Made available in DSpace on 2014-10-09T12:29:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:22Z (GMT). No. of bitstreams: 1 00377.pdf: 1144428 bytes, checksum: ff90dddba23a57911d88d08a78e8557f (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Energia Atomica - IEA

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The syntheses of octasubstituted and unsusbstitituted Gallium(III) chloride and indium(III) chloride phthalocyanines (GaPc and InPc), their photophysical, photochemical and nonlinear optical parameters are hereby presented. The photocatalytic oxidation of 1-hexene using the synthesized GaPc and InPc complexes as well as electrochemical characterization is also presented in this thesis. Fluorescence quantum yields do not vary much among the four Ga complexes, except for complex 21c; therefore it was concluded that the effect of substituents is not significant among them. Solvents however, had an effect on the results. Lower Φ[subscript F] values were obtained in low viscosity solvents like toluene, relative to highly viscous solvents, such as DMSO. The triplet quantum yields were found to be lower in DMSO than in DMF and toluene. The rate constants for fluorescence, intersystem crossing and internal conversion as well as fluorescence and triplet lifetimes are reported. Photodegradation and singlet oxygen quantum yields have also been reported. There was no clear correlation between the latter parameters. It was however established that the four gallium MPcs were stable, within the allowed stability range for phthalocyanines. High quantum yields of triplet state (Φ[subscript T] ranging from 0.70 to 0.91 in dimethysulfoxide, DMSO) and singlet oxygen generation (Φ[subscript greek capital letter delta], ranging from 0.61 to 0.79 in DMSO) were obtained. Short triplet lifetimes 50 to 60 μs were obtained in DMSO). Calculated non-linear parameters of these complexes are compared with those of the corresponding GaPc derivatives and tetrasubstituted GaPc and InPc complexes. The optical limiting threshold intensity (I[subscript lim]) values for the InPc and GaPc derivatives were calculated and compared with those of corresponding tetrasubstituted InPc and GaPc complexes. The octasubstituted were found to be better optical limiters. Photocatalytic oxidation of 1-hexene by GaPc (21a-c) and InPc (22a-c) derivatives is also presented. The photocatalytic oxidation products for 1-hexene were 1,2- epoxyhexane and 1-hexen-3-ol. The % conversion values of 1-hexene and % selectivity of 1,2-epoxyhexane were generally higher for InPc derivatives. Even though InPc derivatives showed better photocatalytic results than GaPc derivatives, the former were less stable relative to the latter. Both type I and type II mechanism were implicated in the photocatalysis mechanism.

In this thesis, the effects of various chemical treatments on the surface modification of bulk InAs are investigated. The study focuses on the chemical processes that occur upon the exposure of the surface to sulphur-, chlorine- and bromine-containing solutions and oxygen, and the resulting changes to the electronic structure of the surface, as deduced from photoluminescence (PL) measurements, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Raman scattering and scanning electron microscopy (SEM). Three processing treatments were evaluated: i) treatment with sulphur-based solutions (Na2S:9H2O, (NH4)2S + S, [(NH4)2S / (NH4)2SO4] + S); ii) etching in halogen-based solutions (bromine-methanol and HCl: H2O); and iii) thermal oxidation. A significant overall enhancement in PL response was observed after chemical treatment or thermal oxidation, which is associated with a reduction in surface band bending. These changes correlate with the removal of the native oxide, in addition to the formation of well-ordered layers of In-S (or In-As)O as a passivating layer, indicating that electronic passivation occurs at the surface. The passivating effect on sulphide treated surfaces is unstable, however, with an increase in band bending, due to reoxidation, observed over periods of a few days. The lowest re-oxidation rate was observed for ([(NH4)2S / (NH4)2SO4] + S). Etching in HCl:H2O and Br-methanol solutions of appropriate concentrations and for moderate times (1 min) resulted in smooth and defect-free InAs surfaces. Etching completely removed the native oxides from the surface and enhanced the PL response. The adsorption of bromine and chlorine onto the InAs surface led to the formation of As-Brx , In-Brx, As-Clx and In-Clxcompounds (x = 1, 2, 3), as inferred from changes in the In 3d3/2; 5/2 and As 3d core level binding energies. The etch rate was found to decrease because of strong anisotropic effects. The improvements in surface properties were reversed, however, if the concentrations of the etchants increased or the etch time was too long. In the worst cases, pit formation and inverted pyramids with {111} side facets were observed. Surface treatments or thermal oxidisation significantly enhanced the PL intensity relative to that of the as-received samples. This was due to a reduction in the surface state density upon de-oxidation, or in some cases, to the formation of a well ordered oxide layer on the surface. The overall increase in PL intensity after treatment is ascribed to a reduction in band bending near the surface. This allows several welldefined peaks not observed or reported previously for bulk InAs (with a carrier concentration n~2x1016 cm-3), to be studied. A combination of PL and XPS measurements before and after the various treatments was used to identify the chemical nature of the impurities giving rise to bound exciton recombination in InAs (111).

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

No description available.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

This dissertation presents the results of experimental research on the nonlinear refraction in InSb and the experimental demonstration of two nonlinear etalon devices using InSb as the active material. The first portion of the dissertation considers the Dynamic Burstein-Moss Shift model for nonlinearities in narrow-gap semiconductors. The physics and the equations are reviewed, and limitations in describing intensity dependent refraction in a semiconductor are considered. These limitations arise from the nonlinear dependence of charge carrier density upon irradiance. The second portion of the dissertation presents experimental measurements made on the nonlinear refraction of InSb at temperatures between 80 K and 182 K, for wavelengths from 5.75 μm to 6.10 μm, where the photon energy lay in the band tail below 100 cm⁻¹. Measurements of the linear absorption were first made with an infrared spectrometer for temperatures from 80 K to 300 K. The nonlinearity was measured by analyzing the transmission through InSb etalons. Nonlinear transmission curves were digitized and stored with an IBM PC-XT, then a curve fit was performed using the nonlinear refractive index as a fiting parameter. Observations are reported of increasing absorption, due in part to a thermal shift of the absorption edge. The second portion of the work presents the theory and demonstration of a bistable etalon using an edge-injected control beam. Plane-wave nonlinear etalon theory is used to describe the operation of such a device, illustrating the way in which switching and logic gate operation can be obtained. Two devices based on this concept are demonstrated: the 3-port device using a single control beam, and the 2SON gate using two control beams to perform two-input logic operation. The extension of the 2SON gate to an array of pixels, and some considerations for optimizing array performance, are considered. Two appendices follow the body of the dissertation, the first describing the preparation of the InSb etalon samples, and the second detailing several procedures for maintenance and operation of the CO laser used.

No description available.