A number of different aspects of Frenkel defect production are discussed in this thesis. Experiments have been performed to characterise the response of sapphire to radiation and to determine the stability, with respect to temperature and subsequent ionising radiation, of the oxygen vacancies produced. The displacement threshold of the aluminium ion has been determined by irradiating with electrons and comparing measured concentrations of the V centre with theoretical values, and evidence is presented for the stability of the F²⁺ centre at liquid helium temperatures. The efficiency of point defect production in sapphire by a variety of ion beams has been estimated by monitoring the oxygen vacancy colour centre concentration. Results are presented for H, D, He, B, N, Ne, Ar and Kr bombardment at both room temperature and 77K. Experimentally determined values of the mean number of oxygen vacancies produced per incident ion are compared with theoretical values. The latter have been computed by solving the Lindhard integral equations to determine the partitioning of energy between the oxygen and aluminium sublattices. The stopping powers and cross sections of Ziegler, Biersack and Littmark have been used in these calculations and give significantly improved estimates of the damage energy. Two main points emerge from this study. Firstly, a significant Z₁ variation of the damage efficiency is noted for low mass ions. Secondly, in contrast to metals (in particular aluminium) no reduction in efficiency has been found in sapphire with increasing ion mass. This is attributed to differences in the 'thermal spike' behaviour, as a consequence of differing thermodynamic properties, between aluminium and its oxide. The implications of both these results for irradiation characterisation are discussed. In the final chapter we discuss the interaction between conduction electrons and ions in the cooling phase of cascades in metals. Differential equations governing the transfer of heat between the two systems are derived and solved numerically, using physically reasonable parameters for cascades in copper and nickel. Large differences are found in the cooling rates of cascades in these two metals. The degree of cooling due to electronic heat transport is shown to depend on the ratio of a parameter T₀, the temperature at which the electron-phonon mean free path reduces to the radius of the Wigner-Seitz sphere, and γ_e, the coefficient of the electronic heat capacity. The participation of the electronic system in cascade evolution is shown to preclude a universal description of damage efficiency on the basis of simple atomic scaling laws.

Zugl.: München, Techn. Univ., Diss., 2010.

This dissertation is an exploratory case study of the archives of Canadian artist Vera Frenkel and their acquisition by Queen’s University Archives in Kingston, Ontario. The research seeks to understand, through empirical investigation, the many factors that shape the artist’s recordkeeping and archives in the personal sphere and contribute to the nature of the eventual archival fonds in the institution. The foundation for the research includes the literatures of archival studies, life narrative, and art. Vera Frenkel’s interdisciplinary art work reflects a deep engagement with questions of truth and fiction. As an aspect of this theme, records and archives play a role in several of her works, often being revealed as problematic sources of evidence. Fundamental to the artist’s approach to interdisciplinarity is a complex layering of elements that builds uncertainty in the viewer. Given these aspects of Frenkel’s work, research that elicits the artist’s testimony about her archives must be able to accommodate a degree of ambiguity in the construction of that testimony. In a series of in situ interviews with the artist in her studio, the author investigated Frenkel’s recordkeeping habits and their relationship to her creative practice. As a data source, these interviews were supplemented by the artist’s photographs and hand-drawn maps of the studio. The author also investigated the processes entailed by archival transfer, examining the extant Vera Frenkel fonds at Queen’s University Archives and interviewing Heather Home, the archivist responsible for the acquisition. Both the personal and institutional spheres were taken into consideration as essential contributors to the nature of Frenkel’s archives as a complex cultural artifact. The research argues for the central role of archives in the acquisition and preservation of contemporary art. It contributes a foundation for understanding the nature of visual artists’ archives.

This dissertation is an exploratory case study of the archives of Canadian artist Vera Frenkel and their acquisition by Queen’s University Archives in Kingston, Ontario. The research seeks to understand, through empirical investigation, the many factors that shape the artist’s recordkeeping and archives in the personal sphere and contribute to the nature of the eventual archival fonds in the institution. The foundation for the research includes the literatures of archival studies, life narrative, and art. Vera Frenkel’s interdisciplinary art work reflects a deep engagement with questions of truth and fiction. As an aspect of this theme, records and archives play a role in several of her works, often being revealed as problematic sources of evidence. Fundamental to the artist’s approach to interdisciplinarity is a complex layering of elements that builds uncertainty in the viewer. Given these aspects of Frenkel’s work, research that elicits the artist’s testimony about her archives must be able to accommodate a degree of ambiguity in the construction of that testimony. In a series of in situ interviews with the artist in her studio, the author investigated Frenkel’s recordkeeping habits and their relationship to her creative practice. As a data source, these interviews were supplemented by the artist’s photographs and hand-drawn maps of the studio. The author also investigated the processes entailed by archival transfer, examining the extant Vera Frenkel fonds at Queen’s University Archives and interviewing Heather Home, the archivist responsible for the acquisition. Both the personal and institutional spheres were taken into consideration as essential contributors to the nature of Frenkel’s archives as a complex cultural artifact. The research argues for the central role of archives in the acquisition and preservation of contemporary art. It contributes a foundation for understanding the nature of visual artists’ archives.

Fuer anorganische Kristalle werden die chemischen Bindungen durch kovalente oder ionische Beitraege dominiert. Im Gegensatz dazu stehen organische Molekuelkristalle, in denen in jedem der Molekuele starke kovalente Bindungen vorherrschen, waehrend die Molekuele untereinander nur relativ schwache Wechselwirkung zeigen. Daher sind die Veraenderungen zwischen den Spektren freier Molekuele und den entsprechenden Kristallen wesentlich geringer als die zwischen einem freien Atom und einem anorganischen Kristall. In einem organischen Kristall kann eine optisch erzeugte elektronische Anregung zwischen verschiedenen Molekuelen transferiert werden. Fuer das Modellsystem PTCDA (3,4,9,10-Perylentetracarbonsaeuredianhydrid) wurden die elektronischen und vibronischen Spektren analysiert und die aus dem Transfer der Anregung resultierende exzitonische Bandstruktur untersucht. Die optische Absorption erzeugt ein Frenkel-Exziton am Dispersionsmaximum in der Naehe des Gamma-Punktes in der Brillouin-Zone. Durch inelastische Streuvorgaenge relaxiert dieses Exziton zum Dispersionsminimum am Rand der Brillouin-Zone. Die Photolumineszenz bei tiefen Temperaturen entsteht daraus durch vertikale Rekombination, wobei der Endzustand eine vibronische Anregung mit endlichem Quasi-Impuls enthaelt. Die berechnete strahlende Rekombinationsrate und die Linienform der Photolumineszenzbande stimmen dabei gut mit den experimentellen Ergebnissen ueberein. Das Modell des Exzitonentransfers im Volumenmaterial kann auf Filme endlicher Dicke verallgemeinert werden, so dass sich die veraenderten optischen Eigenschaften duenner Filme beschreiben lassen. Durch die endliche Zahl der molekularen Monolagen in einem solchen Film ist das energetische Spektrum diskret, wobei die Einhuellenden der exzitonischen Wellenfunktionen entlang der Quantisierungsrichtung an die Zustaende in einem Quantentrog mit unendlich hohen Barrieren erinnern. Das Zusammenspiel von geometrischer Randbedingung und energetischer Lage des molekularen uebergangs in der Randschicht kann sowohl zu einer Rot- als auch zu einer Blauverschiebung der optischen Antwort fuehren.

Chemnitz, Techn. Univ., Diss., 2003.

The specialized pigment-protein complexes involved in the first process of photosynthesis are light-harvesting structures that are composed of networks of chromophores in protein scaffolds. Though light-harvesting complexes vary in chromophore composition and protein structure, they are capable of transferring the absorbed energy as molecular excitation energy from chromophore to chromophore with maximal efficiency. Thus, numerous interdisciplinary studies focus on elucidating energy transfer mechanisms in these biological complexes and how the same principles can be applied to artificial photosynthetic and photovoltaic machines. From advanced spectroscopic measurements and theoretical models, the interaction between the excited electronic states and the nuclear vibrational degrees of freedom is now established to be crucial for efficient energy transfer. In light-harvesting complexes of plants and bacteria, it is now understood that the classical-like vibrational modes of the protein and solvent environment drive energy transfer between the energetically close electronic states of the chromophores. On the other hand, recent spectroscopic measurements on algae light-harvesting complexes discovered signatures of quantized, high frequency vibrational modes of the chromophore. Unfortunately, a deterministic interpretation of the data and the underlying Hamiltonian is hindered due to significant inhomogeneous spectral line-broadening. Though numerous model Hamiltonians have been proposed from theoretical work, various computational approximations employed in these studies necessitate empirical parameter tuning in order to obtain agreement with benchmark linear optical spectra. Thus in this work, we present a simple, but improved, computational prescription to compute the ensemble of Hamiltonians for four closely-related algae light-harvesting complexes. We verify the reliability of our proposed models by comparing simulated optical spectra with experimental measurements. We show that static disorder and inhomogeneous broadening are significant for phycobiliproteins due to large site energy fluctuations. We also show that the nuclear environment plays an important role in defining the trapping state, or the final energy acceptor. Finally, our work for the first time suggests that EET dynamics can be tuned by varying the titration states of the chromophores.

Abstract Nd-modified lead-zirconate-titanate (PNZT) thin films were deposited on MgO(100), Si(100) and Al2O3(1102) single-crystal substrates using the pulsed-laser-ablation technique with a XeCl excimer laser. The post-annealing heat-treatment technique was used for the crystallisation of the films. The structural characterization, microstructure and the chemical composition of the thin films and of the ceramic Pb0.97Nd0.02(Zr0.55Ti0.45)O3 targets after ablation were studied using x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The formation of the particulates on the target surface during the ablation process and the effect of the particulates on the quality of the thin films were studied. Typically, the ferroelectric PNZT thin films for the capacitor structures were deposited at the laser-beam fluence of around 1.0 J/cm2 and annealed at the temperatures from 600 to 700 °C. The dielectric and, especially, the polarization properties and the residual macroscopic stress state of the PNZT thin films were studied. The relationship between the electrical properties of the films and the nature of the stress state was also investigated. The average growth rate of the PNZT films increased linearly with increasing laser-beam fluence above the threshold value of around 0.4 J/cm2. The composition of the PNZT films varied strongly with the deposition laser-beam fluence and annealing temperature. The phase structure of PNZT films ablated from Pb0.97Nd0.02(Zr0.55Ti0.45)O3 targets could be adjusted between tetragonal and rhombohedral structures by changing the incident laser-beam fluence on the target surface. The surface of the target after ablation was covered by the laser-cone structure and the topmost layer of the target was amorphous having TiO2 and ZrO2 structures with separate segregated lead droplets. On MgO substrates, values of the relative dielectric constant er from 430 to 560 and of the remanent polarization εr of the order of 18 μC/cm2 were achieved in PNZT films which were under a compressive stress of the order of 300 MPa. On silicon substrates, εr was around 100 and the polarization properties of the films were modest due to a strong tensile stress of the order of 400 MPa. The Poole-Frenkel conduction mechanism with the activation energy of around 0.2 eV was found responsible for the leakage conductivity in the capacitor structures with PNZT films.

Pendant cette thèse nous avons travaillé sur deux aspects des nanoparticules organiques fluorescentes d’AdamBodipy : leur spectroscopie et leur production avec des tailles contrôlées. La structure cristallographique des cristaux d’Adambodipy a été obtenue par diffraction-X. Nous avons produit des microcristaux (100×10×1µm3) par précipitation dans des solutions de sursaturation faible. Nous avons mesuré leur spectroscopie sous microscope dans la gamme 380nm à 900nm. Les microcristaux sont biréfringents et dichroïques. Nous avons mesuré leur biréfringence en déterminant leurs indices de réfraction suivant les deux axes neutres par le méthode de Swanepoel. Nous avons mesuré des spectres d’absorption suivant les axes neutres. Nous avons calculé ces spectres d’absorption en utilisant la théorie du couplage dipolaire pour les exciton de Frenkel. La valeur du couplage intermoléculaire a été estimée par le modèle classique. Mais pour deux paires particulaires de la maille nous avons comparé cette estimation classique du couplage avec la valeur qui peut être déduite du calcul quantique du dimère par TDDFT. L’ordre de grandeur est vérifié. Le programme s’applique à des nanoparticules formées de N×N×N (N<11) mailles cristallines. Les spectres calculés reproduisent le dichroïsme, l’élargissement des spectres d’absorption, mais il apparaît que les spectres expérimentaux sont écrêtés par la faible dynamique de notre spectrophotomètre sous microscope. Le calcul du spectre de fluorescence prédit une bande polarisée selon la direction b de la maille. L’expérience en distingue deux autres décalée dans le rouge. L’étude de leur polarisation ainsi que de leur dynamique de fluorescence permet d’attribuer ces bandes rouges à des défauts dans la structure cristalline. Les spectres des nanoparticules produites dans la deuxième partie ne sont pas ceux de la forme cristalline. Nous avons pu reproduire ces spectres en introduisant un désordre d’orientation à l’intérieur la structure des N×N×N mailles. La focalisation hydrodynamique 3D, nous a permis de produire des nanoparticules de taille contrôlée sans qu’il y ait précipitation de l’AdamBodipy sur les parois. En réglant le rapport des flux entre la solution organique de colorant et la solution aqueuse non solvant, nous avons pu ajuster la taille des nanoparticules entre 100 et 300nm. La stabilité colloïdale des nanoparticules est assurée par du CTACl en dessous de la CMC. En effet au dessus de la CMC les nanoparticules coexistent avec des micelles chargées en colorant. Les spectroscopies d’absorption et de fluorescence des nanoparticules montrent qu’elles sont amorphes. Nous avons simulé la précipitation des nanoparticules par COMSOL en introduisant une l’hydrodynamique de mélange par diffusion mutuelle de l’eau et de l’éthanol et de diffusion du colorant dans ce mélange. Nos études de la solubilité de l’Adambodipy dans des mélanges organiques/eau, nous ont permis de déterminer la loi de solubilité et d’obtenir des cartes de la super-saturation dans le microdispositif. Nous avons utilisé l’imagerie de fluorescence pour suivre le processus de précipitation. Les images obtenues sont semblables à celles calculées par COMSOL On observe une précipitation à l’interface entre les deux solvants ainsi qu’une précipitation en masse après un temps de résidence qui dépend du rapport des flux. Les déclins de fluorescence collectés en différents points du canal microfluidique peuvent être attribués à trois espèces : le monomère, la nanoparticule et une espèce intermédiaire, un germe. / During this work, we have addressed two aspects of the properties of the fluorescent organic nanoparticles made of Adambodipy: their spectroscopy and their production with controlled sizes. We have produced micro-crystals (100x10x1µm3) by precipitation in solutions of low supersaturation. We have measured their spectroscopy under microscope in the range 380nm to 900nm. The microcrystals are birefringent and dichroic. By adding polarizers on a microscope we have measured their refraction index along the two neutral axes according to the method of Swanepoel. We have measured the two absorption spectra along the neutral axis. We have calculated these absorption spectra using the model of the dipolar coupling for Frenkel excitons. The amplitude of this coupling has been estimated according to the classic model. But for two particular pairs of the cell, we have compared this estimation with the value that can be deduced from the quantum calculation of a dimer by TDDFT. The calculated spectra reproduce the dichroism, the spectral broadening of the absorption spectra but not the experimental peak shape probably because our micro-spectrophotometer levels up at high absorbance. The calculated fluorescence spectra predict a polarized transition along the b direction of the cell. The experiment shows two other red shifted bands. The study of their polarization, as well as their fluorescence lifetime allows us to attribute them to defects in the crystal. The spectra of the nanoparticles produced in the second part of this work are not those of crystals. We have been able to reproduce them theoretically by introducing an orientation disorder inside the periodic structure. The 3D hydrodynamic focusing enables us to produce nanoparticles with controlled size without precipitation of Adambodipy on the wall. We have used the PDMS technology and we moved to a glass tube approach, in order to avoid the diffusion of fluorescence into the PDMS. By adjusting the flow ratio between the inner organic solution of the dye and outer aqueous solution, we can control the size of the nanoparticle between 100nm and 300nm. The stability of the colloidal suspension is maintained by the surfactant CTACl below the CMC. Indeed above the CMC, the nanoparticles exist together with dyes dispersed in micelles. We have simulated using COMSOL the precipitation of the nanoparticles. We have introduced in the calculation the hydrodynamic and mutual diffusion of water and ethanol, as well as the diffusion of the Adambodipy. From our studies of the solubility of Adambodipy in water/ethanol mixtures, we have obtained the saturation curve and we have built the supersaturation maps in the micro-device. We have used Fluorescence lifetime imaging microscopy to follow in situ the precipitation process. From the decay collected in different positions can be attributed to the coexistence of three species : the monomers, the nanoparticles and an intermediate species supposed to be the nuclei. The FLIM shows a precipitation in the diffusion area of the two solvents as well as a massive precipitation after a few hundred of millisecond. The FLIM images are very close to the COMSOL predictions.

<p>Ispitivan je generalisani Frenkel-Kontorova model pod&nbsp;dejstvom spolja&scaron;njih periodičnih sila,&nbsp;i njihov uticaj na &Scaron;apiro stepenike.&nbsp;Deformacija substratnog potencijala prouzrokuje&nbsp;pojavu velikih polucelih i drugih subharmonijskih&nbsp;stepenika u sistemu.&nbsp;Rezultati dobijeni u radu su od značaja&nbsp;u talasima i spinovima gustine naboja&nbsp;kao i u Džozefsonovim spojevima.</p> / <p>Properties of the Shapiro steps in dierent<br />commensurate structures of the ac + dc driven<br />Frenkel-Kontorova model with dierent generalized<br />substrate potential have been examined.<br />Deviation from the sinusoidal potential produces<br />appearance of large subharmonic steps.<br />Presented results could be of great importance<br />for thestudies of all real systems closely related<br />to the dissipative dynamics of the FK model<br />such as studies of the charge- or spin-density wave<br />systems and the systems of Josephson-junction arrays.</p>