Surface studies and density functional theory analysis of ruthenium polypyridyl complexes

In recent years, the computational method Density Functional Theory (DFT) has become more and more important as an effective tool for studying inorganic complexes. This thesis describes computational studies on ruthenium polypyridyltype complexes using DFT. An introduction to the theory behind DFT is presented in the first chapter, as well as a review of previous DFT studies on ruthenium polypyridyl-type complexes. The second chapter describes the details of the computational studies. This includes a description of the basis set, functional, and integration grid. This chapter also describes two pieces of in-house software: GaussSum written to process the output of the computational package Gaussian, and GauStock, which is used to calculate Hirshfeld atomic charges. Chapter 3 examines the electronic structure of a series of complexes related to [Ru(bpy)2(pytrz)]+. The calculated electronic structure is compared with results from experiment. Partial density of states (PDOS) spectra are used to visualise the results. Linkage isomerism and methylation reactions are examined using thermodynamics and, in the case of methylation reactions, also with kinetics. Chapter 4 compares the electronic structure of dinuclear complexes with their corresponding mononuclear analogues. PDOS spectra are used to highlight the changes that occur on addition of a second metal centre. The quality of the predicted Raman frequencies of [Ru(bpy)3]2+ is the focus of Chapter 5. The effect of basis set size, grid size and the inclusion of solvent effects is discussed. The results are compared with the experimental values. Chapter 6 presents the first DFT study of an osmium complex attached to a surface, in this case, to a gold (111) surface. A cluster model is used for the surface. The effect of adsorption on the energy levels of the complex is studied. The effect of oxidation on the adsorbate-substrate bond is also examined. Chapter 7 is an overview of the information available from DFT calculations. DFT is a very useful tool for examining the electronic structure of ruthenium polypyridyl complexes. PDOS spectra highlight changes in electronic structure between related complexes. Trends in oxidation potential are reproduced by the position of the metal PDOS peak. Predicted Raman frequencies agree well with experiment, although a scaling factor is required. Adsorption of an osmium complex on a gold surface causes molecular orbitals close to the surface to shift, while the relative positions of other molecular orbitals remain unchanged. The oxidised complex binds more strongly, due to the change in the nature of the frontier orbitals

Design and characterization of GaAs multilayer CPW components and circuits for advanced MMICs

With the demand of modern wireless communications, monolithic microwave integrated circuit (MMIC) has become a very promising technique as it is mass-productive, low loss and highly integrated. Microstrip and Coplanar Waveguide (CPW) are both widely used in MMIC. Particularly, CPW has seen a rapid increase on research works recent years due to its unique capability including having less parasitic contribution to the circuit. In this thesis, a novel 3-D multilayer CPW technique is presented. Semi-insulating (S.I.) GaAs substrate, polyimide dielectric layers and Titanium/Gold metal layers are employed in this five-layer structure. The active devices are based on GaAs pHEMTs technology provided by Filtronic Compound Semiconductor Ltd. The fabricated components are simulated and characterized by Agilent Advanced Design System (ADS) and Momentum E.M simulator. A novel Open-short-through de-embedding technique is developed and applied to the passive circuits in order to reduce the impact of pads on probing. A new library of components and circuits are built in this work. Various structures of 3-D CPW transmission lines are designed and characterized to demonstrate the low-loss and highly compact characters. Meanwhile, the influence of various combinations of metal and dielectric layers is studied in order to provide designers with great flexibility for the realization of novel compact transmission lines for 3D MMICs. The effect of temperature on the performance of the transmission lines has also been investigated. Moreover, a set of compact capacitors are designed and proven to have high capacitance density with low parasitics. Finally, based on the extraction of pHEMT parameters from circuit characterization and analysis program (IC-CAP), RF switch and active filter MMICs have been designed and simulated to provide references for further development of 3-D multilayer CPW circuits.EThOS - Electronic Theses Online ServiceGBUnited Kingdo