayer transport and island sizes to understand kinetic processes during growth. In a fourth experiment we show how thermal annealing can be used to improve smoothness and to increase the lateral size of crystalline islands of n-alkane (TTC, C44H90) films. We employ real-time optical phase contrast microscopy to track the diffusion across monomolecular step edges which causes the unusual smoothing during annealing. We rationalise the smoothing behaviour with the highly anisotropic attachment energies and low surface energies of TTC.
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Ferreira, Rafael Cintra Hensel 1989. "Estudo do crescimento de filmes nanoestruturados automontados por adsorsão física utilizando medidas de capacitância = Growth study of self-assembled nanostructured films using capacitance measurements." [s.n.], 2016. http://repositorio.unicamp.br/jspui/handle/REPOSIP/330785.
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Orientador: Varlei RodriguesDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Os filmes orgânicos ultrafinos tem permitido funcionalizar superfícies a fim de introduzir propriedades específicas que diferem daquelas apresentadas em escala macroscópica. Um processo versátil para modificar superfícies e criar sistemas multifuncionais é a técnica de automontagem por adsorção física (LbL, do inglês Layer-by-Layer), na qual nanoestruturas são formadas devido a adsorção de moléculas com cargas opostas em arquiteturas moleculares multicamadas. O monitoramento elétrico do crescimento dos filmes é essencial em experimentos nos quais não são permitidas caracterizações ópticas. Além disto, é importante compreender as propriedades elétricas destes filmes devido a sua utilização em sensores capacitivos para análise química. Deste modo, neste trabalho desenvolvemos um equipamento capaz de acompanhar o crescimento de filmes LbL por meio de medidas de capacitância após a deposição de cada camada de polieletrólitos sobre eletrodos interdigitados (IDEs, do inglês Interdigitated Electrodes). Observamos um aumento linear da capacitância devido ao acúmulo de material dielétrico sobre os IDEs, com uma alternância na medida de capacitância de acordo com o polieletrólito depositado, isto é, há uma reversão de carga na camada mais externa quando a adsorção do policátion é compensada pela do poliânion, ou vice-versa. Utilizando o modelo para o potencial eletrostático de um IDE proposto por M. W. Den Otter, desenvolvemos uma nova metodologia para investigar a constante dielétrica da estrutura multicamadas formada. Obtivemos (16 ± 1) para a constante dielétrica do filme LbL (PDDA/CuTsPc), e (21 ± 3) para a arquitetura (PDDA/PSS), ambos em satisfatória concordância com a literatura. Ademais, desenvolvemos um modelo para interpretar o deslocamento na capacitância medida após a adsorção do policátion a fim de determinar sua densidade de carga superficial, que diminuiu de (0,23 ± 0,02) e/µm2 para (0,08 ± 0,01) e/µm2 quando o PDDA (policátion fortemente carregado) foi substituído pelo PAH (policátion fracamente carregado) para ambos os poliânions analisados. Portanto, desenvolvemos um equipamento para monitorar o crescimento de filmes LbL e uma metodologia que permite obter informações sobre o comportamento dielétrico dos filmes a cada camada depositada, o que pode auxiliar na escolha dos materiais e espessura dos filmes LbL utilizados como elementos transdutores em desenvolvimentos futuros
Abstract: Organic ultrathin films have enabled surface¿s functionalization in order to introduce specific properties which differ from those in macroscopic scale. A versatile process to modify surfaces and create multifunctional systems is the layer-by-layer (LbL) technique, in which the nanostructures are formed due to the adsorption of charged molecules in multilayered molecular architectures. The electrical monitoring of the film's growth is essential in experiments in which optical characterizations can not be used. Moreover, it is important to comprehend the electrical properties of these films owing to their application on capacitive sensors for chemical analysis. In this research we developed a home-made setup to keep track of the LbL film¿s growth by measuring the capacitance after each deposited layer onto interdigitated electrodes (IDEs). We have observed a linear increase in the capacitance due to accumulated dielectric material onto the IDEs, along with an alternation in the measured capacitance according to the deposited polyelectrolyte, i.e., a charge reversal of the outermost layer as the polycation adsorption is compensated by the polyanion adsorption, or vice-versa. Using the IDEs electrostatic potential model proposed by M. W. Den Otter, we have developed a new methodology to investigate the dielectric constant of the formed multilayered structure. A dielectric constant of (16 ± 1) was obtained for (PDDA/CuTsPc) films and (21 ± 3) for (PDDA/PSS) architecture, both in satisfactory agreement with the literature. Furthermore, we have developed a model to interpret the capacitance measurement shift after the polycation adsoption in order to investigate its surface charge density, which decreased from (0.23 ± 0.02) e/µm2 to (0.08 ± 0.01) e/µm2 when PDDA (strong polycation) was replaced by PAH (weak polycation) for both analyzed polyanions. Therefore, we have developed an equipment to monitor the LbL film's growth as well as a methodology that enables the obtaining of information about the film dielectric behavior at each deposited layer, which can assist in the choice of the materials and thickness of the LbL films that are used as transductor elements in future developments
Mestrado
Física
Mestre em Física
147530/2014
CNPQ
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Yumnam, Nivedita [Verfasser], Veit [Akademischer Betreuer] Wagner, Veit [Gutachter] Wagner, Dietmar [Gutachter] Knipp, Jürgen [Gutachter] Fritz, and Jean [Gutachter] Geurts. "Self-Assembled Monolayer-Tuned Growth of ZnO Nanorods for Organic Solar Cells / Nivedita Yumnam ; Gutachter: Veit Wagner, Dietmar Knipp, Jürgen Fritz, Jean Geurts ; Betreuer: Veit Wagner." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2018. http://d-nb.info/1160086451/34.
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Dang, Phuong Ngoc. "READILY IMPLANTABLE HIGH DENSITY STEM CELL SYSTEMS WITH CONTROLLED GROWTH FACTOR PRESENTATION FROM BIOACTIVE MICROPARTICLES FOR BONE REGENERATION VIA ENDOCHONDRAL OSSIFICATION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1421864780.
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Fox, Michael Jacob. "Stochastic self-assembly." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34741.
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We present methods for distributed self-assembly that utilize simple rule-of-thumb control and communication schemes providing probabilistic performance guarantees. These methods represents a staunch departure from existing approaches that require more sophisticated control and communication, but provide deterministic guarantees. In particular, we show that even under severe communication restrictions, any assembly described by an acyclic weighted graph can be assembled with a rule set that is linear in the number of nodes contained in the desired assembly graph. We introduce the concept of stochastic
stability to the self-assembly problem and show that stochastic stability of desirable configurations can be exploited to provide probabilistic performance guarantees for the process. Relaxation of the communication restrictions allows simple approaches giving deterministic guarantees. We establish a clear relationship between availability of communication and convergence properties. We consider Self-assembly tasks for the cases of many and few
agents as well as large and small assembly goals. We analyze sensitivity of the presented process to communication errors as well as ill-intentioned agents. We discuss convergence rates of the presented process and directions for improving them.
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Spanton, Robert. "Stateful self-assembly." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355888/.
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Nature shows us many organised structures that form through interactions between their components with little external guidance. These self-assembling systems range from simple crystals to considerably more complex biological structures and organisms. Inspired by these systems, the development of programmable self assembling systems could lead to mass manufacturing processes that produce individually unique items. Current artificial self-assembling systems involve small numbers of centimetre-scale components, and have not resulted in structures anywhere near the complexity seen in natural systems. This thesis argues that to advance artificial self-assembling systems towards this complexity, the statistics of the interactions within self-assembling systems need to be empirically examined and understood. However, the pursuit of this involves the resolution of a variety of technical challenges. These are approached in this work through the development of a self-assembly toolkit that allows the collection of these statistics from a physical system with larger numbers of components than in previous works. A novel capacitive communication interface is developed for the components of this toolkit, which allows messaging between neighbouring components that are constrained to the surface of a plane. As self-assembling components reduce in size towards the microscale, the penalty for incorrect activation of a component’s binding mechanism is likely to increase. With this in mind, this capacitive communication interface is optimised to provide spatial alignment sensing, with the aim of allowing informed binding mechanism activation. The toolkit developed in this work uses components that are constrained to two degrees of freedom of motion. In pursuit of the development of programmable self-assembling components for 3D structures, a new design of alignment sensor for use in 3D is created. Simulation of this sensor, which is developed using an evolutionary algorithm, indicates that it is suited for detecting the alignment of components with three degrees of freedom. Approaches using computer vision are developed for the spatial tracking of the components of the toolkit, allowing the collection of empirical data regarding the interaction of components. The technical advances described within this work will allow the progression of data-driven self-assembly process design.
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Chen, Ho-Lin. "Robust self-assembly /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Ourdjini, Oualid. "Etude par microscopie à effet tunnel de la croissance de polymères 2D sur des surfaces métalliques." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4315/document.
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La croissance de polymères bidimensionnels a été étudiée sous ultra-haut vide sur des surfaces métalliques par microscopie à effet tunnel (STM). La première étude concerne la croissance de réseaux nanoporeux covalents bidimensionnels obtenus par réaction de déshydratation des molécules d'acide 1.4 diboronique (BDBA). Les meilleurs réseaux sont obtenus pour les dépôts à flux élevés sur des substrats d'Argent chauffés à 150°C. La deuxième étude concerne la réaction chimique entre les molécules de 1,2,4,5 tétracyanobenzène (TCNB) et les atomes de Fer. La formation de liaison covalente entre les molécules et les atomes de Fer est thermiquement activée par des recuits à 200°C et permet la formation d'octacyanophtalocyanine de Fer. Ce travail ouvre de nouvelles perspectives pour la fabrication de matériaux 2D originaux obtenus par des réactions chimiques de surfaceThe growth of two dimensional polymers has been studied under ultra-high vacuum on metallic surfaces by scanning tunnelling microscopy (STM). The first study relates on the growth of two dimensional covalent nanoporous networks obtained after dehydratation reaction of the 1,4 diboronic acid benzene molecule (BDBA). The best networks have been obtained with high molecular flux on silver metallic substrates maintained at 150°C during deposition. The second study relates on chemical reaction between the 1, 2, 4, 5 tetracyanobenzene molecule (TCNB) and iron atoms. The reaction takes place after an annealing at 200°C. In that case some iron octacyanophthalocyanine have been successfully synthesised at surfaces. This work opens new perspectives for the fabrication of 2D original materials by chemical reactions on surfaces
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Diebold, Morgane. "Systèmes composites organogélateurs/polymères semi-conducteurs : de la preuve conceptuelle aux matériaux nanostructurés pour l'électronique plastique." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAE002.
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L’amélioration des performances des dispositifs photovoltaïques organiques passe par le contrôle de la morphologie de leurs couches actives. Nous avons cherché à préparer une hétérojonction volumique donneur-accepteur nanostructurée en utilisant la nucléation hétérogène du poly (3-hexylthiophène) (P3HT, donneur) par des fibres d’organogélateurs à base de naphthalène diimide (NDI, accepteur). La première partie de ce travail présente l’étude des propriétés d’auto-assemblage d’organogélateurs à cœur NDI substitué par des groupements amides et des dendrons trialkoxyphényles. Nous avons évalué l’influence de la longueur de la chaîne flexible entre le cœur naphthalène et les groupements amides (2 liaisons C-C pour NDI2 et 4 pour NDI4) sur les propriétés physico-chimiques des organogélateurs. La seconde partie de ce travail met en évidence le polymorphisme du composé NDI2 en identifiant 4 polymorphes ainsi que leurs signatures optiques, spectroscopiques et structurales. Un diagramme de phase de l’état solide du NDI2 est proposé. La dernière partie de la thèse concerne l’élaboration de nano-composites donneur-accepteur entre les organogélateurs à cœur NDI et le P3HT. Le processus de formation en solution de ces nano-composites est analysé en suivant les cinétiques de cristallisation du P3HT par spectroscopie d’absorption UV-Visible et les morphologies obtenues (structures shish-kebab) par microscopie électronique en transmission. L’effet nucléant des organogélateurs sur le P3HT a été montré. Les études en cellules solaires des composés P3HT:PCBM : organogélateur ont prouvé que le rendement de conversion énergétique peut être augmenté en présence d’organogélateursImproving the performances of organic photovoltaic devices requires morphology control of the active layers. Highly nanostructured donor-acceptor bulk heterojunctions were prepared by heterogeneous nucleation of poly (3-hexylthiophene) (P3HT, donor) on naphthalene diimide organogelators fibers (NDI, acceptor). The first part of this work was dedicated to the self-assembly of NDI-core organogelators substituted by amide groups and trialkoxyphenyls dendrons. We evaluated the influence of the flexible chain between the naphthalene core and the amide groups (2 C-C bonds for NDI2 and 4 for NDI4) on the physico-chemical properties of the organogelators.The second part of this work focused on the polymorphism of NDI2 with identification of four different polymorphs with their optical, spectroscopic and structural signatures. A phase diagram of NDI2 in the solid state was determined. The last part of this manuscript concerns the fabrication of donor-acceptor nano-composites between NDI organogelators and P3HT. The formation process in solution of these nano-composites was analyzed by following the crystallization kinetics of P3HT by UV-Vis absorption spectroscopy and the thin film morphology (shish-kebab structures) by transmission electron microscopy. The nucleating effect of various organogelators on P3HT was demonstrated. Solar cells were made from the composites P3HT:PCBM : organogelator and their energetic conversion yield was shown to be increased in the presence of organogelators
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Dillenback, Lisa M. Keating Christine Dolan. "Self-assembly and controlled assembly of nanoparticles." [University Park, Pa.] : Pennsylvania State University, 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2613/index.html.
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Varghai, Daniel. "Tubular Tissue Engineered Scaffold-Free High-Cell-Density Mesenchymal Condensations For Femoral Defect Regeneration." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1497222797338966.
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Williams, Richard James. "Enzyme assisted self-assembly." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496231.
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Self-assembling peptide systems provide a pathway for the formation of complex molecular assemblies from relatively simple designed molecules. Stimuli which have been used to trigger the self-assembly (SA) process in aqueous conditions include temperature, pH, ionic strength, and solvent exchange. Additionally, enzymes may be used to selectively control the self-assembly process; enzymes are uniquely chemo-, regio-, and enantioselective, and work naturally under mild conditions without disrupting biological Interactions.
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De, Vet Christiaan J. F. "Auto-assemblage d'un anthacène fluorescent aux échelles nano- et micrométriques par photoréaction contrôlée." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0333/document.
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Le contrôle spatial et temporel de l'auto-assemblage de molécules fluorescentes en nano-objets organisés et en matériaux mous a été réalisé par photochimie.La photodécarbonylation quantitative du progélifiant dkDDOA sous irradiation génère le super gélifiant 2,3-didécyloxyanthracène (DDOA) à température ambiante et simultanément gélifie le DMSO. DkDDOA est réactif sous excitation avec de la lumière bleue en raison de la fonction alpha-dicétone sensible à la lumière qui est ajoutée au noyau aromatique. De plus,l’ajustement de la couleur de l'émission du gel du bleu au vert a été obtenu en ajoutant un dérivé 1,2-dicétone-5,12-diphényltétracène photo réactif qui donne un 5,12-diphényltétracène émissif vert sensibilisé par un transfert d'énergie efficace.Sous un microscope, l'irradiation laser focalisée permet la structuration de nanofibres émissives sur une surface de verre. Bien que la surface de verre soit non traitée, on peut obtenir des micropattern de nanofibres de DDOA hautement alignées. Ces surfaces émettent une lumière bleue polarisée linéairement, comme le prouve la microscopie de polarisation. L'anisotropie élevée et l'orientation des fibres ont été obtenues en contrôlant la densité de nucléation et la direction de balayage du laser focalisé. Des micropattern orientés perpendiculairement peuvent ainsi être juxtaposés sur la même surfaceThe spatial and temporal control of the self-assembly of fluorescent molecules into organized nano-objects and into soft materials was achieved by photochemistry. The quantitative photodecarbonylation of the progelator dkDDOA under irradiation generates the supergelator 2,3-didecyloxyanthracene (DDOA) at room temperature and simultaneously gelates DMSO. dkDDOA is reactive under excitation withblue light due to the light sensitive alpha-diketone moiety that is added to the aromatic core.Additional colour-tuning from blue to green emission from the gel was achieved by adding a similar photoreactive 1,2-diketone-5,12-diphenyltetracene that yields a green emissive 5,12-diphenyltetracene sensitized through an efficient energy transfer. Under a microscope, focused laser irradiation enables the patterning of blue-emissive nanofibers on to a glass surface. Although the surface is non-treated, micropatterns of highly aligned DDOA nanofibers can be obtained. These surfaces emit linearly polarized blue light,as proven with polarization microscopy. The high anisotropy and the orientation of the fibers was achieved by controlling the nucleation density and the direction of scanning of the focused laser. Perpendicularly oriented micropatterns can thereby be juxtaposed on the same surface
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Mayans, Tayadella Enric. "Self-assembly of phenylalanine derivatives." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461917.
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Since the pioneering work of Reches and Gazit in 2003, in which the formation of diphenylalanine (FF) nanotubes in aqueous solution was discovered, significant efforts have been made to develop a new generation of biomaterials based on the self-assembly of aromatic peptides. From recent investigations, the self-assembly of phenylalanine homopeptides can be understood by a combination of hydrogen bonding and repeated aromatic stacking interactions.
In this Thesis, new phenylalanine homo-oligopeptide derivatives have been synthetized in order to test their self-assembly capability and to examine the influence of the chemical structure and the external conditions. Although, the terminal head-to-tail NH3 +···–OOC interactions in the unprotected homopeptides are shown to stabilize the peptide assemblies, chemical modulation has been introduced through the incorporation of the N- and C- protections, such as aromatic blocking groups (Chapter 4 and 5.2), azide-alkyne coupling groups (Chapter 3.2) or trifluoroacetate anion (Chapter 3.1). In Chapter 4, three FFFF-based peptides have been synthetized to study the role of the head-to-tail NH3 +···–OOC interactions in the assembly of
FFFF-derivatives. Although these interactions are not possible upon the incorporation of the NFmoc and C-OBzl protections, defined hierarchical assemblies arising from p-p stacking interactions have been found.
In Chapter 6, new hybrid polypeptide/polylactide conjugates have been prepared through ring opening polymerizations to reveal the effect of the constitutive polylactide block. Whereas the crystallization from the melt gave rise to spherulites from lamellar arrangements, previously reported phenylalanine-oligopeptide hierarchical morphologies have been observed from diluted solutions.
We report that the homopeptide length also plays a significant role in the supramolecular organization of phenylalanine derivatives. First, in Chapter 5.2, theoretical calculations have indicated that the stability of Phe-homopeptides capped with two fluorenyl functionalities increases with the length of the Phe-segment, adopting an antiparallel b-sheet arrangement. While the existence of diverse polymorphs suggests that p-p stacking interactions involving fluorenyl groups result in different stable conformations, they are more versatile, in terms of molecular selfassociation, than hydrogen bonds. Besides, the capacity of FFF to assemble in very diverse supramolecular structures has been found to be greater than that exhibited by its homologues with an even number of Phe residues (Chapter 5.1). Additionally, spherulites from the prepared diblock copolymers with a distinctive lamellar disposition (i.e. flat-on or edge-on) and/or dendritic structures have been identified in function of the length of the PPhe block (Chapter 6).
Results have evidenced not only the remarkable control exerted by the characteristics of the environment (i.e. the solvents mixture, temperature, the ionic strength, and the peptide concentration) in the organization of the assemblies, but also by the substrate (Chapter 5.3).
Depending on the conditions, molecules can organize into bundled arrays of nanotubes, stacked braids, corkscrew-like, doughnut/volcano-like, spherulitic microstructures and/or triaxial ellipsoid-like nodules. Peptide···peptide interactions, peptide···surface interactions and the surface roughness have been detected as key factors for the shape, dimensions and stability of the hierarchical assemblies. The proposed mechanisms for the formation of supramolecular structures have reflected how the structural nucleation and hierarchical growing are controlled through the
balance between peptide···peptide and peptide···solvent interactions, which in turn are regulated by the peptide concentration and the polarity of the solvent mixture used to dissolve the peptide, respectively.
Tuning the structure of Phe-derivatives by changing the medium used in the mixture, as well as the surface, is a very attractive feature to expand the potential utility of peptide assemblies in different fields, for example as molecular carriers and delivery systems. The wide range of available surfaces offers a valuable tool for the development of bionanotechnological applications based on hierarchical peptide assemblies. Indeed, the ability of plasma treated polystyrene for stabilizing well-defined dendritic structures has been found to be particularly noticeableEn aquesta tesis, nous homooligopèptids derivats de fenilalanina ha estat sintetitzats per tal d'estudiar la seva capacitat d'autoorganització i examinar la influencia de l'estructura química i les condicions externes. Encara que les interaccions NH3+···-OOC cap-a-cua en els homopèptids desprotegits mostren estabilitzar les estructures peptídiques, s'han introduït funcionalitzacions químiques a través de la incorporació de proteccions a N- i C-, com per exemple, grups bloquejadors aromàtics, grups d'acoblament azida-alquí, l'anió trifluoroacetat o un bloc de polilàctide. Diferents capítols estan dedicats a mostrar que la llargada del bloc d'homopèptid també juga un paper rellevant en l'organització supramolecular dels derivats de fenilalanina. Els resultats publicats evidencien no només el control que exerceixen les característiques de l'ambient sinó també del substrat. Les interaccions pèptid··· pèptid, pèptid···superfície i la rugositat superficial han estat assenyalades com a factors clau que defineixen la forma, les dimensions i l'estabilitat de les estructures jerarquitzades.