Дисертації з теми "Surface traps"
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1
Allcock, David Thomas Charles. "Surface-electrode ion traps for scalable quantum computing." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559722.
Анотація:
The major challenges in trapped-ion quantum computation are to scale up few-ion experiments to many qubits and to improve control techniques so that quantum logic gates can be carried out with higher fidelities. This thesis re- ports experimental progress in both of these areas. In the early part of the the- sis we describe the fabrication of a surface-electrode ion trap, the development of the apparatus and techniques required to operate it and the successful trap- ping of 40Ca+ ions. Notably we developed methods to control the orientation of the principal axes and to minimise ion micromotion. We propose a repumping scheme that simplifies heating rate measurements for ions with low-lying D levels, and use it to characterise the electric field noise in the trap. Surface-electrode traps are important because they offer a route to dense integration of electronic and optical control elements using existing microfabrication technology. We explore this scaling route by testing a series of three traps that were microfabricated at Sandia National Laboratories. Investigations of micromotion and charging of the surface by laser beams were carried out and improvements to future traps are suggested. Using one of these traps we also investigated anomalous electrical noise from the electrode surfaces and discovered that it can be reduced by cleaning with a pulsed laser. A factor of two de- crease was observed; this represents the first in situ removal of this noise source, an important step towards higher gate fidelities. In the second half of the thesis we describe the design and construction of an experiment for the purpose of replacing laser-driven multi-qubit quantum logic gates with microwave-driven ones. We investigate magnetic-field-independent hyperfine qubits in 40Ca+ as suitable qubits for this scheme. We make a design study of how best to integrate an ion trap with the microwave conductors required to implement the gate and propose a novel integrated resonant structure. The trap was fabricated and ions were successfully loaded. Single-qubit experiments show that the microwave fields above the trap are in excellent agreement with software simulations. There are good prospects for demonstrating a multi-qubit gate in the near future. We conclude by discussing the possibilities for larger-scale quantum computation by combining microfabricated traps and microwave control.
2
Ge, Yufei S. M. Massachusetts Institute of Technology. "Microfabrication of surface electrode ion traps for quantum manipulation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99280.
Анотація:
Thesis: S.M., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 123-132).
Trapped ions are a promising approach to quantum computation. This approach uses a qubit state which is the atomic state and quantum motional state of a trapped ion to encode information, and uses laser-ion interactions to manipulate the qubit state. A major obstacle to the realization of a practical ion trap quantum computer is decoherence. In trapped ion quantum computation experiments, decoherence is dominated by the uncontrolled heating of ion motional states. In this thesis, we present the detailed microfabrication of several series of surface electrode linear Paul traps made from different electrode materials, followed by the ion motional heating experiment results for these traps. We demonstrate that the ion motional heating strongly depends on fabrication process. In particular, we explore how grain size and grain orientation affect the ion motional heating rate. This thesis is divided into two parts. In the first part, we describe the fabrication of gold, silver, aluminum and niobium traps from different processes, which results in various surface morphologies and grain structures. Ion motional heating rate measurements are then conducted both at cryogenic temperatures and at room temperature. We employ a physical model based on the fluctuating patch potential theory to explain the ion heating behavior. We use gold traps to study the temperature and frequency dependence of the ion heating. We use aluminum traps to study the ion heating dependence on the amorphous dielectric layer. And we use silver traps to study the ion heating dependence on the grain structure. These results suggest that excess ion heating could possibly be suppressed by suitable fabrication selection. In the second part, we present the process of using SU8 to fabricate a multilayer surface electrode point Paul trap, which has the advantage of allowing ion height variation within the same trap and enables testing of the distance dependence of ion heating.
by Yufei Ge.
S.M.
3
Longobardi, Giorgia. "GaN high-voltage transistors : an investigation of surface donor traps." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708516.
4
Meyer, David Thomas. "Design of superconducting transmission line integrated surface-electrode ion-traps." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66036.
Анотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 85-87).
We fabricated superconducting surface electrode ion traps with integrated microwave coplanar waveguides using direct-write optical lithography and a niobium on sapphire process. We then tested these traps in a closed cycle cryostat and used 28 mW of microwave power to excite rotational transitions of trapped strontium chloride molecular ions. We expected that driving these rotational transitions would heat a co-trapped strontium atomic ion cloud. However, we did not see this heating and we must conduct further experiments.
by David Thomas Meyer.
S.M.
5
Blight, S. R. "Surface and bulk traps in materials and devices for GaAs integrated circuits." Thesis, Cardiff University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383250.
6
Navickas, Tomas. "Towards high-fidelity microwave driven multi-qubit gates on microfabricated surface ion traps." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/79060/.
7
Lachenmyer, Nathan S. (Nathan Scott). "Measurements of electric field noise and light-induced charging in cryogenic surface electrode ion traps." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61210.
Анотація:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 85-89).
Ion traps provide an excellent tool for controlling and observing the state of a single trapped ion. For this reason, ion traps have been proposed as a possible system for large-scale quantum computation. However, many obstacles must be overcome before quantum computing can become a reality. In particular, perturbations in the electric field due to noise and electrode charging must be reduced to increase coherence of the motional quantum state. Gold has been a popular choice in the past due to its inert properties; however, it is undesirable due its incompatibility with CMOS technology. This has led to increased research into alternative CMOS-compatible materials, such as aluminum and copper. This thesis presents measurements of electric field noise and light-induced charging in aluminum, copper, and gold surface electrode traps. In addition, the effect of oxide growth on field noise and electrode charging is explored by controlling the thickness of aluminum oxide on several aluminum traps. The measurements show that electric field noise can be suppressed in aluminum traps to approximately 10-18 V2 cm-2 Hz-1, matching the noise exhibited in gold traps, and that copper traps exhibit noise within an order of magnitude of that in aluminum and gold. However, the natural oxide of aluminum poses many problems towards high-performance aluminum ion traps. The electric field noise is shown to be strongly dependent on the oxide thickness, increasing the noise by a factor of about 10 until saturation at a thickness of 13 nm. Charging of surface electrodes is shown to be highly dependent upon the material, but the model presented does not match the experimental data and is found to be incomplete. These results indicate that ion traps made out of CMOS-compatible materials can perform as well as more traditional traps fabricated from gold with respect to heating and charging as long as methods are developed for controlling oxide growth.
by Nathan S. Lachenmyer.
S.B.
8
Antohi, Paul Bogdan. "Cryogenic surface electrode ion traps with integrated superconducting microwave resonators for polar molecular ion spectroscopy." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68866.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 129-144).
Trapped cold molecules open the possibility of studying ultracold chemistry and astrophysical processes in laboratory settings. Their rich internal structure also makes them suitable for quantum information manipulation or for tests of fundamental laws of nature. These experiments require precise control over the molecular internal degrees of freedom. There are few present proposals for trapping and cooling molecules. One proposal is based on confining neutral polar molecules in DC Stark shift traps, but this approach presents some issues. An attractive alternative is to confine polar molecular ions in RF Paul ion traps, which is the focus of this thesis. The objectives here are to develop the theoretical models and to devise the experimental components and methods to investigate the coupling of polar molecular ions' rotational states to the microwave radiation. The new approach presented here is based on co-trapping Sr+ atomic ions together with SrCl+ molecular ions in a cryogenic surface electrode RF ion trap and on using the coupling of the molecular ion's rotational states to an integrated superconducting microwave line or cavity either as a cooling method or for precise rotational spectroscopy. The first part of the thesis describes two theoretical methods for observing the coupling of the microwave radiation to the rotational levels of a molecule. The first method proposed is based on the enhancement of the molecular rotational transition rates by the co-trapped molecular-atomic ions Coulomb collisions. The second method is based on microwave cavity assisted heating or cooling of the molecular ions. The second part of the thesis presents the development of a cryogenic surface electrode RF ion trap with an integrated microwave transmission line/resonator. The ion trap is operated in a 4.2 K closed cycle cryostat.
by Paul Bogdan Antohi.
Ph.D.
9
Hahn, Henning [Verfasser]. "Two-qubit microwave quantum logic gate with 9Be+ ions in scalable surface-electrode ion traps / Henning Hahn." Hannover : Gottfried Wilhelm Leibniz Universität, 2019. http://d-nb.info/1191365204/34.
10
Flynn, Richard A. "Measurement of refractive index and size of microparticles by optical traps generated by vertical cavity surface emitting lasers /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3137217.
11
Lopez, garcia Andres Jenaro. "Contribution à l'étude des propriétés piézoélectriques de nanofils de ZnO et de nanocomposites associés en vue d’une application à la conversion d’énergie mécanique à électrique." Thesis, Université Grenoble Alpes, 2022. http://www.theses.fr/2022GRALT043.
Анотація:
Avec le développement croissant de réseaux sans fil de capteurs de faible puissance pour ce que l’on appelle l’Internet des objets, il est nécessaire de trouver des moyens efficaces d’assurer l’autonomie énergétique des nœuds de détection. Parmi les différentes solutions de récupération d’énergie, la conversion en énergie électrique de l’abondante énergie mécanique présente dans l’environnement est très prometteuse. Dans ce domaine de recherche émergent, les nanofils (NFs) de ZnO ont été fortement étudiés au cours de ces deux dernières décennies, à la fois en tant que tels, et intégrés dans des nanocomposites. À l’échelle nanométrique, ils présentent des propriétés électromécaniques meilleures que le matériau massif, ainsi qu’une intégration facile sur des substrats rigides ou flexibles. Néanmoins, des divergences intrigantes entre les résultats expérimentaux et les simulations numériques disponibles au début de cette thèse ont mis en évidence la nécessité d’une meilleure compréhension du fonctionnement piézoélectrique des composites à base de NF, en particulier pour ce qui concerne deux aspects importants qui avaient été peu traités jusqu’alors: le couplage entre les propriétés piézoélectriques et semi-conductrices dans les simulations numériques et la dépendance des propriétés électromécaniques avec la méthode de croissance des NFs de ZnO ou avec l’influence de l’environnement des NFs dans les expériences.Du point de vue théorique, cette thèse de doctorat étudie le couplage des propriétés piézoélectriques et semi-conductrices des NFs de ZnO et de leur nanocomposites et fournit des lignes directrices d’optimisation pour les applications de transduction électromécanique. Cette étude prend en compte l’influence du niveau de dopage, de la densité de porteurs libres, des pièges d’interface et des paramètres géométriques sur les paramètres électromécaniques. Des simulations numériques de nanocomposites à base de NF de ZnO sous compression mécanique ont été effectuées à l’aide de la méthode des éléments finis (FEM). Expérimentalement, plusieurs modes de microscopie à force atomique (AFM), tels que la microscopie à force piézoélectrique (PFM), la microscopie à force de sonde Kelvin (KPFM) et la microscopie à force atomique conductrice (C-AFM) ont été utilisés, afin de sonder localement les paramètres électriques et électromécaniques qui jouent un rôle clé dans l’efficacité de la réponse piézoélectrique des NFs de ZnO. Nos résultats ont montré que le niveau de dopage, les porteurs libres et les pièges d'interface, ainsi que la dynamique des pièges, doivent être pris en compte pour expliquer l’amplitude et l’asymétrie potentielle de la réponse électromécanique ou l’influence que la géométrie a sur elle. Ils montrent que les propriétés semi-conductrices doivent être prises en compte pour l’analyse des résultats expérimentaux et la conception correcte de dispositifs électromécaniques autonomes basés sur des NFs de ZnO et leurs nanocompositesWith the increasing development of wireless networks of low-power sensors for the so-called internet-of-things, there is a need for efficient ways to ensure the energetic autonomy of sensing nodes. Among the various energy harvesting solutions, converting the abundant mechanical energy present in the environment into electrical energy is very promising. In this emerging field of research, ZnO nanowires (NWs) have been strongly studied during these last two decades, both as such, and integrated into nanocomposite materials. At the nanoscale, they feature improved electromechanical properties compared to bulk, as well as easy integration and manufacturing, on both rigid and flexibles substrates. However, some intriguing discrepancies between the experimental and simulation results available at the beginning of this PhD highlighted the need for a better understanding of the piezoelectric operation of NW-based composites, especially for what concerns two important aspects which had been poorly addressed so far: the coupling between piezoelectric and semi-conducting properties in simulations, and the dependence of electromechanical properties with ZnO NW growth method or with NW surrounding environment in experiments.From the theoretical point of view, this Ph.D. thesis studies the coupling of piezoelectric and semiconducting properties in ZnO NWs and related nanocomposites and provides optimization guidelines for mechanical to electrical transducing applications. It investigates the influence of doping level, free carrier density, interface traps and geometrical parameters on electromechanical parameters. Simulations of ZnO NW-based nanocomposites under mechanical compression were performed using the Finite Element Method (FEM). Experimentally, several atomic force microscopy (AFM) modes, such as piezoelectric force microscopy (PFM), Kelvin probe force microscopy (KPFM), and conducting atomic force microscopy (C-AFM) were used, in order to probe locally electrical and electromechanical parameters which play a key role in the efficiency of the piezoelectric response of ZnO NWs. Our results showed that doping level, free carriers and surface traps, as well as traps dynamics, must be considered in order to explain the amplitude and the potential asymmetry of the electromechanical response, or the influence that geometry has on it. They demonstrate that semiconducting properties should be taken into account for the analysis of experimental results and for the correct design of electromechanical self-powered devices based on ZnO NWs and nanocomposites
12
Campbell, Jonathan A. (Jonathan Alan). "Surface trap for ytterbium ions." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36816.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (leaves 41-42).
We conducted an experiment to load a shallow planar ion trap from a cold atom source of Ytterbium using photoionization. The surface trap consisted of a three-rod radio frequency Paul trap fabricated using standard printed circuit board techniques. The cold atom source was an isotope-selective magneto-optical trap of naturally-occurring Yb isotopes. The confining beams were provided by commercially-available ultra-violet diode lasers locked to an atomic reference using the Dichroic Atomic Vapor Laser Lock technique. We used photoionization from the Yb magneto-optical trap located within the region of the ion trapping potential.
by Jonathan A. Campbell.
Ph.D.
13
Tarasenko, Alexander, and Lubomir Jastrabik. "Surface diffusion of particles over bivariate trap lattices." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-191662.
Анотація:
We investigate the diffusion of particles on heterogeneous lattices with two kinds of nonequivalent sites. General analytical expressions for the chemical and jump diffusion coefficients have been derived in the case of strong inhomogeneity. We have calculated coverage dependencies of the diffusion coefficients and other necessary thermodynamic quantities for some representative values of the lateral pairwise interaction between the particles. The analytical data have been compared with the numerical data obtained by the kinetic Monte Carlo simulations. Almost perfect agreement between the respective results has been found.
14
Tarasenko, Alexander, and Lubomir Jastrabik. "Surface diffusion of particles over bivariate trap lattices." diffusion fundamentals 11 (2009) 103, S. 1-8, 2009. https://ul.qucosa.de/id/qucosa%3A14077.
Анотація:
We investigate the diffusion of particles on heterogeneous lattices with two kinds of nonequivalent sites. General analytical expressions for the chemical and jump diffusion coefficients have been derived in the case of strong inhomogeneity. We have calculated coverage dependencies of the diffusion coefficients and other necessary thermodynamic quantities for some representative values of the lateral pairwise interaction between the particles. The analytical data have been compared with the numerical data obtained by the kinetic Monte Carlo simulations. Almost perfect agreement between the respective results has been found.
15
Eltony, Amira M. (Amira Madeleine). "Sensitive, 3D micromotion compensation in a surface-electrode ion trap." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84871.
Анотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages [47]-53).
Following successful demonstrations of quantum algorithms and error correction with a handful of trapped ions in a macroscopic, machined Paul trap, there is a growing effort to move towards microfabricated traps with all the electrodes on a single chip. These traps, known as surface-electrode ion traps, are more amenable to being shrunk in size and replicated, or integrated with optical components and electronic devices. However, in the shift towards surface-electrode traps, and as traps are miniaturized in general, laser beams are brought closer to electrode surfaces, exacerbating laser-induced charging. Because of their charge, trapped ions are extremely sensitive to stray charges that accumulate on the trap surface. The DC potentials caused by stray charge displace the ion from the null of the RF trapping field, resulting in a fast, driven motion of the ion (known as micromotion) which hinders quantum operations by broadening transitions and causing decoherence. In a surface trap, micromotion detection is difficult as the laser beams used for measurement typically cannot crash into the trap, obscuring ion offsets out of the trap plane. Existing methods for micromotion detection permit ion positioning accurate to the ground state wavepacket size (of order 10 nm), but cannot identify ion offsets out of the trap plane with the same accuracy. Schemes for sensitive compensation often have restrictive requirements such as access to a narrow atomic transition. We introduce a new approach, which permits out-of-plane micromotion compensation to within 10s of nanometers with minimal overhead. Our technique synchronously detects ion excitation along the trap axes when it is driven by secular-frequency sidebands added to the RF electrodes; the excitation amplitude is proportional to the offset from the RF null. We make a detailed theoretical comparison with other techniques for micromotion compensation and demonstrate our technique experimentally.
by Amira M. Eltony.
S.M.
16
Vittorini, Grahame D. "Stability of ion chains in a cryogenic surface-electrode ion trap." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50239.
Анотація:
Cold, trapped atomic ions have enabled the investigation of fundamental physics and generated a rich field of applications. Foremost among these is quantum computation which has recently driven the development of the sophisticated, scalable surface-electrode trap. Despite the many advantages of surface-electrode traps, the typically smaller ion-electrode distance, d, in these traps results in an increased ion heating rate that is proportional to d^(-4) and a decreased trap well-depth that is proportional to d^(-2). These shortcomings can be simultaneously addressed by installing the trap into a cryogenic environment. With this in mind, a closed-cycle, cryogenic ion trapping apparatus that maintains excellent vacuum, is highly modular, has increased optical access, and uses a simple vibration isolation system has been developed.
Single ions are trapped and used to characterize system properties such as the motion of the vibration isolation stage. In order to compare this system to a similar room temperature apparatus, the ion trapping lifetime and heating rate are determined. A single ion also serves as a sensitive electric field probe that is used to measure and compensate stray electric fields across the trap.
Due to the long dark ion lifetimes in this system, it is well-suited to probing the stability of small, linear ion crystals. Linear ion crystals of arbitrary length are built in an automated fashion using transport waveforms and the scaling of dark lifetime with ion number for N <= 6 is investigated. These data are then used to consider the relevance of various loss channels.
17
Siverns, James D. "Yb ion trap experimental set-up and two-dimensional ion trap surface array design towards analogue quantum simulations." Thesis, University of Sussex, 2012. http://sro.sussex.ac.uk/id/eprint/43344/.
Анотація:
Ions trapped in Paul traps provide a system which has been shown to exhibit most of the properties required to implement quantum information processing. In particular, a two-dimensional array of ions has been shown to be a candidate for the implementation of quantum simulations. Microfabricated surface geometries provide a widely used technology with which to create structures capable of trapping the required two-dimensional array of ions. To provide a system which can utilise the properties of trapped ions a greater understanding of the surface geometries which can trap ions in two-dimensional arrays would be advantageous, and allow quantum simulators to be fabricated and tested. In this thesis I will present the design, set-up and implementation of an experimental apparatus which can be used to trap ions in a variety of different traps. Particular focus will be put on the ability to apply radio-frequency voltages to these traps via helical resonators with high quality factors. A detailed design guide will be presented for the construction and operation of such a device at a desired resonant frequency whilst maximising the quality factor for a set of experimental constraints. Devices of this nature will provide greater filtering of noise on the rf voltages used to create the electric field which traps the ions which could lead to reduced heating in trapped ions. The ability to apply higher voltages with these devices could also provide deeper traps, longer ion lifetimes and more efficient cooling of trapped ions. In order to efficiently cool trapped ions certain transitions must be known to a required accuracy. In this thesis the 2S1/2 → 2P1/2 Doppler cooling and 2D3/2 → 2D[3/2]1/2 repumping transition wavelengths are presented with a greater accuracy then previous work. These transitions are given for the 170, 171, 172, 174 and 176 isotopes of Yb+. Two-dimensional arrays of ions trapped above a microfabricated surface geometry provide a technology which could enable quantum simulations to be performed allowing solutions to problems currently unobtainable with classical simulation. However, the spin-spin interactions used in the simulations between neighbouring ions are required to occur on a faster time-scale than any decoherence in the system. The time-scales of both the ion-ion interactions and decoherence are determined by the properties of the electric field formed by the surface geometry. This thesis will show how geometry variables can be used to optimise the ratio between the decoherence time and the interaction time whilst simultaneously maximising the homogeneity of the array properties. In particular, it will be shown how the edges of the geometry can be varied to provide the maximum homogeneity in the array and how the radii and separation of polygons comprising the surface geometry vary as a function of array size for optimised arrays. Estimates of the power dissipation in these geometries will be given based on a simple microfabrication.
18
Li, Heng. "Trap mediated piezoresponse of silicon in the space charge limit." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX039/document.
Анотація:
Cette thèse contribue à l’étude des effets géants et anormaux de piézo-résistance (PZR) observés dans le nano-silicium. La PZR du silicium massif est devenue la clé de voûte de nombreuses technologies dont l’industrie micro-électronique vise des dispositifs de dimensions nanométriques. Il est donc logique d’investiguer la PZR du silicium à ces échelles spatiales où ont été révélé l’existence d’une PZR géante et d’une PZR d’amplitude « normale » mais de signe anormale. Cependant l’origine de ces effets reste peu claire et dans certains cas, leur véracité a été remise en cause. L’ensemble de ces effets semble corrélé à un appauvrissement en porteurs libres où le courant devient limité par la charge d’espace (en anglais SCLC). Pour mettre en lumière la dépendance en contrainte mécanique des taux de capture et d’émission de porteurs libres sur des pièges liés aux défauts cristallins, nous utilisons la technique de spectroscopie d’impédance qui, alliée à la spectroscopie de photoémission, suggère que les pièges en question sont ceux liés aux défauts intrinsèques de surface. La PZR géante n’est observée qu’en dehors du régime stationnaire. Dans le régime stationnaire dans laquelle se situe l’ensemble des études précédentes, bien qu’une PZR géante ne soit pas observée, une PZR de signe anormale est mesurée dans le silicium où une densité de défauts bien choisis a été introduite. Nous démontrons que cette dernière est due à un changement de type de porteur majoritaire induit par la tension appliquée en régime SCLC. Le chapitre 1 aborde l’historique de la PZR jusqu’aux observations de la PZR géante et anomale dans le nano-silicium. Le chapitre 2 présente les modèles physiques de la PZR en régime ohmique. La théorie des SCLCs est ensuite introduite. Le chapitre 3 présente les dispositifs expérimentaux, les procédures de mesure ainsi que les échantillons étudiés. Le chapitre 4 contient les principaux résultats obtenus par la spectroscopie d’impédance. Une PZR géante et nouvel effet de piézo-capacitance sont observés. Une comparaison avec la théorie indique que les dispositifs opèrent dans une régime SCLC en présence de pièges électroniques rapides, et que la PZR géante résulte de la dépendance en contrainte des taux de capture et d’émission de ces pièges. Ceci donne lieu à des changements importants de densités de porteurs hors du régime stationnaire. Ce chapitre se termine sur une discussion, revisitée à la lumière de nos résultats, des effets controversés de PZR géante publiés dans la littérature. Le chapitre 5 traite la mesure de la dépendance en contrainte du « pinning » du niveau de Fermi de surface, réalisée en combinant cartographie Raman et photoémission sur des leviers en silicium statiquement fléchis dont les surfaces sont terminées par une oxyde native. L’observation d’un déplacement du niveau de Fermi de surface pair en contrainte tend à montrer que les défauts intrinsèques de surface (type Pb0) sont à l’origine des effets géants présentés dans le chapitre 4.Le chapitre 6 aborde les mesures en régime stationnaire de PZR du silicium n.i.d. de type n pour laquelle une densité de bi-lacunes de silicium a été introduite. La caractéristique courant-tension montre trois régimes : à basse tension une loi ohmique dominé par les électrons majoritaires ; à des tensions intermédiaires une loi de Mott-Gurney modifiée des trous injectés depuis les contacts p++ ; à haute tension un régime plasma électron-trou. La PZR est déterminée par le porteur majoritaire. A basse tension un comportement du silicium type n est observé (i.e. de signe négatif) tandis qu’aux tensions intermédiaires une PZR similaire à celle du silicium type p est observée (i.e. de signe positive). A haute tension la PZR correspond à la somme de ces, conséquence directe de la présence d’électrons et de trous dans le régime plasma. Le chapitre 7, tout en résumant les conclusions principales de cette thèse développe également les directions futures à explorerThis thesis presents a study of giant, anomalous piezo-resistance (PZR) in depleted nano-silicon. PZR in bulk silicon is a technologically important phenomenon in which mechanical stress changes the electrical resistivity via a change in the charge carrier effective masses. With continued reductions in device dimensions, it is of interest to explore the PZR of silicon micro- and nano-objects in which giant PZR and PZR of anomalous sign have been reported in recent years. The physical origin of these effects remains unclear and in some cases, even the veracity of the claimed results has been questioned. Some basic elements of the claimed effects are agreed upon, for example they occur in surface depleted nanostructures where transport is described by space charge limited currents (SCLC). In this thesis the details of the stress-dependence of the charge trapping and emission rates at fast electronic traps during SCLC transport in fully depleted silicon-on-insulator is probed using impedance spectroscopy. This, combined with an X-ray photo-electron spectroscopy study of statically deflected silicon cantilevers, strongly suggests that giant, non-steady-state PZR is due to stress-induced changes to hole trapping dynamics at intrinsic interface states. In contrast, under steady-state conditions like those used in all previous studies, giant PZR is not observed even in the presence of interface traps. On the other hand, anomalous, steady-state PZR is observed in defect engineered SCLC devices, and is shown to be the result of a voltage bias induced type change of the majority carrier. In chapter 1 the history of PZR is introduced. Prior reports of giant and anomalous PZR are then discussed. Chapter 2 presents the physical description of the PZR in silicon when transport occurs in the Ohmic regime. Both large-signal and small-signal SCLC transport are then introduced. Chapter 3 introduces the experimental details and the samples used throughout this work. Chapter 4 contains the principal impedance spectroscopy results. Giant, anomalous PZR and a novel piezo-capacitance are observed under non-steady-state conditions in fully-depleted silicon-on-insulator. Comparison of theory and data indicate that the devices operate in the SCLC regime in the presence of fast traps, and that the giant, anomalous PZR results from the stress dependence of the charge capture and emission rates of these traps. This in turn yields large changes of the non-equilibrium charge carrier concentrations. The importance of these observations in clarifying the physical origin, and the veracity of previous reports of steady-state, giant PZR, is discussed. Chapter 5 reports a comparison of Raman and XPS maps on statically deflected silicon cantilevers, providing a spectroscopic measurement of the stress-dependence of the pinned surface Fermi level at natively oxidized (001) silicon surfaces. A simplified analysis of the observed even symmetry of the stress-induced Fermi level shifts suggests that intrinsic interface defects (Pb0) are likely responsible for the giant, anomalous PZR reported in Chapter 4. Chapter 6 reports the DC bias dependence of the PZR in n.i.d. n-type, defect engineered silicon devices. The device characteristic exhibits three regimes; an Ohmic regime at low biases dominated by equilibrium electrons, a modified Mott-Gurney regime at intermediate biases dominated by holes injected from p++ contacts, and an electron-hole plasma regime at high biases. In each case the PZR depends on the majority carrier type; at low biases the usual n-type PZR is observed (i.e. the sign is negative); at intermediate biases it switches to the bulk p-type (i.e. positive) PZR; in the plasma regime, the PZR is a combination of the bulk electron and hole values. The results help shed light on observations of anomalous (i.e. sign reversed) PZR in depleted nano-silicon. Finally, chapter 7 summarizes the conclusions and introduces possible future research directions
19
Yu, Hyun Jae. "HIV Traffics Through a Specialized, Surface-accessible Intracellular Compartment During Trans-infection of T Cells by Mature Dendritic Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1266871870.
20
Feng, Wenqian [Verfasser], and Oliver [Akademischer Betreuer] Trapp. "Spatial Surface Functionalization Based on Photo-induced Thiol Reactions / Wenqian Feng ; Betreuer: Oliver Trapp." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180617371/34.
21
Karim, Ali Esmail. "A pH Switchable Responsive Surface for the Trapping And Release of a Hydrophobic Substance." TopSCHOLAR®, 2015. http://digitalcommons.wku.edu/theses/1522.
Анотація:
Solid phase extraction is one of the most widely used techniques to trap and release compounds in a solution. A hydrophobic substance will stick efficiently to a hydrophobic surface (the “like dissolves like” principle). With an introduced response (i.e. pH change), a responsive surface can change from hydrophobic to hydrophilic, weakening the hydrophobic substance’s attraction and thus facilitate in an easy removal. A surface has been prepared having a terminal anthranilic acid (AA) moiety on silica gel particles, microscope slides, and TLC plates in three steps. First, a vinyl group was attached to the surface. Then, this vinyl group was reacted to form a surface carboxylic acid group. Finally, the carboxylic acid group was converted to an amide group that linked to the silica surface. FT-IR, and elemental analysis were used to confirm each step of the synthesis. At low pHs the –COOH group on the AA moiety is neutral and intrahydrogen bonding keeps this moiety’s phenyl (hydrophobic) portion exposed to the surface. The effect has been investigated by measuring contact angles at various pH values. At higher pHs the AA’s carboxylic acid group becomes the charged carboxylate, rendering the surface hydrophilic. Substances can be trapped and released using this unique switching approach. 2-naphthol, for example, is hydrophobic and thus was trapped at lower pHs (pH 4) (hydrophobic surface) and released at higher pHs (pH 10) (hydrophilic surface) on this responsive surface
22
Yuan, Xiaohui. "Characterization of the ligand-binding specificity and transcriptional properties of estrogen receptor homodimeric/heterodimeric complexes." free to MU campus, to others for purchase, 2001. http://wwwlib.umi.com/cr/mo/fullcit?p3036871.
23
Strömberg, Kia. "Notch signaling: from receptor cleavage to chromatin remodeling /." Stockholm, 2005. http://diss.kib.ki.se/2005/91-7140-540-2/.
24
Dhar, Tulika [Verfasser]. "Modification of cell surface proteins by protein trans-splicing using the Npu DnaE Intein / Tulika Dhar." Dortmund : Universitätsbibliothek Technische Universität Dortmund, 2011. http://d-nb.info/1018098720/34.
25
Hwang, Gyuweon. "Surface trap passivation and characterization of lead sulfide quantum dots for optical and electrical applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98741.
Анотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-119).
Quantum dots (QDs) are semiconductor nanocrystals having a size comparable to or smaller than its exciton Bohr radius. The small size of QDs leads to the quantum confinement effects in their electronic structures. Their unique optical properties, including a tunable emission from UV to IR, make QDs attractive in optoelectronic applications. However, further improvements in device performance are required to make them competitive. One well-known factor that presently limits the performance of QD thin film devices is sub-band-gap states, also referred to as trap states. For instance, trap states impair optical properties and device performance by providing alternative pathways for exciton quenching and carrier recombination. Chemical modification of QDs has been commonly used for passivating trap states and thereby improving QD devices. However, the influence of chemical modifications of ligands, QD surfaces, or synthetic routes on electrical properties of QD thin films is not sufficiently characterized. Suppressing the trap states in QD thin films is a key to improve the performance of QDbased optoelectronics. This requires fundamental understanding of trap state source, which is lacking in these materials. In this thesis, I pursue to find a systematic method to control density of trap states by exploring different characterization techniques to investigate trap states in QD thin films. These attempts provide insight to develop a rationale for fabricating better performing QD devices. This thesis focuses on the trap states in IR emitting lead sulfide (PbS) QD thin films, which have great potential for application in photovoltaics, light emitting diodes (LEDs), photodetectors, and bio-imaging. Previously, QD thin films are treated with different ligands to passivate trap states and thereby improve the device performance. Through my work, I pursued to unveil the electrical characteristics and chemical origin of trap states, and develop a strategy to suppress the trap states. First, I hypothesize that surface dangling bonds are a major source of trap states. An inorganic shell layer comprised of cadmium sulfide (CdS) is introduced to PbS QDs to passivate the surface states. Addition of CdS shell layers on PbS QDs yields an enhanced stability and quantum yield (QY), which indicates decreased trap-assisted exciton quenching. These PbS/CdS core/shell QDs have a potential for deep-tissue bio-imaging in shortwavelength IR windows of 1550-1900 nm. However, the shell layer acts as a transport barrier for carriers and results in a significant decrease in conductivity. This hinders the incorporation of the core/shell QDs in electrical applications. An improved reaction condition enables the synthesis of PbS/CdS QDs having a monolayer-thick CdS shell layer. These QDs exhibit QY and stability comparable to thick-shell PbS/CdS QDs. Incorporation of these thin-shell QDs improves external quantum efficiency of IR QD-LEDs by 80 times compared to PbS core-only QDs. In the second phase of my work, I explore capacitance-based measurement techniques for better understanding of the electrical properties of PbS QD thin films. For in-depth analysis, capacitance-based techniques are introduced, which give complementary information to current-based measurements that are widely used for the characterization of QD devices. Nyquist plots are used to determine the dielectric constant of QD films and impedance analyzing models to be used for further analysis. Mott-Schottky measurements are implemented to measure carrier concentration and mobility to compare PbS core-only and PbS/CdS core/shell QD thin films. Drive-level capacitance profiling is employed to characterize the density and energy level of trap states when QD films are oxidized. Lastly, I investigate the chemical origin of trap states and use this knowledge to suppress the trap states of PbS QD thin films. Photoluminescence spectroscopy and X-ray photoelectron spectroscopy show that standard ligand exchange procedures for device fabrication lead to the formation of sub-bandgap emission features and under-charged Pb atoms. Our experimental results are corroborated by density functional theory simulation, which shows that the presence of Pb atoms with a lower charge in QDs contributes to sub-bandgap states. The trap states generated after ligand exchange were significantly reduced by oxidation of under-charged Pb atoms using 1,4-benzoquinone. The density of trap states measured electrically with drive-level capacitance profiling shows that this reduces the electrical trap density by a factor of 40. In this thesis, I characterized trap states and showed that by suppressing the trap states we can modify the electrical properties of QD thin films, which influence the performance of QD devices directly. This work is a starting point to fully analyze the trap states in QD thin devices and thereby provides insight to design a rationale for fabricating better performing QD devices.
by Gyuweon Hwang.
Ph. D.
26
Pruttivarasin, Thaned. "Study of low energy Ytterbium atom-ion charge transfer collisions using a surface-electrode trap." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45339.
Анотація:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 113-114).
We demonstrate a new isotope-selective system to measure low energy charge transfer collisions between ytterbium ions and atoms in the range of collisional energy from 2.2x 10-5 eV to 4.3x 10-3 eV, corresponding to effective temperature from 250 mK to 50 K. The charge transfer collisions are observed by spatially overlapping the 172yb+ ions in the surface-electrode trap and 174Yb atoms in the magneto-optical trap, and measuring ion loss. We confirm that, in the Langevin regime, the charge transfer collisional rate is independent of the collisional energy. The measured Langevin cross section is consistent with a theoretical value for the ytterbium atomic polarizability of 143 a.u., as calculated by Zhang and Dalgarno [1].
by Thaned Pruttivarasin.
S.B.
27
Burrows, Steven Preston. "Infrared Spectroscopic Measurement of Titanium Dioxide Nanoparticle Shallow Trap State Energies." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/31342.
Анотація:
Within the â forbiddenâ range of electron energies between the valence and conduction bands of titanium dioxide, crystal lattice irregularities lead to the formation of electron trapping sites. These sites are known as shallow trap states, where â shallowâ refers to the close energy
proximity of those features to the bottom of the semiconductor conduction band. For wide bandgap semiconductors like titanium dioxide, shallow electron traps are the principle route for thermal excitation of electrons into the conduction band.
The studies described here employ a novel infrared spectroscopic approach to determine
the energy of shallow electron traps in titanium dioxide nanoparticles. Mobile electrons within
the conduction band of semiconductors are known to absorb infrared radiation. As those electrons absorb the infrared photons, transitions within the continuum of the conduction band produce a broad spectral signal across the entire mid-infrared range. A Mathematical expression
based upon Fermiâ Dirac statistics was derived to correlate the temperature of the particles to
the population of charge carriers, as measured through the infrared absorbance. The primary
variable of interest in the Fermi â Dirac expression is the energy difference between the shallow trap states and the conduction band. Fitting data sets consisting of titanium dioxide nanoparticle temperatures and their associated infrared spectra, over a defined frequency range, to the Fermiâ Dirac expression is used to determine the shallow electron trap state energy.
Master of Science
28
Burger, Abri Andre Spies. "Numerical analysis of flow around infinite and finite cylinders at trans-critical Reynolds numbers with and without surface roughness." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97053.
Анотація:
Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: This thesis investigates the flow field and pressure distributions around cylinders at trans-critical Reynolds numbers using the k-ε Realizable turbulence model. A steady state 2-D and 3-D Fluent® model is successfully developed to evaluate the effects of changing various modelling parameters on the static pressure distribution around an infinite and finite cylinder. These parameters include surface roughness, cylinder rotation and air viscosity at the cylinder surface. The subsequent results obtained are compared to each other and to data trends from literature as well as measured experimental results and are found to be in good agreement. In addition a method for calibrating all developed methods based on their shear stress curves over a flat plate model is also successfully developed. The main objective is to find an appropriate single parameter which can be used for the rigorous adjustment of the pressure distribution around a cooling tower, which will allow for improved sensitivity analysis and modelling of cooling tower performance under wind conditions with and without meridional ribs located on the outer shell surface.
AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die vloeiveld en druk verdelings rondom silinders by trans-kritiese Reynolds getalle deur gebruik te maak van die k-ε Realizable turbulensie model. ‘n Bestendige toestand 2-D en 3-D Fluent® model is suksesvol ontwikkel om die uitwerking van die verandering van verskeie model parameters op die statiese druk verdeling rondom ‘n oneindige en eindige silinder te evalueer. Die laasgenoemde parameters sluit in oppervlak grofheid, silinder rotasie en lug viskositeit by die silinder wand. Die daaropeenvolgende resultate wat verkry word, word met data tendense uit die literatuur asook gemete data vanuit eksperimente vergelyk en goeie ooreenkoms i.t.v die data tendense is gevind. Verder is ‘n metode vir die suksesvolle kalibrasie van die ontwikkelde numeriese tegnieke ontwikkel. Die laasgenoemde kalibrasie metode is gebaseer op die vergelyking van skuifspanning kurwes vir vloei oor ‘n plat plaat model. Die hoofdoel van die navorsing is om ‘n geskikte enkele parameter te vind wat gebruik kan word vir die effektiewe aanpassing van die druk verdeling rondom ‘n koeltoring wat sal lei tot verbeterde sensitiwiteits analise en modellering van koeltoring verrigting onder wind toestande met en sonder meridionale ribbes geleë op die buitenste dop oppervlak.
29
Allen, Frances Isabel. "Electron capture by highly charged ions from surfaces and gases." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15720.
Анотація:
In dieser Arbeit werden hochgeladene, mit einer Electron Beam Ion Trap produzierte Ionen für die Erforschung des Elektroneneinfangs von Oberflächen und Gasen eingesetzt. Die Untersuchungen mit Gastargets konzentrieren sich auf die Energieabhängigkeit der Verteilung der K-Schalen-Röntgenstrahlen, die nach Elektroneneinfang in Rydberg-Zustände von Ar-17+ und Ar-18+ Ionen am Ende einer Kaskade von Elektronenübergängen entstehen. Die Ionen werden von der Ionenquelle mit einer Energie von 2 keV/u extrahiert, ladungsselektiert und anschließend bis auf 5 eV/u abgebremst, um dann mit einem Argon Gastarget zu interagieren. Für abnehmende Stoßenergien wird eine Verschiebung des Elektroneneinfangs in Zustände mit niedrigen Drehumpulsquantenzahlen beobachtet. Zum Vergleich wird auch die K-Schalen-Röntgenstrahlung auf Grund des Elektroneneinfangs bei Ar-17+ und Ar-18+ von dem Restgas in der Falle gemessen. Dabei wird eine Diskrepanz zu den Resultaten der Extraktionsversuche festgestellt. Mögliche Erklärungen werden diskutiert. In den Untersuchungen zum Elektroneneinfang von Oberflächen werden hochgeladene Ionen von der Ionenquelle mit Energien von 2 bis 3 keV/u extrahiert, ladungsselektiert und auf Targets gelenkt. Diese bestehen aus Siliziumnitridmembranen mit einer Vielzahl nanometergroßer Löcher, welche mittels eines fokussierten Ionenstrahls in Kombination mit ionenstrahlinduzierter Abscheidung dünner Filme erstellt werden. Es werden hierbei Lochdurchmesser von 50 bis 300 nm mit Formfaktoren von 1:5 bis 3:2 erreicht. Bei den hochgeladenen Ionen handelt es sich um Ar-16+ und Xe-44+. Nach dem Transport durch die Kapillare passieren die Ionen einen elektrostatischen Ladungstrenner und werden detektiert. Der Anteil des Elektroneneinfangs von den Wänden der Löcher ist weitaus geringer als Modellberechnungen vorhersagen. Die Resultate werden an Hand eines Kapillareffekts zur Ionenleitung diskutiert.In this study highly charged ions produced in Electron Beam Ion Traps are used to investigate electron capture from surfaces and gases. The experiments with gas targets focus on spectroscopic measurements of the K-shell x-rays emitted at the end of radiative cascades following electron capture into Rydberg states of Ar-17+ and Ar-18+ ions as a function of collision energy. The ions are extracted from an Electron Beam Ion Trap at an energy of 2 keV/u, charge-selected and then decelerated down to 5 eV/u for interaction with an argon gas target. For decreasing collision energies a shift to electron capture into low orbital angular momentum capture states is observed. Comparative measurements of the K-shell x-ray emission following electron capture by Ar-17+ and Ar-18+ ions from background gas in the trap are made and a discrepancy in the results compared with those from the extraction experiments is found. Possible explanations are discussed. For the investigation of electron capture from surfaces, highly charged ions are extracted from an Electron Beam Ion Trap at energies of 2 to 3 keV/u, charge-selected and directed onto targets comprising arrays of nanoscale apertures in silicon nitride membranes. The highly charged ions implemented are Ar-16+ and Xe-44+ and the aperture targets are formed by focused ion beam drilling in combination with ion beam assisted thin film deposition, achieving hole diameters of 50 to 300 nm and aspect ratios of 1:5 to 3:2. After transport through the nanoscale apertures the ions pass through an electrostatic charge state analyzer and are detected. The percentage of electron capture from the aperture walls is found to be much lower than model predictions and the results are discussed in terms of a capillary guiding mechanism.
30
Delibas, Tughan. "Effects Of Granulated Blast Furnace Slag Trass And Limestone Fineness On The Properties Of Blended Cements." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614072/index.pdf.
Анотація:
The aim of this research was to determine the effects of the fineness of different mineral additives on loss on ignition, heat of hydration, physical, mechanical and chemical properties of blended cements. For that purpose, portland cement clinker was replaced with granulated blast furnace slag (GBFS), natural pozzolan (NP) and limestone (L) at 6%, 20% and 35% replacement levels. Blended cements containing GBFS and NP were ground to a fineness of 3000, 5000 and 6000 cm2/g. Cements containing L were ground to 3000 cm2/g, 4000 cm2/g and 4500 cm2/g. All of the blended cement types mentioned above were both interground and separately ground to the specified fineness levels. Therefore, a total of 57 different cements were produced. Loss on ignition, heat of hydration, chemical, mechanical and physical analyses were performed on the produced cements. Moreover, the chemical analyses of the cements were obtained for cement particles finer (-45&mum) and coarser (+45&mu
m) than 45 &mu
m in order to determine the ingredients of -45 &mu
m, which is known to be more reactive. As a result it was shown that the grindability differences of the cement ingredients affect the properties of blended cements. An increase in the specific surface area increases both the compressive strength and heat of hydration values and adversely affects the loss on ignition values. The results also showed that if the cement particles were ground finer, it was more prone to moisture which resulted in higher loss on ignition values after longer periods.
31
Guilbert-Lepoutre, Aurélie. "Propriétés de surface et structure interne des objets Trans-Neptuniens et des Centaures : un nouveau modèle d'évolution thermique 3D." Paris 7, 2009. http://www.theses.fr/2009PA077246.
Анотація:
Les Objets Trans-Neptuniens et les Centaures constituent l'essentiel des petits corps glaces du Système Solaire. Cette population rassemble de nombreux objets dont les propriétés dynamiques, physiques et chimiques sont extrêmement variées. L'observation de ces objets a longtemps été un défi technique, si bien que leur étude est un domaine de recherche en constante évolution. Les OTNs et les Centaures seraient constitues de diverses glaces. Afin de contraindre la composition a la surface d'un échantillon significatif d'objets, un Large Program ESO a été entrepris au tout début de cette thèse. J'ai en particulier travaille sur les spectres H+K obtenus avec l'instrument SINFONI. J'ai pu mettre en place une technique d'observation et de réduction de données optimisée et performante, dont chaque étape a été largement éprouvée. Chaque spectre a été analyse individuellement, afin de déterminer les composes présents a la surface des objets par le biais d'un modèle de transfert radiatif: des composes comme la glace d'eau ou d'autres volatils ont ainsi pu être détectes. L'observation de certains composes volatils a la surface des OTNs soulevé des questions quant a la possible activité interne de ces objets. J'ai donc développe un nouveau modèle d'évolution thermique tri-dimensionnel, dont la solution mathématique permet de limiter le temps de calcul. Ce modèle permet ainsi de tenir compte des flux de chaleur latéraux et des conditions aux limites 3D, tout en étant performant d'un point de vue temps de calcul. L'influence des paramètres les plus critiques a été testée: temps de formation des objets, conductivite thermique du matériau, etc. Les résultats obtenus fournissent de nouvelles pistes d'interprétation pour les observations d'OTNs et de Centaures. Enfin, j'ai pu réaliser un portrait du Centaure 10199 Chariklo: les données obtenues dans le cadre du Large Program montrent en effet d'importantes variations par rapport aux spectres publies dans la littérature. Plusieurs hypothèses sont envisageables pour expliquer ces changements: variations spatiales, variations temporelles, ou encore sursauts d'activité cometaire. Les données observationneîles seules ne permettent pas de discrimer entre ces différentes explications. L'application du modèle d'évolution thermique 3D permet en revanche d'identifier les hypothèses les plus probables et d'éliminer ainsi l'hypothèse d'activité cometaire qui n'est pas attendue pour cet objetSmall Icy bodies of the Solar System are mainly constituted by Transneptunian Objects and Centaurs. These two populations are composed of numerous bodies, whose dynamical, physical and chemical properties can be very different. Their observations have remained challenging until recently. Thus, the study of the Transneptunian région is a research field in rapid and constant evolution. TNOs and Centaurs should be composed of varions ices. At the very beginning of this thesis, an ESO Large Program has been undertaken, in order to constrain thé surface composition of a significant sample of bodies. I was in charge of the H+K spectra obtained with the new instrument SINFONI. I therefore had to establish an optimized observation technique and a performant data reduction procedure, for which each step has been widely tested. Each spectrum has been analyzed individually, and a radiative transfer model has been applied to determine the surface composition of each object. Absorption bands attributed to water ice and other volatil ices have been detected. The presence of some volatil ices on these objects' surfaces raises questions about the possible internal activity they can undergo. I consequently developed a three-dimensional thermal model, using a mathematical solution limiting the computation time. This new internal evolution model allows to compute lateral beat fluxes and 3D boundary conditions, without any excessive computation time. I tested the influence of the most critical parameters such as the formation time of the objects, the matrix thermal conductivity, etc. The main results throw new leads for the observations interpretation. Finally, I managed to draw a portrait of Centaur 10199 Chariklo: the data obtained in the framework of the Large Program show indeed important variations compared to the previously published ones. Several hypothesis are considered to explain these changes: spatial variations, temporal variations, or cometary outbursts. Observational data alone do not allow to discard any of those three explanations. I therefore applied the 3D thermal model which allows to exclude some temporal variations
32
Korkmaz, Deniz. "Preconcentration Of Volatile Elements On Quartz Surface Prior To Determination By Atomic Spectrometry." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604921/index.pdf.
Анотація:
Hydride generation technique is frequently used for the detection of elements as As, Se, Sb, Sn, Bi, Ge, Te and Pb that form volatile hydrides in solution using a reductant. In this study, a novel quartz trap for on-line preconcentration of volatile analyte species was designed. Pb, Sb and Cd were selected as analyte elements and chemical vapour generation technique was employed for generation of their volatile species in flow systems. The trapping medium was formed by external heating of either the inlet arm of the quartz tube atomizer or a separate cylindirical quartz tube. Generated analyte species were trapped on quartz surface heated to the collection temperature and the collected species were revolatilized when the trap was heated further to releasing temperature and hydrogen gas was introduced in the trapping medium. The conventional quartz T-tube and multiple microflame quartz tube were employed as atomizers. The influence of relevant experimental parameters on the generation, collection and revolatilization efficiencies was investigated. Optimum conditions, performance characteristics of the trap and analytical figures of merit are presented. Experimental design was used for optimizations in some cases. Standard reference materials were analyzed to assess the accuracy of the proposed method. For a collection period of 1.0 minute for Pb, 2.0 minutes for Sb and 3.0 minutes for Cd, 3σ
limit of detections, in pg ml-1, were 19, 3.9 and 1.8, respectively. In cases of Sb and Cd, the limits of detections obtained are the same as the best attained with in-situ trapping in graphite furnaces.
33
BENARDAIS, ALBANE. "Depots de polymere sur surfaces planes et spheriques obtenus par polymerisation plasma a partir d'un melange de trans-2-butene et d'hydrogene." Paris 6, 1997. http://www.theses.fr/1997PA066220.
Анотація:
Pour la fabrication des microcibles pour les experiences d'interaction laser-matiere, un procede de polymerisation plasma basse frequence a ete etudie. Le systeme peut fonctionner avec les substrats dans la decharge ou en post-decharge et permet d'obtenir des polymeres hydrocarbones a partir d'un melange gazeux de trans-2-butene et d'hydrogene. Cette etude comporte deux parties. La premiere consiste en la comprehension des mecanismes de polymerisation plasma lies au reacteur pour mieux optimiser le procede. L'etude des ecoulements des gaz a permis de connaitre la repartition des especes dans l'enceinte reactionnelle et la connaissance du comportement electrique du reacteur nous a permis de definir le type decharge. Les especes presentes dans le plasma ont ete analysees par spectrometrie d'emission et spectrometrie de masse puis des mecanismes reactionnels ont ete proposes. En particulier, le role primordial de l'hydrogene, veritable reactif au meme titre que le trans-2-butene, aussi bien sous sa forme atomique (dans ce cas, l'hydrogene grave legerement la surface du depot en formation et ameliore ainsi son etat de surface) que moleculaire (dans ce cas, il favorise la polymerisation du trans-2-butene), a ete mis en evidence. La deuxieme est l'optimisation du procede afin d'obtenir un point de fonctionnement satisfaisant permettant d'avoir des depots les plus transparents possible, ne contenant que du carbone et de l'hydrogene (et le moins d'oxygene possible) avec un bon etat de surface (rugosite quadratique moyenne < 50 nm) et une bonne conservation dans le temps. Aides de l'etude prealable de caracterisation du reacteur, l'etude des effets des differents parametres (depots dans la decharge ou en post-decharge, pression, debit total des gaz, composition du melange trans-2-butene/hydrogene, puissance electrique, frequence, distance interelectrode) sur la vitesse de depot, la rugosite et la composition chimique du depot a permis de definir les conditions optimales de depot.
34
Brulat-Bouchard, Nathalie. "Les adhésifs automordançants sont-ils plus adaptés à la surface dentinaire préparée avec le laser Er : Yag ? : étude in vitro et sous pression trans-dentinaire." Nice, 2006. http://www.theses.fr/2006NICE4060.
Анотація:
Notre étude se propose d’évaluer les interactions entre trois types d’adhésifs automordançants (le CSE Bond, le XenoIII et le iBOND) et le substrat dentinaire préparé au laser Er : YAG ou à la fraise. Les surfaces préparées avec le laser ont été analysées en microscopie optique, électronique à balayage et en XPS. Nous avons ensuite étudié les interactions entre ces trois adhésifs automordançants et le substrat. Nos études de mouillabilité ont montré que la surface préparée au laser est plus hydrophile et poreuse que la surface fraisée. Les monomères acides des adhésifs automordançants sont eux aussi hydrophiles et pénètrent plus rapidement sur la surface préparée au laser. Un essai mécanique de cisaillement avec pression trans-dentinaire a ensuite été conçu de manière à évaluer l’adhérence du joint dentinaire collé. L’adhérence sur surface fraisée s’est avérée statistiquement équivalente à celle de la surface préparée au laser pour le Xeno III et supérieure pour les deux autres. Le CSE bond présente les meilleurs résultats sur les deux types de surfaces. Les essais de cisaillement réalisés sur le CSE Bond avec pression ont montré des valeurs d’adhérence comparativement plus faibles sur surfaces fraisées alors qu’elles restaient équivalentes sur surfaces préparées au laser. La présence de boue dentinaire sur surface fraisée tend à favoriser l’adhérence d’adhésifs chargés. Cependant, le collage sur une surface propre et préparée au laser, avec ou sans pression trans-dentinaire, est plus reproductible que celui obtenu sur une surface fraisée recouverte de boue dentinaireThe goal of this study is to estimate the interactions between three self etching adhesive systems (CSE Bond, Xeno III and iBond) and dentin prepared using either burr or Re : YAG laser. Optica microscopy, SEM and XPS have been used to characterize lased surfaces. We have then studied the interactions between these three self etching adhesive systems and the substrate. Wettability studies have shown that lased surfaces were more absorbents and porous than burred surfaces. The self etching acid monomers are also absorbents and penetrate faster in lased surfaces. We have then set up a mechanical shearing test in order to evaluate the shearing strength of the bond. Shearing strength seems to be higher on burred surfaces than on lased surfaces. However these in vitro results are obtained on a dry surface which is not really physiological. We have thus adapted the device in order to generate a trans-dentinal pressure using demineralised water. With pressure, CSE Bond shearing strengths appeared to be comparatively lower on burred surfaces but remained equivalent on lased surfaces. We have also carried out a study of resin tags for the three self etching adhesive systems and for the two preparation techniques. The smear layer presence on burred surfaces seems to improve the bonding strength of filled adhesive resin. However these bonding strength measurements on a clean and lased surface – with or without trans-dentinal pressure – are more reproductive than for a burred surface with smear layer
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Dahlström, Johanna, Licette Hansen, Ellen Hartel, Francesca Larsson, and Hanna Pettersson. "Hållbara spårvägar." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-385340.
Анотація:
The Swedish city of Uppsala is growing and will be expanded. To manage the increase in traffic, a tramway is being planned. It is vital to make the construction and the tramway tracks sustainable. This is explored to study carbon dioxide emissions related to tramway track materials as well as their wear and service life. This project investigates sustainability, the tramway track constituents, rail steel, the rails' wear, rail surface treatments that could minimize wear and increase service life, materials surrounding the rails, and the production of the most used materials in tramway tracks. A literature study is conducted to compare different options for materials and treatments. The municipality of Uppsala's climate goals, technical standards and regulations, articles and studies about the mentioned topics, amongst other sources, are considered and compared. The results include a rough estimation of the material consumption and carbon dioxide emissions. Asphalt tracks have the lowest emissions of the different surrounding material options. The steel consumption and carbon dioxide emissions for the vignole rails are less than for grooved rails and the concrete consumption for grass tracks is slightly less compared to edilon tracks. It is also possible to switch from regular perlitic rail steel to bainitic rail steel when needed. Laser hardening, UNSM, and thermal plasma hardening decrease the rails' wear (rates) considering increased surface hardness.Uppsala är en växande stad och därför ska Södra staden byggas ut. Spårvagnstrafik planeras för att hantera den kommande trafikbelastning. Det är viktigt att göra konstruktionen av spårvägen till spårvagnen så hållbar och miljövänlig som möjligt. Detta utreds i denna rapport för att undersöka koldioxidutsläpp från spårvägens material samt dess slitage och livslängd. Rapporten undersöker hållbarhet, hur spårvägarna ser ut och dess olika delar, rälstål, rälernas slitage, ytbehandlingar till rälarna som kan minimera slitage och öka livslängden, samt tillverkningen av de mest förekommande materialen i spårvagnars spårvägar. En litteraturstudie genomförs för att jämföra olika materialvals- och behandlingsalternativ. Uppsala kommuns klimatmål, tekniska standarder och regelverk, artiklar och studier om de nämnda ämnena, bland andra resurser, används och jämförs. Studiens resultat inkluderar en grov uppskattning av materialåtgången och koldioxidutsläpp. Det blir minst koldioxidutsläpp från asfaltsspår när det gäller de omgivande materialen. Stålåtgången och koldioxidutsläppen för vignolräler är mindre än för gaturäler och betongåtgången blir lite mindre för grässpår jämfört med edilonspår. Det är även möjligt att byta från vanligt perlitiskt rälstål till bainitiskt rälstål vid behov. Laserhärdning, UNSM och termisk plasma härdning minskar rälernas slitage med avseende på framförallt ökningar av ythårdhet.
36
Holmquist, Melody L. "Using native mass spectrometry to study the role of homo-oligomeric proteins in gene regulation by using TRAP as a model protein system." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595571760595304.
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Mergler, Stefan [Verfasser]. "Functional expression of temperature-sensitive transient receptor potential channels (TRPs) in cultured human corneal and conjunctival cells : Relevance in the pathophysiology of ocular surface diseases / Stefan Mergler." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2015. http://d-nb.info/1078505403/34.
38
Abdulhasan, Zahraa M. "Impact of combined microprocessor control of the prosthetic knee and ankle on gait termination in unilateral trans-femoral amputees. Limb mechanical work performed on centre of mass to terminate gait on a declined surface using linx prosthetic device." Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/16906.
Анотація:
The major objective of this thesis was to investigate how the use of a recently developed microprocessor-controlled limb system altered the negative mechanical work done by the intact and prosthetic limb when trans-femoral amputees terminated gait. Participants terminated gait on a level surface from their self-selected walking speed and on declined surface from slow and customary speeds, using limb system prosthesis with microprocessor active or inactive. Limb negative work, determined as the integral of the negative mechanical (external) limb power during the braking phase, was compared across surface, speed and microprocessor conditions.
Halting gait was achieved predominantly from negative work done by the trailing/intact. Trailing versus leading limb mechanical work imbalance was similar to how able body individuals halted gait. Importantly, the negative limb work performed on the prosthetic side when terminating gait on declined surface was increased when the microprocessor was active for both slow and customary speeds (no difference on level surface) but no change on intact limb. This indicates the limb system’s ‘ramp-descent mode’ effectively/dynamically altered the hydraulic resistances at the respective joints with evidence indicating changes at the ankle were the key factor for increasing the prosthetic limb negative work contribution. Findings suggest that trans-femoral amputees became more assured using their prosthetic limb to arrest body centre of mass velocity when the limb system’s microprocessor was active. More generally findings suggest, trans-femoral amputees should obtain clinically significant biomechanical benefits from using a limb system prosthesis for locomotion involving adapting to their everyday walking where adaptations to an endlessly changing environment are required.Higher Committee of Education Development in IRAQ (HCED)
39
Gérard, Violaine. "Surfactants in atmospheric aerosols and their role on cloud formation." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1216/document.
Анотація:
Les nuages sont essentiels dans le cycle de l'eau et dans le budget climatique mais certains aspects de leur formation sont encore incompris. La théorie de Köhler prédit que les surfactants devraient favoriser l'activation des particules en goutte de nuage alors que les modèles actuels les considèrent comme négligeables. Au début de ce travail de thèse, quelques études commençaient à démontrer le contraire mais des preuves du rôle de ces composés dans l'atmosphère étaient encore manquantes, d'où l'objectif de ce travail de thèse. Le développement d'une méthode pour déterminer la concentration en surfactants dans les aérosols a conduit aux premières courbes de tension de surface de surfactants atmosphériques dans des aérosols PM2.5 côtiers (Suède), et à l'identification du ratio C/CMC comme paramètre clé contrôlant l'efficacité des aérosols à former des nuages. Une seconde étude a révélé des corrélations fortes entre la présence de nuages et les propriétés intrinsèques des surfactants dans des aérosols PM1 boréaux (Finlande), démontrant pour la première fois le rôle des surfactants dans la formation des gouttes de nuage à partir d'observations directes dans l'atmosphère. Les résultats prédisent un nombre de noyaux de condensation en moyenne quatre fois plus important que lorsque les effets des surfactants étaient négligés, montrant l‘importance d'inclure l'effet des surfactants dans les modèles prédictifs. Cette importance a été confirmée en laboratoire par des expériences sur des gouttes individuelles microniques par l'augmentation de leur taille en présence de surfactants. Enfin, les observations à partir des différentes études indiquent une origine biologique des surfactants dans les aérosols atmosphériquesClouds are essential components of the Earth’s hydrological system and climate but some aspects of their formation are still not completely understood. In particular, although Köhler theory predicts that surfactants should enhance cloud droplet activation, current models consider this role negligible. At the time of this PhD work, a few studies had started to demonstrate the contrary but atmospheric evidence for the role of these compounds was still missing and very little was known about their atmospheric concentrations, sources, and mechanism of action. The objective of this PhD work was to investigate these aspects. A method was developed to quantify surfactant concentrations in aerosols. Its application led to the first absolute atmospheric surfactants’ surface tension curves, in coastal PM2.5 aerosols in Sweden, and to the identification of the ratio C/CMC as the key parameter controlling the cloud-forming efficiency of aerosols. A second study revealed strong correlations between cloud occurrence and intrinsic surfactant properties in boreal PM1 aerosols in Finland, demonstrating for the first time the role of surfactants in cloud formation from direct atmospheric observations. The results predicted Cloud Condensation Nuclei numbers four times larger on average than when neglecting surfactant effects, showing the importance of including surfactant effects in cloud predictions models. The role of surfactants inferred from macroscopic measurements was confirmed by laboratory experiments on individual micron-sized droplets showing an increase of droplet growth in the presence of surfactants. Finally, observations from the different field studies indicated a biological origin for the surfactants present in atmospheric aerosols
40
Renisch, Dennis [Verfasser]. "Installation and operation of a high-temperature surface ion source for the online coupling of TRIGA-SPEC to the TRIGA Mainz research reactor and high-precision mass measurements of transuranium nuclides at TRIGA-TRAP / Dennis Renisch." Mainz : Universitätsbibliothek Mainz, 2016. http://d-nb.info/1105495981/34.
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Soares, Fabiana Andréia Schäfer De Martini. "Interesterificação química e enzimática de misturas de estearina de palma, óleo de coco e óleo de canola para formulação de margarinas com baixa concentração de isômeros trans." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/9/9133/tde-27052015-111527/.
Анотація:
O consumidor está cada vez mais consciente da relação entre dieta e doença, que tem impulsionado as pesquisas sobre alimentos funcionais e seus efeitos sobre o corpo. O papel dos óleos e gorduras na nutrição humana tem sido intensamente estudado e discutido por décadas. Tem sido enfatizada a importância da ingestão de ômega-3, ômega-6 e ômega-9 ácidos graxos redução de ácidos graxos saturados e, mais recentemente, controle da ingestão de ácidos graxos trans. Através da mistura e interesterificação química e enzimática de óleos e gorduras, gorduras trans-livre pode ser produzido. Mistura de gordura, foram formuladas por misturas ternárias de estearina de palma, uma gordura láurica (óleo de coco ou óleo de palmiste) e um óleo poliinsaturado (óleo de canola ou azeite de oliva) em diferentes proporções que foram interesterificadas. Neste trabalho, foram produzidos lipídios estruturados por interesterificação química e enzimática. A interesterificação química foi realizada nas seguintes condições: a 88 °C, 60 minutos de reação, 0,4% de catalisador metóxido de sódio, sob agitação e vácuo. A interesterificação enzimática, sendo realizada com duas lipases comerciais Thermomyces lanuginosa e Rhizomucor miehei, com seletividade sn-1,3. A interesterificação enzimática por batelada foi realizado seguindo um planejamento matriz central compósito rotativo em função da temperatura e da composição do meio, estearina de palma, óleo de palmiste e azeite de oliva e catalisado pelas lipases comerciais. O decréscimo do conteúdo de gordura sólida foi observado a 10 e 35 °C após a interesterificação. O biorreator contínuo foi operado nas seguintes condições: mistura de estearina de palma, óleo de palmiste, azeite de oliva (45:30:25), 10 gr de biocatalisador, 65 °C, com tempo de residência de 7 min e por 226 h para Thermomyces lanuginosa e 188 h para Rhizomucor miehei. A atividade do biocatalisador foi avaliada em termos da diminuição do conteúdo de gordura sólida a 35 °C, o qual é um parâmetro chave na produção de margarinas. O perfil de inativação do biocatalisador pode ser bem descrita pelo modelo de desativação de primeira ordem: meia-vida de 88 e 60 h foram estimados quando Thermomyces lanuginosa e Rhizomucor miehei, respectivamente, foram utilizados. Os óleos puros, as misturas originais e interesterificadas foram avaliados quanto à composição de ácidos graxos e triacilgliceróis, distribuição regioespecífica dos ácidos graxos nos triacilgliceróis, ponto de fusão e amolecimento, consistência, conteúdo de gordura sólida, comportamento de fusão e cristalização, estabilidade oxidativa, estrutura cristalina e polimorfismo. A interesterificação química e enzimática promoveram diminuição de triacilgliceróis trissaturados e triinsaturados e aumento dos monossaturados-diinsaturados e dissaturados-monoinsaturados, o que resultou no respectivo decréscimo dos pontos de fusão e amolecimento, consistência e conteúdo de gordura sólida, aumentando a plasticidade das gorduras. As curvas de fusão e cristalização das misturas foram modificadas pela alteração da composição dos triacilgliceróis pela interesterificação química e enzimática. Estabilidade térmica e a temperatura de oxidação da estearina de palma, óleo de coco e óleo de canola e suas misturas foram dependente da composição de ácidos graxos e independente da interesterificação química. Os resultados mostram que a interesterificação química e enzimática oferecem uma ferramenta útil para a concepção de gorduras com sintonizáveis propriedades físico-químicas, melhorando em relação a esse das gorduras de partida.The consumer is becoming more aware of the relationship between diet and disease, which has driven the research on functional foods and their effects on the body. The role of fats and oils in human nutrition has been intensively studied and discussed for decades. It has been emphasized the importance of intake of omega-3, omega-6 and omega-9 fatty acids, reduction of saturated fatty acids and, more recently, control of intake of trans fatty acids. Through the blend and interesterification of oils and fats, trans-free fats can be produced. Fat blends, formulated by ternary blends of palm stearin, lauric fat (coconut oil and palm kernel oil) and polyunsaturated oils (canola oil and olive oil) were done in different ratios. In this work, were produced by chemical and enzymatic interesterification. Chemical interesterification was performed under the following conditions: at 88°C, 60 minutes reaction times, 0.4% sodium methoxide, under agitation and vacuum. For enzymatic interesterification being carried out with two commercial lipases Thermomyces lanuginosa e Rhizomucor miehei, with selectivity sn-1,3. Batch enzymatic interesterification were performed, following central composite rotatable designs (CCRDs) as a function temperature and media of palm stearin, palm kernel oil and olive oil formulation and catalyzed by a commercial immobilized lipase. A decrease in all SFC values of the blends at 10 °C and 35°C was observed upon interesterification. The bioreactor operated continuously: mixture of palm stearin, palm kernel oil and olive oil (45:30:25, wt %), at 65 °C, at a residence time of 7 min and for 226 h to Thermomyces lanuginosa and 188 h to Rhizomucor miehei.. Biocatalyst activity was evaluated in terms of the decrease of the solid fat content at 35 °C of the blends, which is a key parameter in margarine manufacture. The inactivation profile of the biocatalyst could be well described by the first-order deactivation model: Half-lives of 88 and 60 h were estimated when Thermomyces lanuginose and Rhizomucor miehei, respectively, were used. Pure oil, the original and interesterified blends were examined for fatty acids and triacylglycerols composition, regiospecific distribution of fatty acids in triacylglycerols, melting and softening points, consistency, solid fat content, thermal behavior, oxidation stability, crystalline microstructure and polymorphism. Chemical and enzymatic interesterification caused reduction of trisaturated and triunsaturated and increase in monosaturated-diunsaturated and disaturated-monounsaturated, lowering the initial melting and softening points, consistency and solid fat content, increasing plasticity of fats. Melting and crystallization curves were significantly modified by changing the composition of triacylglycerols by chemical and enzymatic interesterification. The thermal stability and oxidation temperature of palm stearin, coconut oil and canola oil and their blends were dependent on fatty acid composition and independent on chemical interesterification. The results show that the chemical and enzymatic interesterification provides a useful tool to design fats with tunable physicochemical properties, improved compared to that of the starting fats.
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ALMEIDA, Euclides Cesar Lins. "Ultrafast dynamics of nanoscale systems: NaNbO3 nanocrystals, colloidal silver nanoparticles and dye functionalized TiO2 nanoparticles." Universidade Federal de Pernambuco, 2012. https://repositorio.ufpe.br/handle/123456789/18659.
Анотація:
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CNPQ
O principal objetivo deste trabalho foi investigar fenômenos ópticos ultrarrápidos em sistemas nanoestruturados empregando diferentes técnicas espectroscópicas não lineares, tanto no domínio do tempo quanto no domínio da frequência. Para fornecer uma base adequada que permita entender os experimentos feitos nessa tese, os princípios físicos das espectroscopias ópticas não lineares são apresentados. Inicialmente é apresentada uma descrição da função resposta não linear no domínio do tempo. A evolução temporal da polarização óptica, que gera o sinal espectroscópico, é descrita em detalhes usando uma teoria de perturbação diagramática. Técnicas ópticas não lineares são apresentadas, tais como eco de fótons, bombeamento-e-sonda e hole burning, assim como o comportamento dinâmico de um material pode ser interpretado a partir do sinal gerado. A técnica de mistura degenerada de quatro ondas com luz incoerente foi usada para investigar, pela primeira vez, o defasamento ultrarrápido de éxcitons em uma vitrocerâmica contendo nanocristais de niobato de sódio. O tempo de defasamento medido (T2 = 20 fs) indica qu empregada para investigar processos de transferência de carga em colóides com nanopartículas de TiO2 e rodamina 6G. O comportamento do sinal de depleção transiente é comparado com o observado para a rodamina livre suspensa em etanol. A análise dos resultados permitiu atribuir o comportamento de depleção à transferência de carga de estados excitados termalizados das moléculas de corante para a banda de condução do semicondutor e a transferência no sentido inverso do semicondutor para as moléculas.
The main objective of this work was the investigation of ultrafast optical phenomena in selected nanostructured systems employing different nonlinear spectroscopic techniques, either in the time or the frequency domain. To provide an appropriate background to understand the performed experiments the principles of nonlinear optical spectroscopies are presented. Initially a description of the nonlinear optical response function in the time domain is given. The time evolution of the optical polarization, that gives rise to the spectroscopic signal, is described in detail using a diagrammatic perturbation theory. Nonlinear optical techniques are discussed such as photon echoes, pump-and-probe and hole-burning, as well as how the dynamical behavior of a material can be interpreted from the generated signals. The degenerate four-wave mixing technique with incoherent light was used to investigate for the first time the ultrafast dephasing of excitons in a glass-ceramic containing sodium niobate nanocrystals. The short dephasing time measured (T2 = 20 fs) indicates that different dephasing channels contribute for the excitonic dephasing, namely: electron-electron scattering, electron-phonon coupling and fast trapping of electrons in defects on the nanocrystals interface. Low-temperature luminescence experiments were also performed to measure excitonic and trap states lifetimes. The persistent spectral holeburning technique was applied to measure localized surface plasmons dephasing times in colloidal silver nanoparticles capped with different stabilizing molecules. The dependence of T2 with three different stabilizers was demonstrated and theoretically analyzed. The results show that the dephasing times are shorter than the theoretically calculated T2 using the bulk dielectric functions of the metal. This discrepancy is attributed to changes in the electronic density of states at the nanoparticles interface caused by the presence of the stabilizers. Ab-initio calculations based on the Density Functional Theory were performed to further understand the interaction between the nanoparticles and stabilizing agents. The femtosecond transient absorption technique was employed to study the ultrafast dynamics of in-gap states in a glassceramics containing sodium niobate nanocrystals. Two main temporal components were found for the excited state absorption signal: a fast component, with decay time of ≈ 1 ps, and a slower component which is attributed to deep trap states. This slower component is responsible for the excited state absorption contribution in optical limiting experiments previously reported in the literature. The dynamics of the optical limiting in this sample was also studied, in the millisecond range, exciting the sample with a train of femtosecond pulses. The optical limiting behavior reflects the dynamics of population in the excited and trap states and this dynamics was modeled using rate equations for the electronic states’ populations. Finally, the pump-andprobe transient absorption technique was employed to investigate charge-transfer processes in colloids with rhodamine 6G and TiO2 nanoparticles. The transient bleaching signal behavior is compared with the one observed for unlinked rhodamine 6G dissolved in ethanol. The analysis of the results allowed the attribution of the bleaching behavior to charge-transfer from thermalized excited states of the dye molecules to the semiconductor conduction band and to the back charge-transfer from the semiconductor to the molecules.
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Bilyard, Thomas. "Single molecule studies of F1-ATPase and the application of external torque." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:9f369674-4105-4bf1-a0ce-023db1f8bd7f.
Анотація:
F1-ATPase, the sector of ATP synthase where the synthesis of cellular ATP occurs, is a rotary molecular motor in its own right. Driven by ATP hydrolysis, direct observation of the rotation of the central axis within single molecules of F1 is possible. Operating at close to 100% efficiency, F1 from thermophilic Bacillus has been shown to produce ~40pN˙nm of torque during rotation. This thesis details the groundwork required for the direct measurement of the torque produced by F1 using a rotary angle clamp, an optical trapping system specifically designed for application to rotary molecular motors. Proof-of-concept experiments will be presented thereby demonstrating the ability to directly manipulate single F1 molecules from Escherichia coli and yeast mitochondria (Saccharomyces cerevisiae), along with activation of F1 out of its inhibited state by the application of external torque. Despite in-depth knowledge of the rotary mechanism of F1 from thermophilic Bacillus, the rotation of F1 from Escherichia coli is relatively poorly understood. A detailed mechanical characterization of E.coli F1 will be presented here, with particular attention to the ground states within the catalytic cycle, notably the ATP-binding state, the catalytic state and the inhibited state. The fundamental mechanism of E.coli F1 appears to depart little from that of F1 from thermophilic Bacillus, although, at room temperature, chemical processes occur faster within the E.coli enzyme, in line with considerations regarding the physiological conditions of the different species. Also presented here is the verification of the rotary nature of yeast mitochondrial F1. The torque produced by F1 from thermophilic Bacillus, E.coli and yeast mitochondria is the same, within experimental error, despite their diverse evolutionary and environmental origins.
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Chang, Yu-Hsuan, and 張祐瑄. "Investigation on Interface Traps of Planar GaN MOSFETs with Different Surface Treatment." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/347ywr.
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Kirmani, Ahmad R. "Surface Traps in Colloidal Quantum Dot Solar Cells, their Mitigation and Impact on Manufacturability." Diss., 2017. http://hdl.handle.net/10754/625510.
Анотація:
Colloidal quantum dots (CQDs) are potentially low-cost, solution-processable semiconductors which are endowed, through their nanoscale dimensions, with strong absorption, band gap tunability, high dielectric constants and enhanced stability. CQDs are contenders as a standalone PV technology as well as a potential back layer for augmenting established photovoltaic (PV) technologies, such as Si. However, owing to their small size (ca. few nanometers), CQDs are prone to surface trap states that inhibit charge transport and threaten their otherwise wonderful optoelectronic properties. Surface traps have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells, as all of the reports, to date, have relied on spin-coating with sophisticated and tedious ligand exchange schemes, some of which need to be performed in low humidity environments.
In this thesis, we posit that an in-depth understanding of the process-structure-property-performance relationship in CQDs can usher in fresh insights into the nature and origin of surface traps, lead to novel ways to mitigate them, and finally help achieve scalable fabrication. To this end, we probe the CQD surfaces and their interactions with process solvents, linkers, and ambient environment employing a suite of spectroscopic techniques. These fundamental insights help us develop facile chemical and physical protocols to mitigate surface traps such as solvent engineering, remote molecular doping, and oxygen doping, directly leading to better-performing solar cells. Our efforts finally culminate in the realization of >10% efficient, air-stable CQD solar cells scalably fabricated in an ambient environment of high, uncontrolled R.H. (50-65%). As-prepared solar cells fabricated in high humidity ambient conditions are found to underperform, however, an oxygen-doping recipe is devised to mitigate the moisture-induced surface traps and recover device performances. Importantly, these solar cells are fabricated at coating speeds of >15 m min-1 with roll-to-roll compatible techniques such as blade and bar coating requiring 1/25th the CQD material consumed by the standard spin-coated devices, overcoming the two major challenges of manufacturability and scalability faced by CQD PV.
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"Surface Potential Modelling of Hot Carrier Degradation in CMOS Technology." Master's thesis, 2017. http://hdl.handle.net/2286/R.I.44270.
Анотація:
abstract: The scaling of transistors has numerous advantages such as increased memory density, less power consumption and better performance; but on the other hand, they also give rise to many reliability issues. One of the major reliability issue is the hot carrier injection and the effect it has on device degradation over time which causes serious circuit malfunctions.
Hot carrier injection has been studied from early 1980's and a lot of research has been done on the various hot carrier injection mechanisms and how the devices get damaged due to this effect. However, most of the existing hot carrier degradation models do not consider the physics involved in the degradation process and they just calculate the change in threshold voltage for different stress voltages and time. Based on this, an analytical expression is formulated that predicts the device lifetime.
This thesis starts by discussing various hot carrier injection mechanisms and the effects it has on the device. Studies have shown charges getting trapped in gate oxide and interface trap generation are two mechanisms for device degradation. How various device parameters get affected due to these traps is discussed here. The physics based models such as lucky hot electron model and substrate current model are presented and gives an idea how the gate current and substrate current can be related to hot carrier injection and density of traps created.
Devices are stressed under various voltages and from the experimental data obtained, the density of trapped charges and interface traps are calculated using mid-gap technique. In this thesis, a simple analytical model based on substrate current is used to calculate the density of trapped charges in oxide and interface traps generated and it is a function of stress voltage and stress time. The model is verified against the data and the TCAD simulations. Finally, the analytical model is incorporated in a Verilog-A model and based on the surface potential method, the threshold voltage shift due to hot carrier stress is calculated.Dissertation/Thesis
Masters Thesis Electrical Engineering 2017
47
"Improved Model for Excess Base Current in Irradiated Lateral PNP Bipolar Junction Transistors." Master's thesis, 2017. http://hdl.handle.net/2286/R.I.46303.
Анотація:
abstract: A modeling platform for predicting total ionizing dose (TID) and dose rate response of commercial commercial-off-the-shelf (COTS) linear bipolar circuits and technologies is introduced. Tasks associated with the modeling platform involve the development of model to predict the excess current response in a bipolar transistor given inputs of interface (NIT) and oxide defects (NOT) which are caused by ionizing radiation exposure. Existing models that attempt to predict this excess base current response are derived and discussed in detail. An improved model is proposed which modifies the existing model and incorporates the impact of charged interface trap defects on radiation-induced excess base current. The improved accuracy of the new model in predicting excess base current response in lateral PNP (LPNP) is then verified with Technology Computer Aided Design (TCAD) simulations. Finally, experimental data and compared with the improved and existing model calculations.Dissertation/Thesis
Masters Thesis Electrical Engineering 2017
48
Chen, Tsung-Chien, and 陳宗謙. "Design of Surface Magneto-Optical Trap." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/14201571105588055730.
Анотація:
碩士國立中正大學
物理學系暨研究所
100
We design the atom chip system. This system includes ultra-high system, atom chip, current controller and helmholtz coils etc. All the system introduce in the chapter three and four. The goal of this system will using laser cooling and surface magneto-optical trap to capture Rubidium and Cesium cold atoms. We also need to find the best condition to the magnetic trap. Changing the gradient of magnetic to let these two cold atoms collide or overlap. We will also use the phase shifting interferometry to detect the atoms.
49
Fan, Zi-Xuan, and 范子璿. "Surface Magneto-Optical Trap for Rubidium Atoms." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/74430678414215566895.
50
Cheng, Szu-Yang, and 鄭斯陽. "The adsorption and thermal desorption of trans-methylstyrene and trans-stilbene molecules on Ge(100) surface." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/t7t366.
Анотація:
碩士國立臺北科技大學
有機高分子研究所
101
Self-ordered organic molecules on semiconductor surfaces have been investigated extensively. The adsorbed molecules arranged in different ways that affect surface properties of the semiconductor, such as conductivity and chemical reactivity. The organic functionalization of semiconductor surfaces possess wide potential applications such as chemical and biological sensors, corrosion inhibition, insulating film and thin film displays. In this work, the adsorption and thermal desorption of trans-methylstyrene (TMS) and trans-stilbene (TS) on Ge(100) have been studied under the ultra-high vacuum (UHV) condition. The Ge(100) single crystal surface structures were observed at 100, 200, and 300 K by low energy electron diffraction (LEED). Ge(100) was exposed to TMS by direct dose at 100 and 300 K, and by background dose at 300 K. The temperature-programmed desorption (TPD) analysis showed three desorption peaks at (I) 180-210, (II) 300-400, and (III) 400-550 K for molecular desorption of TMS from the Ge(100) surface. Ge(100) was exposed to TS by direct dose at 100 and 200 K, and by background dose at 100 K. The TPD analysis showed two desorption peaks at (I) 220-300 and (II) 300-500 for molecular desorption of TS from the Ge(100) surface.