Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1911. / Cover title. Reprinted from Physical review, vol. 33 (Dec. 1911). Includes bibliographical references.

<p> The standard technique of ellipsometry allows the determination of the optical constants of a substrate material provided either the surface is free of an oxide film or the oxide film thickness and optical constants of this oxide film are known. The majority of ellipsometric measurements performed on materials known to grow natural oxides is done by removing the natural oxide (either by cleaving or etching) and performing the measurements at one angle of incidence in vacuo. These processes perturb the surface and the reported values of optical constants may be questionable. </p> <p> The technique to be presented here assumes the material to be studied has a naturally-occurring oxide. Measurements are performed at several angles of incidence and the optical equations are solved for a self-consistent oxide film thickness until the best fit substrate optical constants have been found. The optical constants of the oxide film are then determined. </p> / Thesis / Master of Science (MSc)

A study was made of the thermoreflectance spectra of a series of five thin film samples spanning the range of composition of the amorphous Ge(x)Te(1-x) binary semiconductors. The experiment was performed over photon energies ranging from 0.5 ev in the infrared to 6 ev in the ultraviolet. The results are plotted for energies above the absorption edge. In the Ge-rich materials there was little structure in the thermoreflectance spectrum. However, there was the development of two peaks in the spectrum as the Te content was increased beyond a 50:50 mixture. The results are analyzed in terms of optical constants and electronic structure. It was found that the energy separation of the peaks in the thermoreflectance corresponded closely to the separation of peaks in the valence band density of states seen in photoemission experiments. The existence of the two peaks indicates a "lone pair" band of energy levels positioned between the valence and conduction bands. This is aditional evidence of two-fold coordination of the Te atoms in these materials. At energies below the band gap there was strong interference due to increased transimission of the film. This made the analysis more complicated. A procedure is discussed for extracting from the modulated interference the specific changes occurring in the optical constants with temperature modulation.

No description available.

The goal of this project was to study the deliquescence kinetics of aerosol particles of atmospheric significance. In the course of this work a novel experimental method was developed, which utilizes the measurement of the water vapor loss in laminar aerosol flow to determine vapor uptake on the aerosol surface. The newly designed flow tube apparatus uses a system of Nafion based dryers and humidifiers, which greatly simplifies the optimization and control of the relative humidity in the aerosol flow. The design, which also utilizes a movable inlet, enables easy variation of the aerosol residence time in the deliquescence reactor, while keeping other experimental conditions constant. In this study, a numerical retrieval procedure was used to characterize aerosols in situ from their IR extinction spectra. The procedure allows that the aerosol size, number distribution, phase and composition be determined, provided the optical constants of all the components (materials) comprising the aerosol are known. For the purpose of studying the deliquescence kinetics of ammonium sulfate aerosol and monitoring their evolution from solid to liquid (state), we have acquired a set of optical constants for a range of (NH4)2SO4 compositions. A set of experiments in a somewhat modified flow tube set up was performed to produce AMS aerosols of known composition, including solid, saturated (water) solution (40 % wt.) and a series of diluted solutions with composition ranging between 40 and 10 % wt. in 5 % increments. The IR spectra of these model aerosols were used to derive the optical constants, using an inversion method proposed by Clapp. The derived refractive indices, which cover the spectral range from 590 to 5990 cm-1 with 2 cm-1 resolution, were compared with those already available in the literature. Using various examples to compare the quality of fittings to experimental spectra, we demonstrated that our optical constants present an improvement relative to those previously reported by B. Toon’s (for crystalline AMS) and S. Martin’s (for AMS solution). The suitability of applying this procedure to ammonium sulfate aerosols and its sensitivity to spectral range was also investigated and discussed. As a preparatory step for the deliquescence kinetics study, our new flow tube apparatus and the tools for the characterization of aerosol were verified in a standard deliquescence experiment performed on (NH4)2SO4 aerosols. The deliquescence process of an equilibrated aerosol flow was monitored as a function of increasing humidity and the deliquescence relative humidity (DRH) determined to be 79.6 ± 0.85 % which is, within experimental uncertainty, in an excellent agreement with the results reported by other research groups. In the kinetic experiment, a flow of solid (NH4)2SO4 aerosols is pre-humidified to a humidity close to, but enough below DRH that there is no detectable amount of liquid aerosols in the system. Such an equilibrated aerosol flow was introduced to the deliquescence reactor where it is further humidified in a controllable manner, by varying the position of the movable inlet. The amount of water transferred to the aerosol through the Nafion membrane was closely monitored, as well as the resulting increase in the water content in the aerosol flow (both gaseous and liquid). This was achieved by measuring the RHs and flow rates of the aerosol and humidification flow, and the characterization of aerosol composition and concentration using their IR spectra. The experimental conditions and aerosol residence times in the reactor where chosen such that no other diluted solution except for saturated (NH4)2SO4 droplets were produced in the process. The number distribution of deliquesced aerosols and the corresponding change in the water content in the aerosol flow were used by a newly developed kinetic model to determine the kinetics of the deliquescence process. Assuming fully developed laminar flow conditions, the water vapor concentration in the flow and its depletion in the presence of aerosol was modeled, to retrieve the value of the water vapor uptake. In the case of micron-sized ammonium sulfate aerosols, which were used in this study, the uptake coefficient,, was determined to be 0.0072 ± 6.54x10-3. The uncertainty associated with this value, as well as the suggested improvements to the experimental procedure and the kinetic model in order to reduce the uncertainty were discussed.

The goal of this project was to study the deliquescence kinetics of aerosol particles of atmospheric significance. In the course of this work a novel experimental method was developed, which utilizes the measurement of the water vapor loss in laminar aerosol flow to determine vapor uptake on the aerosol surface. The newly designed flow tube apparatus uses a system of Nafion based dryers and humidifiers, which greatly simplifies the optimization and control of the relative humidity in the aerosol flow. The design, which also utilizes a movable inlet, enables easy variation of the aerosol residence time in the deliquescence reactor, while keeping other experimental conditions constant. In this study, a numerical retrieval procedure was used to characterize aerosols in situ from their IR extinction spectra. The procedure allows that the aerosol size, number distribution, phase and composition be determined, provided the optical constants of all the components (materials) comprising the aerosol are known. For the purpose of studying the deliquescence kinetics of ammonium sulfate aerosol and monitoring their evolution from solid to liquid (state), we have acquired a set of optical constants for a range of (NH4)2SO4 compositions. A set of experiments in a somewhat modified flow tube set up was performed to produce AMS aerosols of known composition, including solid, saturated (water) solution (40 % wt.) and a series of diluted solutions with composition ranging between 40 and 10 % wt. in 5 % increments. The IR spectra of these model aerosols were used to derive the optical constants, using an inversion method proposed by Clapp. The derived refractive indices, which cover the spectral range from 590 to 5990 cm-1 with 2 cm-1 resolution, were compared with those already available in the literature. Using various examples to compare the quality of fittings to experimental spectra, we demonstrated that our optical constants present an improvement relative to those previously reported by B. Toon’s (for crystalline AMS) and S. Martin’s (for AMS solution). The suitability of applying this procedure to ammonium sulfate aerosols and its sensitivity to spectral range was also investigated and discussed. As a preparatory step for the deliquescence kinetics study, our new flow tube apparatus and the tools for the characterization of aerosol were verified in a standard deliquescence experiment performed on (NH4)2SO4 aerosols. The deliquescence process of an equilibrated aerosol flow was monitored as a function of increasing humidity and the deliquescence relative humidity (DRH) determined to be 79.6 ± 0.85 % which is, within experimental uncertainty, in an excellent agreement with the results reported by other research groups. In the kinetic experiment, a flow of solid (NH4)2SO4 aerosols is pre-humidified to a humidity close to, but enough below DRH that there is no detectable amount of liquid aerosols in the system. Such an equilibrated aerosol flow was introduced to the deliquescence reactor where it is further humidified in a controllable manner, by varying the position of the movable inlet. The amount of water transferred to the aerosol through the Nafion membrane was closely monitored, as well as the resulting increase in the water content in the aerosol flow (both gaseous and liquid). This was achieved by measuring the RHs and flow rates of the aerosol and humidification flow, and the characterization of aerosol composition and concentration using their IR spectra. The experimental conditions and aerosol residence times in the reactor where chosen such that no other diluted solution except for saturated (NH4)2SO4 droplets were produced in the process. The number distribution of deliquesced aerosols and the corresponding change in the water content in the aerosol flow were used by a newly developed kinetic model to determine the kinetics of the deliquescence process. Assuming fully developed laminar flow conditions, the water vapor concentration in the flow and its depletion in the presence of aerosol was modeled, to retrieve the value of the water vapor uptake. In the case of micron-sized ammonium sulfate aerosols, which were used in this study, the uptake coefficient,, was determined to be 0.0072 ± 6.54x10-3. The uncertainty associated with this value, as well as the suggested improvements to the experimental procedure and the kinetic model in order to reduce the uncertainty were discussed.

Thesis (Ph. D.)--Ohio State University, 2008.

We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux directional EUV source has available wavelengths between 8 nm and 62 nm and easily rotatable linear polarization. The polarimeter will aid researchers at BYU in characterizing EUV thin films and improving their understanding of materials for use in EUV optics. This first-time workhorse application of laser high harmonics enables polarization-sensitive reflection measurements not previously available in the EUV. We have constructed a versatile positioning system that places harmonics on the microchannel plate detector with an accuracy of 0.3 mm, which allows a spectral resolution of about 180. We have demonstrated that reflectance as low as 0.2% can be measured at EUV wavelengths and that this data is repeatable to within the error of our source stability (~7% fluctuation). We have compared reflectance data with that taken from the same sample at Beamline 6.3.2 at the Advanced Light Source. This data agrees well from 5 degrees to 30 degrees and the angular locations of the interference fringes also agree.

A new sensor technology based on optical diffraction of visible light shows promise for sensing metal ions and other species that employ chemically-responsive metal oxide and conducting polymer grating elements. These materials undergo reversible redox processes upon interaction with a chemical analyte that subsequently induces changes in the materials refractive index. The two key design parameters of this sensing technique involve preparation of micropatterned sensor elements and the evaluation of appropriate wavelengths for detection of diffracted light. Much of the ability to “tune” a desired sensing response is dictated by the understanding of how factors of size, dimension, crystallinity, morphology, porosity, and heterogeneity influence analyte/sensor interactions (i.e., adsorption, binding, and transport). The effect of composition, structure, and morphology of MoO₃, WO₃, Moₓ W₁₋ₓO₃, IrOₓ and polyaniline grating materials on chemical, electrochemical and optical properties of these systems will be examined by a range of spectroscopic and electrochemical techniques. Comprehensive evaluation and correlation of materials’ optical properties to diffraction-based detection will advance understanding of the capabilities and limitations for the diffraction-based sensing methodology. This information can then used to determine optimal sensing parameters to improve detection limits, enhance sensitivity and increase the dynamic range for detection of model analytes. / text

We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux, directional EUV source has available wavelengths between 10 nm and 47 nm with easily rotatable linear polarization. The polarimeter has allowed us to characterize the optical constants of materials that may be useful for EUV optics. The instrument has a versatile positioning system and a spectral resolution of about 180, and we have demonstrated that reflectance as low as 0.1% can be measured repeatably at EUV wavelengths. We investigate the high harmonic source used for polarimetry measurements by documenting the spatial evolution of the generating laser in a semi-infinite helium-filled gas cell under conditions suitable for harmonic generation. The laser is observed to focus, diverge, and refocus, accompanied by a flattop beam profile and extended harmonic phase matching. We numerically simulate the propagation to investigate these experimental results. We find that harmonic energy comes from the forward portion of the laser pulse, whereas the latter portion gives rise to the incidental double laser focusing. Good phase matching for the harmonics arises in large measure from a balance between the linear phase delay of the neutral atoms and the Gouy shift, which is elongated and nearly linearized when an aperture is partially closed on the beam. We compare reflectance data taken with the polarimeter instrument with expected results from well-characterized samples and find that they agree. To improve repeatability and reduce the effects of systematic measurement errors we have measured the ratio of p- to s-polarized reflectance and shown that optical constants can be extracted from this data as efficiently as from absolute reflectance measurements. These ratio measurements allow more accurate recovery of optical constants than our absolute reflectance measurements for our well-characterized samples. We use the polarimeter instrument and the ratio reflectance technique to determine the optical constants of copper, uranium, and their natural oxides from 10-47 nm. For copper, this measurement resolves previously conflicting data sets, where disagreement on optical-constant values arises from failure to keep samples from oxidizing before measurement. Uranium has been proposed as a high-reflectance material in the EUV for several years, however difficulties with oxidation have prevented its careful characterization previous to this work. We find that measured optical constants for uranium do not agree well with previously accepted theoretical calculations.