The electronic structure and optical properties of metallic nanoshells are theoretically investigated. An efficient implementation of the Time Dependent Local Density Approximation creates the possibility of applying ab initio calculations to real size metallic nanoshells for which experimental data are available. It is proven that, when the dielectric effects of the core, embedding medium and d-electrons are taken into account, the ab initio calculations reproduce the experimentally measured photo-absorption cross section of these unique nanoparticles.

This work reports the successful production of macroscopic assemblies of aligned single walled carbon nanotubes (SWNTs) via filtration in a magnetic field of 25 Tesla. Such assemblies allow an unprecedented capability to characterize and manipulate aligned nanotubes. Surface areas in excess of 100 cm 2 and thicknesses in excess of seven microns thick were produced. A density within a factor of two of close packing was achieved. These assemblies exhibit anisotropy in reflection of polarized light, Raman resonance, electrical transport, and thermal transport. This provides a macroscopic window to exploring the properties of SWNTs and paves the way for many potential applications. This thesis also describes experiments using a combination of electrical and chemical methods, including DC electric fields, amine-derivatization of gold, and thiol-derivatization of SWNTs. These latter experiments preceded the filtration work and provided an essential basis for conceptualizing the successful filtration approach.

An apparatus has been developed for studying the interaction of Rydberg atoms with surfaces, particularly the perturbation of Rydberg states by a nearby surface and the distance from the surface at which resonance ionization occurs. For this purpose, a source of metastable Xe(3P 0,2) atoms was constructed and characterized. Using single photon laser excitation from the 6s'[1/2]0 state, the nf[3/2]1 Rydberg series for n = 16--20 has been observed with signals well above the background. Measurements of the energy levels of these Rydberg states has identified systematic errors in quoted energy levels from earlier work. The isotopic structure of the 20f Rydberg state was resolved, and the effect of Rydberg excitation in an electric field was investigated. Studies are underway to better understand the behavior of Xe(nf) Rydberg atoms in an electric field. This information will be used in subsequent experiments to study Rydberg-surface interactions.

Metal nanoshells consist of a spherical dielectric core surrounded by a metallic shell. The fabrication of silver nanoshells is experimentally described and quantified using Mie scattering theory. These particles are used as surfaced enhanced Raman scattering (SERS) substrates at an excitation wavelength of 1.06 □m. This represents the first time silver particles in solution have been used as SERS substrates at this wavelength. Enhancement factors on the order of 1 x 106 are observed. It is also demonstrated that silver colloidal aggregates deposited on a large silica particle are sufficient to move the surface plasmon to the infrared for surface enhanced Raman spectroscopy. The measured enhancement factors were on the order of 4 x 105. The use of SnCl2 in functionalizing a silica surface as a precursor for metal nanoshell growth is explored along with theoretical calculations of the optical extinctions for nanoshells using different metals, such as copper, nickel, or platinum.

Spin-polarized ion neutralization spectroscopy (SPINS), in which a beam of electron-spin-polarized He+ ions is directed onto a surface and analysis is done of the electrons ejected from the surface as a result of ion neutralization, is a unique tool for surface studies that has unparalleled surface specificity. Using SPINS, we have discovered that the polarization of electrons ejected from Au(100) and Cu(100) is strongly correlated with incident ion polarization. The incident ion, in essence, locally magnetizes the surface, creating a net polarization in the local occupied density of states on the surface. Recent experiments on a CO2-covered surface are also described. The results from these experiments cannot be explained using the traditional Auger or Penning processes. A model is proposed in which the He+ forms a collision complex with one or more CO 2 molecules in the surface layer, making it energetically possible for an electron to be ejected.

Spin-polarized ion neutralization spectroscopy (SPINS), in which a beam of electron-spin-polarized He+ ions is directed onto a surface and analysis is done of the electrons ejected from the surface as a result of ion neutralization, is a unique tool for surface studies that has unparalleled surface specificity. This technique has been used in studies described in this thesis of Mg surfaces and rare gas van der Waals solids. The possibility of plasmon excitation in He+ ion neutralization at Mg has been investigated, but this process is found to be unlikely. Instead, the mechanism for ion neutralization appears to be resonance neutralization followed by electron ejection through Auger deexcitation. Experiments at frozen Xe surfaces found that ion neutralization proceeds by an Auger neutralization-type process above the surface, while experiments at frozen Kr are explained by the formation of two types of collision complexes at the surface, one ejecting an electron by double ionization of a surface atom, the other by single ionization of two surface atoms.

This thesis investigates the interactions between inicrostructural properties and flow conditions in polymeric solutions and in emulsions. An efficient algorithm is presented for Brownian dynamics simulations of semiflexible bead-rod chains with configuration-dependent anisotropic bead friction tensor. The algorithm for the dynamics and the stress generalizes an earlier one restricted to isotropic, configuration-independent friction (Grassia and Hinch 1996); it is based on Morse's (2004) theory of constrained Brownian motion. The dynamics and the non linear viscoelasticity of dilute solutions of semiflexible polymers in shear flow are studied. The effects of chain stiffness and flow strength on the configurational and material properties of semiflexible polymers are discussed. It is shown that such molecules shrink in shear flow and assume highly bent configurations, due to a buckling instability. A theory to predict the onset of strong buckling is presented; according to this theory, worm-like polymer molecules transition from rod-like to flexible-like behavior. The theory is verified by Brownian dynamics, which show a decrease of the average end-to-end distance in flow and a transition from rod-like to coil-like of the shear thinning power law exponent. The dynamics of the collapse of a single, semiflexible polymer in a poor solvent are investigated via Brownian dynamics simulations. The rate of decay of uncollapsed states, the preferential pathways of condensation, and the likelihood and lifespan of the different metastable states are analyzed. The collapsed states are described quantitatively through the spatial correlation of tangent vectors along the chain. The viscoelastic behavior of attractive and repulsive emulsions is compared, to understand the effect of the interaction forces between droplets, and the interplay between microstructural features and rheological properties. The salient finding is that caged attractive emulsions show a viscosity plateau at intermediate shear rate, and the first normal stress difference N1 transitions sharply from nearly zero to negative in this region. Correspondingly, cylindrical flocs form, align along the vorticity, and undergo a logrolling movement. An analysis of the interplay between steric constraints, attractive forces, and composition explains this behavior.

We have used the density functional ab initio method to conduct investigations on the effects of an applied electric field on the chemisorption bonds of adsorbate-surface systems, and on the reactivity of a gas phase semiconductor cluster. In STM current-induced excitation of adsorbates, lateral energy transfer among adsorbates tend to delocalize the excitation, and reduce resolution. We show that the strength of chemical bonds can be increased or decreased depending on the strength and direction of the applied electric field. By shifting the excitation energy of an adsorbate below the tip, energy transfer away from the site can be inhibited, and thereby lead to adsorbate excitation localization. The details of the field-induced shifts of an adsorbate-surface bonding features are shown to depend on their dipolar polarization. In the case of the reactivity of GaAs clusters with ammonia, recent experiments indicate that NH$\sb3$ adsorption rate depends strongly on cluster size, Ga/As composition ratio, and cluster charge state. We characterize the reactivity of NH$\sb3$ at various sites of a $\rm Ga\sb5As\sb5$ cluster in terms of the adsorbate binding energy and charge transfer, showing a strong correlation between the two. The dependence of the cluster reactivity on its charge state is deduced.

Spin-labeling techniques, specifically using electron-spin-polarized 4He+ ions coupled with energy-resolved measurements of the polarization of ejected electrons, are providing significant insight into surface electronic states and the dynamics of the neutralization of charged particles at clean and adsorbate-covered metal surfaces. The electronic structure of surfaces and the process by which charged particles electrically interact with such surfaces are of fundamental interest, yet only partially understood. A powerful technique for studying surface states and interactions has been Ion Neutralization Spectroscopy, in which noble gas ions are directed into a surface, where they are neutralized by electrons from the surface. Energy conservation causes other electrons to be emitted, which are collected and their energy distributions analyzed. Because neutralization takes place outside the surface, this technique serves as a sensitive probe of that part of the material. The current studies expand this technique by analyzing spin-aspects of the interaction. Spin-polarized He+ ions are produced in a radio-frequency driven discharge and directed at selected surfaces. Emitted electrons are analyzed with a retarding grid energy analyzer to determine their energy distributions and a mott polarimeter to measure their spin polarization. Correlating the spins of the outgoing electrons and incoming ions provides previously unavailable information about the dynamics of this reaction. Analysis of the energy distributions and polarization of electrons emitted from Au(100), Cu(100), and Al(100) indicate that neutralization occurs at distances closer to the surface than previously believed, and that for the period during which the ion is close to the surface, its presence causes a spin-dependent perturbation in the local density of electronic states---in essence, it locally magnetizes the surface. Further, the data indicate that surface plasmon excitation, a prominent feature in several theoretical models, does not appear to play a significant role in ion neutralization. Polarization data collected on alkali-covered surfaces clarify the dynamics by which the neutralization process takes place, while CO2 surface studies reveal that the ions undergo a previously unexamined neutralization mechanism which should apply to a broad range of van der Waals solids.

Metal nanoshells consist of a dielectric or semiconducting core coated with a metallic layer of nanometer scale dimensions. Gold nanoshells with silica cores were fabricated by first attaching gold colloid to the surface of the silica spheres and then developing the attached gold into a complete shell. This technique formed continuous gold shells approximately 10 nm thick. By varying the relative dimensions of the core and the shell, the optical resonance of these nanoparticles can be varied over hundreds of nanometers in wavelength, extending from the visible into the infrared region of the spectrum. For a gold nanoshell with a 340 nm core, at shell thicknesses exceeding 15 nm, additional peaks appeared in the UV-visible spectrum. Calculations based on a vector basis solution to Maxwell's equations matched both the position and relative magnitude of these secondary peaks.