As computational methods for the prediction of metallic nanoparticle structure and reactivity continue to advance, a need has developed for simple experimental models that can mimic and confirm theoretical predictions. Dendrimer-encapsulated nanoparticles, or DENs, are ideal to fill this role. DENs are synthesized within poly(amido amine) dendrimer templates which allows for the controlled synthesis of monodisperse nanoparticles in the 50-250 atom (1-2 nm) size range. These are small enough to be accessible to high-level theoretical calculations while being large enough to study experimentally. The research reported here consists of several independent but closely related studies. First, the synthesis, structural, and electrochemical properties of Au@Pt (core@shell) DENs are described. These materials are prepared by underpotentially depositing Cu onto Au DENs followed by galvanic exchange of Cu for Pt. Second, Pb UPD onto Au DENs and a detailed experimental and theoretical study of the resulting core@shell particle structures and catalytic activity is discussed. It is found that no matter how much Pt is deposited onto the surface of Au₁₄₇ DENs, a surface reorganization occurs resulting in similar electrocatalytic activity for the oxygen reduction reaction. Third, an in-depth X-ray absorption spectroscopy study of the structural properties of thiol-capped Au₁₄₇ DENs is described. Here, the surfaces of uncapped Au₁₄₇ nanoparticles are titrated with strongly binding thiol ligands to tune the extent of surface disorder. The effect of the increased surface disorder on the standard EXAFS fitting results is discussed from experimental and theoretical perspectives. Lastly, an in-situ electrochemical study of Au₁₄₇ DENs structure is reported. The key result is that the Au lattice expands during electrochemical surface oxidation. This is an important result for understanding electrocatalytic processes on Au nanoparticle / text

The synthesis and characterization of Pt core/ Cu shell (Pt@Cu) dendrimer-encapsulated nanoparticles (DENs) having full and partial Cu shells deposited via electrochemical underpotential deposition (UPD) is described. Pt DENs containing averages of 55, 147, and 225 Pt atoms immobilized on glassy carbon electrodes served as the substrate for the UPD of a Cu monolayer. This results in formation of Pt@Cu DENs. Evidence for this conclusion is based on results from the analysis of cyclic voltammograms (CVs) for the UPD and stripping of Cu on Pt DENs, and from experiments showing that the Pt core DENs catalyze the hydrogen evolution reaction before Cu UPD, but that after Cu UPD this reaction is inhibited. Results obtained by in-situ electrochemical X-ray absorption spectroscopy (XAS) confirm the core@shell structure. Calculations from density functional theory (DFT) show that the first portion of the Cu shell deposits onto the (100) facets, while Cu deposits lastly onto the (111) facets. The DFT-calculated energies for Cu deposition on the individual facets are in good agreement with the peaks observed in the CVs of the Cu UPD on the Pt DENs. Finally, structural analysis of Pt DENs having just partial Cu shells by in-situ XAS is consistent with the DFT-calculated model, confirming that the Cu partial shell selectively decorates the (100) facets. These results are of considerable significance because site-selective Cu deposition has not previously been shown on nanoparticles as small as DENs. In summary, the application of UPD as a synthetic route and characterization tool for core@shell DENs having well defined structures is established. A study of the degradation mechanism and degradation products of Pd DENs is provided as well. These DENs consisted of an average of 147 atoms per dendrimer. Elemental analysis and UV-vis spectroscopy indicate that there is substantial oxidation of the Pd DENs in air-saturated solutions, less oxidation in N₂-saturated solution, and no detectable oxidation when the DENs are in contact with H₂. Additionally, the stability improves when the DEN solutions are purified by dialysis to remove Pd²⁺-complexing ligands such as chloride. For the air- and N₂-saturated solutions, most of the oxidized Pd recomplexes to the interiors of the dendrimers, and a lesser percentage escapes into the surrounding solution. The propensity of Pd DENs to oxidize so easily is a likely consequence of their small size and high surface energy. Calculations from density functional theory (DFT) show that the first portion of the Cu shell deposits onto the (100) facets, while Cu deposits lastly onto the (111) facets. The DFT-calculated energies for Cu deposition on the individual facets are in good agreement with the peaks observed in the CVs of the Cu UPD on the Pt DENs. Finally, structural analysis of Pt DENs having just partial Cu shells by in-situ XAS is consistent with the DFT-calculated model, confirming that the Cu partial shell selectively decorates the (100) facets. These results are of considerable significance because site-selective Cu deposition has not previously been shown on nanoparticles as small as DENs. In summary, the application of UPD as a synthetic route and characterization tool for core@shell DENs having well defined structures is established. A study of the degradation mechanism and degradation products of Pd DENs is provided as well. These DENs consisted of an average of 147 atoms per dendrimer. Elemental analysis and UV-vis spectroscopy indicate that there is substantial oxidation of the Pd DENs in air-saturated solutions, less oxidation in N2-saturated solution, and no detectable oxidation when the DENs are in contact with H2. Additionally, the stability improves when the DEN solutions are purified by dialysis to remove Pd2+-complexing ligands such as chloride. For the air- and N2-saturated solutions, most of the oxidized Pd recomplexes to the interiors of the dendrimers, and a lesser percentage escapes into the surrounding solution. The propensity of Pd DENs to oxidize so easily is a likely consequence of their small size and high surface energy. / text

This work describes the synthesis of dendrimer-encapsulated nanoparticles (DENs) and the expansion of the characterization ability for these materials. The dendrimer-template method for the synthesis of nanoparticles allows precise control over the size, composition and structure of nanoparticles in the 40-250 atom range. In this size regime, the surface structure of the nanoparticles dominates their catalytic properties. The long term goal of this research is to correlate the structure of these nanoparticles to their catalytic activity, improving the ability to predict superior catalysts a priori. As a prerequisite for this analysis, the precise structure of the catalytically active nanoparticle must be determined. Characterization of nanoparticles in the 1-2 nm region is significantly more difficult than more commonly used nanoparticles of 3-5 nm diameter or larger. Typical characterization of these nanoparticles involves UV-vis spectroscopy for Mie absorbance and transmission electron microscopy for size analysis. This work involves the use of extended X-ray absorption-fine structure (EXAFS) to determine the local structure of the nanoparticles. For monometallic Pt DENs, EXAFS was combined with UV-vis, TEM, X-ray photoelectron spectroscopy (XPS) and electrochemistry to determine that the Pt system is not simply nanoparticles but a more complex, bimodal state. EXAFS has also been used to differentiate between different bimetallic structures. For PdAu DENs, there are two synthetic methods used. When both metals are reduced simultaneously, the resulting nanoparticles have a quasi-random alloy structure. These nanoparticles were then extracted from the dendrimer into an organic solvent by use of alkanethiols. The extraction process changed the alloy structure into Au-core/Pd-shell. When Pd and Au were reduced in sequence, the DENs were formed as a Au-core/Pd-shell material, regardless of the order of the reduction of the metals. The Au-core/Pd-shell structure was also present after extraction. In addition to structural analysis to determine the result of different synthetic methods, EXAFS was also used in situ to measure the structure of Pt DENs during the oxidation of absorbed CO. These in situ measurements are important for determining the structure of the actual catalyst rather than the precursor nanoparticle. In this case, the Pt DENs changed from a bimodal distribution into fully reduced nanoparticles by the application of a reducing potential. The binding of CO to the Pt DENs and subsequent oxidation did not cause measurable agglomeration of the nanoparticles. This reduction of the Pt system by electrochemical means was also explored as a synthetic method. The Pt-dendrimer complex was placed on a TEM grid for electrochemical treatment. A potential step was shown to reduce some of the Pt-dendrimer complexes into Pt nanoparticles of the expected size. However, most of the complexes were not reduced. Therefore, only the standard chemical reduction followed by electrochemical treatment is sufficient to fully reduce the nanoparticle samples. This work has explored additional synthetic methods for the synthesis of monometallic and bimetallic DENs. The use of EXAFS, as well as other advanced characterization techniques, has advanced knowledge of the structure of various DENs. Both the characterization toolset and the synthetic methods will provide a basis for investigations of catalytically active materials. / text

The focus of this diploma thesis is on theoretical basics of dynamic electroneurostimulation, which is an effect of electrical signal on acupuncture points of skin. This technology is used in devices made by russian DiaDENS company. Practical part of this thesis covers design of human skin impedance model. Especially derivation from three-element Cole-Cole model. Elementary, there is design of equivalent circuit of constant phase element and its incorporation into circuit. Then this circuit is designed, simulated and produced. Resulting product is used as a load to measure the characteristics of the DiaDENS device.

Where do beginner readers read in the English, mainstream primary school and where could they read? Emma Jane Dyer This thesis explores design for the beginner reader in Year One by evaluating existing spaces in the English primary school and imagining new ones. Three significant gaps identified in the literature of reading, the teaching of reading and school design are addressed: the impact of reading pedagogies, practices and routines on spatial arrangements for beginner readers inside and beyond the classroom; a theoretical understanding of the physical, bodily and sensory experience of the beginner reader; and the design of reading spaces by teaching staff. The study uses a design-oriented research methodology and framework proposed by Fällman. A designed artefact is a required outcome of the research: in this case, a child-sized, semi-enclosed book corner known as a nook. The research was organized in three phases. First, an initial design for the nook was created, based on multi-disciplinary, theoretical research about reading, school design and architecture. Secondly, empirical research using observation, pupil-led tours and interviews was undertaken in seven primary schools to determine the types of spaces where readers read: spaces that were often unsuitable for their needs. Thirdly, as a response to the findings of phases one and two, the nook was reconceived to offer a practical solution to poorly-designed furniture for reading in schools and to provoke further research about the ideal qualities of spaces for the beginner reader. The study demonstrates how the experience of the individual reader is affected by choices made about the national curriculum; by the size of schools and the spaces within them where readers can learn; by the design of classrooms by teachers; and by regulatory standards for teaching and non-teaching spaces. In developing a methodology that can stimulate and facilitate communication between architects, educators, policy-makers and readers, this thesis offers a valuable contribution to the ongoing challenge of improving school design for practitioners and pupils.