Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 145-153). Also available on the World Wide Web.

Thesis (M.Mat.S.E.)--University of Delaware, 2007. / Principal faculty advisor: Robert L. Opila, Dept. of Materials Science & Engineering. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 178-188).

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Made available in DSpace on 2014-10-09T12:33:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:33:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / O presente trabalho realiza a investigação dos parâmetros hiperfinos, incluindo a sua natureza dinâmica, em compostos ligantes em solução a temperatura ambiente (295 K) e resfriada (77K) através da espectroscopia de Correlação Angular γγ Perturbada (CAP). Para a realização das medidas experimentais, utilizou-se núcleos de prova radioativos de 111In111Cd, 181Hf181Ta e 111mCd111Cd, que decaem através de cascata gama. As amostras foram preparadas diluindo-se soluções com os núcleos radioativos em água, quando se investigou a interação do núcleo de prova com o ligante água; adicionando-se soluções com os núcleos radioativos em solução tampão, quando se investigou a interação do núcleo de prova com os íons ligantes provenientes do próprio tampão (CO32- e HCO31-) e com o OH1-; e adicionando-se soluções com os núcleos radioativos em soluções do ligante ácido etilenodiaminotetracético (EDTA), este em pH entre 4,0 e 5,0, (que corresponde ao pH da própria solução saturada do EDTA) e em solução tampão de pH entre 9 e 10. Assim foi possível investigar os efeitos gerados por cada um desses métodos de preparação de amostras nas medidas CAP. Finalmente foi feita uma análise comparativa para os vários métodos de inserção dos núcleos de prova na amostra, considerando-se aspectos químicos e nucleares. A inexistência de medidas para esse tipo de amostra, justifica a importância dos resultados obtidos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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The coupling between longitudinal-optical (LO) phonons and neutral excitons in two different kinds of InGaAs pyramidal quantum dots embedded in either AlGaAs or GaAs barriers is experimentally examined. We find a slightly weaker exciton-LO-phonon coupling and increased linewidth of the phonon replicas for the quantum dots with GaAs barriers compared to the ones with AlGaAs barriers. These results, combined with the fact that the LO-phonon energy of the exciton is the same for both kinds of dots, are taken as evidence that the excitons mainly couple to LO-phonons within the QDs. / Original Publication:Daniel Dufåker, L. O. Mereni, Fredrik K. Karlsson, V. Dimastrodonato, G. Juska, Per-Olof Holtz and E. Pelucchi, Exciton-phonon coupling in single quantum dots with different barriers, 2011, Applied Physics Letters, (98), 25, 251911.http://dx.doi.org/10.1063/1.3600781Copyright: American Institute of Physicshttp://www.aip.org/

The objective of the proposed research is to establish the technology for material growth by molecular beam epitaxy (MBE) and fabrication of indium gallium nitride/gallium nitride (InxGa1-xN/GaN) heterojunction solar cells. InxGa1-xN solar cell have the potential to span 90% of the solar spectrum, however there has been no success with high indium (In) incorporation and only limited success with low In incorporation InxGa1-xN. Therefore, this present work focuses on 15 - 30% In incorporation leading to a bandgap value of 2.3 - 2.8 eV. This work will exploit the revision of the indium nitride (InN) bandgap value of 0.68 eV, which expands the range of the optical emission of nitride-based devices from ultraviolet to near infrared regions, by developing transparent InxGa1-xN solar cells outside the visible spectrum. Photovoltaic devices with a bandgap greater than 2.0 eV are attractive because over half the available power in the solar spectrum is above the photon energy of 2.0 eV. The ability of InxGa1-xN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics. Using the metal modulated epitaxy (MME) technique in a new, ultra-clean refurbished MBE system, an innovative growth regime is established where In and Ga phase separation is diminished by increasing the growth rate for InxGa1-xN. The MME technique modulates the metal shutters with a fixed duty cycle while maintaining a constant nitrogen flux and proves effective for improving crystal quality and p-type doping. We demonstrate the ability to repeatedly grow high hole concentration Mg-doped GaN films using the MME technique. The highest hole concentration obtained is equal to 4.26 e19 cm-3, resistivity of 0.5 Ω-cm, and mobility of 0.28 cm2/V-s. We have achieved hole concentrations significantly higher than recorded in the literature, proving that our growth parameters and the MME technique is feasible, repeatable, and beneficial. The high hole concentration p-GaN is used as the emitter in our InxGa1-xN solar cell devices.

For polymer-matrix composites (PMCs) that contain insulating matrices and conducting fillers, the electrical properties of the PMCs are especially sensitive to the local concentration of the fillers in the matrix. For PMCs that have phase-segregated microstructures, better prediction of the properties is possible since enhanced control over the distribution of the filler in the matrix can be achieved. In this research, PMMA-ITO nanocomposites were chosen as the composite system in which to explore alternative microstructures, specifically highly phase-segregated microstructures. The microstructures were primarily controlled by varying the ITO particle size and concentration, and the fabrication parameters used to form the nanocomposites. The motivation for this research was to develop correlations between the microstructure and non-destructive measurements in order to improve the predictability of properties in percolating PMCs. As a result of this work, a novel phase-segregated microstructure was discovered, where ITO aggregate-wire structures self-assembled during the composite forming process. Structural analysis of the specimens was conducted primarily using transmission optical microscopy and scanning electron microscopy (SEM). Impedance spectroscopy and optical spectroscopy were the primary NDE characterization tools used for analyzing the variations among the specimens. Ultra-small angle x-ray scattering (USAXS) and stereological techniques were also used to describe the dimensions of the ITO aggregate-wire structures that self-assembled in the PMMA-ITO nanocomposites.