published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Physics / Doctoral / Doctor of Philosophy

The semiconductor industry is continually challenged to maintain the trend identified in 1965 by Gordon Moore of increasing the density of transistors on an integrated circuit. These advances have been achieved by increasing the resolution that can be printed with photolithography, traditionally by decreasing the exposure wavelength. Decreasing the exposure wavelength from 193 nm, the current state of the art, presents significant technical challenges. To circumvent these challenges, resolution can be increased by enabling increases in numerical aperture (without changing the exposure wavelength), using immersion lithography. In immersion lithography, the air gap between the photoresist-coated wafer and lens is replaced with a high refractive index fluid. Immersion lithography has been demonstrated with water as the immersion fluid. With water immersion lithography at 193 nm, the maximum resolution that can be printed can be decreased from 65 nm to 45 nm. To enable further resolution increases, immersion fluids with a higher index than water are needed. The requirements for next generation high index fluids are: an index of refraction higher than water, high transparency, and physical properties similar to water. A variety of methods to identify a high index fluid were completed. First, the optical properties of aqueous solutions of metal cations with varying anions were tested. A series of linear, cyclic, and polycyclic alkanes were also studied, since saturated systems have electronic transitions at wavelengths less than 200 nm, to provide the necessary transparency at 193 nm. Large alkane groups were also incorporated into either the cation or anion of a salt to develop an aqueous solution with the optical properties of a saturated hydrocarbon. In addition to these empirical surveys, a modeling approach was used to develop “designer” absorbance spectra that would correspond to fluids with a high index and low absorbance at 193 nm. Additionally, in Appendix D, the results of an electrochemical study of the diffusion coefficient of ferrocene methanol in poly(ethylene glycol) diacrylate hydrogels of varying molecular weight and water content will be presented. The results of these mass transport studies can be used to qualitatively understand the mass transport characteristics of additional species in the hydrogel. / text

The number of skin cancer cases reported in the United States is increasing every year and nearly equals the total cancer cases detected from every other part of the body. Current detection strategies of skin cancers include a visual examination followed by a tissue biopsy. This procedure is subjective, invasive and time-consuming. Therefore, considering the number of cancer cases reported and the number biopsies performed, there is a critical need for a non-invasive diagnostic aid to help clinicians reduce the significantly large numbers of unnecessary biopsies. This dissertation presents a quantitative method based on optical spectroscopy for performing a non-invasive ‘optical biopsy’ of melanoma and non-melanoma skin cancers. We have developed the hardware, software and optical algorithms necessary to implement such a device. First, we present a novel lookup table-based model for determining the optical properties of tissue that is valid for fiber-based probe geometries with close source-detector separations and in highly absorbing tissue. These optical properties are quantitative parameters that can be correlated with the physiology of tissue. Second, we present experimental validation of the effects of microvasculature pigment packaging on diffuse reflectance spectra. We have conducted experiments using microfluidic devices over a physiologically relevant range of optical properties and blood vessel sizes. Third, we present the development of a probe-based portable and clinically compatible instrument capable of in vivo spectral measurements. The instrument combines two modalities – diffuse reflectance and intrinsic fluorescence spectroscopy – to provide complementary information regarding tissue morphology, function and biochemical composition. Finally, we present the results of a pilot clinical study using our portable instrument to determine the accuracy of spectral diagnosis of non-melanoma skin cancers. Our results show that the mean optical properties and fluorophore contributions of normal skin and non-melanoma skin cancers are significantly different from each other and can potentially be used as biomarkers for non-invasive diagnosis of skin cancer. / text

No description available.

This work involves the synthesis of two types of electro-optic monomers and their corresponding polymers. The first type of monomers contain the p-oxy-α-cyanocinnamate structure and were synthesized from ω-hydroxyalkoxy-substituted benzaldehydes and methyl cyanoacetate. These ω-hydroxy-α-cyanoester monomers show a high degree of electron delocalization. Copolyesters were synthesized by copolymerization of these monomers with methyl 12-hydroxydodecanoate by the standard two-stage, high-temperature polyesterification procedure. The copolyesters, incorporating dipolar units all pointing in the same direction, are soluble and solution- and melt-processable. Second harmonic generation (SHG) measurements on chloroform solutions of the copolymers showed enhancements of χ² as large as 20 relative to the dipolar monomers. These are the first known readily soluble main chain polymers that exhibit SHG behavior. The second type of monomers were acrylates containing substituted phenyl esters of benzoic acid as mesogenic (pendant) groups. Specifically, the mesogenic group contained an oxy-aryl-carboxy-aryl-carboxy-alkyl structure separated from the acrylate carbon-carbon double bond by a spacer group, which had a carboxyethyl-carboxyhexyl structure. A synthetic route was established by synthesizing a model monomer containing a 2-methylpropyl group as the alkyl group at the end of the mesogenic group. The model monomer was polymerized free radically and the resulting polymer found to possess a smectic liquid crystalline phase that became isotropic at 103° C. With the synthetic route established, an optically active monomer containing a (S)-2-methyl-1-butyl group as the alkyl group at the end of the mesogenic group was synthesized and polymerized. The optically active polymer was already in a smectic liquid crystalline phase at room temperature (≈25° C) and the phase persisted up to 72.6° C. These results indicate that it is possible to design polymers containing thermotropic liquid crystalline phases by fixing low molecular weight liquid crystalline molecules to a polymer main chain.

The nonlinear optical properties of a semiconductor-doped glass (SDG) channel waveguide were measured on a picosecond time-scale; namely, fluence-dependent changes in the absorption and the refractive index as well as the relaxation time of the nonlinearity. Slower, thermally-induced changes in the refractive index were also observed. The saturation of the changes in the absorption and the refractive index with increasing optical fluence is explained using a plasma model with bandfilling as the dominant mechanism. The fast relaxation time of the excited electron-hole plasma (20 ps) is explained using a surface-state recombination model. A figure of merit for a nonlinear directional coupler fabricated in a material with a saturable nonlinear refractive index is presented. The measured nonlinear change in the refractive index of the SDG saturates below the value required to effect fluence-dependent switching in a nonlinear directional coupler. Experiments with a channel-waveguide directional coupler support this prediction. However, absorption switching due to differential saturation of the absorption in the two arms of the directional coupler was observed.

This dissertation describes the study of various nonlinear optical effects in both bulk and quantum-confined semiconductors. Transverse effects in increasing absorption optical bistability are considered in bulk CdS for both single beam and wave mixing geometries. Measurement of the temporal response of BiI₃ quantum dots is described using degenerate four-wave mixing and explained theoretically. Finally, the experimental techniques developed to measure the one- and two-photon absorption coefficients of CdS quantum dots in glass are described along with the latest theoretical description and interpretation of the experimental spectra. The basic theory of increasing absorption optical bistability is presented along with experimental observation of this effect in CdS at low temperature. Transverse effects in increasing absorption optical bistability were observed in single beam experiments with CdS at low temperatures. The ring structures observed experimentally are explained theoretically. Degenerate four-wave mixing performed with this nonlinearity is theoretically shown to produce new scattering orders compared with a standard Kerr analysis. Experimental observation of these new scattering orders is presented. The temporal response of the nonlinearity in a solution of BiI₃ quantum dots in acetonitrile is determined using degenerate four-wave mixing. The independent contributions to the phase-conjugate signal are determined for both of the spatial gratings induced in the solution. The observed temporal responses indicated that a thermal mechanism was responsible for the nonlinearity. A theoretical analysis based on a thermal nonlinearity is presented which provides good agreement with the observed responses. The experimental techniques necessary to measure the one- and two-photon absorption coefficients of CdS quantum dots are described. The resultant measurements of quantum dot samples with microcrystallites ranging from 3.6 to 10.8 nm in diameter indicate no splitting of the energy levels associated with the hole. Theoretical spectra indicate this can be partially explained by the inclusion of Coulombic effects of the charged electron-hole pair.

No description available.

The deformation of a mirror's optical surface due to a spacial variation of the coefficient of thermal expansion is examined. Four types of variations of the coefficient of thermal expansion are studied. These represent variations which result after typical manufacturing and/or fabrication processes. Equations describing the deformations resulting from the variations in the coefficient of thermal expansion are derived for some of the cases. Deformations due to more complex variations in the coefficient of thermal expansion are developed empirically using data generated by the finite-element method.