Non conventional gate insulators for MOS devices are generally dielectrics that depart considerably from the classic Si0₂ used extensively in this technology. The work presented here reflects the research and development of an existing compound, Ta₂0₅, and its application as a gate insulator for both MOS capacitors and transistors. The oxide is grown both thermally and anodically from pure sputtered tantalum metal over silicon wafers. Succesful dielectrics suitable for gate insulators were obtained using both methods. High relative permittivity (≃26-28) being characteristic of tantalum pentoxide, offers considerable advantage over classic silicon dioxide gate insulators, however higher leakage currents (100 to 1000 times greater) were encountered in MOS Capacitor samples at room temperature. A method for processing the tantalum metal was developed using the liftoff technique, and it was successfully applied to both MOS capacitors and field effect transistors. Furthermore, devices were fabricated in the form of MOS Transistors, which exhibited good Id vs. Vds characteristics, with Vgs as a parameter. Gate leakage currents were low, as a double dielectric Ta₂0₅ over Si0₂ structure was used as gate insulator. A small signal model of this class of devices is presented, that takes into account the non zero gate leakage current. Another successful technique, interfacial oxidation of Ta₂0₅ over Si, was used in fabricating MOS Capacitors that yielded also low leakage currents and high specific capacitances. The purpose of this Thesis is to report the development at the University of British Columbia of the double gate insulator MOSFET technology based on the Tantalum Pentoxide-Silicon Dioxide (Ta₂0₅/Si0₂) heteromorphic structure. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Finding materials based on non-rare earth metals is vital for the global transition to a more sustainable economy. Discovering useful properties in common metal oxides is a promising avenue for new materials. In this work we have investigated the properties of Ru(x)CoMo(1-x) to evaluate the feasibility of its use as an electrocatalyst for the oxygen evolution reaction (OER). Herein, the plasma spray deposition on FTO and glass is reported as a method for production of low Ru content-CoMo oxide. The material showed a good performance in an alkaline electrolyte for OER, with no loss on stability and overpotentials to achieve a current density of 10 mA cm-2 of 528, 483, 455, 439 mV for 0, 10, 20, and 30 At% of Ru, respectively. The final material is shown to be composed entirely of Co and Mo oxides, as well as Ru which is present in the crystal structure of these metal oxides as observed using optical characterization techniques, XRD, Raman and SEM. With the aim of maximising performance and decreasing the amount of Ru used, we find a Ru content of 20 At% is most optimal for OER in alkaline. We find therefore Ru(0.2)(CoMo)(0.8) to be an effective electrocatalyst for OER in alkaline, while examples from literature outperforms it in other applications, it is still a good basis for further work and development.

A novel structure related to Seperation by Implanted Oxygen (SIMOX) of NiSi2/SiO2/Si is studied for two primary reasons: the importance of metal silicide and insulating oxide in IC devices and the difficulty of direct growth of crystalline silicide on amorphous substrates.

Knowledge of the interfacial reactions between CO/CO2 and transition metal oxide containing slags is more important to understand various metallurgical processes. The present research studied the kinetics of reaction between CO/CO2 and MnOx/TiOx containing Slags. Measurements of the rate of interfacial reaction between CO/CO2 and MnOx/TiOx -CaO-SiO2 Slags were made using 13CO2-CO isotope exchange technique. The dependence of rate constant with respect to the effects of oxygen activity, MnOx/TiOx content, slag basicity and temperature was discussed. It is found that the apparent rate constant increases with increasing MnOx/TiOx content, slag basicity and temperature and decreases while increasing oxygen activity. The apparent rate constants obtained for MnOx/TiOx containing slags show similar behavior to that of FeOx containing slags and the rates gradually increase for TiOx, FeOx and MnOx containing slags at same experimental conditions. The rate constant expressions for MnOx/TiOx containing slags are obtained by using a single charge transfer model. Comparison of calculated and measured rate constants shows that there is a good fit between the two, which implies that the single charge transfer model may be generally applicable. / Thesis / Master of Science (MSc)

An investigation into the parameters that define a good anchor block for a copolymer steric stabilizer was performed. The study focused on the effects of different functional groups on the adsorption properties of polymers. In addition, the effect of chain architecture as well as the impact of a hydrophobic end-group on polymer adsorption properties was determined. To complement the adsorption studies, a streaming potential instrument was built for use in measuring the adsorbed layer thickness of nonionic polymers on SiO₂. The research concluded with an examination of the effect of thermally induced insolubility on adsorption of a hydrogen-bonding polymer. Functional group effects were studied by measuring the adsorption isotherms of poly(2-ethyl-2-oxazoline), PEOX, poly(ethylene oxide), PEO, poly(vinyl alcohol), PVOH, and poly(ethylene imine), PEI, which was modified such that a 1,3-butanediol substituent replaced its imine hydrogens, on SiO₂, TiO₂, and Al₂O₃. PEOX and PEO, relatively basic polymers compared to PVOH were observed to adsorb only on the most acidic metal oxide, SiO₂. PVOH, however, was observed to adsorb on all three metal oxides, but to a lesser degree on SiO2 as compared to the more basic PEOX and PEO. These initial results were indicative of hydrogen-bonding mechanisms, a form of acid-base interaction. The most significant observation in the adsorption studies was that the linear hydroxyl modified PEI materials and their dendritic analogs adsorb on the metal oxides both above and below the i.e.p. This indicates that both electrostatic and hydogen-bonding mechanisms are driving the adsorption. The dendritic polymers, particularly a 4th generation dendrimer based on diaminopropane with a molecular weight of 16,640 g/mol adsorbed at a higher level when compared to the 41.3K g/mol PVOH and 30K g/mol PEOX. In addition to the dual adsorption mechanism, it was determined that the dendritic architecture appears to facilitate adsorption, as does the presence of the hydrophobic endgroup. The level of adsorption for all of the hydroxyl containing linear PEI and dendritic materials on the three metal oxides was high enough for them to be considered as anchor blocks in a copolymer steric stabilizer. The streaming potential instrument used to measure the adsorbed layer thickness on SiO₂. Adsorbed layer thickness of PEOX Mw = 10K and 30K g/mol were measured at approximately 1nm and 4.4 nm, respectively. In the case of the PEOX Mw = 30K g/mol homopolymer, the measured layer thickness was higher than that for a 23K g/mol PEO homopolymer. The degree of polymerization of the PEO is approximately 525, while for the PEOX it was only 300. This result was not expected. Finally, adsorption of PEOX was studied at the cloud point to determine whether insolubility could promote adsorption, while hydrogen-bonding, the room temperature driving force for adsorption, would decrease. Adsorption isotherm measurements were performed at 72 °C, and 75 °C, as the cloud point of the 30K PEOX was determined to be 73 °C. It was apparent that the adsorption decreased as temperature increased, indicating that without hydrogen bonding, thermally induced insolubility does not drive adsorption. / Ph. D.

A temperature-programmed desorption (TPD) study of CO and NH₃ adsorption on MnO(100) with complimentary density functional theory (DFT) simulations was conducted. TPD reveals a primary CO desorption signal at 130 K from MnO(100) in the low coverage limit giving an adsorption energy of -35.6 ±2.1 kJ/mol on terrace sites. PBE+U gives a more reasonable structural result than PBE, and the adsorption energy obtained by PBE+U and DFT-D3 Becke-Johnson gives excellent agreement with the experimentally obtained ΔE_ads for adsorption at Mn²⁺ terrace sites. The analysis of NH₃-TPD traces revealed that adsorption energy on MnO(100) is coverage-dependent. At the low-coverage limit, the adsorption energy on terraces is -58.7±1.0 kJ/mol. A doser results in the formation of a transient NH₃ multilayers that appears in TPD at around 110K. For a terrace site, PBE+U predicts a more realistic surface adsorbate geometry than PBE does, with PBE+U with Tkatchenko-Scheffler method with iterative Hirshfeld partitioning (TSHP) provides the best prediction. DFT simulations of the dehydrogenation elementary step of the ethyl and methyl fragments on α-Cr2O₃(101̅2) were also conducted to complement previous TPD studies of these subjects. On the nearly-stoichiometric surface of α-Cr₂O₃(101̅2), CD₃₋ undergoes dehydrogenation to produce CD₂=CD₂ and CD₄. Previous TPD traces suggest that the α-hydrogen (α-H) elimination of methyl groups on α-Cr₂O₃(101̅2) is the rate-limiting step, and has an activation barrier of 135±2 kJ/mol. DFT simulations showed that PBE gives reasonable prediction of the adsorption sites for CH3- fragments in accordance with XPS spectra, while PBE+U did not. Both PBE and PBE+U failed to predict the correct adsorption sites for CH₂=. When the simulation is set in accordance with the experimentally observed adsorption sites for the carbon species, PBE gives very accurate prediction on the reaction barrier when an adjacent I adatom is present, while PBE+U failed spectacularly. When the simulation is set in accordance with the DFT-predicted adsorption sites, PBE is still able to accurately predict the reaction barrier (<1% to 8.7% error) while PBE+U is less accurate. DFT is also used to complement the previous study of the β-H elimination an ethyl group on the α-Cr₂O₃(101̅2) surface. The DFT simulation shows that absent surface Cl adatoms, PBE predicts an activation barrier of 92.6 kJ/mol, underpredicting the experimental activation barrier by 28.7%, while PBE+U predicts a barrier of 27.0 kJ/mol, under-predicting the experimental barrier by 79.2%. The addition of chlorine on the adjacent cation improved the prediction on barrier by PBE+U marginally, while worsened the prediction by PBE marginally. Grant information: Financial support provided by the U.S. Department of Energy through grant DE-FG02 97ER14751. / Doctor of Philosophy / Nowadays, density functional theory (DFT), a computational approach to chemistry has become increasingly more popular due to it being less computationally expensive than other traditional computational approaches. One major shortcoming of DFT is its inability to explain the electronic interactions within transition metal oxides, where the electronic configuration within one cation is intimately linked to those on adjacent cations. To address this, DFT+U, a variant of DFT, has been developed to better account for these special electronic interactions. However, not enough experimental comparisons have been established to verify the accuracy of DFT and DFT+U. Our lab focuses on providing high quality experimental benchmarks that can be readily compared to by the DFT community. To establish the experimental benchmarks, we use a technique called temperature-programmed desorption (TPD), which focuses on measuring the rate at which gas molecules leave a sample surface populated with a pre-determined amount of gas molecules as the temperature of the surface is raised at constant but slow temperature ramp rate. Through analysis of the results, the adsorption energy can be obtained for a desorption process, or an activation barrier if the desorption is the result of a surface reaction. Some simple calculations involving PBE, a popular functional used in the DFT community, and its variant PBE+U were conducted for comparison purposes. The transition metal oxide surfaces chosen in this study is MnO(100) and of α-Cr₂O3(101̅2), because they both possess the special electronic interactions between their own cations. For adsorption studies, we determined adsorption energies of carbon monoxide (CO), and ammonia (NH₃) on MnO(100) single crystal surface. For CO, TPD study revealed that CO undergoes weak adsorption on the surface, with no dissociation of CO detected. PBE predicts an unreasonable surface adsorption geometry while PBE+U predicts a reasonable one. When coupled with a particular dispersion correction method named DFT-D3 Becke-Johnson, PBE+U predicts a very accurate adsorption energy of CO on MnO(100). TPD shows that NH₃ undergoes a stronger adsorption on MnO(100) with no dissociation of NH₃. Similarly, PBE+U predicted a more reasonable adsorption geometry while PBE did not. Coupled with a dispersion correction named Tkatchenko-Scheffler method with iterative Hirshfeld partitioning (TSHP), PBE+U provides an accurate prediction of adsorption energy. In comparison to previous experimental works based on TPD results, the simple decomposition reactions of an ethyl group and a methyl group were also studied on α-Cr₂O₃(101̅2) surface using DFT. Overall, PBE gave better prediction on the activation barrier than PBE+U did in comparison to experimentally observed barriers.

Natural and synthetic SnO₂ samples were studied using scanning tunneling microscopy (STM). The SnO₂ surface flattens considerably following high temperature treatments up to 1500 K. The conductivity of the synthetic SnO₂ surface is significantly reduced following annealing at temperatures of approximately 1200-1500 K, making tunneling impossible. A decrease in conductivity was not observed for the natural SnO₂ sample following similar high temperature treatments, most likely due to impurities which act as dopants. No atomic scale images were collected on the SnO₂ surface which provided information regarding atomic positions and point defects on the surface. Water adsorption was studied on the stoichiometric Cr₂O₃ (101̲2) surface, using thermal desorption spectroscopy (TDS). Water was the only desorption product observed during TDS. Adsorption is primarily dissociative following exposure to water at 163 K. Approximately, 0.12 monolayers of water dissociate on the clean, nearly stoichiometric Cr₂O₃ (101̲2) surface. The first order kinetics observed for the recombination of dissociated water are not well understood. One possible explanation is that the rate limiting step for desorption involves the breaking of a Cr-O bond resulting in a freely diffusing OH species. The exchange of halogen and oxygen was studied on Cr₂O₃ (101̲2) using Auger electron spectroscopy (AES) and TDS. The exchange of chlorine and oxygen is completely reversible. Chlorine is removed from the Cr₂O₃ (101̲2) surface following exposure to oxygen. Exposure of CFCl₂CH₂Cl reduces the surface oxygen concentration to that of the clean, nearly stoichiometric Cr₂O₃ (101̲2) surface. The exchange of chlorine with oxygen appears to involve only chemisorbed surface oxygen, not bulk lattice oxygen. / Master of Science

Stannic oxide films on glass, deposited by th ·spray technique, are found to be n-type semiconductors. The large carrier concentration (~10¹⁹/cm³) of these films causes the donor level to blend into an impurity band. Annealing the stannic oxide film results in a diffusion of glass components on the film surface which is also accompanied by the increase in the sheet resistance. Donors such as antimony, phosphorus and tellurium raise the infrared absorption and carrier concentration and lower the sheet resistance and extrinsic activation energy. At higher concentrations (≥ 5-10 mole%) the impurities do not act like dopants, instead they become the bulk part of the film which causes an increase in the sheet resistance, infrared transmittance and the extrinsic gap energy. Addition of acceptors like indium and thallium shows an increase in the sheet resistance resulting from the neutralization of the conduction electrons. This also causes the impurity band to shrink and show an increase in the extrinsic activation energy and near infrared transmission. / Master of Science

No description available.

No description available.