Browsing by Subject "gold"
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Item Electrochemical hydrogenation of aromatic compounds chemisorbed at polycrystalline and single-crystal Pd surfaces(2009-06-02) Sanabria-Chinchilla, JeanThe chemisorption and electrochemical hydrogenation of hydroquinone (H2Q) at polycrystalline (pc) Pd, well-ordered Pd(100), and Pd-modified Au(hkl) electrodes were studied using a combination of ultra-high vacuum (UHV) surface spectroscopy, electrochemistry (EC), and electrochemical mass spectrometry (EC-MS). H2Q was found to form a slightly tilted flat-oriented quinone (Q) adlayer, when adsorbed from low concentrations; when chemisorbed from high concentrations, an edgewise-oriented H2Q adlayer was indicated. The hydrogenation of the chemisorbed layer is initiated at potentials before the onset of the hydrogen evolution region. As expected, the kinetics increases as the applied potential is increased, but the hydrogenation pathway appears to be independent of the potential. Hydrogenation in the absence of absorbed hydrogen (sub-surface) was studied at ultra-thin Pd films on Au single-crystal substrates. Hydrogenation and/or potential induced desorption were established, although non-volatile and/or hydrophobic products were detected. In comparison, negative excursions with benzene-coated electrodes resulted in nothing more than potential-induced desorption of the starting material. Negative-potential electro-desorption was more facile at terraces than at steps. Vibrational spectroscopic measurements suggested that hydrogenation occurs one molecule at a time to the fullest extent that resulted in desorption of product; that is, partially hydrogenated species do not exist on the surface.Item Heteroepitaxial Self Assembling Noble Metal Nanoparticles in Monocrystalline Silicon(2013-08-13) Martin, Michael S.Embedding metal nanoparticles in crystalline silicon possesses numerous possible applications to fabricate optoelectronic switches, increase efficiency of radiation detectors, decrease the thickness of monocrystalline silicon solar panels and investigate fundamental properties. Noble metal nanoparticles made of gold or silver are grown in cavities in monocrystalline silicon formed by helium ion implantation and high temperature annealing at depth greater than 500 nm from the surface. Metals are introduced into the system by low energy ion implantation or physical vapor deposited thin film on the surface, and diffused into cavities by heat treatment. Nanoparticles nucleate on the inner surface of cavities heteroepitaxially and form face centered cubic crystal structure in the case of silver. Excessive heat treatment causes metal to be emitted from nanoparticles into bulk after trapping and nanoparticle formation. Helium ion implantation, annealing and diffusion heat treatment conditions have been optimized so that residual crystalline damage, point defects and dislocations, is reduced in monocrystalline silicon substrate.Item Laser-assisted scanning probe alloying nanolithography (LASPAN) and its application in gold-silicon system(2009-05-15) Peng, LuohanNanoscale science and technology demand novel approaches and new knowledge to further advance. Nanoscale fabrication has been widely employed in both modern science and engineering. Micro/nano lithography is the most common technique to deposit nanostructures. Fundamental research is also being conducted to investigate structural, physical and chemical properties of the nanostructures. This research contributes fundamental understanding in surface science through development of a new methodology. Doing so, experimental approaches combined with energy analysis were carried out. A delicate hardware system was designed and constructed to realize the nanometer scale lithography. We developed a complete process, namely laser-assisted scanning probe alloying nanolithography (LASPAN), to fabricate well-defined nanostructures in gold-silicon (Au-Si) system. As a result, four aspects of nanostructures were made through different experimental trials. A non-equilibrium phase (AuSi3) was discovered, along with a non-equilibrium phase diagram. Energy dissipation and mechanism of nanocrystalization in the process have been extensively discussed. The mechanical energy input and laser radiation induced thermal energy input were estimated. An energy model was derived to represent the whole process of LASPAN.Item Mechanical Evaluation of Electronic Properties of Materials(2011-05-02) Nudo, NicholasThe present research focuses on the coupling of mechanical and electrical properties of materials and culminates in a direct connection between applied strain to thin-films, thin-film electron binding energy, the energy loss via plastic deformation provided by an indentation, and the substrate resistance. The methods used in this research include X-ray photoelectron spectroscopy (XPS), nanoindentation, digital optical microscopy, and sputter coat deposition. It is discovered that there is a shift in electron binding energy on the scale of 0.2 eV to 1.4 eV in gold and palladium thin-films sputtered on polyvinylidene fluoride (PVDF) through the application of strain induced by a convex shape. There is a change in the area beneath the load-displacement curve measured via indentation from 5.55 x 10^-10 J to 4.78 x 10^-10 J when the gold-palladium thin-film sputtered on PVDF is changed from the flat arrangement to the convex arrangement. Furthermore, the strain also changed the electrical resistance of aluminum foil, which indicates that the substrate electrical resistance is affected by the induced strain. The internal resistance of a circuit developed for this research changed from 7.76 ohms for flat samples to 8.03 ohms and 8.33 ohms for flat and convex samples, respectively. It is expected that the research can be used to estimate the strain in nanogears and other devices at small length scales.Item Synthesis and Study of Boron and Antimony Lewis Acids as Small Anion Receptors and Ligands Towards Transition Metals(2012-02-14) Wade, CaseyAlthough fluoride is used at low concentrations in drinking water as a means of promoting dental health, it poses a danger at high exposure levels where it can lead to skeletal fluorosis or other adverse effects. Cyanide is notoriously toxic, and its large scale use in industrial processes warrants the need for close monitoring to remain aware of potential contamination of water sources and other environmental resources. Based on these considerations, it is critical to continue to develop improved methods of monitoring fluoride and cyanide concentrations in water. However, molecular recognition of these anions in water poses considerable challenges. For fluoride, this is due largely to its high hydration enthalpy (?Ho = -504 kJ mol-1), which drastically reduces its reactivity in water. Additionally, the strong basicity of cyanide (pKa of (HCN) = 9.3) may obscure its detection in neutral water due to protonation. In addition to achieving detection of these anions in water, it is most desirable to have information of the detection event relayed in the form of a positive, rather than negative, response (i.e., turn-on vs turn-off). The general strategy of appending cationic groups to triarylboranes imparts beneficial Coulombic, inductive, and sometimes chelate effects that have allowed a number of these Lewis acidic receptors to sense fluoride and cyanide in aqueous environments. With the goal of developing new triarylborane-based receptors that show enhanced affinities for these anions, as well as turn-on responses to detection, a series of pyridinium boranes were synthesized and studied. Having recognized that the inherent Lewis acidity of antimony(V) species might be exploited for anion sensing, we also describe initial studies on the ability of tetraorganostibonium ions (R4Sb+) and cationic transition metal-triarylstibine complexes (R3SbM+) to complex fluoride. Finally, the electropositivity of antimony and its ability to form stable compounds in both the +3 and +5 oxidation states have led us to begin investigations into the bonding and redox reactivity of novel metal stibine/stiborane complexes.