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.

Les procédés lithographiques sont de nos jours très utilisés au sein de l’industrie de la microélectronique pour réaliser des matériaux fonctionnels de taille nanométrique. L’obtention de composants de taille de plus en petite (<100 nm) nécessite la mise en œuvre de nouveaux procédés de fabrication. Les travaux de recherches réalisés dans cette thèse portent sur l’étude d’un nouveau concept de lithographie par microcopie à force atomique (AFM). L'objectif principal est d'utiliser la pointe d’un AFM comme outil pour promouvoir des réactions catalysées sur une zone bien définie d’une surface greffée. De cette manière, diverses molécules ont pu être greffées sélectivement et spatialement pour conduire à des objets finis en 3 dimensions. Afin de mieux comprendre le mécanisme réactionnel, différents paramètres physico-chimiques ont été étudiés dans la première partie : vitesse de balayage de la pointe, force appliquée, distance interligne lors de la gravure du motif, largeur de lignes limites, durée de vie de la pointe catalytique et influence de la flexibilité du catalyseur présent sur la pointe. La deuxième partie consiste à la réalisation de nanostructures avec des molécules aux propriétés physico-chimiques particulières (optique, électrique, catalytique) ainsi qu’à la construction de nanostructures tridimensionnelles. Quelques résultats marquants sont l’obtention d’une largeur de ligne limite de 25 nm, d’une surface de greffage minimum de 480 µm² et d’une structure de forme pyramidale composée de trois niveaux moléculaires distincts. / Lithography processes are widely used in the microelectronics industry for the realization of functional materials of nanometric size. To obtain components increasingly small (<100 nm) the development of new manufacturing processes is requires. The research presented in this thesis concerns the study of a new concept of lithography by Atomic Force Microscopy (AFM). The main objective is to use the tip of an AFM as a tool to promote catalysed reactions on a well defined zone of a grafted surface. In this way, diverse molecules could be grafted selectively and spatially to form three dimensioned objects. To better understand the reaction mechanism, different physico-chemical parameters were studied in the first part: the scanning speed of the tip, the strength applied, the interline spacing during the engraving pattern, the width lines limits, the life time of the catalytic tip and the influence of the catalyst flexibility coated to the tip. The second part consists in the realization of nanostructures with molecules that have particular physico-chemical properties (optical, electric, catalytic) and the construction of three-dimensional nanostructures. Some pertinent results are the achievement of line width of 25 nm, a minimum grafted surface of 480 µm² and the formation of a structure of pyramidal shape constituted of three different molecular levels.

<p>Recent trends in materials science have exploited noncovalent monolayer chemistries to modulate the physical properties of 2D materials, while minimally disrupting their intrinsic properties (such as conductivity and tensile strength). Highly ordered monolayers with pattern resolutions <10 nm over large scales are frequently necessary for device applications such as energy conversion or nanoscale electronics. Scanning probe microscopy is commonly employed to assess molecular ordering and orientation over nanoscopic areas of flat substrates such as highly oriented pyrolytic graphite, but routine preparation of high-quality substrates for device and other applications would require analyzing much larger areas of topographically rougher substrates such as graphene. In this work, we combine scanning electron microscopy with polarization modulated IR reflection adsorption spectroscopy to quantify the order of lying down monolayers of diynoic acids on few layer graphene and graphite substrates across areas of ~1 cm². We then utilize these highly ordered molecular films for templating assembly of di-peptide semiconductor precursors at the nanoscale, for applications in organic optoelectronic device fabrication.<br></p><p></p>

Nous cherchons à développer une sonde permettant le relargage sélectif de cations métalliques. Un tel système permettrait de capter et relarguer des cations sans contamination ni perturbation importante de l'environnement proche de l'électrode. Par la suite le dispositif pourrait être miniaturisé et utilisé in vivo. La stratégie adoptée consiste à concevoir des composés possédant un centre redox à proximité d'un ligand ayant une grande affinité vis-à-vis des cations métalliques, en particulier pour le calcium. Des groupes fonctionnels, séparés par un espaceur modulable, permettent le greffage à la surface de l'électrode. Lors de l'oxydation du centre redox initialement neutre, on peut s'attendre à ce que la constante de complexation soit diminuée de manière importante, principalement à cause de la répulsion électrostatique qui tend à éjecter le cation de la cavité. Lors de mon travail de thèse, quatre nouvelles familles de ligands possédant une phénylènediamine comme centre redox ont été synthétisées et étudiées. Parmi ces composés, les dérivés de type " demi-BAPTA " ont permis de démontrer le concept de relargage de calcium pour la première fois en milieu aqueux, à pH physiologique. Cependant, la constante d'affinité étant trop faible pour des applications in vivo, des composés basés sur le ligand BAPTA ont été préparés et s'avèrent prometteurs

La preparació de dispositius moleculars amb aplicacions específiques ha atret una gran atenció durant aquests darrers anys, ja que aquests poden oferir nous avantatges respecte la tecnologia basada en l'òxid de silici. Sovint, per la preparació dels dispositius és necessari dipositar les molècules o material sobre un suport sòlid adequat. L'ordenament i l'empaquetament de les molècules són aspectes crucials per la operació del dispositiu i, per tant, és molt important tenir un bon control de com el dissolvent, el substrat i la funcionalització molecular influeixen en les organitzacions moleculars resultants i en les interaccions intermoleculars. En aquesta Tesi s'han estudiat les organitzacions de dues famílies d'espècies electroactives, els tetratiafulvalens (TTFs) i els radicals policlorotrifenilmetílics (PTMs), que s'han utilitzat per la preparació de transistors orgànics d'efecte de camp (OFETs) i interruptors moleculars, respectivament. Els OFETs estan inclosos dintre del que es coneix com l'electrònica dels plàstics. Alguns derivats de TTFs posseeixen unes característiques electròniques i estructurals apropiades per ser utilitzats com a semiconductors orgànics per OFETs. En aquesta Tesi es descriuen els principals resultats obtinguts en la síntesi i estudi de les propietats elèctriques com a OFETs dels derivats de TTF ditiofetetratiafulvalè (DT-TTF) i el dibenzotetratiafulvalè (DB-TTF). OFETs basats en cristalls que han estat processats a partir de solució, han donat mobilitats molt altes d'1 i 3.65 cm2/Vs, pel DB-TTF i el DT-TTF, respectivament. S'han preparat pel·lícules altament ordenades del DT-TTF utilitzant la tècnica de Zone Casting, i s'han obtingut mobilitats de l'ordre del silici amorf i, per tant, amplien la possibilitat d'utilizar-los en l'electrònica de baix cost.Ja que la miniaturització dels dispositius és un dels principals objectius de l'electrònica molecular, la possibilitat de fabricar-los amb un nombre reduït de molècules és una aproximació molt atractiva. Amb aquesta finalitat, s'han preparat monocapes auto-assemblades (SAMs) basades en radicals PTM. Aquestes compostos són espècies multifuncionals ja que combinen propietats òptiques, magnètiques i electroquímiques. Les SAMs s'han preparat sobre substrats derivats del SiO2 i Au. S'ha demostrat el comportament com a interruptor molecular (químic i electroquímic) dels substrats funcionalitzats amb radicals PTM i s'ha utilitzat la resposta òptica o magnètica per llegir l'estat de l'interruptor. D'altra banda, també s'ha estudiat per microscòpia de força atòmica (AFM) i microscòpia d'efecte túnel (STM) el tipus d'organització que formen alguns derivats de TTF i PTM fisisorbits sobre substrats de diferent naturalesa (grafit, mica i SiO2). L'auto-assemblatge sobre grafit d'un derivat de radical PTM funcionalitzat amb tres cadenes alquíliques llargues ha donat lloc a la formació d'estructures tipus fibril·lars altament ordenades, formades per files magnètiques separades per les cadenes alquíliques, que actuen com a barreres diamagnètiques. En el cas dels TTFs, s'ha estudiat l'organització bi i tridimensional del tricarbometoxitetratiafulvalè (TCM-TTF). S'ha observat que les interaccions molècula-molècula, molècula-substrat i molècula-dissolvent tenen un paper molt important en l'organització resultant, formant-se des de capes fins a fibres moleculars. / The construction of molecular devices with specific applications has attracted a great deal of attention in recent years since they can offer new advantages to well-established silicon-based technologies. Often, to construct a molecular device it is necessary to deposit molecules or material on a suitable substrate. Since the ordering and packing of the molecules are crucial aspects for the operation of the device, it is important to have good control of how solvent, substrate or molecular funcionalitzation influences on the resulting molecular assemblies and the intermolecular interactions. In this Thesis we have studied the organizations of two families of electroactive molecules, tetrathiafulvalenes (TTFs) and polychlorotriphenylmethyl (PTM) radicals, which have been used as the active components of Organic Field Effect Transistors (OFETs) and molecular switches, respectively.OFETs are included in the field of Plastic Electronics. Some TTF derivatives have appropriate structural and electronic characteristics to be used as organic semiconductors in OFETs. The main results related to the synthesis and the electrical properties as OFETs of the dithiophene-tetrathiafulvalene (DT-TTF) and dibenzo-tetrathiafulvalene (DB-TTF) are described in this Thesis. OFETs based on single crystals obtained from solution of these synthesized compounds have resulted in mobilities of 1 cm2/Vs and 3.6 cm2/Vs, for DB-TTF and DT-TTF, respectively, being the later the highest mobility reported for solution-processed devices. Highly ordered films based on DT-TTF were prepared by Zone Casting exhibiting also high mobilities, of the order of 0.2 cm2/Vs. Thus, this technique offers a promising approach to obtain low-cost devices with large area coverage. Since the miniaturization of the devices is one of the main aim in the field of molecular electronics, the possibility to fabricate a device with a small group of molecules is a very attractive approach. With this purpose, self-assembled monolayers (SAMs) based on PTM radicals have been prepared. These are multifunctional species that combine optical, magnetic and electrochemical properties. SAMs of PTM radicals have been formed on silicon dioxide-based substrates and gold. It has been demonstrated that the resulting functionalized substrates can be used as molecular switches (chemical and electrochemical), using the optical and magnetic response to read the status of the switch. We have also studied by AFM and STM the self-assembly of some TTFs and PTMs derivatives physisorbed on surface. A new PTM radical bearing long alkyl chains was synthesized and its self-assembly on graphite was studied by STM at the liquid-solid interface. The self-assembly of this PTM radical gave highly-ordered structures composed by magnetic double rows, formed by the PTM cores, separated by the alkyl chains that act as insulating diamagnetic barriers and determine the spacing between the rows. On the other hand, we have studied the organization of the tetra(carbometoxy)-tetrathiafulvalene (TCM-TTF) and it was observed that depending on the combination of the two main parameters (solvent and substrate) the resulting two-dimensional assemblies can be completely different, ranging from molecular layers to long molecular fibers.

A series of novel metallic nanoparticle and suspension were developed and synthesized for ink-jet printing and spin coating applications. Organic components, such as alkanethiols and amines, were used as new capping agent design. The suspension was characterized by NMR, ESCA, TEM, SEM, EDS, TGA, DTG, DSC, TA-MS for chemical composition and three-dimension SAMs desorption.

The purpose of the work is to employ molecular simulation to further extend the understanding of Self-Assembled Monolayers (SAMs), especially as it relates to three particular applications: organic-inorganic composite membranes, surface treatments in Micro-Electro-Mechanical Systems (MEMS) and organic-surface-modified Ordered Mesoporous Materials (OMMs). The first focus area for the work is the use of SAMS in organic-inorganic composite membranes for gas separations. These composite membranes, recently proposed in the literature, are based on the chemical derivatization of porous inorganic surfaces with organic oligomers. Our simulations achieve good qualitative agreement with experiment in several respects, including the improvement in the overall selectivity of the membrane and decrease in the permeance when increasing the chain length. The best improvement in the overall solubility selectivity is reached when the chains span throughout the pore. The second application focus is on the use of SAMs as coatings in MEMS devices. The work focuses on the modeling of adhesion issues for SAM coatings at the molecular level. It is shown that as the chain length is increased from 4 to 18 carbon atoms, the adhesion forces between two monolayers at the same separations decreases. The third application focus is on the use of SAMs for tailoring surface and structural properties of OMMs, in particular, porous silicas. A molecular study of structural and surface properties of a silica material with a 5 nm pore size, modified via chemical bonding of organosilanes with a range of sizes (C4, C8 and C18) is presented. Grand canonical MC simulations are employed to obtain nitrogen adsorption isotherms for unmodified and modified MCM-41 material models. Furthermore, the density profiles of alkyl chains and nitrogen molecules are analyzed to clarify the differences in the adsorption mechanisms in unmodified and modified materials. The position of the capillary condensation steps gradually shifted to lower pressure values with the increase in size of the bonded ligands, and this shift was accompanied by a gradual disappearance of the hysteresis loop. As the length of the bonded ligands is increased, a systematic decrease in the pore diameter is observed and the multi-layer adsorption mechanism in modified model materials diminishes.

Molecular self-assembly has recently attracted significant attention for possible application in organic electronic and optoelectronic devices, such as self-assembled monolayer field-effect transistors (SAMFETs) and functional self-assembled integrated circuits. Self-assembly combines the advantages of low temperature solution processability, regio-selective monolayer adsorption and nano-scale control of film thickness. Much progress has been made in improving device performance using self-assembled monolayers (SAMs). However, most SAMFET devices reported to date showed current modulation only with submicrometre channels, with low device yields and poor reproducibility as a result of limited lateral interconnection of the semiconducting layer.In an attempt to address these issues, this thesis presents an investigation of the synthesis and properties of conjugated SAM molecules for use as the charge transporting layer in SAMFETs. Chapter 1 gives a comprehensive introduction to SAM-based surface systems, organic semiconductors and their use in OFETs and SAMFETs. Chapter 2 discusses attempts to design and synthesise p-type conjugated molecules capable of self-assembly on oxide surfaces based on a phenylene-bithiophene semiconducting core. The optical and electrochemical properties, as well as the thermal behaviour of these molecules are studied in detail. This theme is carried over to Chapter 3, which describes the synthesis, chemical and physical characterisation of two families of n-type SAM molecules. These molecules consist of NTCDI cores with hexyl or cyclohexyl chains as end-capping groups. Incorporation of a selection of materials as the active layer in OFETs or SAMFETs to evaluate the charge transport is demonstrated in Chapter 4. Monolayer films based on p-type monochlorosilane-terminated SAM molecules are made using the solution assembly technique and characterised by contact angle and AFM. OFETs made from DH-PTTP by both thermal evaporation and spin coating show high mobilities comparable to the best values reported in the literature. Top-contact SAMFETs show a hole mobility of 1.1 × 10-3 cm2V-1s-1 in air, consistent with those of solution processed DH-PTTP based OFETs. Finally, an overview of the project and some suggestions for future work are presented in Chapter 5.

Las nanopartículas (NPs) de metales nobles presentan gran interés tanto por sus propiedades básicas como por la amplia variedad de aplicaciones en las que se utilizan activamente. Para obtener NPs estables y evitar su aglomeración, es necesario utilizaragentes estabilizantes durante la síntesis. Estas moléculas se adsorben sobre la superficie de las NPs y evitan que estas interaccionen directamente con las partículas vecinas. Si bien existen diversas moléculas que pueden ser utilizadas para este fin, uno de los únicos tipos de NPs metálicas cuya distribución de tamaños es estrecha, son estables a lo largo del tiempo y pueden ser obtenidas en forma de polvo, lavadas, y utilizadas como si se tratase de un compuesto químico tradicional, son las NPs cubiertas por tioles. La gran estabilidad de estas partículas está dada por la alta energía del enlace que se forma entre el azufre del grupo tiol y el metal. Resulta, entonces, particularmente interesante estudiar la interfase entre la superficie metálica y las moléculas adsorbidas. En este trabajo se presenta un estudio de la interfase Au-tiol y Pd-tiol en diferentes sistemas que van desde monocapas autoensambladas (SAMs) de tioles sobre superficies planas hasta compuestos poliméricos de tiolatos metálicos, con especial énfasis en las NPs metálicas cubiertas por tioles. El estudio de estos sistemas fue realizado mediante la utilización de diversas técnicas. En todos los experimentos se controlaron las condiciones de medida de manera tal de minimizar los daños producidos sobre las muestras. En los casos en que esto no fue posible, se intentó elucidar qué tipo de daño se estaba produciendo para realizar el análisis de los resultados teniendo en cuenta estos efectos o bien descartar los datos que hayan sido afectados por los mismos.

Problems concerning the planning and practicing of health care currently exist. Countries are spending more funds on medical care without making a discernible dent in the health status of their citizens. This lack of success in obtaining health is obviously a problem for everyone experiencing ill health or the effects thereof It also creates a personal problem for all health workers, because a halt is being called to profligate spending on health that will affect all. The problems underlying tl:e health care crisis are rising costs, unequal distribution, low productivity, poor heali..ii status, and a lack in sensitivity towards the communities it serves. The multi-disciplinary, complex nature of these problems in health care, their magnitude and their inter-relatedness indicate that traditional approaches to health care planning and management have been inadequate or have failed. An alternative approach to solve these problems is to adopt a holistic view, i.e., to see all parts (components) which contribute to the problem as parts of the whole. By viewing the problem as a whole, more enduring solutions may be formulated. The aim of this study was to employ and evaluate the adoption of a systems approach to solve "real life" problems. The Soft Systems Methodology of Peter Checkland was utilized to assess the situation within the Oral Health Service of the SAMS and to identify relevant systems to improve the situation. The need for a Preventive System and a Performance Measurement System was established. These two systems were planned, developed and implemented using and obeying systems rules and techniques. Both these systems were evaluated and found to be highly efficient, effective, cost-effective and made a positive net contribution to the Oral Health Service of the SAMS. It is finally concluded that the adoption of a systems approach to identify and solve "real life" problems was effective and efficient. It is therefore recommended that a systems approach to the management of oral health, and probably health too, should be embraced by the encumbered health industry. / Dissertation (MChD)--University of Pretoria, 1993. / gm2013 / Community Dentistry / unrestricted