Browsing by Subject "surface science"
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Item Chemisorption of Aromatic Compounds on Well-Defined Palladium Surfaces: Studies by Electron Spectroscopy and Electrochemistry(2010-10-12) Li, DingThe chemisorption of aromatic compounds, derivatized with different functional groups, on well-defined Pd(111) surfaces was studied by a combination of Auger electron spectroscopy (AES), low energy electron diffraction (LEED), high resolution electron energy loss spectroscopy (HREELS), and electrochemistry (EC). The results of this work led to the following trends and conclusions: (a) At low concentrations, 2,5-dihydroxythiophenol (DHT) chemisorbs on a Pd surface through both diphenolic ring and thiol group. At high concentrations, it chemisorbs only through the thiol group. (b) There is extensive intermolecular attraction between the co-adsorbed thiolated quinone and thiolated hydroquinone molecules. The interaction occurs through the Pd substrate and not through space. (c) The chemisorption properties of Nheteroaromatic compounds are pH-dependent. When the nitrogen heteroatom is protonated, it becomes very weakly surface-active. When the nitrogen heteroatom is deprotonated, surface activity stronger than the diphenolic ring is exhibited. (d) On a palladium surface, the binding strengths of ligands increase in the order: phenyl ring < quinonoid ring, < N-heteroatom < I < -SH.Item Micro- and nano- scale experimental approach to surface engineer metals(Texas A&M University, 2007-09-17) Asthana, PranayThis thesis includes two parts. The first part reviews the history and fundamentals of surface science and tribology. The second part presents the major research outcomes and contributions. This research explores the aspects of friction, wear, and surface modification for tribological augmentation of surfaces. An effort has been made to study these aspects through gaining insights by fundamental studies leading to specific practical applications in railroads. The basic idea was to surface engineer metals for enhanced surface properties. A micro- and nano- scale experimental approach has been used to achieve these objectives. Novel principles of nano technology are incorporated into the experiments. Friction has the potential to generate sufficient energy to cause surface reactions through high flash temperatures at the interface of two materials moving in relative motion. This allows surface modifications which can be tailored to be tribologically beneficial through a controlled process. The present work developed a novel methodology to generate a functional tribofilm that has combined properties of high hardness and high wear resistance. A novel methodology was implemented to distinguish sliding/rolling contact modes during experiments. Using this method, a super hard high-performance functional tribofilm with ????????????regenerative???????????? properties was formed. The main instrument used in this research for laboratory experiments is a tribometer, using which friction, wear and phase transformation characteristics of railroad tribo-pairs have been experimentally studied. A variety of material characterization techniques have been used to study these characteristics at both micro and nano scale. Various characterization tools used include profilometer, scanning electron microscope, transmission electron microscope, atomic force microscope, X-ray diffractometer, nanoindenter, and X-ray photon spectroscope. The regenerative tribofilms promise exciting applications in areas like gas turbines, automotive industry, compressors, and heavy industrial equipment. The outcome of this technology will be an economical and more productive utilization of resources, and a higher end performance.Item Surface spectroscopic characterization of oxide thin films and bimetallic model catalysts(2009-05-15) Wei, TaoOxide thin films and bimetallic model catalysts have been studied using metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), low energy ion scattering spectroscopy (LEISS), X ? ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) under ultra high vacuum (UHV) conditions. Of particular interest in this investigation was the characterization of the surface morphology and electronic/geometric structure of the following catalysts: SiO2/Mo(112), Ag/SiO2/Mo(112), Au?Pd/Mo(110), Au?Pd/SiO2/Mo(110), and Pd? Sn/Rh(100). Specifically, different types of oxide surface defects were directly identified by MIES. The interaction of metal clusters (Ag) with defects was examined by work function measurements. On various Pd related bimetallic alloy surfaces, CO chemisorption behavior was addressed by IRAS and TPD. Observed changes in the surface chemical properties during the CO adsorption-desorption processes were explained in terms of ensemble and ligand effects. The prospects of translating this molecular-level information into fundamental understanding of ?real world? catalysts are discussed.