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1
O'Neil, David H. "Materials chemistry and physics of the transparent conducting oxides." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670028.
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2
Peters, Kyle C. "Sustainable Materials and Processes for Optoelectronic Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554397264722736.
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3
Norga, Gerd Johan Maria. "Chemistry and physics of metallic contaminants on crystalline silicon surfaces." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10904.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.<br>Includes bibliographical references (leaves 202-210).<br>by Gerd Johan Maria Norga.<br>Sc.D.
4
Kiang, Ching-Hwa Goddard William A. Goddard William A. "Physics and chemistry of advanced nanoscale materials : experiment, simulation, and theory /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10162007-105256.
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5
Forsythe, Martin Blood Zwirner. "Advances in Ab Initio Modeling of the Many-Body Effects of Dispersion Interactions in Functional Organic Materials." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718708.
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Accurate treatment of the long-range electron correlation energy, including dispersion interactions, is essential for describing the structure, dynamics, and function of a wide variety of systems. Among the most accurate models for including dispersion into density functional theory (DFT) is the range-separated many-body dispersion (MBD) method [A. Ambrosetti et al., J. Chem. Phys. 2014, 140, 18A508], in which the long-range correlation energy is computed from a model system of coupled quantum harmonic oscillators. In this work, we seek to extend the applicability of the MBD model by developing the analytical gradients necessary to compute MBD corrections to ionic forces, unit-cell stresses, phonon modes, and self-consistent updates to the Kohn-Sham potential. We include all implicit coordinate dependencies arising from charge density partitioning, as we find that neglecting these terms leads to unacceptably large relative errors in the MBD forces. Such errors would impact the predictive nature of ab initio molecular dynamics simulations employing MBD. We develop a new efficient implementation of the MBD correlation energy and forces within the Quantum ESPRESSO software package and rigorously test its numerical stability and convergence properties for condensed phase simulations. Additionally, we re-parameterize the MBD model for use with a wide variety of generalized gradient approximation exchange-correlation functionals. We demonstrate the efficiency and accuracy of these MBD gradient corrections for optimizations of isolated dispersively bound molecular systems, as well as representative condensed phase systems including adsorbed hydrocarbons, layered materials, and hydrogen-bonded crystals. Where highly accurate reference geometries are available, we find the DFT+MBD method significantly improves the predicted structures of these systems and consistently outperforms popular pairwise-additive DFT-D dispersion corrections. Though significant work remains in the benchmarking and testing of these contributions to the MBD model, we are optimistic that these methodological developments will enable many exciting discoveries of beyond-pairwise dispersive effects in organic materials.<br>Physics
6
Citati, Andrea. "Systematic synthesis and magnetic characterization of palladium nanoparticles with hexanethiolate and phenylethanethiolate ligands." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10159001.
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<p> Palladium nanoparticles have been synthesized using a systematic variation of the two-phase Burst-Schiffrin reaction to specifically tailor their physical properties. Furthermore, hexanethiolate and phenylethanethiolate ligands have been added to kinetically stabilize the nanoparticles and as a consequence the magnetic properties have been altered due the change in ligand-nanoparticle exchange interaction. The magnetic properties of the nanoparticles were then studied via the vibrating sample magnetometer and subsequently compared with similar experiments in the nanomagnetism literature. A distinctive increase in magnetic saturation, remanence and coercivity has been evidenced by comparing the phenylethanethiolate ligand group samples to the hexanethiolate ligand group samples, indicating the importance of capping agents within this popular subject.</p>
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Shaheen, Sean E. "Device physics of organic light-emitting diodes." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289012.
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This work investigated several aspects of OLED device physics. The mechanisms responsible for the efficiency enhancement typically seen when a dye molecule is doped into the emission layer were examined. By comparing the spectra and efficiencies of single-layer devices for varying dopant concentrations, it was found that both charge transfer and energy transfer from the host molecule to the dye dopant are important processes. The measured efficiencies for photoluminescence and electroluminescence were found to be consistent with a simple model developed to explain the functional dependence on the dopant concentration. Work was also done on the enhancement of electron injection from an aluminum cathode using a thin layer of LiF. A double-layer device with the blue emitter DPVBi showed a factor of 50 enhancement in quantum efficiency upon insertion of a LiF layer. This technique has important practical application since it allows for the use of an environmentally-stable aluminum cathode while retaining high device efficiency. The effect of the ionization potential of the hole transport layer on the efficiency of a double-layer device was also investigated. TPD side-group polymers were used as the hole transport layer. The device efficiency was shown to increase as the ionization potential of the hole transport layer was pushed further from the work-function of ITO. This trend was attributed to an improved balance between the injection rates of holes and electrons. A Monte Carlo simulation of a single-layer device was developed which demonstrated the importance of balanced injection to obtain high efficiency. Drawing upon these results, an optimized OLED was fabricated which exhibited a luminous efficiency of 20 lm/W for green emission. This is one of the highest OLED efficiencies reported as of the date of this writing.
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Playford, Helen Y. "Investigating materials with disordered structures using total neutron scattering." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55164/.
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The structures of a variety of disordered materials were determined using the technique of total neutron scattering. The synthesis of various polymorphs of Ga2O3 and related materials was investigated and the structures of the hitherto uncharacterised polymorphs were examined in detail. The structure of y-Ga2O3 was found to be a cubic defect spinel with four partially occupied Ga sites, however, the octahedral Ga coordination environments were found to be distorted from the average cubic structure. The cation distribution in y-Ga2O3 was found to depend on particle size and synthesis method. Examination of the structure of E-Ga2O3 revealed that it is analogous to a disordered, hexagonal form of E-Fe2O3. The poorly crystalline product of the thermal decomposition of Ga(NO3)3.9H2O was found to be a nanocrystalline modification of E-Ga2O3, rather than a distinct phase with the bixbyite structure, as had been previously reported. The structure of a novel gallium oxyhydroxide, Ga5O7(OH), was determined to be analogous to tohdite, Al5O7(OH), and in its thermal decomposition pathway was revealed a new Ga2O3 polymorph: orthorhombic K-Ga2O3. A solvothermal synthetic route to spinel structured ternary gallium oxides, of general formula MxGa3-xO4-y, was developed. The structures of the materials where M = Zn or Ni were found to be consistent with those previously published. The materials where M = Co or Fe possess novel, oxygen-deficient compositions and exhibit interesting magnetic behaviour. A series of cerium bismuth oxides of formula Ce1-xBixO2-1/2x were found to adopt the cubic fluorite structure with significant local distortion due to the preference of Bi3+ for an asymmetric coordination environment. A sodium cerium titanate pyrochlore was also structurally characterised and it was determined that, due to the presence of three different cations on the A site, the local structure required a model with reduced symmetry. In situ neutron scattering experiments were carried out on amorphous zeolite precursor gels in the presence of the reaction liquid. These experiments revealed structural features unique to the gel, and proved that the gel undergoes irreversible structural changes on drying. Preliminary analysis of the gel structure indicated that the Na+ cations play an important role in the development of the ordered zeolitic framework, and revealed no strong evidence for the existence of discrete structural building units in the gel.
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Phillips, Katherine Reece. "Sol-Gel Chemistry of Inverse Opals." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493452.
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Controlling nano to microscale structuration enables one to alter a material’s optical, wetting, mechanical, and chemical properties. Structuration on this scale can be formed from spherical building blocks; in particular, monodisperse, spherical colloids assemble into crystals that can be used to template an ordered, porous structure known as an inverse opal. The structure’s porosity and periodicity provide control over both light (photonic effects) and fluid flow (wetting effects). Controlling the composition allows chemical functionality to be added to the ordered, porous structure. Inverse opals are widely used in many applications that take advantage of these properties, including optical, wetting, sensing, catalytic, and electrode applications; however, high quality structures are necessary to maintain consistent properties. Many of their properties stem from the structure itself, so controlling inverse opals’ structure (including the local composition) provides the ability to control their properties, with the potential to improve some applications and potentially enable additional ones.
This thesis explores how molecular precursors can be used to control colloidal assembly and therefore alter the optical and wetting properties of high quality inverse opals. Using a bio-inspired approach, highly ordered, crack-free, silica inverse opals can be grown by co-assembling the colloidal template with a sol-gel matrix precursor using evaporation-induced self-assembly. Using sol-gel chemistry, the size, shape, and charge of the precursor can be controlled, which can be used to tune the colloidal assembly process. Here, we use the sol-gel chemistry of the precursors to control both the morphology and composition of these photonic structures.
In particular, temperature-induced condensation of the silica sol-gel matrix alters the shape of an inverse opal’s pores (Chapter 2), and silica and titania precursors can be mixed to make hybrid oxide structures (Chapter 3). Additionally, rationally designed precursors enable the fabrication of crack-free inverse opals in materials beyond silica, which we show for titania as a proof-of-concept (Chapter 4). By controlling the structure and composition with sol-gel chemistry, we can tailor both the optical and wetting properties, as discussed in the second part of each chapter; these properties have important effects for the various applications. In this way, sol-gel chemistry can be used to assemble inverse opals with complex functionality.<br>Chemistry and Chemical Biology
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Zhang, Wenbin. "Soft Fullerene Materials: Click Chemistry and Supramolecular Assemblies." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1272303673.
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Szabo, Tamas. "Energy transfer at gas-liquid interface towards energetic materials /." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4797.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on February 29, 2008) Vita. Includes bibliographical references.
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Hodges, Joshua. "In Situ Measurements of Electron-Beam-Induced Surface Voltage of Highly Resistive Materials." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1416.
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This study presents the development, calibration, characterization, and use of new instrumentation for in situ measurements of electron-beam-induced surface voltage. The instrument capabilities allow for measurements of a full range of insulating materials that are of concern to NASA spacecraft charging experts. These measurements are made using moveable capacitive sensor electrodes that can be swept across the sample using an in vacu stepper motor. Testing has shown a voltage range of more than ±30 kV with a low-voltage resolution of 0.2 V. The movable sensors allow for a radial measurement of surface voltage with spatial resolution as low as 1.5 mm. The instrumentation has response time of ~7 s from the time the beam is shut off until the probe is in position to take data and uses computer automation to stabilize the system and acquire data over the period of several days or longer.
Three types of measurements have been made on two prototypical polymeric spacecraft materials, Low-density Polyethylene (LDPE) and polyimide (KaptonTM HN), to illustrate the research capabilities of the new system. Surface voltage measurements were made periodically during the charging process using a pulsed electron beam and subsequently as the surface voltage discharged to a grounded substrate; these were used to obtain information about the material’s electron yields and bulk resistivity. The spatial profile of the voltage across the sample surface was also measured by sweeping the electrode across the surface. Subsequent measurements monitored the time evolution of the magnitude and spatial charge distribution as charge dispersed radially across the sample surface. The results of these measurements are present and compared to literature values validating the instrument’s effectiveness.
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Suratwala, Tayyab Ishaq 1970. "Photostability of laser dyes in sol-gel-derived hosts." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290697.
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Improving the photostability of laser dyes within sol-gel derived hosts has been the focus of this study. To accomplish this, synthetic routes were established to incorporate laser dyes within various sol-gel matrices, the mechanisms of dye photodegradation were determined, and molecular engineering techniques were employed to improve the photostability of the dye doped sol-gel hosts. Various Coumarin (silylated and unsilylated) and Pyrromethene laser dyes were incorporated within sol-gel derived hosts ranging from SiO₂ xerogel films to SiO₂:PDMS Polyceram monoliths which were optically transparent, crack-free, and polishable. Processing parameters, such as the water content and the pre-hydrolysis of the silylated Coumarin dyes, greatly affected the degree of dye bonding. The chemical stability of the Pyrromethene laser dye was also greatly affected by processing parameters, such as the acid/base content. Both the Coumarin and Pyrromethene dyes were found to degrade by photo-oxidation processes. Therefore, it was expected that the photostability would improve by incorporating the dye molecules within molecular cages within the solid hosts, thereby preventing interactions of the dye with photo-reactive impurities such as oxygen. The photostability was found to improve using the following molecular engineering methods: (1) by covalently bonding the dye to the host matrix, where the photostability improvement was attributed to the greater probability of obtaining dye caging with the silylated dye; (2) by removing porosity within the host through control of sol-gel processing and composition, where the photostability improvement was attributed to the elimination of highly photo-reactive dyes located in the pores of the host; (3) by incorporating additives such as bases and hindered amine antioxidants which slowed the steps of the photodegradation process. The fluorescence photostability (fluorescence output intensity as a function of pump pulses) of the dye doped films and monoliths showed a characteristic behavior in the fluorescence output, signified by a rapid initial decay (attributed to dyes located within pores of the matrix) and then a slower long-term decay (attributed to photostable dye molecules located within SiO₂ cages). A model, which applied a Gaussian distribution of the photostabilities of the dye molecules, quantitatively described the observed photostability behavior of the dye doped samples.
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Jiang, Hongwei 1962. "Functionalized siloxane based polymers and network materials for second-order nonlinear optics." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35842.
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We have developed a new chemical methodology, based on simple acid-base hydrolysis of aminosilanes with molecules containing terminal OH groups, to prepare robust siloxane based polymers and organic-inorganic hybrid network materials for second-order nonlinear optics. First, a variety of polymers containing NLO-active chromophores covalently bound to the siloxane backbones, [-R2Si-(O-SiR2)n-O-(NLO-Chromophore)-O-] n (R = CH3 or CH3/C6H4) and [-R2Si-(O-SiR2)n-O-R'-O-(NLO-Chromophore)-O-] n. (R' = -C6H4-C 6H4-C6H4-), were prepared. Their solubility in common organic solvents, and high thermal stability, imparted ease of thin film preparation, and subsequent poling at high temperatures. These polymers exhibit good second-harmonic generation susceptibilities, and the temporal stabilities of the SHG signals were dependent on the polymer backbone and the molecular structures of the NLO chromophoms. A detailed analysis of their physical properties is reported. Then, a methodology of acid-base hydrolysis was used to produce copolymers containing dimethylsiloxane, imide linkages and NLO-active chromophores. These copolymers were soluble in polar solvents, and possessed high thermal stabilities and glass transition temperatures. Easily fabricated and poled thin films of these polymers exhibited good second-order nonlinear optical susceptibilities with long-term temporal stabilities of the second-harmonic generation signals at room temperature. Finally, an alternative approach, based on the same acid-base hydrolysis technique, to prepare organic-inorganic hybrid network material, was developed. In these hybrid materials, NLO-active chromophores such as Disperse Red 19, a pyridinium. salt based dye, and 1-amino-4-nitrobenzene, were covalently locked into silica networks. The hybrids were soluble, and offered ease of processibility in the preparation of good optical quality thin films. The network materials that are akin to the traditional sol-gel approach were also prepared
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Courtney, Ian Anthony. "The physics and chemistry of metal oxide composites as anode materials for lithium-ion batteries." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ49253.pdf.
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Mishchenko, Lidiya. "Biomimetic Engineering of Patterned Surfaces to Control Crystallization: From Colloids to Ice." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10132.
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Numerous natural organisms use chemical and structural patterning to manipulate complex crystal growth and control their aqueous environment. Structural templates such as vesicles and cell walls aid in the growth of nano- and micro-patterned single crystal structures seen in sea urchins, brittlestars, and sea cucumbers. Patterned surface chemistry is used by the Namib dessert beetle for water collection and by the lotus leaf to fend off raindrops. Taking inspiration from natural organisms, structural and chemical patterning is used to achieve extended functionality and better control over the properties of self-assembled colloidal crystals and anti-icing water-repellent surfaces. The first system involves the use of self-assembled colloidal crystals (Part I) as patterned structural templates for synthesizing porous inverse opals (with applications in photonics, tissue engineering, sensing, catalysis). Controlling colloidal crystal assembly poses a technological challenge and Chapter 1 explores how assembling colloids together with a matrix material (silica sol-gel) results in large-scale, ordered, crack-free inverse opal structures. It also discusses the mechanical and optical properties of these large-scale films and investigates the different aspects of this assembly mechanism. Chapter 2 demonstrates several methods for altering the surface chemistry and composition of co- assembled inverse opals in order to add new functionality. Chapter 3 explores how patterned micro- topography can be used to alter direct and inverse opal growth and make novel hierarchical structures. The second system involves using structurally patterned water-repellent (superhydrophobic) surfaces to control condensation and ice crystallization (Part II). Materials that control ice formation are important to aircraft efficiency, highway and powerline maintenance, and building construction. Chapter 1 explores how superhydrophobic materials can be designed to prevent or control impact ice accumulation by limiting the time and area of contact of a droplet with a cold surface. Chapter 2 discusses how our structured, water-repellent surfaces respond to high humidity conditions and condensation. Chapter 3 discusses how localized chemical patterning on various superhydophobic surface geometries can be used to spatially control water condensation and freezing.<br>Engineering and Applied Sciences
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Kress, Oliver Herbert. "Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455.
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Sim, Alec. "Unified model of charge transport in insulating polymeric materials." Thesis, Utah State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3606878.
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<p> Presented here is a detailed study of electron transport in highly disordered insulating materials (HDIM). Since HDIMs do not lend themselves to a lattice construct, the question arises: How can we describe their electron transport behavior in a consistent theoretical framework? In this work, a large group of experiments, theories, and physical models are coalesced into a single formalism to better address this difficult question. We find that a simple set of macroscopic transport equations--cast in a new formalism--provides an excellent framework in which to consider a wide array of experimentally observed behaviors. It is shown that carrier transport in HDIMs is governed by the transport equations that relate the density of localized states (DOS) within the band gap and the occupation of these states through thermal and quantum interactions. The discussion is facilitated by considering a small set of simple DOS models. This microscopic picture gives rise to a clear understanding of the macroscopic carrier transport in HDIMs. We conclude with a discussion of the application of this theoretical formalism to four specific types of experimental measurements employed by the Utah State University space environments effects Materials Physics Group.</p>
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Romero, Trevor Walton. "Quantum diamonds : a discussion of the chemistry, materials science, physics and applications of ternary (Cu-In-S) nanocrystals." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121608.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 33-34).<br>Quantum dots (QDs) are nanometer-sized crystallites of inorganic semiconductors with tunable optoelectronic properties, which has led to a variety of real-world applications beginning in the 1980s, ranging including electronic displays, solar cells, and quantum computers [(Lee, SID), (Tang, Nature Mater.), (Puri, Phys Rev. B)]. However, most high-quality QD materials explored to date have been limited for large-scale application due to toxicity concerns or difficult-to-scale preparative methods. This thesis explores the synthesis and properties of colloidal nanocrystals composed of the non-toxic semiconductor copper indium sulfide (CulnS₂). We report an improved core nanoparticle synthesis with unique compositional control, a rationally-designed precursor for the synthesis of high-quality CulnS₂/ZnS nanocomposites, and describe the dependence on the photophysical properties of CulnS₂/ZnS on core CulnS₂ elemental composition.<br>by Trevor Walton Romero.<br>S.B.<br>S.B. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Page, Samuel John. "The use of solid state NMR to monitor reactions and doping in inorganic materials." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/113823/.
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Solid state nuclear magnetic resonance (NMR) is a powerful probe of inorganic materials systems. Through carefully changing materials compositions and synthesis methods, the impact on the local structure can be investigated. These have been applied to three main materials sectors: Paramagnetic materials in NMR have traditionally suffered from poor resolution due to broadening experienced at the nuclei from localised unpaired electrons. In this work, a fast magic angle spinning (MAS) and low field approach has been applied to these paramagnetic cathode materials to improve this resolution, and elucidate structural information from the investigated materials. The resolution gained from these techniques has been used to highlight differences observed in the 7Li shifts of lithium iron phosphate (LFP) produced by different synthesis techniques. This was found to be related to the cell volume of the LiFePO4 phase. Furthermore, the investigation of V doped LFP by 7Li and 31P MAS NMR has resulted in the observation of many common impurities resulting from synthesis. Additionally, 31Presonances could be identified that were related to V near the phosphorus site, indicating successfully doping in some of the higher Li containing samples. Through 29Si and 17O MAS NMR, changes in the local structure between Ca and Zn doped Stöber nanoparticles are observed. Similarly to other Ca containing materials, incorporation of Ca into the Stöber network has been shown to disrupt Sibridging bonds promoting the formation of non-bridging bonds in the silica network. However, addition of Zn tells a different story. This is first observed in the static measurements, where incorporation of high amounts of Zn leads to no evidence of hydroxyls observed in the Stöber network. Whereas, high resolution transmission electron microscopy (HRTEM) and density functional theory (DFT) calculations confirm the presence of crystalline Zn2SiO4 -II in the nanoparticles. Finally, activation of two series of synthetic sodium- and aluminium substituted calcium silicate hydrate (C-(N)-(A)-S-H) geopolymers are investigated. Increasing the CaO has been shown to increase the disorder of the silica network, and also to promote the increase of crystallinity of the systems through observation of calcium aluminate phases. Additionally, increasing the amount of aluminium relative to the silicon in the system, promotes more of these crystalline phases to form.
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Gunasinghe, Rosi. "Electronic and Magnetic Properties of Carbon-based and Boron-based Nano Materials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2017. http://digitalcommons.auctr.edu/cauetds/64.
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The structural and electronic properties of covalently and non-covalently functionalized graphene are investigated by means of first-principles density-functional-theory. The electronic characteristics of non-covalently functionalized graphene by a planar covalent organic framework (COF) are investigated. The aromatic central molecule of the COF acts as an electron donor while the linker of the COF acts as an electron acceptor. The concerted interaction of donor acceptor promotes the formation of planar COF networks on graphene. The distinctive electronic properties of covalently functionalized fluorinated epitaxial graphene are attributed to the polar covalent C–F bond. The partial ionic character of the C–F bond results in the hyperconjugation of C–F σ-bonds with an sp2 network of graphene. The implications of resonant-orbital-induced doping for the electronic and magnetic properties of fluorinated epitaxial graphene are discussed.
Isolation of single-walled carbon nanotubes (SWNTs) with specific chirality and diameters is critical. Water-soluble poly [(m- phenyleneethynylene)- alt- (p- phenyleneethynylene)], 3, is found to exhibit high selectivity in dispersing SWNT (6,5). The polymer’s ability to sort out SWNT (6,5) appears to be related to the carbon–carbon triple bond, whose free rotation allows a unique assembly. We have also demonstrated the important role of dispersion forces on the structural and electronic stability of parallel displaced and Y-shaped benzene dimer conformations. Long-range dispersive forces play a significant role in determining the relative stability of benzene dimer. The effective dispersion of SWNT depends on the helical pitch length associated with the conformations of linkages as well as π-π stacking configurations.
We have revisited the constructing schemes for a large family of stable hollow boron fullerenes with 80 + 8n (n = 0,2,3,...) atoms. In contrast to the hollow pentagon boron fullerenes the stable structures constitute 12 filled pentagons and 12 additional hollow hexagons. Based on results from density-functional calculations, an empirical rule for filled pentagons is proposed along with a revised electron counting scheme. We have also studied the relative stability of various boron fullerene structures and structural and electronic properties of B80 bucky ball and boron nanotubes. Our results reveal that the energy order of fullerenes strongly depends on the exchange-correlation functional employed in the calculation. A systematic study elucidates the importance of incorporating dispersion forces to account for the intricate interplay of two and three centered bonding in boron nanostructures.
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Venkataraman, Nithya Leela. "Photosensitive Cholesteric Liquid Crystal Materials." Kent State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=kent1248110797.
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Hooper, Thomas J. N. "Solid state nuclear magnetic resonance on quadrupolar nuclei in disordered catalysis based materials." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/101212/.
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The behaviour of a catalyst is intrinsically linked to its structure and, therefore, accurate structural refinements are desired to tune their overall function. Higher functional demands on catalysts systems, require more complex disordered materials which are inherently difficult to characterise with conventional analytical techniques. Solid state NMR is an excellent probe of local order and, hence, is utilised in this thesis for the structural determination of several catalytic related materials. The first direct105 Pd solid state NMR measurements of diamagnetic (K2PdCl6, (NH4)2PdCl6 and K2PdBr6) complexes is reported, thereby introducing an effective 105 Pd chemical shift ranges with respect to the newly proposed 105 Pd chemical shift reference (0.33 M H2PdCl6(aq)). The enormous 105 Pd quadrupolar moment, makes the interaction very sensitive to small structural distortions as demonstrated by the measurable quadrupolar parameters for the three complexes, despite the high symmetry octahedral Pd coordination. The detected deviation from a cubic symmetry, was corroborated by XRD PDF analysis. The 105 Pd quadrupolar parameters are shown to be more sensitive to minute disorder than conventional XRD and other quadrupolar nuclei NMR. Ambient temperature 105 Pd NMR observations of Pd metal determined the Knight shift as K = −3.205 ± 0.006 %, where variations in the 105 Pd Knight shift allowed for detection of defects in the cubic metal structure and for differentiation of Pd nanoparticle sizes. The developed 105 Pd NMR methodology was then applied in a multi-technique structural investigation of doped Pd catalysts, that confirmed the interstitial location of the dopants. The use of the newly developed structure-generation software, supercell, in combination with GIPAW-DFT calculations and solid state NMR, is shown to be a thorough tool for structural determination of disordered materials. The methodology is applied to two phases of the aluminosilicate mullite (3:2 mullite and 2:1 mullite), and provides complete assignment of the 17O,27 Al and 29 Si NMR spectra. The distribution of AlO4/SiO4 sites in the mullite structure is shown to be random, proving the presence of SiO4 moieties in the tritetrahedral (T3O) environments. The observation of said moieties directly contradicts Loewenstein’s avoidance principle. Additionally, a quasi-tetrahedral site with an additional long bond ((Al/Si)O4+1) is discovered and a vacancy adjacent three-coordinated Al site (AlO3[]) is proposed. The findings from this investigation are then applied to the 27 Al MQMAS study of boron doped mullites, providing additional evidence for the AlO3[]motif. A thorough 11 B and 27 Al solid state NMR investigation was undertaken on three series of aluminium borate phases (A9B2, A2B and metastable Al6-xBxO9 (where 1 ≤ x ≤ 3)) with varying Al/B ratios. A solid solution of AlO4 and BO4 tetrahedra was discovered in all three phases (to varying extents), justifying the conflicting compositional/structural reports present in the literature. Differences in the crystallinity of commercially available, sol-gel synthesized, and solid state synthesised A9B2 samples were documented. The solid state NMR study of the disordered phases, A2B and metastable Al6-xBxO9, utilised multiple fields and MQMAS measurements to constrain the simulation of the 1D spectra, which allowed for complete assignment of the structure and corrected previous erroneous reports. An AlO4+1 site, analogous to the discovered mullite environment, is found in both disordered phases.
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Naden, Aaron Benjamin. "Resolving structure-function relations in advanced materials by scanning probe and electron microscopies." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6857/.
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Understanding the links between structural and functional properties is at the heart of materials science and underpins the development of technologically relevant materials. The work presented in this thesis is primarily concerned with development of these links in two distinct material classes by scanning probe and electron microscopies. After a brief overview of the background and instrumentation (Chapters 1 and 2), Chapter 3 concerns the development of structure-function relations in bottom gate, bottom contact organic transistors employing an active layer comprising a blend of diF-TES-ADT and a polystyrene-like binder. These devices are shown to exhibit electrical performances that are competitive with equivalent amorphous Si (a-Si) devices. The nucleation and growth processes of the semiconductor film, leading to the formation of four structurally distinct crystalline diF-TES-ADT regimes, are described, including evidence of layer-by-layer growth when solution processed. These crystalline regimes – or regions of growth – are linked to electrical characteristics by study of a variety of different device components. One of these regions of growth – region D, the 3D crystals – does not appear to have been previously reported for diF-TES-ADT. The structure-function links are enhanced by direct visualisation of the potential drop across the channel of devices using scanning Kelvin probe force microscopy. The different crystalline regimes are rationalised in the context of a first kinetic description of the film formation process, which can be used to make predictions with regards to device optimisation for more commercially viable, shorter channel length devices. In Chapter 4, advanced specimen preparation protocols by means of a focused ion beam instrument are addressed; followed by the applicability, advantages and limitations of electron microscopy for the study of organic transistors, employing electron energy loss spectroscopy. Issues of phase segregation and intermixing are addressed in this context, with a combination of atomic force and electron microscopies proving to be particularly successful. The possibility of identifying different organic materials in the absence of unique elements is explored by investigation of spectroscopic fine structure and plasmon energy analysis using electron energy loss spectroscopy. The ability to assess such issues with nanometre resolution is pivotal to developing a thorough and detailed understanding of this class of device. Chapter 5 considers an entirely separate class of materials, functional metal oxides. An analysis protocol is developed for the quantified assessment of moire fringes arising in scanning transmission electron microscopy. Here, a rigorous and robust mathematical description of the technique is developed and a method for accurate quantification of data is demonstrated. The assessment of strain over large fields of view is investigated and the ability to identify dislocations within crystalline specimens by STEM moire is shown for the first time. Assessment of crystallographic strain over large fields of view with high precision is important for developing structure-function relations of functional oxides since their properties can be carefully controlled by strain engineering. The studies presented here represent an important step forward in understanding this attractive approach.
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Fletcher, Aaron Thomas. "A Study of Alkali-Resistant Materials for Use in Atomic Physics Based Systems." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1506342433540236.
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Manyam, Jedsada. "Novel resist materials for next generation lithography." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1333/.
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Fullerene derivatives have been demonstrated as negative-tone resists for electron beam lithography with impressive capability for high resolution and high plasma etching resistance, due to their carbon-rich nature. Their primary drawback of extremely poor sensitivity has been addressed by implementation of chemical amplification. A three-component chemically amplified negative-tone resist has been developed via the addition of a photoacid generator and a crosslinker to a fullerene derivative. This thesis work presents a significant extension of the previous work. The resists have undergone comprehensive optimisation, and systematic characterisation of electron beam lithography behaviours. In the first part, a systematic study into chemical amplification of negative-tone fullerene resists through variation of resist composition, additive, and resist processing in order to optimise sensitivity, resolution, line width roughness and etch resistance is presented. Sensitivity of sub 10 C/cm2 at 20 keV, half pitch resolution of 20 nm, a minimum sparse feature linewidth of 12 nm, line width roughness of sub 5 nm, and high etch resistance comparable with a commercial novolac resist have been demonstrated. The second part presents the development of a chemically amplified positive-tone fullerene based resists with the advantage of aqueous base solution development. Their lithographic capability is evaluated and discussed.
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Ekstrand, Paul Daniel. "Magnetic relaxation in iron phthalocyanine thin films." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1604875.
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<p> Magnetic relaxation describes the process by which a magnetic system prepared in a non-equilibrium state returns to an equilibrium distribution. Thin film samples of iron phthalocyanine (FePc) are deposited onto heated substrates. Substrates are made of either silicon, or smooth gold on silicon. FePc molecules self-assemble into small crystalline structures. Due to the planar shape of the molecules, iron chains are formed. The length of these chains depends on the deposition temperature of the sample. Here, FePc thin films are saturated in an applied magnetic field of 3 T at low temperatures. The magnetic field is then reduced to 0 T at a rate of either 54 Oe/s or 100 Oe/s. The change of the magnetization at zero-field and constant temperature is recorded over a time interval of 5000 s. A series of 200 nm thick FePc samples are prepared at varying deposition temperatures onto silicon substrates. Based on the separation distance between iron chains, the inter-chain interactions—probably based on dipole interactions—is expected to be small. The intra-chain interactions are modified by the grain size. Using the stretched exponential model, a non-vanishing asymptotic remnant magnetization is found. The value of this asymptote is shown to decay exponentially with measurement temperature, and vanish near 4.5 K. The dynamic response has a peak which becomes higher in temperature with larger grain size up to 180°C, where we expect a phase transition in the thin film morphology. Above 3.2 K, the relaxation time appears activated, but the data is inconclusive at this moment. From these results, we find that both static and dynamic magnetic responses play an important role in FePc thin films in the measured temperature range of 2.5 K to 4.0 K. Asymptotic remnant magnetization, the static variable, is only non-zero below 4 K and importantly depends on the grain size as larger grains tend to make the inter-chain interactions more important.</p>
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Wang, Chien-Lung. "Synthesis and Characterization of C60-Porphyrin Derivatives for Enhanced Photovoltaic Performance through Efficient Charge Generation and Transport." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1301353045.
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Boskovic, Desanka. "Electronic properties of organic semiconductors and low-dimensional materials." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/456582.
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Los semiconductores orgánicos se han convertido en un grupo muy interesante de
materiales por sus buenas propiedades de transporte de carga y aplicaciones tecnológicas
masivas. Entre todos ellos, el rubreno ganó gran interés porque es un semiconductor
orgánico con la movilidad más alta del portador, que puede alcanzar 40cm2=V s
para los agujeros. Aquí ofrecemos una descripción completa de los primeros principios
de las propiedades electrónicas y el acoplamiento electrón-fonón (incluyendo el tipo de
acoplamientos Holstein y Peierls) para los prototipicos cristales de rubreno.
Los materiales de baja dimensionalidad son conocidos por tener propiedades físicas
anisotrópicas y por su baja dimensionalidad, propiedades metálicas y aparición de modulaciones
estructurales, estos materiales se discuten como materiales posibles de CDW. Sin
embargo, el origen real de los CDW en estos materiales nunca ha sido aclarado. Hemos
decidido examinar si alguna inestabilidad de la superficie de Fermi está en el origen de
las modulaciones estructurales en estos compuestos estudiando la estructura electrónica
y calculando la función de Lindhard para varios materiales de baja dimensionalidad.<br>Organic semiconductors became very interesting group of materials because of their
good charge-transport properties and massive technological applications. Among all of
them, rubrene gained grate interest because it is an organic semiconductor with the
highest carrier mobility, which can reach 40cm2=V s for holes. Here we give a full firstprinciples
description of the electronic properties and electron-phonon coupling (including
Holstein and Peierls type of couplings) for the prototypical rubrene crystals. Thereby,
a recipe for circumventing the issue of inaccuracies with low-frequency phonons is presented.
Low dimensional compounds are known for having anisotropic physical properties
and because of their low dimensionality, metallic properties and occurrence of structural
modulations, these compounds are often discussed as possible Fermi surface driven CDW
materials. However, the real origin of the CDWs in these materials has never been
clarified. Thus we have decided to examine if some instability of the Fermi surface is
at the origin of structural modulations in these compounds by studying the electronic
structure and calculating the Lindhard response function for several low-dimensional
materials.
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Bigatti, Marco. "Quantitative studies of the structure and chemistry of materials at the nano- and atomic-scale." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6393/.
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In this thesis electron microscopy was employed to characterise the nanoscale and atomic scale structure and chemistry of organic and inorganic materials. In chapter 4, the thin film morphology of the organic blend of [poly(9,9-dioctylfluorene- co-benzothiadiazole)] (commonly referred as F8BT) and poly[9,9-dioctyfluorene-co- N-(4-butylphenyl)-diphenylamine] (abbreviated as TFB) was investigated, mainly by bright field transmission electron microscopy (BF-TEM). F8BT and TFB are conjugated polymers, which are candidates to replace inorganic semiconductors in many applications because of their simple preparation and processing procedures. The phase separation of the F8BT:TFB blend was investigated at different compositions. Polymer domains were found in the thin film, with sub- micrometer size which varies with concentration. The 1:1 weight ratio sample showed sub-micrometer TFB rich areas in a F8BT matrix, while the 1:4 weight ratio thin film presented F8BT phases, whose areas are mostly below 0.02 μm2, in a TFB layer. Since some electronic applications, especially in optoelectronics, show increased efficiency after addition of quantum dots in the polymer blend, the effect of CdSe quantum dots on the phase separation of the organic blend was investigated together with their effect on the nanoscale morphology. The CdSe quantum dots were found to aggregate in clusters with limited dispersion within the polymer domains, which did not present significantly morphology changes as a consequence of quantum dots (QDs) addition. The atomic structure and chemistry of the inorganic Ba6−3xNd8+2xTi18O54 microwave ceramic was quantitatively investigated in chapter 4, using high resolution scanning transmission electron microscopy (HR-STEM) and electron energy loss spectroscopy (EELS). These materials are an essential part of telecommunication systems, they can be found in components such as resonators and antennas, on account of their high permittivity, temperature stability and the very low dielectric loss at microwave frequencies. The unit cell was refined with sub-Å precision based on extensive data analysis of HR-STEM images and the unit cell structure showed no significant changes as a consequence of changes in composition or cooling rate after annealing. Ba was found to substitute preferentially to specific Nd atomic columns in the structure, and these trends apply across the whole composition range. These results were confirmed by comparisons with image simulations and provided a starting point for improved refinements of X-ray data.
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Beaumont, Nicola L. "Investigating new materials and understanding the ambipolar qualities of organic small molecules for use in organic photovoltaics." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58475/.
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Organic photovoltaics (OPVs) have huge potential for competing with current inorganic photovoltaics in the search for a reliable, renewable source of energy. It is thought that only ~10 % efficiency is necessary for commercialisation and also allows avenues towards flexible, compact, lightweight optoelectronics, with current certified efficiencies already at 12%! Although the current efficiencies have surpassed expectations in order to continue the high progress new materials need to be investigated. Through understanding current materials and utilising new donor and acceptor materials the hopes of achieving higher efficiencies are realistic. Halogenation as a method to modify current organic semiconductors materials has successfully been demonstrated with minimal change to the optical properties. Successful modification of copper phthalocyanines (CuPc) to the fluorinated F16 CuPc derivative resulted in a large change in ionisation potential allowing for its use as an acceptor. This thesis will discuss the modification of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPSEpent) via chlorination in the hopes of achieving a more efficient donor material in single heterojunction devices. Through addition of electron withdrawing groups, the molecular frontier orbitals can be tuned to allow for improved stability towards C60 in solution, larger ionisation potentials which allow for larger interface gaps when used in devices, resulting in improvements in open circuit voltage (Voc), short circuit current (Jsc) and power conversion efficiency. The second part of the thesis will concentrate on the ambipolar qualities of (sub)phthalocyanines and their use as acceptors in conjunction with both the underused acene, tetracene (Chapter 5) and the more widely studied pentacene (Chapter 6). To obtain a strong understanding of using boron subphthalocyanine chloride (SubPc), Cl6-SubPc and ClAlPc as acceptors, UV –Vis absorption, atomic force microscopy (AFM), photoluminescence (PL), photoelectron spectroscopy (PES), space charge limited current (SCLC) theory to gain charge mobilities and devices were explored.
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Alnoor, Hatim. "Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications." Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-141753.
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One-dimensional (1D) nanostructures (NSs) of Zinc Oxide (ZnO) such as nanorods (NRs) have recently attracted considerable research attention due to their potential for the development of optoelectronic devices such as ultraviolet (UV) photodetectors and light-emitting diodes (LEDs). The potential of ZnO NRs in all these applications, however, would require synthesis of high crystal quality ZnO NRs with precise control over the optical and electronic properties. It is known that the optical and electronic properties of ZnO NRs are mostly influenced by the presence of native (intrinsic) and impurities (extrinsic) defects. Therefore, understanding the nature of these intrinsic and extrinsic defects and their spatial distribution is critical for optimizing the optical and electronic properties of ZnO NRs. However, identifying the origin of such defects is a complicated matter, especially for NSs, where the information on anisotropy is usually lost due to the lack of coherent orientation. Thus, the aim of this thesis is towards the optimization of the lowtemperature solution-based synthesis of ZnO NRs for device applications. In this connection, we first started with investigating the effect of the precursor solution stirring durations on the deep level defects concentration and their spatial distribution along the ZnO NRs. Then, by choosing the optimal stirring time, we studied the influence of ZnO seeding layer precursor’s types, and its molar ratios on the density of interface defects. The findings of these investigations were used to demonstrate ZnO NRs-based heterojunction LEDs. The ability to tune the point defects along the NRs enabled us further to incorporate cobalt (Co) ions into the ZnO NRs crystal lattice, where these ions could occupy the vacancies or interstitial defects through substitutional or interstitial doping. Following this, high crystal quality vertically welloriented ZnO NRs have been demonstrated by incorporating a small amount of Co into the ZnO crystal lattice. Finally, the influence of Co ions incorporation on the reduction of core-defects (CDs) in ZnO NRs was systematically examined using electron paramagnetic resonance (EPR).
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Krymowski, Kevin E. "The Effect of Ligand Variation on Two-Dimensional Materials." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1495802952188467.
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Echard, Dalton. "Drying Methods for the Fabrication of Polymer Foam Material." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4096.
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This is a report on the study of the drying of nanoporous polymer foam material fabricated by photolithogtaphic methods. Three drying methods were employed, which were air drying, supercritical drying and freeze drying. After fabrication and drying, physical properties of the polymer foams were measured. These measurements included density of the material, Young’s modulus, surface area, and the shape of the skeletal particles. The measurements determined the effect of the polymer concentration and the effect of drying methods. It was determined that polymer concentration had a much larger effect on the properties of the materials than the drying method.
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Barabanova, Liudmyla. "Frictional Anisotropy of Graphene and Graphene Based Materials." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1461941753.
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Sanzenbacher, Lindsay M. "Raman Spectroscopic Studies of Single Crystal Diamond." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313440154.
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Palme, Jahi. "Investigation of the Addition of Basalt Fibres into Cement." TopSCHOLAR®, 2014. http://digitalcommons.wku.edu/theses/1361.
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Mechanical properties of concrete are most commonly determined using destructive tests including: compression, flexure, and fracture notch specimen tests. However, nondestructive tests exist for evaluating the properties of concrete such as ultrasonic pulse velocity and impact echo tests. One of major issues with concrete (which has cement as its prime ingredient) is that unlike steel it is quasi-brittle material. It tends to want to crack when tensile stresses develop. Fibres have been added to concrete for many years to reduce the amount of and size of cracks cause by temperature changes or shrinkage. In more recent years, significant research has been carried out into the effect of the addition of basalt fibres to cement has on its mechanical strength. As well, developing concrete that is more durable, flexible, stronger, and less permeable than traditional concrete has been explored. It has become important to test and verify improvements that are made to the cement by basalt fibres as well as testing the general strength of concrete to stand up to constant pressure at varied strengths.
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Huzyak, Paige M. "Synthesis and Characterization of Organic-Inorganic Hybrid Materials for Thermoelectric Devices." TopSCHOLAR®, 2016. http://digitalcommons.wku.edu/theses/1600.
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The development of organic-inorganic hybrid materials is of great interest in thermoelectrics for its potential to combine the desirable characteristics of both classes of materials. Thermoelectric materials must combine low thermal conductivity with high electrical conductivity, but in most materials, thermal and electrical conductivity are closely related and positively correlated. By combining the low thermal conductivity, flexibility, facile processing, and low cost of organic components with the high electrical conductivity and stability of inorganic components, materials with beneficial thermoelectric properties may be realized.
Here, we describe the synthesis and characterization of anthracene-containing organic-inorganic hybrid materials for thermoelectric purposes. Specifically, POSS-ANT was synthesized when aminopropylisobutyl-POSS was functionalized with a single anthracene unit via DCC-mediated amide formation. Acrylate-POSS was functionalized with multiple anthracene units in a Heck coupling reaction to synthesize System 1. System 2 was developed through a two-step synthetic process. In the first reaction, (3- acryloxypropyl)methyl dimethyoxy silane was functionalized with anthracene at the 9- position through a Heck coupling reaction. The second reaction was a base-catalyzed solgel process to form polymeric nanoparticles. Finally, System 3 was synthesized through a similar process to System 2, though polymers formed in the initial step. The System 3 precursor was to be developed through a potassium carbonate-catalyzed ether synthesis
from 3-(bromopropyl)trimethoxysilane and 9-anthracene methanol, followed by a basecatalyzed sol-gel process to form nanoparticles. The precursor was never isolated because of premature polymerization during the precursor synthesis step, and polymeric nanoparticles were obtained for System 3 during the sol-gel process. These materials were characterized by TEM to reveal the nanostructures that formed upon evaporation from solution. Future work will focus on the characterization of thermoelectric parameters and incorporation into thermoelectric devices.
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Ball, Molly R. "First Principles Study of Electronic and Magnetic Structures in Double Perovskites." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483702986122186.
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Mishra, Rohan. "First Principles Study of Double Perovskites and Group III-V Compounds." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1345489862.
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Russell, David D. "Design, synthesis, crystal structure and magnetic properties of novel osmium-based B-site ordered double perovskites." Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10011271.
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<p>Transition metal oxides (TMOs) with face centered cubic arrangement of magnetic ions are composed of triangular sub-lattices. When antiferromagnetic (AFM) interactions of the same strengths between all three pathways in triangular settings are in place, spin constraints cannot be fulfilled simultaneously and the system undergoes geometric magnetic frustration (GMF). The purpose of the work presented in this thesis is to better understand the criteria for a system to undergo GMF. To achieve this, the novel B-site ordered double perovskites Ca2ScOsO6 and Ca2.2Mg0.8OsO6 were synthesized in polycrystalline form utilizing the conventional solid-state method. The crystal structure of these compounds were characterized through X-ray diffraction, and magnetic properties were explored through magnetic susceptibility measurements. Employing the spin-dimer analysis method, relative magnetic exchange interactions were calculated and modeled. These novel osmium-based B-site ordered double perovskites were then compared to isostructural compounds to study the effects of the osmium oxidation state on crystal structure and the exhibited properties.
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Fuentes-Hernandez, Canek. "Photorefractive polymer composites with improved operational stability and performance." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280699.
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This dissertation describes advances in the operational stability and performance of polymer composites that used a new hole-transporting polymer matrix, PATPD. Stable operation is achieved when PATPD provides the transport manifold because it prevents the chromophores to act as hole-traps. Operational stability is combined with video-rate compatible response times and large photorefractive nonlinearities, comparable to those obtained with the commonly used hole-transporting polymer PVK. The advances obtained in understanding the impact of chromophore aggregation to the photorefractive properties of such composites will be presented in the framework of a two-trapping site mode. Numerical simulations of the photogenerated current transients and the sensitizer anion build-up will reveal the intricate nature of the trap dynamics when chromophore aggregates can act as hole-traps in a material. Finally, the photorefractive properties of hybrid polymer composites sensitized with CdSe nanoparticles, that currently define the state-of-the-art for the photorefractive performance of this kind of materials, will be presented. The operational stability of hybrid composites is presented for the first time and the limitations to its performance will be analyzed.
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Kim, Myung-Hee Y. "Calculations of the interactions of energetic ions with materials for protection of computer memory and biological systems." W&M ScholarWorks, 1995. https://scholarworks.wm.edu/etd/1539623872.
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Theoretical calculations were performed for the propagation and interactions of particles having high atomic numbers and energy through diverse shield materials including polymeric materials and epoxy-bound lunar regolith by using transport codes for laboratory ion beams and the cosmic ray spectrum. Heavy ions fragment and lose energy upon interactions with shielding materials of specified elemental composition, density, and thickness. A fragmenting heavy iron ion produces hundreds of isotopes during nuclear reactions, which are treated in the solution of the transport problem used here. A reduced set of 80 isotopes is sufficient to represent the charge distribution, but a minimum of 122 isotopes is necessary for the mass distribution. These isotopes are adequate for ion beams with charges equal to or less than 26. to predict the single event upset (SEU) rate in electronic devices, the resultant linear energy transfer (LET) spectra from the transport code behind various materials are coupled with a measured SEU cross section versus LET curve. The SEU rate on static random access memory (SRAM) is shown as a function of shield thickness for various materials. For a given mass the most effective shields for SEU reduction are materials with high hydrogen density, such as polyethylene. The shield effectiveness for protection of biological systems is examined by using conventional quality factors to calculate the dose equivalents and also by using the probability of the neoplastic transformation of shielded C3H10T1/2 mouse cells. The attenuation of biological effects within the shield and body tissues depends on the materials properties. The results predict that hydrogenous materials are good candidates for high-performance shields. Two biological models were used. Quantitative results depended upon model.
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Lai, Chung-Chuan. "Phase Formation of Nanolaminated Transition Metal Carbide Thin Films." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-137367.
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Research on inherently nanolaminated transition metal carbides is inspired by their unique properties combining metals and ceramics, such as higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining the metallic conductivity. The interesting properties are related to their laminated structure, composed of transition-metalcarbide layers interleaved by non-transition-metal (carbide) layers. These materials in thin-film form are particularly interesting for potential applications such as protective coatings and electrical contacts. The goal of this work is to explore nanolaminated transition metal carbides from the aspects of phase formation and crystal growth during thin-film synthesis. This was realized by studying phases in select material systems synthesized from two major approaches, namely, fromdirect-deposition and post-deposition treatment. The first approach was used in studies on the Mo-Ga-C and Zr-Al-C systems. In the former system, intriguing properties have been predicted for the 3D phases and their 2D derivatives (socalled MXenes), while in the latter system, the phases are interesting for nuclear applications. In this work, the discovery of a new Mo-based nanolaminated ternary carbide, Mo2Ga2C, is evidenced from thin-film and bulk processes. Its structure was determined using theoretical and experimental techniques, showing that Mo2Ga2C has Ga double-layers in simple hexagonal stacking between adjacent Mo2C layers, and therefore is structurally very similar to Mo2GaC, except for the additional Ga layers. For the Zr-Al-C system, the optimization of phase composition and structure of Zr2Al3C4 in a thin-film deposition process was studied by evaluating the effect of deposition parameters. I concluded that the formation of Zr2Al3C4 is favored with a plasma flux overstoichiometric in Al, and with a minimum lattice-mismatch to the substrates. Consequently, epitaxial Zr2Al3C4 thin film of high quality were deposited on 4H-SiC(001) substrates at 800 °C. With the approach of post-deposition treatment, the studies were focused on a new method of thermally-induced selective substitution reaction of Au for the non-transition-metal layers in nanolaminated carbides. Here, the reaction mechanism has been explored in Al-containing (Ti2AlC and Ti3AlC2) and Ga-containing (Mo2GaC and Mo2Ga2C) phases. The Al and Ga in these phases were selectively replaced by Au while the carbide layers remained intact, resulting in the formation of new layered phases, Ti2Au2C, Ti3Au2C2, Mo2AuC, and Mo2(Au1-xGax)2C, respectively. The substitution reaction was explained by fast outward diffusion of the Al or Ga being attracted to the surface Au, in combination with back-filling of Au, which is chemically inert to the carbide layers,to the vacancies. The substitution reaction was further applied to Ga-containing nanolaminated carbides, (Cr0.5Mn0.5)2GaC and Mo2GaC, motivated by development of novel magnetic nanolaminates. The former experiment resulted in the formation of (Cr0.5Mn0.5)2AuC, where the retained (Cr0.5Mn0.5)2C layers allowed a comparative study on the magnetic properties under the exchange of Ga for Au. After Au substitution, reduction in the Curie temperature and the saturation magnetization were observed, showing a weakened magnetic exchange interaction of the magnetic (Cr0.5Mn0.5)2 Clayers across the Au. In the Mo2GaC case, an Fe-containing MAX phase, Mo2AC with 50 at.% of Fe on the A site, was synthesized through selective substitution of Au-Fe alloy for the Ga layers, showing the first direct evidence for Fe in the MAX-phase structure. The substitution of Fe did not take place on another Mo2GaC sample tested for Fe exchange only, indicating the essential role of Au in catalyzing the Fe-substitution reaction. The knowledge gained from this thesis work contributes to improved approaches for attaining thin films of nanolaminated transition metal carbides with desired phase composition and crystal quality. The reports on the new nanolaminated phases through exchange interactions are likely to expand the family of nanolaminated carbides and advance their properties, and trigger more studies on related (quasi-) 2D materials.
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Wei, Kaya. "Investigation of Low Thermal Conductivity Materials with Potential for Thermoelectric Applications." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/6049.
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Thermoelectric devices make it possible for direct energy conversion between heat and electricity. In order to achieve a high energy conversion efficiency, materials with a high thermoelectric figure of merit (ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity) are in great demand. The standard approach is to optimize charge carrier transport while at the same time scatter the heat transport, a task that is easier said than done. Improving the electrical properties in order to increase ZT is limited since electrons also carry heat, among other reasons, resulting in higher κ with a higher σ. Low κ materials, whether through complexity or lattice distortion, are therefore of great interest in optimizing the materials’ thermoelectric properties.
In this thesis I will present my investigations on certain material systems that have intrinsically low κ, materials with cage-like or layer-like crystal structure and complex chalcogenides, as well as investigations on nanostructured bulk chalcogenides in order to further lower the κ. In addition, unique transport phenomena that can be described as polaronic-type conduction and lone-pair distortion have been observed in certain materials. This too will be extensively described in this thesis.
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McCausland, Jeffrey A. "Select Applications of Scanning Probe Microscopy to Group XIV Surfaces and Materials." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1510327417528433.
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Lynch, Charlotte Isabella. "First-principles calculations of NMR parameters for materials applications." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:f44b9122-1826-410e-990d-a88dc3bb1432.
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Nuclear magnetic resonance (NMR) is a powerful experimental technique for probing the local environment of nuclei in materials. However, it can be difficult to separate the large number of interactions that are recorded in the resulting spectra. First-principles calculations based on quantum mechanics therefore provide much-needed support for interpreting experimental spectra. In this way, the underlying mechanisms recorded in experimental spectra can be investigated on an atomic level, and trends can be noted with which to guide the direction of future experiments. This thesis presents two cases in which first-principles calculations do just that. The first is an investigation of the perovskite structures of NaNbO<sub>3</sub>, KNbO<sub>3</sub>, LiNbO<sub>3</sub> and the related solid solutions of Na<sub>x</sub>K<sub>1-x</sub>NbO<sub>3</sub>, K<sub>x</sub>Na<sub>1-x</sub>NbO<sub>3</sub> and Li<sub>x</sub>Na<sub>1-x</sub>NbO<sub>3</sub> in order to study how structural disorder affects their NMR parameters. The second investigation involves the calculation of the Knight shift in platinum, palladium and rhodium---in their elemental bulk forms and in a set of surface structures. The Knight shift is a systematic shift in the NMR frequencies of metallic systems. It arises from the hyperfine interaction between the nuclear spins and the spins of the unpaired conduction electrons. When calculating the Knight shift, it is found that the Brillouin zone must be very finely sampled. A discussion of core polarisation is also presented. This is the polarisation of core electrons as a result of their interaction with valence electrons. In the case of Curie paramagnets, core polarisation can have a significant effect on the calculation of hyperfine parameters.
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Armakavicius, Nerijus. "Study of novel electronic materials by mid-infrared and terahertz optical Hall effect." Licentiate thesis, Linköpings universitet, Halvledarmaterial, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-142220.
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Development of silicon based electronics have revolutionized our every day life during the last three decades. Nowadays Si based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, Si cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for a progress in state of the art electronics. Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in the current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene. III-group nitrides have been extensively studied and already have proven their high efficiency as light sources for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for III-group nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions. Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical contact within the structure. Moreover, the use of electrical contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures. The optical Hall effect is an external magnetic field induced optical anisotropy in conductive layers due to the motion of the free charge carriers under the influence of the Lorentz force, and is equivalent to the electrical Hall effect at optical frequencies. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. In principle, a single optical Hall effect measurement can provide quantitative information about free charge carrier types, concentrations, mobilities and effective mass parameters at temperatures ranging from few kelvins to room temperature and above. Further, it was demonstrated that for transparent samples, a backside cavity can be employed to enhance the optical Hall effect. Measurement of the optical Hall effect by generalized ellipsometry is an indirect technique requiring subsequent data analysis. Parameterized optical models are fitted to match experimentally measured ellipsometric data by varying physically significant parameters. Analysis of the optical response of samples, containing free charge carriers, employing optical models based on the classical Drude model, which is augmented with an external magnetic field contribution, provide access to the free charge carrier properties. The main research results of the graduate studies presented in this licentiate thesis are summarized in the five scientific papers. Paper I. Description of the custom-built terahertz frequency-domain spectroscopic ellipsometer at Linköping University. The terahertz ellipsometer capabilities are demonstrated by an accurate determination of the isotropic and anisotropic refractive indices of silicon and m-plane sapphire, respectively. Further, terahertz optical Hall effect measurements of an AlGaN/GaN high electron mobility structures were employed to extract the two-dimensional electron gas sheet density, mobility and effective mass parameters. Last, in-situ optical Hall effect measurement on epitaxial graphene in a gas cell with controllable environment, were used to study the effects of environmental doping on the mobility and carrier concentration. Paper II. Presents terahertz cavity-enhanced optical Hall measurements of the monolayer and multilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed p-type doping for monolayer graphene with a carrier density in the low 1012 cm−2 range and a carrier mobility of 1550 cm2/V·s. For the multilayer epitaxial graphene, n-type doping with a carrier density in the low 1013 cm−2 range, a mobility of 470 cm2/V·s and an effective mass of (0.14 ± 0.03) m0 were extracted. The measurements demonstrate that cavity-enhanced optical Hall effect measurements can be applied to study electronic properties of two-dimensional materials. Paper III. Terahertz cavity-enhanced optical Hall effect measurements are employed to study anisotropic transport in as-grown monolayer, quasi free-standing monolayer and quasi free-standing bilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed a strong anisotropy in the carrier mobilities of the quasi freestanding bilayer graphene. The anisotropy is demonstrated to be induced by carriers scattering at the step edges of the SiC, by showing that the mobility is higher along the step than across them. The scattering mechanism is discussed based on the results of the optical Hall effect, low-energy electron microscopy, low-energy electron diffraction and Raman measurements. Paper IV. Mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect measurements are employed to determine the electron effective mass in an In0.33Ga0.67N epitaxial layer. The data analysis reveals slightly anisotropic effective mass and carrier mobility parameters together with the optical phonon frequencies and broadenings. Paper V. Terahertz cavity-enhanced optical Hall measurements are employed to study the free charge carrier properties in a set of AlGaN/GaN high electron mobility structures with modified interfaces. The results show that the interface structure has a significant effect on the free charge carrier mobility and that the sample with a sharp interface between an AlGaN barrier and a GaN buffer layers exhibits a record mobility of 2332±73 cm2/V·s. The determined effective mass parameters showed an increase compared to the GaN value, that is attributed the the penetration of the electron wavefunction into the AlGaN barrier layer.
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Wu, Kun-Ta. "The Road to Colloidal Self-Replication." Thesis, New York University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614913.
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<p> Self-replication exists everywhere in nature from bacteria to human beings. Several generations of scientists have worked on self-replication in nature. However, a more challenging breakthrough is to self-replicate through lifeless matter, such as colloids. To accomplish this paradigm shift, technically, we need to investigate thermodynamics, kinetics, multi-functionality, mobility, and the formation of specific covalent bonds of DNA-coated colloids. These are the essential studies for realizing colloidal self-replication. </p><p> We present and experimentally test a mean field thermodynamic model for DNA-functionalized colloidal aggregation and find excellent agreement when accounting for the binding configurations between a pair of particles and adding an additional entropic term due to restricted configurations for DNA bound to both surfaces. We study the kinetics of aggregation as a function of DNA coverage and salt concentration over the range: 4 minutes - 79 hours. The fundamental factor is an intrinsic hybridization time for a pair of complementary DNA in solution retarded by Coulomb repulsion, and the entropic search for inter-particle binding configurations. We investigate the flexibility of the DNA colloid system for colloidal architecture by evaluating theoretically and experimentally the number of specific associations each of our colloids can have with its neighbors. In theory, we find that our particles can recognize up to 76 different particles due to intrinsic properties of DNA hybridization and sequence combination while in experiment we confine that up to 40 different particles can be bound. A practical limit is ∼100. To demonstrate the utility of our "polygamous particles," we synthesize a dual-phase material, which by control process forms either gels or liquids at the same temperature. </p><p> "Sticky" particles typically have low mobility. We demonstrate a novel solution to this problem by combining depletion and DNA interactions, and we successfully synthesize crystals and designed hexagon clusters. Finally, we use cinnamate-modified DNA to control formation of specific covalent bonds and develop a new DNA photolithography. We functionalize a patterned area on a gold surface by a controlled UV light pattern.</p>
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Chilkunda, Raghunath 1965. "Fundamental aspects of particulate contamination of tungsten and thermal oxide wafers during chemical-mechanical polishing." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282301.
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Chemical-mechanical polishing (CMP) has emerged as a new processing technique for achieving a high degree of planarity (< 10 μm) for submicron devices in very large scale integrated (VLSI) process technology. Metal as well dielectic films can be planarized using CMP. Polishing of tungsten (W) and interlayer dielectric (SiO₂) films is carried out using alumina (Al₂O₃) based slurries which typically contain acids, complexing and oxidizing agents. One of the challenges of CMP is the effective removal of slurry particles (e.g., Al₂O₃) that are deposited on the wafer (e.g., W) surface during polishing. Control of particulate deposition during CMP as well as the development of post CMP cleaning techniques to remove deposited particles require an understanding of the surface and solution chemistry of the wafers and particles under polishing conditions. In this research, an attempt is made to develop an understanding of the importance of the electrostatic interactions in particle deposition using electrokinetic potential data, particle deposition results from small scale polishing experiments and calculated interaction energies between a particle and wafer surface. The electrokinetic potential of tungsten, thermal oxide (SiO₂) wafers and alumina particles were measured as a function of solution chemistry. The measured electrokinetic potential data was used to calculate the interaction energy between an alumina particle and a wafer (e.g., W) surface using the well known DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.