Browsing by Subject "tantalum"
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Item Synthesis, Characterization and Reactivity of Electrophilic Organometallic Compounds of Ruthenium, Tantalum and Silicon(2014-12-11) Ramirez, RodrigoThe work presented herein will discuss the synthesis, characterization and reactivity of electrophilic organometallic compounds of ruthenium, tantalum, and silicon in order to explore unusual properties, reactivity, or structure. Several of the chemical species described are cationic, electronically and coordinatively unsaturated, and require the use of weakly coordinating anions in order to retain their high electrophilic character. The first study consisted in the devolpment of a method to synthesize C?alkylated carborane anions of the type [RCB11Cl11]^? (R = Me, Et, Pr, Bu, Hex) was developed, in order increase the solubility of its salts in weakly coordinating organic solvents. Salts of these C?alkylated anions form crystalline compounds. On the basis of this work, the possibility of the synthesis of a silylium?like zwitterionic compound was investigated. The compound was designed around the anionic [CB11Cl11]^? fragment, attached covalently via the C?vertex to a silylium?type cation through a methylene linker. Its synthesis was succesfuly achieved, and an X?ray diffraction study of this compound revealed that the cationic silicon center is stabilized intramolecularly by weak coordination to a chlorine atom on the ortho B?Cl ring of the anionic fragment. This compound retains the fundamental structural and chemical features of its two?component counterparts, but it is extraordinarily insoluble in weakly coordinating organic solvents. This feature can be traced back to the inherent molecular symmetry and charge distribution. The synthesis of a family of d^6 ML5 and d^6 ML6 ruthenium triflate complexes of the pincer (P2C=)Ru(X) (X = Cl, H, OAc, acac) architecture by ligand exchange using Me3SiOTf will be presented. It was speculated that metathesis of chloride with the more weakly coordinating triflate would be a convenient way to generate compounds that could be potential Lewis?acidic precatalysts. These compounds can be regarded as synthetic equivalents of truly cationic complexes, with the added advantage that no need for the isolation of highly reactive species is necessary. Finally, the reactivity of (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl towards internal and terminal alkynes was investigated. In addition to this, chloride abstraction from (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl was effected, in order to potentially enhance any reactivity towards internal and terminal alkynes. It was found that, upon chloride abstraction from neutral (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl, a reversible C?H bond activation process at PMe3 takes place, concomitant with protonation of the carbyne to form two cationic, isomeric alkylidenes of the type [(?^5?C5Me5)Ta(=CHPh)(CH2PMe2)(PMe3)]^+. In terms of reactivity towards alkynes, it was found that both the neutral and cationic systems form stable tantalacyclobutadienes, one of which was characterized structurally through an X?ray diffraction study.Item Tribo-electrochemical Characterization of Tantalum during Electrochemical-Mechanical Polishing (ECMP)(2012-02-14) Gao, FengElectrochemical Mechanical Polishing (ECMP) has become increasingly important due to the continuous decrease of the device size in integrated circuit (IC) fabrication. Tantalum (Ta) is a promising material as a substitute for copper in ICs. This dissertation studies the tribology and electrochemistry of Ta ECMP. The present research uses experimental combined analysis approaches. A specially designed experimental setup assembling a tribometer and a potentiostat was used to carry out Ta ECMP. The friction force and electrochemical reactions were measured simultaneously. Using this setup, we found the factors which affected the frictional behaviors of Ta during ECMP. The technique of single frequency electrochemical impedance spectroscopy (EIS) was employed to investigate the material removal mechanisms in Ta ECMP. The results presented the competing mechanisms of removal and formation of a surface oxide layer of Ta. In order to further the investigation in a nanoscale, the atomic force microscope (AFM) was used to measure the material removal rate. The Preston equation for the Ta ECMP was established. A new methodology was developed to study the oxidation state and process of Ta during ECMP. Through comparing the material removal rate measured by using the AFM and the calculated one via the Faraday?s law, the distribution of the Ta suboxides and pentoxide, as well as the oxidation process, was revealed. The oxidation process was strongly dependent of the applied anodic potential, thickness of the oxide layer, mechanical forces, and surface orientation. A polymer environmental cell was designed and produced. Using this cell and AFM, it was found that the material removal in the nanometer scale was a function of the surface orientations. This research is beneficial for optimization of the Ta ECMP process. This dissertation includes six chapters. After Introduction and Motivation and Objectives, the material, setup, and testing conditions are discussed in Chapter III. Chapter IV discusses the tribology and material removal mechanisms in Ta ECMP, while Chapter V the oxidation of Ta during ECMP, followed by Conclusions and Future Work.