No description available.

Indium tin oxide (ITO) films were deposited onto the glass substrate by rf reactive magnetron sputtering method. Deposition was performed by changing processing conditions, such as rf power, process pressure and substrate temperature. The structural, optical and electrical properties of ITO films have been characterized by X-ray diffraction, optical transmittance and sheet resistance. In the process of ITO deposition, we change rf power and fix process pressure at room temperature. And we change process pressure after finding low sheet resistance by changing rf power at room temperature. The low sheet resistance of 35 £[/¡¼ was obtained at room temperature. In addition, we change the substrate temperature while keeping the same rf power and process pressure. When the temperature is 400¢J, the sheet resistance as low as 6.98 £[/¡¼ was obtained. The diffraction peaks on (211), (222), (400), and (440) directions were observed by XRD analysis. Under high temperature (300¢J) deposition the transmittance and diffraction peaks of the films were found to change with different rf power and process pressure. However, the sheet resistances are about the same during the interest for both rf power and process pressure. The UV-visible spectra indicate that the optical transmittance of all the films is between 65 % ~ 90 % at visible range.

Microstructure evolution at different stage of charge-discharge process of the SnO2 thin film electrode of the secondary lithium battery was studied in this work. In particular, the identity and amount of various phases were monitored as the lithium were inserted or exacted from the electrode. The SnO2 thin film ,though a negative-electrode material ,served as the positive electrode in the charge-discharge process .The counter electrode was a pure lithium foil. As obtained from the X-ray diffraction examination, £]-Sn phase increased gradually as the discharging process proceeded, reacting a maximum at the ending point of discharging(0.05V). The£]-Sn phase then decreased gradually as the charging process proceed and finally disappeared at the end of charging(2.5V). TEM observation indicates that SnO2 was present at the initial stage of discharging (up to ~0.91V),and at replaced at the end of discharging by£]-Sn which showed some agglomeration. Cracks on the thin film were observed by SEM offer discharging. They were formed due to the expansive caused by the formation of low-density phases.

In this research, cetyltrimethylammonium bromide (CTAB) is used as organic template and hydrous tin chloride (SnCl4) is used as inorganic precursor to prepare mesostructured SnO2 powder. The synthesis is carried out in the room temperature using NH3(aq) as pH-modifier. The changing variables in the synthesis process include: the mixing sequence of CTAB(aq), SnCl4(aq) and NH3(aq), the molar ratio of CTAB/SnCl4 (R), the pH value of the mixture and the aging time of the mixture. The X-ray diffraction (XRD) results show that the pH value of the mixture is the determining factor for the successful synthesis of mesoporous powder. On the other hand, the mixing sequence is of no consequence on the formation of the mesostructure. For solutions of pH<1 and R=0.2, 0.5 or 1, a crystalline phase of organic-inorganic complex is found in the final products, which hinders the hydrolysis and condensation of the inorganic precursor and hence the formation of mesoporous structure. For powders derived from the solutions of pH=2~5, the diffraction peak of mesoporous structure appears and becomes more intense with increasing pH value. For solutions of pH>7, mesoporous powders are obtained constantly. As mesoporous powder is also obtained from solution of R=0.01, it is concluded that the formation of surfactant cylinders and the subsequently packed hexagonal arrays are not fulfilled during the cooperation assembly process of organic and inorganic moleculars because the concentration of CTAB is far below the critical concentration for rod micelle (~10wt0/0). On the other hand, surfactant rod micelles instead of mesoporous structure is found in the powder derived from the basic solution of R=10 (CTAB: 5 g, SnCl4: 0.5 g). This implies that in spite of the formation of CTAB rod micelles, the mesostructured SnO2 powder can not be obtained without sufficient amount of Sn-precursor . According to the model of mesostructure synthesis, in current work, surfactant ions (S+), inorganic ions (I+) and counter ions (X-) are connected in the form of S+X-I+ through the electrostatic attraction and their cooperation assembly results in mesoporous structure. As pH valueincreases instantly as NH3(aq) is added into CTAB(aq), it is concluded that CTA+OH- does not exist and X- is Br- or Cl- instead of OH-. Finally, the mesostructure obtained in this work collapse after a calcination of 5000C for two hours. Therefore, a great deal needs to be done to improve the thermal stability in the future.

Submicron tin oxide (SnO2) was obtained from thermal decomposition of tin oxalate (SnC2O4) precipitated at room temperature from amixture of solutions of tin (II) chloride (SnCl2) and oxalic acid (H2C2O4). Aqueous precipitation of SnC2O4 was firstly investigated by parametersvariation of starting material concentrations, addition methods and mixing times. Upon calcination, SnO2 powder tacky and subsequent grinding was found to cause nanosized SnO2 particles to agglomerate into plates. Aqueous??alcohol precipitation was then developed, based on the previously conducted aqueous precipitation Stabilisation of SnO2 suspensions was found to be better in aqueous rather than non??aqueous media, as determined by zeta potential analysis and sedimentation tests. A detailed concept of the effects of zeta potential and sedimentation (enhanced sedimentation region (ESR)) on colloidal processing, i.e., suspension stability, was introduced. Two systems, Sn??Al??O and Sn??Si??O, were investigated at their invariant temperatures and ternary phase diagrams, which haven??t been reported elsewhere, were constructed (at nine isothermal temperatures each). The binary diagram for the system SnO2??SiO2, which has not been reported in the literature, was constructed. The systems compatibilities were confirmed experimentally at 1000oC, with incidental finding of micron??sized fibres of single crystal SnO2 with preferential [110] growth direction obtained. It was also deduced that 1000oC can be used for SnO2 coatings sintering without undesired reaction or mutual solubility. Successful electrophoretic deposition (EPD) of commercial SnO2 powder on dense sapphire was obtained by the use of pH 2 SnO2 suspension, but not with pH 9 suspensions leading to a review of the basis for EPD requirements in terms of suspension properties. Thus, another conceptual approach to EPD processing and setup was proposed in terms of zeta potential, suspension stability and net particle charge. Obtained homogeneous deposition of commercial SnO2 powders contradicted the findings of published works of EPD on insulating dense substrates. Thus critical factors in the design of EPD processing on dense insulating substrates and associated mechanisms responsible for the deposition were developed. However, EPD of synthesised SnO2 powders yielded inhomogeneous coatings, even with voltage application of up to 30 V. Microcell effects, which were deduced based on localised particle leaching in the suspension, were proposed. Although deposition was relatively unsuccessful, this demonstrated possibility of aqueous EPD with the usage of high voltages without occurrence of water electrolysis which hasn??t been observed in literature.

No description available.

Porous tin oxide nanotubes were obtained by vacuum infiltration of tin oxide nanoparticles into porous aluminum oxide membranes, followed by calcination. The porous tin oxide nanotube arrays so prepared were characterized by FE-SEM, TEM, HRTEM, and XRD. The nanotubes are open-ended, highly ordered with uniform cross-sections, diameters and wall thickness. The tin oxide nanotubes were evaluated as a substitute anode material for the lithium ion batteries. The tin oxide nanotube anode could be charged and discharged repeatedly, retaining a specific capacity of 525 mAh/g after 80 cycles. This capacity is significantly higher than the theoretical capacity of commercial graphite anode (372 mAh/g) and the cyclability is outstanding for a tin based electrode. The cyclability and capacities of the tin oxide nanotubes were also higher than their building blocks of solid tin oxide nanoparticles. A few factors accounting for the good cycling performance and high capacity of tin oxide nanotubes are suggested. / Singapore-MIT Alliance (SMA)

Abstract A thin film deposition system using ultrasonic atomization is designed and constructed. Solution containing precursors is transported by carrying gas to the heated substrate where deposition is accomplished by pyrolysis. Tests including series of varying flow rate of carrying gas and varying substrate temperature were carried out with solutions of SnCl4 precursor in C2H5OH solvent and N2 as carrying gas. Also, TaCl5 was used as dopant to improved the electrical conductivity. The effects of doping in crystallinity, surface morphology, optical transmittance and electrical conductivity of the deposited thin films were examined and the optimal percentage of doping for electrical conductivity and optical transmittance was found. XRD reveals that the thin film was amorphous when the deposition temperature was below 350¢J. Polycrystalline thin films with grains size of 30~50nm were obtained with deposition temperature of 400~500¢J and N2 flow rate of 2.5 ~10 l/min. SEM examination reveals that porosity increases with increasing deposition temperature and N2 flow rate, which consequently reduces the electron mobility, as seen in Hall measurement. No discernible difference was observed between the morphology of the doped and undoped thin films. As shown in the UV-Visible spectra representative transmittance of all films at 550nm radiation ranges between 70% and 82%. No discernible effect was observed for Ta-doping. Hall measurement reveals that Ta-doping increases the electron mobility and carrier concentration by several times and one order of magnitude, respectively. The minimum resistivity is 1.2*10-1 £[- cm occurring at 4 at% Ta doping.

This dissertation has focused on the study of the ITO/organic heterojunction and the chemistries therein, it proposes appropriate strategies that enhance the interfacial physical and electronic properties for charge injection with application to organic thin-layer devices. We focused on four major aspects of this work: i) To characterize the ITO surface and chemistries that may be pertinent to interaction with adjacent organic layers in a device configuration. This developed a working model of surface and provided a foundation for modification strategies. Characterization of the electronic properties of the surface indicate less than 5% of the geometrical surface is responsible for the bulk of current flow while the rest is electrically inactive. ii) To determine the extent to which these chemistries are variable and propose circumstances where compositional changes can occur. It is shown that the surface chemistry of ITO is heterogeneous and possible very dynamic with respect to the surrounding environment. iii) To propose a strategy for modification of the interface. Modification of ITO surfaces by small molecules containing carboxylic acid functionalities is investigated. Enhancements in the electron transfer rate coefficient were realized after modification of the ITO electrode. The enhancements are found to stem from a light etching mechanism. Additionally, an elecro-catalytic effect was observed with some of the modifiers. iv) Apply these modifications to organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs). Enhancements seen in solution electrochemical experiments are indicative of the enhancements seen for solid state devices. Modifications resulted in substantially lower leakage currents (3 orders of magnitude in some cases) as well as nearly doubling the efficiency.An additional chapter describes the creation and characterization of electrochemically grown polymer nano-structures based on blazed angle diffraction gratings. The discussion details the micro-contact printing process and the electro-catalytic growth of the conductive polymers PANI and PEDOT to form diffraction grating structures in their own right. The resulting diffraction efficiency of these structures is shown to be sensitive to environmental conditions outlining possible uses as chemical sensors. This is demonstrated by utilizing these structures as working pH and potentiometric sensors based on the changing diffraction efficiency.

In this thesis, investigations into fabricating tin oxide hydrogen gas sensors from films assembled by the deposition of tin clusters are reported. The tin clusters were formed in a UHV compatible cluster apparatus by DC magnetron sputtering and inert gas aggregation. Through SEM imaging, it was found that the morphology of tin cluster assembled films deposited onto silicon nitride substrates was highly coalesced. The coalescence between the clusters was significantly reduced by reacting the clusters with nitrogen before they were deposited. This resulted in granular films with a grain size close to that of the deposited clusters. The coalesced and granular tin films were used to fabricate tin oxide conducti-metric gas sensors. This was done by depositing the tin films onto gold contacts and then oxidising them by baking them at 250°C for 24 hours. The sensors were tested using a purpose built gas test rig. It was found that the sensors with the granular film morphology were much more sensitive to 500 ppm, 1000 ppm, and 5000 ppm of hydrogen at 200°C in ambient air with zero humidity. This was attributed to the smaller grain size and the larger surface area of the granular films.