The left visual field attentional advantage: No evidence of different speeds of processing across visual hemifields.

Temporal-order judgment (TOJ) and simultaneity judgment (SJ) tasks are used to study differences in speed of processing across sensory modalities, stimulus types, or experimental conditions. Matthews and Welch (2015) reported that observed performance in SJ and TOJ tasks is superior when visual stimuli are presented in the left visual field (LVF) compared to the right visual field (RVF), revealing an LVF advantage presumably reflecting attentional influences. Because observed performance reflects the interplay of perceptual and decisional processes involved in carrying out the tasks, analyses that separate out these influences are needed to determine the origin of the LVF advantage. We re-analyzed the data of Matthews and Welch (2015) using a model of performance in SJ and TOJ tasks that separates out these influences. Parameter estimates capturing the operation of perceptual processes did not differ between hemifields by these analyses, whereas parameter estimates capturing the operation of decisional processes differed. In line with other evidence, perceptual processing also did not differ between SJ and TOJ tasks. Thus, the LVF advantage occurs with identical speeds of processing in both visual hemifields. If attention is responsible for the LVF advantage, it does not exert its influence via prior entry.

Design and study of self-assembled functional organic and hybrid systems for biological applications

The focus of self-assembly as a strategy for the synthesis has been confined largely to molecules, because of the importance of manipulating the structure of matter at the molecular scale. We have investigated the influence of temperature and pH, in addition to the concentration of the capping agent used for the formation of the nano-bio conjugates. For example, the formation of the narrower size distribution of the nanoparticles was observed with the increase in the concentration of the protein, which supports the fact that γ-globulin acts both as a controller of nucleation as well as stabiliser. As analyzed through various photophysical, biophysical and microscopic techniques such as TEM, AFM, C-AFM, SEM, DLS, OPM, CD and FTIR, we observed that the initial photoactivation of γ-globulin at pH 12 for 3 h resulted in small protein fibres of ca. Further irradiation for 24 h, led to the formation of selfassembled long fibres of the protein of ca. 5-6 nm and observation of surface plasmon resonance band at around 520 nm with the concomitant quenching of luminescence intensity at 680 nm. The observation of light triggered self-assembly of the protein and its effect on controlling the fate of the anchored nanoparticles can be compared with the naturally occurring process such as photomorphogenesis.Furthermore,our approach offers a way to understand the role played by the self-assembly of the protein in ordering and knock out of the metal nanoparticles and also in the design of nano-biohybrid materials for medicinal and optoelectronic applications. Investigation of the potential applications of NIR absorbing and water soluble squaraine dyes 1-3 for protein labeling and anti-amyloid agents forms the subject matter of the third chapter of the thesis. The study of their interactions with various proteins revealed that 1-3 showed unique interactions towards serum albumins as well as lysozyme. 69%, 71% and 49% in the absorption spectra as well as significant quenching in the fluorescence intensity of the dyes 1-3, respectively. Half-reciprocal analysis of the absorption data and isothermal titration calorimetric (ITC) analysis of the titration experiments gave a 1:1 stoichiometry for the complexes formed between the lysozyme and squaraine dyes with association constants (Kass) in the range 104-105 M-1. We have determined the changes in the free energy (ΔG) for the complex formation and the values are found to be -30.78, -32.31 and -28.58 kJmol-1, respectively for the dyes 1, 2 and 3. Furthermore, we have observed a strong induced CD (ICD) signal corresponding to the squaraine chromophore in the case of the halogenated squaraine dyes 2 and 3 at 636 and 637 nm confirming the complex formation in these cases. To understand the nature of interaction of the squaraine dyes 1-3 with lysozyme, we have investigated the interaction of dyes 1-3 with different amino acids. These results indicated that the dyes 1-3 showed significant interactions with cysteine and glutamic acid which are present in the side chains of lysozyme. In addition the temperature dependent studies have revealed that the interaction of the dye and the lysozyme are irreversible. Furthermore, we have investigated the interactions of these NIR dyes 1-3 with β- amyloid fibres derived from lysozyme to evaluate their potential as inhibitors of this biologically important protein aggregation. These β-amyloid fibrils were insoluble protein aggregates that have been associated with a range of neurodegenerative diseases, including Huntington, Alzheimer’s, Parkinson’s, and Creutzfeldt-Jakob diseases. We have synthesized amyloid fibres from lysozyme through its incubation in acidic solution below pH 4 and by allowing to form amyloid fibres at elevated temperature. To quantify the binding affinities of the squaraine dyes 1-3 with β-amyloids, we have carried out the isothermal titration calorimetric (ITC) measurements. The association constants were determined and are found to be 1.2 × 105, 3.6× 105 and 3.2 × 105 M-1 for the dyes, 1-3, respectively. To gain more insights into the amyloid inhibiting nature of the squaraine dyes under investigations, we have carried out thioflavin assay, CD, isothermal titration calorimetry and microscopic analysis. The addition of the dyes 1-3 (5μM) led to the complete quenching in the apparent thioflavin fluorescence, thereby indicating the destabilization of β-amyloid fibres in the presence of the squaraine dyes. Further, the inhibition of the amyloid fibres by the squaraine dyes 1-3, has been evidenced though the DLS, TEM AFM and SAED, wherein we observed the complete destabilization of the amyloid fibre and transformation of the fibre into spherical particles of ca. These results demonstrate the fact that the squaraine dyes 1-3 can act as protein labeling agents as well as the inhibitors of the protein amyloidogenesis. The last chapter of the thesis describes the synthesis and investigation of selfassembly as well as bio-imaging aspects of a few novel tetraphenylethene conjugates 4-6.Expectedly, these conjugates showed significant solvatochromism and exhibited a hypsochromic shift (negative solvatochromism) as the solvent polarity increased, and these observations were justified though theoretical studies employing the B3LYP/6-31g method. We have investigated the self-assembly properties of these D-A conjugates though variation in the percentage of water in acetonitrile solution due to the formation of nanoaggregates. Further the contour map of the observed fluorescence intensity as a function of the fluorescence excitation and emission wavelength confirmed the formation of J-type aggregates in these cases. To have a better understanding of the type of self-assemblies formed from the TPE conjugates 4-6, we have carried out the morphological analysis through various microscopic techniques such as DLS, SEM and TEM. 70%, we observed rod shape architectures having ~ 780 nm in diameter and ~ 12 μM in length as evidenced through TEM and SEM analysis. We have made similar observations with the dodecyl conjugate 5 at ca. 70% and 50% water/acetonitrile mixtures, the aggregates formed from 4 and 5 were found to be highly crystalline and such structures were transformed to amorphous nature as the water fraction was increased to 99%. To evaluate the potential of the conjugate as bio-imaging agents, we have carried out their in vitro cytotoxicity and cellular uptake studies though MTT assay, flow cytometric and confocal laser scanning microscopic techniques. Thus nanoparticle of these conjugates which exhibited efficient emission, large stoke shift, good stability, biocompatibility and excellent cellular imaging properties can have potential applications for tracking cells as well as in cell-based therapies. In summary we have synthesized novel functional organic chromophores and have studied systematic investigation of self-assembly of these synthetic and biological building blocks under a variety of conditions. The investigation of interaction of water soluble NIR squaraine dyes with lysozyme indicates that these dyes can act as the protein labeling agents and the efficiency of inhibition of β-amyloid indicate, thereby their potential as anti-amyloid agents.

Atomic nanolithography patterning of submicron features: writing an organic self-assembled monolayer with cold bright Cs atom beams

Cs atom beams, transversely collimated and cooled, passing through material masks in the form of arrays of reactive-ion-etched hollow Si pyramidal tips and optical masks formed by intense standing light waves, write submicron features on self-assembled monolayers (SAMs). Features with widths as narrow as 43 ± 6 nm and spatial resolution limited only by the grain boundaries of the substrate have been realized in SAMs of alkanethiols. The material masks write two-dimensional arrays of submicron holes; the optical masks result in parallel lines spaced by half the optical wavelength. Both types of feature are written to the substrate by exposure of the masked SAM to the Cs flux and a subsequent wet chemical etch. For the arrays of pyramidal tips, acting as passive shadow masks, the resolution and size of the resultant feature depends on the distance of the mask array from the SAM, an effect caused by the residual divergence of the Cs atom beam. The standing wave optical mask acts as an array of microlenses focusing the atom flux onto the substrate. Atom 'pencils' writing on SAMs have the potential to create arbitrary submicron figures in massively parallel arrays. The smallest features and highest resolutions were realized with SAMs grown on smooth, sputtered gold substrates.

Semisynthetic aminoglycoside antibiotics : toward biomimetic synthesis, evasion of bacterial resistance and reduced toxicity

Les antibiotiques aminoglycosidiques sont des agents bactéricides de grande valeur et d’efficacité à large spectre contre les pathogènes Gram-positifs et Gram-négatifs, dont plusieurs membres naturels et semisynthétiques sont importants dans l’histoire clinique depuis 1950. Des travaux crystallographiques sur le ribosome, récompensés par le prix Nobel, ont démontré comment leurs diverses structures polyaminées sont adaptées pour cibler une hélice d’ARN dans le centre de codage de la sous-unité 30S du ribosome bactérien. Leur interférence avec l’affinité et la cinétique des étapes de sélection et vérification des tARN induit la synthèse de protéines à basse fidélité, et l’inhibition de la translocation, établissant un cercle vicieux d’accumulation d’antibiotique et de stress sur la membrane. En réponse à ces pressions, les pathogènes bactériens ont évolué et disséminé une panoplie de mécanismes de résistance enzymatiques et d’expulsion : tels que les N acétyltransférases, les O phosphotransférases et les O nucleotidyltransférases qui ciblent les groupements hydroxyle et amino sur le coeur des aminoglycosides; des méthyl-transférases, qui ciblent le site de liaison ribosomale; et des pompes d’expulsion actives pour l’élimination sélective des aminoglycosides, qui sont utilisés par les souches Gram-négatives. Les pathogènes les plus problématiques, qui présentent aujourd’hui une forte résilience envers la majorité des classes d’antibiotiques sur le bord de la pan-résistance ont été nommés des bactéries ESKAPE, une mnémonique pour Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa et Enterobacteriaceae. La distribution globale des souches avec des mécanismes de résistance envers les standards cliniques aminoglycosides, tels que la tobramycine, l’amikacine et la gentamicine, est comprise entre 20 et 60% des isolées cliniques. Ainsi, les aminoglycosides du type 4,6-disubstitués-2-deoxystreptamine sont inadéquats comme thérapies anti-infectieuses à large spectre. Cependant, la famille des aminoglycosides 4,5-disubstitués, incluant la butirosine, la neomycine et la paromomycine, dont la structure plus complexe, pourrait constituter une alternative. Des collègues dans le groupe Hanessian et collaborateurs d’Achaogen Inc. ont démontré que certains analogues de la paraomomycine et neomycine, modifiés par désoxygénation sur les positions 3’ et 4’, et par substitution avec la chaîne N1-α-hydroxy-γ-aminobutyramide (HABA) provenant de la butirosine, pourrait produire des antibiotiques très prometteurs. Le Chapitre 4 de cette dissertation présente la conception et le développement d’une stratégie semi-synthétique pour produire des nouveaux aminoglycosides améliorés du type 4,5 disubstitués, inspiré par des modifications biosynthétiques de la sisomicine, qui frustrent les mécanismes de résistance bactérienne distribuées globalement. Cette voie de synthèse dépend d’une réaction d’hydrogénolyse de type Tsuji catalysée par palladium, d’abord développée sur des modèles monosaccharides puis subséquemment appliquée pour générer un ensemble d’aminoglycosides hybrides entre la neomycine et la sisomicine. Les études structure-activité des divers analogues de cette nouvelle classe ont été évaluées sur une gamme de 26 souches bactériennes exprimant des mécanismes de résistance enzymatique et d’expulsion qui englobe l’ensemble des pathogènes ESKAPE. Deux des antibiotiques hybrides ont une couverture antibacterienne excellente, et cette étude a mis en évidence des candidats prometteurs pour le développement préclinique. La thérapie avec les antibiotiques aminoglycosidiques est toujours associée à une probabilité de complications néphrotoxiques. Le potentiel de toxicité de chaque aminoglycoside peut être largement corrélé avec le nombre de groupements amino et de désoxygénations. Une hypothèse de longue date dans le domaine indique que les interactions principales sont effectuées par des sels des groupements ammonium, donc l’ajustement des paramètres de pKa pourrait provoquer une dissociation plus rapide avec leurs cibles, une clairance plus efficace et globalement des analogues moins néphrotoxiques. Le Chapitre 5 de cette dissertation présente la conception et la synthèse asymétrique de chaînes N1 HABA β substitutées par mono- et bis-fluoration. Des chaînes qui possèdent des γ-N pKa dans l’intervalle entre 10 et 7.5 ont été appliquées sur une neomycine tétra-désoxygénée pour produire des antibiotiques avancés. Malgré la réduction considérable du γ N pKa, le large spectre bactéricide n’a pas été significativement affecté pour les analogues fluorés isosteriques. De plus, des études structure-toxicité évaluées avec une analyse d’apoptose propriétaire d’Achaogen ont démontré que la nouvelle chaîne β,β difluoro-N1-HABA est moins nocive sur un modèle de cellules de rein humain HK2 et elle est prometteuse pour le développement d’antibiotiques du type neomycine avec des propriétés thérapeutiques améliorées. Le chapitre final de cette dissertation présente la proposition et validation d’une synthèse biomimétique par assemblage spontané du aminoglycoside 66-40C, un dimère C2 symétrique bis-imine macrocyclique à 16 membres. La structure proposée du macrocycle a été affinée par spectroscopie nucléaire à un système trans,trans-bis-azadiène anti-parallèle. Des calculs indiquent que l’effet anomérique de la liaison α glycosidique entre les anneaux A et B fournit la pré-organisation pour le monomère 6’ aldéhydo sisomicine et favorise le produit macrocyclique observé. L’assemblage spontané dans l’eau a été étudié par la dimérisation de trois divers analogues et par des expériences d’entre croisement qui ont démontré la généralité et la stabilité du motif macrocyclique de l'aminoglycoside 66-40C.

Selbstassemblierte Monolagen und magnetisch strukturierte Submonolagen mit dia- und paramagnetischen Molekülen sowie Einzelmolekülmagneten auf Phthalocyanin- und Subphthalocyanin-Basis

Mit dieser Arbeit wurde die Selbstassemblierung von dia- und paramagnetischen Molekülen sowie Einzelmolekülmagneten auf Goldsubstraten und magnetisch strukturierten Substraten untersucht. Dazu wurden drei verschiedene Klassen an Phthalocyaninderivaten verwendet: Diamagnetische Subphthalocyanine, paramagnetische Phthalocyaninatometalle und Diphthalocyaninatolanthanidkomplexe. Alle synthetisierten Verbindungen sind peripher thioethersubstituiert. Die Alkylketten (a: n-C8H17, b: n-C12H25) vermitteln die Löslichkeit in vielen organischen Solventien und sorgen für eine geordnete Assemblierung auf einer Oberfläche, wobei die Bindung auf Gold hauptsächlich über die Schwefelatome stattfindet. Die aus Lösung abgeschiedenen selbstassemblierten Monolagen wurden mit XPS, NEXAFS-Spektroskopie und ToF-SIMS untersucht. Bei der Selbstassemblierung auf magnetisch strukturierten Substraten stehen die Moleküle unter dem Einfluss magnetischer Streufelder und binden bevorzugt nur in bestimmten Bereichen. Die gebildeten Submonolagen wurden zusätzlich mit X-PEEM untersucht. Die erstmals dargestellten Manganphthalocyanine [MnClPc(SR)8] 1 wurden ausgehend von MnCl2 erhalten. Hier fand bei der Aufarbeitung an Luft eine Oxidation zu Mangan(III) statt; +III ist die stabilste Oxidationsstufe von Mangan in Phthalocyaninen. Der Nachweis des axialen Chloridoliganden erfolgte mit Massenspektrometrie und FIR- sowie Raman-Spektroskopie. SQUID-Messungen haben gezeigt, dass die Komplexe 1 vier ungepaarte Elektronen haben. Bei den Subphthalocyaninen [BClSubpc(SR)6] 2 wurde der axiale Chloridoligand mit dem stäbchenförmigen Phenolderivat 29-H substituiert und die erfolgreiche Ligandensubstitution durch NMR- und IR-Spektroskopie sowie Massenspektrometrie an den Produkten [BSubpc(SR)6(29)] 30 belegt. Der Radikalcharakter der synthetisierten Terbiumkomplexe [Tb{Pc(SR)8}2] 3 wurde spektroskopisch nachgewiesen; SQUID-Messungen ergaben, dass es sich um Einzelmolekülmagnete mit einer Energiebarriere U des Doppelpotentialtopfs von 880 K oder 610 cm-1 bei 3a handelt. Zunächst wurden die SAMs der Komplexverbindungen 1, 2, 30 und 3 auf nicht magnetisch strukturierten Goldsubstraten untersucht. Die Manganphthalocyanine 1 bilden geordnete SAMs mit größtenteils flach liegenden Molekülen, wie die XPS-, NEXAFS- und ToF-SIMS-Analyse zeigte. Die Mehrzahl der Thioether-Einheiten ist auf Gold koordiniert und die Alkylketten zeigen ungeordnet von der Oberfläche weg. Bei der Adsorption findet eine Reduktion zu Mangan(II) statt und der axiale Chloridoligand wird abgespalten. Das beruht auf dem sog. Oberflächen-trans-Effekt. Im vorliegenden Fall übt die Metalloberfläche einen stärkeren trans-Effekt als der axiale Ligand aus, was bisher experimentell noch nicht beobachtet wurde. Die thioethersubstituierten Subphthalocyanine 2 und 30 sowie die Diphthalocyaninatoterbium-Komplexe 3 sind ebenfalls für SAMs geeignet. Ihre Monolagen wurden mit XPS und NEXAFS-Spektroskopie untersucht, und trotz einer gewissen Unordnung in den Filmen liegen die Moleküle jeweils im Wesentlichen flach auf der Goldoberfläche. Vermutlich sind bei diesen Systemen auch die Alkylketten größtenteils parallel zur Oberfläche orientiert. Im Gegensatz zu den Manganphthalocyaninen 1 tritt bei 2b, 30a, 30b und 3b neben der koordinativen Bindung der Schwefelatome auf Gold auch eine für Thioether nicht erwartete kovalente Au–S-Bindung auf, die durch C–S-Bindungsbruch unter Abspaltung der Alkylketten ermöglicht wird. Der Anteil, zu dem dieser Prozess stattfindet, scheint nicht mit der Molekülstruktur zu korrelieren. Selbstassemblierte Submonolagen auf magnetisch strukturierten Substraten wurden mit dem diamagnetischen Subphthalocyanin 2b hergestellt. Der Nachweis der Submonolagen war schwierig und gelang schließlich durch eine Kombination von ToF-SIMS, NEXAFS Imaging und X-PEEM. Die Analyse der ToF-SIMS-Daten zeigte, dass tatsächlich eine Modulation der Verteilung der Moleküle auf einem unterwärts magnetisch strukturierten Substrat eintritt. Mit X-PEEM konnte die magnetische Struktur der ferromagnetischen Schicht des Substrats direkt der Verteilung der adsorbierten Moleküle zugeordnet werden. Die Subphthalocyanine 2b adsorbieren nicht an den Domänengrenzen, sondern vermehrt dazwischen. Auf Substraten mit abwechselnd 6.5 und 3.5 µm breiten magnetischen Domänen binden die Moleküle bevorzugt in den Bereichen geringster magnetischer Streufeldgradienten, also den größeren Domänen. Solche Substrate wurden für die ToF-SIMS- und X-PEEM-Messungen verwendet. Bei größeren magnetischen Strukturen mit ca. 400 µm breiten Domänen, wie sie aufgrund der geringeren Ortsauflösung dieser Methode für NEXAFS Imaging eingesetzt wurden, binden die Moleküle dann in allen Domänen. Die diamagnetischen Moleküle werden nach dieser Interpretation aus dem inhomogenen Magnetfeld über der Probenoberfläche heraus gedrängt und verhalten sich analog makroskopischer Diamagnete. Die eindeutige Detektion der Moleküle auf den magnetisch strukturierten Substraten konnte bisher nur für die diamagnetischen Subphthalocyanine 2b erfolgen. Um die Interpretation ihres Verhaltens bei der Selbstassemblierung in einem inhomogenen Magnetfeld weiter voranzutreiben, wurde das Subphthalocyanin 37b dargestellt, welches ein stabiles organisches TEMPO-Radikal in seinem axialen Liganden enthält. Das paramagnetische Subphthalocyanin 37b sollte auf den magnetisch strukturierten Substraten in Regionen starker magnetischer Streufelder binden und damit das entgegengesetzte Verhalten zu den diamagnetischen Subphthalocyaninen 2b zeigen. Aus Zeitgründen konnte dieser Nachweis im Rahmen dieser Arbeit noch nicht erbracht werden.

Layer-by-Layer Assembly of Carbon Nanotubes Incorporated in Light-Addressable Potentiometric Sensors

The integration of carbon nanotubes in conjunction with a chemical or biological recognition element into a semiconductor field-effect device (FED) may lead to new (bio)chemical sensors. In this study, we present a new concept to develop field-effect-based sensors, using a light-addressable potentiometric sensor (LAPS) platform modified with layer-by-layer (LbL) films of single-walled carbon nanotubes (SWNTs) and polyamidoamine (PAMAM) dendrimers. Film growth was monitored for each layer adsorbed on the LAPS chip by Measuring current-voltage (IIV) curves. The morphology of the films was analyzed via atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM), revealing the formation of a highly interconnected nanostructure of SWNTs-network into the dendrimer layers. Constant current (CC) Measurements showed that the incorporation of the PAMAM/SWNT LbL film containing LIP to 6 bilayers onto the LAPS Structure has a high pH sensitivity of ca. 58 mV/pH. The biosensing ability of the devices was tested for penicillin G via adsorptive immobilization of the enzyme penicillinase atop the LgL film. LAPS architectures modified with the LbL film exhibited higher sensitivity, ca. 100 mV/decade, in comparison to ca. 79 mV/decade for all unmodified LAPS, which demonstrates the potential application of the CNT-LbL Structure in field-effect-based (bio)chemical sensors.

Perpendicularly self-oriented and shape-controlled L1(0)-FePt nanorods directly synthesized by a temperature-modulated process

The synthesis and self-assembly of tetragonal phase-containing L1(0)-Fe(55)Pt(45) nanorods with high coercive field is described. The experimental procedure resulted in a tetragonal/cubic phase ratio close to 1:1 for the as-synthesized nanoparticles. Using different surfactant/solvent proportions in the process allowed control of particle morphology from nanospheres to nanowires. Monodisperse nanorods with lengths of 60 +/- 5 nm and diameters of 2-3 nm were self-assembled in a perpendicular oriented array onto a substrate surface using hexadecylamine as organic spacer. Magnetic alignment and properties assigned, respectively, to the shape anisotropy and the tetragonal phase suggest that the self-assembled materials are a strong candidate to solve the problem of random magnetic alignment observed in FePt nanospheres leading to applications in ultrahigh magnetic recording (UHMR) systems capable of achieving a performance of the order of terabits/in(2).

Postural control as a function of self- and object-motion perception

The goals of this study were to examine the visual information influence on body sway as a function of self- and object-motion perception and visual information quality. Participants that were aware (object-motion) and unaware (self-motion) of the movement of a moving room were asked to stand upright at five different distances from its frontal wall. The visual information effect on body sway decreased when participants were aware about the sensory manipulation. Moreover, while the visual influence on body sway decreased as the distance increased in the self-motion perception, no effects were observed in the object-motion mode. The overall results indicate that postural control system functioning can be altered by prior knowledge, and adaptation due to changes in sensory quality seem to occur in the self- but not in the object-motion perception mode. (C) 2004 Elsevier B.V.. All rights reserved.

In situ real-time investigation of Organic Ultra-Thin-Film transistors: growth, electrical properties and biosensing applications

Organic electronics has grown enormously during the last decades driven by the encouraging results and the potentiality of these materials for allowing innovative applications, such as flexible-large-area displays, low-cost printable circuits, plastic solar cells and lab-on-a-chip devices. Moreover, their possible field of applications reaches from medicine, biotechnology, process control and environmental monitoring to defense and security requirements. However, a large number of questions regarding the mechanism of device operation remain unanswered. Along the most significant is the charge carrier transport in organic semiconductors, which is not yet well understood. Other example is the correlation between the morphology and the electrical response. Even if it is recognized that growth mode plays a crucial role into the performance of devices, it has not been exhaustively investigated. The main goal of this thesis was the finding of a correlation between growth modes, electrical properties and morphology in organic thin-film transistors (OTFTs). In order to study the thickness dependence of electrical performance in organic ultra-thin-film transistors, we have designed and developed a home-built experimental setup for performing real-time electrical monitoring and post-growth in situ electrical characterization techniques. We have grown pentacene TFTs under high vacuum conditions, varying systematically the deposition rate at a fixed room temperature. The drain source current IDS and the gate source current IGS were monitored in real-time; while a complete post-growth in situ electrical characterization was carried out. At the end, an ex situ morphological investigation was performed by using the atomic force microscope (AFM). In this work, we present the correlation for pentacene TFTs between growth conditions, Debye length and morphology (through the correlation length parameter). We have demonstrated that there is a layered charge carriers distribution, which is strongly dependent of the growth mode (i.e. rate deposition for a fixed temperature), leading to a variation of the conduction channel from 2 to 7 monolayers (MLs). We conciliate earlier reported results that were apparently contradictory. Our results made evident the necessity of reconsidering the concept of Debye length in a layered low-dimensional device. Additionally, we introduce by the first time a breakthrough technique. This technique makes evident the percolation of the first MLs on pentacene TFTs by monitoring the IGS in real-time, correlating morphological phenomena with the device electrical response. The present thesis is organized in the following five chapters. Chapter 1 makes an introduction to the organic electronics, illustrating the operation principle of TFTs. Chapter 2 presents the organic growth from theoretical and experimental points of view. The second part of this chapter presents the electrical characterization of OTFTs and the typical performance of pentacene devices is shown. In addition, we introduce a correcting technique for the reconstruction of measurements hampered by leakage current. In chapter 3, we describe in details the design and operation of our innovative home-built experimental setup for performing real-time and in situ electrical measurements. Some preliminary results and the breakthrough technique for correlating morphological and electrical changes are presented. Chapter 4 meets the most important results obtained in real-time and in situ conditions, which correlate growth conditions, electrical properties and morphology of pentacene TFTs. In chapter 5 we describe applicative experiments where the electrical performance of pentacene TFTs has been investigated in ambient conditions, in contact to water or aqueous solutions and, finally, in the detection of DNA concentration as label-free sensor, within the biosensing framework.

Extended donor and acceptor molecules for organic electronics

Die Untersuchung von halbleitenden Materialien auf der Basis von organischen Molekülen stellt ein Gebiet der angewandten Forschung an der Schwelle zur industriellen Nutzung dar. Geringes Gewicht und hohe mechanische Flexibilität ermöglichen völlig neue Produkte, die mit anorganischen Halbleitern nicht zu realisieren sind. Die Herstellung von Bauteilen wie Transistoren, Solarzellen oder Leuchtdioden aus organischen Materialien ist ein komplexes Gebiet, das einer Vielzahl von unterschiedlichen Optimierungen bedarf, um eine konkurrenzfähige Leistung zu erreichen. Die synthetische organische Chemie bietet vielfältige Möglichkeiten, mit maßgeschneiderten Lösungen zum Optimierungsprozess beizutragen. Zum einen können neue aktive Materialien hergestellt werden mit besserer Leistung und leichterer Verarbeitbarkeit. Zum anderen sind Substanzen zugänglich, die z.B. bei der Ladungsträgerinjektion hilfreich sein können.rnIn dieser Arbeit wurde an beiden dieser Fronten gearbeitet. Dabei lag die Entwicklungsstrategie darin, ausgedehnte π-konjugierte Moleküle herzustellen, die entweder besonders elektronenarme Akzeptoren oder elektronenreiche Donoren darstellen. Die genaue Kontrolle der elektronischen Niveaus stellt einen wichtigen Bestandteil dar, um niedrige elektrische Kontaktbarrieren zu Metallen zu erreichen und ausreichend stabile Materialien zu erreichen.rnDer erste Fokus der Arbeiten lag in der Funktionalisierung von Coronen. Dieser PAH stellt einen guten Kompromiss bezüglich seiner Größe dar: Er ist groß genug, um Diffusion in andere Schichten von Bauteilen zu vermeiden, aber nicht zu groß, um Verarbeitung durch Vakuumsublimation zu ermöglichen. Bislang sind praktisch keine Coronen-Derivate in der Literatur beschrieben, weshalb eine neue Synthese entwickelt werden musste, die die Einführung starker Donor- und Akzeptorfunktionalitäten erlaubt. Die photochemische Cyclodehydrierung von substituierten [2.2.2]paracyclophan-trienen stellte sich als hervorragende Möglichkeit heraus, dies zu bewerkstelligen. Es wurde eine Reihe von methoxy-substitutierten Coronenen mit unterschiedlicher Symmetrie hergestellt. Mittels optischer Spektroskopie konnte gezeigt werden, dass Methoxygruppen wenig Einfluss auf die elektronischen Eigenschaften von Coronen haben. Unter Spaltung der Methylether und anschließender Oxidation allerdings sind Coronenketone zugänglich, welche bis zu drei α-Diketongruppen besitzen. Diese Moleküle sind enorm starke Akzeptoren, was durch Cyclovoltammetrie und Vergleich zu anderen Akzeptoren eindrucksvoll gezeigt werden konnte. Die Sublimation dieses Akzeptors auf die Oberfläche von Metallen zeigt einen dramatischen Einfluss auf die Austrittsarbeit dieses Metalls, was zur Herstellung eines ohmschen Kontakts zu organischen Halbleitern von außerordentlichem Nutzen ist. rnDen zweiten Teil der Arbeit bilden Benzodithiophen enthaltende Polymere, die für den Einsatz als aktive Komponente in elektronischen Bauteilen entwickelt wurden. Nach systematischer Strukturoptimierung wurde ein Polymer enthalten, welches in einem Feldeffekt-Transistor auf Standard-Silizium-Substraten Ladungsträger-Mobilitäten über 0,1 cm2/Vs erreicht mit großer Reproduzierbarkeit und ausgezeichneter Transistor-Charakteristik. Es konnte gezeigt werden, dass die durch die Monomergeometrie erzeugte Kurvung des Polymers zu einem optimalen Kompromiss aus Löslichkeit und effektiver Packung darstellt. Auf für industrielle Anwendungen besonders interessanten polymer-basierten Substraten wurde eine noch erheblich bessere Leistung gezeigt. Auf einem PET-Substrat wurden Feldeffekt-Mobilitäten von 0,5 cm2/Vs gemessen mit überzeugenden Reproduzierbarkeit und Stabilität.rnDamit konnte in der Arbeit ein bedeutender Beitrag zur Weiterentwicklung von Materialien für den Einsatz in elektronischen Bauteilen geleistet werden. Die Substanzen versprechen noch erhebliches Potenzial nach intensiver Optimierung und wurden deshalb zum Patent angemeldet.rn

Lipophilic nucleosides: studies toward self-assembled functional materials

Molecular self-assembly takes advantage of supramolecular non-covalent interactions (ionic, hydrophobic, van der Waals, hydrogen and coordination bonds) for the construction of organized and tunable systems. In this field, lipophilic guanosines can represent powerful building blocks thanks to their aggregation proprieties in organic solvents, which can be controlled by addition or removal of cations. For example, potassium ion can template the formation of piled G-quartets structures, while in its absence ribbon-like G aggregates are generated in solution. In this thesis we explored the possibility of using guanosines as scaffolds to direct the construction of ordered and self-assembled architectures, one of the main goals of bottom-up approach in nanotechnology. In Chapter III we will describe Langmuir-Blodgett films obtained from guanosines and other lipophilic nucleosides, revealing the “special” behavior of guanine in comparison with the other nucleobases. In Chapter IV we will report the synthesis of several thiophene-functionalized guanosines and the studies towards their possible use in organic electronics: the pre-programmed organization of terthiophene residues in ribbon aggregates could allow charge conduction through π-π stacked oligothiophene functionalities. The construction and the behavior of some simple electronic nanodevices based on these organized thiopehene-guanosine hybrids has been explored.

Dynamical Casimir effect and the structure of vacuum in quantum field theory

Some of the most interesting phenomena that arise from the developments of the modern physics are surely vacuum fluctuations. They appear in different branches of physics, such as Quantum Field Theory, Cosmology, Condensed Matter Physics, Atomic and Molecular Physics, and also in Mathematical Physics. One of the most important of these vacuum fluctuations, sometimes called "zero-point energy", as well as one of the easiest quantum effect to detect, is the so-called Casimir effect. The purposes of this thesis are: - To propose a simple retarded approach for dynamical Casimir effect, thus a description of this vacuum effect when we have moving boundaries. - To describe the behaviour of the force acting on a boundary, due to its self-interaction with the vacuum.

From supramolecular sheets to fibers and back: establishing the critical parameters that govern the morphology of pyrene-based self-assembled materials

The precise arraying of functional entities in morphologically well-defined shapes remains one of the key challenges in the processing of organic molecules1. Among various π-conjugated species, pyrene exhibits a set of unique properties, which make it an attractive compound for the utilization in materials science2. In this contribution we report on properties of self-assembled structures prepared from amphiphilic pyrene trimers (Py3) consisting of phosphodiester-linked pyrenes. Depending on the geometry of a pyrene core substitution (1.6-, 1.8-, or 2.7- type, see Scheme), the thermally-controlled self-assembly allows the preparation of supramolecular architectures of different morphologies in a bottom-up approach: two-dimensional (2D) nanosheets3 are formed in case of 1.6- and 2.7-substitution4 whereas one-dimensional (1D) fibers are built from 1.8- substituted isomers. The morphologies of the assemblies are established by AFM and TEM, and the results are further correlated with spectroscopic and scattering data. Two-dimensional assemblies consist of an inner layer of hydrophobic pyrenes, sandwiched between a net of phosphates. Due to the repulsion of the negative charges, the 2D assemblies exist mostly as free-standing sheets. An internal alignment of pyrenes leads to strong exciton coupling with an unprecedented observation (simultaneous development of J- and H-bands from two different electronic transitions). Despite the similarity in spectroscopic properties, the structural parameters of the 2D aggregates drastically depend on the preparation procedure. Under certain conditions extra-large sheets (thickness of 2 nm, aspect ratio area/thickness ~107) in aqueous solution are formed4B. Finally, one-dimensional assemblies are formed as micrometer-long and nanometer-thick fibers. Both, planar and linear structures are intriguing objects for the creation of conductive nanowires that may find interest for applications in supramolecular electronics.

From supramolecular sheets to fibers and back: establishing the critical parameters that govern the morphology of pyrene-based self-assembled materials

The precise arraying of functional entities in morphologically well-defined shapes remains one of the key challenges in the processing of organic molecules1. Among various π-conjugated species, pyrene exhibits a set of unique properties, which make it an attractive compound for the utilization in materials science2. In this contribution we report on properties of self-assembled structures prepared from amphiphilic pyrene trimers (Py3) consisting of phosphodiester-linked pyrenes. Depending on the geometry of a pyrene core substitution (1.6-, 1.8-, or 2.7- type, see Scheme), the thermally-controlled self-assembly allows the preparation of supramolecular architectures of different morphologies in a bottom-up approach: two-dimensional (2D) nanosheets3 are formed in case of 1.6- and 2.7-substitution4 whereas one-dimensional (1D) fibers are built from 1.8- substituted isomers. The morphologies of the assemblies are established by AFM and TEM, and the results are further correlated with spectroscopic and scattering data. Two-dimensional assemblies consist of an inner layer of hydrophobic pyrenes, sandwiched between a net of phosphates. Due to the repulsion of the negative charges, the 2D assemblies exist mostly as free-standing sheets. An internal alignment of pyrenes leads to strong exciton coupling with an unprecedented observation (simultaneous development of J- and H-bands from two different electronic transitions). Despite the similarity in spectroscopic properties, the structural parameters of the 2D aggregates drastically depend on the preparation procedure. Under certain conditions extra-large sheets (thickness of 2 nm, aspect ratio area/thickness ~107) in aqueous solution are formed4B. Finally, one-dimensional assemblies are formed as micrometer-long and nanometer-thick fibers. Both, planar and linear structures are intriguing objects for the creation of conductive nanowires that may find interest for applications in supramolecular electronics.

Organic Semiconducing Thin Films: Device Applications and Beyond

Thesis (Master's)--University of Washington, 2016-06