Au cours des dernières décennies, les chromophores organiques “push-pull” ont vu leur intérêt grandir en raison de leurs applications potentielles dans les domaines des transistors à effet de champ, de l'optique non linéaire, des OLEDs, et du photovoltaïque. Dans le cadre de la conception de cellules photovoltaïques, ces structures moléculaires correctement organisées sur une surface devraient permettre d’améliorer l’interface donneur/accepteur, l’absorption optique, et d’augmenter le volume de la couche active. Nous avons développé une synthèse en plusieurs étapes de nouvelles molécules “push-pull” comportant une tête réactive thiol autorisant la formation de monocouches moléculaires auto-assemblées (SAM) sur surfaces d’or ou d’ITO. En variant les groupements donneur, accepteur, et l’espaceur il a été possible de moduler les propriétés optiques et électroniques.Les produits obtenus possèdent une forte absorption de lumière et peuvent donc être efficaces pour le photovoltaïque. Les monocouches moléculaires finales des chromophores avec ou sans nanoparticules d’or ont été étudiées principalement par angles de contact, techniques de spectroscopie IR, UV-Vis, XPS, et par microscopie à sonde locale (STM, AFM). Les matériaux ainsi obtenus à base de SAMs de chromophores “push-pull” et de nanoparticules de métaux nobles ont ensuite caractérisés électriquement et optiquement pour évaluer leur utilisation potentielle pour la conversion de l’énergie photovoltaïque. / During the past decades, the synthesis of organic donor-acceptor (D/A) “push-pull” chromophores has been of considerable interest because of their potential use in nonlinear optics, LEDs, field effect transistors, and photovoltaics (PV). As a part of the design of the PV cells, these molecular structures correctly arranged on a surface should improve the donor/acceptor interface, the optical absorption, and increase the volume of the active layer. We have developed a multi-step synthesis of new “push-pull” molecules bearing a thiol reactive group enabling to form self-assembled monolayers (SAM) on gold or ITO surfaces. Combining various donor, acceptor, and spacer moieties we could tune the “push-pull” optical and electronic properties. The obtained “push-pull” products exhibit a high light absorption and can thus be effective in PV applications. Final SAMs with and without nanoparticles were studied mainly by contact angles, UV-vis, IR and XPS spectroscopy, ellipsometry and near-field microscopy (STM and AFM). As-obtained organic layers were then electrically and optically characterized to assess their potential use in the field of PV energy conversion.

Le contrôle des propriétés physicochimiques et de l’état de surface des solides constituent un enjeu majeur pour le développement des biotechnologies, et notamment des bio-capteurs. Pour des applications en analyse et diagnostic biologique, la fonctionnalisation des surfaces à base de silicium peut être réalisée grâce à la formation d’un nano-film organique appelé SAM (Self-Assembled Monolayer). L'objectif de ce travail de thèse est ainsi de synthétiser des monocouches sur des substrats de silice afin de les rendre biofonctionnels en vue de développer une plateforme de biodétection polyvalente.Pour ce faire, deux types d'agents de couplages ont été envisagés : l'un possédant un motif azoture et l'autre une biotine. L’obtention de ces deux types de molécules a fait l’objet d’un travail de synthèse permettant d’aboutir à de nouveaux organosilanes fonctionnels directement greffables sur des surfaces de SiO2. La biofonctionnalité est introduite sur le substrat par la biotine, soit directement lors de la formation de la SAM, soit par chimie click sur les monocouches fonctionnalisées par des azotures.Les différentes surfaces obtenues ont ensuite été caractérisées par Spectroscopie Infrarouge de Réflexion–Absorption par Modulation de Polarisation (PM-IRRAS) et par Microscopie de Force Atomique (AFM). La bioactivité des SAMs biotinylées a enfin été évaluée par un protocole mettant en jeu une streptavidine modifiée par une enzyme (la HRP) capable de catalyser des réactions d’oxydoréduction de molécules chromogènes. / Control of surface physicochemical properties is a key aspect for the development of many biotechnological tools, such as biosensors. For analysis and diagnostic, the functionalization of silica-based surfaces may be carried out through the creation of an organic nano-film named a Self-Assembled Monolayer (SAM). The main goal of this PhD work is thus to synthesize monolayer on SiO2 substrates in order give them biofunctionality, aiming at developing a versatile biodetection platform.In order to do so, we focused on the synthesis of two types of coupling agents, either bearing an azide moiety or a biotin. This organic synthesis work led to two new sorts of functional organosilanes which can be directly grafted onto silica surfaces. Biofunctionality itself is introduced by the biotin, either through the formation of the monolayer or through click chemistry on azide-functionalized SAMs.Said surfaces were then fully characterized using Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) an Atomic Force Microscopy (AFM). Bioactivity of biotinylated surfaces was then monitored using streptavidin conjugated with HRP in order to catalyze the redox reaction of chromogenic substrates.

This work is aimed at the preparation and morphological and spectroscopic characterization of the interphase nanocomposite (NC) two-dimensional (2D) self-assembled systems of Ag and Au nanoparticles (NPs). The NPs were functionalized with the following ligands with terpyridine end-groups: 2,2′:6′,2′′-terpyridine (tpy), 4'-(2-thienyl)-2,2':6',2''- terpyridine (T-tpy), α,ω-bis(terpyridyl)-2,2'-bithiophene (tpy-2T-tpy) and α,ω-bis(terpyridyl)- 2,2':5',2''-terthiophene (tpy-3T-tpy). The morphological analysis of transmission electron micrographs proves the preservation of the average interparticle distance in closely spaced NP pairs, independent of the ligand. The value of the total average interparticle distance increases in the order: tpy < T-tpy < tpy- 2T-tpy < tpy-3T-tpy, while the average occupied area fraction in the same order decreases. The morphological descriptors (i.e. interparticle distance and occupied area fraction) were found to correlate with the shift of the SPE (surface plasmon extinction) maxima of NCs (tpy > T-tpy > tpy-2T-tpy > tpy-3T-tpy). The results show that the shift of SPE band maximum depends on the degree of surface plasmon delocalisation rather than on the value of the average interparticle distance in closely spaced NP pairs. The smaller are the islands formed by closely...

RésuméLes monocouches auto-assemblées d'ADN immobilisées sur électrodes d'or sont à la base de nombreux biocapteurs électrochimiques. Le contrôle du comportement interfacial de l'ADN par le biais d'un champ électrique est intéressant pour la détection de polymorphisme nucléotidique simple (PNS). La caractérisation in situ de monocouches d'ADN à l'échelle moléculaire est importante pour la fabrication de biocapteurs robustes, fiables et sensibles.La thèse porte sur la détection du PNS dans l'ADN par le biais d'hybridation/dénaturation induite par le champ électrique. La microscopie de fluorescence sous conditions électrochimiques est utilisée comme méthodologie de détection et outil de caractérisation de l'interface d'ADN. À cette fin, des séquences d'ADN marquées par des sondes fluorescentes sont immobilisées sur des électrodes d'or sous forme de monocouches auto-assemblées (SAM) thiolées.Premièrement, les SAMs sont composées de séquences cibles présentant ou non une mutation ponctuelle. La relation entre le potentiel appliqué et la dénaturation du double brin est étudiée. La dénaturation électrochimique est observée à -0,25 V vs Ag / Deoxyribonucleic acid (DNA) self-assembled monolayers (SAMs) immobilized on gold electrodes are the basis of many electrochemical biosensors. Control of the interfacial behavior of DNA by means of an electric field is of interest for sensing applications such as the detection of single nucleotide polymorphisms (SNPs). Moreover, the in situ characterization of immobilized DNA monolayers at a molecular level is important for the fabrication of robust, reliable and sensitive sensors.The thesis aims at studying the discrimination between DNA strands containing SNPs on the basis of electric-field assisted hybridization/denaturation of DNA. In situ electrochemical fluorescence microscopy is used as a detection methodology and characterization tool for DNA interfaces. For this purpose, fluorescently labeled DNA sequences are immobilized at gold electrodes as thiol SAMs.First, the SAMs under investigation were composed of perfect match or SNP-containing target sequences. The relationship between the applied potential and the denaturation of DNA duplexes was investigated. Electrochemical melting was observed at -0.25 V vs. Ag / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The surface of biomaterials can induce contacting blood to coagulate, similar to the response initiated by injured blood vessels to control blood loss. This poses a challenge to the use of biomaterials as the resulting coagulation can impair the performance of hemocompatible devices such as catheters, vascular stents and various extracorporeal tubings [1], what can moreover cause severe host reactions like embolism and infarction. Biomaterial induced coagulation processes limit the therapeutic use of medical products, what motivates the need for a better understanding of the basic mechanisms leading to this bio-incompatibility [2] in order to define modification strategies towards improved biomaterials [3]. Several approaches for the enhancement of hemocompatible surfaces include passive and active strategies for surface modifications. The materials’ chemical-physical properties like surface chemistry, wettability and polarity are parameters of passive modification approaches for improved hemocompatibility and are the focus of the present work. In the present study self assembled monolayers with different surface functionalities (-COOH, -OH, -CH3) were applied as well as two-component-layers with varying fractions of these, as they allow a defined graduation of surface wettability and charge. The ease of control over these parameters given by these model surfaces enables the evaluation of the influence of specific surface-properties on biological responses. To evaluate the effects of different surface chemistry on initial mechanisms of biomaterial induced coagulation, the surfaces were incubated with protein solution, human plasma, blood cell fractions or fresh heparinised human whole blood. Indicative hemocompatibility parameters were subsequently analysed focusing on protein adsorption, coagulation activation, contact activation (intrinsic/ enhancer pathway), impact of tissue factor (extrinsic/ activator pathway) and cellular systems (blood platelets and leukocytes).

Diese Arbeit beinhaltet unsere Studien an selbstorganisierenden Monoschichten (engl. SAM = self- assembled monolayer) einiger aromatischer Thiole auf Gold- und Kupferoberflächen. Die Bildung von Monoschichten von Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin auf Au und Cu wurde untersucht und charakterisiert. Das abschirmende Verhalten und die strukturelle Anordnung dieser Monoschichten wurden mit Hilfe elektrochemischer und spektroskopischer Methoden geprüft und bestimmt. Zyklische Voltammetrie und oberflächenverstärkte Raman Spektroskopie wurden intensiv zur Aufklärung von Elektronentransferreaktionen an diesen mit SAMs modifizierten Oberflächen genutzt. Elektrochemische Studien von Monoschichten aus Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin in 0,1 M wässriger KClO4-Lösung lassen schlussfolgern, dass diese Moleküle schwefelseitig an die Substratoberfläche gebunden sind. In 0,1 M wässriger KClO4-Lösung aufgenommene zyklische Voltammogramme an Gold- und Kupferoberflächen, welche mit oben genannten, aromatischen Thiolen beschichtet wurden, legen nahe, dass Adsorptionsschichten von Thiophenol und 1,4-Dithiobenzol eine stärkere Tendenz zum Abschirmen besitzen als andere. Durch das Einbringen von Kupferproben, welche mit genannten aromatischen Thiolen behandelt wurden, in 0,1 M Silbernitrat-Lösung können sehr leicht Silber-Nanodendritstrukturen erhalten werden. Abscheidezeit und Konzentration der Silbernitrat-Lösung haben einen großen Einfluss auf das Wachstum der Silber-Nanodendritstrukturen auf den modifizierten Kupferproben. Diese Silber-Nanodendritstrukturen besitzen eine hohe katalytische Aktivität hinsichtlich der Oxidation von Hydroquinon. Untersuchungen zur Korrosion an polykristallinem Kupfer, welches mit obigen aromatischen Thiolen modifiziert wurde, in 0,1 M Silbernitrate-Lösung ließen vermuten, dass dieses Kupfersubstrat mehr anodisches Verhalten zeigte als reines Kupfer bei ähnlichen Bedingungen. Zyklische Voltammetrie an wie oben behandeltem Kupfer in 0,1M wässriger KClO4-Lösung zeigte, dass die Geschwindigkeit der Kupferauflösung bei diesen Messungen erhöht war gegenüber anderen, in welchen reines Kupfer bei identischen Bedingungen eingesetzt wurde. / It deals with our studies on self-assembled monolayers of aromatic thiols on gold and copper surfaces. Monolayer formation of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mer¬cap¬to¬pyridine and 2-mercaptopyridine on Au and Cu surfaces was studied and characterized. The blocking behaviour and structural arrange¬ments of these monolayers were evaluated and characterized using electrochemical and spec¬troscopic techniques. Cyclic voltammetry and surface enhanced Raman spectroscopy were extensively used for the study of electron transfer reactions on these SAM modified surfaces. Electrochemical and spectroelectrochemical studies of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mercaptopyridine and 2-mercaptopyridine monolayers in aqueous solution of 0.1 M KClO4 suggest that these molecules adsorbed to substrate. Cyclic voltammetry of gold and copper covered with these aromatic thiolates recorded in aqueous solution of 0.1 M KClO4 suggests that adlayers of thio¬phenol and 1,4-dithiobenzene exhibit more blocking behavior than the other ones. Silver nanodendritic structures are easily produced by placing copper samples modified with these aromatic thiolates into 0.1 M silver nitrate solution. Deposition time and concentration of silver nitrate solution have great influence on growing up silver nanodendritic structures on the surface of modified copper samples. These silver nanodendritic structures exhibit electrocatalytic activity towards the oxidation of hydroquinone. Corrosion investigation of polycrystalline copper modified with these aromatic thiolates in 0.1 M silver nitrate solution suggest that copper substrate might be more anodic compared to bare copper under identical condition. Cyclic voltammetry of copper modified with these aromatic thiolates suggests that the rate of dissolution copper in aqueous solution of 0.1 M KClO4 is higher than bare copper in the same condition.

No description available.

Das Cu-Cu-Bonden ist eine vielversprechende lötfreie Fine-Pitch-Verbindungstechnologie für die 2,5D- und 3D-Systemintegration. Diese Bondtechnologie wurde in den letzten Jahren intensiv untersucht und wird derzeit für miniaturisierte mikroelektronische Produkte eingesetzt. Allerdings, stellt das Cu‑Cu-Bonden zum einen sehr hohe Anforderungen an die Oberflächenplanarität und -reinheit, und zum anderen sollten die Bondpartner frei von Oxiden sein. Oxidiertes Cu erfordert erhöhte Bondparameter, um die Oxidschicht zu durchbrechen und zuverlässige Cu-Cu-Verbindungen zu erzielen. Diese Bondbedingungen sind für viele sensible Bauelemente nicht geeignet. Aus diesem Grund sollten alternative Technologien mit einer einfachen Technik zum Schutz von Cu vor Oxidation gefunden werden. In dieser Arbeit werden selbstorganisierte Monolagen (SAMs) für den Cu-Oxidationsschutz und die Verbesserung der Cu-Cu-Thermokompression- (TC) und Ultraschall- (US) Flip-Chip-Bondtechnologien untersucht. Die Experimente werden an Si-Chips mit galvanisch aufgebrachten Cu-Microbumps und Cu-Schichten durchgeführt. Die Arbeit beinhaltet die umfassende Charakterisierung der SAM für den Cu-Schutz, die Bewertung der technologischen Parameter für das TC- und US-Flip-Chip-Bonden sowie die Charakterisierung der Cu-Cu-Bondqualität (Scherfestigkeitstests, Bruchflächen- und Mikrostrukturanalysen). Eine Lagerung bei tiefen Temperaturen (bei ‑18 °C und ‑40 °C) bestätigte die langanhaltende Schutzwirkung der kurzkettigen SAMs für das galvanisch abgeschiedene Cu ohne chemisch-mechanische Politur. Der Einfluss der Tieftemperaturlagerung an Luft und der thermischen SAM-Desorption in einer Inertgasatmosphäre auf die TC-Verbindungsqualität wird im Detail analysiert. Die Idee, mit Hilfe der US-Leistung SAM mechanisch zu entfernen und gleichzeitig das US-Flip-Chip-Bonden zu starten, wurde in der Literatur bisher nicht systematisch untersucht. Die Methode ermöglicht kurze Bondzeiten, niedrige Bondtemperaturen und das Bonden an Umgebungsluft. Sowohl beim TC- als auch beim US-Flip-Chip-Bonden zeigt es sich, dass die Scherfestigkeit bei den Proben mit SAM-Passivierung um ca. 30 % höher ist als bei unbeschichteten Proben. Das Vorhandensein von Si- und Ti-Bruchflächen nach den Scherfestigkeitstests ist für die Proben mit der SAM-Passivierung typisch, was auf eine höhere Festigkeit solcher Verbindungen im Vergleich zu ungeschützten Proben schließen lässt. Die Transmissionselektronenmikroskopie (TEM) zeigt keine SAM-Spuren im zentralen Bereich der Cu-Cu-Grenzfläche nach dem US-Flip-Chip-Bonden. Die Ergebnisse dieser Arbeit zeigen die Verbesserung der Bondqualität durch den Einsatz von SAM zum Schutz des Cu vor Oxidation im Vergleich zum üblicherweise angewandten Cu-Vorätzen. Das gefundene technologische Prozessfenster für das US-Flip-Chip-Bonden an Luft bietet eine hohe Bondqualität bei 90 °C und 150 °C, bei 180 MPa, bei einer Bonddauer von 1 s an. Die in dieser Arbeit gewonnenen Erkenntnisse sind ein wichtiger Beitrag zum Verständnis des SAM-Einflusses auf Chips mit galvanischen Cu-Microbumps, bzw. Cu-Schichten, und zur weiteren Anwendung der Cu-Cu-Fine-Pitch-Bondtechnologie in der Mikroelektronik. / Cu-Cu bonding is one of the most promising fine-pitch interconnect technologies with solder elimination for 2.5D and 3D system integration. This bonding technology has been intensively investigated in the last years and is currently in application for miniaturized microelectronics products. However, Cu-Cu bonding has very high demands on the sur-face planarity and purity, and the bonding partners should be oxide-free. Oxidized Cu requires elevated bonding parameters in order to break through the oxide layer and achieve reliable Cu-Cu interconnects. Those bonding conditions are undesirable for many devices (e.g. due to the temperature/pressure sensitivity). Therefore, alternative technologies with a simple technique for Cu protection from oxidation are required. Self-assembled monolayers (SAMs) are proposed for the Cu protection and the improvement of the Cu-Cu thermocompression (TC) and ultrasonic (US) flip-chip bonding technologies in this thesis. The experiments were carried out on Si dies with electroplated Cu microbumps and Cu layers. The thesis comprises the comprehensive characterization of the SAM for Cu protection, evaluation of technological parameters for TC and US flip-chip bonding as well as characterization of the Cu-Cu bonding quality (shear strength tests, fracture surface and microstructure analyses). The storage at low temperatures (at ‑18 °C and ‑40 °C) confirmed the prolonged protective effect of the short-chain SAMs for the electroplated Cu without chemical-mechanical polishing. The influence of the low-temperature storage in air and the thermal SAM desorption in an inert gas atmosphere on the TC bonding quality was analyzed in detail. The approach of using US power to mechanically remove SAM and simultaneously start the US flip-chip bonding has not been systematically investigated before. The method provides the benefit of short bonding time, low bonding temperature and bonding in ambient air. Both the TC and US flip-chip bonding results featured the shear strength that is approximately 30 % higher for the samples with SAM passivation in comparison to the uncoated samples. The presence of Si and Ti fracture surfaces after the shear strength tests is typical for the samples with the SAM passivation, which suggests a higher strength of such interconnects in comparison to the uncoated samples. The transmission electron microscopy (TEM) indicated no SAM traces at the central region of the Cu-Cu bonding interface after the US flip-chip bonding. The results of this thesis show the improvement of the bonding quality caused by the application of SAM for Cu protection from oxidation in comparison to the commonly applied Cu pre-treatments. The found technological process window for the US flip-chip bonding in air offers high bonding quality at 90 °C and 150 °C, at 180 MPa, for the bonding duration of 1 s. The knowledge gained in this thesis is an important contribution to the understanding of the SAM performance on chips with electroplated Cu microbumps/layers and further application of the Cu-Cu fine-pitch bonding technology for microelectronic devices.

Understanding charge transport through molecular junctions and factors affecting the conductivity at the single molecule level is the first step in designing functional electronic devices using individual molecules. A variety of methods have been developed to fabricate metal-molecule-metal junctions in order to evaluate Single Molecule Conductance (SMC). Single molecule junctions usually are formed by wiring a molecule between two metal electrodes via anchoring groups that provide efficient electronic coupling and bind the organic molecular backbone to the metal electrodes. We demonstrated a novel strategy to fabricate single molecule junctions by employing the stabilization provided by the long range ordered structure of the molecules on the surface. The templates formed by the ordered molecular adlayer immobilize the molecule on the electrode surface and facilitate conductance measurements of single molecule junctions with controlled molecular orientation. This strategy enables the construction of orientation-controlled single molecule junctions, with molecules lacking proper anchoring groups that cannot be formed via conventional SMC methods. Utilizing Scanning Tunneling Microscopy (STM) imaging and STM break junction (STM-BJ) techniques combined, we employed the molecular assembly of mesitylene to create highly conductive molecular junctions with controlled orientation of benzene ring perpendicular to the STM tip as the electrode. The long range ordered structure of mesitylene molecules imaged using STM, supports the hypothesis that mesitylene is initially adsorbed on the Au(111) with the benzene ring lying flat on the surface and perpendicular to the Au tip. Thus, long range ordered structure of mesitylene facilitates formation of Au-π-Au junctions. Mesitylene molecules do not have standard anchoring groups providing enough contact to the gold electrode and the only assumable geometry for the molecules in the junction is via direct contact between Au and the π system of the benzene ring in mesitylene. SMC measurements for Au/mesitylene/Au junctions results in a molecular conductance value around 0.125Go, two orders of magnitude higher than the measured conductance of a benzene ring connected via anchoring groups. We attributed this conductance peak to charge transport perpendicular to the benzene ring due to direct coupling between the π system and the gold electrode that happens in planar orientation. The conductance we measured for planar orientation of benzene ring is two order of magnitude larger than conductance of junctions formed with benzene derivatives with conventional linkers. Thus, altering the orientation of a single benzene-containing molecule between the two electrodes from planar orientation to the upright attached via the linkers, results in altering the conductivity in a large order. Based on these findings, by utilizing STM imaging and STM-BJ in an electrochemical environment including potential induced self-assembly formation of terephthalic acid, we designed an electrochemical single molecule switch. Terephthalic acid forms large domains of ordered structure on negatively charged Au(111) surface under negative electrochemical surface potentials with the benzene ring lying flat on the surface due to hydrogen bonding between carboxylic acid groups of neighboring molecules. Formation of long range ordered structure facilitates direct contact between the π system of the benzene ring and the gold electrodes resulting in the conductance peak. On positively charged Au(111), deprotonation of carboxylic acid groups leads to absence of long range ordered structure of molecules with planar orientation and absence of the conductance peak. In this case alternating the surface (electrode) potential from negative to positive charge densities induces a transition in the adlayer structure on the surface and switches conductance value. Hence, electrochemical surface potential can, in principle, be employed as an external stimulus to switch single molecule arrangement on the surface and the conductance in the junction. The observation of conductance switching due to molecule’s arrangement in the junction lead to the hypothesis that for any benzene derivative, an orientation-dependent conductance in the junction due to the contact geometry (i.e. electrode-anchoring groups versus direct electrode-π contact) should be expected. Conventional techniques in fabricating single molecule junctions enable accessing charge transport along only one direction, i.e., between two anchoring groups. However, molecules such as benzene derivatives are anisotropic objects and we are able to measure an orientation-dependent conductance. In order to systematically study anisotropic conductivity at single molecule level, we need to measure the conductance in different and well-controlled orientations of single molecules in the junction. We employed the same EC-STM-BJ set up for SMC measurements and utilize electrochemical potential of the substrate (electrode) as the tuning source to variate the orientation of the single molecule in the junction. We investigated single molecule conductance of the benzene rings with carboxylic acid functional groups in two orientations: one with the benzene ring bridging between two electrodes using carboxylic acids as anchoring groups (upright); and one with the molecule lying flat on the substrate perpendicular to the STM tip (planar). Physisorption of these species on the Au (111) single crystal electrode surface at negative electrochemical potentials results in an ordered structure with the benzene ring in a planar orientation. Positive electrochemical potentials cause formation of the ordered structure with molecules standing upright due to coordination of a deprotonated carboxyl groups to the electrode surface. Thus, formation of the single molecule junction and consequently conductivity measurements is facilitated in two directions for the same molecule and anisotropic conductivity can be studied. In engineering well-ordered two-dimensional (2-D) molecular structures with controlled assembly of molecular species, pH can be employed as another tuning source for the molecular structures and adsorption in experiments conducted in aqueous solutions. Based on simple chemical principles, amine (NH2) groups are hydrogen bond acceptors and donors. Amines are soluble in water and protonation results in protonated (NH3+) and unprotonated (NH2) amine groups in acidic and moderately acidic/neutral solutions, respectively. Thus, amines are suitable molecular building blocks for fabricating 2-D supramolecular structures where pH is employed as a knob to manipulate intermolecular hydrogen bonding leading to phase transitions. We investigated pH induced structural changes in the 1,3,5–triaminobenzene (TAB) monolayer and the formation/disruption of hydrogen bonds between neighboring molecules. Our STM images indicate that in the concentrated acidic solution, the protonated amine groups of TAB are not able to form H-bonds and long range ordered structure of TAB does not form on the Au(111) surface. However, in moderately acidic solution (pH ~ 5.5) at room temperature, protonation on the ring carbon atom generates species capable of forming H-bonds leading to the formation of the long range ordered structures of TAB molecules. Utilizing EC-STM set up, we investigated the controllable fabrication of a TAB 2-D supramolecular structure based on amine-amine hydrogen bonding and effect of pH in formation of ordered/disordered TAB network. / Chemistry

Surface plasmon resonance (SPR) sensors using multiwavelength light coupling are investigated to probe changes in refractive index that occur as a result of chemical or biochemical processes. Traditional SPR sensors have used angle modulation to facilitate detection at the sensor surface; however, the multiwavelength approach is novel and brings new functionality to SPR sensors. The multiwavelength sensors are constructed on both fiber optic and bulk waveguides such as prisms. A thin metal film is deposited on the waveguide surface to support the surface plasmon (SP) mode. The evanescent field produced by light propagating through the waveguide can be coupled into the surface plasmon mode thus attenuating the transmitted light. This coupling is dependent upon phase matching between the light wavevector and the surface plasmon wavevector. The wavevectors are directly related to the wavelength of light, thickness of analyte on the sensor surface and the refractive index of the analyte. As these parameters change, the light output from the sensor will be affected. Other thin films can be subsequently deposited on the metal to functionalize the sensor surface for a particular analyte of interest. A theoretical background and details of the sensor construction is given. The developed sensors are tested in a variety of application systems. Experimental results for refractive index sensing in bulk liquid applications is shown. Observed sensitivity approaches that of conventional SPR techniques. Alkyl-thiol monolayer systems are studied to investigate kinetics of formation and the thickness resolution of the sensor. A biochemical system is investigated to compare the sensors with other immunoassay techniques. Ionic self-assembled monolayer (ISAM) systems are investigated to probe structure and determine their usefulness as an immobilization layer for biochemical species. A mathematical model based on Fresnel reflection equations is developed to predict sensor response. This model can be used to selectively vary sensor parameters to optimize the response for a specific analyte system or to calculate system parameters based on experimental results. Results from the various experiments are compared with the model. Experimental results and interpretations are discussed along with future work and potential improvements. Classical SPR sensors are also discussed along with comparisons with the multiwavelength sensors. Future improvements to SPR sensors design are considered, as is the application of the technology to high-throughput drug screening for pharmaceuticals. / Ph. D.