Browsing by Subject "Optical properties"
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Item Optical Properties of Saharan Dust and Asian Dust: Application to Radiative Transfer Simulations(2012-07-16) Fang, GuangyangBecause the bulk optical properties of dust are largely dependent on their chemical composition, published reports from numerous dust field studies enabled us to compile observation data sets to derive the effective complex refractive indices of Saharan and Asian dust. We considered the individual mineral components as aggregates and used the Bruggeman approximation to derive the effective refractive indices. Using the results, we calculated the single-scattering properties, including phase matrix, single-scattering albedo and asymmetry factor, with a combination of the T-matrix method and an improved geometric optics method (IGOM). The single-scattering properties were averaged by the measured particle size distribution to provide bulk optical properties for radiative transfer simulations. Using a Rapid Radiative Transfer Model (RRTM), the radiative forcing of mineral dust was computed at both the top of the atmosphere and the surface. By analyzing samples from various in-situ measurements, we assumed the Saharan and Asian dust to have average volume compositions and average aspect ratios. The effective refractive indices for Saharan and Asian dust were derived based on the assumed composition models. Bulk optical properties were integrated using the modified log-normal particle size distributions. The aspect ratio assumed in this study is 1.6 for both Saharan and Asian dust. The longwave radiative (IR) forcings at the top of the atmosphere (TOA) and at the surface were found to be positive and sensitive to wavelength. The shortwave (solar) radiative forcing at TOA, was also positive, but may possibly have been due to the strong absorption components considered in the composition models.Item The refractive index and absorbance of aqueous and organic fluids for immersion lithography(2009-05) Costner, Elizabeth A.; Willson, C. G. (C. Grant), 1939-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.Item Synthesis, stabilization, and controlled assembly of organic and inorganic nanoparticles for therapeutic and imaging applications(2009-12) Tam, Jasmine Man-Chi; Johnston, Keith P., 1955-Nanoparticles have garnered much attention in pharmaceutical and biomedical fields because their small size and high surface area facilitate drug absorption, improve access to cells and organs, and enhance optical imaging. However, delivery of nanoparticles to the body is not always feasible or effective. Here, nanoparticle assemblies (flocs or clusters) for pulmonary drug delivery and biomedical imaging in cells are shown to facilitate delivery, interactions with cells, and manipulation of optical properties of inorganic/organic nanocomposites. The formation of aggregates by physical techniques and their mechanisms are described in detail. For pulmonary delivery, particles with aerodynamic diameters between 1-5 [mu]m deposit efficiently in the deep lungs. However, crystalline, non-porous, poorly water soluble drugs of this size require long dissolution times, limiting absorption by the body. Therefore, drug dissolution must be “decoupled” from deposition to improve absorption. To address this challenge, drug nanoparticles were dispersed within 4-[mu]m water droplets when administered via nebulization or as micron-sized flocs using a pressurized metered dose inhaler (pMDI). Upon deposition in aqueous media, the aerosolized nanoparticle assemblies dissociated into constituent nanoparticles, raising the available surface area for dissolution and increasing dissolution rates, relative to solid particles. Poorly water soluble drug nanoparticles were prepared using a controlled precipitation (CP) or thin film freezing (TFF) process, in which stable nanoparticles (30-300 nm in diameter) with high potencies (>90 wt% drug) were produced by rapidly nucleating drug solutions in the presence of strongly adsorbing polymers or by freezing, respectively. Amorphous, nanoparticles prepared by CP produced stable aqueous dispersions with high fine particle fractions (FPF) of 77% and total emitted doses (TED) of 1.5 mg/min upon nebulization. CP and TFF also produced anisotropic particles (aspect ratios >5), which formed stable suspensions in a hydrofluoroalkane propellant. Inefficient packing of anisotropic particles formed loose, open flocs that stacked upon each other to prevent settling. Upon pMDI actuation, atomized propellant droplets shear apart and template portions of the floc to yield porous particles with high FPFs (49-64%) and TEDs (2.4 mg/actuation). The controlled assembly of gold nanoparticles into clusters is also of great interest for biomedical imaging and therapy because clusters exhibit improved near infrared absorbance (where blood and tissue are most transparent), relative to single spherical particles, and can biodegrade into clearable particles. Gold nanoparticles (5 nm) were assembled into clusters between 30 to 100 nm in diameter with high gold loadings, resulting in strong NIR absorbance. The assembly was kinetically controlled with weakly adsorbing polymers by manipulating electrostatic, van der Waals, steric, and depletion forces. Furthermore, clusters assembled with a biodegradable polymer deaggregated back into primary particles in physiological media and within cells. This kinetic assembly platform is applicable to a wide variety of fields that require high metal loadings and small particle sizes.