Thesis--University of California, Berkeley, 1959. / Includes bibliographical references (p. 81-84).

The syntheses of tetra- and octa-substituted phthalocyanine complexes of titanium (IV) oxide vanadium (IV) oxide and tantalum (V) hydroxide and their electrochemical characterisation are presented in this work. The structures and purity of these complexes were confirmed by NMR, infrared and mass spectroscopies and elemental analysis. They show good solubility in most common solvents especially non-viscous solvents such as dichloromethane and chloroform. The cyclic voltammograms (CV) showed reversible to quasi reversible behavior for all the reduction couples and the oxidation peaks were irreversible. Spectroelectrochemistry of the complexes confirmed metal and ring redox processes for TaPc and TiPc derivatives and ring based processes only for VPc complexes. The synthesis of gold nanoparticles and their conjugation with the new phthalocyanines was carried out. Similarly, single walled carbon nanotubes were conjugated to selected tantalum complexes and the characterization of all the nanomaterials and their conjugates using different techniques that include TEM, XRD and AFM is also presented in this work. The photophysical and photochemical properties and photocatalytic oxidation of cyclohexene properties of the newly synthesised in the presence of gold nanoparticles were investigated. The compounds were stable, well within the stability range for phthalocyanines. The singlet oxygen quantum yield values increased drastically in the presence of gold nanoparticles. The photocatalytic products obtained from the reaction were cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexene-1-one and 1,4-cyclohexanediol. The percentage conversion values, yields and selectivity values improved significantly in the presence of AuNPs. Singlet oxygen was determined to be the main agent involved in the photocatalytic oxidation of cyclohexene. The electrocatalytic oxidation of bisphenol A and p-nitrophenol was carried out using nickel tetraamino phthalocyanine and all the newly synthesised metallophthalocyanine in the presence of gold nanoparticles and single walled carbon nanotubes. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc, TiPc and VPc complexes. The presence of single walled carbon nanotubes further improved electron transfer and minimised electrode passivation.

La conception de structures complexes requiert une connaissance exhaustive des matériaux utilisés à la fois au niveau macroscopique et au niveau microscopique. Dans le cas du tantale, peu d'études ont été menées pour des sollicitations cycliques et pour l'influence du vieillissement (au sens de la diffusion des atomes interstitiels vers les dislocations) sur le comportement macroscopique et sur les champs locaux de déformation. Afin de mieux comprendre les mécanismes microstructuraux régissant la déformation, cette étude mène de front des essais avec un suivi de déformation à l'échelle locale couplés à une modélisation adaptée, autorisant la prise en compte explicite de la microstructure.Dans un premier volet, une étude macroscopique du vieillissement et du comportement cyclique du tantale est présentée. Plusieurs techniques expérimentales ont été utilisées, mettant en évidence la propagation d'une bande de localisation de la déformation lors de l'entrée en plasticité. En parallèle, un modèle phénoménologique EKMC (de Estrin, Kubin et McCormick) rendant compte du comportement macroscopique (notamment du pic de traction dû au vieillissement statique) a été identifié ; permettant ensuite des investigations numériques sur les manifestations de la localisation de la déformation.Ensuite, l'étude a été poursuivie à l'échelle locale à la fois expérimentalement et numériquement. Pour ce faire, des matrices micrométriques de plots en nickel ont été déposées à la surface d'un échantillon. Les images sucessives autorisent le calcul des cartes de déformation expérimentales lors d'un essai de traction interrompu. La modélisation explicite de la microstructure a été rendue possible par la génération d'agrégats polycristallins spécifiques avec des conditions de surface libre. L'étude de l'influence de la prise en compte du vieillissement sur l'hétérogénéité des champs locaux de déformation a permis de confronter ces derniers avec les champs expérimentaux.Enfin, une étude multi-échelles du comportement en fatigue a été effectuée. Un essai de fatigue interrompu avec observations microscopiques et construction de cartes de déformation a été réalisé. L'hétérogénéité de déformation locale a ainsi été identifiée et quantifiée, jusqu'à l'amorçage de fissures. Une simulation d'une sollicitation équivalente a été réalisée sur un agrégat polycristallin, permettant la comparaison directe des champs locaux de surface. Des investigations approfondies ont été menées sur l'agrégat pour mettre en place un critère d'amorçage basé sur des grandeurs physiques en accord avec l'expérience. / Designing complex structures requires an exhaustive knowledge of the materials used at both macroscopical and microscopical scales. In the case of tantalum, only few studies have been focused on the cyclic behaviour and on static strain aging's (aging in the sense of atoms diffusion to dislocations) influence on macroscopical behaviour and on the local strain fields. In order to extend the comprehension of microstructural mechanisms driving deformation, this study deals with experiments following the local strain fields evolution and with an appropriate modelling, taking into account microstructure explicitly.In a first step, a macroscopical study of aging and cyclic behaviour is presented. Several experimental techniques have been used in order to highlight a strain localisation band propagation associated to the anomalous yield point phenomenon. In parallel, a phenomenological EKMC (from Estrin, Kubin and McCormick) macroscopic model has been adopted, capturing the macroscopic behaviour (especially the anomalous yield point associated to static strain aging) ; and then used for several numerical investigations about the strain localisation occurence.Then, the study has been continued at the microscale in both numerical and experimental matters. Thus, several micrometrical matrixes of nickel dots have been led on the sample's surface. The have then been used for the experimental strain maps computation during an interrupted tensile test. The explicit computation of the microstructure through a specific generation of polycrystalline aggregates using free surface conditions has permitted to study the influence of aging on the local strain fields heterogeneity and to compare them with the experimental ones.Finally, a multi-scale study of the cyclic behaviour has been carried out. An interrupted fatigue test with microscopic observations and strain maps computations has been carried out, permitting the identification and quantification of the local strain heterogeneity up to the crack initiation. A computation of an equivalent loading has been done on a polycrystalline aggregate in order to set up a fatigue criterion based on physical quantities in agreement with experimental datas.

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

Increasing demand for high-density memories has necessitated the search for new materials with higher dielectric constants to satisfy the minimum charge storage density requirements. Several materials such as Ta₂O₅, BST¹, BBT² are being investigated to replace the currently used Si based oxide/nitride dielectrics. Among the materials under investigation, Ta₂O₅ is one of the most promising, especially from the fab compatibility point of view. Ta₂O₅ thin films offer a six-fold increase in dielectric constant compared to conventional dielectrics. However, the significant improvement in dielectric constant is offset by higher leakage currents compared to conventional dielectrics. Improvement in both, dielectric and insulating properties is required for the successful integration of Ta₂O₅ thin films into devices. In the current research work, it was demonstrated that by chemically modifying the tantalum pentoxide matrix, significant improvements in its electrical properties can be achieved which would enable the fabrication of a reliable high-density memory device. In the present work, the effects of Al addition on Ta₂O₅ thin films were systematically studied. The structural and electrical properties of these chemically modified thin films were investigated in detail to establish their potential for device applications. The effects on dielectric and insulating characteristics due to incorporation of Al in Ta₂O₅ matrix were studied in capacitor configuration. A metallorganic solution decomposition (MOSD) technique was used to deposit thin films onto Pt coated Si(100) substrates. The capacitors were fabricated by sputter depositing Pt electrodes on the top surface of the films. The dielectric and insulating properties of pure and modified Ta₂O₅ thin films and their dependence on film composition, processing temperature, and the thickness were discussed and an attempt was made to provide theoretical understanding for the experimental observations. The dielectric and insulating properties of Ta₂O₅ were found to be significantly modified by addition of Al. It was observed that Al addition has decreased the leakage currents approximately by an order of magnitude and improved thermal and bias stability characteristics of Ta₂O₅ capacitors. For example, the leakage currents in crystalline pure Ta₂O₅ thin films were found to be 4.5 x 10⁷ A/cm² in a 1MV/cm dc field which decreased to 3.4 x 10⁸ A/cm² for 10% Al modified Ta₂O₅ thin films. A typical dielectric constant of 42.5 was obtained for 10% Al modified Ta₂O₅ thin films. This is significantly higher compared to the commonly reported dielectric constant of 25 to 35 for Ta₂O₅ thin films. This enhancement was attributed to strong (100) orientation exhibited by both pure and modified Ta₂O₅ thin films. The high dielectric constant, low dielectric loss, low leakage currents and low temperature coefficient of capacitance suggest the suitability of Al modified Ta₂O₅ as a capacitor dielectric for future generation DRAM applications. ¹Barium strontium titanate, ²Barium bismuth tantalate / Master of Science

No description available.

No description available.

The focus of this research is to study the interaction between copper and the diffusion barrier/adhesion promoter. The behavior of copper sputter-deposited onto sputter-cleaned tantalum nitride is investigated. The data show that copper growth on tantalum nitride proceeds with the formation of 3-D islands, indicating poor adhesion characteristics between copper and Ta0.4N. Post-annealing experiments indicate that copper will diffuse into Ta0.4N at 800 K. Although the data suggests that Ta0.4N is effective in preventing copper diffusion, copper's inability to wet Ta0.4N will render this barrier ineffective. The interaction of copper with oxidized tantalum silicon nitride (O/TaSiN) is characterized. The data indicate that initial copper depositions result in the formation a conformal ionic layer followed by Cu(0) formation in subsequent depositions. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 800 K, copper "de-wetting" occurs for temperatures above 500 K. These results indicate that in conditions where the substrate has been oxidized facile de-wetting of copper may occur. The behavior of a sputter-deposited Cu0.6Al0.4 film with SiO2 (Cu0.6Al0.4/SiO2) is investigated. The data indicate that aluminum segregates to the SiO2 interface and becomes oxidized. For copper coverages less than ~ 0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. These data are in contrast with the observed behavior of copper metal deposited onto SiO2 (Cu/SiO2). The data for Cu/SiO2 show that copper does not wet SiO2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu0.6Al0.4/SiO2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K, while Cu diffusion into SiO2 occurs ~ 600 K. These data indicate that aluminum alloyed with copper at the SiO2 interface serves as an effective adhesion promoter and thermal diffusion barrier.

A combined experimental and computational study on the reversible ortho-metalation exhibited by the triosmium cluster Os3(CO)10(dppm) (dppm = 1,1-bis(diphenylphosphino)methane is reported. The conversion of nonacarbonyl cluster HOs3(CO)9[-PhP(C6H4)CH2PPh2] to Os3(CO)10(dppm) is independent of added CO and exhibits a significant inverse equilibrium isotope effect (EIE). Reductive coupling of the C-H bond in HOs3(CO)9[-PhP(C6H4)CH2PPh2] leads to the formation of agostic C-H and two distinct aryl-π species prior to the rate-limiting formation of the unsaturated cluster Os3(CO)9(dppm). Heating the unsaturated dimer H2Re2(CO)8 with Cp*Rh(CO)2 (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) at elevated temperature affords the new trimetallic clusters H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6, and the spiked-triangular cluster HRhRe3Cp*(CO)14. H2Re2(CO)8 reacts with Cp*2Rh2(CO)2 under identical conditions to furnish H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6 as the principal products, in addition to the tetrahedral cluster H2Rh2Re2Cp*2(CO)8. H2RhRe2Cp*(CO)9 undergoes facile fragmentation in the presence of halogenated solvents and the thiols RSH (where R = H, C6H4Me-p) to afford the structurally characterized products Cp*Rh(-Cl)3Re(CO)3, S2Rh3Cp*(CO)4, Cp*Rh(-Cl)(-SC6H4Me-p)2Re(CO)3, and Cp*Rh(-SC6H4Me-p)3Re(CO)3. The new hydrazido-substituted compounds TaCl(NMe2)3[N(TMS)NMe2] (TMS = tetramethylsilyl) and Ta(NMe2)4[N(TMS)NMe2] have been synthesized and their structures established by X-ray crystallography. The latter product represents the first structurally characterized octahedral tantalum(V) complex containing a single hydrazido(I) ligand in an all-nitrogen coordinated environment about the metal center. The fluxional properties of the amido and hydrazido ligands in these new compounds have been established by VT 1H NMR spectroscopy (VT = variable temperature). Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD (ALD = atomic layer deposition) precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.

The TaSiO6 films, ~8Å thick, were formed by sputter deposition of Ta onto ultrathin SiO2 substrates at 300 K, followed by annealing to 600 K in 2 torr O2. X-ray photoelectron spectroscopy (XPS) measurements of the films yielded a Si(2p) binding energy at 102.1 eV and Ta(4f7/2) binding energy at 26.2 eV, indicative of Ta silicate formation. O(1s) spectra indicate that the film is substantially hydroxylated. Annealing the film to > 900 K in UHV resulted in silicate decomposition to SiO2 and Ta2O5. The Ta silicate film is stable in air at 300K. XPS data show that sputter-deposited Cu (300 K) displays conformal growth on Ta silicate surface (TaSiO6) but 3-D growth on the annealed and decomposed silicate surface. Initial Cu/silicate interaction involves Cu charge donation to Ta surface sites, with Cu(I) formation and Ta reduction. The results are similar to those previously reported for air-exposed TaSiN, and indicate that Si-modified Ta barriers should maintain Cu wettability under oxidizing conditions for Cu interconnect applications. XPS has been used to study the reaction of tert-butylimino tris(diethylamino) tantalum (TBTDET) with atomic hydrogen on SiO2 and organosilicate glass (OSG) substrates. The results on both substrates indicate that at 300K, TBTDET partially dissociates, forming Ta-O bonds with some precursor still attached. Subsequent bombardment with atomic hydrogen at 500K results in stoichiometric TaN formation, with a Ta(4f7/2) feature at binding energy 23.2 eV and N(1s) at 396.6 eV, leading to a TaN phase bonded to the substrate by Ta-O interactions. Subsequent depositions of the precursor on the reacted layer on SiO2 and OSG, followed by atomic hydrogen bombardment, result in increased TaN formation. These results indicate that TBTDET and atomic hydrogen may form the basis for a low temperature atomic layer deposition (ALD) process for the formation of ultraconformal TaNx or Ru/TaNx barriers. The interactions of sputter-deposited ruthenium with OSG at 300 K have been studied by XPS for Ru coverages from ~ 0.1 monolayer to several monolayers, using in-situ sample transfer between the deposition and analysis chambers. The results indicate Stranski-Krastanov (SK) type growth, with the completion of the first layer of Ru at an average thickness corresponding to 1 monolayer average coverage. Ru(0) is the only electronic state present. XPS core level spectra indicate weak chemical interactions between Ru and the substrate. A less pronounced tendency towards SK growth was observed for Ru deposition on parylene. Deposition of Ru on OSG followed by electroless deposition of Cu resulted in the formation of a shiny copper film that failed the Scotch® tape test. Results indicate failure mainly at the Ru/OSG interface.