Les interactions entre les interfaces liquide/liquide et liquide/solide interviennent dans de nombreux domaines et procédés industriels. Cependant, ces interactions ont été très peu étudiées par le passé. Nous nous concentrons ici sur le drainage spontané de solutions aqueuses de sel ou de tensio-actifs pressées entre une goutte d'huile et une surface en verre. Expérimentalement, une goutte d'huile est immergée dans de l'eau et approchée d'une surface solide ; le film d'eau pressé résultant draine et adopte une forme “dimple” due au gradient de pression. Par la suite, le film d'eau relaxe vers son épaisseur uniforme d'équilibre.Les profils d'épaisseur spatio-temporels du film sont mesurés par microscopie d'interférences en réflexion. Nous avons étudié la dynamique de drainage ainsi que l'état d'équilibre du système en présence de sel et/ou de tensio-actifs. Tout d'abord, nous réalisons une description quantitative de l'ensemble de la dynamique de drainage. Trois régimes sont identifiés pour une solution aqueuse d'électrolyte : un régime dominé par la pression capillaire, un second mixte décrit par les pressions capillaire et de disjonction, et un troisième dominé par la pression de disjonction. Ces régimes sont modélisés dans le cadre de l'approximation de lubrification. En particulier, le rôle de la pression de disjonction est étudié avec précision dans la limite de la portée des interactions électrostatiques. Nous déduisons des lois analytiques simples permettant de décrire la dynamique de drainage, découplant ainsi les effets des pressions des effets géométriques. Par ailleurs, nous montrons que l'ajout de tensio-actifs ne modifie pas qualitativement les régimes de drainage, à l'exception de concentrations supérieures à la concentration micellaire critique. En effet, à de très faibles épaisseurs, l'huile mouille alors partiellement le solide, ralentissant ainsi le drainage de l'eau piégée au centre du dimple.Nous mesurons la condition aux limites à l'interface eau/huile. Nous confirmons ainsi l'effet Marangoni, mentionné dans la littérature, résultant du gradient de concentration d'espèces (impuretés ou tensio-actifs) adsorbés à l'interface. Nous montrons que l'interface eau/huile est en général de type solide et donc que la vitesse tangentielle est nulle à l'interface. Cependant, pour des concentrations faibles en espèces adsorbées, nous mettons en évidence pour la première fois un contre-courant à l'interface eau/huile résultant de l'approche de la goutte et d'une cinétique lente d'adsorption des tensio-actifs.Par la suite, nous nous concentrons sur l'état d'équilibre du système, soit par mouillage de l'huile sur le solide, soit par formation d'un film d'eau homogène stable. Dans le cas d'un film d'eau stable, l'équilibre résulte d'une égalité entre la surpression dans la goutte et la pression de disjonction du film. En variant le rayon de la goutte, nous montrons qu'il est possible de mesurer l'évolution de la pression de disjonction avec l'épaisseur du film. Cette évolution peut être entièrement décrite par les interactions entre les interfacées chargées. Pour de grandes surpressions de goutte, ou de petites longueurs de Debye, l'huile mouille le solide. Nous montrons que la dynamique de mouillage dépend fortement de la concentration en tensio-actif lorsqu'elle est inférieure à la concentration micellaire critique. La vitesse de la triple ligne de contact peut varier de quatre décades. Nous attribuons ces comportements à l'adsorption du tensio-actif aux interfaces eau/huile et eau/verre, et en particulier à la possible formation de monocouches ou bicouches sur le solide. / The interactions between liquid/liquid and solid/liquid interfaces are involved in many industrial processes and fields. However, they have been poorly studied in the past. We focus here on the spontaneous drainage of aqueous solutions of salt or surfactants squeezed between an oil drop and a glass surface. Experimentally, an oil drop immersed in water is driven towards a solid surface; the resulting squeezed water film drains and adopts a dimple shape due to the pressure gradient, and further relaxes to its equilibrium uniform thickness. The thickness profile of the film is measured in space and time by reflection interference microscopy. We have studied both the drainage dynamics and the final equilibrium state reached by the system in presence of salt and/or surfactants. First, we quantify and provide a full description of the drainage dynamics. Three regimes are identified in an aqueous electrolyte: a capillary dominated regime, a mixed capillary and disjoining pressure regime, and a disjoining pressure dominated regime. These regimes are modeled within the lubrication approximation, and the role of the disjoining pressure is precisely investigated in the limit of thicknesses smaller than the range of electrostatic interactions. We derive simple analytical laws describing the drainage dynamics, thus providing tools to uncouple the effect of the film geometry from the effects of the disjoining or capillary pressures. We show that the addition of surfactants does not qualitatively modify the drainage regimes, except at concentrations larger than the critical micellar concentration and very small film thicknesses in which the oil can partially wet the solid, thus slowing down the drainage of the remaining trapped water. In addition, we provide measurements of the boundary condition at the oil/water interface. We confirm the role of Marangoni flows, suggested in the literature and resulting from concentration gradients of species (impurities or surfactants) adsorbed at the interface. We thus show that a solid-like, no-slip boundary condition is generally met at the oil/water interface. However, for low concentrations in adsorbed species, we evidence for the first time a reverse flow at the interface resulting from the approach of the drop and the slow adsorption kinetics of surfactants. In a second part, we focus on the equilibrium state reached by the water film, i.e. either wetting of the solid surface by the oil drop or formation of a stable water film between the drop and the solid. In the latter case, equilibrium results from the balance of the capillary pressure in the drop and the disjoining pressure. By varying the droplet radius, we show it is possible to measure the variations of the disjoining pressure with the film thickness, and that they can be fully described by taking into account the interactions between the charged interfaces. For large capillary pressures or short Debye lengths, the oil wets the solid surface and we show the wetting dynamics is strongly modified depending on surfactant concentration below the cmc: the velocity of the oil/water/solid triple line varied over four decades. We ascribe the observed behaviors to surfactant adsorption at the oil/water and solid/water interfaces, and in particular to the possible formation of surfactant mono or bi-layers on the solid.

L'oxydation spontanée de la dopamine en solution légèrement basique a été étudiée sur la base de la publication de Lee [Science, 318:426-430, 2007], et le produit de la réaction a été identifié comme de la mélanine. La capacité de la mélanine de lier des groupements amines de façon covalente a été confirmée par la quantification des sites de liaison correspondants. En outre il est possible de rédisperser des agrégats de mélanine dans des solutions fortement basiques. Les grains de mélanine ainsi obtenus ont été utilisés pour construire des films multicouches avec le poly(diallyldimethyl ammonium) (PDADMA). Différentes méthodes d'oxydation de la dopamine pour former des films de mélanine à l'interface solide-liquide ont été développées. Toutes les méthodes mènent à la formation de films continus de mélanine ayant des morphologies de surface similaires. Elles deviennent imperméables à des sondes électrochimiques à partir d'une épaisseur de l'ordre de 10 nm. Une plus grande perméabilité à des sondes chargées positivement ou neutres qu'à des sondes négatives a été confirmée. L'adsorption de protéines à des revêtements de mélanine a été expliquée par une combinaison d'interactions électrostatiques et covalentes. Pour arriver à cette explication le potentiel zêta de dépôts de mélanine a été mesuré en fonction du pH. La formation de la mélanine dans des films multicouches de poly(L-lysine) (PLL) et de hyaluronate (HA) a été étudiée: la mélanine est capable de remplir des films (PLL-HA)n de manière homogène, et les composés ainsi obtenus peuvent être détachés de leurs substrats comme membranes autosupportées préparées par une méthode biomimétique sous conditions douces.

<p>The principles of dye-sensitized solar cells were studied and are outlined in this thesis. An overview of the basic steps needed to create a DSC isfollowed by detailed experimental information on how to assemble the solar cells that were fabricated in this project. They were based on synthesizednanocrystalline ZnO thin films sensitized by chlorophyll a as well as isolated photopigments from spinach leaves. The nanocrystals werestudied using XRD, and it was confirmed that three different methods of synthesis resulted in ZnO crystals of a few nanometers. The solar cellswere assembled with Au electrodes in a sandwich configuration and their photovoltaic properties were measured. Overall light-to-electricity conversionwas low with the highest efficiency being 0.21 %. An astonishingly low efficiency of 0.0003 % was noted for a thin film which was not thermallytreated, and it is suggested that heat-treatment is of great importance. It was also found that photopigments from spinach can be extractedeasily and used as molecular sensitizer without any demanding purification steps.</p>

<p>The development and implementation of a metal gate technology (alloy, compound, or silicide) into metal-oxide-semiconductor field effect transistors (MOSFETs) is necessary to extend the life of planar CMOS devices and enable further downscaling. This thesis examines possible metal gate materials for improving the performance of the gate stack and discusses process integration as well as improved electrical and physical measurement methodologies, tested on capacitor structures and transistors. </p><p>By using reactive PVD and gradually increasing the N₂/Ar flow ratio, it was found that the work function (on SiO₂) of the TiN_x and ZrN_x metal systems could be modulated ~0.7 eV from low near nMOS work functions to high pMOS work functions. After high-temperature anneals corresponding to junction activation, both metals systems reached mid-gap work function values. The mechanisms behind the work function changes are explained with XPS data and discussed in terms of metal gradients and Fermi level pinning due to extrinsic interface states.</p><p>A modified scheme for improved Fowler-Nordheim tunnelling is also shown, using degenerately doped silicon substrates. In that case, the work functions of ALD/PVD TaN were accurately determined on both SiO₂ and HfO₂ and benchmarked against IPE (Internal Photoemission) results. KFM (Kelvin Force Microscopy) was also used to physically measure the work functions of PVD TiN and Mo deposited on SiO₂; the results agreed well with <i>C-V</i> and <i>I-V</i> data.</p><p>Finally, an appealing combination of novel materials is demonstrated with ALD TiN/Al₂O₃/HfAlO_x/Al₂O₃/strained-SiGe surface channel pMOS devices. The drive current and transconductance were measured to be 30% higher than the Si reference, clearly demonstrating increased mobility and the absence of polydepletion. Finally, using similarly processed transistors with Al₂O₃ dielectric instead, low-temperature water vapour annealing was shown to improve the device characteristics by reducing the negative charge within the ALD Al₂O₃.</p>

The objective of this thesis is to provide an initial demonstration of the feasibility of constructing highly transparent active electronic devices. Such a demonstration is successfully achieved in the fabrication of ZnO-based thin film transistors (TFTs) exhibiting transparency greater than ~90% in the visible portion of the electromagnetic spectrum and prototypical n-channel, enhancement mode TFT characteristics. Electrical characterization studies of these ZnO-based transparent TFTs and of CuYO��� / ZnO / ITO p-i-n heterojunction diodes serve to elucidate the mechanisms responsible for the behavior of these devices in particular, and of transparent electronic devices in general. Energy band analysis of the degenerate semiconductor / insulator heterojunction yields insight into the phenomenon of charge injection into an insulator, with important implications for the analysis of devices containing heterojunctions of this nature. Finally, a novel technique for simultaneously characterizing carrier injection into an insulator and interface channel formation, the capacitance-(voltage, frequency) [C-(V,f)] technique, is proposed and employed in the characterization of ZnO-based TFT structures. / Graduation date: 2003

The development and application of a combinatorial sputtering thin film technique to screen potential scintillation material systems was investigated. The technique was first benchmarked by exploring the binary lutetium oxide-silicon oxide material system, which successfully identified the luminescence phases of the system, Lu2SiO5 (LSO) and Lu2Si2O7 (LPS). The second application was to optimize the activator concentration in cerium doped LSO. The successfully optimized cerium concentration in the thin film LSO of 0.34 atomic percent was much greater than the standard cerium concentration in single crystal LSO. This lead to an intensive study based on temperature dependent steady-state and lifetime photoluminescence spectroscopy to understand the different concentration quenching mechanisms involved in the bulk single crystal versus the thin film LSO. The results were used to develop configuration coordinate models which were employed to explain the observed concentration dependent behavior. The nature of single crystal LSO:Ce concentration quenching was determined to be due to radiative energy transfer, and ultimately self-absorption. For the thin films it was found self-absorption was not a dominant factor due to the thin dimension of the film and also its nano-crystalline nature. Instead, the photoluminescence excitation and emission spectra as a function of concentration demonstrated the concentration quenching behavior was due to an increase in defect-mediated non-radiative transitions with increasing cerium. The final application of the thin film screening technique was the exploration of the ternary Lu2O3-SiO2-Al2O3 material system doped with cerium. It was found that the presence of aluminum and silicon hindered LSO and Al5Lu3O12 (LuAG) emission, respectively. However, the presence of aluminum was found to increase LPS emission intensity. The percent of aluminum in the LPS phase was estimated at 2.5 atomic percent.

Ink-jet printing offers an ideal answer to the emerging trends and demands of depositing at ambient temperatures picoliter droplets of oxide solutions into functional thin films and device components with a high degree of pixel precision. It is a direct single-step mask-free patterning technique that enables multi-layer and 3D patterning. This method is fast, simple, easily scalable, precise, inexpensive and cost effective compared to any of other methods available for the realization of the promise of flexible, and/or stretchable electronics of the future on virtually any type of substrate. Because low temperatures are used and no aggressive chemicals are required for ink preparation, ink-jet technique is compatible with a very broad range of functional materials like polymers, proteins and even live cells, which can be used to fabricate inorganic/organic/bio hybrids, bio-sensors and lab-on-chip architectures. After a discussion of the essentials of ink-jet technology, this thesis focuses particularly on the art of designing long term stable inks for fabricating thin films and devices especially oxide functional components for electronics, solar energy conversion, opto-electronics and spintronics. We have investigated three classes of inks: nanoparticle suspension based, surface modified nanoparticles based, and direct precursor solution based. Examples of the films produced using these inks and their functional properties are: 1) In order to obtain magnetite nanoparticles with high magnetic moment and narrow size distribution in suspensions for medical diagnostics, we have developed a rapid mixing technique and produced nanoparticles with moments close to theoretical values (APL 2011 and Nanotechnology 2012). The suspensions produced have been tailored to be stable over a long period of time. 2)In order to design photonic band gaps, suspensions of spherical SiO2 particles were produced by chemical hydrolysis (JAP 2010 and JNP 2011 - not discussed in the thesis). 3) Using suspension inks, (ZnO)1-x(TiO2)x composite films have been printed and used to fabricate dye sensitized solar cells (JMR 2012). The thickness and the composition of the films can be easily tailored in the inkjet printing process. Consequently, the solar cell performance is optimized. We find that adding Ag nanoparticles improves the ‘metal-bridge’ between the TiO2 grains while maintaining the desired porous structure in the films. The photoluminescence spectra show that adding Ag reduces the emission intensity by a factor of two. This indicates that Ag atoms act as traps to capture electrons and inhibit recombination of electron-hole pairs, which is desirable for photo-voltaic applications. 4) To obtain and study room temperature contamination free ferromagnetic spintronic materials, defect induced and Fe doped MgO and ZnO were synthesized ‘in-situ’ by precursor solution technique (preprints). It is found that the origin of magnetism in these materials (APL 2012 and MRS 2012) is intrinsic and probably due to charge transfer hole doping. 5) ITO thin films were fabricated via inkjet printing directly from liquid precursors. The films are highly transparent (transparency &gt;90% both in the visible and IR range, which is rather unique as compared to any other film growth technique) and conductive (resistivity can be ~0.03 Ω•cm). The films have nano-porous structure, which is an added bonus from ink jetting that makes such films applicable for a broad range of applications. One example is in implantable biomedical components and lab-on-chip architectures where high transparency of the well conductive ITO electrodes makes them easily compatible with the use of quantum dots and fluorescent dyes. In summary, the inkjet patterning technique is incredibly versatile and applicable for a multitude of metal and oxide deposition and patterning. Especially in the case of using acetate solutions as inks (a method demonstrated for the first time by our group), the oxide films can be prepared ‘in-situ’ by direct patterning on the substrate without any prior synthesis stages, and the fabricated films are stoichiometric, uniform and smooth. This technique will most certainly continue to be a versatile tool in industrial manufacturing processes for material deposition in the future, as well as a unique fabrication tool for tailorable functional components and devices. / <p>QC 20120907</p>

The development and implementation of a metal gate technology (alloy, compound, or silicide) into metal-oxide-semiconductor field effect transistors (MOSFETs) is necessary to extend the life of planar CMOS devices and enable further downscaling. This thesis examines possible metal gate materials for improving the performance of the gate stack and discusses process integration as well as improved electrical and physical measurement methodologies, tested on capacitor structures and transistors. By using reactive PVD and gradually increasing the N2/Ar flow ratio, it was found that the work function (on SiO2) of the TiNx and ZrNx metal systems could be modulated ~0.7 eV from low near nMOS work functions to high pMOS work functions. After high-temperature anneals corresponding to junction activation, both metals systems reached mid-gap work function values. The mechanisms behind the work function changes are explained with XPS data and discussed in terms of metal gradients and Fermi level pinning due to extrinsic interface states. A modified scheme for improved Fowler-Nordheim tunnelling is also shown, using degenerately doped silicon substrates. In that case, the work functions of ALD/PVD TaN were accurately determined on both SiO2 and HfO2 and benchmarked against IPE (Internal Photoemission) results. KFM (Kelvin Force Microscopy) was also used to physically measure the work functions of PVD TiN and Mo deposited on SiO2; the results agreed well with C-V and I-V data. Finally, an appealing combination of novel materials is demonstrated with ALD TiN/Al2O3/HfAlOx/Al2O3/strained-SiGe surface channel pMOS devices. The drive current and transconductance were measured to be 30% higher than the Si reference, clearly demonstrating increased mobility and the absence of polydepletion. Finally, using similarly processed transistors with Al2O3 dielectric instead, low-temperature water vapour annealing was shown to improve the device characteristics by reducing the negative charge within the ALD Al2O3.

Thin-film solar cells based around the absorber material CuIn1-xGaxSe2 (CIGS) are studied with respect to their stability characteristics, and different ways of modelling device operation are investigated. Two ways of modelling spatial inhomogeneities are detailed, one fully numerical and one hybrid model. In the numerical model, thin-film solar cells with randomized parameter variations are simulated showing how the voltage decreases with increasing material inhomogeneities. With the hybrid model, an analytical model for the p-n junction action is used as a boundary condition to a numerical model of the steady state electrical conduction in the front contact layers. This also allows for input of inhomogeneous material parameters, but on a macroscopic scale. The simpler approach, compared to the numerical model, enables simulations of complete cells. Effects of material inhomogeneities, shunt defects and grid geometry are simulated. The stability of CIGS solar cells with varying absorber thickness, varying buffer layer material and CIGS from two different deposition systems are subjected to damp heat treatment. During this accelerated ageing test the cells are monitored using characterization methods including J-V, QE, C-V and J(V)T. The degradation studies show that the typical VOC decrease experienced by CIGS cells subjected to damp heat is most likely an effect in the bulk of the absorber material. When cells encapsulated with EVA are subjected to the same damp heat treatment, the effect on the voltage is considerably reduced. In this situation the EVA is saturated with moisture, representing a worst case scenario for a module in operation. Consequently, real-life modules will not suffer extensively from the VOC degradation effect, common in unprotected CIGS devices.

Reliability, besides the performance, is one of the important key factors of success of any technology. While a product should perform at best as desired, it must also be capable of working for intended period of life without any degradation or wear-out failure, caused by any operational parameter. For example it does no good to manufacture a super fast microprocessor if that fails within few seconds. For the product to meet the intended reliability we must understand the mechanisms that lead to unreliability or failure of the devices. The efforts to understand the fundamental physics of the mechanisms that lead to the failure of the devices has developed a branch of physics named as “reliability physics” of “physics of failure”. On the basis of the understanding of failure mechanism, new design rule can be followed and new material can be applied to improve the reliability of the product. Microelectronic technology also, which is one of the fastest growing technology, has been facing challenges posed by the reliability issues from time to time. There are number of physical failure mechanisms that can affect the reliability of a microelectronic device. Time dependent dielectric breakdown (TDDB), hot carrier damage and current induced damage of interconnects are only to name a few common mechanisms. Among these, the failure of interconnects due to current has been the oldest and persistence reliability issue since the beginning of development of the microelectronic technology. Understanding the physics of the processes that lead to failure of a current carrying film is the main interest of this thesis work. In this investigation, we have carried out a systematic study to understand stability of metal nanowires against damage caused by current stressing and its size dependency. We observe the wires of smaller diameter, having an electronic mean free path larger than or comparable to its diameter are more stable against current stressing. In wires of larger diameter (100 nm or more) the probability of the damage is more. This probably is due to presence of grain boundary type extended defects that allow low energy diffusion path. To our knowledge this is the first experimental investigation to study the stability of nanowires against high current and in-situ measurement of noise during current stressing on them. In the previous investigations by other groups observed that the nanowires without any passivation got damaged by stressing current density which was even lower than the one we used for stressing. To our knowledge this is the first observation of long lasting stability of nanowires, of dimension down to 15 nm, when they are encapsulated in dielectric, an environment that an interconnect has to see in the real integrated circuit devices. In the second chapter we will describe the sample preparation method, characterization of samples and the experimental setups we had used. The results of in-situ noise measurement are described in the third chapter. We will describe our in-situ scanning thermal microscopy study in the fourth chapter. Then in the fifth chapter, we will present our simulation investigations on current induced damage of film. Finally, we will put the concluding remarks on this thesis work and the results in the sixth chapter. We have studied similar damage processes in metal nanowires also. In an appendix we will present our approach and major results of this investigation.