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Dissertations / Theses on the topic 'Electrope'
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1
Tavener, P. "Electron spectroscopy of electrode materials." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370304.
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Hoffrogge, Johannes Philipp. "A surface-electrode quadrupole guide for electrons." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-155503.
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Ceres, Donato Marino Lewis Nathan Saul Barton Jacqueline K. "Electron transfer at DNA-modified electrodes /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-06202006-113417.
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Koep, Erik Kenneth. "A Quantitative Determination of Electrode Kinetics using Micropatterned Electrodes." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10524.
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Interfacial polarization resistances limit the performance of many thin film solid-state devices, especially at low temperatures. To improve performance, a fundamental understanding of the electrode kinetics that govern interfacial reaction rates must be developed. The goal of this work is to determine site-specific reaction mechanisms and the relative significance of various reactions in order to quantify optimum structural parameters within the cathode microstructure. Key parameters include the length of triple phase boundary (TPB), the quantity of exposed electrolyte/electrode surface, and the ratio of electrolyte to electrode material. These parameters, when studied in a specific system, can be incorporated into broader models, which will encompass the specific conductivity of each component to develop an optimized three-dimensional network.
The emphasis of this work is the systematic control and manipulation of potential cathodic reaction sites in order to develop an understanding of the relative importance of specific reaction sites. Since the physical dimensions of reaction sites are relatively small, an approach has been developed that utilizes micro-fabrication (similar to that used in integrated-circuit fabrication) to produce small and highly controlled microstructures.
Investigations were made into the nature and reactivity of Triple Phase Boundaries (hereafter TPB) through the use of patterned platinum electrodes since only the TPBs are active in these electrodes. After the processing details of micro-fabrication were established for the platinum electrodes, patterned Mixed-Ionic/Electronic Conducting (MIEC) electrodes were fabricated and studied using impedance spectroscopy to determine the contributions from the MIEC surface versus the TPB. Systematically changing the geometry of the MIEC electrodes (thickness and line width) allowed for the determination of the effect of ambipolar transport within the MIEC on the activity of MIEC surfaces versus the TPB. This information is critical to rational design of functionally graded electrodes (with optimal particle size, shape, porosity and conductivity). In addition to experimental studies, representative patterned electrode samples were made available for collaborative studies with surface scientists at other institutions to provide additional techniques (such as Raman Spectroscopy) on the carefully designed and controlled cathode surfaces.
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Kilburger, Sébastien. "Réalisation et caractérisations d'hétérostructures à base de couches minces de LiNbO3 pour des applications en optique intégrée." Limoges, 2008. https://aurore.unilim.fr/theses/nxfile/default/f9760bed-4f20-4c57-8bed-a82d7d55e49f/blobholder:0/2008LIMO4061.pdf.
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Le niobate de lithium (LiNbO3 : LN) est un matériau largement utilisé en optique de par ses propriétés électrooptiques et non linéaires très intéressantes. Il est utilisé en particulier sous forme massive dans les dispositifs actifs tels que les modulateurs électrooptiques. Son utilisation sous forme de couches minces offrirait l’avantage de diminuer fortement la distance inter-électrodes et d’améliorer le facteur de recouvrement entre les champs optique et appliqué tout en facilitant l’intégration et la miniaturisation des dispositifs. Notre travail a consisté, dans un premier temps, à optimiser, à partir des méthodes utilisant les plans d’expériences, les conditions de dépôt par ablation laser de couches minces de LN épitaxiées sur des substrats en saphir. Les caractérisations structurales et microstructurales ont mis en exergue la très bonne qualité cristalline des films réalisés. Ces films d’épaisseur moyenne 150 nm permettent une propagation à faibles pertes (≤1 dB/cm) compatible avec une utilisation en tant que guides d’ondes. Dans un second temps, nous nous sommes intéressés au choix du type d’électrode nécessaire à la conception d’un modulateur électrooptique. Notre choix s’est porté sur le matériau ZnO. Nous avons démontré que les couches de LN étaient épitaxiées sur ZnO lui-même épitaxié sur saphir. Aucun guidage n’a pu être mis en évidence dans l’hétérostructure LN/ZnO/saphir car elle présente des pertes optiques importantes en raison de la valeur trop élevée de la conductivité des films de ZnO (σ ≥ 500 S. M-1). Pour remédier à ce problème, des simulations numériques ont montré que l’utilisation d’une couche de ZnO moins conductrice permettait de diminuer les pertes, une étude de LN/ZnO peu conducteur/saphir (σ < 50 S. M-1) a d’ailleurs mis en évidence une propagation optique. Ainsi, une hétérostructure LN/ZnO peu conducteur/ZnO conducteur/saphir serait une bonne solution pour envisager une modulation électrooptique d’un faisceau lumineuxLithium niobate (LiNbO3: LN) is a widely used optical material due to its interesting electrooptical and non linear properties. LN is particularly used as bulk technology in active devices such as electrooptical modulators. Thin films offer the advantage of strongly decreasing the distance between electrodes and improving the recovering factor of optical and applied fields and allow integration and devices size reduction. Firstly, our work has consisted in optimizing from experimental designs the deposition parameters leading to the elaboration by laser ablation of epitaxially grown lithium niobate films onto sapphire substrate. Structural and microstructural characterizations underline the very high quality of as-grown layers. These ones, exhibiting an average thickness of 150 nm, allow light propagation with low losses (≤1 dB/cm) compatible with the aim of wave guide’s use. Secondly, we focused on the electrode’s choice necessary for the electrooptical modulator conception. ZnO material was chosen. We have demonstrated an epitaxial growth of lithium niobate onto ZnO film itself epitaxially grown onto sapphire. Nevertheless, no guiding mode has been highlighted in LN/ZnO/sapphire heterostructure because of important optical losses attributed to high conductive values (σ ≥ 500 S. M-1) of the ZnO thin layers. To solve this problem, numerical simulations helped us to put forward the necessity of introducing a ZnO low conductive values buffer layer in order to decrease the optical losses. The study of such a structure allowed us to highlight an optical propagation. So, a LN/low conducting ZnO/highly conducting ZnO/sapphire heterostructure would certainly be a suitable solution to envisage the electrooptical modulation of a light beam
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Hamann, Thomas William Lewis Nathan Saul Lewis Nathan Saul. "Interfacial electron-transfer reactions at semiconductor electrodes /." Diss., Pasadena, Calif. : California Institute of Technology, 2007. http://resolver.caltech.edu/CaltechETD:etd-12272004-162841.
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Taylor, M. E. "Substrate and electrode effects in inelastic electron tunnelling spectroscopy." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235265.
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Inelastic Electron Tunnelling Spectroscopy is a powerful and versatile technique for obtaining vibrational densities of states of amorphous materials and adsorbed molecules. The experimental device, or tunnel junction, consists of two metal electrodes separated by a thin (2nm) layer of the material under study. This thesis looks at features in the tunnelling spectrum due to electrode phonons, and also at the effects of substrate roughness on the spectrum. Two coupled linear chains are used to model the vibrational behaviour of joined lattices in order to consider the penetration of phonons of one material into the other; penetration does not occur unless the two chains have very similar properties. Work with Al-I-Al-Pb tunnel junctions confirms the model results, as no sign is seen of lead phonon peaks in the tunnelling spectrum. However, other workers have seen lead peaks in Al-I-Ag-Pb junctions, and invoked phonon penetration in explanation. Microscopic examination of similarly prepared silver films reveals that they are pinholed; and this, it is argued, gives rise to the lead peaks. Results are presented on the magnitudes of electrode phonon structure in tunnelling spectra, and models for the occurrence of these features are reviewed. It is argued, from comparison of the experimental data with bulk self energies from superconducting tunnelling, that the electron-phonon coupling responsible is characteristic of the bulk metal; interaction does not take place in the barrier. This is consistent with the linear chain model. The effects of roughening tunnel junctions with calcium fluoride substrates are studied. Little change is noted with undoped junctions, but investigation of formate-doped junctions confirms the loss in dopant peak intensity seen by other workers and some variation is noticed in the rate of loss of intensity between C-H and CO2 modes. The mechanism which best explains these observations is that roughening encourages penetration of the organic layer by atoms of the top electrode metal.
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Ren, Yan-Ru. "Orbital spin-splitting factors for conduction electrons in lead." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25961.
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A detailed experimental study has been made of the spin-splitting factors ℊc for magnetic Landau levels associated with conduction electrons in extremal orbits on the Fermi surface of lead. This information has been derived from the waveform of the de Haas-van Alphen (dHvA) quantum oscillations in the magnetization of single-crystal lead spheres at temperatures of about 1.2 K and with applied magnetic fields in the range 50-75 kG. A commercial spectrum analyzer has been used to provide on-line values of the harmonic amplitudes in the dHvA waveform, and the values of ℊc have been extracted from the relative strengths of the harmonics.
Serious systematic errors in ℊc can arise on account of waveform distortions caused by the small and subtle difference between the externally applied field H and the magnetizing field B acting on the conduction electrons. In 1981 Gold and Van Schyndel demonstrated that these 'magnetic-interaction' distortions could be suppressed to a large extent by using negative magnetic feedback to make the induction B within the sample be the same as H (or very nearly so). This thesis describes the first in-depth application of the magnetic-feedback technique to the systematic study of any metal. Particular attention has been paid to the effect of sample inhomogeneity, and Shoenberg's treatment of the magnetic interaction in a non-uniform sample has been generalized to include magnetic feedback. This theory accounts well for many features in the experimental data, especially those which remained a puzzle in the earlier work of Gold and Van Schyndel.
Experimental ℊc values are given for the first time for most of the extremal orbits on the lead Fermi surface and for high-symmetry directions of the magnetic field. Indeed these are the most detailed data reported for any polyvalent metal. The ℊc factors for the different orbits and field directions are found to span the range from 0.56 to 1.147. These large net deviations from the free-electron value ℊ₀ = 2.0023 are consequences of the strong spin-orbit and electron-phonon interactions, and an attempt has been made to separate these two contributions to the ℊ-shifts.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Gardel, Emily Jeanette. "Microbe-electrode interactions: The chemico-physical environment and electron transfer." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11185.
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This thesis presents studies that examine microbial extracellular electron transfer that an emphasis characterizing how environmental conditions influence electron flux between microbes and a solid-phase electron donor or acceptor. I used bioelectrochemical systems (BESs), fluorescence and electron microscopy, chemical measurements, 16S rRNA analysis, and qRT-PCR to study these relationships among chemical, physical and biological parameters and processes.Engineering and Applied Sciences
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Seon, Hongsun 1965. "Electrode erosion and arc stability in transferred arcs with graphite electrodes." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=108637.
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Arc stability and erosion behavior were studied on a hollow graphite DC cathode in an argon atmosphere at atmospheric pressure. It was found that the arc stability is associated with the electron emission mode transition of the cathode operation. Estimation of current densities, SEM pictures, Fast Fourier Transform (FFT) of total voltage, and measurement of cathode surface temperature supported this. Stable arcs are in the thermionic emission regime while unstable arcs in the thermofield emission regime. Higher argon gas flow rate is believed to cause the shift of the mode from the thermofield emission to the thermionic emission by increasing the arc root temperature through steepening the thermal gradient at the arc root and increasing ionization phenomena inside the arc. Sharp cathode tip geometry usually leads to the thermionic emission while a rounded tip geometry encourages the thermofield emission. For the unstable arcs, the high voltage fluctuation resulted from the jumping of the arc root between different cathode spots and changes in the arc length. In the stable arcs, however, the voltage was almost constant because of the absence of arc jumping. The standard deviation of the voltage was used as the arc stability indicator and was less than 3 V for the stable arc in this transferred arc system.The erosion rate of the cathode in this work ranged from 0.41 to 2.61 mug/C. At 150 A runs the arc stability strongly influenced the erosion rate; as the arc stability increased, the erosion rate decreased. Higher currents runs (300 and 400 A), however, showed the opposite trend because of the carbon vapor redeposition. The total erosion rates of 150 A runs were separated into the stable (Es) and the unstable (Eu) erosion rate. The Eu was more than 3 times higher in this work. It is believed that the thermofield emission of the unstable arcs produced more erosion because of the higher local heat flux to the cathode spots.
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Papageorgiou, George. "Counting electrons on helium using a single electron transistor." Thesis, Royal Holloway, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415196.
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Lee, Garett Gordon Walter. "Magnetoelectrocatalysis: enhanced heterogeneous electron transfer reactions at modified electrodes, Grätzel cells, and manganese dioxide electrodes." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/2563.
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Magnetoelectrocatalysis is a physical, catalytic process. When magnetic microparticles are incorporated at an electrode surface, increases in current and system efficiency are observed. These enhancements have been observed in both homogeneous and heterogeneous systems. Here, the effects of magnetic fields on three separate, yet related, systems are analyzed: fundamental heterogeneous rate constants at modified electrodes, dye sensitized solar cells (DSSC), and manganese dioxide electrodes for supercapacitor applications.
Previous studies of magnetic field effects on homogeneous systems utilized the cation exchange polymer Nafion and transition metal redox probes, such as tris(bipyridine)ruthenium(II) chloride. At electrodes modified with Nafion films, redox probes experience current enhancement in the presence of a magnetic field. This effect is attributed to increased self exchange, known as Dahms Ruff conduction or hopping between redox species. Here, the impacts of magnetic fields on heterogeneous electron transfer, the electron transfer between the redox probe and solid-state electrode, are demonstrated. A derivative of Nafion, TMODA Nafion is used to study the effect. For transition metal complex redox probes, peak splitting in cyclic voltammagrams are lower for magnetically modified electrodes as compared to analogous nonmagnetic films.
The effects of magnetic modification of DSSCs are analyzed. DSSCs are photoelectrochemical cells (PECs) that convert incident light (photons) to electrical power (electrons). DSSCs, or Grätzel cells, are heterogeneous, excitonic devices which undergo multiple electron transfer reactions to complete this process. For studies here, magnetic modification of the electrodes occurs in the semiconductor layer. Enhancements in current density, fill factor, and power output are observed in variety of systems, both n-type and p-type, on glass and PET substrates, utilizing different magnetic microparticles.
Lastly, the effects of magnetic fields on the electrochemistry of electrolytic manganese dioxide (EMD) electrodes are examined. Manganese dioxide is an abundant, naturally occurring oxide of manganese that is used ubiquitously in alkaline batteries. manganese dioxide; is a complex material, existing, as many transition metal oxides do, in several polymorphs, each with unique properties. For the studies here, the use of manganese dioxide as a capacitor material in mild aqueous systems is considered. In comparison to traditional electrochemical capacitors, manganese dioxide undergoes both non-faradaic and faradaic charge storage. Magnetic field effects look to exploit this faradaic, pseudocapacitant behavior as a mechanism for increasing this power source's energy and power density.
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Bartlett, Philip Lindsay. "Complete numerical solution of electron-hydrogen collisions." Bartlett, Philip Lindsay (2005) Complete numerical solution of electron-hydrogen collisions. PhD thesis, Murdoch University, 2005. http://researchrepository.murdoch.edu.au/225/.
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This thesis presents an extensive computational study of electron-impact scattering and ionisation of atomic hydrogen and hydrogenic ions, which are fundamental to many diverse disciplines, from astrophysics and nuclear fusion to atmospheric physics. The non-relativistic Schrodinger equation describes these collisions, though finding solutions for even hydrogen, the simplest electron-atom collision, has proven to be a monumental task. Recently, Rescigno et al [Science 286, 2474 (1999)] solved this equation in coordinate space using exterior complex scaling (ECS), and presented the first electron-hydrogen differential cross sections for ionisation that matched with experiment without requiring uncontrolled approximation. This method has significant potential for extension to larger collision systems, but its large computational demand has limited its energy range and target configurations, and its application to discrete final-state collisions has been largely unexplored.
Using radically different numerical algorithms, this thesis develops methods that improve the computational efficiency of ECS by two orders of magnitude. It extends the method to calculate discrete final-state scattering cross sections and enhances the target description to include hydrogenic ions and excited initial states. In combination, these developments allow accurate solutions over a broad range of energies and targets, for both scattering and ionisation, including the important near-threshold energy region where accurate calculations have been unavailable. The refined ECS method implemented in this work now offers complete numerical solutions of electron-hydrogen collisions, and its computational efficiency will facilitate its future application to more complex targets. The thesis culminates with the first ab initio quantum mechanical confirmation of ionisation threshold laws for electron-hydrogen collisions [Bartlett and Stelbovics, 2004, Phys. Rev. Lett. 93, 233201], which have resisted confirmation through the complete solution of the Schrodinger equation for more than half a century.
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Anbumony, Kasi Lakshman Karthi Lee Soo-Young. "Analysis and correction of three-dimensional proximity effect in binary E-beam nanolithography." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2006%20Fall/Theses/ANBUMONY_KASI_19.pdf.
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Schäfer-Bung, Boris, and Mathias Nest. "Correlated dynamics of electrons with reduced two-electron density matrices." Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2010/4177/.
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We present an approach to the correlated dynamics of many-electron systems. We show, that the twoelectron reduced density matrix (2RDM) can provide a suitable description of the real time evolution of a system. To achieve this, the hierarchy of equations of motion must be truncated in a practical way. Also, the
computational effort, given that the 2RDM is represented by products of two-electron determinants, is discussed, and numerical model calculations are presented.
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Krecinic, Faruk [Verfasser]. "Ultrafast electron diffraction and imaging using ionized electrons / Faruk Krecinic." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1142155447/34.
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Miller, Nathan A. "Using electron-tunneling refrigerators to cool electrons, membranes, and sensors." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315773.
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Hardy, Thomas M. "Superconductivity with strongly correlated electrons and an electron-phonon interaction." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/34947.
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The effect on the stability of the superconducting phase due the addition of an electron–phonon interaction to a repulsive Hubbard model is studied. Our Hubbard–Fröhlich Hamiltonian includes electron hoping, the on-site Coulomb repulsion, vibrating ions (phonons) and the electron–phonon interaction. A Lang–Firsov transformation is used to integrate out the phonon degrees of freedom. The transformation reduces the model to simple a Hubbard Hamiltonian with an additional long-range electron–electron attraction. A variational Monte Carlo technique, with a projected BCS trial function, is used to investigate the ground state energies of our transformed Hubbard–Fröhlich Hamiltonian. For various electron densities, with a d-wave superconducting order parameter, it is found that the inclusion of the electron-phonon interaction significantly enhances the condensation energy (the energy required to break paired electrons). We show that increasing the strength of the electron-phonon interaction increases the condensation energy. It is also found that even with an infinite on-site repulsion, where the resonating valence bond state cannot exist, the EPI does still lead to a d-wave superconducting state. In addition we examine, analytically, the coexistence of ferromagnetism and superconductivity. Allowing different masses for spin-up and spin-down electrons in a BCS-type Hamiltonian two new branches in the energy spectrum are found. Including a spatially varying order parameter a new expression for the pairing amplitude of finite momentum pairs is derived.
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Bowling, Robert John. "Effects of microstructure on heterogeneous electron transfer at carbon electrodes /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487671108306195.
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DuVall, Stacy Hunt. "Electron transfer kinetics of catechols on modified glassy carbon electrodes /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488199501404497.
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Colla, Massimiliano. "Experiments with a metastable helium atomic trap /." View thesis entry in Australian Digital Theses Program, 2006. http://thesis.anu.edu.au/public/adt-ANU20060828.104229/index.html.
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Hoffrogge, Johannes Philipp [Verfasser], and Peter [Akademischer Betreuer] Hommelhoff. "A surface-electrode quadrupole guide for electrons / Johannes Philipp Hoffrogge. Betreuer: Peter Hommelhoff." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1033270865/34.
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Blum, Richard Alan. "An Electronic System for Extracellular Neural Stimulation and Recording." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16192.
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A system for extracellular neural interfacing that had the capability for stimulation and recording at multiple electrodes was presented. As the core of this system was a custom integrated circuit (IC) that contained low-noise amplifiers, stimulation buffers, and artifact-elimination circuitry. The artifact-elimination circuitry was necessary to prevent the activity of the stimulation buffers from interfering with the normal functioning of the low-noise amplifiers.
The integrated circuits were fabricated in in a 0.35 micron CMOS process. We measured input-referred noise levels for the amplifiers as low as 3.50 microvolts (rms) in the in the bandwidth 30 Hz-3 kHz, corresponding to the frequency range of neural action potentials. The power consumption was 120 microwatts, corresponding to a noise-efficiency factor of 14.5. It was possible to resume recording signals within 2 ms of a stimulation, using the same electrode for both stimulation and recording.
A filtering algorithm to remove the post-discharge artifact was also presented. The filtering was implemented using a field-programmable gate array (FPGA). The filtering algorithm itself consisted of blanking for the duration of the stimulation and artifact-elimination, followed by a wavelet de-noising. The wavelet de-noising split the signal into frequency ranges, discarded those ranges that did not correspond to neural signals, applied a threshold to the retained signals, and recombined the different frequency ranges into a single signal. The combination of the filtering with the artifact-elimination IC resulted in the capability for artifact-free recordings.
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Bao, Yunjuan. "Theoretical study of spin transport in low-dimensional systems." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40687570.
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Henningsson, Anders. "Ion Insertion into Electrode Materials Studied with X-Ray and Electron Spectroscopic Methods." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2002. http://publications.uu.se/theses/91-554-5268-X/.
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Yoon, Kwansik. "The effect of the electrode composition on electron transfer through an electroactive monolayer." Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=771.
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Thesis (M.S.)--West Virginia University, 1999.Title from document title page. Document formatted into pages; contains xi, 96 p. : ill. (some col.) Includes abstract. Includes bibliographical references.
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Euler, Luisa. "Impedance and Stimulation Comfort of Knitted Electrodes for Neuromuscular Electrical Stimulation (NMES) : Influence of electrode construction and pressure application to the electrode." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-23896.
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Neuromuscular electrical stimulation (NMES) is a modality of electrotherapy which is aiming to restore and improve muscle function by injecting small levels of current into the muscle using different types of electrodes. Advantages are seen in using textile electrodes which can be integrated into wearables. Previous research has been done for the development of textile stimulation electrodes. However, the focus has not been on the electrode construction itself. Therefore, the influence of electrode construction parameters of knitted electrodes as well as of the electrode condition, i.e. wet or dry, on the skin-electrode impedance and on the perceived stimulation comfort were analysed. Further, the application of pressure to the electrode was investigated. It was found that the electrode condition is the most important parameter for the electrode performance as a wet electrode showed a lower impedance and an improved stimulation comfort with a better skin contact. Followed by this, the pressure was the second most important factor, especially for dry electrodes. A higher pressure reduced the skin-electrode impedance and improved the skin contact in dry condition. Nevertheless, dry electrodes with a high applied pressure still performed worse than wet electrodes. Regarding the electrode design, the most important factor was the electrode size. A bigger size reduced the impedance. Nevertheless, for the application in NMES, a smaller electrode size is to be preferred as it improved the stimulation selectivity and thus, a lower NMES level was required to induce a plantarflexion without affecting the stimulation comfort. The other investigated construction parameters (binding, yarn density, shape) only showed minor influences on the electrode performance. Therefore, the possibilities of applying pressure to the electrode to improve the performance of dry textile electrodes should be further investigated.
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Green, Stephen John. "Liquid-phase electron transfer on oxocuprate electrodes in the superconducting state." Thesis, University of Exeter, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359552.
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Xafenias, Nikolaos. "Cr(VI) removal in bioelectrochemical systems with electrodes as electron donors." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/363130/.
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Hexavalent chromium (Cr(VI)) is a highly toxic and soluble substance present in a wide range of industrial effluents. An effective treatment method is the biochemical Cr(VI) reduction to the less toxic trivalent chromium (Cr(III)), and such a transformation has recently been demonstrated in bioelectrochemical systems. However, depending on the pH of the catholyte, a biocatalyst might be required in the cathode and also the process can be very much inhibited by Cr(III) products which tend to form on the electrode surface and deactivate it. Herein is demonstrated how an electrophilic bacterium, that is Shewanella oneidensis MR-1, can be used as a bacterial catalyst in Cr(VI) reducing cathodes of bioelectrochemical systems. Starting with potentiostatically controlled experiments (-500 mV vs. Ag/AgCl for 4 h), the abiotic cathode’s (AC) performance was shown to be affected by the Cr(VI)-reduction products that are deactivating the cathode and are severely inhibiting further Cr(VI) reduction. The presence of metal chelators like lactate delayed this deactivating effect and enhanced the system’s performance to a large extent; in the presence of 30 mM lactate, the AC delivered approximately 3 times more electrons to Cr(VI). In addition, approximately 15 times more electrons were delivered when 5 μM of the electron shuttle riboflavin was also added in the AC. However, the presence of riboflavin did not have any effect in the absence of lactate. The MR-1 biocathode also exhibited an enhanced current production and Cr(VI) reduction, though the pre-treatment conditions were found to be important. When pre-treated in an aerated chamber with a poised electrode at +300 mV vs. Ag/AgCl, the MR-1 biocathode mediated 70% more electrons than the AC with 30 mM lactate, and only 39% more electrons when the electrode was initially poised at -500 mV vs. Ag/AgCl. Cr(VI) reduction was also enhanced, with a decrease in concentration over the 4 h operating period of 9 mg L-1 Cr(VI) in the aerobically pretreated MR-1 chamber, compared to only 1 and 3 mg L-1 in the AC without lactate and in the AC with 30 mM lactate respectively. On the other hand, when pre-treated anaerobically in the presence or absence of Cr(VI), the performance of the MR-1 biocathode was not much different than that of the AC with 30 mM lactate. The positive effect of lactate was further demonstrated in microbial fuel cell (MFC) cathodes, where maximum power densities produced were up to 44 times the power densities reported elsewhere for abiotic cathodes (8.8 mW m-2 vs. 0.2 mW m-2 at pH 7) and at similar levels to the power densities of biotic cathodes at pH 6 and 7. Considerable Cr(VI) reduction was also observed at alkaline pH abiotic cathodes and maximum power densities were 31 times the ones reported elsewhere for biotic cathodes at pH 8 (21.4 mW m-2 vs. 0.7 mW m-2). In MFCs, the presence of MR-1 enhanced the performance of pH 7 cathodes; in the presence of 30 mM lactate, the MR-1 biocathode bioelectrochemically reduced 3 times the amount of Cr(VI) reduced by the AC with the same amount of lactate. Compared to the results in the absence of an electrode, the MFC results suggested that different Cr(VI) reduction pathways could be utilised by MR-1 when the electron donor is in the poised electrode form rather than in the lactate form. In conclusion, effective and continuous Cr(VI) reduction with associated current production were achieved when MR-1 and lactate were both present in the biocathodes.
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Moreira, Leandro Malard. "Raman spectroscopy of graphene:: probing phonons, electrons and electron-phonon interactions." Universidade Federal de Minas Gerais, 2009. http://hdl.handle.net/1843/ESCZ-7ZFGDY.
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Since the identification of mono and few graphene layers in a substrate in 2004, intensive work has been devoted to characterize this new material. In particular, Raman spectroscopy played an important role in unraveling the properties of graphene systems. Moreover resonant Raman scattering (RRS) in graphene systems was shown to be an important tool to probe phonons, electrons and electronphononinteractions. In this thesis, by using different laser excitation energies, we obtain important electronic and vibrational properties of mono- and bi-layer graphene. For monolayer graphene, we determine the phonon dispersion near the Dirac point for the in-plane transverse optical (iTO) mode and the in-plane longitudinal acoustic (iLA) mode. These results are compared with recent theoretical calculations for the phonon dispersion around the K point. For bilayer graphene we obtain the Slonczewski-Weiss-McClure band parameters. These results show that bilayer graphene has a strong electron-hole asymmetry, which is larger than in graphite. In a gating experiment, we observe that the change in Fermi level of bilayer graphene gives rise to a symmetry breaking, allowing the observation of both the symmetric (S) and anti- symmetric (AS) phonon modes. The dependence of the energy and damping of these phonons modes on the Fermi level position is explained in terms of distinct couplings of the S and AS phonons with intraand inter-band electron-hole transitions. Our experimental results confirm the theoretical predictions for the electron-phonon interactions in bilayer graphene. We also study the symmetry properties of electrons and phonons in graphene systems as a function of the number of layers, by a group theory approach. We derive the selection rules for the electron-radiation and for the electron-phonon interactions at all points in the Brillouin zone. By considering these selection rules, we address the double resonance Raman scattering process. The selection rules for monolayer and bilayer graphene in the presence of an applied electric field perpendicular to the sample plane are also discussed.Desde a identificação de uma ou poucas camadas de grafeno em um substrato em 2004, trabalhos intensivos tem sido feitos para se caracterizar esse novo material. Em particular, a Espectroscopia Raman Ressonante tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. A Espectroscopia Raman Ressonante também tem se mostrado como uma ferramenta importante para se estudar fônons, elétrons e interações elétron-fônon em grafeno. Nesta tese, ao usarmos diferentes energias de laser de excitação, nós obtivemos propriedades importantes sobre as estruturas eletrônicas e vibracionais para uma e duas camadas de grafeno. Para uma monocamada de grafeno, nós determinamos a dispersão de fônons perto do ponto de Dirac para o modo óptico transversal no plano (iTO) e para o modo acústico longitudinal no plano (iLA). Comparamos nossos resultados experimentais como cálculos teóricos recentes para a dispersao de fônons nas proximidades do ponto K. Para a bicamada de grafeno, nós obtivemos os parâmetros de estrutura eletrônica do modelo de Slonczewski-Weiss-McClure. Nossos resultados mostram que a bicamada de grafeno possue uma forte assimetria elétron-buraco, que por sua vez é mais forte que no grafite. Em experimentos aplicando uma tensão de porta, variamos o nível de Fermi em uma bicamada de grafeno, o que levou uma quebra de simetria, deixando assim ambos os modos de vibração simétricos (S) e anti-simétricos (AS) ativos em Raman. A dependência da energia e do amortecimento desses modos de fônons com a energia de Fermi é explicada através do acoplamento elétron-buraco intra- ou inter- banca. Nossos resultados experimentais deram suporte às previsões teóricas para interações elétron-fónon em uma bicamada de grafeno.
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Smith, Neil Ronald. "USING ELECTRON BEAM LITHOGRAPHY TO MAKE ELECTRODES FOR SINGLE MOLECULE ELECTRONICTS." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1123213432.
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Siedlein, Rupert V. "A search for excited electrons in electron-proton collisions at HERA /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487854314871133.
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Chen, Peihong. "Effects of surface chemistry on electron transfer kinetics at carbon electrodes /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487935573773327.
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Dogbe, John Kofi. "Comparing cluster and slab model geometries from density functional theory calculations of si(100)-2x1 surfaces using low-energy electron diffraction." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258835.
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Barron, Olivia. "Gas diffusion electrodes for high temperature polymer electrolyte membrane fuel cells membrane electrode assemblies." University of the Western Cape, 2014. http://hdl.handle.net/11394/4323.
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Philosophiae Doctor - PhDThe need for simplified polymer electrolyte membrane fuel cell (PEMFCs) systems, which do not require extensive fuel processing, has led to increased study in the field of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) applications. Although these HT-PEMFCs can operate with less complex systems, they are not without their own challenges; challenges which are introduced due to their higher operation temperature. This study aims to address two of the main challenges associated with HT-PEMFCs; the need for alternative catalyst layer (CL) ionomers and the prevention of excess phosphoric acid (PA) leaching into the CL. The first part of the study involves the evaluation of suitable proton conducting materials for use in the CL of high temperature membrane electrode assemblies (HT-MEAs), with the final part of the study focusing on development of a novel MEA architecture comprising an acid controlling region. The feasibility of the materials in HT-MEAs was evaluated by comparison to standard MEA configurations.
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Marikkar, Fathima Saneeha. "Molecular Design of Electrode Surfaces and Interfaces: For Optimized Charge Transfer at Transparent Conducting Oxide Electrodes and Spectroelectrochemical Sensing." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193952.
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This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.
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Myedi, Noluthando. "Electrochemical kinetics and sensing of conjugated dienes in acetonitrile." University of the Western Cape, 2011. http://hdl.handle.net/11394/5424.
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>Magister Scientiae - MScThis thesis focuses on the electroanalysis of some dienes (2-methyl-1.3-butadiene (MBD), tran-1.3-pentadiene (PD), 1.3-cyclohexadiene (CHD) and 3-cyclooctadiene (COD)) found in gasoline and the development of simple electrochemical diene sensors. The detection of dienes in fuels is important as they readily polymerise and form gum in fuel tanks. The electroctivity of the dienes was studied with glassy carbon electrode (GCE) and Pt electrode in tetrabutylammonium perchlorate (TBAP)/acetonitrile solution. Polyaniline-polystyrene sulfonic acid (PANi-PSSA) composite films were electro-deposited or drop-coated on GCE, with and without gold nanoparticles (AuNPs) and characterized by cyclic voltammetry (CV), high resolution transmission electron microscopy (HRTEM) and ultraviolet-visible (UV-vis) spectroscopy. Both composite polymers were found to be of nanofibral structure, and the spherical gold nanoparticles were dispersed uniformly within the polymer. The dienes exhibited no redox peaks on GCE/PANi-PSSA and GCE/PANi-PSSA/AuNPs electrode systems from -1.0 V to +1.5 V, beyond which PANi would overoxidize and lose its electroactivity. Therefore, cyclic voltammetry and steady state amperometry of the four dienes (MBD, PD, CHD and COD) were studied with unmodified Pt and GCE electrodes. Subtractively normalised interfacial-fourier transform infra-red (SNIFTIR) spectroscopic studies of the dienes were performed with Pt electrode. SNIFTIR data showed that there was a definite electro-oxidation of 1.3-cyclohexadiene as electrode potential was changed from E = 770 mV to E = 1638 mV. Severe electrode fouling was observed when steady state amperometric detection of CHD, as a representative diene, was performed on Pt electrode. Randel-Sevčik analysis of the CVs of the dienes on Pt electrode gave diffusion coefficient (Dox) values of 10.65 cm²/s, 9.55 cm²/s, 3.20 cm²/s and 3.96 cm²/s for CHD, COD, PD, and MBD, respectively. The corresponding detection limits (3σn-1) were 0.0106 M, 0.0111 M, 0.0109 M, and 0.0107 M.
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Ho, Wah On. "Direct electron transfer peroxidase enzyme electrodes and their application to electrochemical immunoassay." Thesis, University of Newcastle Upon Tyne, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384829.
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Bao, Yunjuan, and 暴云娟. "Theoretical study of spin transport in low-dimensional systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687570.
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Singh, Kanwardeep. "A comparison of electrode recruitment characteristics and muscle fatigue using intramuscular and nerve trunk electrodes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37980.pdf.
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Santana-Aguiar, Francisco Aurelio. "Characterisation of electrode microarrays produced photolithographically and with thiol self-assembled monolayers on gold electrodes." Thesis, Durham University, 2009. http://etheses.dur.ac.uk/45/.
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The macroscale electrochemical theory breaks down with microstructures smaller than the dimensions of the diffusion layer, showing that such electrodes have significant quantitative effects and qualitative advantages. The great advantage of microelectrodes over macroelectrodes is the minimisation of interference, which gives rise to much lower detection limits. Microelectrodes have much reduced ohmic drops and capacitive effects and can be used in the absence of supporting electrolyte. These features have opened a growing interest in the fabrication and application of microelectrodes in various areas. There are different microelectrode geometries, but disc type is the most used. Microelectrode arrays have been proposed as a way of increasing the magnitude of the current (produced for a single microelectrode), while maintaining the advantages of the single microelectrode. Although the inlaid microdisc microelectrode can be considered as one the most popular microelectrode geometry, there is also a need to consider conical recessed, recessed and protruding microdiscs as photolithographic microfabrication techniques often result in non-ideal geometries. It has been proved using surface imaging techniques such as scanning Kelvin nanoprobe (SKN), scanning electron microscopy (SEM) and white light interferometer microscopy that conical recessed electrodes with gradient potential along the recessed walls are formed during standard photolithographic methods for producing microelectrode arrays. Microarrays are ubiquitously used for high-throughput measurements using various signal transduction techniques. Ideally each sensor in a microarray platform should perform optimally to ensure an error free response. In this thesis, a simple method for designing a microelectrode array platform (MEA) is described, allowing a ‘defective’ cluster of sensing arrays to be easily identified. It is possible to extend this concept for multiple analyses on a single chip. Molecular electronic is a promising technology which would be an alternative. The concept of molecular electronics is the use of single molecules or arrays, or layers of molecules for the fabrication of electronic components such as wires, switches, and storage elements. Indeed, functionalised thiol monolayer-based microelectrode array may provide unique possibilities, facilitating electrochemical measurements involving electron transfer via electron tunnelling. The conjugated structure of rigid, linear molecule increases greatly the rate of electron transfer across the monolayer. Charge transfer and self-assembly characteristics of novel fully conjugated molecules molecular wires (synthesised at the Department of Chemistry and Centre for Molecular and Nanoscale Electronics, Durham University) assembled on flat gold electrodes are evaluated using Marcus model of electron-transfer and tunnelling theory. The behaviour of these wires is compared with heptanethiol and dodecanethiol SAMs. A preliminary study for application of self-assembled monolayer of molecular wires in microelectrode arrays for multiple analyses on a single chip has been successfully reached.
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Rykaczewski, Konrad. "Electron beam induced deposition (EBID) of carbon interface between carbon nanotube interconnect and metal electrode." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31773.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Dr. Andrei G. Fedorov; Committee Member: Dr. Azad Naeemi; Committee Member: Dr. Suresh Sitaraman; Committee Member: Dr. Vladimir V. Tsukruk; Committee Member: Dr. Yogendra Joshi. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Charoensirithavorn, Patcharee. "Studies on electron transport process in one-dimensional nanostructured electrode for dye-sensitized solar cells." Kyoto University, 2009. http://hdl.handle.net/2433/126415.
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Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第14966号
エネ博第209号
新制||エネ||46(附属図書館)
27404
UT51-2009-M880
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)准教授 佐川 尚, 教授 八尾 健, 教授 尾形 幸生
学位規則第4条第1項該当
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Cass, Michael Jeaffreson. "Simulations of electron transport at semiconductor electrodes and in dye sensitised solar cells." Thesis, University of Bath, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425886.
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Harper, Alice C. "Modified Electrodes for Amperometric Determination of Glucose and Glutamate Using Mediated Electron Transport." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28098.
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The main goal of this research was to develop an easy to prepare and sensitive biosensor that would be able to detect glutamate in solution using ionic self-assembly methods. This was accomplished by preparing an ionically-self-assembled monolayer that included an electron transport mediator and an enzyme that would generate a current proportional to the concentration of analytes in solution. Biosensors were produced for the detection of glucose and glutamate.
Ferrocene poly(allylamine) (FePAA) was assembled on negatively charged self-assembled monolayer and shown to be electrostatically bound by cyclic voltammetry. Model films were made of FePAA and poly(styrenesulfonate) to determine if multilayer films could be assembled using electrostatic assembly. These experiments demonstrated that 7 bilayers is the maximum number of bilayers oxidizable by the heterogeneous reaction at the electrode surface.
ISAMs were then assembled on a 2 mm gold electrode and on a gold fiber microelectrode using FePAA and glucose oxidase. Using cyclic voltammetry, these ISAMs were shown to be able to oxidize glucose in solution. The LOD was determined to be lower for the microelectrode than for the 2 mm gold electrode, which was expected, while both compared well to the literature. The Km? were found to be smaller than other glucose biosensors while the Icat increased with increasing number of bilayers. This demonstrated that the GluOx is making good electrical contact with the layer below. These glucose oxidase ISAMs, however, do not exhibit structural stability in flow-injection experiments.
As a solution to the ISAM modified electrodes degrading in the flowing system, a covalently modified surface was developed. Using cyclic voltammetry, these covalently modified surfaces were shown to be able to oxidize glucose in solution. The LOD of the covalently modified 2 mm gold electrode was calculated to be lower than the 2 mm ISAM modified gold electrode, due to the fast heterogeneous kinetics on the covalently modified electrode surface. The Km? and Icat for the covalently modified 2 mm gold electrode were found to be the similar to the 2 mm ISAM modified gold electrode indicating that the covalently modified electrodes will be a suitable replacement. The covalently modified surfaces exhibit excellent structural stability and detect much lower glucose amounts in flow-injection experiments.
ISAMs were subsequently assembled on gold fiber microelectrodes using FePAA and glutamate oxidase. Glutamate was able to be detected in solution at biologically significantly quantities using cyclic voltammetry. The Km? was shown to be comparable to literature values and Icat was shown to increase with increasing number of bilayers. These results demonstrate that an ISAM constructed using FePAA/GlutOx is a feasible way to detect glutamate in a system.Ph. D.
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Emanuelsson, Christian. "Scanning Electron Microscopy study of Macbat regeneration effect on lead-acid battery electrodes." Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-27971.
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Electrodes from lead-acid batteries were studied using scanning electron microscopy and energy dispersive spectroscopy. This to observe the effects of cycling on the batteries and how a capacity recovery process, known as Macbat regeneration, affected the active material with focus on hard sulphation. First, two new batteries were cycled for two months and electrodes from them were studied when the batteries were new, cycled, fully charged after cycling and regenerated after cycling. Then electrodes from a separate battery that had been used in industry was studied prior to and after Macbat regeneration. On the cycled batteries it was found that after the cycling of the batteries no hard sulphation were present on the electrodes. The study of the separate battery showed that the battery had hard sulphation in its electrodes and that the Macbat regeneration was able to remove hard sulphation both on the surface of the electrodes and also inside the active material.Elektroder från bly syra batterier studerades med hjälp av svepelektronmikroskopi och energidispersiv spektroskopi. Detta för att observera effekterna av cykling på batterierna och hur en process för kapacitet återhämtning, kännd som Macbat regenerering, påverkade det aktiva materialet med fokus på hård sulfatering. Först blev två nya batterier cyklade i två månader och elektroder från dem studerades när batterierna var nya, cyklade, fulladdade efter cykling och regenererade efter cykling. Sedan studerades elektroder före och efter Macbat regenerering från ett separat batteri som hade använts i industri. På de cyklade batterierna fann man att efter cyklingen av batterierna fanns ingen hård sulfatering på elektroderna. Studien av det separata batteriet visade att batteriet hade hård sulfatering i elektroderna och att Macbat regenereringen kunde ta bort hård sulfatering både på ytan och även inne det aktiva materialet.
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Blidberg, Andreas. "Iron Based Materials for Positive Electrodes in Li-ion Batteries : Electrode Dynamics, Electronic Changes, Structural Transformations." Doctoral thesis, Uppsala universitet, Strukturkemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-317014.
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Li-ion battery technology is currently the most efficient form of electrochemical energy storage. The commercialization of Li-ion batteries in the early 1990’s revolutionized the portable electronics market, but further improvements are necessary for applications in electric vehicles and load levelling of the electric grid. In this thesis, three new iron based electrode materials for positive electrodes in Li-ion batteries were investigated. Utilizing the redox activity of iron is beneficial over other transition metals due to its abundance in the Earth’s crust. The condensed phosphate Li2FeP2O7 together with two different LiFeSO4F crystal structures that were studied herein each have their own advantageous, challenges, and scientific questions, and the combined insights gained from the different materials expand the current understanding of Li-ion battery electrodes. The surface reaction kinetics of all three compounds was evaluated by coating them with a conductive polymer layer consisting of poly(3,4-ethylenedioxythiophene), PEDOT. Both LiFeSO4F polymorphs showed reduced polarization and increased charge storage capacity upon PEDOT coating, showing the importance of controlling the surface kinetics for this class of compounds. In contrast, the electrochemical performance of PEDOT coated Li2FeP2O7 was at best unchanged. The differences highlight that different rate limiting steps prevail for different Li-ion insertion materials. In addition to the electrochemical properties of the new iron based energy storage materials, also their underlying material properties were investigated. For tavorite LiFeSO4F, different reaction pathways were identified by in operando XRD evaluation during charge and discharge. Furthermore, ligand involvement in the redox process was evaluated, and although most of the charge compensation was centered on the iron sites, the sulfate group also played a role in the oxidation of tavorite LiFeSO4F. In triplite LiFeSO4F and Li2FeP2O7, a redistribution of lithium and iron atoms was observed in the crystal structure during electrochemical cycling. For Li2FeP2O7, and increased randomization of metal ions occurred, which is similar to what has been reported for other iron phosphates and silicates. In contrast, triplite LiFeSO4F showed an increased ordering of lithium and iron atoms. An electrochemically induced ordering has previously not been reported upon electrochemical cycling for iron based Li-ion insertion materials, and was beneficial for the charge storage capacity of the material.
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Bao, Yunjuan. "Resonant spin Hall effect in two-dimensional electron systems." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B34627819.
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Gould, Timothy John, and n/a. "Correlation and Response in Spherical Many-Electron Systems." Griffith University. School of Science, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030818.125106.
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Ab initio prediction of the electronic properties of solids is traditionally performed using groundstate Density Functional Theory. These methods are unreliable however, for a class of important problems involving weak attractive forces. These problems include (i) the energetics of hydrogen storage and metal interactions in graphene, (ii) cohesion properties of some polymer systems and (iii) possibly, the weak hydrophobic forces in biomolecules. For these cases a more powerful method than groundstate DFT are timedependent DFT (tdDFT) methods related to the Random-Phase Approximation (RPA). All of these methods proceed by looking at the dynamic density-density response function, whose long-ranged properties naturally lead to the weak forces referred to above. In this thesis we have tested these ideas by investigating electronic response and correlation on the predicted properties of spherical atoms. We have developed and tested a variety of approximations to the timedependent response function through approximations of the tdDFT class and a new method involving greater self-consistency in the screening equation, the inhomogenous STLS approach. Through the development of new methods and computer code, we have solved the response equation allowing us to test our approximations on atoms. Calculation of certain dynamic and static properties of a variety of atoms within our approximations generally agree well with known results. In this thesis we have calculated excitation energies of Helium, dipole polarisabilities and C6 van der Waals (vdW) coefficients of a variety of atoms, and groundstate correlation energies Ec of some atoms. The excitation spectra of Helium generated in our new PGG+c approximation are in good agreement with experiment. The dipole polarisabilities are generally in good agreement with known results, with the exception of Magnesium, Beryllium and Sodium. The C6 coefficients are a little poorer with the exception of Helium where they are nearly exact. Correlation energies are generally reasonable in the PGG+c approximation although they are considerably less accurate than the other properties we have calculated for all atoms other than He. The ISTLS correlation energy of Helium is within 5% suggesting that this method may perform well for larger atoms where our present numerical techniques require improvement. These generally positive results suggest that the approximations we have developed may be applied to more complicated systems such as those described above with good results.
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El, Barraj Ali. "Growth and electro-thermomigration on semiconductor surfaces by low energy electron microscopy." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0393.
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Dans ce mémoire sont abordées quelques études sur la croissance, l'électromigration et la thermomigration de la surface des semiconducteurs tels que le Ge(111), le Si(100) et le Si(111). Sur le plan expérimental, la Microscopie à Electrons Lents (LEEM) nous a permis d'accéder à la dynamiques des phénomènes in situ et en temps réel. Nous étudions l'électromigration et la thermomigration sur la surface de Si(100) qui présente deux reconstructions de surfaces (2x1) et (1x2) selon l'orientation des dimères. Nous montrons que l'anisotropie de diffusion peut affecter le sens de mouvement des nanostructures (trous et îlots). Nous étudions aussi l'électromigration et la thermomigration sur la surface de Si(111). Nous montrons que les trous (1x1) dans la phase (7x7) bougent dans le sens opposé au courant électrique, et dans le même sens du gradient thermique. Nous avons obtenu la charge effective et le coefficient de Soret des atomes de Si en présence d'un courant électrique et d'un gradient thermique. Enfin est abordée l'étude de la nucléation, la croissance et la coalescence dynamique de gouttelettes d'Au sur la surface d'Au/Ge(111), ainsi que l'électromigration des domaines 2D d'Au/Ge(111)-(√3x√3) dans la phase (1x1)This thesis is focused on the study of the growth, electromigration and thermomigration of nanostructures on the surface of semiconductors such as Si(100), Si(111) and Ge(111). On an experimental viewpoint, Low Energy Electron Microscopy (LEEM) allows us to access to the dynamics of the phenomena in situ and in real time. We have studied under electromigration and thermomigration the motions of 2D monoatomic holes and islands on the Si (100) surface. We have shown that diffusion anisotropy due to (2x1) and (1x2) surface reconstructions can affect the direction of motion of nanostructures. We have also studied electromigration and thermomigration of Si (111) surface. We show that 2D-(1x1) holes in the (7x7) phase move in the direction opposite to the electric current, while in the direction of the thermal gradient. We have obtained the effective charge and the Soret coefficient of Si atoms in presence of an electric current and a thermal gradient. At last, the nucleation, growth and dynamic coalescence of Au droplets on Au/Ge(111) surface is studied, and the electromigration of 2D Au/Ge(111)-( √3x√3) domains on Au/Ge(111)-(1x1) surface