Please read the abstract in the front of the document. / Dissertation (MSc)--University of Pretoria, 2009. / Physics / unrestricted

Orientador: Peter Alexander Bleinroth Schulz / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-13T03:40:09Z (GMT). No. of bitstreams: 1 PaezGonzalez_CarlosJose_M.pdf: 17726649 bytes, checksum: 92453a3b81784c5899922a7943ef209f (MD5) Previous issue date: 2009 / Resumo: Neste trabalho estudamos a localização dos modos vibracionais de três modelos simples do DNA: cadeia unidimensional,dupla cadeia e o modelo de quatro cadeias; nestes modelos substituímos os grupos atômicos por massas efetivas ligadas entre si com molas. Para cada modelo calculamos e diagonalizamos a matriz dinâmica obtendo os modos vibracionais e suas freqüências. Cada componente de um modo vibracional representa a amplitude da oscilação nesse sitio, permitindo calcular a razão de participação e a fiutuação relativa desse modo. A partir destas grandezas se mostrou que nos sistemas quasi-unidimensionais (dupla cadeia e quatro cadeias) existe um intervalo a baixas freqüências onde todos os modos vibracionais são estendidos independentemente da seqüencia e as possíveis constantes de mola. / Abstract: ln this work we studied the localization of vibrational modes of three simple models of DNA: unidimensional chain, double chain and the model of falir chains. ln these models, atomic groups were replaced by effective fiasses linked to each other by springs. For each model, the dynamic matrix was calculated and diagonalized obtaining the vibrational modes with their frequencies. Each component of a vibrational mode represents the amplitude of the oscillation in that site, allowing the calculation of the participation fatia and the relative fluctuation of that mode. From these quantities we showed that there is a range at low frequencies in quasi-one-dimensional systems (double chain and falir chains) where alI vibrational modes are extended regardless the sequence and spring constants. / Mestrado / Física da Matéria Condensada / Mestre em Física

Ab initio and density functional theory calculations confirm Craig's assignment of the fundamental vibrational modes of tetrafluorooxirane with the exception that assignments of the C-F stretching modes v9 (b1) and v13 (b2) should be exchanged. The calculated structural parameters are in good agreement with results of microwave studies except for the C-C bond length for which all the calculated results are slightly too long.

Results of ab initio and density functional theory calculations on the structure and vibrational frequencies of hypophosphite anion indicate earlier experimental assignments of the fundamental vibrational modes are correct while the recent reassignments of several modes proposed by Bickley et al. are inconsistent with the calculated results.

Compound semiconductors are the foundation of many electronic and optoelectronic devices. As a result semiconductor epitaxy can be viewed as the first significant step in device engineering. Accurate and reliable characterization methods are needed to measure semiconductor properties including optical, electrical, vibrational and crystal structure. In this thesis, the epitaxy of ZnTe thin films on sapphire substrate by Pulsed Laser Deposition system at different growth temperatures is studied. The texture analysis is inspected by Two Dimensional X-Ray Diffraction. The lattice constant of the films and strain studies are investigated by High Resolution X-Ray Diffraction. UV-Vis spectroscopy is applied to find absorption edge in ZnTe thin film in order to estimate optical bandgap. These common characterization methods reveal the great effect of growth temperature on crystalline and optical properties of ZnTe thin films. In addition, Raman spectroscopy is used for the first time in the Preston's group to examine vibrational modes in ZnTe thin films. This new characterization method, which is the main focus of this thesis, uncovers some new features of ZnTe thin films not accessible through other techniques. In this thesis, optimum experimental conditions, instrumentation and data analysis of Raman observations in thin films are studied in detail. The final results are in good agreement with other characterization methods and they can justify crystalline and optical observations. These results demonstrate that Raman spectroscopy is a non-destructive characterization method applicable to thin film analysis. / Thesis / Master of Applied Science (MASc)

Technological advances require novel solutions for contactless energy transfer. Many engineering applications require unique approaches to power electrical components without using physical wires. In the past decade, awareness of the need to wirelessly power electrical components spawned many forays into the field of wireless power transfer (WPT). WPT techniques include capacitive energy transfer, electromagnetic inductive power transfer, electromagnetic radiative power transfer, electrostatic induction, and acoustic energy transfer. Acoustic energy transfer (AET) has many advantages over other methods. These advantages include lower operating frequency, shorter wavelengths enabling the use of smaller sized receiver and transmitter, extended transmitter-to-receiver distance therefore more manageable design constraints, achieving lower attenuation, higher penetration depth, and no electromagnetic losses. Most AET systems operate in the ultrasonic frequency range and are more commonly referred to as ultrasonic acoustic energy transfer (UAET) systems. Through-wall UAET systems are constructed of a transmitter bonded to a transmission elastic layer, which in turn is bonded to a receiver. The transmitter and receiver layers are constructed of a piezoelectric material. Piezoelectric materials behave according to the piezoelectric effect, which is when a material generates an electric charge in response to mechanical strain. The transmitter utilizes the reverse of the piezoelectric effect. A sinusoidal input voltage is applied to the transmitter, inducing vibrations in the transmitter. The vibration-induced acoustic waves emanating from the transmitter travel through the initial bonding layer, the transmission layer, and the final bonding layer to the receiver. In turn, the acoustic waves cause the receiver to deform and undergo strain. This induces a flow of charge in the receiver, which is an electric current. The receiver feeds current to a resistive load. In this manner, energy is acoustically transferred between two transducers without wires. The performance of UAET systems can be evaluated based on power transfer efficiency, voltage magnification, and input admittance. UAET systems require extensive modeling before experimental assembly can be attempted. The analytical models of UAET are either based on the mechanics of the constitutive relations of piezoelectricity and solid mechanics or using equivalent circuit methods. The equivalent circuit method approximates the physics of the UAET system with electrical assumptions. The mechanics-based method is the most comprehensive description of the physics of all the intermediate layers in a UAET system. The mechanics-based method has been based on the assumption that the UAET system is operated in the thickness mode of vibration, i.e., piston-like vibration mode where the transmitter and receiver disks vibrate only in the thickness direction. This poses an issue for disks with aspect ratios between 0.1 and 20 because the piezoelectric transducers vibrate in both the radial and thickness modes. In addition to this assumption, most of the works on UAET models only have accounted for the piezoelectric and transmission layers. The effects of the bonding layers were not considered. Bonding the piezoelectric layers to the transmission layer introduces epoxy material with mechanical properties that are not accounted for. The epoxy layers are extra barriers to the transmission that introduce attenuation and alter the vibrational and acoustical behaviors of the UAET system. Investigations into UAET commonly focus on metal through-wall applications. Alternate transmission layer materials are not investigated and the impact of varying mechanical properties on the performance of a through-wall UAET system has not been comprehensively studied. Even with the metal transmission layers, the impact of the metal thickness has not been extensively investigated thoroughly. This work addresses the issues of the thickness-mode assumption in UAET modeling, the effects of epoxy layers, the impacts of the metal layer geometry, and the performance of UAET systems with alternate transmission layer materials. Particularly, (1) we showed that the thickness-mode assumption, that has been used in the UAET modeling leads to inaccurate results. (2) We modified the available acoustic electro- elastic theoretical modeling to include the effects of radial modes as well as the epoxy bonding layers. (3) We showed that the geometry of the elastic/metal layer requires optimization for peak system efficiency. (4) The results show that using alternate transmission layer materials impacts the performance of UAET systems. The results of this work were investigated using an improved 5-layer analytical model and finite element modeling in COMSOL Multiphysics. / Master of Science / Wireless power transfer (WPT) is an innovative solution to the problem of powering sophisticated technological applications. Such instances include the powering of implanted medical devices, recharging inaccessible sensor networks, and wireless powering of components in sealed containers. Acoustic energy transfer (AET) is a feasible WPT method that addresses these needs. AET is based on the propagation of acoustic waves to a piezoelectric receiver which converts the vibrations caused by incident acoustic waves into electrical energy. Most AET systems operate in the ultrasonic frequency range, and so AET can also be referred to as ultrasonic acoustic energy transfer (UAET). Through-wall UAET systems are constructed from a transmitter that is bonded to a transmission elastic layer. The transmission layer is bonded to a receiver. The transmitter and receiver are made of a piezoelectric material. This thesis addresses the modeling process of through-wall UAET systems. In previous works, the fundamental assumption has been that such systems vibrate purely in the thickness mode. Additionally, other investigations did not comprehensively analyze the effects of the bonding layers, ascertain the performance of non-metal transmission layers, or provide practical insight on the effect of the resistive loading on such systems. This work addresses all these issues with a mathematical framework and finite element modeling results.

Diese Arbeit befasst sich mit der vibronischen Kopplung zweier angeregter Elektronenniveaus in Diphenylhexatrien (DPH) und mit der Rolle von Schwingungsmoden beim ultraschnellen photoinduzierten intramolekularen Elektronentransfer in Betain-30. Mit Hilfe von Pikosekunden-zeitaufgelöster Kohärenter Antistokes Ramanspektroskopie im angeregten Zustand des DPH haben wir zum ersten Mal das Auftreten zweier extrem frequenzverbreiterter Ramanlinien beobachtet, die gegenüber dem C=C Streckschwingungsbereich zu höheren Wellenzahlen verschoben sind. Beide Ramanlinien lassen sich mit Erhöhung der Lösungsmittelpolarisierbarkeit um mehr als 50 cm-1 in Richtung niedrigerer Frequenzen verschieben. Zur Erklärung des Sachverhalts werden zwei Modelle diskutiert: (i) die Existenz zweier Isomere im ersten angeregten Elektronenniveau des DPH und (ii) vibronische Kopplung der beiden Elektronenniveaus durch eine niederfrequente asymmetrische bu Schwingungsbewegung (pseudo-Jahn-Teller Effekt). Mit Hilfe von stationärer Ramanspektroskopie und insbesondere Messungen der Stokes- und anti-Stokes-Ramanspektren mit Pikosekunden-Zeitauflösung, die Beteiligung von Molekülschwingungen beim Elektronentransfer in Betain-30 wurde untersucht. Zum ersten Mal wurde eine modenspezifische Kinetik der Ramanaktiven Schwingungen nach Elektronen Rücktransfer in Betain-30 beobachtet. Die hochfrequenten Ramanaktiven Moden werden beim Elektronen Rücktransfer bevorzugt, was zu einer nicht-thermischen Besetzung der Schwingungen führt. Das ist zumindest qualitativ in Übereinstimmung mit Rechnungen die auf Fermi's Goldener Regel basieren. Eine Thermalisierung zwischen den beobachteten Ramanaktiven Moden stellt sich frühestens 10 ps nach Anregung ein. Die Thermalisierung in dem gesamten Molekül ist aber noch nicht beendet. / This thesis deals with vibronic coupling effects between two excited electronic singlet states in Diphenylhexatriene (DPH), and with the role of vibrational modes in photoinduced ultrafast electron transfer in Betaine-30. By using the picosecond time-resolved Coherent Antistokes Raman Spectroscopy method, it was possible to observe for the first time two very broad and unusual up-shifted vibrational frequencies in the excited singlet state of DPH, which have frequencies higher than frequency region of the C=C stretching mode. These two frequencies shift towards lower frequencies with increasing solvent polarizability. Two explanations have been discussed: (i) the simultaneous existence of two rotamers, where the two frequencies originate from "different molecules" and (ii) a model of vibronic coupling by an asymmetric low frequency bu-mode (pseudo-Jahn-Teller effect). By using the picosecond time-resolved anti-Stokes Raman spectroscopy method, we observed for the first time mode-specific excitation of vibrational modes after back-electron transfer in Betaine-30. In the primary event, high frequency Raman active modes are most effective in accepting energy, which leads to a non-thermal distribution of the relative populations of Raman active modes. This is qualitatively in accordance with predictions derived from Fermi's Golden Rule. Although energy transfer between the Raman active modes has been finished after about 10 to 15 ps, thermalization is not yet complete in the whole molecule.

ASR, est une protéine photo réceptrice qui lie la base protonée de la rétine de Schiff dans deux conformations de l'état fondamental. La protéine particulière consiste en un système modèle dans lequel I'effet de l'environnement protéique sur la dynamique d'isomérisation des deux isomères peut être étudié. Dans cette thèse, une étude approfondie sur les protéines mutées ponctuellement est présentée, où la variable est l'environnement protéique. Les résultats montrent des différences significatives entre les durées de vie des états excités des deux isomères et les durées de vie plus courtes ou plus longues commentées en termes de mélange électronique Sl/S2. En complément, le développement expérimental d'un spectromètre à absorption transitoire (T.A) et d'un dispositif de spectroscopie électronique bidimensionnelle (2DES) fonctionnant respectivement dans les domaines spectral NIR et UV-Vis. Avec cette configuration, deux impulsions colinéaires à verrouillage de phase d'une durée inférieure à 10fs sont générées, où. la précision interférométrique sur le contrôle du retard entre les deux impulsions de pompe permet d'effectuer des mesures 2DES. / ASR, is a photoreceptor protein that binds the protonated Schiff base of retinal in two ground state conformations. The particular protein consists a model system where the effect of the protein environment on the isomerization dynamics of the two isomers can be investigated. In this thesis an extended study on point mutated proteins is presented where the variable is the protein environment. The results show significant differences between the two isomers excited state lifetimes with the shorter or longer lifetimes commented in terms of Sl/S2 electronic mixing. Supplementary, the experimental development of a Transient absorption spectrometer (T.A) and a Two-dimensional electronic spectroscopy setup (2DES) operating in the NIR and UV-Vis spectral range respectively are described. The 2DES spectrometer is based on translating wedges made out of birefringent material producing two collinear phase-locked pulses with sub-I Ofs duration. The interferometric precision on controlling the delay between the two pump pulses allows to perform 2DES measurements on systems absorbing in the 360-430 nm range allowing to resolve the excitation process spectrally.

Die Kombination aus Breit-Band Spektroskopie-Methoden ermöglicht eine umfassende Einsicht in das elektronische System von Molekülen im angeregten Zustand. Am Beispiel des Riboflavin in saurer Umgebung wird der Protonen-Transfer aus der Lösung auf den Chromophor mittels transienter Absorption und -Fluoreszenz im S1-Zustand beobachtet. Mittels transienter Absorption- und Femtosekunden-stimulierter Raman-Spektroskopie wird der Populationstransfer in den elektronischen Grundzustand im beta-Karotin verfolgt und charakterisiert werden. / The combination of broadband spectroscopic methods allows a comprehensive view of the electronic system of molecules in the excited state. On riboflavin in acidic environment the proton-transfer is observed with transient absorption and -flurescence in the S1-state. With transient absorption and femtosecond-stimulated Raman-spectroscopy the population transfer into the electronic ground-state is followed and characterized.

This report employs advanced Raman spectroscopy techniques to investigate the fundamental properties of 9-AGNRs comprehensively. It is divided into two main sections addressing distinct aspects of 9-AGNR behavior. In the first section, Polarization Raman spectroscopy (PRS) probes phonon mode symmetries in 9-AGNRs. Our analysis reveals deviations from predicted symmetries, suggesting the presence of lattice defects. We also investigate specific phonon modes (G, D, and RBLM), providing insights into lattice integrity. The second section employs temperature-dependent Raman spectroscopy to explore the thermal properties of 9-AGNRs. This dynamic analysis quantifies vibrational mode responsiveness to temperature variations using the Grüneisen parameter (χ). Comparisons across various carbon-based materials uncover distinct sensitivities and stabilities. This research advances our understanding of 9-AGNR properties, with implications for nanomaterial science and potential applications. / Denna rapport använder avancerade Raman spektroskopitekniker för att på ett omfattande sätt undersöka de grundläggande egenskaperna hos 9-AGNRs. Den är uppdelad i två huvudsektioner som tar upp distinkta aspekter av 9-AGNR beteende. I det första avsnittet sonderar Polarisation Raman spektroskopi (PRS) fononlägessymmetrier i 9-AGNRs. Vår analys avslöjar avvikelser från förutsagda symmetrier, vilket tyder på närvaron av gitterdefekter. Vi undersöker också specifika fononlägen (G, D och RBLM), vilket ger insikter om gitterintegritet. Den andra sektionen använder temperaturberoende Raman-spektroskopi för att utforska de termiska egenskaperna hos 9-AGNRs. Denna dynamiska analys kvantifierar vibrationslägets känslighet för temperaturvariationer med hjälp av Grüneisen-parametern (χ). Jämförelser mellan olika kolbaserade material avslöjar distinkta känsligheter och stabiliteter. Denna forskning främjar vår förståelse av 9-AGNR-egenskaper, med implikationer för nanomaterialvetenskap och potentiella tillämpningar.