Browsing by Author "Wolfgang, John A."
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Item Hot electron dynamics and impurity scattering on gold nanoshell surfaces(2000) Wolfgang, John A.; Nordlander, Peter J.Recent ultrafast pump-probe experiments studying the relaxation rate of an optically excited hot electron distribution on Au/Au2S gold nanoshells indicate that this relaxation rate can be modified by the chemical environment surrounding the shell. This work will begin a theoretical investigation of the effect of chemical adsorbates---solvents and impurities---upon nanoshell hot electron dynamics. The effects of water, polyvinyl alcohol (PVA), sulfur, p-aminobenzoic acid, p-mercaptobenzoic acid and propylamine adsorbates are examined for their electronic interaction with a noble metal surface. p-Aminobenzoic acid is found to have a very large dipole moment when adsorbed to the metal surface, in contrast to p-mercaptobenzoic acid, propylamine and water. This correlates well to the experimentally observed results where nanoshells dispersed in an aqueous soulution with p-aminobenzoic acid display a faster relaxation rate compared to nanoshells dispersed in a pure water, aqueous propylamine or aqueous p-mercaptobenzoic acid environments. This thesis will also introduce a non-equilibrium Green's function approach, based on the formalism developed by Baym and Kadanoff, to model the dynamics of a hot electron distribution. The model will be discussed in terms of a simple potential scattering mechanism, which may in later work be expanded to include more complex electron-electron and electron-phonon interactions. Lastly acoustic oscillation modes are calculated for solid gold spheres and gold-silicon nanoshells. These modes describe an effect of electron-phonon coupling between the hot electron distribution and the nanoshell lattice, whereby the electronic energy is converted into mechanical energy.Item Inelastic ion scattering from semiconductor surfaces(2000) Wolfgang, John A.; Nordlander, Peter J.Recent experimental investigations into charge transfer during ion/semiconductor surface collisions indicate dependence of the scattered ion's neutralization probability upon the target surface's local electronic environment along the scattered ion trajectory. This work presents qualitative modeling of these experiments demonstrating how the target surface's local electrostatic potential and charge density modify the scattered ion's neutralization rates. These models have been applied to Ne+ scattering and S- recoil from CdS {0001} and {0001¯} surfaces as well as Ne + scattering from intrinsic, n- and p-doped Si(100)-(2x1) surfaces. Correlation between electrostatic surface potential and ion neutralization probability has been shown for ion scattering from the CdS surfaces. Ne + neutralization during scattering from the Si(100)-(2x1) surface correlates to local surface charge density along the ion trajectory. Variations in ion neutralization rate for the intrinsic, n- and p-doped surfaces have been correlated to band bending at the Si surface.