Porous antimony-doped tin oxide (ATO) cathodes formed by supercritical CO2 (SCCO2) treatment for silver electro-deposition devices were proposed. The porous ATO cathode with a thickness of 1.4£gm was formed by coating the nano-particle ATO solution on ITO glass. The porous structure of the cathodes was obtained by applying SCCO2 treatment at 60oC on the spin-coated ATO thin films. A layer of electrolyte(formed by AgI, NaI and DMSO)was enclosed by two electrodes to to form a so-called¡§sandwich¡¨ structure. After the fabrication process, white paint was spray on the back side of the glass substrate. Due to the thickness of the ATO cathode, the cathode is observed to be transparent during the oxidation process. The Black state of the device was observed during the reduction of silver molecules which were anchored onto the surface of the 1.4£gm thick ATO cathode. The average transmission contrast ratio of 4.4 was obtained in visible spectrum at a driving voltage of 1V and a saturation current density of 3.1 mA/cm2. In addition to that, 0.5 cm by 0.5 cm device with 65£gm cell gap and 0.08 M electrolyte concentration, an electrochromic switching time of 3.7 seconds was achieved .

Le moussage du polypropylène (PP) et du polystyrène (PS) par le scCO2 est étudié de manière systématique avec l’accent sur la relation entre le procédé, la microstructure et les propriétés mécaniques. La première partie de cette thèse porte sur l’amélioration de la résistance au choc du PP par cristallisation induite par le scCO2. Dans un deuxième temps, le PP fortement orienté avec des structures shish-kebab et sphérolite est utilisé pour étudier l’influence de la structure cristalline sur la nucléation et la croissance des cellules pendant le procédé de moussage sous le scCO2. Ensuite, les influences des conditions de moussage ainsi que celles des paramètres structuraux de la mousse de PS ont été étudiées. Les mousses de PS à cellules isotropes ont été comparées avec celles de PS à cellules orientées. Enfin, un procédé de moussage discontinu en deux étapes est développé afin de produire des mousses de PS à cellules bi-modales en utilisant le scCO2 en tant qu’agent de moussage. Cette structure unique de petites et grandes cellules réparties de manière homogène au travers de l’ensemble du volume de la mousse confère à cette dernière des propriétés particulières. / In this work, scCO2 induced foaming of PP or PS is systematically studied with emphasis on the relationship between process, microstructure and mechanical properties. The first part of the thesis deals with the toughening of iPP by scCO2 induced crystallization for the fine separation of rigid crystalline domains and soft amorphous ones in the polymer matrix. The highly oriented iPP with “shish-kebab” and “spherulite” are then used for CO2 foaming to investigate the effect of crystalline structure on the formation of cell nucleation and growth. In addition, the effect of the foaming conditions and the cell structural parameters of PS foams on the mechanical properties are studied systematically. PS foams with isotropic cell morphology and oriented cell one are prepared. Finally, a two-step depressurization batch process is developed to produce bi-modal cell structure PS foams by using scCO2 as the blowing agent. This unique cell structure with both small and large cells homogenously distributed throughout the entire volume of the foam sample might have particular properties.

In this study, The bottom electrode¡]TiN¡^, middle insulator ¡]Sn¡GSiO2¡^, and top electrode ¡]Pt¡^ were deposited respectively by sputtering technique for fabricating the resistive random access memory with metal-insulator-metal structure. Experimental results were indicated that Sn-dopped SiO2 RRAM could be operated over 105 times and retention time was kept stable at thermal stress up to 85 ¢J over 104 s. In the previous researches, we had known that the supercritical carbon dioxide¡]SCCO2¡^ fluids could efficiently to passivate the traps in the devices. The leakage current of dielectric film would be reduced significantly after SCCO2 fluids treatment. To improve the dielectric properties of Sn-dopped SiO2 films, the SCCO2 fluids technology was introduced in this study. After SCCO2 fluids treatment, the leakage current of devices was reduced significantly, because the HRS conduction mechanism was transformed from Poole-Frenkel conduction to Schottky emission and the LRS conduction mechanism was transformed from Ohmic conduction to Hopping conduction. Addtionally, RTA treatment was introduced to improve the Sn-dopped SiO2 films. It could also reduce leakage current of devices after RTA treatment. At last, we used constant current forming to find the process of electrons hopping conduction.

Non-volatile memory can keep the data without supplying power, and it is suitable for portable electronic products due to the advantage of low power consumption. In current industrial production, high-temperature and long-time process are necessary for the fabrication of non-volatile memory, which are heavy loadings on production capacity and lots cost. Therefore, decreasing the temperature of the process is a trend. Recently using the oxidation treatment of supercritical carbon dioxide fluid can efficiently decrease the temperature of the process. In this thesis, the mixture layer of Zn, Sn, and SiO2 is applied to reduce the temperature of process, and to employ the defects of ZnO and SnO2 as floating gate for electron storage to fabricate the nonvolatile memory device. Zn and Sn are applied due to the low temperature melting points. To ensure the layer of cosputtering with Zn and Sn to be able to successfully fabricate as nano material device, the process of traditional rapid temperature annealing treatment was applied for first step. The co-sputtered Zn-Sn-SiO2 thin film was deposited on the tunneling oxide layer, and then the thin film was treated with varied annealing temperature to precipitate ZnO and SnO2 nanocrystals. After that, the C-V measurement is applied to analyze the change of the electrical and material properties. Using a positive bias, the electrons are injected into the oxide layer, by the threshold voltage the offset is occurred, which is defined as the memory window of the memory effect, and the property of nonvolatile memory will be applied. In addition, no matter the charge is injected from the gate oxide or tunnel oxide, the defects position of DLTS¡¦s peak is with the same property. The supercritical carbon dioxide fluid technology has been performed to study the memory effect. The capability of electron injection, storages and the defect, in the storage layer were studied by the C-V measurement and DLTS. The experiment confirmed that the Zn-Sn alloy has the memory property after it been treated by the supercritical carbon dioxide fluid technology. It has shown that Zn can promote to the storage capability ability due to the formation of deep level defects of SnO2 from the DLTS spectra. A new species is found at 0.93 eV with low activation energy and high capability of electron storage. The defect formation mechanism of Zn, ZnO, Zn-O-Si, Sn, and SnO are analyzed by found by the XPS and DLTS. The device fabrication using Zn-Si alloy and supercritical carbon dioxide fluid technology has the potential to reduce the process temperature and to improve the memory property of nonvolatile memory device.

The resistance random access memory (RRAM) is one of the most popular of the next generation memories with the high operating speed, reliability and the smallest miniature size. RRAM has metal-insulator-metal structure that can greatly reduce the difficulty of entry, but the biggest problem is how to choose the insulator. We selected silicon-based materials to match the intergrated circuits manufacturing process. In this work, sputtering titanium doping in the silicon oxide thin film has a stable characteristic of resistance switching. By material analyzing, we found that supercritical carbon dioxide fluid (SCCO2) treatment can passivate the silicon oxide defect and the self-reduction of titanium oxide, but it also brought OH group into our thin film. So we observed the interface type characteristic of resistance switching. Using constant voltage sampling experiment extract the reaction rate constant (k) and the active energy, prove that the reaction is caused by OH injection. Double-layer structure with titanium-doped and carbon-doped silicon oxide RRAM promote lower operating current by hopping conduction, which is caused by graphite oxide doping. The Space-Charge Limited Current mechanism for high limited current is proven by COMSOL electric field simulation.

No description available.

Introduction Un fluide supercritique (SCF) est une substance dont la température et la pression sont à la fois au-dessus de leurs valeurs essentielles qui sont définies comme le point critique. Le point critique (Pc) désigne le point où les phases gaz, liquide et phase supercritique coexistent et il peut être observé expérimentalement par une opacité critique. Les propriétés des SCFs sont différentes de celles des liquides et des gaz ordinaires. Près de la densité critique, les SCFs affichent des propriétés qui sont dans une certaine mesure intermédiaire entre celles d'un liquide et un gaz. Parmi les fluides supercritiques, le scCO2 a certainement un excellent potentiel de développement pratique en raison de ses faibles conditions critiques (Tc = 31 °C, Pc = 74 bars), et en raison de la nature non-polaire et faible des forces de van der Waals impliquant le CO2. Les espèces hydrophiles (tels que des acides aminés, des protéines et de nombreux catalyseurs) sont souvent insolubles dans le scCO2. De toute évidence, il existe une limitation de l'application de dioxyde de carbone supercritique. Récemment, dans le but de remédier à cet inconvénient, une approche plus efficace consiste à utiliser des tensioactifs appropriés pour produire des micro-émulsions eau/CO2 ou micelles inverses. Consan et Smith ont testé la solubilité de plus de 130 agents tensioactifs disponibles dans le commerce dans le scCO2 à 50 °C et de 10 à 50 MPa. Tous sont très peu solubles ou seulement légèrement solubles dans le scCO2, de sorte qu'ils ne pouvaient pas être utilisés comme surfactants pour ce milieu. Toutefois, certains matériaux non polaires de bas poids moléculaire peuvent se dissoudre dans le scCO2, et sont utilisés avec succès pour divers procédés industriels tels que l'extraction par fluide supercritique, la chromatographie en fluide supercritique et en tant que milieu réactionnel. / Supercritical fluid is a substance whose temperature and pressure are both above their critical values which are defined as the critical point. Similarly to the triple point which defines the zero-variance point for the solid, gas and liquid states, the critical point (Pc) denotes the point where the gas, liquid and supercritical phases coexist and it can be experimentally observed through a critical opacity. Properties of SCFs are different from those of ordinary liquids and gases. Close to the critical density, SCFs display properties that are to some extent intermediate between those of a liquid and a gas. For example, a SCF may be relatively dense and dissolve certain solids while being miscible with permanent gases and exhibiting high diffusivity and low viscosity. In addition, SCFs are highly compressible and the density (and therefore solvent properties) can be "tuned" over a wide range by varying pressures and temperatures. Among supercritical fluids, scCO2 certainly has excellent potential for practical development not only because of its low critical conditions (Tc = 31 °C, Pc = 74 bar), but also due to some other factors such as: CO2 is non-toxic. Its threshold air concentration for working conditions is as high as 5000 ppm. By means of comparison, a daily exposition to 10 ppm of chloroform is considered hazardous. CO2 is non-flammable. This constitutes another very competitive advantage compared to halogenated solvents. Its high pressure vapour-superior to 60 bar-allows its complete removal from processed materials. Thus, CO2 is one of the two solvents fully approved by the Food and Drug Administration (FDA), along with water. CO2 has a low reactivity and is inert towards oxidation. It is also a non-transferring species for radicals. Heat and mass transfer are significantly enhanced in scCO2 due to its properties of low viscosity and densities. Its low surface tension allows wetting structured materials better than liquids usually do. However, besides the cost of high-pressure vessels, CO2 still has intrinsic physical disadvantages: A low cohesive energy density which confers a weak solvent strength to CO2. CO2 is a Lewis acid through its electron-deficient carbon. It thus reacts reversibly with strong Lewis bases such as primary and secondary amines. But this can be turned into an advantageous property for the capture of CO2 by amine-based solvents and surfactants, polymers and solvents that possess CO2-responsive moieties such as guanidines and amidines. CO2 is a poison for Ziegler-Natta and palladium-based catalysts due to the formation of CO. Due to the non-polar and weak Van der Waals forces of CO2, most lipophilic and hydrophilic species (such as amino acids, proteins and many catalysts) are often insoluble in scCO2. Obviously, it is a limitation for the application of supercritical carbon dioxide. Recently, in order to overcome this disadvantage, the most effective approach is to use suitable surfactants to produce water-in-CO2 microemulsions or reverse micelles. Consan and Smith tested the solubility of over 130 commercially available surfactants in scCO2 at 50 °C and 10-50 MPa. All of them were rarely soluble or only slightly soluble in scCO2, so they could not be employed as surfactants in scCO2.

The fluids that are operated above their critical temperature and pressure are known as supercritical fluids (SCFs). SCFs replaces the conventional organic solvents in the chemical processes due to their attractive properties such as liquid like densities, gas like diffusivities, negligible surface tension, lower viscosity and high compressibility. Carbon dioxide, being non-toxic, non-flammable with ambient critical temperature and moderate critical pressure, is the most widely used SCF in many chemical processes. Supercritical carbon dioxide (SCCO2) finds applications in industrial processes such as extraction and separation processes. The feasibility of a supercritical process can be determined from the solubility of solute in SCF. For the efficient design of a SCF process, the effects of temperature and pressure on the solubility of a solid should be examined thoroughly. In general, the solute of interest is not present alone; it is present along with many other components in the compound. The solute has to be extracted or separated from matrix of components. Therefore, it is important to determine the mixture solubilities in SCCO2. The mixture solubility of a solute is not same as that of pure component solubility. The presence of the other component alters the solubility of the solute to a greater extent; hence the effects of the other components present along with the solute, temperature and pressure need to be known to understand the mixture behavior of the solute in SCCO2. The solubilities of solid isomers (ortho-, meta-, para-) in SCCO2 vary to a greater extent. This huge difference in the solubilities of isomers is due to interactions between the molecules. The high solubility of an isomer in SCCO2 might be due to the solute-solvent interactions. The interactions between the molecules are significant in the solid mixtures solubilities in SCCO2. This research work focuses on experimental determination and modeling of mixture solubilities of solids in SCCO2. The solubilities of several pairs of isomers have been experimentally determined at different temperatures and pressures. These include the ternary solubilities of ntrophenols, nitrobenzoic acids and dihydroxy benzene isomers mixtures in SCCO2. The experimental solubilities of nitrophenol (meta- and para-) isomers mixture have been determined. This study includes the effect of temperature, pressure and each isomer on the ternary mixture solubilities of nitrophenol mixtures. The enhancements in the ternary solubilities of nitrophenols over their binary solubilities and the selectivity of SCCO2 for the nitrophenol mixture have been discussed in detail. The solubilities of dihydroxy benzene (ortho-: pyrocatechol, meta- : resorcinol and para-: hydroquinone) isomers in SCCO2 have been determined at various temperatures and pressures. The ternary solubilities of pyrocatechol and resorcinol and quaternary solubilities of pyrocatechol, resorcinol and hydroquinone mixtures in SCCO2 have been investigated. The effect of each isomer on the mixture solubilities of other isomers has been included in this work. Selectivity for dihydroxy benzene isomers and variation of solubilities enhancements with temperature and pressure has been presented in this study. The equilibrium mixture solubilities of nitrobenzoic acid isomers (meta- and para) mixture have been studied. The variation of mixture solubilities and their enhancements with temperature and pressure has been thoroughly analyzed. Selectivity of SCCO2 for this nitrobenzoic acid mixture has been studied in detail. The increase or decrease in the ternary solubilities of the solid mixtures that have been considered in this study is due to the interactions between the molecules. The ternary solubilities of m-nitrophenol increase whereas they decrease for pnitrophenol for the nitrophenol solid mixture. Quaternary solubilities of dihydroxy benzene isomers (pyrocatechol + resorcinol + hydroquinone) increases compared to their pure component solubilities. The ternary solubilities of pyrocatechol increases while resorcinol decreases over the pressure range at different temperatures (except 338 K) considered in this study. The mixture solubilities of p-nitrobenzoic acid of nitrobenzoic acid isomers increase to a greater extent. An average of separation efficiency of 70%, 85% and 90% has been observed for ternary solid mixtures of nitrophenol, nitrobenzoic acid and dihydroxy benzene isomers respectively. Modeling of high pressure multi-component systems is useful to understand the behavior of the mixtures. Moreover, the experimental determination of multicomponent solubilities of solids in SCCO2 is tedious and time consuming; hence the modeling of mixture solubilities is essential. The interactions between the molecules have been incorporated in the association theory and a five parameter equation with two constraints has been derived for binary systems. The new equation correlates the solubilities of m-dinitrobenzene in this study along with 72 other systems available in literature. Seven new model equations have been developed to correlate ternary (2 for cosolvent (solid + cosolvent + SCCO2) systems; 5 for solid mixtures in SCCO2) solubilities of solids in SCCO2. A new model equation for cosolvent ternary systems has been derived by using the concepts of association of molecules. The model equation contains seven adjustable parameters with three constraints and correlates mixture solubilities in terms of temperature, pressure, density and cosolvent composition. The interactions between the molecules have been included in the association theory then the number of parameters decreased to five with two constraints. The performance of the newly developed equations has been evaluated for 32 ternary systems with various cosolvents along with experimental data of mdinitrobenzene in methanol cosolvent of this study. The same association theory has been extended to ternary (solid mixtures + SCCO2) solubilities of solids in SCCO2 and two new equations have been derived with and without incorporating interactions between the molecules. Both the equations have five adjustable parameters with three constraints for the equation which has been derived from association theory alone and two constraints for the equation which has been derived by considering the interactions between the molecules in the association theory. A new model equation has been derived by combining solution model with Wilson activity coefficient model to account for nonidealities of the solute. This equation has four adjustable parameters and no constraints on the parameters. The non-idealities of both solutes in the solution model have been included and two more equations with no constraints on the parameters have been developed. One equation uses NRTL activity coefficient model which results in three adjustable parameters while the other equation with five parameters has been obtained from Wilson activity coefficient model for solid mixtures solubilities in SCCO2. The performance of the newly developed equations has been evaluated for the solid mixtures (ternary systems) in SCCO2. The equations with constraints make them limited for few systems and the equations with no constraints are able to correlate the solubilities of solids of all the ternary systems that are available in literature along with the generated ternary experimental data of this study. The quaternary solubilities of solids have been correlated by using a five parameter model equation which has been derived by combining solution and Wilson activity coefficient models. The equation for the quaternary systems does not have constraints on the parameters; hence can be applied for quaternary systems. The equation correlates the quaternary solubilities of solids in terms of temperature, pressure, density and cosolute compositions. Chapter 1 gives a brief introduction on the solubilities of solid mixtures and their behavior in SCCO2. Chapter 2 presents the experimental setup and the solubility data of binary, ternary and quaternary systems determined in this study. Chapter 3 focuses on the models that have been derived to correlate the solubilities of solids in SCCO2. Chapter 4 discusses in detail about the results obtained in this research work. Chapter 5 briefly summarizes the work and presents major conclusions. The new equations that have been developed here are first of its kind for the ternary and quaternary systems. These equations give information about the nonidealities of the systems. The nature of the interactions between the molecules can be determined from the parameters of the equations which incorporate interactions between the molecules. The multi-component solubilities of the solids can be correlated by using the semi-empirical equations that have been derived in this research.

Porous metal oxides formed by supercritical carbon dioxide (SCCO2) treatments at low temperature were used for displays, solar cells, and light emitting diodes (LEDs) applications. The SCCO2 fluid, also known as green solvents, exhibits low viscosity, low surface tension and high diffusivity as gases, and high density and solubility same with liquids. In this thesis, we successfully fabricated porous antimony-doped tin oxide (ATO) and porous indium tin oxide (ITO) by the SCCO2 treatments. In addition, the treatment can also be used to improve the work function and surface energy of ITO anode of an organic LED (OLED). The performance of the OLEDs was drastically enhanced in comparison with that of the devices without any ITO surface treatments. First, the porous ATO films were formed by the SCCO2 treatment for absorption of silver molecules in silver electro deposition devices. The porosity, resistivity and average optical transmittance of the porous ATO film in visible wavelength were 43.1%, 3 £[-cm and 90.4%, respectively. For the silver electro deposition devices with the porous ATO film, the transmittance contrast ratio of larger than 12 in visible spectrum was obtained at an operating voltage of 1.5 V. Furthermore, for the 0.25 cm2 device, the switching time of 4.5 seconds was achieved by applying a square-wave voltage ranging from 1.5 to -0.2 V between the electrodes. On the other hand, the porous ITO with low refractive index was prepared by SCCO2/IPA treatment on gel-coated ITO thin films. The high refractive index of the ITO film was achieved by long-throw radio-frequency magnetron sputtering technique at room temperature. The index contrast (£Gn) was higher than 0.6 between porous ITO and sputtered ITO films. The large £Gn is useful for fabricating conductive anti-reflection (AR) and high reflection (HR) structures using the porous ITO on sputtered ITO bilayers. The weighted average reflectance and transmittance of 4.3% and 83.1% were achieved for the double-layer ITO AR electrode with a sheet resistance of 1.1 K£[/¡E. For HR structures, the reflectance and sheet resistance were 87.9% and 35 £[/¡E with 4 periods ITO bilayers. Finally, the SCCO2 treatments with strong oxidizer H2O2 were proposed to modify surface property of ITO anode of a fluorescent OLED. The highest work function and surface energy of 5.5 eV and 74.8 mJ/m2 was achieved by the SCCO2/H2O2 treatment. For the OLED with 15 min SCCO2 treatment at 4000 psi, the turn-on voltage and maximum power efficiency of 6.5 V and 1.94 lm/W were obtained. The power efficiency was 19.3% and 33.8% higher than those of the OLEDs with oxygen plasma treated and as-cleaned ITO anodes.