The major part of my dissertation consists of thin films deposited using atomic layer deposition on flat and powder substrates. It details the various optimization experiments for process parameters like dose time, purge time, temperature, and pressure on silicon shards and powder substrates. Spectroscopic ellipsometry (SE) was used to characterize these films over a wide wavelength range (191-1688 nm). An optical model with a BEMA (Bruggeman effective medium approximation) layer was used to fit the ellipsometric data to investigate the optical properties of the alumina surface. The optimized process parameters on the flat surfaces were used for coating powder substrates. I propose a set of experiments to optimize the conditions for coating of powders and high aspect ratio structures by atomic layer deposition (ALD). The coated powders were analyzed by surface analytical techniques like X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, energy X-ray dispersive spectroscopy (EDAX), and BET. The first chapter introduces the technique of atomic layer deposition, and details its advantages and limitations over conventional thin film deposition techniques like chemical vapor deposition and physical vapor deposition. The second chapter details the initial deposition experiments performed on flat surfaces and characterization of thin films using surface analytical tools. I conducted multi-sample analysis on eleven different thin films for calculation of optical constants of alumina. The third chapter introduces thin film deposition experiments performed on powder substrates, several challenges associated with achieving conformal thin films and characterization. The fourth chapter details the experiments to achieve unilateral ALD achieved on one side of the substrates. The fifth chapter details various unconventional materials including liquid water, Coca-Cola, a coffee bean, nitrogen gas, human tooth, and printed office paper, which were analyzed by near ambient pressure XPS (NAP-XPS). This dissertation contains appendices of other tutorial articles I wrote on obtaining optical constants liquid samples using spectroscopic ellipsometry, and good experimental techniques for maintenance of vacuum equipment.

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A series of picosecond excite-probe experiments was performed on various concentrations of aqueous and ethanolic solutions of rhodamine B in order to determine the existence of dimerization in those solutions. The goals of the research presented in this dissertation were twofold. Initially, various techniques of time-resolved spectroscopy were to be employed to further characterize the ground and excited-state molecular properties of the aqueous RB dimer. The information obtained, and the techniques developed in that study would then be utilized in an effort to secure evidence which would support or refute the claims of rhodamine B dimerization in an ethanolic solution.

The well-known spectroscopic binary ϕ Per is a peculiar compact system, composed of a Be star with an O-type subdwarf companion. A set of nearly 400 spectra in the red and blue regions from Ondřejov and Potsdam Observatories as well as spectra published in the BeSS database were examined. From the radial velocities of Hα, Hβ, and Hγ emission lines and FUV observations from the IUE and HST, a new precise ephemeris was determined. The revised values of M sin3 (i) are 11.84 and 1.48 M (with uncertainties of 0.64 and 0.09 M ), re- spectively, for the primary and secondary. In addition, the system shows cyclic variations (with a time scale of about 5 years) in the profiles of Balmer lines, manifested in their radial velocities, central intensities and V/R ratios. Understanding complex stellar systems requires combining multiple types of ob- servations and creating models of sufficient complexity. In our case, a combination of interferometric visibilities from the CHARA/VEGA array, spectral energy dis- tribution as well as individual spectral lines were used. Radiative-transfer compu- tations were performed with the program PYSHELLSPEC, and physical parameters of the ϕ Per primary and the surrounding disc were derived. They correspond to an evolved system, in which most of mass was transferred from the secondary to...

Indiana University-Purdue University Indianapolis (IUPUI) / Up-to-date and accurate information on soil properties is important for precision farming and environmental management. The spatial information of soil properties allows adjustments of fertilizer applications to be made based on knowledge of local field conditions, thereby maximizing agricultural productivity and minimizing the risk of environmental pollution. While conventional soil sampling procedures are labor-intensive, time-consuming and expensive, remote sensing techniques provide a rapid and efficient tool for mapping soil properties. This study aimed at examining the capacity of hyperspectral reflectance data for mapping soil organic matter (SOM), total nitrogen (N) and total phosphorus (P). Soil samples collected from Eagle Creek Watershed, Cicero Creek Watershed, and Fall Creek Watershed were analyzed for organic matter content, total N and total P; their corresponding spectral reflectance was measured in the laboratory before and after oven drying and in the field using Analytical Spectral Devices spectrometer. Hyperion images for each of the watersheds were acquired, calibrated and corrected and Hyperion image spectra for individual sampled sites were extracted. These hyperspectral reflectance data were related to SOM, total N and total P concentration through partial least squares (PLS) regressions. The samples were split into two datasets: one for calibration, and the other for validation. High PLS performance was observed during the calibration for SOM and total N regardless of the type of the reflectance spectra, and for total P with Hyperion image spectra. The validation of PLS models was carried out with each type of reflectance to assess their predictive power. For laboratory reflectance spectra, PLS models of SOM and total N resulted in higher R2 values and lower RMSEP with oven-dried than those with field-moist soils. The results demonstrate that soil moisture degrades the performance of PLS in estimating soil constituents with spectral reflectance. For in-situ field spectra, PLS estimated SOM with an R2 of 0.74, N with an R2 of 0.79, and P with an R2 of 0.60. For Hyperion image spectra, PLS predictive models yielded an R2 of 0.74 between measured and predicted SOM, an R2 of 0.72 between measured and predicted total N, and an R2 of 0.67 between measured and predicted total P. These results reveal slightly decreased model performance when shifting from laboratory-measured spectra to satellite image spectra. Regardless of the spectral data, the models for estimating SOM and total N consistently outperformed those for estimating total P. These results also indicate that PLS is an effective tool for remotely estimating SOM, total N and P in agricultural soils, but more research is needed to improve the predictive power of the model when applied to satellite hyperspectral imagery.

Ultra-thin films (UTFs) are important in many applications, seen in the semiconductor industry, in chromatography, in sensing, in microfluidics, in aerospace, and in robotics. They also protect materials from corrosion, change surface energies, limit water intrusion into materials, allow material self-cleaning and self-healing, provide scratch resistance, and impart other specific chemical properties. In many cases, UTFs drastically alter surface properties and therefore their applications. It is imperative that proper and consistent characterization be performed on coatings to confirm and understand their desired properties. In Chapter two, Al oxidation under MgF2 protective layers is studied using real time X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). These tools allowed me to monitor Al oxidation for both short (hours) and long (months) periods of time. XPS revealed the chemical changes that took place in these materials as a function of time, and these changes were verified with SE. These studies help increase an understanding of aluminum changes under MgF2 protective layers. The third chapter demonstrates ab initio calculations guided X-ray photoelectron spectroscopy (XPS) analysis of surfaces functionalized with fluorinated silanes. This study addresses deficiencies in the literature where CF2:CF3 ratios from experimental XPS data do not match theoretical CF2:CF3 ratios. In a systematic approach, I developed semi-empirical models directed both by ab initio calculations and adjustable, empirical parameters. These models were effective in describing the raw data and exceeded fitting methods used in literature. In Chapter four, SiO2 UTFs with variable thicknesses deposited on Eagle XG® glass substrates are characterized. Challenges associated with this work consisted of similar optical functions of the film and substrate as well as backside reflections from the substrate. These obstacles were met using a multi-sample analysis (MSA), a variable angle spectroscopic ellipsometric approach, and mechanical abrasion/roughening of the substrate backside. With these approaches, I developed a model that precisely fit the data collected from all the samples and gave the correct optical function of the material along with thickness values for each film. Surface characterization represents a commitment of resources. It takes time to make measurements, and it takes time to analyze and understand the results. As presented in this work, I increase understanding of ultra-thin films at interfaces using both a multi-tool approach as well as using multiple analytical methods on data collected from each tool.

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Aim of this student research project was to develop an Aluminium Oxide (Al2O3 ) ALD process from trimethylaluminum (TMA) and Ozone in comparison of two shower head designs. Then studying the detailed characteristics of Al2O3 ALD process using various measurement techniques such as Spectroscopic Ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM). The real-time ALD growth was studied by in-situ SE. In-situ SE is very promising technique that allows the time-continuous as well as time-discrete measurement of the actual growth over an ALD process time. The following ALD process parameters were varied and their inter-dependencies were studied in detail: exposure times of precursor and co-reactant as well as Argon purge times, the deposition temperature, total process pressure, flow dynamics of two different shower head designs. The effect of varying these ALD process parameters was studied by looking upon ALD cycle attributes. Various ALD cycle attributes are: TMA molecule adsorption (Mads ), Ligand removal (Lrem ), growth kinetics (KO3 ) and growth per cycle (GPC).

The work presented in this thesis is concerned with development of spectroscopic detection methods based on absorption spectroscopy using semiconductor lasers, with particular ref- erence to the field of medical diagnostics through breath analysis. The first part of this thesis deals with the design and testing of a prototype analyser for simultaneous monitoring of the exchange gases O₂ , CO₂ and H₂O in breath. The aim of this analyser is to provide information required to monitor respiration, with potential use in intensive care monitoring or during anaesthesia. The relatively high concentrations of these gases in breath and read- ily available diode laser sources make detection in the near-infrared (NIR) ideal. However, the relatively weakly absorbing A-band O₂ transitions at 760 nm require the application of a sensitive spectroscopic method, cavity enhanced absorption spectroscopy (CEAS). In contrast, CO₂ and H₂O are monitored using direct single pass absorption spectroscopy, with transitions arising from the 2ν₁ + ν₃ band at 2 μm and ν₁ + ν₃ band at 1.3 μm, respectively. It has been demonstrated that these gases can be detected simultaneously over a short pathlength (2.74 - 4 cm) in the respiratory flow by combining various spectroscopic methodologies and real-time data analysis. This analyser is shown to offer a viable alter- native for monitoring respiration, exhibiting absolute detection limits of changes of 0.26 % O₂ , 0.02 % CO₂ and 0.003 % H₂O with a 10 ms time resolution, which are comparable to current mass spectrometry based methods, but without their inherent delays. Following this, investigations into the detection of the main gas constituents in breath in the NIR employing noise-reduction modulation based spectroscopic techniques, namely wavelength and frequency modulation (WMS and FMS respectively) are also reported. The described WMS studies on water at 1.37 μm provide a demonstration of conventional WMS detection, as well as a “proof-of-principle” example of a relatively new approach to calibrating the non-absolute information obtained from a WMS absorption signal. Typically WMS spectra are calibrated using mixtures of known gas concentrations or an absolute direct absorption spectrum where possible. In this work however, a self-calibrating method, the phasor decomposition method (PDM), is employed and the returned concentration from this calibration is compared to direct absorption measurement. From this, the calculated concentration using the PDM is found to differ by 9 % from the concentration value obtained by direct absorption, providing an alternative method of calibration for when direct absorption measurements are not possible. The use of FMS in the NIR is also demonstrated as a potential alternative to CEAS for monitoring O₂ at 760 nm. FMS detection is performed on atmospherically broadened O₂ and a time-normalised α_min(t) of 2.45 ×10⁻⁶ cm⁻¹ s^1/2 is obtained, which is two orders of magnitude less sensitive than the value of α_min(t) = 2.35 ×10⁻⁸ cm⁻¹ s^1/2 obtained with CEAS. This combined with the experimental requirements of an FMS system, make its use for detection of O₂ a less practicable option compared to CEAS for real-time breath analysis. The latter work in this thesis involves a change in focus to detection of trace gases in breath in the mid-infrared (MIR). The move of spectroscopic detection to the MIR exploits the larger absorption cross-sections available in this region, and to achieve this, a relatively new form of semiconductor laser, the quantum cascade laser (QCL) is used. The design of a continuous wave QCL spectrometer at 8 μm and its operating characteristics are demon- strated and improvements in its performances are also discussed. This QCL system is then utilised to demonstrate the potential of monitoring species in breath, namely the narrow- band absorber methane and the broadband absorber acetone, taking into consideration the potential interference from other absorbing species in breath and the different spectroscopic characteristics exhibited by these molecules. Finally, the potential to further improve the sensitive detection of trace gases in breath in the MIR is also investigated with studies on the use of CEAS and multipass cells. In this work, the molecule of interest is the biomarker OCS, using transitions of the 2ν₂ band at 1031 cm⁻¹ , that are probed using a 10 μm QCL. The application of CEAS in the MIR is not as well developed as in the NIR, and the experimental consequences of using optical cavities at these wavelengths, where equipment tends to be more limited, are investigated and sensitivities discussed in the context of other literature. The experimental procedure of optimising a cavity for CEAS using the off-axis alignment method is also studied in detail, as well as the addition of WMS to further improve the signal quality. An effective absorption pathlength of ∼ 100 m was achieved in the cavity, with a bandwidth reduced α_min(BW) of 1.7 ×10⁻⁷ cm⁻¹ Hz^−1/2 using WMS CEAS achieved. With the poorer quality optics and limitations in equipment in the MIR for CEAS experiments, the use of a multipass cell, a 238 m Herriott cell, is also investigated as an alternative to the use of an optical cavity at 10 μm. Detection of OCS using direct absorption and WMS is demonstrated in the Herriott cell, achieving α_min(BW) = 2.03×10⁻⁸ cm⁻¹ Hz^−1/2 using WMS. This shows an improvement in sensitivity compared to WMS CEAS, and also shows the potential for future work on biomarker detection, as it approaches the ∼ ppb levels required for breath analysis.