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1
Bradley, Michael Scott. "Engineering J-aggregate cavity exciton-polariton devices." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53196.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 143-159).
Research efforts in solution-based dye lasers and organic light-emitting devices (OLEDs) have led to advances in materials engineering and fabrication technology, propelling the field of organic solid-state photonics. Active areas of photonic research in organic systems include solid-state lasers (in both VCSEL and DFB form factor), low-threshold optical switches, and photodetectors. In all of these areas, thin films of "Jelley aggregates," or J aggregates, offer a promising materials platform thanks to their narrow linewidth and high oscillator strength at room temperature, properties resulting from delocalization of excitations across multiple strongly-coupled molecules. By placing these films in an optical microcavity, the aggregates exhibit additional strong-coupling to the cavity electric field, creating light-matter quasi-particles known as exciton-polaritons, even at room temperature. In this thesis, I discuss my research on the properties of J-aggregate thin films and on advancing the device and materials engineering of strongly-coupled devices based on J-aggregate thin films to the level of those in inorganic semiconductor systems. Exciton-polariton systems have been extensively studied at cryogenic temperatures in II-VI and III-V semiconductor quantum well systems in the past two decades as potential low-threshold VCSELs.
(cont.) J-aggregate-based exciton-polaritons systems, however, offer many device and engineering challenges, including: understanding the role of inhomogeneous vs. homogeneous broadening in the J-aggregate optical response, fabricating higher-quality microcavities with the ability to pump the polaritons at high intensities, and lateral patterning on the single-micron scale of organic microcavities. These topics are addressed and the outlook of organic exciton-polariton device research discussed.
by M. Scott Bradley.
Ph.D.
2
Walker, Brian J. (Brian Jacob). "Nanocrystal/J-aggregate constructs : chemistry, energy transfer, and applications." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65479.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.Vita. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 119-128).
The interaction of light with matter is one of the most central subjects to modern chemistry. Two types of materials, semiconductor nanocrystals and J-aggregates of cyanine dyes, have been developed chiefly due to their potential for interacting with light in interesting and productive ways. At the same time, existing spectroscopy and microscopy tools enable the study of these photonic materials, their dynamics, and their interactions. Although semiconductor nanocrystals and J-aggregates have complementary physical properties, the coupling between them requires new methods to control the interface between the organic (J-aggregate) and inorganic (nanocrystal) material. This thesis is about the interfacial chemistry, photophysical characterization, and selected applications of J-aggregated cyanine dyes conjugated with semiconductor nanocrystals. Chapter 1 begins with a brief review of J-aggregates and semiconductor nanocrystals together with referrals to other scources and motivation for the present work. Because the electronic excited states of both J-aggregates and semiconductor nanocrystals are characterized by a bound electron-hole pair, they can be grouped under the class of excitonic materials, and the coupling of J-aggregates with excitonic inorganic materials is reviewed. To control J-aggregate/nanocrystal interactions, it is important to preserve the aggregate structure while achieving favorable energy transfer. This challenge is the subject of Chapters 2 and 3, in which new ligand chemistry was developed to achieve near-unity energy transfer efficiency from the J-aggregates to the nanocrystal quantum dots in solution (Ch. 2) and in a solid state thin film (Ch. 3). These hybrid J-aggregate/nanocrystal constructs result in emission enhancement through energy transfer across the organic/inorganic interface, with the strongly-coupled J-aggregates serving as optical antennae to the nanocrystals. In the process, it was discovered that the ligand directs formation of J-aggregates onto the nanocrystal surface. In Chapter 4, the template-directing ligand is used on semiconductor nanowires grown from solution to realize a new photodetector design. Here, the excitation energy transfers from J-aggregated dyes to the nanowires, enhancing the photocurrent of the device and creating an artificial solid-state photodetector whose self assembly and aggregated antenna molecules are analogous to a photosynthetic light harvesting complex. Additionally, the nanowire/J-aggregate self-assembly generalizes to J-aggregates of three different color dyes (red/green/blue), providing a wavelength selectivity absent in biological light harvesting. In Chapter 5, the kinetics of indium phosphide (InP) semiconductor nanocrystal synthesis is discussed. InP is benficial for nanocrystal applications in biology or display technologies, as it does not contain lead or cadmium. However, the molecular mechanism of InP nanocrystal synthesis had been essentially unexplored. By studying the reaction kinetics of InP synthesis, a mechanism is proposed for InP. As in the case of the chemistry described in Chapters 2-4, it is clear that non-covalent interactions are vital to achieving control during nanocrystal synthesis.
by Brian J. Walker.
Ph.D.
3
Cao, Yumeng Melody. "Photostabilization of J-aggregate cyanine dyes for exciton-polariton based devices." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118061.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 67-69).
Organic molecules are becoming a commonly used material in strongly coupled systems as they possess large exciton binding energies and huge oscillator strengths that have allowed for the creation of room temperature polariton condensates, superfluids, and other exotic phenomena. Using J-aggregates, the aggregated form of cyanine organic dyes, we have previously fabricated light-emitting devices that demonstrated the first ever electrically pumped polariton emission, as well as critically coupled resonators with record high effective absorption constants. Although there are many promising applications for organic exciton-polariton devices, state-of-the- art devices suffer from rapid photodegradation at higher photon densities, which presently limits their eventual implementation into a viable technology. To achieve stable devices, we need to isolate the causes of photodegradation. Specifically, we studied the photoluminescence stability of J-aggregate thin films under different atmospheric conditions. Our results indicated that J-aggregates maintain both better emission and stability in high humidity environments in comparison to oxygen-rich atmospheres. Furthermore, we show an order of magnitude improvement in the photostability via encapsulation of the film with a hygroscopic sugar encapsulant. These results are highly promising and suggest future pathways for the realization of functional and stable polariton-based devices which we will explore in this thesis.
by Yumeng Melody Cao.
S.M.
4
Tischler, Jonathan Randall 1977. "Electrically pumped polariton emission in a J-aggregate organic light emitting device." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/88358.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 46-47).
by Jonathan Randall Tischler.
S.M.
5
Fylymonova, I., Yu V. Malyukin, and A. V. Sorokin. "Migration of Frenkel Excitons in PIC J-aggregates." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35095.
Full textAbstract:
Using luminescent exciton traps, an efficiency of the exciton migration in J-aggregates of pseudoisocyanine
dye in solutions has been investigated. Applying a modified Stern-Volmer equation for an analysis of
the J-aggregates luminescence quenching by the trap, the quenching of 50% of PIC J-aggregates luminescence
at the ratio PIC/trap = 70:1 has been found. To increase the exciton migration efficiency, the Jaggregate
structure was improved by the formation of a "J-aggregate-surfactant” complex. It results in
35% enhancement of the exciton migration efficiency in PIC J-aggregates.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35095
6
Shirasaki, Yasuhiro. "Efficient Föster energy transfer : from phosphorescent organic molecules to J-aggregate thin film." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46500.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 53-54).
This thesis demonstrates the first ever use of Forster resonance energy transfer (FRET) to increase the quantum efficiency of a electrically pumped J-aggregate light emitting device (JLED). J-aggregate thin films are highly absorptive films that have potential applications in a new class of optoelectronic devices, known as polaritonic devices. These devices, which utilize strong coupling between light and matter, include room temperature low power optical switches and low threshold lasers. Recent work has shown that a J-aggregate strong-coupling device can be powered not just optically but also electrically. However, since J aggregates are engineered for their optical and not electrical properties, exciting them electrically is very inefficient. JLED efficiency can be improved by first exciting phosphors that readily form excitons and then employing FRET to excite the J aggregates. Attaining high efficiency can make electrical pumping a viable option to power polaritonic devices.
by Yasuhiro Shirasaki.
M.Eng.
7
Steeg, Egon. "Investigations on growth and structure of silver and silver halide nanostructures formed on amphiphilic dye aggregates." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19577.
Full textAbstract:
Diese Arbeit beschäftigt sich mit dem Wachstumsmechanismus von Silberjodid Nanodrähten. Das Wachstum wurde über einen Zeitraum von Minuten bis hin zu Tagen untersucht. Im frühen Stadium bilden sich Silbernanopartikel innerhalb der Farbstoffröhren, welche als Keime für das weitere Wachstum von isolierten Drahtstücken dienen. Der Durchmesser dieser Drähte wird durch den Innendurchmesser der Röhren definiert. Im letzten Stadium wachsen diese Drahtstücke zusammen bis sie das gesamte Aggregat füllen. Dieser Wachstumsprozess impliziert einen Transport von Silber Ionen durch die Wand der Röhre. Das Wachstum der Drähte setzt sich weiter fort nachdem das Template gleichmäßig mit Drähten gefüllt ist und zerstört die Röhren in der Folge. Die Kristallstruktur der Drähte wurde sowohl mit hochauflösender Elektronenmikroskopie als auch Elektronenbeugung untersucht. Das Silberjodid konnte aufgrund seiner charakteristischen Wurtzite Struktur in der beta-Phase identifiziert werden. Da der Lösung nur Silbernitrat beigesetzt wurde, konnte die Quelle der Jod-Ionen als Verunreinigung im Farbstoffpulver ausgemacht werden. Das fragmentierte Wachstum der Drähte von verschiedenen Startpunkten aus führt zu Kristallen mit einkristallinen Domänen von mehr als 100 nm Länge. Eine bevorzugte Orientierung der Kristallstruktur relativ zur Aggregatachse wurde gefunden und durch die Molekülstruktur der Aggregate erklärt. Basierend auf diesen Ergebnissen wurde ein Model zum Wachstum von Silberjodid Nanodrähten im Inneren eines röhrenförmigen Molekülaggregats entwickelt. Es wurde angenommen, dass das Wachstum an Silberkeimen beginnt, die durch Photooxidation der bereits vorhandenen Jod Ionen mit Silber Ionen während der Belichtung der Probe gebildet werden. Diese Silberkeime ermöglichen die Bildung von stabilen Silberjodid Kristalliten und das nachfolgende Wachstum zu Drähten. Die Ergebnisse zeigen einen möglichen Weg zur Synthese von Metall-Halogenid Strukturen innerhalb von Farbstoffröhren.This thesis reports on the growth mechanism of silver iodide nanowires as revealed by conventional as well as cryogenic transmission electron microscopy. The growth, initiated by short illumination with UV light, has been observed over time scales ranging from minutes to days. In an early stage, within the tubular aggregates nanoparticles are formed which act as seeds for continuous growth of separate pieces of wires. The diameter of the wires is determined by the inner diameter of the tubes. In the final state, the pieces of wire totally fill the aggregate. The growth process indicates transport of at least silver ions through the tubular wall membrane. After homogeneously filling the template the wires grow onwards over the diameter of the nanotubes, destroying it in the process. The crystal structure of the wires was investigated by means of high resolution transmission electron microscopy and selected area electron diffraction. The silver iodide could be clearly identified in its beta-phase by its typical wurtzite structure. Since only silver nitrate was added to the solutions, the source of the iodide ions could be attributed to impurities within the dye powder itself. The fragmented growth of the wires from separate seeds leads to nanowires consisting of single crystalline domains exceeding 100 nm in length. A preferential orientation of the crystal lattice planes with respect to the aggregate axis was observed which is explained by the molecular structure of the aggregates. Based on these findings a model for the growth of silver iodide nanowires within the inner space of the tubular molecular aggregate is presented. The growth is assumed to start at silver seeds that are formed due to photo-oxidation of the already present iodide ions by the silver ions during the illumination of the sample. These silver seeds facilitate nucleation of silver iodide and subsequent growth into wires.
8
Kaidel, Björn [Verfasser], and J. [Akademischer Betreuer] Müller-Quade. "Fault-Tolerance and Deaggregation Security of Aggregate Signatures / Björn Kaidel ; Betreuer: J. Müller-Quade." Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/120500193X/34.
Full text
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Ovchinnikov, O. V., M. S. Smirnov, A. O. Dedikova, B. I. Shapiro, T. S. Shatskikh, and A. N. Latyshev. "Spectral Manifestation of Hybrid Association of Zn0.7Sd0.3S Colloidal Quantum Dots with J-Aggregates of Thiacarbocyanine Dye." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35329.
Full textAbstract:
Spectral properties of mixtures of Zn0.7Sd0.3S colloidal quantum dots with mean diameter value of
3.5 nm with the molecules of 3,3'-di(γ-sulfopropil)-9-ethyl-4,5,4',5'-dibenzo-thiacarbocyanine betaine pyridine
salt (DEC), prepared in gelatin were investigated. The obtained data indicated that the formation of
well-luminescent trans-J-aggregates and spectral tuning in the position of the absorption band of DEC and
the luminescence band of quantum dots, providing requirements for resonant energy transfer in the hybrid
associate are the determinant factors in the increase of the luminescent emission of DEC molecules, interacting
with Zn0.7Cd0.3S colloidal quantum dots.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35329
10
Schebsdat, Erik [Verfasser], and Daniel J. [Akademischer Betreuer] Strauss. "Neural Correlates of Binaural Interaction Using Aggregate-System Stimulation in Cochlear Implantees / Erik Schebsdat ; Betreuer: Daniel J. Strauss." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1209947307/34.
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11
Ouart, André. "Von "chiralen" Superhelices zu achiralen Nanostrukturen." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2000. http://dx.doi.org/10.18452/14572.
Full textAbstract:
In dieser Arbeit wurden spektroskopische und strukturelle Untersuchungen an chiralen und achiralen supramolekularen Nanoarchitekturen von J-Aggregaten achiraler Cyaninfarbstoffe durchgeführt. Als Modellsysteme wurden Tetrachlorobenzimidacarbocyanin- Farbstoffe mit unterschiedlichen 1,1´-Dialkyl- und 3,3´-Bis-acidoalkyl-Gruppen verwendet. Zur Charakterisierung der Nanostrukturen wurden statische spektroskopische Methoden - UV/Vis-Spektroskopie, Circulardichroismus (CD)- und Fluoreszenzspektroskopie -, Röntgenkristallstrukturanalyse,sowie kryogene Transmissionselektronenmikroskopie (Cryo-TEM) verwendet. Die delikate Balance der Wechselwirkungskräfte, wie z. B. hydrophobe Wechselwirkung, Dispersionswechselwirkung, sowie Wasserstoffbrücken, führt bei der J-Aggregation von strukturell ähnlichen achiralen Chromophoren zu "chiralen" Superhelices und achiralen nanoskopischen Bändern. Durch Kombination der hydrophoben und hydrophilen Eigenschaften von Tensiden mit den unikalen Eigenschaften von J-Aggregaten entstehen Nanoröhren und Vesikel. Diese Nanostrukturen sind daher vielversprechende Kandidaten für künstliche Lichtsammel- und Antennensysteme.In this work spectroscopic and structural investigations were performed on chiral and achiral supramolecular nanoarchitectures of J-aggregates of achiral cyanine dyes. Tetrachlorobenzimidacarbocyanine dyes with different 1,1´-Dialkyl- and 3,3´-Bis-acidoalkyl- substituents were used as model systems. To characterize these nanoarchitectures static spectroscopic methods - UV/vis-spectroscopy, circular dichroism (CD)- and fluorescence-spectroscopy -, x-ray crystal structure analysis, as well as cryogenic transmission electron microscopy (cryo-TEM) were used. The delicate balance of intermolecular forces, like hydrophobic interaction, dispersion forces, as well as hydrogen bonds, leads by J-aggregation of structural similar achiral chromophores to "chiral" superhelices and achiral nanoscopic ribbons. By combination of the hydrophobic and hydrophilic properties of surfactants with the unique properties of J-aggregates nanotubules and vesicles are built. These nanostructures are hopeful candidates for artificial antenna and light harvesting systems.
12
Al-Khatib, Omar. "Structure and optical properties of complex aggregate-structures of amphiphilic dye-systems." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16612.
Full textAbstract:
In dieser Arbeit werden Untersuchungen an selbstorganisierten, tubulären J-Aggregaten amphiphiler Cyaninfarbstoffe, 3,3’-bis(2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’-dioctylbenzimidacarbocyanine, im Weiteren C8S3 genannt, dargestellt. Ziel der Arbeit ist es an die Aggregate eine Lage Polyelektrolyte zu adsorbieren, sowie nachzuweisen, dass diese Methode geeignet ist, um einen Energietransfers zwischen dem Aggregat und funktionellen Gruppen in der Adsorbatschicht zu erreichen. Die tubulären Aggregate sind supramolekulare Strukturen, die sich spontan und selbstorganisiert aufgrund des amphiphilen Charakters der Cyaninfarbstoffe in wässrigen Lösungen bilden. Die Farbstoffe ordnen sich in einer Doppelschicht an, die die Wand der Röhren bildet mit etwa 13 nm Durchmesser und Längen bis zu 1 µm und mehr. Die Aggregate bilden exzitonische Anregungen aus, die sich in einer typischen Rotverschiebung (J-Aggregat) der optischen Absorption sowie einer charakteristischen Aufspaltung in mehrere schmale Banden zeigt. Die negative Oberflächenladung der Aggregate wird genutzt, um positiv geladene Polyelektrolyte (PE) anzulagern. Drei exemplarische PE, die sich in Ladungsdichte und Persistenzlänge unterscheiden, werden untersucht. In allen drei Fällen ist es gelungen Aggregate mit einer 2-3 nm dicken Polyelektrolytschicht zu umhüllen, wobei die molekulare Ordnung der Aggregate nur geringfügig gestört wird. Durch Einsatz von Farbstoffdotierten Polyelektrolyten konnten Experimente zum Nachweis des Förster-Energietransfer durchgeführt werden. Die Farbstoffdotierungen sind kovalent an die PE gebunden, wodurch sie in der PE-Umhüllung lokalisiert sind. Durch Wahl geeigneter Farbstoffe konnte ein Energietransfer vom Farbstoff (Donator) zum Aggregat als auch umgekehrt vom Aggregat zum Farbstoff (Akzeptor) nachgewiesen werden. Es ergeben sich hohe Transferraten, da die Farbstoffe in der PE-Schicht deutlich dichter am Aggregat liegen, als die theoretisch berechneten Förster-Radien.The following dissertation deals with investigation on tubular J-aggregates of amphiphile cyanine-dyes, 3,3’-bis(2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’-dioctylbenzimidacarbocyanine (C8S3). Aim of this work is to adsorb a layer of polyelectrolyte on C8S3-aggregates and to proof the capability of this method to establish an energy-transfer between the aggregate and functional groups in the adsorbate-layer. The tubular aggregates are supramolecular structures, that form entirely spontaneous and self-organized due to amphiphilic character of the investigated cyanine-dye derivative in aqueous solution. These dyes arrange themselves in a double-layer, assembling the hull of the tubular structure, with outer tube-diameters of approximately 13 nm and length of more than 1 µm. Due to the regular and dense arrangement of the dyes excitonic excitation establishs with the structure, that causes a J-aggregate typical red-shift in absorption and a characteristic band-splitting. The aggregates offer a negative surface-charge in aqueous solution. This is utilized to adsorb oppositely charged polyelectrolytes (PE) by electrostatic adsorption. It is shown exemplarily for three different kinds of PE that differ in charge-density and persistence-length. In all three cases a successful PE-wrapping of 2-3 nm thickness has been performed. The molecular order within the aggregates has been disturbed only weakly. Dye-labelled PE experiments proof Förster-energytransfer. The dye-labels are covalently bound to PE, fixing and localizing the labels in the wrapping-layer. With appropriate dye-labels an energy-transfer from labels in the coating (donor) towards the aggregate and vice versa, from aggregate to the dye-labels (acceptor) has been revealed. Caused by the localisation of the labels within the PE-coating, the distances of aggregate and label are always smaller than the theoretically calculated Förster-radii, resulting in a high efficiency of the transfer-rates.
13
Roden, Jan. "Lichtabsorption und Energietransfer in molekularen Aggregaten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-68387.
Full textAbstract:
Aggregate aus Molekülen, in denen die Moleküle über ihre elektronischen Übergangsdipole miteinander wechselwirken, finden wegen ihrer besonderen optischen und Energietransfer-Eigenschaften vielfach Anwendung in Natur, Technik, Biologie und Medizin. Beispiele sind die wechselwirkenden Farbstoffmoleküle, die in den Lichtsammelkomplexen Photosynthese betreibender Lebewesen Sonnenlicht absorbieren und die Energie als elektronische Anregung hocheffizient zu Reaktionszentren weiterleiten, oder Aggregate aus tausenden von organischen Farbstoffmolekülen in einem flüssigen Lösungsmittel. Die Wechselwirkung der Moleküle (Monomere) führt zu über mehrere Moleküle delokalisierten angeregten elektronischen Zuständen, die die Energietransfer-Dynamik und die Absorptionsspektren der Aggregate prägen.
Die Lichtabsorption und der Energietransfer in molekularen Aggregaten werden oft stark von Vibrationen beeinflusst, sowohl von internen Vibrationsfreiheitsgraden der Monomere als auch von Vibrationen der Umgebung (z. B. das Proteingerüst in Lichtsammelkomplexen oder eine Flüssigkeitsumgebung), an die die elektronische Anregung koppelt.
Da es schwierig ist, diese Vibrationen in die theoretische Beschreibung des Transfers und der Spektren einzubeziehen, ist ihr genauer Einfluss noch nicht gut verstanden. Um dieses Verständnis zu verbessern, entwickeln wir in dieser Arbeit neue Berechnungsmethoden und untersuchen damit die Auswirkungen der Vibrationen.
Zuerst betrachten wir die diskreten internen Vibrationsfreiheitsgrade der Monomere. Dazu haben wir eine effiziente numerische Methode entwickelt, die es uns erlaubt, mehrere Freiheitsgrade pro Monomer explizit einzubeziehen und die volle Schrödinger-Gleichung zu lösen. Mit den Modellrechnungen können wir experimentelle Aggregat-Spektren der Helium-Nanotröpfchen-Isolation-Spektroskopie, mit der man die einzelnen Vibrationslinien der Monomere auflösen kann, zum ersten Mal quantitativ reproduzieren.
In früheren theoretischen Behandlungen wurde oft nur ein einziger Vibrationsfreiheitsgrad pro Monomer berücksichtigt – nun zeigen wir, dass die Einbeziehung möglichst vieler Freiheitsgrade für eine realistische Beschreibung von Aggregat-Spektren wichtig ist.
Um neben den internen Vibrationen auch den Einfluss der Umgebung beschreiben zu können, nutzen wir den Zugang offener Quantensysteme und nehmen an, dass die elektronische Anregung an ein strukturiertes Kontinuum von Vibrationsfreiheitsgraden koppelt. Erstmals wenden wir die sogenannte nicht-markovsche Quanten-Zustands-Diffusion auf die molekularen Aggregate an, wodurch wir mit Hilfe einer Näherung Spektren und Transfer mit einer sehr effizienten stochastischen Schrödinger-Gleichung berechnen können. So
können wir Merkmale gemessener Aggregat-Spektren, wie das schmale J-Band und das breite strukturierte H-Band, in Abhängigkeit der Anzahl der Monomere und der Wechselwirkungsstärke zwischen den Monomeren beschreiben. Auch können wir den Übergang von kohärentem zu inkohärentem Transfer erfassen.
Eine für den Transfer relevante Größe ist die Anzahl der kohärent gekoppelten Monomere im Aggregat. Diese schätzt man häufig aus der Verschmälerung des Aggregat-Spektrums ab. Wir finden jedoch für verschiedene Spektraldichten des Vibrationskontinuums sehr unterschiedliche Verschmälerungen des Aggregat-Spektrums, die wir analytisch erklären. So zeigen wir, dass die bisherige einfache Abschätzung der Anzahl der kohärent gekoppelten Monomere nicht gerechtfertigt ist, da die Verschmälerung stark vom angenommenen Modell abhängt.
14
Roden, Jan. "Lichtabsorption und Energietransfer in molekularen Aggregaten." Doctoral thesis, Max-Planck-Institut für Physik komplexer Systeme, 2010. https://tud.qucosa.de/id/qucosa%3A25573.
Full textAbstract:
Aggregate aus Molekülen, in denen die Moleküle über ihre elektronischen Übergangsdipole miteinander wechselwirken, finden wegen ihrer besonderen optischen und Energietransfer-Eigenschaften vielfach Anwendung in Natur, Technik, Biologie und Medizin. Beispiele sind die wechselwirkenden Farbstoffmoleküle, die in den Lichtsammelkomplexen Photosynthese betreibender Lebewesen Sonnenlicht absorbieren und die Energie als elektronische Anregung hocheffizient zu Reaktionszentren weiterleiten, oder Aggregate aus tausenden von organischen Farbstoffmolekülen in einem flüssigen Lösungsmittel. Die Wechselwirkung der Moleküle (Monomere) führt zu über mehrere Moleküle delokalisierten angeregten elektronischen Zuständen, die die Energietransfer-Dynamik und die Absorptionsspektren der Aggregate prägen.
Die Lichtabsorption und der Energietransfer in molekularen Aggregaten werden oft stark von Vibrationen beeinflusst, sowohl von internen Vibrationsfreiheitsgraden der Monomere als auch von Vibrationen der Umgebung (z. B. das Proteingerüst in Lichtsammelkomplexen oder eine Flüssigkeitsumgebung), an die die elektronische Anregung koppelt.
Da es schwierig ist, diese Vibrationen in die theoretische Beschreibung des Transfers und der Spektren einzubeziehen, ist ihr genauer Einfluss noch nicht gut verstanden. Um dieses Verständnis zu verbessern, entwickeln wir in dieser Arbeit neue Berechnungsmethoden und untersuchen damit die Auswirkungen der Vibrationen.
Zuerst betrachten wir die diskreten internen Vibrationsfreiheitsgrade der Monomere. Dazu haben wir eine effiziente numerische Methode entwickelt, die es uns erlaubt, mehrere Freiheitsgrade pro Monomer explizit einzubeziehen und die volle Schrödinger-Gleichung zu lösen. Mit den Modellrechnungen können wir experimentelle Aggregat-Spektren der Helium-Nanotröpfchen-Isolation-Spektroskopie, mit der man die einzelnen Vibrationslinien der Monomere auflösen kann, zum ersten Mal quantitativ reproduzieren.
In früheren theoretischen Behandlungen wurde oft nur ein einziger Vibrationsfreiheitsgrad pro Monomer berücksichtigt – nun zeigen wir, dass die Einbeziehung möglichst vieler Freiheitsgrade für eine realistische Beschreibung von Aggregat-Spektren wichtig ist.
Um neben den internen Vibrationen auch den Einfluss der Umgebung beschreiben zu können, nutzen wir den Zugang offener Quantensysteme und nehmen an, dass die elektronische Anregung an ein strukturiertes Kontinuum von Vibrationsfreiheitsgraden koppelt. Erstmals wenden wir die sogenannte nicht-markovsche Quanten-Zustands-Diffusion auf die molekularen Aggregate an, wodurch wir mit Hilfe einer Näherung Spektren und Transfer mit einer sehr effizienten stochastischen Schrödinger-Gleichung berechnen können. So
können wir Merkmale gemessener Aggregat-Spektren, wie das schmale J-Band und das breite strukturierte H-Band, in Abhängigkeit der Anzahl der Monomere und der Wechselwirkungsstärke zwischen den Monomeren beschreiben. Auch können wir den Übergang von kohärentem zu inkohärentem Transfer erfassen.
Eine für den Transfer relevante Größe ist die Anzahl der kohärent gekoppelten Monomere im Aggregat. Diese schätzt man häufig aus der Verschmälerung des Aggregat-Spektrums ab. Wir finden jedoch für verschiedene Spektraldichten des Vibrationskontinuums sehr unterschiedliche Verschmälerungen des Aggregat-Spektrums, die wir analytisch erklären. So zeigen wir, dass die bisherige einfache Abschätzung der Anzahl der kohärent gekoppelten Monomere nicht gerechtfertigt ist, da die Verschmälerung stark vom angenommenen Modell abhängt.
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Spitz, Christian. "Exzitonische Anregungen in zylindrischen J-Aggregaten von organischen Farbstoffen." [S.l. : s.n.], 1999. http://www.diss.fu-berlin.de/1999/15/index.html.
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Heijs, Dirk Jan. "Optical dynamics in multichromophore systems." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2006. http://irs.ub.rug.nl/ppn/29788381X.
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Dimitriev, O., V. Petrenko, Yu Slominski, and I. Mazarchyk. "Formation of J-aggregates of Thiamonomethincyanine Dyes in the Presence of CdTe Nanoparticles." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35442.
Full textAbstract:
The conditions of formation of J-aggregates for three types of thiamonomethincyanine dyes, whose
structure is differed by end groups, are studied depending on their concentration and type of interaction
with CdTe nanoparticles with size of about 3 nm in aqueous dispersions. The influence of dye structure on
the efficiency of formation of J-aggregates in solutions and in films was found. It was found that quantum
dots (QDs) of CdTe stabilized by thioglycolic acid can adsorb J-aggregates of the dye molecules on their
surface. It was shown for the first time that the hybrid structure of dye-CdTe can be formed through the
interaction of negatively charged dye molecules and negatively charged surface of the QDs through the
formation of neutral aggregates. It was not found any processes of energy transfer from dye to the particles
of CdTe neither for the dimer - CdTe system nor for the J-aggregates – CdTe system.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35442
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Eisele, Dörthe Melitta. "Optical, structural and redox properties of nanotubular j-aggregates of amphiphilic cyanine dyes." Aachen Shaker, 2009. http://d-nb.info/1002585198/04.
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Hestand, Nicholas James. "Effects of Charge-Transfer Excitons on the Photophysics of Organic Semiconductors." Diss., Temple University Libraries, 2017. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/432457.
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ChemistryPh.D.
The field of organic electronics has received considerable attention over the past several years due to the promise of novel electronic materials that are cheap, flexible and light weight. While some devices based on organic materials have already emerged on the market (e.g. organic light emitting diodes), a deeper understanding of the excited states within the condensed phase is necessary both to improve current commercial products and to develop new materials for applications that are currently in the commercial pipeline (e.g. organic photovoltaics, wearable displays, and field effect transistors). To this end, a model for pi-conjugated molecular aggregates and crystals is developed and analyzed. The model considers two types of electronic excitations, namely Frenkel and charge-transfer excitons, both of which play a prominent role in determining the nature of the excited states within tightly-packed organic systems. The former consist of an electron-hole pair bound to the same molecule while in the later the electron and hole are located on different molecules. The model also considers the important nuclear reorganization that occurs when the system switches between electronic states. This is achieved using a Holstein-style Hamiltonian that includes linear vibronic coupling of the electronic states to the nuclear motion associated with the high frequency vinyl-stretching and ring-breathing modes. Analysis of the model reveals spectroscopic signatures of charge-transfer mediated J- and H-aggregation in systems where the photophysical properties are determined primarily by charge-transfer interactions. Importantly, such signatures are found to be sensitive to the relative phase of the intermolecular electron and hole transfer integrals, and the relative energy of the Frenkel and charge-transfer states. When the charge-transfer integrals are in phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits J-aggregate characteristics including a positive band curvature, a red shifted main absorption peak, and an increase in the ratio of the first two vibronic peaks relative to the monomer. On the other hand, when the charge-transfer integrals are out of phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits H-aggregate characteristics including a negative band curvature, a blue shifted main absorption peak, and a decrease in the ratio of the first two vibronic peaks relative to the monomer. Notably, these signatures are consistent with those exhibited by Coulombically coupled J- and H-aggregates. Additional signatures of charge-transfer J- and H-aggregation are also discovered, the most notable of which is the appearance of a second absorption band when the charge-transfer integrals are in phase and the charge-transfer and Frenkel excitons are near resonance. In such instances, the peak-to-peak spacing is found to be proportional to the sum of the electron and hole transfer integrals. Further analysis of the charge-transfer interactions within the context of an effective Frenkel exciton coupling reveals that the charge-transfer interactions interfere directly with the intermolecular Coulombic coupling. The interference can be either constructive or destructive resulting in either enhanced or suppressed J- or H- aggregate behavior relative to what is expected based on Coulombic coupling alone. Such interferences result in four new aggregate types, namely HH-, HJ-, JH-, and JJ-aggregates, where the first letter indicates the nature of the Coulombic coupling and the second indicates the nature of the charge-transfer coupling. Vibronic signatures of such aggregates are developed and provide a means by which to rapidly screen materials for certain electronic characteristics. Notably, a large total (Coulombic plus charge-transfer) exciton coupling is associated with an absorption spectrum in which the ratio of the first two vibronic peaks deviates significantly from that of the unaggregated monomer. Hence, strongly coupled, high exciton mobility aggregates can be readily distinguished from low mobility aggregates by the ratio of their first two vibronic peaks. Analysis of the spatial dependence of the intermolecular interactions reveals that all four aggregate types (HH-, HJ-, JH-, JJ-) can be achieved by enforcing the appropriate crystalline packing arrangement. Such tunability is possible due of the different length scales over which the natures of the two coupling sources interconvert from J-like to H-like; whereas the nature of the Coulombic coupling is known to be sensitive to displacements on the order of half the molecular length, the nature of the charge-transfer mediated exciton coupling is sensitive to geometric displacements of approximately a carbon-carbon bond length. It is proposed that such sensitivity should allow for fine tuning of the total excitonic coupling via modifications in the packing structure, as determined, for example, by the side chains. Several examples of the different aggregate types are provided throughout this dissertation as the model is used to probe the excited state character of several relevant conjugated organic systems. Such examples include pentacene and 7,8,15,16-tetraazaterrylene (TAT) along with several derivatives from the perylene family.
Temple University--Theses
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Ouart, André. "Von "chiralen" Superhelices zu achiralen Nanostrukturen spektroskopische und strukturelle Untersuchungen von J-Aggregaten achiraler Cyaninfarbstoffe /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961717823.
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Eisele, Dörthe M. [Verfasser]. "Optical, Structural and Redox Properties of Nanotubular J-aggregates of Amphiphilic Cyanine Dyes / Dörthe M Eisele." Aachen : Shaker, 2010. http://d-nb.info/1120864127/34.
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Aberra, Guebrou Samuel. "Influence des plasmons de surface propagatifs sur la cohérence de systèmes optiques." Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00798779.
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Cette thèse expérimentale s'est attachée à l'étude des effets induits par l'extension spatiale desplasmons de surface sur l'émission de matériaux organiques et inorganiques. Le système estformé d'un ensemble d'émetteurs localisés émettant principalement des plasmons de surfacedélocalisés. Dans un premier temps, nous nous sommes intéressés à l'imagerie par microscopieplasmon, technique de plus en plus utilisée dans divers domaines, notamment la biologie. Nousavons montré que l'émission détectée en un point provient essentiellement de l'environnementet non du point observé, définissant ainsi un cercle d'influence lié à la longueur de propagationdu plasmon de surface. Quand le plasmon interagit plus fortement avec des émetteurs, ilpeut entrer en régime de couplage fort. Ce couplage fort se traduit par un changement dansles énergies du système et par l'apparition de nouveaux états hybrides excitons-plasmons, lespolaritons. Les différents émetteurs localisés (des chaines de colorants agrégés) ne sont alorsplus indépendants entre eux. Des mesures de diffusion montrent un effet collectif induit par lecouplage fort. Ces expériences ont été confirmées par des mesures de cohérence spatiale, réaliséesen ajoutant une expérience de fentes d'Young au dispositif de microscopie plasmon. Ilapparait qu'un état cohérent étendu sur plusieurs microns se forme, conformément aux prévisionsthéoriques. L'ensemble d'émetteurs se comporte alors comme une macromolécule, dontl'interaction est induite par le plasmon de surface.
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Wallack, Matthew Niles. "Investigations of the C8S3 J-aggregate." 2012. http://hdl.handle.net/2152/19659.
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This research project entails analyses of both alcoholic route C8S3 J-aggregate bundles and the interactions of a polyethylene glycol additive with alcoholic route C8S3 J-aggregates. First, the C8S3 J-aggregate bundles are characterized by both polarized and non-polarized spectroscopy methods. Orientation of the tubular bundled molecular complex was achieved, depending on the experiment, through a combination of flow cell experiments and cover slip deposited sample analysis. Next, isolated alcoholic route C8S3 J-aggregates were investigated using a polyethylene glycol (PEG) additive which has been shown, through absorbance and fluorescence emission spectroscopy, to selectively and reversibly remove the outer wall of the J-aggregate tubule. Spectroscopic analyses have indicated that the addition of a PEG additive left behind an in-tact inner wall tubule without the use of oxidizing agents, a feat never before accomplished with the C8S3 monomer.text
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Kaiser, Theo E. "J-Aggregates of Tetraphenoxy-Substituted Perylene Bisimide Dyes." Doctoral thesis, 2009. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-43544.
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In dieser Doktorarbeit wurde gezeigt, dass die sehr begehrte J-Aggregation funktionaler Perylenbisimid-Chromophore durch geeignetes Design der monomeren Bausteine erreicht werden kann. Hierzu war einerseits die Selbstanordnung durch ein Zusammenwirken von Wasserstoffbrücken und Pi-Pi-Wechselwirkungen zu begünstigen, und andererseits eine Anordnung in kolumnaren Stapeln zu verhindern, was durch Kern-Verdrillung mittels sterisch anspruchsvollen Substituenten gelang. Desweiteren gaben Selbstanordnungsstudien neue Einblicke in den dynamischen Aggregationsprozess niedrigdimensionaler langgestreckter Aggregate mit stark exzitonisch gekoppelten Chromophoren. Die Beziehung zwischen bekannten Cyaninfarbstoffen, wie der von THIATS mit dem vorliegenden PBI 1a wurde durch Absorptions- und Fluoreszenzspektroskopie bei Tieftemperaturen von 5 K bis Raumtemperatur untersucht. Die vormals beispiellosen funktionalen Eigenschaften der PBI-Aggregate, welche aus der J-artigen exzitonischen Kopplung herrühren, sind vielversprechend für die Anwendung in optoelektronischen Bauteilen und für die PhotovoltaikIn conclusion, the present thesis demonstrates that the highly desired J-type aggregation of functional perylene bisimide chromophores can be achieved by proper design of monomeric building blocks that direct self-assemble by mutual effects of hydrogen bonding and pi-pi interaction, and on the other hand, are prevented to assemble in columnar stacks owing to their twisted pi-conjugated core and sterically demanding substituents. Furthermore, the self-assembly studies gave new insights into the dynamic aggregation process of low-dimensional extended assemblies with strongly excitonically coupled chromophores. The relationship between commonly known cyanine dye aggregates like that of THIATS and that of the present PBI 1a was investigated by absorption and fluorescence spectroscopy at low temperatures down to 5 K. The formerly unprecedented functional properties of PBI aggregates that are expressed in J-type excitonic coupling hold promise for application in optoelectronic and photovoltaic devices
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Clark, Katie Ann. "Optoelectronic properties and energy transport processes in cylindrical J-aggregates." Thesis, 2014. http://hdl.handle.net/2152/25919.
Full textAbstract:
The light harvesting systems of photosynthetic organisms harness solar energy by efficient light capture and subsequent transport of the light’s energy to a chemical reaction center. Man-made optical devices could benefit by mimicking these naturally occurring light harvesting processes. Supramolecular organic nanostructures, composed of the amphiphilic carbocyanine dye 3,3’-bis- (2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’- dioctylbenzimida-carbocyanine (C8S3), self assemble in aqueous solution to form tubular, double-walled J-aggregates. These J-aggregates have drawn comparisons to light harvesting systems, owing to their optical and structural similarities to the cylindrical chlorosomes (antenna) from green sulfur bacteria. This research utilizes optical spectroscopy and microscopy to study the supramolecular origins of the exciton transitions and fundamental nature of exciton energy transport in C8S3 artificial light harvesting systems. Two J-aggregate morphologies are investigated: well-separated, double-walled nanotubes and bundles of agglomerated nanotubes. Linear dichroism spectroscopy of flow-aligned nanotubes is used to generate the first quantitative, polarized model for the complicated C8S3 nanotube excitonic absorption spectrum that is consistent with theoretical predictions. The C8S3 J-aggregate photophysical properties are further explored, as the Stokes shift, quantum yield, and spectral line broadening are measured as a function of temperature from 77 – 298 K. The temperature-dependent emission ratios of the C8S3 J-aggregate two-band fluorescence spectra reveal that nanotube emission is well described with Boltzmann partitioning between states, while the bundles’ is not. Finally, understanding energy transport in these materials is critical for the proposed use of artificial light harvesting systems in optoelectronic devices. The spatial extent of energy transfer in individual C8S3 J- aggregate structures is directly determined using fluorescence imaging. We find that aggregate structural hierarchy greatly influences exciton transport distances: impressive average exciton migration distances of ~ 150 nm are measured along the nanotubes, while these distances increase to over 500 nm in the bundle superstructures.text
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Kaiser, Theo E. [Verfasser]. "J-aggregates of tetraphenoxy-substituted perylene bisimide dyes / vorgelegt von Theo E. Kaiser." 2009. http://d-nb.info/1009630032/34.
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Mo, Gary Chia Hao. "Structure and Application of Photosensitive Self-assembled Pseudoisocyanine J-aggregates on Membrane Surfaces." Thesis, 2011. http://hdl.handle.net/1807/29815.
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Understanding the assembly of monomeric components into specific molecular motifs is a central theme in materials and surface engineering. Motif designs, specifically using a controllable template, can yield materials with desired optical or electronic properties. The objective of this thesis is to understand the aggregate size, packing, and monomer orientation for the cationic dye, pseudoisocyanine. These organic molecules assemble into crystals in solution, on planar bilayer templates, and on the membranes of living cells. Pseudoisocyanine J-aggregates were found to form on top of the heterogeneous lipid domains in a phospholipid bilayer. This behaviour is limited to a few headgroup chemistries and lateral packing motifs, allowing one to control aggregation via a combination of these two factors. These aggregates are low-dimensional and display polymorphism. Using atomic force microscopy and visible-light spectroscopy, distinct optical characteristics can be correlated to different bilayer templated J-aggregate morphologies. The molecular packing of a similar J-aggregate crystal was resolved using both atomic force microscopy and selected area electron diffraction. The infrared absorption spectra of different polymorphs also displayed distinct differences. These separate examinations enabled a perspective that clarifies the geometry, packing, orientation, and size of templated J-aggregates. Insights into the templating of J-aggregates on the molecular scale reveals that they are sensitive reporters of membrane phase in adherent cells, and are compatible with established cell biology techniques. Lipid domains in live mammalian cells were visualized using fluorescent J-aggregates in combination with endogenous marker proteins of the endocytic process. Analysis of live cell images and additional biophysical work revealed that pseudoisocyanine J-aggregates formed on domains of the anionic lipid bis(monoacylglycerol)phosphate. Only by using J-aggregates can this lipid be shown to form well-ordered domains during endosomal maturation, leading to multivesicular body formation. These data demonstrate that a correlated optical and topographical approach is necessary to understand the structure of fluorescent molecular assemblies, and form the basis for utilizing such aggregates in a biological context.
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Spitz, Christian [Verfasser]. "Exzitonische Anregungen in zylindrischen J-Aggregaten von organischen Farbstoffen / vorgelegt von Christian Spitz." 1999. http://d-nb.info/961937270/34.
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Pitigala, Kankanakage Don Duleepa P. "Heterojunction Structures for Photon Detector Applications." 2013. http://scholarworks.gsu.edu/phy_astr_diss/63.
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The work presented here report findings in (1) infrared detectors based on p-GaAs/AlGaAs heterojunctions, (2) J and H aggregate sensitized heterojunctions for solar cell and photon detection applications, (3) heterojunctions sensitized with quantum dots as low cost solar energy conversion devices and near infrared photodetectors.
(1)A GaAs/AlGaAs based structure with a graded AlGaAs barrier is found to demonstrate a photovoltaic responsivity of ~ 30mA/W (~ 450mV/W) at the wavelength of 1.8 mm at 300K. Additionally the graded barrier has enhanced the photoconductive response at 78 K, showing a responsivity of ~ 80mA/W with a D*=1.4×108 Jones under 1V bias at 2.7 mm wavelength. This is an approximately 25 times improvement compared to the flat barrier detector structure, probably due to the improved carrier transport, and low recapture rate in the graded barrier structure. However, these graded barrier devices did not indicate a photoresponse with photoconductive mode at 300K due to high shot noise. Additionally, two generation-recombination noise components and a 1/f noise component were identified.
A series of GaAs/AlGaAs multilayer hetero-junction structures were tested as thermal detectors. A superlattice structure containing 57% Al fraction in the barrier and 3 × 1018 cm-3 p-doped GaAs emitter showed the highest responsivity as a thermal detector with a TCR of ~ 4% K-1, at 300K.
(2)The photovoltaic properties of heterojunctions with J-/ H- aggregated dye films sandwiched between n– and p-type semiconductors were investigated for potential application as solar cells and IR detectors. Films of cationic dye Rhodamine-B-thiocyanate adsorbed on Cu2O substrate are found to form organized dye layers by self-assembled J- aggregation, resulting in large red-shifts in the photo -response. Additionally, cells sensitized with a pentamethine cyanine dye exhibited a broad spectral response originating from J- and H-aggregates. The photocurrent is produced by exciton transport over relatively long distances with significant hole-mobility as well as direct sensitized injection at the first interface.
(3) A ZnO/PbS-QD/Dye heterostructure had enhanced efficiency compared to ZnO/Dye heterostructure as a solar cell. Furthermore, a ZnO/PbS-QD structure has demonstrated UV and NIR responses with 4×105V/W (390 nm) and 5.5×105 V/W (750 nm) under 1V bias at 300K.
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Ouart, André [Verfasser]. "Von "chiralen" Superhelices zu achiralen Nanostrukturen : spektroskopische und strukturelle Untersuchungen von J-Aggregaten achiraler Cyaninfarbstoffe / von André Ouart." 2000. http://d-nb.info/961717823/34.
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Walker, Erin Kate. "Transparent carbon electrodes for spectroelectrochemical studies." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-5954.
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This dissertation describes the assessment and use of carbon optically transparent electrodes (C-OTEs) based on pyrolyzed photoresist films (PPFs) as a platform for spectroelectrochemical investigations. C-OTEs are examined for use in UV-Vis spectroelectrochemistry and electrogenerated chemiluminescence and compared to non-transparent glassy carbon (GC) and the conventional transparent electrode indium tin oxide (ITO). Chapter 1 provides a general overview of transparent electrodes, carbon electrodes, and spectroelectrochemistry. Chapter 2 details a UV-Vis spectroelectrochemical investigation of electrogenerated graphitic oxides (EGO) on the surface of the C-OTE in the presence of KCl. X-ray photoelectron spectroscopy and time of flight secondary ion mass spectroscopy are used to determine EGO composition. Several supporting electrolytes are investigated to determine the mechanism of EGO formation. Chapter 3 details experiments to electrochemically access the exciton emission from self-assembled double-walled tubular J-aggregates via electrogenerated chemiluminescence (ECL). Optimization of ECL intensity with respect to the coreactant concentration and the supporting electrolyte pH is performed on opaque glassy carbon electrodes. ECL and fluorescence spectra are compared, and C-OTEs are utilized to determine the source of disagreement between the spectra. Chapter 4 describes the preparation and characterization (i.e. transparency, thickness, sheet resistance, rms roughness, and electroactive surface area) of C-OTEs and explores C-OTEs for general use in ECL under a variety of conditions. Simultaneous cyclic voltammograms and ECL transients are obtained for three thicknesses of PPFs and compared to non-transparent GC and the conventional transparent electrode ITO in both front face and transmission electrode cell geometries. Despite positive potential shifts in oxidation and ECL peaks, attributed to the internal resistance of the PPFs that result from their nanoscale thickness, the PPFs display similar ECL activity to GC, including the low oxidation potential observed for amine coreactants on hydrophobic electrodes. Overall, C-OTEs are promising electrodes for spectroelectrochemical applications because they yield higher ECL than ITO in both oxidative-reductive and reductive-oxidative ECL modes, are more stable in alkaline solutions, display a wide potential window of stability, and have tunable transparency for more efficient detection of light in the transmission cell geometry. Future directions for this research are discussed in Chapter 5, which outlines several approaches to designing and improving spectroelectrochemical sensors.text
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Paquin, Francis. "Effet de la microstructure sur les propriétés excitoniques des polymères semi-conducteurs semi-cristallins." Thèse, 2014. http://hdl.handle.net/1866/11673.
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Les polymères semi-conducteurs semicristallins sont utilisés au sein de diodes
électroluminescentes, transistors ou dispositifs photovoltaïques organiques. Ces matériaux peuvent être traités à partir de solutions ou directement à partir de leur
état solide et forment des agrégats moléculaires dont la morphologie dicte en grande
partie leurs propriétés optoélectroniques. Le poly(3-hexylthiophène) est un des polymères semi-conducteurs les plus étudiés. Lorsque le poids moléculaire (Mw) des
chaînes est inférieur à 50 kg/mol, la microstructure est polycristalline et composée
de chaînes formant des empilements-π. Lorsque Mw>50 kg/mol, la morphologie est
semicristalline et composée de domaines cristallins imbriquées dans une matrice de
chaînes amorphes.
À partir de techniques de spectroscopie en continu et ultrarapide et appuyé
de modèles théoriques, nous démontrons que la cohérence spatiale des excitons
dans ce matériau est légèrement anisotrope et dépend de Mw. Ceci nous permet
d’approfondir la compréhension de la relation intime entre le couplage inter et
intramoléculaire sur la forme spectrale en absorption et photoluminescence. De plus,
nous démontrons que les excitations photogénérées directement aux interfaces entre
les domaines cristallins et les régions amorphes génèrent des paires de polarons liés
qui se recombinent par effet tunnel sur des échelles de temps supérieures à 10ns. Le
taux de photoluminescence à long temps de vie provenant de ces paires de charges
dépend aussi de Mw et varie entre ∼10% et ∼40% pour les faibles et hauts poids
moléculaires respectivement. Nous fournissons un modèle permettant d’expliquer
le processus de photogénération des paires de polarons et nous élucidons le rôle de
la microstructure sur la dynamique de séparation et recombinaison de ces espèces.Microstructure plays a crucial role in defining the optoelectrical properties of conjugated polymeric semiconductors which can be used in light harvesting and generating devices such as organic light emitting diodes, field effect transistors or photovoltaic devices. These polymers can be processed from solution or solidstate and form photophysical aggregates, consequently providing a complex network which controls the fate of any photogenerated species. poly(3-hexylthiopene) is one of the most studied polymeric semiconductor. In this material, the molecular weight (Mw) of the polymer governs the microstructure and highly impact the optical and electronic properties. Below Mw≈ 50 kg/mol, the polymer chains forms polycrystalline domains of π-stacked molecules while high Mw (>50 kg/mol) consists of a two-phase morphology of molecularly ordered crystallites that are embedded in amorphous regions. Such morphology provides a bidimensionnal network hosting both neutral excitations, known as Frenkel excitons, and polarons. By means of steady-state and ultrafast spectroscopy experiment and backed up theoretical modeling, we demonstrate that the spatial coherence of such excitations are anisotropic in the lattice and depends on the Mw of the polymer, providing a deep understanding of the interplay between interchain (excitonic) and intrachain coupling in polymer aggregates. Moreover, we show that direct excitation at the interface between molecularly ordered and amorphous regions generates tightlybound charge pairs which decay via quantum tunneling over >10 ns. The yield of delayed photoluminescence arising from the recombination of those charge pairs varies between ∼10% and ∼40% for low and high Mw films respectively. We provide a quantitative model that describes the photogeneration process of those geminate polaron pairs and determine the role of the microstructure in the charge separation and recombination processes.