Tesis sobre el tema "Assembly characterization"

Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, May, 2020
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 60-68).
On-orbit assembly missions typically involve humans-in-the-loop and use large custom-built robotic arms designed to service existing modules. The concept of on-orbit robotic assembly of modularized CubeSat components supports use cases such as rapidly placing failed nodes within a constellation of satellites and monitoring damaged assets in Low Earth Orbit. Despite the recent proliferation of small satellites, there is a lack of planned demonstrations of spacecraft manufactured through the on-orbit assembly as well as the servicing of small satellites in space. Key gaps limiting in-space assembly of small satellites are (1) the lack of standardization of electromechanical CubeSat components for compatibility with commercial robotic assembly hardware, and (2) testing and modifying commercial robotic assembly hardware suitable for small satellite assembly for space operation. Working towards on-orbit robotic assembly, we report on progress addressing both gaps.
Toward gap (1), the lack of standardization of CubeSat components for compatibility with commercial robotic assembly hardware, we have developed a ground-based robotic assembly of a 1U CubeSat using modular components and Commercial-Off-The-Shelf (COTS) robot arms without humans-in-the-loop. Two 16 in x 7 in x 7 in dexterous robot arms, weighing 2 kg each, are shown to work together to grasp and assemble CubeSat components into a 1U CubeSat. We assess performance for a subset of five commercial robotic arm sensors and find the force-torque (FT) sensor as the most efficient sensor for use at the end-effector and brushless motors as the best sensor for use at other joints. We report on the feasibility of sensing and grasping CubeSat components robotically, while using Inverse Kinematics to target, position and maneuver the robot arms.
Addressing gap (2) in this work, solutions for adapting power-efficient COTS robot arms to assemble highly-capable radiation-tolerant CubeSats are examined. We also analyze the systems engineering process for in-space CubeSat robotic assembly systems. Lessons learned on thermal and power considerations for overheated motors and positioning errors were also encountered and resolved. We find that COTS robot arms with sustained throughput and processing efficiency have the potential to be cost-effective for future space missions.
by Ezinne Uzo-Okoro.
S.M.
S.M. Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences

During differentiation, changes in chromatin proteins lead to the establishment and maintenance of gene expression patterns. Histone H3 trimethylated at lysine 4 (H3K4me3) by the trithorax group (trxG) gene family Mixed lineage leukemia (MLL) is associated with active genes. H3K27me3 is trimethylated by the Polycomb group (PcG) Enhancer of Zeste (EZH2) at repressed genes. In Drosophila embryos, trxG and PcG proteins but not H3K4me3 or H3K27me3 are stable to DNA replication. In contrast, methylated histones are detected on nascent DNA in Drosophila and murine cell lines. Therefore some aspect of chromatin assembly or histone trimethylation must differ in different cells. My first aim was to determine if there is a change in the abundance of methylated histones at the replication fork in undifferentiated versus differentiated murine ES cells using two novel in vivo assays. Most undifferentiated ES cells lack early H3K4me3 and H3K27me3, but after 4 days of differentiation, most cells have early trimethylation of H3K4 and H3K27. I propose that the change in kinetics of histone methylation correlates with differentiation. To test this hypothesis, I carried out similar experiments on cells dissociated from day 9.5 (E9.5) and 14.5 (E14.5) murine embryos. In E9.5 cells there are two populations of cells, one that lacks methylated histones and the other contains methylated histones on nascent DNA. By E14.5 most cells exhibit H3K4me3 and H3K27me3 on nascent DNA. To determine if the presence of histone methyltransferases could account for the changes in histone methylation, I tested MLL1 and a subunit of the EZH2 complex, Su(z)12. Both are present continuously on nascent DNA, suggesting that their activity is regulated. Methylation and acetylation antagonize each other at the same residue. However I showed that the presence of acetylated H3K27 is not anticorrelated with H3K27me3 in most murine embryos cells. My results using inhibitors of the appropriate histone acetyltransferase were not conclusive owing to toxicity of the inhibitors. Overall, my results support the hypothesis that trimethylation of H3K4 and H3K27 on nascent DNA is developmentally regulated.

G-Wires are supramolecular DNA structures composing of a quadruplex stem. These structures have been reported to have potential for photo and electrical conductance. However, this has yet to be realized. This thesis is concerned with the rational design of DNA sequences in order to form well-structured G-Wires through optimized self-assembly and characterization of the products. Previous investigation has demonstrated that the quadruplex topology formed from G-rich DNA can be controlled through geometric constraints. These constraints can be imposed through various sequence arrangements which lead to specific structural features. A set of systematically varied DNA sequences were designed to form G-Wire structures. These sequences underwent self-assembly in a range of assembly conditions and the self-assembly products were characterized by a range of techniques such as gel-electrophoresis, NMR, UV-spectroscopy and fluorescence spectroscopy. The findings of this investigation have shown that the rational design of DNA sequences successfully resulted in the formation of architecture with unique optical properties and significantly increased quantum yields. This work has the potential to further the ability of G-Wire structure to be utilized within multicomplex nanodevices in applications such as diagnostic sensing and nanoelectronics.

This study details the dielectrophoretic assembly and mechanical characterization of boron nitride nanotubes on silicon chips with gold electrodes. The chips were fabricated from 4in round silicon wafers with a 100nm-thick low stress silicon nitride insulating layer on the top and bottom. The electrodes were patterned using photo- and electron-beam lithography and dry etching, and the wafers were cut into 4 x 6mm chips. The boron nitride nanotubes studied were obtained from NIA and were synthesized via a unique pressurized vapor/condensor method, which produced long, small-diameter BNNTs without the use of a catalyst. These nanotubes were studied due to their desirable mechanical and electrical properties, which allow for unique applications in various areas of science, engineering, and technology. Applications span from magnetic manipulation to the formation of biocomposites, from nano-transistors to humidity and pH sensors, and from MRI contrast agents to drug delivery. The nanotubes and nanotube bundles characterized were suspended over gaps of 300 to 500nm. This study was unique in that assembly was performed using dielectrophoresis, allowing for batch fabrication of chips and devices. Also, stiffness measurements were performed using AFM, eliminating the reliance of other methods upon electron microscopes, and allowing for imaging and measurements to occur simultaneously and at high resolution. It was found that DEP parameters of V = 2.0Vpp, f = 1kHz, and t = 2min provided the best results for mechanical testing. The nanotubes tested had suspended lengths of 300nm, the width of the electrode gap, and diameters of 15–65nm. Chips were imaged with both scanning electron microscopy and atomic force microscopy. Force-displacement measurements with atomic force microscopy were used to find stiffness values in the range of 1–16N/m. These stiffness values, when plugged into a simple double-clamped beam model, indicated Young’s moduli of approximately 1–1600GPa. Within this wide range, it was shown that a decrease in diameter strongly correlated exponentially to an increase in Young’s modulus. Work in this study was divided between assembly and characterization. Therefore, a lot of time was spent working to optimize dielectrophoresis parameters, followed by SEM and AFM imaging. Parameters that were adjusted included DEP voltage and time, pre-DEP sonication times, as well as adding a centrifuging procedure to attempt to better separate nanotube bundles in solution. Another method discussed but not pursued was the use of surfactants to agitate the solution, thus separating the nanotubes. The reason this material in particular was so difficult to separate was twofold. First, the small size of the nanotubes—individual BNNTs have diameters on the order of ∼5 nanometers—generates very strong nanoscale van der Waals forces holding the nanotubes together. Larger nanotubes—with diameters on the order of 50 to 100nm or more—suffer less from this problem. Also, the dipoles created by the boron-nitrogen bonds cause attraction between adjacent nanotubes. The results shown in this thesis include DEP parameters, SEM and AFM images, and force- displacement curves leading to nanotube stiffness and Young’s modulus values. The force-displacement tests via AFM are also detailed and explained.

The quadruplex formalism describes structural features of unimolecular quadruplex topologies having three loops, described herein as archetypal quadruplexes. The work described here provides a further development of the formalism, based on experimental and conceptual work. Dihedral angles of clockwise and anticlockwise propeller loops were analyzed and found to adopt comparable angles. These loops were also used to define limitations of propeller loop progression, reducing theoretically feasible topologies to 14. Glycosidic bond angle (GBA) conformations throughout the stem for 2, 3-, and 4-stacked versions of each of these 14 topologies have been detailed. Control elements of quadruplex structure have been established, including cation selection, loop length, and loop length relationship to number of stacking tetrads in quadruplex stem. A method to control the design of archetypal G-quadruplexes is proposed, based on rules of precedence. Four atomistic detail solution structures have been derived and structural models deposited in the Protein Data Base: 5J6U, 5J05, 5J4P, 5J4W. Aromatic protons of guanines protruding into grooves of quadruplex structures were evaluated by chemical shift to generate a method of chemical shift indexing. Although currently of limited use, it allows key inferences to be made before sequence-specific assignment of NMR signals, enabling a rapid decision to be reached regarding whether to pursue full structure determination. Investigation of the near-UV region of CD spectropolarimetry enabled derivation of a qualitative method to assess the number of stacking tetrads for two types of stem, representing an improvement on the current CD fingerprint approach to characterize three types of quadruplex stem. Significant steps in deriving the formalism have been made, which describe and predict structural elements of archetypal quadruplexes. These advances represent a major development in understanding of control of G-quadruplex folding. However, they are only one contribution to the advances needed for complete reproducible control of all quadruplex topologies.

The successful applications of nanoparticles require the ability to tune their properties by controlling size and shape at the nanoscale. In metal nanomaterial research, the optical properties have been of interest especially because of the applications to medical diagnostics and nanooptics. It is important to prepare nanoparticles of well-defined shape and size for properly characterizing the optical properties. We describe improved seed mediated synthesis of gold nanorods (GNRs) producing a high yield of NRs with low polydispersity and few byproducts. The efficient separation of GNRs from mixture of shapes is achieved by understanding the hydrodynamics of nanoparticles undergoing centrifugation. The optical properties of resulting refined GNRs are compared to predictions of existing theories, and the main parameters affecting them are discussed. GNRs with well defined aspect ratios are introduced into a polyvinyl alcohol matrix by means of solution-casting techniques. The film is drawn to induce the uniaxial alignment of GNRs to be used as color polarizing filters. We prepare GNR polarizing filter with different peak positions ranging from visible to near infra red by using different aspect ratio of NRs. To utilize GNRs to make nanoscale devices, spatial organization is required. We characterize the self-assembly of GNRs observed on a TEM grid. The drying process is accompanied by complex hydrodynamic and thermodynamic events, which create rich range of patterns observed. Being anisotropic in shape, the rods can form liquid crystal (LC) assemblies above a certain concentration. We observed LC phase of GNRs by resorting to an evaporation of aqueous NR solution. The convective flow caused by the solvent evaporation carries NRs from the bulk solution to solid-liquid-air interface, which makes the solution locally very concentrated driving the phase transition of NRs. We calculate the order parameter from various assemblies observed, and compare the observed phase behavior to the one expected on the basis of theory.

The unique properties of gold nanoparticles make them excellent candidates for applications in electronics, sensing, imaging, and photothermal therapy. Though abundant literature exists for isotropic gold nanoparticles, work on nanoparticles of different shapes has been gaining interest recently. Anisotropic gold nanoparticles, such as nanorods and nanoprisms, have tunable optical properties in the visible and near-infrared regions. Through synthesis and surface modification, the production of various shapes of these gold nanoparticles can be controlled to meet different applications. Two different types of gold nanorods were used in this thesis. The first type was stabilized with cetyltrimethylammonium bromide (CTAB) and had aspect ratios of 3-4 (defined as the nanorod length divided by the diameter). The second type was synthesized using CTAB and benzyldimethylhexadecylammonium chloride (BDAC) in a binary surfactant system which produced aspect ratios greater than 4. The nanorods were characterized with UV-Vis spectroscopy and transmission electron microscopy (TEM). Two types of bowl-shaped macrocyclic compounds called resorcinarenes were used to direct self-assembly of the nanorods. The first type of resorcinarene (R2S) consisted of thiol(SH)-terminated alkyl chains on both rims. The second type (R1S) contained thiol-terminated alkyl chains on only one rim. The monolayer formation of these resorcinarenes on planar gold surfaces was studied and characterized by FTIR spectroscopy. Resorcinarene-mediated assembly of gold nanorods was monitored with UV-Vis spectroscopy, dynamic light scattering (DLS), and TEM. In addition to gold nanorods, gold nanoprisms were synthesized through a kinetically-controlled reduction route in the presence of CTAB. The linking of nanoprisms using resorcinarenes was also explored.

Due to the increasing number of components involved in Radio Frequency design, integration and packaging become an important topic of developing power-efficient and cost-effective solutions. Furthermore, interconnections are a key factor in such a topic because they are heavily used in Radio Frequency engineering, especially in the Fifth Generation. Among the interconnections, bond wires are one of the most commonly used.In micro assembly design, it is crucial to understand and model the behavior of each component, including interconnections. Radio Frequency engineers usually use the bond wire models in the software directly without questioning if the model actually has the same behavior as the fabricated one. Therefore, how to accurately model and characterize the bond wires becomes valuable, and furthermore, how the physical dimensions affect the transmission performance. This Master’s thesis project aims to solve this problem by building simple models for single bond wire and double bond wires with coupling, and verifying them by electromagnetic simulation and measurement.The project has built bond wire models in Matlab and in electromagnetic simulators NI AWR and ANSYS HFSS. The actual test structures are also fabricated using the bonding machine, and measured by vector network analyzer. A sufficient amount of data has been collected from these sources and then analyzed. The proposed analytical model of bond wires is valid after comparing its results with those from simulation and measurement. In addition, the effect of the loop height and separation distance on the transmission performance is studied and has a well verified conclusion.This thesis work will be helpful to Radio Frequency engineers, who use bond wires in the micro assembly of their design. They would be able to characterize the bond wires more accurately and adjust the physical dimensions in order to achieve the desired performance.
På grund av det ökande antalet komponenter i radiofrekvensdesign, integration och förpackning blivit ett viktigt ämne för att utveckla energieffektiva och kostnadseffektiva lösningar. Sammankopplingar är en nyckelfaktor i ett sådant ämne, eftersom de är starkt används i radiofrekvensteknik. Bland dem, bondtrådar är en av de vanligaste.Det är viktigt att förstå och modellera beteendet hos varje komponent. Därför hur att noggrant modellera och karakterisera bondtrådarna blir ett värdefullt problem, och dessutom, hur de fysiska dimensionerna påverkar överföringsprestanda.Projektet har byggt bondtrådsmodeller i Matlab och i elektromagnetiska simulatorer NI AWR och ANSYS HFSS. De faktiska teststrukturerna tillverkas också med hjälp av bindningsmaskinen och mäts av vektornätverksanalysatorn. Den föreslagna analysmodellen för bindningstrådar är giltig efter att ha jämfört dess resultat med dem från simulering och mätning. Dessutom studeras effekten av slinghöjden och separationsavståndet på transmissionens prestanda och har en väl verifierad slutsats.

This thesis was focused on the preparation and on the characterization, of functional thin films for molecular electronics and energetics. In the first part of this work a nanoscale electrical investigation of molecular wires was discussed. Molecular wires were prepared as a self assembled array on gold by means of a bottom up approach that exploits the coordination of metal with terpyridine-based ligands. These molecular wires were characterized by using different techniques. The formation and growth of the molecular films has been demonstrated by ToF-SIMS, XPS and UV-Vis spectroscopy. Structural information was obtained from NEXAFS measurements, that demonstrated that wires grow vertically to the surface and that the orientation doesn t change during the growth. The electrical characterization was performed by using the conductive atomic force microscopy (C-AFM) technique, that allowed to determine the molecular conduction mechanisms of these systems. The second part of the work was focused on the development of methodologies for functionalization of oxide substrates, suitable for applications in the field of dye sensitized solar cells. The ZP methodology has been applied, and the amount of surface coverage as well as the stability of the formed layers has been studied by using a phosphonate derivative of rhodamine B. Then the ZP method was applied to the preparation of different systems of interest in solar energy conversion, including a self assembled bilayer on TiO2 made out a dendrimeric complex of Ru (II) (the sensitizer) and a polyoxometallate (the catalyst) that can act as an electrode for photo -induced water splitting. Finally, the general problem of obtaining molecular depth profiling of organic materials has been discussed. In particular, a SIMS method (NO-assisted cluster-SIMS) has been studied, that gives promising results in this direction. With the aim of studying the applicability of the method to polymer-based multilayers, well-controlled layered systems have been prepared by means of layer-by-layer polyelectrolyte deposition. C60-SIMS depth profiling of these systems highlighted the possibility of obtaining a good profile depends heavily on the order in which layers with different radiochemical behavior are deposited. The cluster-SIMS technique was applied to the study of a system of interest in molecular electronics. In particular the measured C60-SIMS profiles provided evidence of in-depth inhomogeneous distribution of oligothiophenes in binary blends formed by oligomers with different molecular weight.

Oligomeric surfactants, sometimes referred to as gemini surfactants, consist of two or more amphiphilic ‘monomer’ units linked together by spacer groups. The chemical identity of the spacer group is unconstrained, and it joins the individual units at or near the hydrophilic headgroups. Oligomeric surfactants display a range of interesting properties, including very low critical micelle concentrations, high surface activity and unusual rheology and self-assembly. Consequently they have many potential applications, both scientific and industrial. Until now, their use has been limited by the cost of their synthesis, which in some cases involve long and difficult procedures. This project developed from the idea that a synthesis based on polymerization could prove a useful and versatile method for producing these surfactants. The chemical starting point for this project was a series of polymerizable surfactants (‘surfmers’), upon which polymerization was performed. Two families of surfmers were investigated, both cationic and based on methacrylate and vinylpyridinium moieties respectively. The physical behaviour of these surfactants – a number of which are new – was investigated using standard techniques; these included the determination of the critical micelle concentration, characterization of phase behaviour, neutron scattering and surface adsorption. In producing oligomers, the initial focus was on free-radical polymerization, with control of molecular weight to be achieved by chain-transfer techniques. Due largely to analysis problems, this work proved unsuccessful. In its place a new reaction, not based on conventional polymerization methods, has been developed. The vinylpyridinium surfmers mentioned above readily undergo addition across the double bond to produce alkyl ring substituents. Under basic conditions, these alkylpyridiniums undergo an elimination/addition reaction in which they link together to form oligomers. This reaction can be started or stopped by raising or lowering the pH of the reaction solution, and has been performed in both organic and aqueous solutions. It is referred to in this thesis as LELA(Linkage by ELimination/Addition). The LELA reaction was used to produce mixtures of oligomers, the phase behaviour and surface adsorption of which were examined. Small-angle neutron scattering was used to monitor the reaction in real time and identify changes in self-assembly as the average oligomer length increased. Progress was also made towards a chromatographic protocol that would allow mixtures to be separated into their components and the pure oligomers to be studied. Finally, some of the compounds studied display interesting pH-dependent chromophoric properties which were also found to occur with other simple alkylpyridinium species. They are tentatively ascribed to inter- and intramolecular charge-transfer complexes, and evidence towards this conclusion was collected and is presented along with relevant calculations.

Doctor of Philosophy (PhD)
Oligomeric surfactants, sometimes referred to as gemini surfactants, consist of two or more amphiphilic ‘monomer’ units linked together by spacer groups. The chemical identity of the spacer group is unconstrained, and it joins the individual units at or near the hydrophilic headgroups. Oligomeric surfactants display a range of interesting properties, including very low critical micelle concentrations, high surface activity and unusual rheology and self-assembly. Consequently they have many potential applications, both scientific and industrial. Until now, their use has been limited by the cost of their synthesis, which in some cases involve long and difficult procedures. This project developed from the idea that a synthesis based on polymerization could prove a useful and versatile method for producing these surfactants. The chemical starting point for this project was a series of polymerizable surfactants (‘surfmers’), upon which polymerization was performed. Two families of surfmers were investigated, both cationic and based on methacrylate and vinylpyridinium moieties respectively. The physical behaviour of these surfactants – a number of which are new – was investigated using standard techniques; these included the determination of the critical micelle concentration, characterization of phase behaviour, neutron scattering and surface adsorption. In producing oligomers, the initial focus was on free-radical polymerization, with control of molecular weight to be achieved by chain-transfer techniques. Due largely to analysis problems, this work proved unsuccessful. In its place a new reaction, not based on conventional polymerization methods, has been developed. The vinylpyridinium surfmers mentioned above readily undergo addition across the double bond to produce alkyl ring substituents. Under basic conditions, these alkylpyridiniums undergo an elimination/addition reaction in which they link together to form oligomers. This reaction can be started or stopped by raising or lowering the pH of the reaction solution, and has been performed in both organic and aqueous solutions. It is referred to in this thesis as LELA(Linkage by ELimination/Addition). The LELA reaction was used to produce mixtures of oligomers, the phase behaviour and surface adsorption of which were examined. Small-angle neutron scattering was used to monitor the reaction in real time and identify changes in self-assembly as the average oligomer length increased. Progress was also made towards a chromatographic protocol that would allow mixtures to be separated into their components and the pure oligomers to be studied. Finally, some of the compounds studied display interesting pH-dependent chromophoric properties which were also found to occur with other simple alkylpyridinium species. They are tentatively ascribed to inter- and intramolecular charge-transfer complexes, and evidence towards this conclusion was collected and is presented along with relevant calculations.

Adiponectin, a hormone that homo-oligomerizes into trimer, hexamer, or higher molecular weight (HMW) species, is involved in maintaining insulin sensitivity in muscle and liver. Interestingly, its functions appear to be oligomer-specific. Recent data suggest that HMW levels are decreased in obesity and insulin resistance, although, the cause for this decrease is not known. Impaired assembly to the octadecamer represents one possible reason for decreased HMW adiponectin in insulin resistance and type 2 diabetes, but mechanisms by which HMW adiponectin assembles are unknown. This dissertation discusses the progress that we have made regarding formation of HMW adiponectin in vitro.I found that disulfide bonds are important in the assembly process to octadecameric adiponectin, but are not required for stability of the octadecamer itself. We showed that hydrogen peroxide accelerated oligomerization to the octadecamer through formation of disulfide bonds, while alkylation of the cysteines led to inhibition of both oligomerization and disulfide bond formation. Using comparative native/denaturing polyacrylamide gel electrophoresis (PAGE), dynamic light scattering, and tandem mass spectrometry, we demonstrated that octadecamer is stable in the absence of disulfide bonds by using multiple biochemical and biophysical assays. In addition, oxidized adiponectin oligomerizes to octadecamer far slower than reduced adiponectin. To further evaluate the role of disulfide bonds in the formation to octadecamer, we analyzed the role of reduction potential on adiponectin oligomerization. We observed that under immediate oxidizing conditions, hexamers and trimers form. Oxidized hexamer can form HMW adiponectin through disulfide bond rearrangement using beta-mercaptoethanol (βME) or increasing the total concentration of glutathione under oxidizing conditions. To further understand the role of disulfide bonds, we showed that zinc increased the oligomerization to octadecamer. This effect was associated with decreased initial disulfide bonding during the assembly to the octadecamer. In summary, these data suggest the rate of disulfide bond formation and the ability to undergo disulfide bond isomerization are important in the oligomerization process of HMW adiponectin.

Mucins, the main macromolecular constituent responsible for gel-forming property in mucus, have great potential to act as new biological hydrogel for medical applications. Click chemistry reaction is an attractive tool to be applied in both bioconjugation and material science to form covalent bonds between molecules. Herein the click chemistry reaction of tetrazine-norbornene ligation was adapted to form click mucin hydrogel using purified commercial available bovine submaxillary mucin (BSM). This study included the characterization, purification and chemical modification of commercial available BSM. The flow filtration purification was chosen after investigating the effectiveness and yields of four different purification strategies. The reactivity of tetrazine and norbornene-functionalized BSM was evident from the formation of robust mucin hydrogel within minutes after mixing the two components.
Mucin, den viktigaste makromolekylära beståndsdel som ansvarar för den gelbildande egenskapen i slem, har stor potential att fungera som en ny biologisk hydrogel för medicinska tillämpningar. Klick-kemi reaktioner är attraktiva verktyg som kan användas i både biokonjugering och materialvetenskap för att bilda kovalenta bindningar mellan molekyler. I detta projekt användes renat kommersiellt köpt bovint submaxillärt mucin (BSM) i en klick-kemi reaktion för att sammanlänka tetrazin och norbornylen. Denna reaktion anpassades för att bilda en mucin hydrogel. Detta projekt inkluderade karakterisering, rening och kemisk modifiering av kommersiellt köpt BSM. Flödesfiltrering valdes som reningsmetod efter undersöking av effektivitet och utbyte av fyra olika reningsstrategier. Reaktiviteten hos tetrazin och norbornen-funktionaliserad BSM var uppenbar från bildandet av robust mucin hydrogel inom några minuter efter de två komponenterna sammanblandats.

This dissertation contains six chapters detailing recent advances that have been made in the synthesis and characterization of metal-semiconductor hybrid nanocrystals (HNCs), and the applications of these materials. Primarily focused on the synthesis of well-defined II-VI semiconductor nanorod (NR) and tetrapod (TP) based constructs of interest for photocatalytic and solar energy applications, the research described herein discusses progress towards the realization of key design rules for the synthesis of functional semiconductor nanocrystals (NCs). As such, a blend of novel synthesis, advanced characterization, and direct application of heterostructured nanoparticles are presented. Additionally, for chapters two through six, a corresponding appendix is included containing supporting data pertinent to the experiments described in the chapter. The first chapter is a review summarizing the design, synthesis, properties, and applications of multicomponent nanomaterials composed of disparate semiconductor and metal domains. By coupling two compositionally distinct materials onto a single nanocrystal, synergistic properties can arise that are not present in the isolated components, ranging from self-assembly to photocatalysis. While much progress was made in the late 1990s and early 2000s on the preparation of a variety of semiconductor/metal hybrids towards goals of photocatalysis, comprehensive understanding of nanoscale reactivity and energetics required the development of synthetic methods to prepare well-defined multidimensional constructs. For semiconductor nanomaterials, this was first realized in the ability to tune nanomaterial dimensions from 0-D quantum dot (QD) structures to cylindrical (NR) and branched (TP) structures by exploitation of advanced colloidal synthesis techniques and understandings of NC facet reactivities. Another key advance in this field was the preparation of "seeded" NR and TP constructs, for which an initial semiconductor QD (often CdSe) is used to "seed" the growth of a second semiconductor material (for example, CdS). These advances led to exquisite levels of control of semiconductor nanomaterial composition, shape, and size. Concurrently, many developments were made in the functionalization of these NCs with metallic nanoparticles, allowing for precise tuning of metal nanoparticle deposition position on the surface of preformed semiconductor NCs. To date, photoinduced and thermally induced methods are most widely used for this, providing access to metal-semiconductor hybrid structures functionalized with Au, Pt, Ag2S, Pd, Au/Pt, Ni, and Co nanoparticles (to name a few). With colloidal nanomaterial preparation becoming analogous to traditional molecular systems in terms of selectivity, property modulation, and compositional control, the field of nanomaterial total synthesis has thus emerged in the past decade. With a large toolbox of reactions which afford selectivity at the nanoscale developed, to date it is possible to design a wider array of materials than ever before. Only recently (the past ~ 5 years), however, has the transition from design of model systems for fundamental characterization to realization of functional materials with optimized properties begun to be demonstrated. The emphasis of chapter 1 is thus on the key advances in the preparation of metal-semiconductor hybrid nanoparticles made to date, with seminal synthetic, characterization, and application milestones being highlighted. The second chapter is focused on the synthesis and characterization of well-defined CdSe-seeded-CdS (CdSe@CdS) NR systems synthesized by overcoating of wurtzite (W) CdSe quantum dots with W-CdS shells. 1-dimensional NRs have been interesting constructs for applications such as solar concentrators, optical gains, and photocatalysis. In each of these cases, a critical step is the localization of photoexcited excitons from the light-harvesting CdS NR "antenna" into the CdSe QD seed, from which emission is primarily observed. However, effects of seed size and NR length on this process remained unexplored prior to this work. Previous work had demonstrated that, for core@shell CdSe@CdS systems, small CdSe seed sizes (< 2.8 nm in diameter) resulted in quasi-type II alignment between semiconductor components (with photoexcited electrons delocalized across the structure and holes localized in the CdSe seed), and large seed sizes (> 2.8 nm) resulted in type I alignment (with photoexcited electrons and holes localized in the CdSe seed). Through synthetic control over CdSe@CdS NR systems, materials with small and large CdSe seeds were prepared, and for each seed size, multiple NR lengths were prepared. Through transient absorption studies, it was found that band alignment did not affect the efficiency of charge localization in the CdSe core, whereas NR length had a profound effect. This work indicated that longer NRs resulted in poor exciton localization efficiencies owing to ultrafast trapping of photoexcited excitons generated in the CdS NR. Thus, with increasing rod length, poorer efficiencies were observed. This work served to highlight the ideal size range for CdSe@CdS NR constructs targeted towards photocatalysis, with ~ 40 nm NRs exhibiting the best rod-to-seed localization efficiencies. Additionally, it served to expand the understanding of exciton trapping in colloidal NC systems, allowing development of a predictive model to help guide the preparation of other nanorod based photocatalytic systems. The third chapter describes the synthesis of Au-tipped CdSe NRs and studies of the effects of selective metal nanoparticle deposition on the band edge energetics of these model photocatalytic systems. Previous studies had demonstrated ultrafast localization of photoexcited electrons in Au nanoparticles (AuNP) (and PtNP) deposited at the termini of CdSe and CdSe@CdS NR constructs. Also, for similar systems, the hydrogen evolution reaction (HER) had been studied, for which it was found that noble metal nanoparticle tips were necessary to extract photoexcited electrons from the NR constructs and drive catalytic reactions. However, in these studies, energetic trap states, generally ascribed to surface defects on the NC surface, are often cited as contributing to loss of catalytic efficiency. In this study, we found that the literature trend of assuming the band-edge energetics of the parent semiconductor NC applies to the final metal-functionalized catalyst did not present a complete picture of these systems. Through a combination of ultraviolet photoelectron spectroscopy and waveguide based spectroelectrochemistry on films of 40 nm long CdSe NRs before and after AuNP functionalization, we found that metal deposition resulted in the formation of mid-gap energy states, which were assigned as metal-semiconductor interface states. Previously these states had only been seen in single particle STS studies, and their identification in this study from complementary characterization techniques highlighted a need to further understand the nature of the interface between metal/semiconductor components for the design of photoelectrochemical systems with appropriate band alignments for efficient photocatalysis. The fourth chapter transitions from NR constructs to highly absorbing CdSe@CdS TP materials, for which a single zincblende (ZB) CdSe NC is used to seed the growth of four identical CdS arms. These arms act as highly efficient light absorbers, resulting in absorption cross sections an order of magnitude greater than for comparable NR systems. In the past, many studies have been published on the striking properties of TP nanocrystals, such as dual wavelength fluorescence, multiple exciton generation, and inherent self-assembly owing to their unique geometry. Nonetheless, these materials have not been exploited for photocatalysis, primarily owing to challenges in preparing TP from ultrasmall ZB-CdSe seed size (owing to phase instability of the zincblende crystal structure), thus preventing access to quasi-type II structures necessary for efficient photocatalysis. In this study, we successfully break through the type I/quasi-type II barrier for TP NCs, reclaiming lost ground in this field and demonstrating for the first time quasi-type II behavior in CdSe@CdS TPs through transient absorption measurements. This was enabled by new synthetic protocols for the synthesis and stabilization of ultrasmall (1.8 – 2.8 nm) ZB-CdSe seeds, as well as for the synthesis of CdSe@CdS TPs with arm lengths of 40 nm. Easily scalable, TPs were prepared on gram scales, and the quasi-type II systems showed dramatically enhanced rates of selective photodeposition of AuNP tips under ultraviolet and solar irradiation. These are promising materials for photocatalytic and solar energy applications. The fifth chapter continues with the study of CdSe@CdS TPs, and elaborates on a new method for the selective functionalization of the highly symmetrical TP construct. Previous studies had demonstrated that access to single noble metal NP tips was vital for efficient photocatalytic HER from NR constructs. However, TP materials have been notoriously difficult to selectively functionalize, owing to their symmetric nature. Using a novel photoinduced electrochemical Ostwald ripening process, we found that initially randomly deposited AuNPs could be ripened to a single, large (~ 7 nm) AuNP tip at the end of one arm of a type I CdSe@CdS TP with 40 nm arms. To demonstrate the selectivity of this tipping process, dipolar cobalt was selectively overcoated onto the AuNP tips of these TPs, resulting in dipolar Au@Co-CdSe@CdS TP nanocrystals. These particles were observed to spontaneous self-assemble into 1-D mesoscopic chains, owing to pairing of N-S dipoles of the ferromagnetic CoNPs, resulting in the first example of “colloidal polymers” (CPs) bearing bulky, tetrapod ("giant t-butyl") pendant groups. The sixth chapter elaborates further on the preparation of colloidal polymers, further extending the analogy between molecular and colloidal levels of synthetic control. One challenge in the field of colloidal science is the realization of new modes of self-assemble for compositionally distinct nanoparticles. In this work, it was found that Au@Co nanoparticle dipole strength could be systematically varied by tuning of AuNP size on CdSe@CdS nanorods/tetrapods. In the first example of a colloidal analogue to reactivity ratios observed for traditional chain growth polymerization systems, highly disparate AuNP tip sizes (and thus final Au@Co NP dipole strength) were found to result in segmented colloidal copolymers upon dipolar self-assembly, whereas similar AuNP tip sizes ultimately led to random dipolar assemblies. Clearly visualized through incorporation of NR and TP sidechains into these colloidal polymers, this study presented a compelling case for continued exploration of colloidal analogues to traditional molecular levels of synthetic control.

These days, organic photovoltaic devices (OPV) have received a large interest from both academic and industrial researchers as alternative energy source to replace petroleum and nuclear fission. New organic semi-conductors (OSC) are actively researched since these materials can be purified and processed by solution techniques that are cheaper than those required for silicon. The current record efficiency is 8.3%. Further improvement of the OPV performances is desired in order to decrease both the pay-back time of the device and the price of the energy produced. On that purpose, academic research is focused on two main axes: (i) develop new organic materials characterized by high charge mobilities for both p-type (holes) and n-type (electrons) semi-conduction and (ii) increase as much as possible the contact surface between both p-type and n-type OSC (p-n junction), where the electric charges are created.

In the frame of this PhD thesis, we proposed to investigate this second aspect by building the interface at a nanoscopic scale, creating a molecular heterojunction. Liquid crystalline (LC) materials composed of donor-acceptor dyads were chosen as OSC since they can lead to complex supramolecular structures made of two interpenetrated networks: the first one is related to the donor and provides holes transport, while the second one is related to the acceptor and affords electrons conduction. In this context, we decided to synthesize new donor-acceptor molecules composed of a phthalocyanine (donor) covalently connected to a fullerene (acceptor) through a non-conjugated bridge and to investigate their supramolecular assembly in solution and solid state. This specific molecular structure was inspired from a mesogenic phthalocyanine developed earlier in our laboratory and the very popular fullerene derivative referred to as PCBM.

Four dyads with different bridge lengths were prepared via multi-step synthesis. Two key steps are: (i) the formation of low-symmetry A3B phthalocyanines bearing three mesogenic substituents and one hydroxyl-terminated chain and (ii) the esterification of these phthalocyanines with the carboxylic acid homologue of PCBM.

In solution, no electron transfer from the phthalocyanine to the fullerene is evidenced in the ground state. On the contrary fluorescence quenching indicates that a photo-induced charge transfer takes place. Also, cyclic voltammetry measurements confirmed that both phthalocyanine and fullerene moieties act as independent &
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references.
When a gold nanoparticle is coated with two dislike ligands, the ligands selfassemble on the nanoparticle surface and the phase separation occurs based on the miscibility and the size mismatch of two ligands, and the sizes of nanoparticles. When the size of the gold core is approximately between 3-8 nm, the stripe-like ordered domains of two ligands are formed. The stripe-like structure is not favored when you consider only the enthalpy. However, the long ligands obtain extra free-volumes when they are surrounded by the short ligands due to the curvature of a nanoparticle, hence, the entropy increases when two ligands are mixed on the nanoparticle surface. The balance between enthalpy and entropy leads to the state where the stripe-like arrangement of two ligands is thermodynamically the most stable. When the size of the gold core becomes smaller, the entropy contribution becomes less and less relevant, since the gain of free-volume when two different ligands are closely placed is smaller due to the larger curvature of smaller nanoparticles. Under this condition, the final morphology is primarily determined by the enthalpy of separation. Therefore, for small particles, two ligands phase separate into two bulk phases, resulting the Janus nanoparticles. In the first part of this thesis, we demonstrate that gold nanoparticles with a core diameter smaller than 1.5 nm form Janus nanoparticles in many ligand combinations. We used four different nanoparticles and different techniques to confirm the presence of a majority of Janus particles. All of them show similar cut-off sizes for the Janus-to-stripe transition. In the second part of this thesis, we show nanoparticle hydrogels using the selfassembly of the stripe nanoparticles. One of unique surface properties of the stripe nanoparticle is divalency. A particle coated with stripe-like domains implies two defect points at the poles of NPs. These two polar defects can be selectively functionalized with molecules that in turn can act as handles for further assemblies. The network structure is formed only using ionic interaction between NPs, and it requires both divalent anionic nanoparticles and divalent cations. Gels are investigated to determine their properties using rheological characterization.
by Hyewon Kim.
Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.
Includes bibliographical references (leaves 28-29).
This research focused on methods for regulating arrangement of self-assembled block copolymers by understanding fabrication conditions and their effects on the polymers on flat and patterned substrates. Block copolymer self-assembly is a simple and low cost process for creating lithographic masks with features under 100nm in dimension. These patterns can be transferred to more permanent materials for applications in electronics, magnetic devices, as well as sensors and filters. Polystyrene-poly(ferrocenyldimethylsilane) block copolymer thin films were characterized in terms of their spin curves, PSF spherical domain cross sectional area distributions, and correlation distances. Optimal fabrication conditions were selected from studying polymer behavior on flat substrates and then used for templated substrate studies. Substrates that were templated with grooves produced quantized numbers of rows of spherical domains ranging from 4 to 7. Behavior in these grooves was characterized in terms of groove width constraints, cross sectional domain area distributions, and row ordering. For all templated arrays, the lengths of ordered regions were more than 2 fold higher than the diameters of ordered regions of arrays on flat substrates. The characterization accomplished in this work will be used to compare block copolymers with similar volume fractions of the blocks that allow sphere microdomain formation but of different molecular weights. The ultimate goals are to establish how the molecular weight of this block copolymer affects its self assembly on templated and on flat substrates and to use this factor as well as fabrication conditions and template geometries to engineer arrays with desirable properties.
by Marianna Shnayderman.
S.B.

The layer-by-layer molecular-level manipulation of ionic polymer have been utilized to fabricate ultrathin multilayer films (SAMp). In this process, monolayers of polycations and polyanions are sequentially adsorbed onto a substrate surface by alternately dipping the substrate into aqueous solutions of poly(vinylamine) backbone azo (PDYE), poly(sodium 4-styrenesulfonate) (PSS), and poly(al1ylamine hydrochloride) (PAH). The ionic attractions developed between the oppositely charged polymers promote strong interlayer adhesion and a uniform and linear multilayer deposition process. UV/Vis absorbance, contact angle, and ellipsometry measurements revealed that in all cases the bilayer deposition process was linear and highly producible from layer to layer and film thickness of up to 1 µm can be easily obtained by repeating the deposition process. The typical thickness of bilayer film depend on the solution concentration. Contact angle and UV/Vis spectroscopy measurements demonstrated that the deposition time for a full monolayer coverage of azo dye and PAH was about 20 seconds. Our results showed that the mechanical stability of these SAMp films was remarkable, and SAMp films can only be removed from the substrate by scraping. SAMp films are stable in the common organic solvents and even in the high acidic media (6M HCl aqueous solution). The conformation of these films are thermally stable at high temperature. In an attempt to develop patterned surfaces of sulfonate and thiol functionality, close-packed, well-ordered (3-mercaptopropyl)trimethoxysilane (MPS) monolayer were formed on the surfaces of single crystal silicon, quartz, and glass by allowing hydrolyzed silane to self-assemble from a dilute hydrocarbon solution. The films of MPS were irradiated with an ozone-producing UV light source results in efficient conversion of the surface-localized thiol groups to sulfonated groups, a complete photo-oxidation of the thiol surface was obtained and characterized by x-ray photoelectron spectroscopy (XPS) and contact angle measurements. Sulfonated self-assembled films can be used as good organic templates for the deposition of SAMp films and for micropatterning of organic surfaces based on our results. Such results significantly extend the application of SAMp films since the sulfonate-functionalized surface can be introduced into the surfaces of aromatic polymers, metals, ceramics, semiconductors, and plastics. So that the process of SAMp deposition can be carried out onto many different substrate surfaces. The novel self-assembly technique combined with photolithography was used to develop three different methods of micropatterning fabrication in an attempt to achieve the goal of full-color flat-panel display. The characteristic of distinguishing our methods from the existed ones is that the patterning is done first and then the vertical multilayers were built-up on the patterned areas. Moreover, in this process, SAMp films were used as active species. Scanning Electron Microscopy (SEM) was employed to confirm the patterning technique. In order to block the further growth of the second film type on the sites of first film type, several molecules with inert function groups were tried. UV/Vis absorbance and contact angle measurements revealed that dodecyltrimethylammonium bromide (DTAB) atop the PAH/PSS SAMp film could prevent further adsorption of the ionic polymers.
Ph. D.

Burkholderia cenocepacia is an opportunistic pathogen causing chronic lung infections in patients with cystic fibrosis, which are difficult to treat, creating a pressing need for alternative prevention and control measures. B. cenocepacia possesses several glycoforms, encompassing the peptidoglycan, lipopolysaccharide and glycoproteins, which are crucial for viability and bacterial cell functioning. The biosynthetic machineries of these glycoconjugates are essential components in determining the final structural composition of bacterial cells, and share a common theme. In this study, three critical components involved in glycan transport and assembly in B. cenocepacia were characterized. First, MurJBc was identified as the peptidoglycan cell wall flippase responsible for the transport of lipid II molecules across the inner membrane to be incorporated into the growing peptidoglycan mesh. MurJ was essential for viability of B. cenocepacia and peptidoglycan synthesis. Second, the protein O-glycosylation cluster, which encodes the necessary proteins for the stepwise assembly of the lipid-linked O-glycan in the cytoplasm and its translocation across the inner membrane prior to the glycan incorporation to target proteins, was unravelled. Results uncovered that all Burkholderia share a common glycan that is antigenic in humans. Furthermore, dramatic pleiotropic phenotypes were associated with protein O-glycosylation in B. cenocepacia, which demonstrates that this process is critical for the normal physiology of these bacteria. Third, LpxLBc was shown to be the only late acyltransferase responsible for penta-acylation of lipid A in B. cenocepacia. It has an important role in LPS transport and survival under stress conditions including the intracellular environment of macrophages. In conclusion, data in this thesis support the notion that the glycan transport and assembly machineries in Burkholderia are required for the ability of this bacterium to thrive in different niches. Further, this work exposes novel antibiotic targets and potential vaccine antigens for future development into therapeutic alternatives to control Burkholderia infections.

A number of compounds were synthesized with the ultimate goal being the synthesis of C₂ symmetric molecules which displayed thermotropic liquid crystalline behaviour. The compounds prepared were 4-alkoxy benzophenones, 3,4-bis-alkoxy benzophenones, 4- alkoxy dibenzylidene acetones, 3,4-bis-alkoxy dibenzylidene acetones and 4-alkoxy- 1, 9-diphenyl-nona-l,3,6,8-tetraen-5-ones. The length of the linear alkoxy side chain was varied from C₆H₁₃ to C₁₂H₂₅. All compounds were characterized by FTIR, ¹H, and ¹³C NMR spectroscopy. Mesophase behaviour of the synthesized compounds was investigated using differential scanning calorimetry and polarizing optical microscopy. It was determined that both the alkoxy side chain length, as well as the number of alkoxy side chains have an effect on the ability of this class of C₂ symmetric compounds to selfassemble into liquid crystalline phases. In addition, the overall core size and extent of conjugation also affected mesophase formation. The mono-alkoxy benzophenones and dibenzylidene acetones were non-mesogenic, while all four of the mono-alkoxy 1,9- diphenyl-nona-l,3,6,8-tetraen-5-ones (alkoxy side chain of lengths C₆H₁₃, C₈H₁₇, C₁₀H₂₁ and C₁₂H₂₅)self-assembled into nematic liquid crystalline phases. Increasing the number of alkoxy side chains from one to two per aromatic moiety helped induce liquid crystalline formation: the corresponding bis-C₆H₁₃ benzophenone and bis-C ₆H₁₃, bis C₈H₁₇, and bis-C₁₀H₂₁ dibenzylidene acetones were mesogenic, displaying smectic A (benzophenone) and nematic (dibenzylidene acetone) mesophases respectively.

In this study, the main objective was to investigate the tolerance of platinum based binary anode catalysts for CO poisoning from 10ppm up to1000ppm and to identify the
best anode catalysts for PEMFCs that tolerates the CO fed with reformed hydrogen.

Thesis (Ph.D.) -- University of Maryland, College Park, 2009.
Thesis research directed by: Dept. of Materials Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Thesis (Ph. D.)--University of Maryland, College Park, 2009.
Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Chlamydomonas reinhardtii is a unicellular biflagellate green alga which has the ability to perceive external light and alter its swimming behavior in response. A specialized light sensing structure, the eyespot, is responsible for this sensory ability. The eyespot is composed of photoreceptors and signal transduction components thought to be localized to the plasma membrane of the cell, and an organized arrangement of carotenoid-filled lipid granules in the chloroplast underlying the plasma membrane. To identify the components involved in eyespot assembly, a screen for eyespot assembly mutants (Lamb, et al., 1999) identified four new loci deficient in eyespot assembly. Herein, we demonstrate the eyespot assembly mutants are generally capable photobehaviors, though the phenotype of the mutant strain affects the nature and manner in which the photobehaviors are affected. Additionally, we report on the isolation of a tagged allele of EYE2. Using DNA adjacent to the tag site, the EYE2 gene was isolated. Attempts to localize the protein in vivo were unsuccessful. The EYE2 gene encodes a protein which contains a putative thioredoxin active site motif. Transformants harboring a mutant EYE2 gene with the more C-terminal cysteine changed to serine possess eyespots and are phototactic. This substitution has only been observed to be tolerated in protein disulfide isomerases; we hypothesize that the function of EYE2 in eyespot assembly may be through the rearrangement of disulfide bonds in substrate proteins that function more directly in eyespot assembly.

This dissertation presents new insight into the ability of small molecule passivated NCs to achieve intimate approach distances, despite being well passivated, while developing guiding principles in the area of ligand mediated microstructure control and the resulting macroscopic optical and electronic properties that close packing of high quality NCs enables. NC ligand coverage will be characterized quantitatively through thermogravimetric analysis (TGA), and qualitatively by photoluminescence and electroluminescence, in the case of functional devices; illustrating the importance of practitioner dependent control of ligand coverage through variations in the dispersion precipitation purification procedure. A unique examination of the relative contribution of energy and charge transfer in NC LEDs will demonstrate the ability to achieve charge transfer, at a level competitive with energy transfer, to well passivated NCs at various wt% loading in a polymer matrix. The observation of potential dependent recombination zones within an active layer further suggest novel, NC surface passivation mediated control of blend microstructure during solution processing towards the development of a bi-continuous network. Next, NC self-assembly and resulting microstructure dependent optical and electronic properties will be examined through electroluminescence and high-resolution transmission electron microscopy (TEM) micrographs of functional NC/polymer bulk heterojunction LEDs. The joint characterization of NC optical properties, and self-assembly microstructure provide a deeper understanding of the significant and inseparable effects of minimal changes in NC surface passivation on structure and function, and emphasize the potential to rely on strongly passivating ligands to control physical properties and processing parameters concurrently towards higher efficiency devices via low cost processing. Finally, micro-contact printing of blazed transmission gratings, using stable dispersions of core and core/shell NCs will be shown to produce close packed assemblies of NCs forming near-wavelength luminescent superstructures separated in space. We show the dominant contribution of a two-monolayer thick sharp interface CdS shell to the diffraction efficiency, and necessarily the refractive index, of the NCs, independent of core size. Utilization of these gratings as in-coupling elements at various positions within a device architecture are also examined. These new observations were achieved by unprecedented control of NC architecture during dispersion processing, while maintaining high luminescence, made possible by optimized NC surface passivation. These studies enable the formation of new LED architectures, and new optoelectronic devices based on angle resolved, monochromatic fluorescence from diffraction gratings prepared from simple solution processing approaches. Further, the novel observation of angle amplified interfering fluorescence from these features is argued to be a result of long range radiative coupling and superradiance enabled by the monodispersity and high-quality NC surface passivation described herein.

Two series monodispersed nanoparticles of hydroxylpropyl cellulose (HPC) and functionalized poly-N-isopropylamide (PNIPAM) particles have been synthesized and used as building blocks for creating three-dimensional networks, with two levels of structural hierarchy. The first level is HPC nanoparticles were made from methacrylated or degradable cross-linker attached HPC. These nanoparticles could be stabilized at room temperature by residual methacrylate or degradable groups are present both within and on the exterior of HPC nanoparticles. Controlled release studies have been performed on the particle and networks .The nearly monodispersed nanoparticles have been synthesized on the basis of a natural polymer of hydropropylcellulose (HPC) with a high molecular weight using the precipitation polymerization method and self-assembly of these particles in water results in bright colors. The HPC nanoparticles can be potential using as crosslinkers to increase the hydrogels mechanical properties, such as high transparency and rapid swelling/de-swelling kinetics. The central idea is to prepare colloidal particles containing C=C bonds and to use them as monomers - vinylparticles, to form stable particle assemblies with various architectures. This is accomplished by mixing an aqueous suspension of hydrogel nanoparticles (PNIPAM-co-allylamine) with the organic solvent (dichloromethane) to grow columnar crystals. The hydrogels with such a unique crystal structure behavior not only like the hydrogel opals, but also have a unique property: anisotropy.

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xv1, 151 p.; also includes graphics. Includes abstract and vita. Advisor: Mark Parthun, Dept. of Biochemistry. Includes bibliographical references (p. 138-151).

Throughout recent history scientists have struggled to elucidate the biochemical and biophysical mechanisms that guide the assembly of macromolecular structures. The early models of "sub-assembly" or "self assembly" attempted to explain how individual components could interact in a precisely regulated manner to form higher-ordered complex biological structures. Subsequent studies, using viral systems as assembly models, demonstrated how protein-protein and protein-nucleic acid interactions assist in lowering the thermodynamic barriers that typically disfavor assembly.Due to their simplicity, viruses provide an ideal system to investigate the biophysical mechanisms that drive the assembly of complex biological structures. Proper virion assembly requires numerous macromolecular interactions that proceed along an ordered morphogenetic pathway. While structural proteins are incorporated into the final product, morphogenesis is equally dependent upon scaffolding proteins, which are not included in the mature virion. Since the identification of scaffolding proteins in the bacteriophage P22, homologues have been discovered in many systems. Scaffolding proteins play multiple roles during morphogenesis by inducing protein conformational switches and lowering the thermodynamic barriers to promote virion assembly, while ensuring the efficiency and fidelity of the final product.

Copper is an essential cofactor of two mitochondrial enzymes: cytochrome c oxidase (COX) and the mitochondrial localized fraction of Cu-Zn superoxide dismutase (Sod1p). Copper incorporation into these enzymes is facilitated by a growing number of metallochaperone proteins. Here we describe two novel copper chaperones of COX, Cmc1 and Cmc2. In Saccharomyces cerevisiae, both Cmc1 and Cmc2 localize to the mitochondrial inner membrane facing the intermembrane space. Cmc1 and Cmc2 are essential for full expression of COX and cellular respiration, contain a twin Cx9C domain, and are conserved from yeast to humans. Additionally, the presence or absence of these proteins not only determines full assembly of functional COX but also affects metallation of Sod1 suggesting these proteins might play a role on co-modulation of copper transfer to COX and Sod1. CMC1 overexpression does not rescue the respiratory defect of cmc2 mutants or vise versa. However, Cmc2 physically interacts with Cmc1 and the absence of Cmc2 induces a 5-fold increase in Cmc1 accumulation in the mitochondrial membranes. We conclude that Cmc1 and Cmc2 have cooperative but non-overlapping functions in cytochrome c oxidase biogenesis.

The work in this dissertation consists of a two-part study concerning molecular-based electronics and atomic layer deposition (ALD). As conventional âtop-downâ silicon-based technology approaches its expected physical and technical limits, researchers have paid considerable attention to âbottom-upâ approaches including molecular-based electronics that self assembles molecular components and ALD techniques that deposit thin films with atomic layer control. Reliable fabrication of molecular-based devices and a lack of understanding of the conduction mechanisms through individual molecules still remain critical issues in molecular-based electronics. Nanoparticle/molecule(s)/nanoparticle assemblies of âdimersâ and âtrimersâ, consisting of two and three nanoparticles bridged by oligomeric ethynylene phenylene molecules (OPEs), respectively, are successfully synthesized by coworkers and applied to contact nanogap electrodes (< 70 nm) fabricated by an angled metal evaporation technique. We demonstrate successful trapping of nanoparticle dimers across nanogap electrodes by dielectrophoresis at 2 VAC, 1 MHz, and 60 s. The structures can be maintained electrically connected for long periods of time, enabling time- and temperature-dependent current-voltage (I-V) characterization. Conduction mechanisms through independent molecules are investigated by temperature dependent I-V measurements. An Arrhenius plot of log (I) versus 1/T exhibits a change of slope at ~1.5 V, indicating the transition from direct tunneling to Fowlerï­Nordheim tunneling. Monitoring of the conductance is also performed in real-time during trapping as well as during other modification and exposure sequences after trapping over short-term and long-term time scales. The real-time monitoring of conductance through dimer structures during trapping offers immediate detection of a specific fault which is ascribed to a loss of active molecules and fusing of the nanoparticles in the junction occurring mostly at a high applied voltage (â¥3 VAC). After successful trapping, the sample exposure to air reveals a small rapid decrease in current, followed by a slower exponential increase, and eventual current saturation. This work also reports on the dependence of electron transport on molecular length (2 to 4.7 nm) and structure (linear-type in dimers and Y-type in trimers). The extracted electronic decay constant of ~0.12/à and effective contact resistance of ~4 Megaohmï indicate a strong electronic coupling between the chain ends, facilitating electron transport over long distances. A three terminal molecular transistor is also demonstrated with trimers trapped across nanogap electrodes. The source-drain current is modulated within a factor of 2 with a gate bias voltage of -2 to +2 V. A subthreshold slope of ~110 mV/decade is obtained. Finally, we report on both fundamental understanding and application of atomic layer deposition. First, in situ analysis tools such as quartz crystal microbalance and electrical conductance measurements are combined to reveal direct links between surface reactions, charge transfer, and dopant incorporation during ZnO and ZnO:Al ALD. Second, the ability of ALD to form uniform and conformal coating onto complex nanostructures is explored to improve the ambient stability of single molecules/nanoparticle assemblies using Al2O3 ALD as an encapsulation layer. In addition, the ability to shield the surface polarity of ZnO nanostructures using Al2O3 + ZnO ALD, leading to hierarchical morphology evolution from one-dimensional ZnO nanorods to three-dimensional ZnO nanosheets with branched nanorods during hydrothermal growth is investigated.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references.
A low-temperature, ambient pressure solution synthesis of colloidal InN nanoparticles is presented. This synthesis utilizes a previously dismissed precursor and results in individual, non-aggregated nanoparticles with long-term solubility and stability in organic solvents. These nanoparticles are wurtzite phase with a measured bandgap as low as 0.79 eV and average size of 6.2 nm. Based on this synthesis, indium-rich InGaN nanoparticles were synthesized and characterized. Chemical, structural, and optical analysis indicated up to 10% gallium incorporation before encountering the miscibility gap. Using CdSe nanoparticles as a model system, M13 bacteriophage-mediated, two-dimensional nanoparticle assembly was examined as a route for scaleable, large-area nanoparticle films. The method uses close-packed, self-assembly of M13 on layer-by-layer deposited polyelectrolyte surfaces and was able to assemble aminated nanoparticles with strong specificity.
by Jennifer Chia-Jen Hsieh.
Ph.D.

Protein-protein interactions participate in the assembly, regulation, and processivity of all molecular "machines." In this dissertation, a series of genetic and biochemical approaches have been used to analyze the protein-protein interactions which participate in the formation of the Herpes Simplex Virus Type 1 replisome. The emphasis of these studies lies on the herpes helicase-primase complex, its assembly, regulation, and processivity. The herpes helicase-primase is a heterotrimeric complex encoded by the viral UL5, UL52, and UL8 genes. The yeast two-hybrid system was used to generate a protein linkage map of the herpes replisome and to characterize the interactions among the three subunits of the helicase-primase (UL5, UL52, and UL8). Deletion analysis and co-immunoprecipitation, were used to show that a 548 amino acid carboxy-terminal fragment of UL52 interacts with UL8, while a 350 amino acid N-terminal fragment is required for interaction with UL5 and may also be involved in the regulation of the strength of interaction with UL8. Comparative sequence analysis suggested that the functional interactions among the subunits of the helicase-primase encoded by alpha-herpesviruses may differ from those of the helicase-primases encoded by the beta- and gamma-herpesviruses. Expression and purification of the UL5 subunit of the helicase-primase in the absence of UL52 resulted in an inactivating but reversible catalytic deficiency in UL5. UL52 corrected this deficiency when added subsequently. Based on these results, a proposal is suggested here that UL52 regulates the activity of UL5 by inducing conversion of UL5 from an inactive to an active conformation, and/or by contributing amino acid residues to the catalytic site. Finally, evidence from a combination of biochemical approaches suggested that the HSV-1 helicaseprimase is a monomeric ATPase with a non-globular shape and that it belongs to the group of helicases which use an inchworming mechanism for unwinding DNA.